Cyan – Magenta – Yellow – Key

jaims put this on the wishlist:

There goes my wish

I have a couple of colleagues that work as artists/drawers.
They are using photoshop -among other sw- on a regular basis, but both would like to swap to a cheaper/non proprietary tool.

I’ve been talking to them about the gimp -and meetthegimp.org of course, which both of them love :-)- but seems like they are missing some stuff they need on a draw tool. Therefore, I’m not talking here of using the Gimp as a photo editing tool, mind you.

The number one issue for one of them is the CMYK stuff. He says he needs to be able to convert the color map from RGB to CMYK.

I told him I’d be investigating that point.

And, to start with, Gimp happens not to support CMYK natively. But I’ve found that there are several plugins that can be helpful with it: lcms, separate and separate+. But I haven’t been able to use them to generate a jpg file based on cmyk (my colleague sent me 2 jpg’s, the normal one and the cmyk-ed one).

And then, I don’t know if this stuff is also meaningful to us, people that use gimp for photo editing; I think that maybe would be in case of printing pictures to paper.

Rolf, if you find that interesting or you have already fought your way through the cmyk issues, I think it’d be nice to make a show on it. Drawer folks and cmyk issues is just another way of meeting the gimp after all 🙂

Saludos

What I know about that fits on a postcard. Let me try to explain that far.

Let me start with the safe part – your CRT or LCD you are looking at. It uses an additive colour model and adds red, blue and green light in equal parts to get a perfect white background. The black letters are dark – they emit no light. This is the RGB model Gimp uses.

Printing uses a subtractive colour model and combines all colours out of cyan, magenta, yellow and black, also called “key”. Subtractive, because you take some parts of the spectrum away from the light that would reflect from white paper. If you print this text on perfectly white paper, all the light that falls between the letters will be reflected and all the light that hits the letters will be absorbed by the ink.

Black absorbs all parts of the spectrum in an equal amount. You can print with it a gradient from light gray (tiny drops with wide spaces between them) until solid black. But what is with red?

For red you have to absorb green and blue. Yellow absorbs green, magenta blue. So a red letter on a printout would be printed with tiny magenta and yellow ink drops. Cyan absorbs red – and when you add some cyan, you get a darker red.

But here are two problems. Real world CMY inks don’t add up to black – you get a muddy brown. And the coloured inks are way more expensive than the black ones. So instead of adding 10 cyan to get a darker red you would reduce yellow and magenta by 10 and add 10 black.

This “colour separation” seems not to be as easy as it sounds. Gimp can separate (Colours/Components/Decompose and look for CMYK) and even store CMYK TIFF files with a plugin. But the print people want to do more – I have no idea what.

Is there somebody out there with a clue about this stuff? Someone who can do a video? Or talk to me in an interview?

27 thoughts on “Cyan – Magenta – Yellow – Key

  1. This comes up every time “GIMP sucks because it can’t do CMYK separations, Photoshop is god!!!” I’m frankly bored with this topic.

    The sanest response I’ve ever read is, “I have done many professional jobs with GIMP, so I know what I’m talking about here, let the printers do it.”

  2. I know something about it, and I was contemplating doing a video about it, but I didn’t want to offend you by getting into the holy wars about CMYK.

    I’ll whip something up for you.

  3. Well, to start with, lemmie state that since I’ve been looking for info on this subject, I’m aware that this is a hotspot where flame wars gimp vs photoshop can easily arise.
    In this sense, yesterday I read an interesting article (http://kde-artists.org/node/355). I think the moral on the story would be a bit on Tuzsda’s side: ‘the gimp is a wonderful tool and you can do a lot of things with it’.

    In my case, I tell you I’m a proud user of the Gimp to do all my photo editing, it fulfills all my needs, I really love it, I feel completely comfortable with it.

    I truly believe in the opensource approach, and I can’t help it but recommend opensource os-es and apps to close friends and family.
    That’s how I found that some people out there find that cmyk is important for them, in this case my two drawer pals.
    And this is why I started to seek info on the subject.

    All that being said, it would be really nice of you Andrew if some day you put your 2 cents on the topic.
    No holy wars intended, I think that learning more on image editing can’t be harmful.
    If there is an issue with cmyk and the gimp, the more Gimp lovers understand it, the greater is the probability that someone can contribute to solve it.

    That’s the more powerful asset of the opensource move after all, everyone is up to put hands on work and help to get better sw.

    And of course, thank you Rolf for bringing the topic to the front page!

  4. As I said above, I have never needed CMYK for my stuff. My printer (the hardware one) uses that but does the conversion in the printer driver. It is fed with RGB. If I give away a picture to be printed, I use also RGB in a TIFF or JPG file. And I think this is true for most of the users.

    But there are some others that have a legitimate need for this. People who want to build up a business from scratch and don’t even have the proverbial “Dad’s Garage” to start from – and definitely no money to pay for Photoshop or to outsource the conversion job. I think most of them sit in the not so rich countries (Greetings to Gilberto from Brazil who is just starting on that way) but there are enough poor people in the rich countries too. Half of the kids in my class depend on welfare. 🙁 And they haven’t got lazy parents, just bad luck.
    For them access to Open Source software in production quality can be the difference. Just think about this business model: Making promotional leaflets for local shops. Take pictures, write copy, do the layout, make the files ready for print, have the stuff printed and get your local youth gang to distribute the stuff. 😉 You only need an old digital camera (2 Mpix would be already overkill), a Pentium 1 running Linux, time and some money to pay for the first print job.

    I don’t think there will be a flame war here. On top of the page is a magic sign that keeps away the Photoshop Fanboys 😉 and between us: Photoshop is a fantastic tool. It has a lot of advantages over GIMP and I can understand every professional who uses it to earn her bread or every photo hobbyist, who buys it instead of another lens because she feels she can be more productive with it. I can’t stand the people who pirate it and then complain about the “shortcomings” of GIMP. But we who use it and like it, we have the right (not to complain but) to ask the GIMP team for some features we feel are missing.

    Andrew, please make that video! And I have contacted a friend, former professional printer, for an interview about this stuff.

  5. jaims,

    Let me say that I love GIMP, too. I want it to succeed, and I prefer it to the other OSS image manipulation software out there (and I’m no fan of Photoshop).

    I would like to avoid the holy wars, since GIMP is a great tool, and while there are some complaints, they should be accurately portrayed, and not exaggerated or dismissed.

    (anyways, I’m off to church, and then I’ll record a video).

  6. Dear Saludos,

    full CMYK Support is missing in Gimp, what’s true. But the question is what do they need? Just to say “He says he needs to be able to convert the color map from RGB to CMYK.”, is too little information. What is his workflow?
    Do they need CMYK editing or is CMYK export OK?

    P.S.
    And if we talk about CMYK we must talk about color management, too.

  7. Great, this thread is getting hot 🙂

    I understand the point of Rolf, and I agree, opensource can help people that can’t afford expensive software to succeed. Not only on image edition but in other areas too.

    Andrew, I never thought you weren’t loving the Gimp :-), but I thought, reading your previous post, that things like flamewars happen, and I wanted make sure I’m making myself clear. I really appreciate your offering to share your knowledge on the topic.

    And Tobias, my name is actually Jaims (Saludos is a spanish word to say ‘goodbye’, more or less :-)), I have understood that my friend wants to be able to export as cmyk because for him the colors on the eventually printed copies of his drawings are important.
    He says that there is always a difference between the rgb and cmyk versions. I don’t know exactly what the workflow is, but I think that he must be working directly on cmyk color map,
    or at least, he converts every now and then so he can compare and control the final result…

    Thank you all and ‘saludos’ to all 🙂

  8. jaims:
    “I have understood that my friend wants to be able to export as cmyk because for him the colors on the eventually printed copies of his drawings are important.”
    ..
    Is he aware that you can do soft-proof in GIMP? (and also, I think, in Photoshop)? With an accurate color profile for the monitor, accurate color profile for the image (probably an sRGB’ or sRGB profile), and an accurate color profile for the printer, you can use ‘view->display filters’, add a ‘soft-proof’ filter, and then toggle it on and off to see the difference between the displayed image and the result you are likely to get.

    Rolf and I have talked about doing an episode about color management, which I may be able to participate in soon (when I finally have a working PC). We could cover this topic more thoroughly as part of that.

    For now, I think it is definitely important for your friend to try soft-proof, or if he has already, explain why it is not sufficient for his purposes.

    As others have said, typically printers accept sRGB’ image data, so if his printer requires CMYK, we need to know that too. If it doesn’t, I don’t understand why he would need CMYK.

  9. Well, that didn’t work out as I had hoped. I’m still receiving the Catholic channel over my microphone during the day, so I had to wait for night to record, and my screencasting software (XVidCap) isn’t so hot.

    But it’s done, and I think it explains a bit of the issue.

    I’ve put it up on rapidshare, since I’m currently without personal webspace:

    http://rapidshare.com/files/98350656/cmykpodcast.mpeg.html

    EDIT BY ROLF: Mirror on meetthegimp video server
    most times faster and always without ads:
    http://meetthegimp.podzilla.de/cmykpodcast.mpeg


    Also, I made an error when I was talking about registration. I should have said that the black area, when properly trapped, will appear best with superblack, and that the superblack (50%C, 50%M, 50%Y, 100%K; paper typically can’t absorb more than that) will help keep the border well-defined.

    jaims:

    I didn’t want you to think that I was one of the people who gets heated over CMYK.

    GIMP is great, it’s getting better, and there are plans to include CMYK support in the future (through GEGL).

  10. Also, color management would be a good topic. The more I learn about color management, the more I want to curl up into a little ball and pretend it doesn’t exist, like Bigfoot or vampires.

    So I would like to hear someone else talk about it.

  11. David: I’ll try to talk to him asap (today after finishin work hopefully) and try to clarify these points. I’ll give feedback in this thread.

    Andrew: thank you for making the effort, I’m downloading your the stuff, I’ll give it a deep look when I finish my work. And I never thought you were going to get heated on that, just happened to think that it’s better to be careful. Not only ’cause the hypothetical holy wars with other readers in this thread, but because the gimp developers deserve all my respect, I don’t want to sound like I’m complaining or I’m so picky 🙂

    Thank you all, more on this later

  12. Andrew, I also think this is a great video. It has some ‘deep knowledge’ for a novice like me, which means that I’ll have to give a second watch to it …

    Very kind of you, thank you very much.

    Rolf, I think that the original question is broadening, now we have to learn/clarify stuff on cmyk but also in colour management.

    But I think that from this thread some interesting stuff is being revealed as subject to study and get understood.

    And I also feel that everyone here is being kind and helpful, which is always something good.

  13. Hi there.

    Finally I’ve been talking to my drawer friend.
    I wanted to explain him every suggestion you have put in this thread, and to find up what is his workflow to explain it to you.

    So, with the workflow:
    -> he’s delivering his works to several editor companys, which in turn release them to their printers.
    My friend is aware that printers often allow to print an image from rgb color, but in the particular case of his customers, all of them happen to work with printers that need to be fed with cmyk images.
    This seems to be the most common scenario with professional printers here in Barcelona (Spain).
    My friend has had plenty of problems with the results of his works being printed, and the best approach to avoid them is releasing cmyk images.

    -> therefore, hi works on his drawings with cmyk from the very beginning.
    He also states that a common mistake is to work with rgb and convert to cmyk just prior to send the works to the editor/printer, as one can find nasty surprises with colors being very different from the intended ones, and then he can lose all the job done.
    But we have found a really nice surprise here.
    I told him yesterday to download the adobe cmyk file mappings and to use view/display filters/add proof color -web coated fogra28 (iso 12647-2:2004)- intent=relative colorimetric…
    Et voilà! He’s able to work on a cmyk basis, and he likes it! Many thanks to David Gowers here, as he suggested this point.
    One extra would be that you can have a 2nd view of the drawing (through view/new view), which allows to work with 2 instances of the drawing in parallel: rgb and cmyk.
    There’s one thing missing here, though. It is that in the pallette he can pick up colors on a rgb basis, which are not the cmyk colors he’d be ‘brushing’ on the cmyk-filtered drawing.
    This is not so important because he says he knows very well the colors he need, even on a rgb basis, and then I suspect that maybe I’ll find a workaround for this.
    He says that having a real cmyk pallette would be a commodity, but he can work without it in the meanwhile.

    -> so far, so good; the main issue now would be the ability to save the image as cmyk.
    He can work with the cmyk filter, but he still can’t save the job as cmyk.
    So this would be the main reason not to use the Gimp.
    I know that there are a couple of plugins that would allow to save as cmyk.
    I’ll have to invest some more time on this, as the one I have tried (separate) doesn’t work 100% ok, and it should be able to save the image as jpg (not tiff).

    I have also explained to him the upcoming GEGL library stuff (thanks to be given to Andrew A. Gill for his nice webcast) and he’s looking forward to the next versions of the Gimp working with that.
    He has just sent me a mail this morning, he says he’s happy with the Gimp now that he knows it a bit more in deepth, and he ensures that he’ll be using it; but that he knows that he’ll still have to use other apps to do some stuff.
    He has also told me that he’ll be investigating on the (many) features on the Gimp, as he feels it’s really powerful.

    By the way, he has sent me several of his drawings to make his points clearer (rgb, cmyk by phoshop, cmyk by corel painter…)
    If you feel that it would be nice to take a look at them, I can ask him for permission and publish them (on 23hq.com for instance).

    Well, this is a long enough post.
    I hope I’ve been able to make these points clearer (sorry for my english when it is not good enough), as I think they can be illustrative for an (hypothetical 🙂 ) chapter of mtg on cmyk.

  14. The image gets a bit clearer…. 😉

    Please ask him for permission to publish these images. If he is reluctant, let him slap his logo/copyright over it to make them useless for other purposes than making a point.

    What I still don’t understand is savin CMYK in a JPEG. Isn’t JPEG strictly RGB?

  15. CMYK is a must for prepress people. RGB is not the only color space to postprocess images in. CMYK provides some tricks not possible in RGB, so L*a*b* does. Besides things like trapping (making sure different colors of regions that are close to each other do not mix) do not makes as much sense in RGB as they do in CMYK. So just exporting to CMYK is not much. It sure works for some cases, but not for all.

  16. Well, I have finally asked for permission and published some 4 drawings.
    It’s 2 drawings made with the gimp, and then I have changed the color mode to cmyk.

    You can take a look at these pictures on http://www.23hq.com/jaims/album/2944601

    You will found something extrange there: the cmyk-converted ones, can’t be displayed at all by the browser! Or, at least, I haven’t been able to do so, I’ve tried with firefox and with iexplore too.

    That being said, Rolf: I don’t understand either how come photoshop saves jpg with cmyk. I have no idea. But it does 🙂

    Alexandre: I have read something ’bout the importance of prepress, but I have to confess that I can hardly understand much of the stuff on the cmyk topic, the ‘trapping’ thing that you mention and all.
    Do you think that working in rgb mode with the colour proof filter set to cmyk can do the trick?

  17. In general, you cannot trap in RGB space. I’ve been looking for Creative Commons licensed images dealing with trapping, but no luck. I do, however, have a few examples that will help to explain:

    First, rich black:

    http://www.prepressure.com/design/basics/richblack

    The other inks make the black appear darker than it should, and you get funky effects. I saw an example once where someone overprinted 100%K on two other colors, you could see little shapes of other colors running through there.

    I’ll see if I can’t whip up and example for you guys.

    And here’s one for trapping:

    http://www.prepressure.com/design/optimize_design

    If you have a two colors that touch, it’s often useful to create a very small border between them of both colors. Again, I’ll see if I can whip up an example.

  18. This is an interesting thread. I have next to zero knowledge of prepress, CMYK, etc. So this is very instructive.

    @Andrew.
    Thanks for the link to prepressure.com It contains a wealth of information. I will order “Getting it printed”. A second hand for just $12 is a bargain. Thanks again.

  19. Yes, this is being a definitely worthy and instructive thread.

    I have the feeling that people around here do know a lot of things about this and other image editing stuff, and I think that is great the way you are sharing those knowledge…

    Thanx!

  20. OK. I found some real-world trapping and rich black examples:

    http://www.23hq.com/andrewagill/photo/2947647

    This brochure should have used rich black. You can see that the black is actually printed on top of other colors, and you can actually see the other colors through it.

    http://www.23hq.com/andrewagill/photo/2947644

    An example of misregistration. Look at the white gap in the lower right corner of the green boxes. I can’t tell if it really was trapped or not. but increasing trapping would remove the gap.

    http://www.23hq.com/andrewagill/photo/2947643?

    An example of good trapping. There’s a very small border where the circle touches the graphic around it. You can see that no matter where you move the circle, it will still have that border.

  21. Thanks for the examples. It is very illustrative.

    I am amazed how different actually the printing from the screen world is. It is not just a matter of different colour spaces.

  22. I’m a long-time Photoshop user, and often interested in The Gimp and when i did a search on gimp cmyk I came upon this discussion. I hope this is still of interest.

    Most photographers/artists don’t need to do a cmyk conversion themselves. However, I work in a government agency, and my workflow includes shooting the photos, converting raw to jpg for our designer to work with. After she has a design approved, she lets me know which photos actually appear, and i go back to the originals, resize, retouch and convert to cmyk tifs. She includes these into her InDesign project and it goes to the printer for press printing. I never convert to cmyk for anything other than press printing.

    In that conversion process I can view colors that just will not translate well to the cmyk inks. Perhaps the colors are too bright, or too true (you can’t get a real red, 255,0,0 with cmyk inks), and you’ll see in the process that the colors will shift. Or perhaps the colors convert and you see a slight shift, it’s too yellow, and you can adjust that a little in the cmyk file before you save it. These are things you might not see until you get a proof back, and folks in the printing industry know that a chromakey or an inkjet proof is still not the same thing as a press proof.

    (Aside: Sometimes the designer will want me to grayscale and then duotone the image to match some key color in her design. She can give me Pantone numbers and cmyk percentages to create match those Pantone inks.)

    We’ve always had this problem. Ten years ago we were complaining that color prints weren’t as vibrant as our transparencies, of course impossible since the slide is being viewed with transmitted light and has a contrast ratio 10 times that of a print viewed by reflected light. A color print from a press is ever worse than a color photolab print, inks can’t give the contrast range that dyes can. (remember that we’ve been struggling for pigment inkjet printers that can give the same range as a dye inkjet printer – same situation)

    So I’m still interested in being able to do a cmyk conversion, and edit it, in Gimp. Otherwise, I’m still trapped in Photoshop. I don’t dislike Photoshop at all, I just hate paying for upgrades. 🙂 And I’d really like to get rid of Windows!

  23. CMYK processing is pretty high on the list of stuff to be implemented, I think. After 16 bit. 😉
    Your description has underlined the importance of this feature. It’s a small group of people that need it – but they are at key parts of the whole work flow.

    Thanks for sharing your experience!

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