Printing (5): when conversion gets tricky

Every now and again, you will come across an image that doesn’t easily converts from *RGB profile to your printer profile. It will degrade a lot no matter which conversion policy you use, it hurts your eyes on screen (when converted) and even more so when printed. And of course it is your favorite image or the one that you promised a printout to a friend.

So now how to fit a larger gamut into a smaller (print) one? That is normally the job of the Color Management Engine to ensure the best possible conversion from one gamut to another according to the conversion policy (perceptual or relative). But when the result of that operation is really poor, it may be worth to have a look at what is going on and see if there is a corrective action to take on the file before converting.

What is going on? Check up with ICC Examin

We already used Argyll to generate a vrml file for gamut comparison between AdobeRGB and printer gamut. Thanks to Kai-Uwe Behrmann Cinepaint offers ICC Examin plugin that allows you to view in 3D your file color points, *RGB gamut and print gamut.

ICC Examin uses OpenGL for 3D viewing so depending on your graphic card, driver, use of Compiz (…), ICC Examin may or may not work for you. In my case (Radeon 9550 with OSS driver) the 64bits Gutsy version is broken, but the 32bits version works out of the box. So in the Image menu, chose “Watch colors 3D” (version 2 just gives you more details). Wait a few seconds for ICC Examin to process your file and then you get 3 new windows showing:

  • detailed information about the current profile (AdobeRGB)
  • a choice of which information to display and how
  • a 3D view of your image color points and the current profile gamut (AdobeRGB):

iccexamin1.jpg

You can navigate and move around the 3D representation to see how your image (the dots) fits inside the profile. Obviously, this just shows that the image fits inside an AdobeRGB gamut (duh!). Now if you go back to Cinepaint and enable softproofing (view / proof display), this is what you get:

iccexamin2.jpg

Much more interesting: this is a 3D view of AdobeRGB gamut (in grey), my image colors (the dots) and my printer gamut (in colors). I can see exactly how it fits – or not: which colors from my image are off the printer gamut and by how much.

You can also modify what and how you want to see the gamuts / image data in this dialog – whether you want to see your image dots, editing profile and print profile, if they need to be in colors or B&W and their transparency:

iccexamin3.jpg

This really helps understand what is going on in the profile conversion phase and why conversion gives this (unwanted) result. You may have noticed that ICC Examin doesn’t look like a standard GTK application. Indeed, it is based on FLTK (web, wiki) which is the GUI toolkit of choice for the next generation of Cinepaint-Glasgow (if it ever sees the dawn).

Softproofing: getting an idea of the result on the fly

We briefly mentioned softproofing as a way to enable the preview of the Printer profile in ICC Examin but guess what? that is not the main usage of softproofing. Basically, softproofing allows you to simulate on the fly the result of an ICC print profile conversion.

In Cinepaint, you chose your proof profile (your printer profile) in the Color Management preferences and enable it in the image / proof display menu. Now the idea is that you have on your screen a simulation of what your print will look like. Because this means quite a few conversions (from AdobeRGB to the print profile including the monitor profile somewhere) and since printing is basically adding Cyan Magenta Yellow to a white paper while a monitor prints Red Green Blue colors on a black background, the result is not 100% accurate. But it is good enough to give an idea of what to expect from a print. It is even possible to simulate paper rendition.

There is also a possibility to enable the “out of gamut” alarm which shows you which areas of your image are out of your print gamut. So if you want to check precisely which colors are out of (your print) gamut and by how much, use ICC Examin. If you want to see which areas of your image have out of (print) gamut colors, use softproofing with gamut alarm.

And the beauty of it all is that all the other functions of Cinepaint are available: you can tweak your image curves by checking directly the effects of your modification on a print simulation. So you can effectively modify your image so that you get the best possible result for this particular print profile.

Tweaking the file

Now what to do to enhance the file? I wish there was a magic trick but there isn’t – otherwise, it would be implemented in the CMS conversion routine. However, here are a few bullet points that can be of use:

  • If you have applied heavy curve changes in post-processing, it may be a good idea to restart from your original file and redo your post-processing steps with the softproofing enabled – this allows you to make sure you don’t go too far in any of the steps and end up with a print optimized version of your image file.
  • Don’t over-saturate – because monitors can display lots of colors we tend to add more and more saturation to images because it gives them this “pop” effect. Paper prints are limited in saturation but that doesn’t mean that the final result will be less pleasing to the eye. I once removed 20 saturation points in an image to print it: it kept beautiful nuances (that were otherwise destroyed by conversion) and the end result was much more natural than the saturated version.
  • If there is a particular spot that “ruins” the conversion use masks – select the problematic region and modify it locally. Because it may require quite drastic changes in the colors selection, it may be tricky to get an invisible junction between the modified area and the rest of the image. Do it in 2 or 3 steps: create a large mask, modify colors a bit, create a smaller one, modify again, etc. This technique saved two very important images for me.
  • Have a stock of smaller size paper (of the same type as the “big one”) that you can use for trials. If what you see on screen looks good enough (but it was tricky to get there) print a small version of your image, leave it to dry and check it the following day without the monitor direct comparison. Ask for an external opinion – sometimes we are so “in it” that we miss the obvious default (“Yuck! your print is all yellow”) or sometimes we are nitpicking on things that no-one will notice – careful with that though, what an untrained eye will not notice can still hurt a connoisseur’s eye.

9 times out of 10, conversion is a routine operation. But when it starts to get tricky, there is rarely an easy way out and what is on this page is just sharing my (sometimes painful) experiences. I would be glad to hear from you if you have further input about the subject🙂

Well, let’s just finish with (sort of) a Xmas pic. This is the one that I used to illustrate ICC Examin (yes, it is a gradation of blue to black) – and an easy one to convert for printing.

xmas_tree.jpg

15 Responses to Printing (5): when conversion gets tricky

  1. Joel, that is an excellent article again and you really wet my mouth to try printing myself.
    Your illustrational pic is excellent, wonderful soft tones you display here.

    Regards – Markus

  2. jcornuz says:

    Hi Markus,

    Thank you very much for your comment – images are what it is all about, after all.

    Re: printing, this “I made it from start to finish” is one of the great pleasures of digital photography – so I can only encourage you having a go at printing. Just make sure you budget enough money for paper, ink and an ICC profile, I think you will have great fun.

    Take care,

    Joel

  3. Hi Joel,

    still stepping from the left foot to the right and pondering pros and cons of the different printers available. I do like large formats, so I’d like to by an A3 format one. The HP 9180 has got excellent ratings but is still really expensive… The Epson and Canon printers seem to deliver excellent results, too, but their driver situation seems to be a lot worse than with the HP models – at least according to linuxprinting.org

    Do you consider bying a larger format printer, and if so, what are your considerations?

    Regards – Markus

  4. jcornuz says:

    Hi Markus,

    Tough one. I am not in the market for a new printer for now, but here are a few bullet points with my thoughts on the matter:
    – I would definitely go for A3 size with pigment based inks (to be able to chose my paper)
    – HP Linux has worked really well for me, apart for margins settings which were a pain to set up.
    – HP has had very good B&W support through dedicated inks (although support for that feature in Linux was still “work in progress” last time I checked)
    – I am not sure Canon is really a possibility (last Chasseur d’Images tests the Canon 9500 as “not so great” and says it is the first Canon printer of this type – probably too new to be supported under Linux anyway).
    – Epson is the big player in printing but you want to check the printer support in Gutenprint – also with older Epson models, you had to switch between mat and glossy black inks with a purge loosing quite a bit of ink. That is one point to remember. The more recent models have solved the problem (AFAIK) but maybe they are too recent to work with Gutenprint.

    Last word: inkjet printing is of very high quality generally speaking – I get stunning result even with a 4 years old machine; so with the right ICC profiles you can’t be very wrong.

    If I were to look for a printer, I would either go for HP (bucks allowing) or hunt for an Epson which a) is supported in Gutenprint b) doesn’t has the 2 black inks “problem” c) has a way to print B&W (but profiles from Christophe Métairie help with that. If such an Epson exists, I don’t know…

    I hope this helps. Good luck with your choice🙂

    Take care,

    Joel

  5. I ordered a custom icc profile for my epson 1400 printer. I received it but I get the message:
    (invalid utf-8 string) in the window when I try to enter it in gimp. I don’t have a clue what I am doing wrong…. I profiled my monitor using spyder2 and argyll and it worked great.

    any ideas??? Help!

  6. BDion says:

    a quick google search on ‘invalid utf-8 string gimp’ turn up a number of post reporting this problem, (most dating to last year). It appears this is a GTK issue???. I could not find an end user fix.

    A more in-depth search may turn up better results.

  7. I wish to obtain an icc profile for my printer using Gimp. I have guten print but the settings are all over the place. I thought that Gimp could use ICC printer profile for printing. I need this if I am going to stay with linux as my current printouts look like crap.

    1. where to order an ICC printer profile in the states that will work with gimp.

    2. what do I do with the profile? Does it go into gimp using the CYMK profile? or is there a way to install it into linux (ubuntu). Help!!!!

  8. Greg M. says:

    Jeff, I just ordered one from Booksmart studio in Rochester for $40, but I also found Profiles by Cathy which looked pretty good too. I think she charges $35. I’m not linking since I am not advertising, but a quick google search should turn these up for you, and a few others I am sure.

  9. These also work with linux? Have you used them with Gimp? How are you entering the profile??

  10. Greg M. says:

    As long as you print the samples from linux it should work fine. In GIMP, I think you have to convert the image to the printer’s color profile before you print, which is the same way cinepaint works, but it should work. As for whether my specific printer profile works, I’ll let you know in a few days. I haven’t received it yet.

    Did you read this article yet on getting your printer profiled? https://jcornuz.wordpress.com/2007/12/06/printing-3-printer-color-management/
    I’m pretty certain it would work the same way for GIMP.

  11. Ok, All of this I know. What I don’t know is once I print out the targets, and send them, and receive the printer ICC profile. What exactly do I do with it???

    The only setting in gimp that I can see for printer profile is for “Printer Simulation Profile”. That is under Preferences -> Color Management.

    I installed the monitor icc profile by following the instructions in argyll. How do I install an ICC printer profile in either linux, or gimp????

  12. BDion says:

    you copy the icc file to either/or both:

    /home/user-name/.color/icc

    /usr/share/color/icc

  13. Greg M. says:

    I believe you convert the image to the color profile of the printer right before you send it to the printer by going to Image => Mode => Convert to Color Profile, then you choose the printer color profile in the file chooser. Now you should be able to see on the screen exactly how it should look on paper.

    This is the same process that Joel described for doing this with Cinepaint.

  14. jeffegg2 says:

    Ahhh, I was thinking it would be all in the background. I couldn’t see applying the profile to the image directly. It just seems messy, but what can you do?

  15. Pat yourself on the back for another brilliant article.

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