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Thread: How to print photos with correct colors - color management, darktable and gimp

  1. #11

    Re: How to print photos with correct colors - color management, darktable and gimp

    Don't forget that there are also grades of ink. The price of color ink cartridges that are specifically intended for high-end photo printing cost MUCH more than the generic stuff. However, as you noted, in this case the cost factor probably has to do with the non-ink features of the cartridge.

    All of this is thoroughly discussed on web sites devoted to cameras and photo printing. That is, unless you are having a software problem, or a problem with the computer-printer interface, the use of color with Ubuntu/Gimp is much the same as it is for Mac/Photoshop or anything else. The *.icc and *.icm files are the same. The meaning of "gamut" and "perceptual" is the same. The only difference AFAIK is that Photoshop and other commercial software can do pre-press color separations in a format acceptable to commercial presses, whereas it's a challenge to do it with Gimp. But you don't need that.

    So, to learn more about color, your best bet is to find your way to a site about cameras and printing. Before you do that, learn what the HSV and L*ab color modes do. Wikipedia has a good article on the subject. If you get into serious color adjustments, you may find that it's easier to edit in HSV or L*ab mode than in RGB.

  2. #12
    Join Date
    Apr 2011
    Ubuntu 11.04 Natty Narwhal

    Smile Re: How to print photos with correct colors - color management, darktable and gimp

    @Rallg, thank you for your help. Now I can start to experiment with papers and inks.

    That's bad news, by coincidence I was just searching for a CISS sytem for my neighbours MX410. They are expensive!! I suppose because the cartridges have the print head attached. They are £90 here in the UK, by comparison a six colour system for my Epson R300 costs just £25 and comes with 600ml of ink.
    Yep, it's indeed expensive, but still a lot cheaper then to buy cartages all the time. Two sets of original canon cartage, or four sets of after-market cartages cost the same as one set of this CISS and in ml the CISS is nearly ten times of a normal cartage.

    But we're a bit off topic now, so I'll mark the thread as solved.
    Once again thank you all for the help and advice!

  3. #13

    Re: How to print photos with correct colors - color management, darktable and gimp

    I should have done this earlier...

    A few posts back, it was noted that softproofing (also known as color proof) was showing large areas of out-of-gamut, depending on the profile used.

    I have a photo with some out-of-gamut speckles for a particular *.icc profile. But I've checked that using a non-Gimp program that is professionally used for that purpose.

    However, when I looked for out-of-gamut with the same profile, same image in Gimp, Surprise! It showed vast out-of-gamut areas. I double-checked using another method, and it's clear that Gimp is wrong. It tried with several *.icc profiles, so it's not that there is a simple file error in one of the *.icc files.

    So I did a web search, and sure enough (over at Flickr) there were reports of excessive out-of-gamut in Gimp.

    Thus, it may be that Gimp's softproof feature needs rework.

    From the user perspective: Two kinds of color are likely to be out-of-gamut. One kind is intense, saturated bright colors. Those are usually "not found in nature," and if you're photographing something with man-made colors, you'll just have to live with the slightly less saturated color rendition.

    The other kind of out-of-gamut are very dark but saturated colors. The reason they are out-of-gamut is because the paper can only hold so much ink in an area; usually it cannot take high doese of all four ink colors. Such out-of-gamut color often appear as speckles in shadow areas. They are unimportant, because you couldn't see much color detail there anyway. Unless you are photogrphic a modern art painting that consists of various shades of off-black, I wouldn't worry about it.

    The general consensus among amateur photographers who are not trying to do commercial images for mass-printing is: forget about out-of gamut.

    Here's an exercise you can try. DO THIS ON A COPY, NOT THE ORIGINAL PHOTO:

    1. Start with a *.jpg image of something that has a mix of very bright and very dark areas. Do not use "print simulation mode."

    2. Colors > Components > Decompose > CMYK to produce a new image with four black-and-white layers.

    3. In the new image, set the foreground color to 404040 (which is 25% gray). Bucket Fill: Mode=Multiply, Whole Selection. Do this for all four layers.

    4. For each layer, change its mode from Normal to Addition.

    5. Flatten to one layer. In this image, the lightest areas use the most combined ink, the dark areas use little ink.

    6. A cheap ink/paper combination might permit only 60% total ink dose (240 out of 4x100). Let's suppose that you are using that. Then, 60% of 255 (white) would be about 154. Go to Colors > Threshold and set the threshold level to 154.

    7. You now have a black-white image (no gray) in which the white areas show places where the color is too deep for the printer. Those spots are out-of-gamut due to ink carrying load.

    Note that this method doesn't show areas that are out-of-gamut for bright saturated colors.

    EDIT: I did some more searching on the web. Apparently, Gimp has a long history of reporting excessive out-of-gamut when the color is very dark. Don't worry about it.
    Last edited by Rallg; August 6th, 2012 at 02:11 AM. Reason: Looked up more info

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