Wide Load: Tips for Printing LARGE

Background

Wide format printers are getting cheaper and more economical, making large prints like 13x20, 20x30, and larger possible even for the advanced amateur.  Logic dictates that a wide format inkjet printer is nothing more than a big printer and that printing to a wide format printer should be no different than printing to your typical desktop inkjet except that it allows you to work with larger page sizes.  Unfortunately there are a lot of snags that you may encounter when printing (very) large prints.  Most involve printer/driver setup and are easily corrected while others may require a rethink on how you have your equipment connected, what type of equipment you are using to print, whether or not your current hard drive has the capacity for wide format printing, whether or not you need more RAM, etc.  Let's take a look at printing large and we'll try to cover all the common missteps in the minefield.  We'll keep both Qimage and PhotoShop in mind for this article as those are popular PC/Windows printing applications and are the applications that I deal with most in wide format printing.

 

Page Size


Wide format printers often handle paper/page size differently than your average inkjet, particularly with respect to borderless or "no margins" printing.  First, it is important to realize that there are two methods that drivers use to perform borderless printing: expand page and expand prints. In the expand page mode, the driver simply increases the size of the page so that it is larger than the physical paper size. In this borderless printing mode, the driver will actually show a printable area larger than the physical paper size.  For example, a 16 inch wide roll may show as 16.23 inches across in your printing software. What is actually happening is that the driver is printing approximately .12 inches off the left and right edges of the roll. With this method, it is important to print your large prints in the center of the page.  For example,  use "centered" or "optimal/spaced" in Qimage.  This will ensure that the "overspray" that extends off the edges of the paper is minimized and you won't lose the edges of the print because they are printing up against one edge or the other.  If you use something like "compact" or "optimal", Qimage will place the print at the left edge of the paper and .12 inches of the print will be off the page, cropping the print slightly. Epson calls this expand page mode "Retain Size" in their latest wide format drivers. In the older (7600/9600) drivers, this was the only option available so no options were visible.  What you need to keep in mind with the expand page mode is that the driver expands the page size so that it extends slightly beyond the edges of the paper.  In doing so, it is possible to print off the edge of the paper and lose some of your prints.  Try to avoid this "clipping" by not printing anything all the way against the left/right edges of the paper when aligning your prints on the page preview on screen.

The other method of borderless printing (one that is used on most standard inkjet printers) is the expand prints mode. In this mode, the printable area remains the size of the paper (16.0 inches across for example), but prints are expanded in size. With this mode, you can specify 16 inches as the width and the driver will "artificially" expand the print to 16.23 inches so that the print is large enough for some overspray to the left/right: the overspray eliminates tiny slivers of unprinted paper at the edges due to slight misalignment of the paper. This mode is more common but often more confusing because every print you send will be slightly larger than what you specified. Even if you print 4x6 prints on a 16x20 page, the 4x6 prints will be just slightly larger than 4x6 and this may confuse people or prompt them to blame the printing software for the size problem when in fact it is the driver that took the 4x6 print and expanded it after the fact. If the expand prints mode (called "Auto Expand" by Epson in their latest wide format drivers) is being used, Qimage does have an option that can defeat the size expansion so that you can obtain prints of the specified size without the driver expanding them. See "Page Formatting", "Borderless Overspray/Expansion" in Qimage.  Some drivers even allow you to turn this expansion off (or at least reduce it) by dragging the "amount of extension" slider all the way to the left in the driver.  Keep in mind that doing this produces less overspray so any "sloppiness" in the paper loading mechanism may show up as unprinted slivers on the edges of the print.

 

Understanding software differences WRT sizing

All software including PhotoShop and Qimage must work within the
limitations of the printer which are defined by the driver. If you specify an impossible task, like printing a 16x20 print on 16x20 paper without using borderless printing, different software may handle the request differently. For example, if you don't specify borderless printing, the maximum size print allowable on 16x20 paper using the Epson 4800 is 15.766 x 19.333 inches. If you try to print a 16x20 using PhotoShop, you will be told that the print size is larger than allowed but you will be given a "Proceed" option. If you proceed, PhotoShop will print at 16x20 but will clip the edges of the print and you'll end up with a 15.766 x 19.333 inch print that has the edges missing. In Qimage, you will be told that the print size is larger than one page and will be asked if you want a poster. If you say no, you'll end up with a 15.766 x 19.333 inch print (same size as PhotoShop) but without the edges cropped off. These are just two different ways of handling the same problem and in both cases you end up with (no more than) a 15.766 x 19.333 inch print: a printer/driver limitation.  It is important to recognize how different programs handle sizing tasks and in particular, what happens when you try to print sizes that do not fit on the paper.  Whatever printing software you use, be familiar with how it handles sizing discrepancies.

 

Spooling options

Qimage will almost always send more (potentially much more) data to the driver than PhotoShop or other printing programs due to Qimage's interpolation process. As such, you must make sure that the printer is set up properly for large format printing. Not having the printer/spooler set up properly may result in partial prints, no print at all, or crashes due to the system not being able to handle the [large] amount of data being handed to the driver.  First and foremost, go to control panel, select "printers and faxes", and right click on your printer. Select "Properties" from the right click menu and then click the "Advanced" tab. If "Enable Advanced Printing Features" is checked at the bottom, UNcheck this option. This is the cause for 98% of printing troubles when printing large prints as this feature can only handle a small amount of data and isn't meant for photographic printing so the option should remain UNchecked.  The other options on that tab usually make little difference but I recommend checking "Spool print documents so program finishes printing faster" and also "Start printing immediately". Those options will ensure the best use of resources on the machine. Finally, click the "Print Processor" button and make sure that the right side is set to "RAW". If any other data type is selected, it is likely your photographic printing will not work properly. Click "OK" to save the changes.

 

Maximum print sizes

Some online sources report that the maximum print length in PhotoShop CS2 is about 90 inches. I have not confirmed this, but I can tell you that when set up properly, Qimage has no length limit. PhotoShop and most other applications that print photos try to send the image all-at-once to the driver: they basically hand off the entire original image at once and simply specify a print size for that image. Depending on the initial image size and specified print size, this all-at-once printing method can overwhelm the driver/spooler and lockups/crashes may ensue. Qimage has a "smart" handoff to the driver that passes the data in smaller chunks that don't overwhelm the system and can allow for much larger prints. With Qimage, you are only bound by the amount of RAM, virtual memory, and hard drive space available and by how well your print driver handles the printing task when dealing with the large amount of data normally used for big prints. Most of the big print failures that I've seen fall into three categories:

(1) Printer is connected through a network. I have not yet seen a reliable setup when printing through a network and working with large prints. My advice here is just don't do it! In fact, if your wide format printer is connected via an Ethernet cable, switch to USB and print directly to the printer via a local machine connected directly to the printer. There are dozens of complications that arise when trying to send large amounts of print data across a network so if at all possible, print from a machine that is directly connected to the wide format printer as a local printer. You will avoid a lot of hassles this way!  It may be possible, depending on many factors, to have a reliable network printing setup to a wide format printer, but the complications are so diverse and varied that I don't dare get into that here.  When dealing with "wide loads", it is best to avoid network connections altogether!

(2) Don't upsample originals. I've seen people scan 8x10 photographs at 2400 PPI ending up with a 1.4 GB file thinking they want the most resolution possible for printing large. In this case, the original photo only holds maybe 300 PPI of real information so scanning the photo at 600 PPI and then letting Qimage handle the interpolation makes more sense (and often produces better results). Your system and the driver will have enough to do processing your 10 foot long print, so don't hand it a 1-2 GB file unless you truly have enough resolution in the original to support it.  If you have enough pixels in the original to support the resolution of the final image (like a montage or panorama using a dozen photos from a dSLR), your original images have reason to be big, but don't "oversample" lower resolution photos or "overscan" media at ridiculous PPI as this may do nothing but hurt you in the long run!  Taking a 30MB original, for example, and resampling it to 400MB might make sense if you plan to print from PhotoShop, but if you are printing with Qimage, do not upsample that 30MB image because Qimage will do all the upsampling at print time very efficiently and with much less resources (RAM and hard drive space) if you simply print the original 30MB image!

(3) When using a photo editor or other software to prepare a final image for print, use a less proprietary and more internationally accepted standard like the TIFF format or even the JPEG format for the final image to be printed.  Other formats such as Adobe's PSD format often have more overhead and put more stress on your system, not to mention that the public spec for such formats is often far behind what is used in the latest version of the software that creates those files.  You may often be dealing with very large images when printing large prints.  To decrease the overall resource requirements for the job and make the whole process go smoother, use a standard format like an 8 bit/channel TIFF file with no alpha channels and no layers! All print drivers are 8 bits/channel so there is rarely any need to carry 16 bit/channel through to the final print-ready image as it is just going to end up getting converted back to 8 bits/channel anyway for the print driver.  Using PSD or layered TIFF's can put more strain on memory resources and may cause longer print times or even an occasional crash as the system tries to read a 400 MB image and print the 3.7 GB of data needed for a 720 PPI 40x60 inch print.  For printing large, I recommend 2 GB of RAM with both the minimum and maximum virtual memory set to 4 GB.  This should avoid most disk swapping unless your originals are extremely large.

(4) You can never have too much free hard drive space when printing large prints!  Printing a 44 inch wide print that is several feet long can take 5 GB (yes, gigabytes) of hard drive space or more.  As a general/safe rule of thumb, try to keep 10 GB free on the drive where your print driver spools data.  If you print with Qimage, Qimage will not need much hard drive space to process the job but it is passing a lot of data to the driver and the driver will in turn cache that data to disk while it is spooling.  Due to Qimage's high quality interpolation, it will almost always send more data to the driver than your average printing program, so don't assume that you have enough drive space just because you were able to print a print through some other software.  Qimage rarely has a problem processing the job and will finish its printing task, but after the printing task is over (sometimes before), I've seen the print driver itself crash even when several gigabytes of free space remain on the drive so don't be fooled into thinking it isn't a drive space problem just because you have a few gigabytes free on the drive!

(5) I have assisted professionals with the above tips and have printed prints as large as 44 inches wide by as much as 10 feet long (44 x 120 inches) with no problem using Qimage.  When printing super large prints like this with Qimage, however, I would recommend setting Qimage to interpolate no higher than 360 PPI for the final print.  That means that if the page resolution (current driver base resolution) shown above the preview page on Qimage's main window shows 720 x 720 PPI or 600 x 600 PPI, set your interpolation levels to "High".  If the resolution shown above the preview page is 360 x 360 or 300 x 300, set your interpolation level to "Max".  When printing huge banners, you rarely need the maximum 600 x 600 or 720 x 720 offered by the driver, so setting Qimage's interpolation level to "High" instead of "Max" will cause it to interpolate to 1/2 the listed PPI.

When printing prints larger than about 20x30 inches:
Qimage's preview page shows	Set interpolation levels to
MORE than 720 x 720	Med
600 x 600 up to 720 x 720	High
Below 600 x 600	Max

Use the above table as a good rule of thumb for printing prints larger than 20x30 inches to avoid system overload.  Under 20x30 inches: just keep the interpolation levels set to "Max".  While there should be no problem printing at "Max" interpolation level in Qimage well beyond this arbitrary 20x30 size on a capable machine, it will take longer to process and will increase the strain on the entire system (particularly with respect to hard drive space).

 

Summary

Hopefully the above tips will help clear up some of the confusion and questions being tossed around from people printing in wide format, particularly when using the latest Epson wide format printers which have some new options.  I print wide format myself and have helped others like local camera store employees who printed 44 inch wide prints 10+ feet long from Qimage to display on the front of their store using the above tips. Most of the issues with printing large involve just setting up the equipment, system, and driver properly. I occasionally run into something out of the ordinary, but most of the time the information on this page is all you need to resolve any wide format printing problems even when they occur in software other than my own Qimage.

 

Mike Chaney

Interpolation: Magical or Mythical?

Background

Years ago, when most of us were taking photos using cameras with 1-3 MP (megapixel) resolution, interpolation or "upsampling" was a hot topic.  To get decent photos at larger sizes of 8x10 and beyond, the ability to upsample photos seemed more of a necessity than an option.  Don't do it and you might end up with jagged edges.  Do it and it would smooth over the jaggies to make the photo a bit softer but without the pixelization artifacts that made the photo look more like a bad video capture than a good photo.  Fast forward to present time.  With cameras approaching and soon surpassing the 8-10 MP mark, is there really much call for interpolation?  How important is it and what does the best job?  It seems that specialized interpolation software and plugins have lost little steam and people are still spending $200 on packages that claim to do the best job adding pixels.  Do you really need these expensive solutions?  How much better do they do than your average photo editor?  Let's take a look.
 

 

The problem

Interpolation attempts to hide a problem that can be described simply as not having enough pixels for the amount of space where they are displayed.  The effect is similar to walking too close to your TV.  Get too close and you start to be able to see the individual pixels and these are distracting when you are trying to see the overall picture.  The same occurs when you take a limited number of pixels and try to "stretch them out" over a large area.

Let's look at a crop from a larger picture:

This tiny crop looks pretty good.  We can tell that it is the wheel of a car and we don't notice anything strange about it.  Take the exact same image, however, and display it larger (4x) and we get:

Now we can see that we simply don't have enough pixels for this larger size: the spokes on the wheel look more like saws than straight lines and the outline of the chrome part of the wheel looks jagged and not smooth.

 

The solution

To get rid of the visually distracting pixelization in the above larger image, we can use interpolation methods to add pixels to the image.  The pixels in the original (smaller photo) describe the data that we have to work with, so interpolation cannot add any true data to the image, but it can smooth over some of the rough edges and can add "apparent detail" by predicting what should appear between pixels in the original image.  Look at interpolation like making a prediction.  If I showed you the sequence A C E G, you could make a logical assumption and fill in the missing letters to get ABCDEFG.  Are B, D, and F really the missing letters though?  You were thinking of the alphabet, when the missing letters could have really been from a person's name: A CHENG.  This just goes to show that you can only "guess" so much information when you are missing a significant portion of that information.

What does interpolation do to the above large/pixelated image?

Without interpolation

PhotoShop "bicubic smoother" interpolation

Qimage "pyramid sharper" interpolation

The top image shows what the photo would look like at the 4x expanded size without interpolation.  By using interpolation, we are able to smooth out the distracting jagged look (center and bottom photo) and improve the overall appearance of the photo.  Note that in doing so, we've reduced or eliminated the coarse look of the image but the image now looks a bit soft (blurry).  This is a necessary tradeoff, since there is simply not enough data from the original to determine which edges should be sharp and which edges might be slightly out of focus due to depth of field, lens distortions, etc.  Older methods such as the bicubic methods used in PhotoShop tend to do a good job while more advanced methods like fractal resampling, edge directed resampling, or the pyramid resampling method available in Qimage (bottom image above) tend to do even better by further reducing jagged edges to produce an even smoother result.

 

Understanding the tradeoffs

The above is a 4x upsample which is considered fairly "radical".  The truth is that if you have a recent model digital camera, you will probably never need to resample to the degree shown above.  When you print your photos, a slight upsample or downsample may be needed, but you'll rarely ever need a drastic change in resolution to get a good print unless you do extreme crops or billboard size printing.  The most important thing is to use a good interpolation algorithm to interpolate to the PPI (pixels per inch) used by your printer, or an integer multiple thereof.  Some print drivers don't do such a great job of interpolation so if you send them an "oddball" size by just printing the original, you may end up with prints that have jagged edges.  This can be true even if you send the printer too many pixels, as some drivers don't even handle downsampling well!  One example showing the problem can be seen in Imaging Resource's review of the Olympus P400 dye sub printer.  Notice near the end of the page how the 400 PPI image looks much worse (more jagged) than the image that was downsampled to 314 PPI (the PPI of the printer) first.  This illustrates the importance of being able to resample to the PPI used by the printer prior to sending images to the print driver.

We can see some of the benefits and tradeoffs of upsampling in the above samples, but downsampling is just as important.  When we take an image consisting of concentric circles of increasing frequency and downsample that image with an appropriate amount of antialiasing, we get the following result showing a single set of rings emanating from the center:

Qimage default downsampling (includes antialiasing step)

If we take the same image and downsample using a standard downsampling routine without first performing the antialiasing step, we get:

PhotoShop bicubic sharper downsampling (does not include antialiasing)

As can be seen in this second example, lack of antialiasing has caused extra patterns to appear that were not in the original image.  While at first it may look like the second example has more "detail", in fact the extra detail is nothing more than artifacts caused by the resampling algorithm trying to consider data beyond the frequency limit.

 

A balanced approach

A well balanced interpolator will be able to downsample without aliasing artifacts while also being able to upsample without jaggies or over-softening the image.  Old tried and true methods such as bicubic or lanczos are usually good enough for most upsampling needs.  More advanced methods can increase visual quality for very large prints or special jobs, but be aware that there is only so much detail you can "add" to an image.  Some of the newer interpolation methods try to make all edges as sharp as possible and while these methods can make upsampled results appear sharper, they often tend to break the correlation between sharpness and depth of field and can make results look a bit like fingerpaintings.  Methods that produce smooth (jaggy free) images but don't try to sharpen, on the other hand, can appear a bit too blurry.  As with many things, there are tradeoffs to each method.

The key to the best results with any interpolation method is often to pick the appropriate amount of sharpening.  Interpolation methods that produce softer results can often handle much more sharpening before showing any artifacts, so a touch of extra sharpening can correct that soft look.  Similarly, a slight edge blur can remove that "painterly" feel of some of the sharper interpolation methods if needed.  Generally the more you stretch an image (the more interpolation you use), the more sharpening will be needed to compensate.  "Smart printing" tools like Qimage and some PhotoShop print sharpening plugins take all this into account and can automatically apply the proper amount of final sharpening based on the resolution of the original, the size of the final print, the resolution of your printer, and other factors to allow the print to be the most visually consistent at any size.

Probably the most important thing to realize in this entire article is that there is only so much you can do to "invent" data that is not there and when displaying or printing photos, you have to go to extremes in most cases to be able to see the difference between interpolation methods.  If you are captivated by some software or plugin that claims to do a much better job at interpolation, my suggestion would be to download a trial or do a search for reviews of the product before you buy.  I've seen some ridiculous samples posted on interpolation software websites showing a vast difference between their method and others, only to download the software and find out that it really does no better than the old bicubic method.  When you consider what the image "should" look like versus what we get out of various interpolators on the market, there really is very little difference between the better ones.  If you find yourself about to plunk down $200 for an interpolation program or plugin, you might want to think twice.  There are interpolation programs out there that offer a wide variety of methods for less than $50 that do as good or better than the high priced software.

Just for a sense of "calibration", one of the better methods available produced this result for the car wheel:

Some interpolation algorithms may render this image a little sharper, with a little more/less jagged edges, but the result will always be pretty similar to the above as far as the overall amount of detail that can be seen.  Now consider what this image would look like if we had taken it with enough resolution to begin with and didn't need to interpolate:

This final image clearly shows the limitations of interpolation.  Interpolation can reduce the appearance of artifacts like jagged edges but it simply cannot retrieve detail that is not there.  The 4x reduced image simply has only 1/16th the amount of data which means that 94% of the data in the interpolated result had to be "guessed" in the above samples.  Visually, the interpolated result is miserable in comparison to this last sample above regardless of the method used, but technically the result isn't too bad considering the fact that you started with only about 6% of the data you needed and you guessed at the other 94%!
 

 

Bottom line

The bottom line here is that interpolation can and does help improve the visual quality of images.  That said, don't expect magical results and beware of some of the mythical claims out there.  If you work for a magazine that normally starts with extreme crops and blows them up to 8x10 photos for print, you might be in the market for specialized interpolation software that allows you to pick the best method for each image/situation.  Just be aware that many of the "miraculous" results displayed on the web sites for some of these interpolation programs and plugins are quite exaggerated.  Better to try them first if they have a trial than to spend a significant amount of money and find out later that they really don't do much better than what you already have.  Finally, keep in mind that if you have a 5+ megapixel camera and you normally don't do much cropping nor printing above 8x10 size, interpolation method may never be a concern for you.  More important will be to find software that gives you the most benefit as far as the time it saves you and the quality of the final result.

Mike Chaney

Lighting, Viewing, and Metamerism

Background

Metamerism.  It might sound like a word that can only be understood by techno geeks, but it affects nearly everything you print.  Have you ever noticed that the colors in your printed photos look good under daylight from a window but those colors change under fluorescent or incandescent lighting?  Blue skies may turn purple under certain lighting, skin tones may look more yellow/orange, and grays may take on a color cast.  B/W prints often suffer from metamerism more than color prints and they can look neutral under some lighting only to take on a red or green color cast as you move the prints around your office or home.  Metamerism is often an issue when buying carpet, trying to match clothing color, drapes, and other items.  Colors may appear to match nicely in the store but when you get home, the colors look completely different in the lighting in your house.  This is metamerism in action.  In this article we'll take a look at metamerism, what causes it, and look at our options for controlling it.
 

 

Understanding how we perceive colors

The first thing we need to understand is how people perceive color.  Our eyes, like most photographic equipment, see color by using three primary color receptors: red, green, and blue.  By "sampling" the amount of red, green, and blue light present, our eyes can determine the color of an object.  Equal amounts of red and green let us perceive the color yellow.  Equal amounts of red and blue allow us to perceive magenta.  By varying the amounts of red, green, and blue light, we can see any color in the visible spectrum.  Image capture devices (cameras, scanners) record RGB intensities similar to the way our eyes record them and we use output devices (monitors, printers) to put these primaries back together so that our eyes see the same RGB intensities that were present in the original scene.  While printers use different primaries (a form of cyan, magenta, and yellow) the end result is the same: the devices try to put the data back together so that the red, green, and blue sensors in our eyes see the same intensities (or very close) as those in the original image.  Doing this "record and playback" successfully gives you an accurate representation of color in a printed (or displayed) photograph.
 

 

Primaries versus the color spectrum

It all sounds simple so far.  Unfortunately, while any color can be "simulated" by using primaries like red, green, and blue, spectral distribution is also important.  Think about a rainbow.  In every rainbow, we can see all the visible colors from red, orange, yellow, green, blue, indigo, and violet and all colors in between.  As the wavelength of the light changes from red to violet through the range of colors in the rainbow, the wavelength of light changes from say 700 nm (red) to 400 nm (violet).  If we had a light bulb that could reproduce any wavelength we desire by just turning a knob, we could turn the knob to about 580 nm and we would see yellow.  If we look at the spectral distribution of color for this light, we'd see a single spike of color at the 580 mark on the rainbow-colored graph.  The graph would show the rainbow of colors from violet to red across the bottom with a single vertical spike in the yellow location.

Now instead of a single yellow bulb, consider two bulbs: a red bulb and a green bulb.  The red and green bulbs will produce two spikes on the spectral distribution graph: a spike at red and a spike at green.  The graphs look completely different, but if we set the intensities just right and mix the red/blue light together, our eyes will perceive the two colors as the same because both "excite" the red and green cones in our eyes to the same degree.  So we can arrive at the same perceived color with very different lighting.  At this point, you might be tempted to say "who cares", but this is the first step to understanding metamerism.
 

 

How lighting affects prints

We all know that different lighting can affect the way you perceive color.  People are starting to buy bulbs that are advertised as more "natural" to improve the appearance of people (or other objects) in the home.  What makes different bulbs and different lighting technology more desirable?  First we have to consider the light spectrum from above.  Lets start with the sun.  Sunlight or "daylight" is considered full spectrum.  Full spectrum simply means that you have a relatively even distribution of every color in the spectrum from violet through red.  If you look at the spectral distribution of sunlight, you'd see a relatively straight line across the graph indicating that every color from violet, blue, cyan, green, yellow, orange, red are all present at nearly the same intensity.  This is the very definition of "white": the presence of all colors at once.

In contrast to daylight, most man-made lighting such as fluorescent and incandescent lighting has a very "spiky" distribution of wavelengths.  Our eyes may be able to adjust to any of these light sources, but each color in the spectrum may not be represented equally.  Here is a page showing the spectral distribution of different light sources.  As you can see, fluorescent lighting has a large green component but is deficient in red.  This can make fluorescent lighting look a bit green.  Conversely, incandescent lighting has a larger red component and is deficient in green and blue, making objects (or the light itself) look orange.

When we print photos, our printers distribute ink/dye with the assumption that we have full spectrum lighting as our viewing source.  We really have to assume full spectrum lighting because there is so much variation in lighting of even the same type (incandescent, fluorescent) that to do otherwise would only make the problem worse.  Because our printers reproduce color using primaries like cyan, magenta, and yellow, uneven distribution of light from a non full spectrum light source can shift colors due to the way the "spikes" created by our printer's cyan, magenta, and yellow inks happen to align with the spikes in our light source.  If our light source has a "valley" in the spectrum in the blue area and a "peak" in the red area, this might have the affect of enhancing the yellow ink while subduing the cyan ink.  Move to a different light source, and the opposite may be true, forcing the perceived color to change.  It's sort of like watching a runner who is pacing at a steady rate.  As long as the runner keeps pace, it doesn't matter whether the ground between his steps is solid or he is running on the tops of well placed poles because he doesn't use the ground that he isn't stepping on.  Place poles where he is stepping and he'll do fine.  As soon as he changes his pace, however, and his stride no longer matches the placement of the poles, he falls.  Same idea with matching your lighting with the color distribution of your inks.
 

 

So how do we deal with metamerism?

We have to consider the spectral distribution of light plus the spectral distribution of our inks to understand and control metamerism.  Sound complicated?  You bet!  So complicated in fact that there really is no simple answer.  Even if you use ICC profiles to get the best color for your printed photos, almost all ICC profiles are designed to produce accurate color under full spectrum lighting (D50).  View your prints under most indoor lighting, and your results may vary.  Some printers have inks that are more or less prone to metamerism, and some individual inks can cause more of a problem than others.  For example, the yellow ink in some printers has been found to be a major contributor to metamerism, so some specialized (mostly B/W related) software is designed to try to use less yellow ink so that your prints don't shift color as much from room to room.  It really is a complicated issue, but there are things that you can do to take control of metamerism.

The best (and relatively inexpensive) way to deal with metamerism in a controlled environment is to buy better lighting.  While Solux bulbs probably produce the best metamerism-free lighting, there are other options available that do a relatively good job.  For example, most home and garden centers now carry "daylight" or "natural" fluorescent bulbs for your home or office.  They are more expensive than regular office fluorescents but you can still probably replace all of the 48 inch fluorescent bulbs in a small office for less than the cost of a few packs of photo paper!  Most of these bulbs are labeled with a CRI (Color Rendering Index).  The closer the number to 100 (perfect daylight), the better.  A CRI of 90 would be considered good, 95-98 very good, and anything above 98 exceptional.  Not only will these bulbs help prevent color surprises in your prints, they also brighten the room and often give more of a revived feeling to the surroundings.

If you are printing B/W photos, you may want to invest in specialized software that produces B/W prints that are less prone to metamerism.  Most inkjet printers do not just use black ink to produce B/W prints: they still use a mix of black plus some of the color inks.  To understand why printers still need to place color ink on the paper when printing B/W photos is another article in itself, but most print drivers don't offer a "black ink only" option.  To make matters worse, most black inks aren't truly neutral anyway!  Our eyes can be more sensitive to color casts in B/W prints because we are very sensitive to slight color casts when we know the entire photo should be neutral.  If you find that your B/W prints shift color when moving to different lighting, you might want to consider a RIP (Raster Image Processor) designed for your printer such as QuadTone RIP.  In most cases though, an accurate ICC profile for your printer will do a decent job.

Also be aware that different printing technologies suffer from metamerism to different degrees.  Pigment based printers usually suffer from metamerism more than dye based printers, however, the latest pigment based printers have far fewer problems than the earlier models such as the Epson 2000P and 2200 which are known to produce prints more prone to metamerism.
 

 

Summary

Most people will probably go through life unaware of the issue of metamerism and to be honest, the problem is rarely so severe that people complain about it.  For those who are concerned with color accuracy and producing the best photos, however, there may be some situations where colors are difficult to match and knowing that metamerism can be an issue can at least allow you to deal with the problem.  As a general rule of thumb, metamerism is most evident in printed photos, so if you are having trouble with color matching in your printed photos, always take the photo to a window or take it outside to see if the problem persists under full spectrum lighting.  You might just be dealing with a particular color that is affected by metamerism.  It can be a tedious and losing battle to try to tweak colors under difficult lighting, so it's always a good idea to try daylight when dealing with color issues in printed photos just to identify where the problem is coming from.  This might not make the fix any easier if you must deal with difficult lighting or your photos must be displayed under that lighting, but at least if we can see and identify our enemy, we have more options in how to deal with it.

 

Mike Chaney

Shopping for a New Monitor

Background

Is your old monitor getting hard on your eyes?  Aging CRT monitors can be a real headache as they get older, lose contrast, and their ability to resolve crisp detail fades.  You've decided that the time has come to get a new monitor but your friend is telling you to get an LCD monitor while some coworkers swear by CRT monitors.  Who's right?  What are the pros and cons and what do you look for when shopping for a new monitor?  Let's see if we can give you the basics to allow you to decide for yourself.
 

 

CRT Monitors

Cathode Ray Tube (CRT) monitors have been around for a long time, have been refined over the years, and have a large following.  All this refinement means that there are some incredible CRT monitors on the market from your low end 15 inch "el cheapo" CRT all the way up to larger gamut 22 inch high end graphics station CRT monitors costing almost $5,000.  Still, the average digital photography enthusiast will likely notice that the selection of CRT monitors available at your local computer or electronics store is dwindling and stepping aside to make way for the LCD market.  At one popular computer warehouse store I found 18 CRT monitors compared to 89 LCD monitors.  At another, 7 CRTs to 51 LCD monitors. 

Seeing this swing from CRT to LCD, if you do decide on a CRT, are you going to be looking at an 80 pound paperweight in just a year or two?  Probably not, but it's worth looking into the reasons behind the apparent near demise of the CRT monitor to see what is driving these trends.  We'll get to that after we take a quick look at LCD monitors.
 

 

LCD Monitors

When LCD monitors finally started taking hold just a couple of years ago, selections were minimal and quality was questionable.  Anyone who had used a laptop two years ago would probably grimace at the thought of putting a "laptop screen" on their desk.  They had limited resolution, poor contrast, and color changed drastically when you moved your head from side to side and looked at the display at an angle.  LCD monitors have actually come a long way in just the past year or two.  They now offer much wider viewing angles (although there is always some fluctuation in color when viewing from an angle), their contrast  or "dynamic range" now bests almost any CRT, and they are faster than they used to be and don't have any significant "smearing effect" seen on some old laptop LCD displays.  In addition, the latest LCD displays offer crispness and clarity that even the high end CRTs can't match, especially when dealing with static non-moving images and text.  Let's take a look at some of the pros and cons of both CRT and LCD monitors in the next section.
 

 

CRT versus LCD

You guessed it: life is full of tradeoffs.  While LCD monitors seem to be the up and coming trend, CRTs still offer some advantages that may be important to some.

LCD Pros:

• "Pixel perfect" clarity: CRTs may look blurry in comparison once you've seen an LCD.

• Lightweight and easy to move around.

• Thin panel can often be scooted farther back on the desk without bumping into the wall.

• LCD monitors consume much less power than a CRT, reducing demands on other devices such as uninterruptible power supplies.

• High contrast: bright whites and dark blacks.

• Flicker free: LCD monitors don't "scan" the same way that CRT monitors do so you will never see any flicker on an LCD monitor.

• LCD monitors can't be magnetized like a CRT and are therefore less susceptible to distortions caused by speakers and other nearby devices.

• LCD monitors don't create static like a CRT and therefore collect less dust.

LCD Cons:

• Unlike CRT monitors which can be run at any resolution up to the max listed resolution, LCD monitors really only operate "properly" at their native resolution, limiting you to just one option for resolution.

• Color (especially of photos) can change slightly at an angle.  On larger (19 inch plus) LCD monitors, slight differences in color can even be visible on the same color displayed in the middle of the screen versus the edges due to the differing angle of view.

• A slight smearing effect can sometimes occur when watching video especially when the video shows fast moving objects.  Such objects can sometimes leave a trail.

• LCD monitors are prone to having dead pixels that appear as tiny bright/dark dots.

• LCD monitors can be more difficult to profile than a CRT and require a special LCD profiling device that may cost more than a CRT profiling device.

CRT Pros:

• CRT monitors are generally much cheaper than the same size LCD monitor.

• CRT monitors can run at any desired resolution up to the max listed resolution.

• CRT monitors can display high speed video without smearing.

• CRT monitors usually show no or minimal color change when viewed from an angle.

CRT Cons:

• CRT monitors can be bulky and difficult to move around.

• CRTs consume much more power than an LCD.

• CRTs are generally not as crisp and sometimes appear blurry or soft compared to a good LCD monitor (for still pictures or text).

• CRTs create static that attracts dust.

• CRTs often deliver less contrast (duller picture).

• The picture on a CRT generally degrades faster over time than an LCD.
   

 

Some things to look for

I could ramble on about dot pitch, dynamic range, viewing angles, and other tech jargon, but the best advice I can give is to go to your favorite computer/electronics store (preferably one with a large selection of monitors), and see for yourself.  Look at still photos, motion video, and text on each monitor and see which you like best and which model is easiest on your eyes for the work you do.  Keep in mind that a lot of electronics superstores may not have the staff or the knowledge to adjust each monitor so that it is working properly.  For example, they may be running a 1280 x 1024 LCD display at 1024 x 768 resolution which will make the display look horrible.  Ask the help at the store to be sure that the LCD displays are all running at their "native" resolution because if they are not, you really can't effectively compare LCD monitors.

Here's a quick checklist for shopping for a monitor:

• If you have an idea about the type of monitor you want beforehand, do a search using your favorite search engine and look up some of the models listed for sale where you plan to shop.  Read user reviews and/or print them for the models you might be interested in and bring them to the store.  Some online retail outlets have user reviews that can be very helpful.

• It is actually easier to shop for a CRT because you can just evaluate video, still photographs, and text on screen and make a judgment.

• When dealing with LCD monitors, know what resolution you prefer beforehand.  Most LCD monitors up to about 19 inches are going to be 1280 x 1024 and you'll have to run them at that resolution to get the most out of them.  The next step up are 1600 x 1200 resolution LCD monitors and that jump usually means a pretty significant jump in price too.  If you think you'd like to run your monitor at 1600 x 1200 resolution, you'll likely have to spend more than a thousand dollars on an LCD.  If that's out of your budget but you still need the higher resolution, you may be stuck with a limited selection of CRTs.

• When looking at LCD monitors, assuming they are being run by Windows and that you have access to the desktop, right click on the desktop background and select "Properties".  Then click the "Settings" tab at the top and look at what is listed in "Screen resolution".  For an LCD monitor, the number listed there should match the resolution listed on the little tag on the shelf in front of the display (hopefully there is one).  If there is a mismatch, the LCD display is being driven at the wrong resolution and any visual comparison is fruitless.

• Know your workflow.  Do you work with video more than stills?  If so, be aware of the LCD smearing effect.  Display video on both LCD and CRT monitors to see if you can see any smearing or "trails" when video is being displayed on the LCD.  Some LCDs are better than others in this area.  Smearing or trails on some of the better LCD models is negligible.

• When looking at the LCD monitors, move your head from side to side with a colorful photo displayed on the screen.  Do the colors change or dull when you move your head from side to side?  Is the effect enough to bother you?  Will you sometimes be viewing from an angle or need to have more than one person view the monitor at a time, say for presentation or evaluation purposes?  Generally the more expensive LCD models will have this under control as they have a wider "viewing angle".  Some of the cheaper ones may cause more noticeable changes when viewed from an angle.

• If you spend a lot of time in a word processor, spreadsheet program, or other application that requires text, open up WordPad or something that shows text and see how easy the different models are on your eyes.  You don't want to go to a store and buy a monitor that displays an awesome red rose only to come home and start your normal work on a legal paper to find out that text rendering is terrible on that monitor!

• Finally, take into account the size and shape of the display itself.  Is it going to fit on your desk at an appropriate height and distance from your eyes?  Whatever you do, don't buy a big CRT monitor only to bring it home and find out that it is so deep that it hits the wall and forces you to view it too close.  There's a lot of discretion here as far as size, distance, and exactly what you are using the monitor for.  Common sense and a measuring tape is probably all you need here.

 

 

Summary

With LCD monitors becoming more popular, my incentive for writing this short article was to give potential buyers enough information to make the right decision when purchasing a new monitor.  I often get asked what to look for when shopping for an LCD monitor or whether LCD is really better than CRT, so this article may at least give you the basics of what to look for so you can decide for yourself.  Hopefully I've covered the major points and have identified some potential stumbling blocks in the process of buying a new monitor so that these stumbling blocks and potholes can be avoided.  If you are thinking about replacing your aging monitor with the latest technology, it always helps to know what to look for since the way you shop for an LCD monitor can be different from how you shopped for your last CRT.  In the end, buy whatever fits both your needs and your eyes best.  After all, it is you who will be looking at it most of the time.

 

Mike Chaney

Understanding Embedded Image Info

Background

Ask someone to define "digital photo" and they'll probably tell you some things about taking photos on a digital camera, viewing them on a monitor, and printing them on a printer.  Let's face it, that's what most of us do: point, shoot, view, and print.  The "casual" digital photographer may never realize that there is more to their images than the picture that gets displayed or printed.  There is a host of information stored in most images taken straight from the camera.  Of course the picture itself takes up 99% or more of the data in the image, but do you know what else is embedded in your photos?  Let's take a look at some common embedded information to see if it can help us in any way.
 

 

The image header

The file that contains your image also has a header that contains information such as the file format (JPEG, TIFF, etc.), the resolution of the image (3000 x 2000 for a 6 megapixel image for example), how the image is encoded (RGB for example), and some other useful tidbits that help software to decode the photo inside the image file.  In addition to this basic information, "extended" information about the photo may also be included such as whether the flash was on or off during the shot, the distance from the camera to the subject, the shutter speed, aperture, and even GPS information on some cameras.  The information (both basic and extended) is usually stored at the beginning of the file, hence the term "file header".  The actual photo is normally stored immediately after the header in the file.  Let's take a look at some common types of "extended" information that can be embedded in digital photos.
 

 

Embedded EXIF information

By far the most common and most standardized embedded image information is EXIF, short for Exchangeable Image File format.  Today nearly all digital cameras embed EXIF information in each image.  This information usually includes dozens of parameters that describe the shot such as the shutter speed (1/250 for example), the aperture (f/2.8 for example), date/time of the shot, flash on/off, ISO equivalent film speed, and many more.  In addition to shot-specific information, there are also many fields that get repeated from shot to shot such as the camera manufacturer, camera model, lens type, firmware version, etc.  Information such as shutter speed and aperture can help in diagnosing problems such as motion blur, depth of field issues, etc.  If you are not familiar with these terms and you tend to point-and-shoot most of the time, these fields may be less useful to you.  Some information, however, such as the date and time of the shot can be useful to everyone since file dates get changed and almost never indicate the date and time that the actual picture was taken.

Some image formats such as the Windows bitmap format (BMP) do not support embedding of extended header information, so you'll find EXIF information in file types such as JPEG, TIFF, or raw but if you save your images in an older format such as BMP, TGA, etc. the header information may be "stripped" from the file since the file format doesn't support it.  Be aware of this should you resave an image in a different format and find that the embedded information has been lost in the copy.  As with any type of file [header] format, EXIF has its limitations.  The EXIF data stored in photos from your digital camera is mostly technical in nature and doesn't allow for much (if any) end-user editing so you cannot really use EXIF to store user data or comments.  To view EXIF information stored in your photos, you can use a tool like Qimage.  Simply roll your mouse cursor over thumbnails in the thumbnail grid in Qimage for example, and some of the more important/common EXIF data will be displayed on the status bar on the bottom of the window.  To view some of the less common fields from the extensive EXIF information in your images, try a dedicated EXIF viewing tool like Exifer.
 

 

Embedded ICC profiles

While the EXIF header in your images does have a field called "color space", use of this data is very limited because the only two values allowed in the EXIF color space field are (1) sRGB and (2) unspecified.  This basically means that there is no way to tell what color space (ICC profile) to use if the color space is not sRGB (a standard color space for the PC/Windows platform).  For this reason, an ICC profile describing the specific color space of the image may be embedded in the file as well.  When an ICC profile is embedded in the image, most ICC aware (color managed) software applications will automatically recognize the embedded profile by reading it from the image header.  If you are using a color managed workflow, embedded profiles become quite useful because they take the guesswork out of how to interpret the color in photos and how to translate that color to your monitor and printer.
 

 

Embedded IPTC information

One popular data format called IPTC, short for International Press Telecommunications Council, allows users to enter their own data and have it stored in the embedded image header.  Developed initially for the journalism community, the data field names can be a bit cryptic.  As a result, some programs give the fields more readable names that don't necessarily follow the standard.  IPTC allows the user to enter information such as keywords, description, location the picture was taken, photographer's name, priority, etc.  Many photo editing tools allow you to view and edit the IPTC information in images.  One good thing about putting your own information into the original image is that the image can be passed along to others with the image itself unchanged.  The ability to write comments and other information into an image can give the photo itself more meaning to those who may view it out of context.
 

 

Other embedded data formats

We round out our look at embedded information with a few embedded data formats that were developed to help printers reproduce more faithful color.  First up is Epson's PIM (Print Image Matching) and PIM II.  Knowing that full color management using ICC profiles can be more complicated than some users would like due to availability of profiles (or lack thereof) for various devices, Epson introduced PIM as an answer for matching the color from your digital camera to the print.  Once PIM was introduced, many manufacturers started making their (newest) digital cameras PIM compatible by embedding the necessary PIM info in the header of each image captured by the camera.  While not as robust and arguably not as accurate as full color management using (accurate) ICC profiles, PIM and PIM II do offer a way to transfer information like contrast, saturation, lighting, etc. from the camera to the printer to allow the printer to adjust to different image capture conditions.

About a year after the release of the initial PIM from Epson, EXIF released their EXIF 2.2 format also known as "EXIF Print" at the time.  A more industry-wide and more standard format, EXIF 2.2 endeavored to encompass much of what Epson's PIM was doing in a format that was already being used by all manufacturers, i.e. a format considered by most as less "proprietary".  EXIF 2.2 offered capabilities similar to PIM with respect to recording the image capture conditions to produce a better print, but proved to be a bit less "automatic" than PIM because the latter had a more defined workflow.  PIM was seen by many as a more defined solution whereas EXIF 2.2 or "EXIF Print" was seen as "here's some data about the image: use it however you like". 

So far, solutions like PIM, PIM II, and EXIF 2.2 have yet to take off and solidify themselves as the standard for managing printed color.  In my own opinion, the reasons for these solutions not taking root in the industry as the be all/end all solution for printer color management are twofold: (1) color management via ICC profiles is already the established and accepted international professional standard for color management of any device and (2) PIM and EXIF 2.2 solutions tend to be a bit less robust and less "scientifically accurate" than using ICC profiles.  Both of these points are reasons that many third party photo and printing applications do not support the special "plugins" needed to decipher and make use of PIM and EXIF 2.2 printing.   A very robust and accurate international standard for color management already exists through the ICC (International Color Consortium) in the form of ICC profiles and third party add-ons for supporting ICC profiles have been readily available for years.
 

 

Summary

Hopefully this article has given you a taste for some of the information that can be embedded in images from your digital camera.  If any of the above information appeals to you or you think that any of the mentioned data would be of benefit to you, simply plug in terms like EXIF, PIM, IPTC, and ICC into your favorite search engine and you can spend hours looking at additional information and downloading tools to allow you to view and manipulate the data.  There's a whole hidden world of information in your images that maybe you didn't even know existed.  Sometimes you don't know how useful the information can be until you have it in front of you.  :-)

 

Mike Chaney

Soft Proofing Basics

Background

We've touched on many aspect of color management in previous articles, but have not dealt with soft proofing until now.  If you've read some of my prior articles on color management and you have started using a color managed workflow with accurate image, monitor, and printer profiles, you may have heard about or noticed a feature called "soft proofing".  In this article, we describe what soft proofing can do for you and how it should be used in a color managed workflow.

What is soft proofing?

Soft proofing, available in some ICC aware software such as my own Qimage photo printing software and other high end photo editors, allows you to see how your printer will render the colors in an image by displaying a "simulation" of the print on screen.  Seeing what the print will look like by viewing a simulation of the print on your monitor can be helpful as it may allow you to evaluate different printer profiles and rendering intents without wasting paper/ink.  Anything that can improve our ability to make the right choice with respect to printer profile and rendering intent can save you time and resources.  Keep in mind that soft proofing simulates how your printer will reproduce colors in an image, so we use soft proofing to compare color rendition not other aspects such as sharpness or fine detail.  If you are viewing what a print should look like on your screen, how accurate can this simulation be?  Read on to find out what factors are involved in getting an accurate soft proof.

Under the hood

Soft proofing of a print by viewing a simulation of the print on a monitor requires three things: an image profile, an accurate monitor profile, and an accurate printer profile.  When you soft proof an image on screen, the ICC engine in the software you are using will follow these two steps to produce the soft proof:

1. First the image will be color converted from the image profile (the profile tagged on the image) to the printer profile.

2. Once colors have been converted to the printer profile, a second color conversion is performed that converts color from the printer profile to your monitor profile.

By converting to color used by the printer and then converting the printed color to the color used by the monitor, we can simulate the color of the print on the monitor.  At this point, it should become clear that both the monitor and printer profile must be 100% accurate for soft proofing to be truly accurate.  Since the printer profile is used twice in these color conversions, both the "forward" and "reverse" look up tables in the printer profile must be accurate and the monitor profile must be accurate as well.  Any inaccuracies in either the monitor or printer profile will cause color errors in the soft proof and will cause the on screen "simulation" to differ from the actual print.  Add in some metamerism (the fact that printed color might look different under different lighting) and the fact that your monitor cannot display all the colors that your printer can display (and vice versa), and you end up with some serious limitations in what soft proofing can accomplish.

Soft proofing in practice

Given that inaccuracies and gamut differences can add up to discrepancies between a soft proof and the actual print, what is the best way to utilize the information provided by a soft proof?  Fortunately, if you have an accurate custom monitor profile created via a monitor colorimeter (device that attaches to the monitor to measure color and create a profile) and an accurate printer profile based on the specific printer, paper, and ink you are using, the soft proof simulation on screen will most likely look very much like the print with respect to color.  There may be some differences brought about by certain lighting conditions or differences in color gamut such as the fact that your printer can produce yellows and cyan colors beyond the reach of your monitor, but overall, the soft proof should generally match the print.  The unfortunate side of the equation is that few of us have both monitor and printer profiles that are so accurate that soft proofing results in an exact match.

 

The proof is in the printing

If you are having trouble getting your prints to match your screen, soft proofing is not going to work well for you by definition.  A no-match condition between the print and your screen indicates that either the monitor profile, the printer profile, or both have inaccuracies that cause errors in color rendition.  These inaccuracies will manifest themselves in a mismatch between the soft proof and the actual print.  Since few of us really know how accurate our profiles are until we gain some experience with them, the best advice I can give is to run some test prints!  I cannot stress this point enough, in that the true proof is in the printing.  I can't count how many times I have gotten email from people who have been stopped in their tracks and refuse to print because their soft proof "doesn't look good" only to run a test print and find out that the actual print looks fine and the error was in the soft proofing, the monitor profile, or some other part of the process.  Soft proofing is also unable to account for errors such as using the wrong paper, printing on the wrong side of the paper, switching to a different ink, clogged nozzles, or even having one obscure setting not set properly in the print driver.  Because there are so many factors involved, always run a test print to be sure your soft proof isn't telling you the wrong story.  Once you've run a few test prints and have compared those to the equivalent soft proofs on screen, you'll be able to get an idea about how well soft proofing is working for you.

So by all means, use soft proofing if you like, but never use it as a substitute for printing.  Soft proofing should be used only when you know you have accurate monitor and printer profiles and even then, only to judge overall "look and feel" of the color.  Soft proofing can be helpful if you are working with a special image and you are wondering whether "perceptual" or "relative colorimetric" rendering intent would be better for that image.  It is not a good tool, however, to determine which of four different printer profiles works best with the paper you are using: you'll need to produce test prints using each of the four profiles to make the best decision and to see the true subtleties that only the printer can print.  Soft proofing is a useful tool for evaluating overall color but if you are working on specific aspects of color such as trying to get just the right shade for your friends yellow sweater, be sure to print a small test print to be sure you aren't being fooled by differences between the soft proofed image and the actual print.

Mike Chaney

Whatever Happened to JPEG2000?

Background

In 2001, the official release of the JPEG2000 spec sent ripples through the digital imaging industry.  Camera and software manufacturers had already started planning a quick path that would lead us all to hardware and software upgrades that would make our web browsers, imaging software, and cameras even better by allowing use of this new "wavelet" based image compression scheme which provides higher quality images using even less storage space than the old JPEG standard.  Back in 2001, it was thought that the changeover from JPEG to JPEG2000 would be well on its way by 2003 and by 2004 it was expected to be the new standard for file storage in digital cameras.  So what happened?  It's now 2005 and there are still no digital cameras that support JPEG2000 and support for this new standard really only made it into "mainstream" digital imaging software within the last year or two.  Did JPEG2000 fall on its face?  Did it not live up to the hype?  Read on and I'll give you my own insights into the subject.

JPEG2000: All show and no go?

The obvious guess as to why JPEG2000 acceptance has been slow might be that it was all hype.  Nothing could be further from the truth, however, as JPEG2000 certainly outperforms the old JPEG standard.  JPEG2000 images can retain much more detail than a JPEG image compressed to the same size.  In addition, the JPEG2000 standard allows for lossless compression, greater than 8 bit/channel support, and other features not in the JPEG spec.  Take a look at the image below.

The original image at the top has been highly compressed (about 60:1) to produce the two images on the bottom.  You can easily see how much better JPEG2000 does (right above) at this level of compression.  We must look elsewhere to discover why JPEG2000 has gained acceptance slower than expected, as it clearly does perform.

Backward Compatibility

 

One issue with the new format is that JPEG2000 is not backward compatible.  That is, it isn't just a rewrite of the JPEG standard and JPEG2000 code cannot be used to read JPEG files.  For this reason, completely new code has to be written to address JPEG2000 images and if you also want to support the older JPEG standard, you must rely on having the old code present at the same time.  JPEG2000 images are really quite different from JPEG images so backward compatibility with the JPEG standard doesn't make much sense.  Nevertheless, it is a completely new image format and not just an upgrade of an existing one, which can ultimately limit the speed with which it is accepted into the market.

Complexity

The wavelet technology used to create and decode JPEG2000 images is much more complex than the code used for JPEG images.  With increased complexity comes an increase in code size, increase in memory requirements, and a decrease in performance.  What this means is that reading and writing of JPEG2000 images will take longer and will require more complex software that needs more memory to run.  Speed and greater memory usage are often tradeoffs for quality in digital imaging.  The fact is, some of the initial code released for the JPEG2000 standard was very slow (up to 10 times slower than JPEG).  Many saw this as unacceptable for the perceived difference in quality when using only moderate to low compression (the above example is one of extreme compression that you wouldn't normally see in practical terms).  It took a year or two for the algorithms to be tweaked to the point that good JPEG2000 code today runs "only" about 2-3 times slower than code for JPEG images, depending on compression level.

 

The Waiting Game

Let's face it.  JPEG images are already quite good.  An 18 megabyte image from a 6 megapixel dSLR camera can be compressed into a 2 megabyte image with almost no visible degradation in image quality.  You really have to zoom in and look hard to see any difference between the 18 megabyte (TIFF) original and a 2 megabyte JPEG.  The fact that camera memory keeps getting larger and cheaper doesn't help JPEG2000 either.  Most people will not care that their 1 GB memory card that cost them maybe 85 bucks will "only" hold 500 JPEG images and it could probably hold 1500 JPEG2000 images at similar quality.  The fact that your camera will take 2-3 times longer to store JPEG2000 images on the camera card, potentially affecting shooting/buffering speeds, might also make it a tough sell for people using high end (read fast) cameras and those who have the need for speed.

I believe that due to the tradeoffs involving compatibility, speed, and code complexity, hardware and software manufacturers are in a sort of stalemate.  It appears that software manufacturers who develop mainstream tools like photo editors, image management, and web browsers are waiting for camera manufacturers to start supporting JPEG2000 as a native format in cameras and other devices.  In turn, the camera manufacturers are waiting for global acceptance of the format in tools like web browsers, image management tools, photo editors, and other software.  Nobody seems to be jumping at the opportunity to do it themselves because for most companies, it is all about cost/benefit.  Do you spend the resources required to update the processing chips in your cameras when millions are already on the market with the old JPEG format and memory cards are so high in capacity and cheap?  Do the software companies spend the resources to include JPEG2000 support when none of the hardware can save JPEG2000 "JP2" files?  This "wait and see" attitude along with advances in areas like storage capacity make JPEG2000 look a little less "juicy" than it did five years ago.

 

The Current State of JPEG2000

Whether or not JPEG2000 becomes the defacto standard for compressed images remains to be seen.  It's actually a shame that people seem to care less and less about storage space and that a technologically advanced standard like JPEG2000 just sits waiting for someone to jump on it and lead it down the road to success.  Right now, with all cameras still using the old JPEG format, JPEG2000 AKA "J2K" or "JP2" has become an image format for the "elite" who have specialized needs such as storing a high volume of images in limited space.  Instead of becoming the new standard for compressed images, it has become more of a "toolbox" feature that allows people to re-encode images into a smaller size for special [storage] needs.  It seems like the web would be the first logical place for JPEG2000 to take off as web space and download times could outweigh most performance issues related to decoding and displaying the images.  Hopefully the makers of software such as web browsers will take note and start to support JPEG2000 on the web.  I believe JPEG2000 still has a chance to make it into mainstream hardware like digital cameras, phones, PDA's, and especially the web.  Some applications may never overcome the tradeoff of performance and code complexity, but in my heart of hearts, I still have to believe that JPEG2000 is just slow in acceptance... not dead!

Mike Chaney

Understanding Rendering Intents

Background

Let's take a break from print driver settings this month and talk about rendering intents.  Rendering intents are an often misunderstood concept of color management that can affect how you use your ICC profiles.  As usual, I'll try to keep things as simple as possible in order to assist in the understanding of how rendering intents affect results when you select perceptual, relative colorimetric, saturation, and absolute colorimetric intents when using ICC profiles.  That said, it is impossible to discuss this subject accurately without getting into some technical detail so if you feel like you are getting lost, stick with it and we'll summarize it in the end to hopefully put some meaning into the tech talk.  If you've read information on other sites regarding rendering intents and you think you know all there is to know about them, please read on as there is an abundance of inaccurate information on the web regarding rendering intents and how they actually work. 

Why are rendering intents needed in the first place?

Color management (the use of ICC profiles) is a game of give and take and involves many compromises.  The main reason that we make compromises in color management is because the gamut (range of colors available) on one device is often very different from another.  A bright saturated blue color displayed on your monitor for example may not be reproducible on your printer because your printer simply cannot make that color.  In this case, we would say that the example blue color is in the monitor's color gamut but outside the printer's color gamut.  Trying to reproduce a reasonable visual representation for colors that are out of range on a device is what rendering intents are all about.  For example, we may use tricks like reducing the saturation of the entire print so that a color that is out of range still appears a bit more vibrant than ones that are in range.  Rendering intents simply use different methods  to "trick" the eye into believing that the print can reproduce irreproducible colors.

Visual representation of color gamuts

The above represents the gamut of colors available in the Adobe RGB color space (red wire frame) and the gamut of the Canon i9900 printer using Canon Photo Paper Pro (solid color gradient).  The hue and saturation of the color (red, green, blue, orange, etc.) is represented in the 2 dimensional X/Y axes while the luminance (brightness) is on the Z axis.  The red wire frame shows the range of all possible colors available in your image if your image is stored in Adobe RGB color space.  The solid gradient indicates the range of all possible colors reproducible by your printer.  As you can see, most of the printer's color gamut is contained within the Adobe RGB wire frame but small sections like the bright yellow peak that protrudes through the Adobe RGB gamut (middle-left) indicate that there are some colors that the printer can reproduce that cannot be captured in the image.  There are also large sections of the Adobe RGB color space like the empty space in the wire frame on the bottom-right that indicate colors that might be present in your original image that cannot be reproduced by your printer.  It is the handling of these "out of range" colors that we'll refer to in discussing the rendering intents below.

Relative Colorimetric Intent

If we look at the 3D gamut representation above, we can see that our Adobe RGB images might have colors (lower right of the red wire frame) that cannot be reproduced by our printer and that same image might also have colors that are inside both the solid gradient and the wire frame, indicating that those colors are in our image and they are reproducible on the printer.  One way to handle the mismatch of gamuts is to: (a) render all colors that are present in the image and are directly reproducible by the printer to the proper color and (b) render all colors that are outside the printer gamut to the nearest color on the edge of its gamut (called the "gamut hull").  The gamut hull, visible in the above graphic, simply represents the extremes of what the color space or device can reproduce and usually represents colors that are bright and saturated.  Other colors inside the hull (not on the surface) are simply colors that are less vibrant so that they are not as close to the extremes of what the color space or device can reproduce.

Looking at the gamuts above, all colors that are inside both the solid gradient and also the red wire frame are not a problem: we can render those directly from the image color to the same color on the print.  Colors that lie inside the wire frame but are outside the solid gradient are colors that are in your image but are not reproducible on the printer.  For those, we look at the gamut hull (solid gradient above) and we pick the point on its surface that is closest in distance to the color we are trying to make in the wire frame.  This method obviously has some drawbacks.  Since there are many colors inside the image gamut that can map to the same point on the printer gamut hull, it means that we may see banding in our prints as a particular gradient (like blue sky for example) might all map to the same spot on the hull of the printer's gamut.  On the positive side, at least all of the colors that are reproducible by the printer are reproduced accurately.

Note that the small section of yellow that protrudes through the wire frame indicates colors that the printer can reproduce but cannot be contained within our original image.  Since the image cannot contain those colors, we need not worry about trying to reproduce them in the context of rendering intents because they cannot be present in the image.

 

Perceptual Intent

As mentioned above, relative colorimetric intent has the benefit of being able to reproduce all colors that are reproducible.  That is, if the printer can reproduce the color, it will... accurately.  The down side to relative colorimetric intent is that we often have images that exceed the printer's gamut and when this happens, we may see banding (sometimes called posterization) of color in the prints.

Perceptual intent is a rendering method that tries to get around the fact that out-of-range colors might result in banding.  With perceptual intent, we compress or "squash" the gamut of the image down a bit so that not as much of the wire frame sticks out beyond the solid gradient of our printer's gamut.  If we squash the gamut of the image so that the wire frame is smaller, there won't be as many colors in the image that can't be reproduced on the printer.  This will eliminate or at least reduce the amount of banding in the prints because more colors (in our image) are now in range of the printer.

When we artificially squash the image gamut down to try to fit more of it inside the printer's smaller gamut, we generally end up with a print that has reduced saturation.  If we reduce saturation by only a little, our eyes may not notice the difference on the print other than the colors not being quite as vibrant as those under the non-squashed relative colorimetric intent.  All things being relative, the print can look better because although it is a bit less vibrant in color, the banding present in the relative colorimetric rendering is gone or at least reduced substantially.

Other than reduced color vibrancy, there is another down side to perceptual intent.  The current ICC CMM (color management model) is not a "smart" model meaning that it cannot and does not examine the gamut of the actual image before trying to compress it to fit in the printer's gamut.  While the gamut available to your original image (the red wire frame) is large, your actual image may only contain a few dull colors like some green foliage and people wearing light pastel clothing.  All colors in your image in this case may be reproducible by the printer.  A "smart CMM" might be able to look at the original image and determine that it doesn't need any squashing to be printed.  Unfortunately, the CMM does not have any knowledge about the image being rendered and must perform a sort of "blind rendering" that assumes that all possible colors must be taken into account whether or not they actually exist in your image!

Some misinformation on the web would lead you to believe that because the CMM cannot account for image gamut, that it simply compresses the entire gamut of the color space used by the image so that it fits inside the printer's gamut.  This is, however, also not true.  Squashing the entire color space where the image resides into the printer's color space would amount to taking the entire wire frame above and shrinking it in size so that no corners protrude through the printer's solid gamut in the diagram.  As you may be able to see by the graphic, that would be an extreme amount of compression that would result in noticeable color desaturation.  In addition, it would mean that the same image encoded in two different color spaces of different sizes (say sRGB and Adobe RGB) would result in two different prints with different amounts of desaturation even though the original images should appear the same as they both have all the same colors:  they are just encoded differently.

What all this amounts to is the fact that perceptual intent basically uses an arbitrary amount of gamut compression (squashing) in order to reduce the banding effects that might be present in relative colorimetric intent.  The amount of compression, which will show up in the printer's ICC profile, is really up to the creator of the printer profile.  What is normally done is that when creating a printer profile, the available gamut of the printer is taken into account and a level of compression is chosen so that most colors that are likely to be seen in a photograph will be "pulled back" into the printer's gamut.  If it sounds "wishy washy", that's because it is!  Many web sites point out the original concept of rendering intents and point out that relative colorimetric intent clips the gamut while perceptual compresses it, but these "ideal" concepts are not what is ultimately going on behind the scenes in the CMM.

 

What does all this mean?

By now you are probably either kicking yourself for even reading this article because it seemed so simple before, or you're getting close to deciding to just use perceptual intent and not worry about the whole subject of rendering intents.  :-)  My purpose, however, is not to confuse but to inform.  I want people to understand the limitations of color management as it exists today and to understand what is really going on not just the high level concepts.  If I were to try to put all of the above as simply as possible, I'd say:

Perceptual Intent: Use this method for most of your work especially if you intend to just set it and leave it alone.  Perceptual intent will produce prints with accurate hue and while overall saturation levels may be a bit less, you are unlikely no notice this by just examining the print by itself.  In addition, this method reduces artifacts like banding in blue skies.

Relative Colorimetric Intent: Use this rendering method in certain cases where reproducing accurate colors is paramount.  This rendering intent is often used when your original image contains only a narrow range of colors.  As an example, if you are reproducing an image of the Grand Canyon and there are only rust colored Earth tones in the scene, perceptual intent may take some of the clarity out of the photo because of the compressed color gamut and because there aren't a variety of other colors present for our brains to get a relative "lock" on the entire scene.  Using relative colorimetric intent in this case should make the texture of the rock look more realistic and more defined because all of the colors in the photo are likely to be within the gamut of the printer due to the fact that they are not bright, saturated colors.

 

What about the other intents?

We have two intents left, but I won't spend much time on those since they are of little/no value when reproducing photographs.

Absolute Colorimetric Intent: Absolute colorimetric tries to reproduce the exact colors recorded in the original scene.  Sounds even better than relative colorimetric until you realize that absolute colorimetric intent reproduces these colors with no regard (no adaption) for the illuminant or light source.  Simply put, using absolute colorimetric intent will usually result in awful color shifts because our eyes will try to adapt to the illuminant (white of the paper, color temperature of the monitor, etc.) and the same color may look different under different lighting.  As such, absolute colorimetric is used mainly for reproduction of specific colors like reproductions of fabric or logo colors.

Saturation Intent: With perceptual rendering intent, we may sometimes notice that colors have been a bit desaturated to fit bigger gamuts into smaller ones.  To overcome this sense of desaturation, the saturation rendering intent tries to keep accurate saturation while shifting other factors like the hue of the color.  This intent can be useful for things like screen captures, bar graphs, and other images where the hue of the color is less important than the overall "pop" of the image.  Simply put, in photographs, people are more likely to notice that a stop sign looks too magenta than the stop sign not being vibrant enough.  The converse is true when displaying a pie chart where people are much less likely to care that the red in the pie chart looks a little shifted toward magenta but the presentation may have less "impact" if the entire pie chart looks dull!

 

Summary

These are the games we play when trying to fool our eyes into believing that a print or an image on the monitor looks the same as it did when it was recorded/captured and what is really going on behind the scenes when we make the decision about which rendering intent to use.  Hopefully the information in this article has given you a bit more solid a foundation to stand on when dropping down that often misunderstood selection called "rendering intent".

Mike Chaney

Using ICC Profiles with Canon Printers

Background

Last month we discussed how to properly utilize ICC profiles with Epson printers.  This month we focus on the use of profiles with Canon printers.  Many of the latest Canon printers come with ICC profiles.  Unfortunately, they have cryptic file names such as CNB5CCA0.ICM and descriptions that aren't much more help than the file name such as "Canon i960 PR1".  Do you know how to make use of these profiles or even what paper they are for?  If not, read on and we'll try to make using these profiles as simple as possible.  As we did last month, we will assume for the purpose of this article that you have ICC (color managed) software such as Qimage or PhotoShop that you will be using to print photos.

What is a profile?

An ICC profile is a file that describes how to achieve accurate color on your printer with a certain type of paper. You need to have a profile for the specific paper (and ink) you are using. For more information on what profiles are and how they work, read my August 2004 article entitled "Over the gamut and through the woods" .

Finding the right profile

If you have a newer model Canon printer, it may have come with ICC profiles that installed automatically from the software CD that comes with the printer. The following profiles install with the Canon i960 driver for example:

File name	Description	Paper Type	Quality Setting
CNB5CCA0.ICM	Canon i960 PR1	Photo Paper Pro	1
CNB5CCB0.ICM	Canon i960 PR2	Photo Paper Pro	2
CNB5CDA0.ICM	Canon i960 MP1	Matte Photo Paper	1
CNB5CEA0.ICM	Canon i960 SP1	Photo Paper Plus Glossy	1

In addition to the above profiles, you may find another more generic profile called CNBJPRN2.ICM with the description "BJ Color Printer Profile 2000".  This CNBJPRN2 profile is too generic to be of much use and isn't a "real" printer profile, but is more of a color matrix shaper.  As such, use of this generic profile should be avoided and profiles for specific paper/quality types should be used like the ones above.  Your Canon printer may have profiles with slightly different names, but just remember that the description includes the printer model followed by the paper type (PR = Photo Paper Pro, MP = Matte Photo Paper, and SP = Photo Paper Plus Glossy), and finally the quality setting at the end (1, 2, 3, etc.).  Using the profile description (visible in your photo editor or printing software in the profile selection dialog), you should be able to choose the right profile for your printer and Canon paper.

If you are unable to locate any profiles for your printer or the paper you are using, you could try downloading and installing the latest driver for your printer.  It is possible that profiles will be installed with the driver.  To obtain the latest driver for your Canon printer, go here and use the dropdown menus to locate your printer.  You can then download and install the driver.

If you are just not able to find any ICC profiles on the Canon web site for your printer (or paper that you are using), you could always create an ICC profile yourself using a tool like Profile Prism, but the intent of this article is to illustrate how to use readily available profiles for Canon paper.

Finding the WRONG profile!

Please remember that printer profiles are designed for a specific printer, a specific paper type, and specific print driver settings. Don't try to use a profile designed for Canon Photo Paper Pro with a different brand paper for example. The paper may look the same and people may think it behaves the same way in your printer, but you will likely be wasting your time and ink since profiles only work with one type of paper. Similarly, profiles for a previous (older) model printer will likely not work properly either since the printer hardware is probably slightly different and the driver may be slightly different as well.

General overview of using printer profiles

Let's assume you have located the profile for your printer and paper. There are two steps in using the profile and if both steps are not performed correctly, you can end up with horrible color in your prints (most often either green/yellow color cast or dull/dark/muddy prints). Let's look at the two steps to properly utilizing a profile below.

Step 1: Print driver setup

First we have to set all print driver settings to those required by the profile. Print driver setup is usually accessed via "File", "Printer Setup" or by clicking "File", "Print" and selecting "Properties" for your printer. A profile will only work with one specific set of driver parameters. If you choose any parameter incorrectly such as selecting the wrong paper type, wrong quality setting, selecting "Vivid Photo" from the "Effects" tab, etc. the profile will not work properly. If the profile you are using came with a "readme" file, be sure to view the contents of that file and set the driver settings accordingly. If there is no readme file that outlines driver settings (there rarely is), you may have to rely on the file name. You need to know the printer model, the type of paper, and the printing mode (quality setting) as a minimum.

Let's use the Canon i960 and Photo Paper Pro as an example. The i960 driver CD installs several profiles, one of which is "Canon i960 PR1". By the description, we can tell that this is the profile for the i960 printer with Photo Paper Pro and is designed to be used with the driver set to quality level 1. The following driver settings are appropriate for use with this profile:

Once the "Custom" and "Manual" radio buttons have been checked above and the "Grayscale Printing" checkbox UNchecked, click the first "Set" button on the right of the window under "Print Quality".  The following window will appear:

Slide the Quality slider to the right so that it rests under the "1" for quality.  Click the "Diffusion" button next to Halftoning and click "OK" to accept.  Now back on the main driver window (first window above) click the second "Set" button under "Color Adjustment".  The following window will appear:

Make sure that the "Intensity" slider and all four color sliders are set to zero (center position), UNcheck the "Enable ICM" check box and set "Print Type" to "None".  Click "OK" to accept.  Now back on the main driver window, click the "Effects" tab at the top.  The following window will appear:

On the "Effects" window, be sure to UNcheck all check boxes so that no effects are selected.  Click "OK" to accept these settings, return to the main driver window, and click "OK" to accept all the settings on all of the above windows.

Your Canon driver screens may look a bit different than the above i960 driver screens, but most Canon drivers are very similar.

Step 2: Select the profile in your printing software

Now that we have opened our print driver setup window and have selected all the proper parameters in the driver itself, we must make the proper selections in our printing software to tell that software which profile to use. Step 1 of the process (above) simply prepares the driver to accept profiled data. It is in step 2 that our printing software must apply the profile. To do this, we need only tell our printing software which profile to use by giving it the file name. Refer to the steps below to see how to perform steps 1 and 2 in Qimage and PhotoShop.

Workflow for Qimage and PhotoShop

Qimage:

Step 1 (from above):

• In Qimage, click "File", "Printer Setup" from the main menu.

• Select your printer and click "Properties" for that printer.

• Follow the screens from step 1 above to set the print driver settings.

Step 2 (from above):

• Click "Settings" from the main menu and then "Color Management".

• Click the "Enabled" box under "Printer" toward the middle of the window.

• Click the browse "..." button in the "Printer" group.

• Click the "All Windows Profiles" on the lower right of the window.

• Scroll through the list and double click on the proper profile (for example "Canon i960 PR1").

• Leave rendering intent set to "Perceptual" with "Black Point Compensation" checked.

• Click "OK".

• Add photos to the queue and print.

PhotoShop:

Step 1 (from above):

• In PhotoShop CS, click "File", "Print with Preview" from the main menu. In prior versions of PhotoShop, click "File", "Print Options".

• Click "Page Setup".

• Click "Printer" at the bottom of the window.

• Select your printer and click "Properties" for that printer.

• Follow the screens from step 1 above to set the print driver settings and click "OK" to return to the "Print with Preview" window.

Step 2 (from above):

• Back on the "Print with Preview" window, check "Show More Options".

• Drop down and select "Color Management".

• Under "Print Space" at the bottom, drop down "Profile" and select the proper profile (for example "Canon i960 PR1").

• Set "Intent" to "Perceptual" and check "Use black point compensation".

• Click the "Print" button and print your photo.

Once step 1 and 2 have been performed you can print any photos you like and they will all be profiled using the printer profile you selected in step 2. Note that Qimage remembers all software and print driver settings even if you exit Qimage and come back later, so step 1 and 2 will only have to be performed once and will only need to be redone if you change print driver settings for some other purpose/profile. PhotoShop will not remember your settings so you'll need to redo both steps above each time you print or save your settings from the print driver window if your driver has that option.

Most problems with using profiles are caused by an error in one of the two steps above:

1. Failure to set print driver settings appropriately such as paper type, print quality, and print type "none".

2. Forgetting to turn on the profile in your printing software.

As long as you always insure that the print driver settings are set properly per the readme file that comes with the profile (or per the instructions in step 1 if no readme is provided) and that you have told your printing software which profile to use, you'll get accurate color for all your photos.

Mike Chaney

Using ICC Profiles with Epson Printers

Background

Most new Epson printers like the R1800 come with ICC profiles for various papers and even if you have an older printer, Epson may have added some ICC profiles for your printer to their printer software download pages. Increased availability of profiles means that there are a lot of people out there asking how to use them. While I applaud Epson for taking the lead in providing more and more ICC profiles for their printers and papers, documentation for how to use these pre-made profiles is scarce. Do you know where to find these profiles, what they are, and how to properly utilize them? If not, read on and we'll try to make using these profiles as simple as possible. Since driver settings are handled a bit differently for different model printers, we'll focus on using profiles with Epson printers in this article. We will assume for the purpose of this article that you have ICC (color managed) software such as Qimage or PhotoShop that you will be using to print photos.

What is a profile?

An ICC profile is a file that describes how to achieve accurate color on your printer with a certain type of paper. You need to have a profile for the specific paper (and ink) you are using. For more information on what profiles are and how they work, read my August 2004 article entitled "Over the gamut and through the woods" .

Finding the right profile

If you have a newer model Epson printer, it may have come with ICC profiles that can be installed from the software CD that comes with the printer. For example, the R1800 has an installation option for installing the ICC profiles. If your installation CD does not have an option for installing profiles, you may want to explore the CD anyway to search for files ending with *.icm or *.icc to see if there are some "hidden" profiles on the CD. If you find any, you can right click and select "Install Profiles". If you find any profiles on your software installation CD that came with the printer, they will likely be for the most popular Epson papers such as Epson Premium Glossy, Premium Luster, etc. Remember that one profile is needed for each paper type.

If your software installation CD does not contain any ICC profiles, there may be some available on the Epson printer support web page. Simply scroll through the list, find your printer, and click on it. On the next page, click "Drivers & Downloads". If any profiles are available for your printer, there will be a link for "ICC Profiles". Sometimes some ICC profiles are included with the "PIM" plugin, so you might check the PIM download as well if all else fails. If no link is visible that references ICC profiles, most likely Epson has not gotten around to creating any for your printer yet.

If you are just not able to find any ICC profiles on the Epson web site for your printer (or paper that you are using), you could always create an ICC profile yourself using a tool like Profile Prism, but the intent of this article is to illustrate how to use readily available profiles for Epson paper.

Finding the WRONG profile!

Please remember that printer profiles are designed for a specific printer, a specific paper type, and specific print driver settings. Don't try to use a profile designed for Epson Premium Glossy Photo Paper with a different brand paper for example. The paper may look the same and people may think it behaves the same way in your printer, but you will likely be wasting your time and ink since profiles only work with one type of paper. Similarly, profiles for a previous (older) model printer will likely not work properly either since the printer hardware is probably slightly different and the driver may be slightly different as well.

Also be aware that the old Epson profiles that you may find on your hard drive (these are usually files that start with EE_ followed by a number) should be avoided because they are not designed to be used outside the print driver itself and are generally quite inaccurate. Newer profiles are normally files that start with SP (for Stylus Photo) followed by your printer model number and paper type: for example SPR1800 PrmGlsy BstPhoto.icc.

General overview of using printer profiles

Let's assume you have located the profile for your printer and paper. There are two steps in using the profile and if both steps are not performed correctly, you can end up with horrible color in your prints (most often either green or magenta color casts). Let's look at the two steps to properly utilizing a profile below.

Step 1: Print driver setup

First we have to set all print driver settings to those required by the profile. Print driver setup is usually accessed via "File", "Printer Setup" or by clicking "File", "Print" and selecting "Properties" for your printer. A profile will only work with one specific set of driver parameters. If you choose any parameter incorrectly such as selecting the wrong paper type, wrong resolution, selecting "PhotoEnhance", etc. the profile will not work properly. If the profile you are using came with a "readme" file, be sure to view the contents of that file and set the driver settings accordingly. If there is no readme file that outlines driver settings, you may have to rely on the file name. You need to know the printer model, the type of paper, and the printing mode (quality setting) as a minimum.

Let's use the R1800 and Premium Glossy Photo Paper as an example. The R1800 software CD installs several profiles, one of which is SPR1800 PrmGlsy BstPhoto.icc. By the file name, we can tell that this is the profile for the R1800 printer with Premium Glossy Photo Paper and is designed to be used with the driver set to the "Best Photo" quality setting. Unless otherwise specified (in a readme file), use the following print driver settings:

Note that the important settings are circled in red. Options that are not circled such as "High Speed" or "Edge Smoothing" can be set to on or off as you like since they won't affect color enough to cause problems with the profile. Your Epson driver screens may look a bit different than the above R1800 driver screens, but the most important thing is to be sure to select the paper type, quality, and select the "no color adjustment" mode. Other printers may list the quality setting as a DPI number such as 1440 or 2880 instead of "Best Photo", but the idea is the same. If the file name or an associated readme file doesn't give you any information at all about how to set the print driver settings, there is no point using the profile. A profile is basically of no use unless you can at least identify the paper it is for and the print quality used in the driver.

Step 2: Select the profile in your printing software

Now that we have opened our print driver setup window and have selected all the proper parameters in the driver itself, we must make the proper selections in our printing software to tell that software which profile to use. Step 1 of the process (above) simply prepares the driver to accept profiled data. It is in step 2 that our printing software must apply the profile. To do this, we need only tell our printing software which profile to use by giving it the file name. Refer to the steps below to see how to perform steps 1 and 2 in Qimage and PhotoShop.

Workflow for Qimage and PhotoShop

Qimage:

Step 1 (from above):

• In Qimage, click "File", "Printer Setup" from the main menu.

• Select your printer and click "Properties" for that printer.

• Follow the screens from step 1 above to set the print driver settings.

Step 2 (from above):

• Click "Settings" from the main menu and then "Color Management".

• Click the "Enabled" box under "Printer" toward the middle of the window.

• Click the browse "..." button in the "Printer" group.

• Click the "All Windows Profiles" on the lower right of the window.

• Scroll through the list and double click on the proper profile (for example "SPR1800 PrmGlsy BstPhoto.icc").

• Leave rendering intent set to "Perceptual" with "Black Point Compensation" checked.

• Click "OK".

• Add photos to the queue and print.

PhotoShop:

Step 1 (from above):

• In PhotoShop CS, click "File", "Print with Preview" from the main menu. In prior versions of PhotoShop, click "File", "Print Options".

• Click "Page Setup".

• Click "Printer" at the bottom of the window.

• Select your printer and click "Properties" for that printer.

• Follow the screens from step 1 above to set the print driver settings and click "OK" to return to the "Print with Preview" window.

Step 2 (from above):

• Back on the "Print with Preview" window, check "Show More Options".

• Drop down and select "Color Management".

• Under "Print Space" at the bottom, drop down "Profile" and select the proper profile (for example "SPR1800 PrmGlsy BstPhoto.icc").

• Set "Intent" to "Perceptual" and check "Use black point compensation".

• Click the "Print" button and print your photo.

Once step 1 and 2 have been performed you can print any photos you like and they will all be profiled using the printer profile you selected in step 2. Note that Qimage remembers all software and print driver settings even if you exit Qimage and come back later, so step 1 and 2 will only have to be performed once and will only need to be redone if you change print driver settings for some other purpose/profile. PhotoShop will not remember your settings so you'll need to redo both steps above each time you print or save your settings from the print driver window if your driver has that option.

Most problems with using profiles are caused by an error in one of the two steps above:

1. Failure to set print driver settings appropriately: paper type, print quality, and color management mode such as "no color adjustment".

2. Forgetting to turn on the profile in your printing software.

As long as you always insure that the print driver settings are set properly per the readme file that comes with the profile (or per the instructions in step 1 if no readme is provided) and that you have told your printing software which profile to use, you'll get accurate color for all your photos.

Mike Chaney

Can't take just one byte? 48 bit images.

Background

In this month's article, we dabble in the world of 16 bit per channel (48 bit) images. Your camera or scanner might support these higher bit depth images but what are they? What do they do? When do you use them? And most important, are they worth it being that they are double the size of a normal 24 bit image?

Bits, nibbles, bytes, and words

Most people are aware that anything digital (computers, cameras, scanners) operate using lots of ones and zeros where 1=on and 0=off. The most basic unit of measure in a computer is known as the bit: a bit can only be on or off.

Next in the line of common measures is the nibble. A nibble contains 4 bits, each of which can be turned on or off independently and it turns out that there are 16 different combinations you can get by turning 4 bits on/off in different patterns, allowing us to count from 0 to 15 with 4 bits.

The most well known measure is the byte. A byte contains 8 bits and allows you to count from 0 to 255 because there are 256 different ways you can arrange 8 bits by turning each one on/off individually. Most images that you see on the web such as JPEG images are stored by assigning RGB values to each pixel (dot) in the image (brightness/intensity values for red, green, and blue) and most images use 8 bits for each color channel. 8 bits for red, 8 bits for green, and 8 bits for blue give you 24 bits and allow you values of 0-255 for each primary color. Starting with 0,0,0 (black) and moving through all possible combinations up to 255,255,255 (white) gives us 16,777,216 possible colors in a 24 bit image.

A little less known measure is the word. A word contains 16 bits and allows you to count from 0 to 65535. While a byte only allows values ranging from 0 to 255, two bytes together that form 16 bits allow you to have much greater precision. Allowing values from 0 to 65535 for each of the red, green, and blue primary colors for each pixel means that you can address a total of over 281 trillion colors! A 48 bit image still covers the exact same color range as a 24 bit image: 0,0,0 black to 65535,65535,65535 white and everything in between. The difference is that you can define the range with many more steps to make much finer gradients. It is similar to having a ruler that only has measurements down to 1/8 inch and then putting marks down to 1/32 inch for finer measurement. You haven't changed the fact that an inch is an inch, but you can better define your position within that inch with finer gradations.

281 trillion colors? Do we really need that?

It has been argued that the human eye can discern about 10 million different colors, so is 281 trillion really necessary? The notion sounds ludicrous until you consider the variety of conditions that we try to "sample" with our images and how we sometimes post process them before they are ready for display. Your monitor and printer are 8 bit per channel (24 bit) devices that can "only" display 16.8 million colors so 24 bit images is all they understand or need. Your camera or scanner however, may not have captured the image in a ready-to-display condition so manipulation can actually reduce that 16.8 million color range significantly. Let's take a look at why.

Consider an example where your most well composed wedding photo was underexposed due to improper metering. Instead of capturing brightness values from 0-255 for each primary color, your camera may have only used the lower half of that range (0-128). For those familiar with histograms, this histogram would appear weighted to the left with nothing in the highlights and the image itself would look very dark. Of course, you'll try to fix this by increasing the exposure (brightness) of the image so that 0-128 gets "stretched" to (let's say) 0-255 and now there are things in the photo from true black to true white. The problem in stretching 0-128 to 0-255 to brighten the image is that you are now using only half the available values in the 0-255 range: 0,2,4,6,8,10, etc. You have effectively taken yourself from a system that can display 16.8 million colors down to one that tries to cover the same color range with only about 2 million steps, and you have probably also increased noise (grain) in the process! At 2 million colors, you risk being able to see the steps between each color in some smooth areas like blue skies and other gradients and the result may look like banding or posterization in the image. Similar effects can occur even in a properly exposed image if you have to make significant changes in color such as might be needed to correct improper white balance, a "blown out" red sweater, or other color issues.

48 bit images from your camera/scanner

The biggest benefit of capturing raw images with your camera or scanner, that is, images with a high bit depth such as 48 bits, is that they allow for more latitude when making corrections. In the above example of underexposure, a 48 bit image would be reduced from 0-65535 values down to 0-32767. Even if you "rescale" that range to brighten up the image, you still have plenty of steps in the scale to create a properly exposed final 24 bit image to feed your monitor/printer without risking banding because the 24 bit image only needs 256 steps for each color and you still have 32768 to work with. Keep in mind that when a 48 bit image is converted to 24 bits, the range 0-65535 is simply scaled down to 0-255.

Scanners have their own light source so they are typically not prone to the same environmental factors that cause things like under/over exposure in cameras, so the 48 bit scanning modes are a bit less useful than raw capture mode on cameras. Basically the closer you can guarantee that your image will be to the proper exposure and color, the less need there will be for higher bit depth images like 48 bit TIFFs. There are some exceptions such as using super wide color spaces, but that's beyond the scope of this article and is usually not an issue for the vast majority of work. For scanners, I typically never use the 48 bit capture mode just because the conditions rarely warrant it, the "scene" is usually very reproducible, and scanner sensor noise levels often exceed the threshold that would give any real benefit with 48 bit images anyway.

Cameras are another story. I tend to always try to shoot in raw mode and process with a professional level raw conversion tool because photographs capture moments in time that are usually impossible to recreate. Set your camera to JPEG mode and underexpose that one important shot and you stand a good chance of not being able to salvage it. If you are shooting in raw capture mode, the extra precision offered by the higher bit depths captured in raw files often allows you enough leeway to get acceptable shots of even the worst cases of underexposure and (to a lesser extent) overexposure.

Real world advice on 48 bit images

To be honest, if your scanner typically returns scans that need very little manipulation and are generally properly exposed right out of the box, I see no need to use 48 bit capture mode on a scanner for most work.

If your camera, however, supports a raw capture mode and you are willing and have the time to do the post processing work to develop those "digital negatives", it can really save you from time to time and can often lead to better image quality just because you are allowing a more powerful computer process the raw data rather than letting the camera do it before it makes a JPEG for you. Even if you never make any mistakes, raw images often show greater resolution and sharpness and higher color accuracy than the camera can deliver in JPEG mode.

Once you have your 48 bit images in hand, make whatever exposure or color corrections you need and feel free to save the final version as a normal 24 bit TIFF or even JPEG when you feel it is ready for display/print. Remember that nothing is lost in having the final/edited version saved as a 24 bit file to make it available to other software such as photo editors, printing software, and email programs: it saves space and your monitor/printer will want a 24 bit image anyway as they don't understand 48 bit data.

Mike Chaney

Size Matters: Paper Size vs. Print Size

Background

This month we deal with another topic that seems simple on the surface but can get rather complex when you actually start dealing with it. In this article we uncover some differences in how paper is handled by printers and we'll learn how to avoid some common problems that can leave you rather surprised at the difference between the size you chose to print and the size that actually comes out of the printer.

How your printer sees your paper

Loading a sheet of 8.5 x 11 paper into your printer seems like such a simple thing. You might be tempted to think that your printer sees the same 8.5 x 11 paper that you see and that it should be able to print any size print up to 8.5 x 11 on that paper. Unfortunately it is rarely that simple. Most printers default to a mode that can only print on a portion of that 8.5 x 11 paper. Your printer for example, may only be able to "address" an 8.0 x 10.7 inch portion of the paper. To make matters worse, the 8.0 x 10.7 rectangle that is available for printing on the 8.5 x 11 paper is usually off-center meaning that you could print something as large as 8.0 x 10.7 but if you do, it will not appear centered on the page.

So you've fed a sheet of 8.5 x 11 photo paper into your printer only to discover that the printer can only use an 8.0 x 10.7 inch area on that paper, leaving uneven borders around the edge that the printer sees as inaccessible. The reason that your printer cannot print in these edge/border areas is due to physical limitations of the printer itself. The print head must have enough time to accelerate for example and get up to a constant speed before spraying ink and must decelerate at the opposite side of the page, creating the left/right borders. The paper itself must be able to load and be moved accurately by the rollers, which creates the top/bottom borders. These limitations mean that there is a "printable area" on the page that is smaller than the paper itself, and that this printable area is a an area inside which the printer can operate optimally to produce the highest quality prints. There are often driver options that can affect these limitations, so read on.

Understanding print driver jargon

We already mentioned some limitations which may not allow you to use an entire sheet of paper from edge to edge and top to bottom. These limitations cannot be overcome by printing software because the limitations are part of the printer's physical design. If you are willing to live with some compromises, however, they can sometimes be overcome or changed by selecting certain options in the print driver. Let's take a look at some common print driver options that allow you to change the printable area on a given page.

Note that not all options are available in all drivers

• No options checked: If none of the options below are checked, it is likely that your printer will only be able to print to a portion of the page as described above. If you do not specifically select any options most printers will have a border along all 4 edges ranging from about .1 inches up to possibly .6 inches. This leaves you with a maximum print size that is smaller than your paper size of 8.5 x 11. Note that some drivers call this default printable area "maximum" in contrast to "centered" below.

• Centered: Some drivers have a "centered" option. This option simply adds more margin to the default margins so that the printable area is centered. If the default margins for top and bottom are .3 on top and .5 on the bottom for example, the "centered" option will simply add .2 inches to the top margin so that both the top and bottom margins are .5 inches. Obviously this option has an undesirable side effect in that it will always reduce the size of the printable area. In our example, unchecked you might have been able to print 10.7 inches tall and now with "centered" checked, you can only print 10.5 inches tall.

• Borderless or "no margins": Many newer printers offer a "borderless" mode activated by checking the "borderless" checkbox in the driver, usually under the "Page Setup" tab in the driver. Checking this box actually activates quite a number of features along with some compromises. Note that borderless mode may not be available (selectable) for all paper sizes and all types of paper, so you may find the option disabled when you are printing on 8.5 x 11 paper while it is available for 4x6, 5x7, and 8x10 paper. All printer models are different in which paper sizes and paper types support borderless printing. Borderless mode, if it is available for the paper size you are using, will allow you to print on the entire paper surface, but doing so will create a number of issues to be aware of (see "The borderless conundrum" below). Note that "no margins" is similar to borderless except that "no margins" generally only removes the left/right margins: top/bottom margins remain.
  

The borderless conundrum

We've discussed how most printers and print drivers behave in their default configuration and that you will likely not be able to produce a print as large as the full paper size you are using. Many newer drivers, however, offer an option called borderless printing. Borderless printing basically allows you to put ink on the entire page without having any white space or "borders" on the left, right, top, or bottom. Activating borderless printing by checking "borderless" or "no margins" in the print driver, however, does more than just allow your printer to access the entire page, and creates a new set of issues to deal with.

• Quality: Most of the time, print quality will decline near the edges of the paper. You may be warned about this when you select borderless in the driver. Honestly, I've never seen any noticeable decline in print quality except some slight banding on older printers. The difference in print quality in the middle of the page versus the edges is subject to many factors including printer model and the type of paper being used.

• Overspray: First we have to realize that paper loading mechanisms are not perfect. There is some "slop" when your printer loads the paper and it can be off by as much as 1mm left-to-right when loading and the paper rarely aligns perfectly parallel with the guides. This slop in the mechanism means that if you were to print a 4x6 print on 4x6 paper, you would end up with tiny slivers of white on one side and a tiny sliver of the print missing off the other edge. The bigger the print size, the harder it is to keep the paper aligned through the entire printing process. To overcome this problem, most drivers create some overspray which actually prints part of your photo off the edge of the paper onto a sponge. That way, if the paper slips a bit one way or the other, something is still being printed all the way up to (and beyond) the edge of the paper, thus eliminating white slivers at the edges of the paper.

• Expansion: If you print a photo at 4x6 inches on 4x6 paper, for overspray to be able to account for slack in paper loading, there obviously must be some expansion (enlargement) of the image. In reality, your 4x6 photo has to be expanded to something like 4.2 x 6.2 inches so that about .1 inch of the photo prints off the edge of the paper. This is where most of the confusion begins with borderless printing. Due to the fact that your print driver expanded your 4x6 print and is printing part of the photo off the edge of the paper, there will be some cropping of the image at the edges. Some print drivers allow you to adjust the "amount of extension" but be aware that most drivers will not allow you to turn expansion (AKA extension) off completely because doing so usually results in small slivers of white on one or more edges.

• Print size surprises: Due to the way print drivers enlarge images when borderless mode is selected, your prints will always be a little larger than the size chosen. This is usually not a big problem if you are printing one photo that covers the entire page such as a 4x6 on 4x6 paper because the fact that the photo is slightly enlarged to 4.2 x 6.2 and a small sliver of the photo is missing at the edges will go unnoticed unless important parts of the photo are very close to the edges. If you decide to print four 3x2 prints on borderless 4x6 paper, however, you will notice that your 3x2 prints are a little larger than expected due to borderless size expansion. You may also notice that a small piece of your 3x2 prints is missing along each edge of the paper because the side adjacent to the edge of the paper will have some "overspray" that printed beyond the edge of the paper. These issues can be confusing when exact cropping and sizing are needed. It can be very difficult to obtain exact cropping and sizing when using a print driver in borderless mode.

• Printer maintenance surprises: If you are someone who prints almost everything in borderless mode, you may eventually be surprised with a printer maintenance message after printing thousands of borderless prints. Most printers keep track of how much ink is being sprayed onto the overspray sponges or overspray tanks and you may get a message that the printer needs maintenance to clean/empty the sponge/tank that holds the ink overspray. You may not even be able to continue printing until the maintenance is performed. The counter that tells the printer when the overspray sponge/tank might be full is only incremented when borderless mode is being used so be aware that excessive borderless printing may actually result in extra printer maintenance. Please don't email me and ask how many borderless prints you should expect before this happens because I have no idea and I do not believe that information is readily available. :-) I only know from experience that I've seen it happen on inkjet printers from more than one manufacturer.
  

Some borderless printing tips

• Borderless printing is usually fine if you are printing a single photo per sheet such as one 4x6 on 4x6 borderless paper, one 5x7 on 5x7 borderless paper, etc. The fact that the driver slightly enlarges the photo so that some of it prints beyond the edge of the paper is of little consequence for most snapshots.

• You should probably try to avoid borderless printing if being able to get an exact crop (an exact portion of the image) or being able to print at a specific size is paramount. When important details in the image lie near the edges or there is a frame that is being printed around the image, remember that your print is being "stretched" a bit so it won't be exactly the size that you specified and also remember that your frame or other important details near the edge of the photo may be cut off slightly. Borderless mode is also not recommended when printing posters that span multiple pages because it is likely that the edges of your poster will not align properly.

• Many Canon print drivers offer a selection called "amount of extension". If you slide the "amount of extension" slider all the way to the left, you can actually disable the driver expansion but be aware that doing so may cause small slivers of white border to appear on your paper because the paper cannot align exactly every time. Most other non-Canon drivers do not allow you to completely disable the print size expansion but some allow you to select less/more overspray which equates to less/more expansion.

• Qimage has an option that allows you to disable borderless print expansion even if the driver does not allow it to be disabled. You can click "Page", "Borderless Overspray/Expansion" and then choose "disable" and Qimage will reverse the effects of the print driver enlarging your photos. While disabling overspray/expansion will ensure that your prints print at exactly the size chosen, you will be subject to the slop in the printer's paper loading mechanism and you may see some small slivers of white along one or more edges. If your printer's paper loading mechanism is consistent in that it always loads the paper a little too far left creating a tiny white sliver on the left of the page, you can compensate using margins in Qimage. With a little experimentation, this method of borderless printing will allow you to get exact sizes without the driver's artificial enlargement and will also allow you to eliminate all but the thinnest sliver of unprinted white border.

• Whether your driver allows you to disable expansion completely in the driver or you do it with software such as Qimage, be aware that with expansion disabled, you will now be printing exactly the size that you specified. Printing exactly a 4x6 on paper that is exactly 4x6 inches means that any slop in the paper loading mechanism is going to show up on your prints as a white sliver on one side and a sliver of the image missing off the opposite side. Loading more sheets of paper or even a different brand paper may cause paper to load differently which can cause the slop in the loading mechanism to change. In general, you can usually remove all but a tiny hairline margin that may or may not be bothersome depending on the type of work you are doing. Just be aware that disabling borderless expansion has its tradeoffs.
  

Summary

Your printer has some inherent physical limitations that will likely not allow it to print over the entire surface of the paper you are using regardless of paper size. These limitations are recorded as unprintable margins which are reported to printing software. Printing software will honor these limitations/margins. Unprintable margins can be eliminated by using borderless printing mode, if available in the print driver, but borderless printing opens up a new set of potential problems such as unwanted print (size) enlargement and cropping due to overspray and expansion by the driver. Being aware of the limitations of each printing mode as they relate to what you can actually print on your paper will help you avoid surprises when printing.

Mike Chaney

Color Management in a Nutshell

Background

In my Over the Gamut and Through the Woods column from August 2004, I made an attempt to explain how to use color management and ICC profiles. In this article, we take a step back in order to discover whether or not we really need color management and we'll discuss some alternatives. As you can see by the August 2004 article, moving into a color managed workflow requires the use of ICC profiles which you may not be familiar with initially. In addition, acquiring these profiles is not always free and may require at least some minor investment. Ultimately, your investment of some time and money can pay off in the form of more accurate color on screen and in print, but is it worth it?

The naked eye

Assessing color by eye is a simple process that involves some very complex issues. We may look at a printed photo and discover that it looks very dull with washed out colors. This is a simple assessment but it can be caused by a multitude of problems. Simply cranking up the saturation on the image and reprinting may solve the problem to your satisfaction, or it may create other problems like loss of detail in bright colors like blue sky. You might even look at a printed photo in your office under fluorescent lights and notice that a blue flower looks too purple, only to take the same print to a window and the flower appears the proper shade of blue under outdoor lighting.

Assessing our needs

Rather than try to understand all these interactions, why they happen, and the possible fixes, let's ask ourselves some simple questions to help us determine whether or not we really need to step into the world of color management and ICC profiles.

1. Are you happy with color in your photos? This is ultimately the driving force behind color management for most people. If you take photos with your camera, print them, give them to friends and family, and everyone thinks they look great, you probably don't need color management. The only problem here is that many people who used to think their prints looked perfect say they didn't know what they were missing after they tried a true color managed workflow. It is very difficult to "imagine" how your photos could look better on screen or in print without seeing the difference. If you strive to get the best reproduction of your photos and you are open to the possibility that they can be improved, read on.

2. Do your photos look very close to the same (color-wise) on screen compared to your prints? A common problem with non color managed workflows is that there are often differences in color when you compare a print to what gets displayed on your monitor. Everything might look reasonable until you run across that one purple sweater that just doesn't look right in print but looks fine on screen, or the orange beach ball that looks fine in print but looks too yellow on screen. If you are generally happy with the way your photos appear on screen and in print but you find a few of these scattered nagging issues, color management and the use of ICC profiles is the most straightforward way of correcting "oddball" problems with color. Trying to correct them using other (manual) image editing methods often corrects the problem at hand, but creates a new one somewhere else.

3. If you've decided to try a color managed workflow, are you willing to make the investment in time/money? It takes some time to learn how to use ICC profiles, learn where to activate them in your software, and learn how to use different options that relate to the use of ICC profiles. My Over the Gamut and Through the Woods column from August 2004 goes a long way toward that understanding. It may take a few hours of reading and using your ICC aware software to get up to speed, but we're normally not talking weeks/months of experience or anything really overly complicated once you understand the basics. As far as monetary investment, see below for a breakdown.
   

The color management investment

Time and money are the major costs of a color management workflow. It will take a little reading to understand how to use ICC profiles in a color managed workflow and may actually complicate your workflow a bit if, for example, you change from one type of photo paper to another and now find that you need to acquire a new ICC profile for the new paper. In a non color managed workflow, you would just print on the new paper and experiment a bit. If you see something you don't like, you can change some print driver options or tweak the image and reprint. In a color managed workflow, use of the new paper is less of a manual effort and more of a scientific measurement process. While it may take some extra time up front to print test targets and create an ICC profile for the new paper, it does at least guarantee some level of color accuracy and in the long run may save a lot of time by eliminating reprints, manual tweaks, and fiddling with image edits.

So let's say you'd like to give it a try, but what about the monetary investment? If you use your monitor as a "draft" view, are mainly concerned about color accuracy in prints, and don't do a lot of image editing with respect to color, you might be able to get by with just profiling your printer to create an ICC profile for the printer. A low cost printer profiling tool such as my own Profile Prism is a good investment for getting color accurate prints by allowing the profiling of any printer/ink/paper combination. Such a tool will cost about $79. But what if you don't have a scanner? A good flatbed scanner is required to be able to profile a printer because a scanner is used to "read" the printed target along with a reference target to make the adjustments in the profile. If you have an old scanner or your current scanning software is inadequate, the scanner may not be good enough to create accurate printer profiles. If that's the case, add about $100 to $120 for a good scanner like the Canon LiDE 80 that is capable of creating excellent printer profiles when combined with scanner based printer profiling software.

Starting from scratch, we can now create our own printer profiles for any inket or dye sub printer, paper, and ink combination for a monetary investment of about $200. Considering the price of ink, photo paper, and time, that's not bad, but what about the monitor? If you do decide to do some edits and work on color in your images, your monitor may also need a profile because the edits you do on screen might not look the same when you print. Although your printer is printing accurate color via a printer ICC profile, your monitor may have some issues with accuracy. You can do a visual "calibration" of your monitor using a monitor calibration tool like Adobe Gamma or the monitor calibration tool that comes with Profile Prism, but realize that this is not as accurate as profiling. To create a truly accurate profile for your monitor and "close the loop" on color management, you will need to buy a colorimeter that attaches to your monitor. The colorimeter takes actual readings and creates an accurate profile. You can get a good monitor colorimeter with software for $250 to $300 at places like ColorVision or Monaco Systems.

When we add these up, we're at $500 to take total control of color. The input device (camera) needs a profile too, but it is beyond the scope of what most people will be able to do to create camera profiles. The better/professional cameras usually come with a "color space" setting which is the same thing as a profile. For example, set your camera to sRGB color space, and all images from the camera will be in the sRGB color space profile. Set it to Adobe RGB, and all images will use the Adobe RGB profile. If not specified or selectable in your camera, sRGB is the only real choice. Just remember that a full color managed workflow requires an accurate ICC profile for both the input device (camera/scanner) and the output device (monitor/printer). If you are missing an ICC profile on either side of the input/output equation, accuracy may be questionable.

Go or no?

Ultimately your decision on whether or not to adopt a color managed workflow will depend on your wants and needs. If you are a professional or a semi-pro who occasionally sells prints or does work for publications, you will probably want to use color management because the benefits will show in your work and your time/money invested will come back to you. Color management via ICC profiles is currently the only method of dealing with color that can actually ensure some level of scientific accuracy in the results. If you are a "casual shooter" who prints a few photos from time to time and you don't consider digital photography a hobby, you may be hard pressed to justify the time and money investment required in a color managed workflow.

This certainly doesn't mean you need to be a pro to justify color management. You might simply be someone who takes pride in their photography and you want that to show in your photos. Different combinations of equipment (cameras, scanners, monitors, and printers) work better together and you might be using a combo that produces very adequate results without fooling with color management. On the other hand, you may be someone who has been plagued with inaccuracy in certain colors in your prints and you want a better way to solve the problem than the endless moving of sliders in your image editor. Some problems are very difficult to solve by manual tweaking but are easily solved using color management. Here is just one example of how different equipment can render different results and how color management can bring them together in a scientific, measurable way with no (or very little) manual tweaking.

Mike Chaney

Coming to Terms with DPI, PPI and Size

Background

I get a lot of questions about DPI, PPI and image size, enough to indicate that a lot of people are having trouble grasping some of these concepts when applied to their images. In this article, we'll try to make the terms and concepts of DPI, PPI, and physical size a little less of a mystery while at the same time offering some simpler methods of dealing with image/file size and resolution.

Understanding the terms

DPI or "dots per inch" is a term that normally describes the resolution of a printer since printers produce colors by placing colored dots on a piece of paper. A printer that has a resolution or DPI rating of 2400 can place 2400 individual dots of color within a one inch span on the page. If the printer is listed as a 2400 x 1200 printer, the printer can place 2400 dots in an inch across the page and 1200 dots in an inch down the page. A 2400 x 1200 printer can therefore place about 3 million dots in a 1 inch x 1 inch square on the paper. Resolutions of 2400 x 1200 DPI, 5760 x 1440 DPI, etc. are typical for inkjet printers.

Dye sub printers are usually between 300 and 500 DPI. Why the difference? Dye sub printers can produce continuous tone color, meaning that every dot on the page can be an arbitrary color of up to 16.7 million possibilities. With an inkjet printer, the printer can only "spit" a few different colors (up to maybe 32 in some cases) for each dot, so much smaller dots are used in combination to simulate continuous color. A dye sub printer might place a single dot of gray on the page for example, while an inkjet printer might lay down 32 intermingled dots (16 black and 16 empty/white) in the same area in an 8x4 pattern to "simulate" gray by using half black dots and half white dots. Let's not get too caught up in printer technology, however, and just remember that DPI refers to a printer's capability to place individual dots on the page.

PPI or "pixels per inch" is a term that most often indicates the resolution of an image file (a JPEG, TIFF, etc.) when that image file is displayed/printed at a certain size. For example, if you take a photo with your 6 megapixel camera that produces a 3000 x 2000 pixel image, that 3000 x 2000 pixel image will be 300 PPI only if displayed/printed at a size of 10 x 6.67 inches, 150 PPI if displayed/printed at a size of 20 x 13.33 inches, and so forth. The bigger you display/print that 3000 x 2000 image, the less PPI you have to work with because the same number of pixels (6 million) is being spread over a larger area. As you can see, PPI (resolution) and image size are directly related. With respect to resolution (PPI) and image size, increasing one will always decrease the other, and vice versa because there are always 6 million pixels in your 3000 x 2000 images from your camera and the number of captured pixels does not change.

One Size Fits All

When you look at an image that was captured using your 6 megapixel (MP) camera, it will most likely be stamped with an arbitrary resolution such as 300 PPI. A 3000 x 2000 pixel image from a Canon 10D camera for example has 300 PPI recorded in the image file as its "resolution". With 3000 x 2000 pixels in the image, 300 PPI only equates to one size: 10 x 6.67 inches. When you open this image in your photo editor, it will tell you that the image is 3000 x 2000 pixels, 300 PPI, and its size is 10 x 6.67 inches. Does that mean that you should print all images from that camera at 10 x 6.67 inches? Does it mean that 10 x 6.67 is the maximum size you can print?

Of course, stamping an image file that came from a camera with a physical size is completely arbitrary and an almost "backward" way of thinking because the scene that you photographed with the camera most likely wasn't 10 x 6.67 inches nor is it likely that you will always print all your photos at 10 x 6.67 inches. So why put information in the image file that gives it a physical size of 10 x 6.67 inches? The answer is that 300 PPI is just a general guideline often used in the industry for "minimum resolution for true photo quality". In reality, it is possible to print excellent quality photos far above and below the 300 PPI "photo quality" threshold, so the resolution/size that you see in an image when you open that image in a photo editor is rather arbitrary and should not be considered a magic number.

For most workflows involving editing and printing images, an image should not have a physical size until that image is displayed or printed on a device and you shouldn't need to worry about size or resolution until print time. You can't change the number of captured pixels in the image anyway, so resolution is determined (automatically) by size at print time. Scanners are the exception to this way of thinking since they scan an object with a known size at a chosen resolution and you may wish to reproduce scanned material at the same (scanned) size. Having to deal with image resolution/size up front when working with photographs from a camera, however, is a major point of confusion for many people because typical photo editing software will tell you that your photograph is 10 x 6.67 inches and you begin to wonder what you have to do to print a 4x6, 5x7, 11x14, or some size other than the size indicated in the image file. As a result, a lot of people end up resampling (interpolating) their images to 300 PPI at the new/desired print size as the first step, then editing them, and finally printing. Such a workflow can and often does cause image degradation due to applying the interpolation at the wrong point in the process. Interpolation to a desired print size/resolution should be the last step in the workflow.

Instead of working backwards from an arbitrary size of 10 x 6.67 inches and 300 PPI and then trying to figure out what you have to do to print the size you want, it makes more sense to simply remember that you have 6 million captured or "original" pixels to work with: an image that has 3000 x 2000 pixels. Physical size (inches or cm) is not something that should be dealt with until you determine what size you need at display/print time. Leaving the image at its original resolution (3000 x 2000) and resizing it only at print time allows you to edit one copy of the image and then create different print sizes from the same original. Just remember that the larger you choose to display or print, the lower the resolution (PPI) that 3000 x 2000 image will be. If you print your 3000 x 2000 image at a size of 6x4, you'll have 500 PPI of data available in the original image because 3000 / 6 is 500. If you print the same image at 24 x 16 inches, your 3000 x 2000 pixels will have to be stretched across a much larger space and you'll only have 125 PPI from the image available at that size.

If 300 PPI is generally considered good enough resolution to reproduce printed photographs, 500 PPI is more resolution than you need so your 6x4 will look fine. Does 125 PPI mean that you cannot print a 24 x 16 inch print because that is so much lower than the 300 PPI considered "photo quality"? No. Not necessarily. What it means is that the image probably will not be quite as sharp at 24 x 16 as it is at 6x4 when viewed closely. Resampling that 3000 x 2000 image to a higher resolution before printing can make that 125 PPI available in the image go a lot farther. Let's see how we can make use of all this information in the most effective way.

Making the most of it

The key to understanding how to deal with resolution and size is to realize that there is only one thing that is stable and will never change with regard to your photograph that came out of the camera: it has a given resolution and that resolution is static and will not change. If you have a 6 MP camera that outputs a 3000 x 2000 pixel image file, that's the data you have to work with: 6 million pixels. How you choose to "spread out" those pixels on screen or in print is up to you. Print the image at a small size like 6x4, and you'll get a very sharp print. Print it at a larger size such as 10x8, 14x11, or more, and your print will begin to reduce in sharpness and detail, but depending on the methods used to print, you can often get very good photographs down to 150 PPI (20 x 13.3 with a 6 MP image) and even lower. The key is in how you stretch your 6 million pixels to cover a larger area.

As an example of "stretching", you could take your 3000 x 2000 image and upsample/interpolate the resolution to 6000 x 4000 before you print at that 20 x 13.3 size and in doing so, increase the image resolution to 300 PPI. Interpolation is a way of "extrapolating" data between pixels to create more pixels than were recorded in the original. While this does not add any real data to the image in the sense that only 6 million pixels were recorded, a good interpolation algorithm can predict what a higher resolution image might look like and can reduce artifacts such as jaggies. Click on this link to view how various interpolation methods can improve image quality. Note that the "pixel resize" version is what the small image on the upper right looks like displayed at the larger size. By using different interpolation methods, we are able to reduce or eliminate the pixelization or "jaggies" that occur from displaying a low resolution image at a large size. Also note that while the images are improved by interpolation, they are no match for the original image on the top/left that was photographed at the higher resolution to begin with. Needless to say, there is no substitute for real data, but interpolation can improve things quite a bit when printing at large sizes! As such, resampling (interpolating) can improve print results when printing large sizes that cause resolution to drop below 300 PPI.

Given the fact that our original image (photograph) contains all the pixels that the device could record and therefore the maximum amount of data available to you, I would recommend doing all work such as color changes, cloning out blemishes, and even any sharpening needed because the original appears too soft without changing the size or resolution of the image. Remember that interpolated/resampled pixels are based on the original/captured pixels so resampling first and then editing only serves to increase the pixel count of the images you are working with. It makes more sense to edit an image that is 6 million pixels and then interpolate to 12 million pixels than to create 12 million pixels up front and have to edit twice as many pixels.

Once any needed changes have been made to the original image, the image can then be resized or interpolated to the desired resolution for printing. If you are using a photo editor, you can enter the desired print size (say 11x14), enter a resolution (PPI), and check "resample" so that the photo editor will interpolate the image to the chosen size and resolution. Size is often the easy part because you know the size you want to print. For resolution, you want to use a multiple of the actual/physical printer resolution. For Canon/HP printers that would be 300 PPI for typical photos or 600 PPI for optimal quality with the finest details. For Epson printers, 360 PPI for photo quality or 720 PPI for photo quality with the finest details possible. If you use a dye sub printer, always resample to the "native" resolution of the dye sub printer, 314 PPI, 320, 480, etc. Note that depending on how effective your print driver is at stretching (or shrinking) the image to fit on the paper, you may get better results if you always resample to a multiple of the printer resolution, even if you start with a higher resolution than needed. For example, when printing to a dye sub printer that runs at 314 DPI, the 6x4 print from that 6 MP camera will likely print better if you downsample the 500 PPI image down to 314 PPI before sending it to the printer! In this case, sending an image to the printer at 314 PPI actually produces better results than sending it at the higher (but mismatched) 500 PPI!

Of course, it's always nice to have a tool that will do all these calculations for you so that you never have to worry about anything other than making color, levels, and a few other adjustments on the original, allowing the software to automatically interpolate to the best possible quality at print time. Qimage is such a tool that will allow you to correct the original image (in Qimage or using a photo editor) without ever having to worry about DPI, PPI, or size. Simply make any changes you like on the original without modifying the size or resolution of the image and Qimage will handle all the sizing and PPI calculations when you tell it the size you would like to print, and will automatically resample to the optimal resolution for your printer at print time using advanced interpolation and sharpening methods. While I did write Qimage and take the opportunity to plug it here, it does allow you to work with images in a much simpler and much more "forward" approach where you edit the original pixels and let the software worry about size, PPI, and DPI at the appropriate time: when you are ready to print. It is probably the easiest way to avoid the backward mentality of dealing with images that have arbitrary size and resolution stamps that can often prompt users to deal with resolution/size at inappropriate times.

In Summary:

I hope this article will assist in the understanding of PPI, DPI, and image size and will offer an approach that is easier for most to work with. Photographic images such as JPEG and TIFF images come with a size/resolution stamp that can be useful when doing things like scanning prints and reproducing them at the same size. When scanning a given size media in a scanner, recording the original size of the media can be useful because it tells us how to reproduce that media at the same size. If you want to reproduce the scanned media at an arbitrary or different size, however, or print a photo that came from a camera, such resolution/size recordings in the image become arbitrary and often confuse the issue. When you are capturing images at the resolution limit of a device and/or you intend to reproduce those images at an (arbitrary) size of your choosing, it is best to just leave the images at their native/captured resolution and only interpolate/resample the images if necessary at print time since that is the only time at which assigning a physical size to an image makes sense.

Resampling images as a first (or early) step and then editing them is a common mistake that can cause problems when working with images that you'd ultimately like to be able to reproduce at more than one size. For example, resampling an image to 300 PPI at 11x14 and then editing color and other aspects of the image can cause trouble if at a later time you would like to print some 16x20 prints from the edited image. The edited image has already been resampled to 300 PPI at 11x14 and resampling it again to 300 PPI at the new 16x20 size means that the image has gone through two resampling/interpolation steps which can degrade the image and not give you the best possible results.

Mike Chaney

In a fog over sharpening?

What is sharpening?

Simply put, sharpening is an image editing technique that allows us to make slightly blurry or out of focus images look in focus, clear, or "sharp". While sharpening cannot fix obvious focus problems where the subject in our photo is simply not focused properly, it can allow us to add that final "punch" to the photo to make the jump from just "in focus" to "tack sharp". Sharpening doesn't really add any real detail to images, however, it can accentuate details to make them more obvious on screen or in print. Our task with sharpening is to find that delicate balance that makes our photos look clear and sharp without making them look overdone.

Why do we need sharpening?

The first step in understanding how to use sharpening is understanding why we need it in the first place. In a perfect world, our cameras would record every pixel in our images perfectly and those pixels would be rendered perfectly on screen and in print. Unfortunately, devices like cameras and printers have their limitations and one of these limitations involves sharpness. Due to the way cameras capture an image, for example, there is always some smoothing which "leaks" information from one pixel into surrounding pixels.

Imagine a single point of light in an image such as a star in the distance in a perfectly focused frame. Even if that point falls on only a single pixel on the camera's sensor, the algorithms that put together the final image will spread that point of light into neighboring pixels making the point look less focused (blurry). Add to this the fact that most cameras have antialiasing filters that blur the image slightly before it even gets to the sensor and the fact that no lens is perfect, and we start to understand why there is a need for sharpening to undo the appearance of some of this blurring. Sharpening can take that point of light that was spread into neighboring pixels and bring some of that spread out information back closer to what should have been recorded (a single pixel of light). The mechanisms in the image capture process that cause blurring are not limited to point sources of course since edges/lines are also affected such as a sharp edge on a car door, power lines against sky, and other fine details. Sharpening can help reverse blurring in those areas as well.

Where to apply sharpening

Sharpening should be viewed as a way to compensate for deficiencies in the way devices capture or render images. If we use sharpening to undo the inherent blurring effects of a device, we have done the best we can do because the result will be closer to reality with respect to sharpness. There is often a state of confusion with respect to where and when to apply sharpening so here are a few recommendations.

Sharpening the original image:

The sharpness of an image that just came out of your camera depends on many factors: focus, lens, whether you shot in raw or JPG mode, etc. In general, we want the image to have a realistic level of sharpness when viewed on screen at 100% zoom (1:1). The first sharpening step is viewing the image you intend to display/print in your image editing software at 100% (1:1) zoom and setting the sharpness level so that the image on screen has the correct amount of sharpness. If the image came from a JPG stored on your camera, you may not need any sharpening because the camera may have already applied an appropriate level of sharpening. When dealing with the original image from the camera (or an image converted through raw conversion software), the goal is to apply an appropriate level of sharpening (if needed) to make the image look as accurate as possible on screen at 100% (1:1) zoom. Doing so will insure that we have the best rendition of the original image possible and will insure that we have effectively reversed the appearance of blurring as much as possible to give us an image that is true to the original scene.

Sharpening at print time:

There is a lot of confusion on the web and in imaging circles in general regarding how to sharpen images for print. There are even numerous programs and plugins out there designed to take the guesswork out of this step. Let's start by looking at the print sharpening step at a high level. The purpose of print sharpening is to make the print appear clear and sharp at any print size. That is, we've already set the sharpness of the original image by sharpening the image itself and now we want to make sure that the appropriate level of sharpness is carried through to our prints no matter what size we decide to print.

Sounds easy but there are actually a lot of factors that need to be considered when sharpening prints. The larger the print for example, the more sharpening needs to be applied because you are stretching the same number of pixels (from the original image) over a larger space. You also don't want your sharpened edges to be so tiny that they become lost in the print, so you don't want to upsample an image to 720 PPI for your Epson printer and then apply an unsharp mask of radius 1 because your edges will be so fine that the sharpening will not show up in print (more on actual sharpening parameters in the next section below).

"Smart Sharpening" in Qimage is designed to take all these factors (and more) into consideration to allow you to set the appropriate level of sharpening at print time based on your own printer and paper. Software and plugins such as Nik Sharpener Pro also allow you to take control of sharpening factors in both images and printing and are a bit more feature rich than Qimage, but are a bit less "automatic" and generally take more time and experience to grasp.

We understand "when" but what about "How"?

There are actually a lot of different techniques that allow sharpening of images. Sharpening can be as simple as clicking "Sharpen" in your photo editor, or as complex as converting images to Lab color space and sharpening only the luminance channel using unsharp mask. Let's try to keep it simple and just focus on the most common and one of the most flexible sharpening techniques: unsharp mask.

Unsharp mask, unlike the name implies, is actually a method of sharpening. It is called "unsharp mask" because it uses a blurred copy (an unsharp copy) of the image to compare to the original in order to sharpen. Here are the parameters associated with unsharp mask:

• Radius: the radius defines how "thick" the sharpened edges will be after the sharpening process. A radius of 1 will produce very fine/thin edges while a radius of 3 will produce "fatter" edges that are more noticeable.

• Strength: strength defines how obvious the sharpening effect will be. Higher strength will result in more sharpening. Note that radius and strength work together. If you sharpen with a larger radius, you might need less strength than if you sharpen with a small radius. As an example, radius 1 and strength 100 will be less noticeable than radius 2 and strength 75.

• Threshold: threshold or "clipping" defines which parts of the image are affected by the sharpening. When the threshold is set to zero, the entire image is sharpened equally. When the threshold is set higher, less prominent edges are excluded so that things like backgrounds, sky, and other smooth objects are not made noisy by the sharpening algorithm.

Notes on sharpening:

Typical "starting values" for applying moderate sharpening using unsharp mask might be radius 1, strength 80 up to about radius 3, strength 120. In general, when sharpening an original from your camera, you want to use a radius of between 1 and 2 pixels with whatever strength you feel appropriate because the in-camera blurring effects normally don't reach beyond about a 2 pixel radius.

There are various "artifacts" that can get you into trouble when using sharpening. For example, picking a radius that is too large and/or a strength that is too high can cause "sharpening halos" which look like a ghost of the original edge just beside/around that edge. For example, oversharpening can cause power lines against a blue sky to get darker and sharper, but can also cause a light halo on the outside of the power lines that can make them look like they are glowing. Using a threshold that is too high can often cause strange effects in the image because unless you sharpen the entire image the same way, you can break the relationship between less/more prominent edges. One negative effect of setting threshold too high is the image having a "charcoal painting" or embossed look.

There is a lot of information on the web regarding sharpening techniques, a lot of which can be confusing and even incorrect. Some of the best resources I have found are those at digitalsauces.com :

Digital Sauces Sharpening Introduction

Using the Sharpening Functions in Qimage

Sharpening in Adobe PhotoShop

If you would like more information on the Sharpening Equalizer in Qimage, see this article .

In Summary:

Sharpening is a technique that is so broad that you can make it as simple or as complex as you like. Unless you are sharpening for artistic expression, I recommend using sharpening functions to compensate for deficiencies that cause blurring in images. That is, we compensate for any blurriness or softness in the original by applying an unsharp mask to sharpen the image back to its original/intended clarity (or perception thereof). We also apply sharpening at print time to insure that our prints are as sharp as the image viewed on screen. Hopefully this article has given you a baseline understanding of when to use sharpening and has touched on a few of the methods of how to apply that sharpening.

Mike Chaney