Mike Chaney's Tech Corner

Hi all,

Having a bit of a problem with my canvas prints coming out with the wrong dimensions.

I'm printing onto roll canvas at 604mm (24inch). Today I pulled in an image with custom borders and fold marks, the original size dimensions were 751.1mm x 550mm at 180ppi as reported by qimage. I selected original size and checked that when hovering the dimensions were the same which they were.

When it printed I measured with a ruler and found that I had lost about 5mm from both the horizontal and vertical edge.
The weirdest thing is that when I measured the fold marks, one side was correct and the other had lost about 3 or 4mm. So what it looks like is that in one direction it is shrinking uniformly and in the other it is just shrinking the outside 150mm border.

I've been noticing that when I wrap my canvas that in one dimension it's always perfect and in the other what should be at the side is showing on the front, today's the first time I've actually measured the print so that explains it.

In the print driver I've selected 'banner', page size is defined as 610mm x 760mm for this image and save roll paper is checked.

Any ideas? Is it simply a case of making the page bigger, maybe q is deciding that it won't fit and scaling it down by a fraction to compensate?

Thanks in advance.

sQ

I've just checked out the 'Printing on roll paper without setting paper size' post, maybe this is the problem.

I'm currently leaving only 10mm extra length on the paper, q centers the image which only leaves a border of around 4 or 5mm and my print driver border is set to 3mm, could this be the issue?

Cheers

sQ

Hi sQ
This may not be much help but some comments:
You said the roll width is 605mm (24") which does not tie up with what you set as the page size: 610mm  ???
The driver page margins of 3mm should allow you to get the 550mm print width within the printable width of 599mm.
Q will warn you when it does that. It does not distort image aspect ratio either.
Terry

Another observation:
I suggest that you look at how you are positioning the fold lines etc. in your editor, perhaps that is where the error is coming from ::)
Why don't you use the very good canvas wrap features of Qimage Ultimate; guide lines etc are included.
Terry

Thanks Terry, in the print driver it's 610mm and in q it reports as 604mm, so actually I guess q is taking into account the 3mm margins. I don't get any warnings so in that case I'm still confused as to why the image is being shrunk?

As for the fold lines they're perfect in the editor, the issue is that it is printing 5mm smaller in both dimensions so obviously the fold lines shrink along with everything else (albeit in a baffling way). As for the gallery wrap feature, it will only get you half way there. Excellent as it is there's always something that needs cloning out and where the horizon isn't perfectly level (artistic effect not wonky photographs) it won't work at all. I'd need to print it to file and then open that in an editor anyway.

The only other thing that I can think of is that in my editor at the dimensions specified the ppi is at 179.832, when it's opened in q it is rounded to 180, I wonder if the .168ppi could add up to the missing 5mm when it's rounded up in q? That being said it should be irrelevant as I thought q takes care of all that when it calculates the exact dimensions you ask for...

Anyway.

Thanks again.

sQ

No, forget that theory, with a ppi of 180 exactly it'll only lose just over half a mm across the whole image.

Is it possible that the paper could be shrinking, that would explain the randomness of the fold line measurments. I hope not though!

One more idea:
You said, If that is the case, then that is what Qimage is sending to the driver so the driver could be messing things up.
Please check your driver for any scaling that has been set; do this from Qimage.
Also, check that you haven't got an override ppi set in Qimage for Custom-Original Size.

Personally, I don't go for so called embedded sizes with a linear size and ppi. In reality, an image does not have a linear size until it's printed. The Qimage way is to use Qimage to set the linear dimension(s), you know exactly where you are then. Perhaps you need  rehab from photoshop methods  ;D
And what about trying Qimage Ultimate canvas wrap borders and guide lines?
Terry.

I have metric phobia. I admit that. Terry helps me to get out of the fetal position when I read a question based on mms and not inches.
Nevertheless, I have to chime in here with Terry.
I would use HELP RESET PRINTER Settings.
Then just reset your needs such as paper choice, quality choice, printer profile setting if you use one, leaving any sizing or anything to do with position or scale untouched.
Then as Terry said, (even using Metric units) Tell Qimage what size print to make.
If it is an odd size, then use Custom/ and type in the size you want.
The ppi will set itself properly based on the print size.
That's all there is to it.
Fred

Ok, I'll have a look at the driver settings and do a reset anyway and start from scatch. Definately something wrong somewhere.

I know what you mean about the linear ppi being irrelevant when it hits q but unfortunately I still need to use it to get the measurements right for the custom borders in ps. The gallery wrap feature is fine if you can select your own images to print but when you get other peoples family snaps the borders always need work. Fine for a cheap ikea print but if someone's paying you I don't want to end up with extra mirrored feet on the bottom edge or extra eyes etc. Anyway, that's not really the issue, it's my missing 5mm. I'm starting to feel really petty now, it's only 5mm!

Cheers for your help guys, I'll let you know how I get on. 

By the way, does anyone think that the canvas shrinking is a possibility. It's a high quality poly cotton so I hope not. Would explain the way the scaling is different on each dimension. Or is this a ludicrous idea? It hasn't been varnished yet.

No it's not  ;)
Qimage is a precision printing program so we expect to get accurate sizes, the printer and media would always bee the limitation.
Sorry, don't know about canvas shrinkage; there are a few on this forum who print canvas, so hopefully, they'll chime in.
Terry

I think we're looking at the wrong problem. It is merely that the image you import from photoshop is not printing to the correct size (or rather the size you expect). The fact that the image contains a border or wrap is not relevant (except that is the convenient place for you to take measurements). I understand what you are saying about not being able to use the canvas wrap features of QI, but I use it exclusively for my own prints.

The image size that QI shows will be the image size you get (try inches instead of mm), provided you've not messed with borderless settings, and the printer is accurately set up, and the media loaded correctly. It is unlikely that your canvas is shrinking :). However, you will be stretching your canvas over a frame, so maybe a few mm smaller is a good thing ;).  I expect there is a video or two on printing to accurate size. You can check the printer accuracy, by printing an image, say 20 inches square, and measuring it. There are settings (certainly for most Epsons), deep inside the service mode, for adjusting the print accuracy

If you are fixing the canvas with staples to the frame, at the back of the frame, then I guess you have a white border to the wrap area. Make that white border smaller, keeping the image and wrap the same size, so that the total image width is less than whatever qi says is the printable width of the canvas roll, and set the size to the actual size of this new image. The unprintable edge of the canvas can still be used for staples, of course. When you've sorted it out, then write down the relevant details for dpi, pixels, etc. that you see in qi, and photoshop. You will then be able to produce a spread-sheet, or otherwise calculate the size of image and border that photoshop needs in order to correctly print the size you want in QI. It will be easier if you consider the wrap as a percentage/proportion of the image, then you can choose whatever you want in ps, pixels or inches or whatever, and get it accurately sized in QI.

Don't bother with trying to get photoshop inches into QI inches, deal with pixels, as others have alluded to.

Best wishes,

Ray

Ray said
SQ said
You can use QU canvas wrap borders after you have cloned out any unwanted items and if there are other features on the image that don't look good if they are mirrored, use the QU stretch canvas border which will disguise any such problems.
There we are, there's a Qimage solution to (almost) eveything  ;D
Terry

If it's the subject's feet or eyes that are near the edge, as the op said earlier (other folk's images), you can't clone them out in the original image so they do not show in the QI gallery wrap. I don't think you can work on the wrap in the image editor, so the wrap has to made in some other software. I print my own images, mainly landscapes, so it is not so much of a problem, but it often would be better if you could edit the wrap.

Best wishes,

Ray

Cheers guys,

I know what you're saying about the gallery feature Terry but the cloning I'm talking about is on the borders, the image itself I don't want to touch and I don't really like the stretch effect, maybe I'm just too picky? :-\

and Ray, I think I understand what you're saying but the workaround seems like q isn't up to the job and I'm sure that's not the case. You said that the image size that QI shows will be the image size you get, as I'm not getting the size that qimage shows (less 5mm in both dimensions) there has to be a problem in the driver or something though I can't think what. Haven't been able to check yet but if I can get q to print the right size then all the fold marks etc (even layed out in photoshop) will be in the right area (within a mm) and I'll be happy. I guess if I don't figure it out the solution is to tell qimage to print the image 5mm larger and then when it prints it too small it'll be the right size (ooh I feel dirty just thinking about it).

sQ

Sorry if I'm starting to sound annoyed by the way, I appreciate you all chipping in, sure you've all got better things to do. Technology eh?!

It seems to me that you are trying to print near the limits of the canvas width, without understanding the settings within Qimage or your printer driver. That is why I suggested you started by printing a 20 inch square (or if you want to use metric, then 500mm would do  - just an easy size a bit below your canvas width - but remember which size you use). Just draw a square in Photoshop with a ten pixel wide brush, say, (you needn't waste ink) and crop the image to make it exactly square, with the colour at the edge of the image - we do not want a white border. When you get the image into QI, set the size to 500mm, and print it. Note your driver settings, if you've selected borderless printing/whatever, or in QI if you've selected anything else under the page formatting menu. Make sure you've set the page size in the driver to something like 24inches square. Measure the print on all four sides. If it is not square, or it's not within a mm or so of the 500mm, then let us know the measurements you get, and the details of your qi settings and printer driver settings.

Hi

Canvas shrinkage is a known problem with inkjets. The actual amount can vary depending on the make of canvas used, and you can compensate for it by using the paper feed adjustment in the printer driver as it is usually consistent. There are a couple of threads in the Epson LF Yahoo group (you may have to join to see them).

http://tech.groups.yahoo.com/group/EpsonWideFormat/message/84206

http://tech.groups.yahoo.com/group/EpsonWideFormat/message/86415

HTH

Brian

Hello again,

So, Ray, my fault for not making it totally clear about the image I sent to print. The image that I created did indeed have the gallery edges and also a white border (2.5cm) to allow for the staples. The difference is that around the white border also had a black border just like you suggested in your test square example, that way I have cut lines but also it can't be considered as unprintable white space, so that when the dimensions in q are specified the entire image is printed. That's how I came up with the measurements being 5mm short. So...

On to Brian's comment about shrinkage, I've followed the links and it turns out that this is a common issue and so compensations must be made. Looks like we're back to you again Ray and your percentages and speadsheet, the yahoo post is talking specifically about the same media that I'm using (Breathing colo(u!)r) and the general thought is a percentage of 101.8% should be added to the length to allow for shrinkage. That just happens to be the suggestion for this brand but others will all vary.

My shrinkage does seem to be in both directions to a degree but it does seem to be that lengthwise along the roll it is shrinking evenly across the whole image therefore everything moves including the fold lines BUT across the width only the outside couple of inches seem to be moving so the fold marks aren't affected to a noticable degree.

Now I've applied varnish the shrinkage is now in the region of 10mm fyi.

I'm going to have a look at the feed adjustment and other settings too to see if anything else is messed up (I'll let you know) but for now it does seem like a question of making trial and error compensations until I get it right. Luckily my prints vary only from 30-75cm so I don't imagine there'll be a huge difference with settings across that range.

I guess if I stretch the finished image just across its length by the 101.8% as suggested it'll shrink back to its proper size. hmmm

Thanks again guys.

sQ

SQ,

On the Qimage side of the equation, Qimage will always show you exactly the size that is being sent to the printer so if you look in the queue or on the preview page and you see 12.34 x 45.67: that's exactly the size that is being sent to the driver because Qimage is showing you the width and height of the actual data in the queue ready to go to the driver.  In other words: it can't be wrong.  If you get anything but that exact size, you know the shrinkage (or expansion, as is sometimes the case) is being caused by a factor outside of Qimage: something beyond Qimage's control.

I guess you've already determined that the issue is shrinkage (trying hard not to reference a Seinfeld episode)  ;D but a good way to definitively determine if that is what is occurring is to measure the paper width before and after printing.  Don't assume the paper is exactly what the manufacturer says either: actually measure the width before it goes through the printer.  Then measure it afterward.  The after number will be smaller if it's canvas shrinkage.

Also keep in mind that a given canvas will rarely shrink by the same amount.  The amount of ink used (depending on the photo's subject matter) and even the colors used in the print will alter the final shrinkage amount.  You might be able to get a decent average but you'll never get it exact.

Mike

Hadn't even occurred to me to measure the whole canvas width, or that different images would vary in shrinkage, of  course it makes perfect sense when you think about it. Anyway, looks like we're resolved on this one. In a nutshell, canvas is a pain and forget about pixel perfection, it's not going to happen! Thanks to everyone for all your help, I've learned quite a bit over the last couple of days. Though mostly how my life isn't going to get any easier. haha

Cheers again.

sQ