Profile Prism
Procedure for profiling a scanner

Topics of Interest

Using Profile Prism Software

• Setting profile details and parameters

• Opening the image of the color target

• Placing the corner crop marks

• Jiggle corners option

• Checking target alignment

• Reviewing messages: target measurements and evaluations

• Generating the ICC profile

• Final review of any additional messages

• Scanners and metamerism

• Utilizing your profiles: where to store ICM files, etc.

Quick start instructions for profiling a scanner:

Note that scanning software varies greatly from one manufacturer to another. While the quick start instructions below describe the overall process of creating a scanner profile along with some recommended settings, we recommend reading and being familiar with the detailed instructions in the following section as well.

1. Place IT8 target on scanner glass.
2. Place piece of black construction paper on top.
3. Close scanner lid.
4. Open scanning software set software settings as recommended here.
5. Scan the target and make sure target is not rotated in the scanned image.
6. Bring image into Profile Prism and place four corner markers.
7. Evaluate the messages to determine exposure, lighting, etc.
8. Repeat 6-10 to correct any warnings.
9. After placing four corner markers, set PP options as follows:
   • Type of device to profile: camera/scanner
   • Reference target: same as that shown on lower/right of ref. target
   • Profile description: scanner model and other info as desired
   • File name: click "..." and select a name for the ICC profile
   • Profile for: highest accuracy
   • White balance: allow profile to fix WB
   • Tone reprod. curves: do not normalize
   • Manual adjustments: all "normal" or zero
10. Click "Create Profile"

Note: When scanning normal photos and using the profile developed above, it is important to scan photos using steps 1-5 above so that your photos are scanned under the same conditions as those used to create the profile.

The following describes the process for creating an ICC profile for a scanner using Profile Prism:

I. Acquiring the Image(s)

Before we use the software to create an ICC profile, we must do what we can to ensure that a quality image of the reference target is acquired. In this step, we must scan the IT8 reference target with the best settings possible. The reference target has 288 separate color patches that cover a wide range of colors. The object here is to acquire an image of this target with your scanner.

1. Scanner preparation: clean the scanner glass with glass cleaner to ensure a quality scan. For best results, we recommend scanning with a black background. If your scanner has a white background on the underside of the scanner lid, cut a piece of black construction paper to the size of the scanner glass. You will use this paper in the next step.
   
   
2. Target preparation: Place the reference target face down on the scanner glass and flush against the edge/top to ensure good alignment. Place the black piece of construction paper (cut in step 1) on top and close the lid.
   
   
3. Scanning software: Open your scanning software and set scanning settings as recommended for your scanner.
   
   
4. Scanning: To ensure that the scanner is fully warmed up, we recommend scanning the reference target twice and saving the second scan (discard the first scan). We have found that many scanners (especially Epson scanners) overexpose the first scan in a sequence if the scanner lamp was off prior to the scan sequence.
   

II. Using the Software

Step 1: Specify profile details

Before telling Profile Prism to generate your ICC profile, you need to specify a name, description and some options. Below is a description of each entry.

• Type of Device to Profile: Since we are profiling a scanner in this section, select "Camera/Scanner" for this setting.
  
  
• Profile Description: Enter a description for the profile such as "Acme 800 scanner profile".
  
  
• File Name: To save your profile to the system color folder (c:\windows\system\color for example), click the "..." browse button and enter a new file name in the "Save As" dialog or select an existing profile to overwrite. You may also type a file name directly into the edit box if you like, however, if a file name is typed without specifying a path, the profile will be saved in the folder where Profile Prism is installed. For example, entering "test" in the file name field will result in a profile named "test.icm" being stored in your \program files\prism folder.
  
  
• Profile For: Profile Prism can create very accurate profiles, however, since some scanners can be inaccurate in very narrow bands of the color spectrum, profiles for these scanners can make images look noisy. This is due to the fact that you are taking a very narrow band of color and expanding it to have wider "separation". In doing so, shadow/background noise may be enhanced. Generally the more expensive scanners can be used in "Highest Accuracy" mode. If you find that your profiles create noisy images or images that have posterization artifacts, however, you may need to switch to "Smoother Gradients". The "Smoother Gradients" method sacrifices a (small) amount of accuracy to ensure that there are no large color variations. If you are unsure, always start with "Higher Accuracy" and only use "Smoother Gradients" if you have a problem with image noise.
  
  
• Tone Reproduction Curve: If you are profiling a camera or scanner, you may select from the following choices for how Profile Prism generates the tone curve for your profile:
  • Normalize: The Normalize option is the default selection and should be used whenever you want to reproduce accurate (linear) tonality on a device like a camera or scanner set to automatic settings.  On such devices, exposure is relative and often changes from one capture to the next, so normalizing the tone reproduction curves will adjust for any slight deviation in exposure of the test target in order to create curves that will work well with any shot regardless of how it is exposed.  Note that when profiling some devices, particularly cameras where tonality may be dependent on the scene, it is not always desirable to produce linear tone curves as they may often appear "dull" due to reduced contrast.  If you would like your profile to correct hue errors without affecting tonality (brightness or contrast), see the "Gamma Match" options below.
  • Do Not Normalize: This option should be used when profiling a calibrated scanner that has a consistent (not automatic) exposure every time.  If you have software that can produce a "raw" scan, for example, where exposure is identical in every scan, use this option.  Since "Do Not Normalize" tries to exactly match the intended tone reproduction curve based on the shot of the test target, you wouldn't want to use this option when profiling a camera because you are unlikely to get the exact same exposure when you shoot different scenes.
  • Gamma Match: Select one of the following Gamma Match options if you would like your profile to correct hue errors such as color shifts or saturation problems without affecting tonality.  When profiling many scanners and cameras, it is often desirable to be able to correct problems such as reds shifted to orange, purples turning blue, undersaturation of yellow, and other color shift/saturation problems while letting the device and its user settings determine the tone curve.  Most cameras/scanners use tone reproduction curves that include "enhancements" to make images more vibrant in order to obtain a "film like" quality.  The "Normalize" and "Do Not Normalize" options try to correct the curves in order to make them linear/accurate and the result is often a dull or hazy appearance.
    • Gamma Match (Auto): Being able to produce a profile that corrects hue shifts and saturation without affecting tone curves depends on the ability to discover the "base" tone curve; that is, what the tone curve should have looked like before the device altered it to make the photos have more pop and vibrance.  For example, the camera being profiled may have started with a typical gamma 2.2 tone curve and then altered that curve to make the shadows a bit darker and the highlights a bit brighter.  In order to reproduce tone curves as the camera intended (without altering them), Profile Prism must find/use the underlying gamma 2.2 curve as the tone reproduction curve in the profile.  Some devices (and raw conversion software) use an underlying tone reproduction curve of gamma 2.2, others (typically raw conversion software) use gamma 1.8 or 1.0 when color management is turned off as it would be when you create a profile.  Profile Prism should be able to detect the underlying/base tone reproduction curve when you select Gamma Match (Auto).  In most cases, you will not need the manual options below, but if you know the underlying/base tone reproduction curve and Profile Prism is having trouble detecting it (because the curve was modified too much by the device to be able to detect it), use one of the manual Gamma Match options below.
    • Gamma Match (2.2): Use Gamma Match (2.2) if you know that the base tone reproduction curve used by the device is gamma 2.2.  If you are profiling in-camera JPEG's or images that have been saved to a common work space like Adobe RGB or sRGB, or even ProPhoto RGB, the base curve will be gamma 2.2.  All but a few of the common working color spaces are gamma 2.2 so if your images have been saved with an embedded color space, it is likely gamma 2.2.
    • Gamma Match (1.8): Use Gamma Match (1.8) if you know that the base tone reproduction curve used by the device is gamma 1.8.  Some raw conversion tools (like Capture One when using "Embed Camera Profile") and a few rarely used working spaces like Apple RGB and Colormatch RGB use gamma 1.8.
    • Gamma Match (1.0): Use Gamma Match (1.0) if you know that the base tone reproduction curve used by the device is gamma 1.0.  Some raw conversion tools (like Bibble with color management turned off) and some raw scans use gamma 1.0.  If the image of the target looks extremely dark when you open it in Profile Prism, chances are the base gamma was 1.0.
  
  
• White Balance: Again, since scanners have a static light source, it is best to use "allow profile to fix WB" when profiling a scanner. If color casts appear in neutral gray areas, however, this may be an indication that the exposure/color of your scanner is not "locked" and changes from scan to scan. If color casts appear in gray areas, select "device dictates WB" instead so that your profile will assume that the device knows how to capture neutral shades.
  
  
• Brightness: Choose the "Normal" setting if you would like your profiled images to have an ideal tone curve (100% accurate brightness). Set this parameter to a positive value if you would like to increase brightness and shadow detail, and a negative value if you would like your profile to render images with darker shadows and an overall darker appearance. Note that the brightness here actually operates on a gamma curve, so a more accurate name for this parameter would be "gamma". The term "Brightness" is used simply so that it is a more recognizable and less confusing term.
  
  
• Contrast: Choose the "Normal" setting if you would like your profiled images to have an ideal tone curve (100% accurate contrast). Set this parameter to a positive value if you would like your profile to render images with higher contrast, and a negative value if you would like your profile to render images with less contrast. Although the "Normal" setting will ensure accurate contrast in the profile, some photographers may prefer higher contrast results to add more "pop" to images and increase separation between foreground and background. Most digital cameras and film processors deliver pictures with higher than normal/accurate contrast. Higher contrast tends to hide noise in the shadows and give a more "intense" or "sharper" feel to images, however, it also tends to destroy some amount of shadow detail. Since anything other than the "Normal" setting is considered an "effect" or "enhancement", the other values are available purely as a personal preference since many people prefer more contrast than provided by a totally accurate tone curve. The "Normal" setting also provides the greatest possible detail in the image, so if your normal workflow includes any type of post processing using a photo editor, it may be best to use the "Normal" contrast setting since this will ensure that the image has maximum detail.
  
  
• Saturation: Choose the "Normal" setting if you would like your profiled images to have ideal saturation. Set this parameter to a positive value if you would like your profile to render images with more saturation, and a negative value if you would like your profile to render images with less saturation.
  
  
• Bias Settings: The red, green, and blue bias values may be used to control unwanted color casts or to introduce different coloring effects. For example, if the profile produces a noticeable yellow cast, setting the red and green bias settings to negative values will reduce yellow in the profile. Bias changes can be made to the entire profile (if "bias includes grays" is checked) or only to non-neutral colors (if "bias includes grays" is not checked). Scanners can suffer from hue shifts when scanning papers with different white points, while digital prints can be affected by metamerism (prints having a different appearance under different light), paper brighteners, and other issues. These are just a few examples where bias settings can come in handy by allowing manual "tweaks" when necessary. Note: always create profiles with bias settings at zero and only change the color bias in your profile if you deem it necessary.
  
  
• Reference Target: This reference file identifies the actual color for all color patches on your IT8 color target and is how Profile Prism knows the actual colors on your target. Simply look at the name of the data file listed here and make sure that the same name/number is listed on your reference target in the lower right corner. Note that the target "version" is sometimes referred to as the target "charge". If the version/charge listed in the dropdown does not match the version/charge listed in the lower right of the reference target, select the proper file name that matches. Once you have verified this entry, it is not necessary to change it unless you start using a different paper target that has a different version number stamped in the lower right corner.
  

Step 2: Open and crop the image of the target

1. Click "File", "Open Image" and browse to the folder that contains the image of the reference target. Select one of the images and it will appear in the image crop area in the upper right of the window.
   
   
   
2. Next, locate the upper/left edge of the target in your image. To do this, use the horizontal/vertical scroll bars on the bottom or right of the image to scroll, or simply click on the image in the window and drag it left/right/up/down using the hand.
   
   
   
3. Next, click the upper left crop corner button.
   
   
   
4. Your mouse cursor will now change to an upper-left box corner when you move the cursor into the image area. Move this corner to the very edge of the target, placing it at the upper left edge of the black rectangle that surrounds the row/column labels as shown below. The corner marker is shown below as a black/white dashed line.
   
   
   
5. Once positioned here, left click to place the corner mark. You will notice a red corner mark on the target image. If the corner mark is not exactly on the outside edge of the black corner as shown, simply repeat steps 3 and 4 until placed properly.
   
   
6. Repeat steps 3 through 5, locating the other three corners of the target and placing their corner marks appropriately. Note that the top two corner markers should be placed at the edge of the outer/black rectangle surrounding the text row/column labels and the bottom two corner markers should be placed below the gray scale. Properly placed corner markers are shown below:
   
   
   
7. Once all four corners of the target have been identified, the four "corner buttons" will only appear when you hover over them with the mouse. When all four corner buttons are "deactivated" and your target evaluation messages appear in the "Messages" area, you'll know that you have finished the cropping step. In addition, Profile Prism will overlay white "punchouts" on each color patch to verify alignment. The white punchouts should appear within each individual color patch on the target.
   
   Note regarding the "Jiggle corners" option: If the "Jiggle corners" option above the image is checked, Profile Prism will "jiggle" all four corner markers to try to obtain the most accurate target alignment. Note that this option may move the red corner markers so that they no longer align perfectly with the edges of the target. This is normal since obtaining the best overall/average alignment of the white punchouts may require moving some/all corner markers slightly. To place the corners manually without Profile Prism moving them, simply uncheck the "Jiggle corners" box and place the four corner markers again.
   
   
8. Simply move around the target and make sure that proper alignment exists by ensuring that each individual color patch contains a white punchout and that none of the white punchouts appear to overlap into neighboring color patches.
   
   
9. Finally, review your messages. At this point, Profile Prism has examined the image of the target and has evaluated white balance, exposure, and lighting of the target. The details of this evaluation are displayed in the "Messages" box on the lower portion of the window. Here is a list of messages that are displayed at this point:

• Histogram: The histogram that displays in the lower left corner of the window after cropping a target can provide useful information about the capture of your color target. The histogram shows the distribution of pixel brightness values from left (black) to right (maximum brightness). The higher the curve, the more pixels contain that level of brightness. Ideally, brightness should be distributed from left to right on the graph with no large "clumps" of data on the left or right. A large spike on the left of the histogram indicates that some shadow detail on the target was clipped (not visible because it is completely black or zero in one or more RGB color channels). A large spike on the right side of the histogram indicates that some highlight detail on the target was clipped (not visible because it is completely white or maximum in one or more RGB color channels). Depending on the device being profiled, it may be impossible to achieve an "ideal" histogram where brightness is distributed throughout the entire 0-255 data range, but try to minimize "clumping" of data on the left/right as much as possible. Below are some examples of "good" and "bad" histograms.
  
  Good histograms:
  
  The above shows a typical histogram of the IT8 reference target. The red endpoint markers on the left/right are very short, indicating that only a very small amount of data is at minimum/maximum brightness.
  
  Bad histograms:
  
  The above histograms show data that is not uniformly distributed indicating improper exposure of the image. The graph on the left, although it certainly captures the entire range of brightness values in the image, is underexposed. With the histogram compressed into the lower portion of the graph, less data range is available for profiling and the resulting profile may not be as accurate as it could be if the brightness values were more evenly distributed. The image that generated the left histogram above will look dark and dull.
  
  The histogram in the middle shows two problems. First, the red line on the right (although relatively short), indicates that some pixels in the image were at their maximum brightness (255). Also, notice how the data doesn't start until about 1/3 from the left. This indicates that there are no dark pixels in the image which compresses the capture range and makes black look gray. The image that generated this histogram will appear with a "haze" since contrast is lowered by the absence of true blacks and dark colors.
  
  Finally, the histogram on the right shows a very large red (maximum) indicator on the right, indicating that many pixels were at their maximum brightness. This image is very overexposed and will not profile accurately. In addition, the histogram on the right also shows a red spike on the left indicating that some pixels were at zero (minimum) which can indicate loss of shadow detail. The image that generated the right histogram above will look super bright and oversaturated as well as being very contrasty. Unfortunately, images like this are what many scanners capture when set at their default values. Such images will have very vibrant color and a high level of "pop", but are far from realistic and will not profile well because much of the color target (in the shadows and highlights) cannot be captured due to data/pixels being "off the scale" by being too dark or too bright.
  
  When possible, all of the above conditions should be avoided/minimized by tweaking the scanning software controls if possible. The problem must be corrected up front (at scan time) and must not be corrected with photo editors after the fact since this cannot bring back clipped data that was lost due to an overexposed scan. Overexposure or clipping can normally be addressed by setting "shadow" to zero, "highlight" to 255, and gamma to 1.0 in your scanning software. If the white patch in the lower left of your targets is not clipped, but there is still a red line on the right of your histogram indicating some values at maximum (255), it is possible that the scanner is oversaturating. In that case, reducing saturation by 25% normally will bring the saturation into range and prevent the saturation clipping.
  
  
• Exposure: Proper exposure is judged by the brightness of the white patch on the target (bottom left of the IT8 target). An ideal exposure will return RGB values of about 240,240,240 for that patch. Profile Prism will report an underexposure if the values drop below about 220 and an overexposure above 250. If the image is overexposed, some values could be clipped (beyond the recording range of the scanner) causing problems with highlights. If the image is underexposed, the image could look washed out when the profile is used because only part of the scanner's tone curve was captured.
  
  
• White balance: Exact white balance indicates that there is no color cast to true grays/white on the target. Profile Prism will indicate whether white balance is inaccurate and to what extent. The percentage displayed is the amount that the RGB channels differ when evaluating a neutral color patch. Since neutral color patches should have equal RGB values, a 5% value here would indicate that there is a 5% color cast in neutral colors (a 5% difference between the minimum RGB value and the maximum RGB value for a neutral color patch). The higher this number, the more inaccurate the white balance. Inaccuracies in white balance will cause inaccuracies in the profile because there will be a color cast over the entire target. Note that white balance is not normally an issue (and is rarely "controllable) in scanners.
  
  
• Lighting variance: Like white balance, the lower the number here, the better. This is the maximum variance in lighting measured around the edge of the IT8 target. A value of 5% indicates that there is a 5% variance in lighting. That is, the darkest part of the target is 5% darker than the lightest. In a perfect scan, there would be no variance in lighting across the target. Variables like reflections inside the scanner bed and reflections from the target itself can cause minor variations in lighting. There are two things you can do to improve lighting when scanning. The first is to ensure that you scan with a black background (black construction paper). The second is to move the reference target closer to the middle of the scanner glass rather than placing it against the edge/top.
  
  
• Pixels at min/max brightness and clipping:
  Pixels at min/max brightness: When Profile Prism examines an image of a target, it will determine the range of brightness values captured in the target, that is, the darkest and brightest pixel values found on the image of the target. Due to limitations of the capture device or simply due to the brightness range found on the target, these minimum/maximum values need not always be 0 and 255. An image of a target, for example, may range from 4-251, meaning that the darkest pixels found were a brightness of 4 and the brightest were 251. Profile Prism will report the number of color patches that contained at least some pixels that were at minimum or maximum brightness. Obviously, there must always be a darkest and brightest patch on the target, so at least two patches will always be reported as containing these darkest/brightest pixels. If a large number of color patches are marked as containing the darkest or brightest possible values however, it may indicate a problem. The message displayed will start with "Note:" if there are less than ten color patches containing min/max brightness and "WARNING:" if there are ten or more color patches that contain pixels at min/max brightness. A large number of patches that contain min/max brightness could indicate that the device that captured the image of the target simply "ran out of room" and bottomed/topped out. In a case where many color patches contained pixels of min/max brightness, since many pixels were found at min/max brightness, it is likely that at least some of them could not be properly recorded and the actual value could not be determined. Some things that can cause such a "truncated" range include: overexposure, oversaturation, inappropriate gamma setting, etc. If you get 10 or more patches at min/max brightness, try changing the exposure (shadow and highlight values on a scanner for example), the saturation setting, or the gamma setting to see if it brings more patches into range.
  
  Clipping: In contrast to color patches that contain some bottomed/topped out pixels, clipping can occur in more extreme cases. Clipping is a condition where all pixels in a measured color patch are at their min/max value or there was some anomaly in the measurement that indicates that the values in those patches cannot be depended upon to be accurate. There are three conditions that can cause clipping: (1) every pixel measured in the color patch was at min/max value, (2) no incidental variation (noise) was found in pixels: they were all measured at exactly the same value, or (3) no difference was found between two consecutive color patches. Any of these three conditions normally indicates that the value measured is probably not accurate. Once again, try altering exposure, saturation, or gamma settings to compensate. The number of clipped patches (marked with a black "X" marker) should be minimized since this indicates that the entire target could not be captured and may result in less accurate profiles.
  
  "X" markers and what they mean:
  Green "X": A green "X" indicates that some pixels were at the minimum value (shadow threshold). Since some pixels were at minimum value and some were not, this often indicates that the color patches in question are simply the darkest measured patches on the target. If only a few patches contain green "X" markers, no problem is indicated. If a large number of green "X" markers appear however, it could mean that the color is at or near the minimum brightness value detectible by the device. In the case of many green "X" markers, your capture device may simply not be detecting dark colors reliably and this could be an indication of underexposure, inappropriate gamma setting, or simply a limitation of the device being able to capture darker colors.
  
  Red "X": A red "X" indicates that some pixels were at the maximum value (highlight threshold). Since some pixels were at maximum value and some were not, this often indicates that the color patches in question are simply the brightest measured patches on the target. If only a few patches contain red "X" markers, no problem is indicated. If a large number of red "X" markers appear however, it could mean that the color is at or near the maximum brightness value detectible by the device. In the case of many red "X" markers, your capture device may simply not be detecting bright colors reliably and this could be an indication of overexposure or oversaturation.
  
  Black "X": A black "X" on a color patch indicates that the color patch was clipped. This condition is worse than pixels being at min/max value since it indicates a problem where inaccurate capture of the color patch is nearly guaranteed. See "Clipping" above.
  
  Scrolling through clipped patches: To locate and scroll through the clipped patches on the target to view them, simply click on the "WARNING/Note: n patches are at minimum/maximum value..." message in the message box on the bottom of the window. Each time you click on the message, Profile Prism will move to the next clipped patch on the target.
  
  Densitometer: To further assist with evaluating the colors in your captured target image, Profile Prism offers a densitometer that can be used to view the measurements for each color patch. After all four crop corners have been placed on a target image, you can point to any color patch on that target and right click to see Profile Prism's evaluation of that color patch. You will be able to view the original measured color of the patch. Using the densitometer, you can determine which color channel is clipping (if clipping occurred) and the exact color that was measured. Note that when examining color patches that are clipped with a black/green "X" marker, you will rarely see RGB values at their minimum/maximum value because you are viewing the RGB average over many pixels. Only some pixels were found to be clipped, so the average measured values will not normally show clipping.

NOTE: After you click "Create Profile" and the profile creation process has completed, the final messages displayed in the "Messages" box will be saved and associated with the image file that was used to create the profile. To recall the messages for a previous profiling session, simply click "File", "Recall Messages For" and select the image file used to create the profile. The messages will be recalled from the last time a profile was created based on that image.

Step 3: Generate the profile

Now it's time to sit back and let Profile Prism do its number crunching.

1. Click the "Create Profile" button in the lower left corner.
   
   
   
2. Note that Profile Prism will be performing billions of mathematical operations in the process of creating your profile, so it may take several minutes to generate a profile. You may follow progress by observing the progress bar at the bottom of the window.
   
   
3. Note that once profile generation is complete, the location of your new profile is visible on the status bar at the bottom of the window.
   
   
4. Make a final review of the messages displayed in the "Messages" box. Were any messages added? Profile Prism will add messages as the profile is being generated. These messages are:

• WARNING - color patches detected out of correction range: Like an evaluation of "Fail" in the spectral sample range, this warning message is very rare and will normally not appear. It indicates that Profile Prism found color patches on the target that are so far off that it could not correct those colors completely. While some color patches may not be 100% accurate in the profiled image if this message appears, it doesn't mean that the error will be visible. In fact, the profiled colors will always be more accurate than the original. This message simply means that Profile Prism was only able to improve the colors but not able to make them 100% accurate. This message usually indicates that there are large errors in color rendering by the device in a small range of colors in the spectrum.

III. Scanners and Metamerism

Metamerism is defined as a shift in color when viewing the same subject under different types of light sources. If you have ever matched clothing or fabric by examining against a swatch in a retail store only to find that what matched perfectly in the store is quite different under your home lighting, you have fallen victim to metamerism. Some types of lighting are good for evaluating colors while other light sources are inherently poor. Sunlight, for example, is a very good light source for evaluation of color due to direct sunlight having a smooth, full spectrum of color. Fluorescent and incandescent lights are examples of light sources that often bring out metamerism due to their poor coverage of the light spectrum.

All photographic media are prone to metamerism to some degree. To make matters worse, the cold cathode fluorescent tubes used as light sources in most scanners can bring out metamerism in prints since scanner light sources are neither full spectrum nor do they offer smooth coverage of the light spectrum. The photographic media used to create standard IT8 targets often shifts toward magenta under scanner illumination. The resulting profile will compensate for the magenta cast on the IT8 target by adding green. The profile will work perfectly for the scan of the IT8 target but since normal (film based) photographs will likely not contain the same magenta metamerism shift as the IT8 target, this often makes IT8 based scanner profiles appear too green when used on other media. Fortunately, there are ways to compensate for metamerism caused by the scanner light source and differing media.

Unfortunately there is no way to measure the effect of metamerism to compensate for it automatically. You may find yourself scanning a variety of media and the characteristics of that media with respect to metamerism will not be known. Fortunately, Profile Prism does offer two methods of dealing with metamerism when profiling a scanner. Simply put, if noticeable color shifts occur when using a scanner profile developed using the recommended settings at the top of this page, try changing "White Balance" from the recommended "Allow profile to fix WB" to "Device dictates WB" instead. When "White Balance" is set to "Device Dictates WB", Profile Prism will use the scanner's internal tone curves to compensate for metamerism in the IT8 target. This will result in a profile that works properly assuming no metamerism is present in the media you are scanning.

In addition, you may also use the matte CRxxxxxx target to profile your scanner (see camera profiling instructions for information on use of the matte target). The matte target is less affected by metamerism than the IT8 target and may provide more balanced results under your scanner's light.

IV. Utilizing Profiles Generated by Profile Prism

Note that the above instructions relate to generating an ICC profile for scanners. Since an ICC profile is a standardized method for describing how a scanner records color information, using these profiles with images from your scanner is a task left up to your imaging/editing software. Inexpensive software does exist which allows you to fully utilize ICC profiles for color management of images, batch conversion, etc. One such ICC aware application is Qimage, also produced by ddisoftware, Inc.. As stated elsewhere, consult the help or users manual of whatever ICC aware imaging/editing software you are using for assistance in making use of your ICC profiles once created. In Qimage, some relevant links that provide help and understanding of ICC profiles are:

Understanding ICC Profiles
Qimage Learn by Example: ICC Profiles Section

Note that whatever software you use, there is a standardized folder for which ICC profiles are normally stored. The following are "standard" locations for ICC profiles depending on the operating system used. It is recommended that you save your profiles in these locations since most software will look here for them:

Windows 95, 98, 98SE, ME: \windows\system\color
Windows NT/2000: \winNT\system32\spool\drivers\color
Windows XP: \windows\system32\spool\drivers\color