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  • CMYK Vs. RGB

    Greetings,

    During my time at school, I have always been taught to print in CMYK and to reserve RGB for on screen display. For our in-house work, I usually print in CMYK on our multi-function color copier, and everything comes out perfect. However, we’ve been having some problems printing in CMYK whenever we outsource our print work.

    I first ran into a problem while using an online printer to obtain some business cards for a few of our employees. The printer specified that they required a CMYK file that can be uploaded. I uploaded our files (in CMYK) to their servers and received an “Invalid File Type” error. I then converted the files to RGB an uploaded them. They went through successfully. We received the business cards a few days later. They looked perfect. No difference in color from screen to print.

    Then we ran into bigger problems. Last week we sent off a banner to be printed to a local printer in PDF format. I forgot to convert the file to CMYK, so the printer printed the banner as RGB. Despite being in RGB, the banner looked spectacular. Vivid colors and excellent quality. Yesterday, we got last minute notice that one of the images on the banner had to be switched out and the banner reprinted. I informed the printer and sent him the new PDF (this time in CMYK). I got a call from the printer last night telling me that whenever he tried to print the new PDF, any white areas on the banner would appear as beige. At first, I thought this might be a problem on the printer’s side, but then he reprinted the original file I gave in (in RGB) as a test, and it came out perfect. He snapped a photo of the two banners. You can see the printed difference here: http://www.frontierkemper.com/image/cmykrgb.jpg. Ugly, eh? I ended up having to convert the PDF back to RGB in order for the banner to print correctly.

    So, what am I doing wrong? I’m not very experienced in the area of color profiles or anything like that. I’m just surprised because I was always told to print in CMYK. As of now, it seems as though RGB is a more stable and colorful approach.

    If anyone has any input, advice, suggestions, or help you can offer, please let me know. Thanks in advance for any responses!

  • #2
    I am almost 100% positive it has to do with the profile he is running and you are running. Could also possibly be some funky issue with his RIP software...

    Some printers do require you to sedn RGB files and they convert it themselves. Some won't even toch it if you send them an RGB file by mistake. All depends on the printer you are using and how nice they are to you
    Professional Pixel Pusher — Designing the world around you. | Working daily to reach 10,000 hours of practice.

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    • #3
      It has to do with the fact that RGB has a higher Gamut than CMYK. Whenever we wanted our prints to "POP", we'd keep the RGB profile.
      My Site

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      • #4
        Every now and then at my print shop, I would use RGB on the color laser printers to get things to appear more vibrant. I really don't know how that online printer printed everything out, but at least on a press, I can't see how you could hit the out-of-gamut colors on a four color press using C-M-Y-K.

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        • #5
          Colour spaces == Not fun.

          First, you have to remember that there is no one RGB colour space, there are a bunch of them. sRGB, the most common one, is a lowest common denominator deal. It contains the colours that most RGB devices should be able to handle. If you're working for the web, you should be using sRGB.

          The Adobe RGB is a bit different, though. Although RGB has a wider colour gamut than CMYK, there are colours that CMYK can hit that RGB can't - and, obviously, colours that RGB can hit that CMYK can't. Adobe RGB is designed to include more of the colours that are available in a CMYK space than sRGB can. If you're working for print, you should probably be using Adobe RGB.

          (Though if you recieve an sRGB image, and you're not making any substantial changes to it, you shouldn't convert it to Adobe RGB).

          A lot of desktop printers are actually designed to take RGB images, and do the conversion themselves. That means that if you send them a CMYK image, it gets converted to RGB for sending to the printer and then to whatever the printer uses internally (something similar to, but not quite what we mean by CMYK) for actual printing. If you're sending to a desktop printer, you're better off sending it an RGB image.

          For a press, you'll get the best colours by sending your printer a CMYK image that was converted correctly. Depending on the printer and their equipment, though, you may get better results sending them an RGB image than a CMYK image that has been converted incorrectly.

          Or, it may be worse.

          You need to make sure that you're getting the right colour profiles for the printer in question.

          Comment


          • #6
            You sent a banner file as pdf? And the printer took it?
            You're brave.

            A lot of my 'banner' printers (super-wide format) want RGB Native files so they can apply their custom profiles to them. And those profiles depend on the machine and the media being run.

            You really really have to be careful when you just 'swap' profiles. You shouldn't do that. Clicking CMYK mode in the Mode menu is just plain wrong. Convert to profile and ASK THE PRINTER what profile to use. (There are, as always, exceptions to this rule. There are times to assign a profile as well.)

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            • #7
              Originally posted by PrintDriver
              You sent a banner file as pdf? And the printer took it?
              You're brave.

              A lot of my 'banner' printers (super-wide format) want RGB Native files so they can apply their custom profiles to them. And those profiles depend on the machine and the media being run.

              You really really have to be careful when you just 'swap' profiles. You shouldn't do that. Clicking CMYK mode in the Mode menu is just plain wrong. Convert to profile and ASK THE PRINTER what profile to use. (There are, as always, exceptions to this rule. There are times to assign a profile as well.)
              Well, yeah, if you're printing something weird (and as far as I can tell, PD only ever prints stuff that's weird ) then you might well have to send off images in RGB or whatever.

              And clicking CMYK mode in the menu will work fine - if your colour preferences are set correctly for the job that you're doing. Which they're probably not...

              Comment


              • #8
                As PD will tell you, many large format devices are RGB, and yes it makes sense to keep the job there if you can when handing off. It also makes sense to callout any spot colours (logos, themes, etc.) so that the techs can target the output for a best match. And use a standard RGB profile so that they can know where to start.

                Of course, another option is LAB, the de facto Photoshop standard. Tehcnically, it's an even truer color standard--only, both sides really need to really understand how that works through the chain.

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                • #9
                  Hewligan, I beg to differ on the mode menu click switch. Just changing the color space by assigning a profile that way does not always work even with the proper color settings.

                  Broacher, I don't know of anyone who uses LAB colors in wide format. Actually, it's getting to a point where I'm not sure that some of the newer entries into the field even know what a profile is, or care... Quality and caring is a commodity in short supply these days.

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                  • #10
                    A CMYK mode switch is exactly the same as doing a convert to profile with a source space of the document's current profile and a destination space of your current CMYK profile.

                    If your current CMYK profile is your intended output profile, it's exactly the same as doing an convert to profile.

                    Of course, if you're dealing with different printers, who want different profiles, then you're either going to have to keep changing your profile or use convert to profile.

                    LAB colour sounds like a great idea, but I don't think I've ever actually seen it used in practice. Well, except I did once see a photoshop guru show a great technique for producing a really good greyscale image using LAB colur, but I can't remember how he did it

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                    • #11
                      The thing with LAB is since it's the universal 'reference' space for Photoshop, if you do your work in RGB and then hand it off as LAB, then you reduce the potential errors that could occur when a RGB to RGB profile conversion takes place (as LAB is wide enough to accommodate any RGB spectral dimensions). So in theory, you tune things up the way you want them in a tuned RGB environment, save to LAB and handoff -- with no profile. Since it's the 'standard' space used in profile to profile conversion, you can't embed a profile into a LAB image.

                      On the other side, the receiver opens the LAB and converts it back to RGB using their specific profile, thereby ensuring maximum conversion fidelity, and minimizing any 'clippling' that might occur between two RGB spaces.

                      Mind you, this is for RGB to RGB handoff. And yes, there is always room for misinterpretation and error in any process. (There's no such thing as 'idiot proof' in my opinion, it's just a gradient)

                      LAB space in practice? Absolutely. There are corrections and other things that are only possible in this mode. But don't my word for it, take Dan Margulis, a bona fide colour guru who also wrote a very interesting book on this topic called:

                      Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace

                      http://www.amazon.com/Photoshop-LAB-.../dp/0321356780


                      I've only read a few sample chapters on line, but I'm saving up my sheckles for a copy myself.

                      Comment


                      • #12
                        Thank you for all of the responses. All are very informative.

                        Print Driver, you are correct in what you say about profiles. To be honest, I don't know much about profiles, but I do care.

                        I have looked through Adobe's online manual to better understand profiles with no luck. There's nothing there for beginners. Are there any links or books that you could recommend for a beginner beginning to use profiles?

                        Thanks again.

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                        • #13
                          Originally posted by Broacher
                          The thing with LAB is since it's the universal 'reference' space for Photoshop, if you do your work in RGB and then hand it off as LAB, then you reduce the potential errors that could occur when a RGB to RGB profile conversion takes place (as LAB is wide enough to accommodate any RGB spectral dimensions). So in theory, you tune things up the way you want them in a tuned RGB environment, save to LAB and handoff -- with no profile. Since it's the 'standard' space used in profile to profile conversion, you can't embed a profile into a LAB image.

                          On the other side, the receiver opens the LAB and converts it back to RGB using their specific profile, thereby ensuring maximum conversion fidelity, and minimizing any 'clippling' that might occur between two RGB spaces.

                          Mind you, this is for RGB to RGB handoff. And yes, there is always room for misinterpretation and error in any process. (There's no such thing as 'idiot proof' in my opinion, it's just a gradient)

                          LAB space in practice? Absolutely. There are corrections and other things that are only possible in this mode. But don't my word for it, take Dan Margulis, a bona fide colour guru who also wrote a very interesting book on this topic called:

                          Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace

                          http://www.amazon.com/Photoshop-LAB-.../dp/0321356780


                          I've only read a few sample chapters on line, but I'm saving up my sheckles for a copy myself.
                          I've achieved good color correction for cmyk using the lab color space, matching original oil paintings for critical clients. Also, our old scanner using Heidelberg's Topaz software worked in lab and viewed in cmyk. Never achieved as good color sinse.
                          WYSIWYG

                          Comment


                          • #14
                            Originally posted by Broacher
                            The thing with LAB is since it's the universal 'reference' space for Photoshop, if you do your work in RGB and then hand it off as LAB, then you reduce the potential errors that could occur when a RGB to RGB profile conversion takes place (as LAB is wide enough to accommodate any RGB spectral dimensions). So in theory, you tune things up the way you want them in a tuned RGB environment, save to LAB and handoff -- with no profile. Since it's the 'standard' space used in profile to profile conversion, you can't embed a profile into a LAB image.

                            On the other side, the receiver opens the LAB and converts it back to RGB using their specific profile, thereby ensuring maximum conversion fidelity, and minimizing any 'clippling' that might occur between two RGB spaces.

                            Mind you, this is for RGB to RGB handoff. And yes, there is always room for misinterpretation and error in any process. (There's no such thing as 'idiot proof' in my opinion, it's just a gradient)

                            LAB space in practice? Absolutely. There are corrections and other things that are only possible in this mode. But don't my word for it, take Dan Margulis, a bona fide colour guru who also wrote a very interesting book on this topic called:

                            Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace

                            http://www.amazon.com/Photoshop-LAB-.../dp/0321356780


                            I've only read a few sample chapters on line, but I'm saving up my sheckles for a copy myself.
                            a small workshop i attended skimmed the surface of LAB (they were also very admiment that you pronounce it, 'L.A.B.', no 'lab' for whatever reason), but it sounds that is is super powerful! i actually HAVE the book above for prob. at least 6 mos. or so, but i'm stooopid intimidated to pick it up for some reason.....

                            this reply didn't really contribute a damn thing, did it?

                            I'd also be interested to see anything related about diff. profiles and their uses.
                            color.... i hate it.
                            almost as much as i hate fonts.

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                            • #15
                              Okay. I think I might just understand a bit about profiles now. So, here's the next question.

                              When I am working on a design, should I simply work in RGB or sRGB on the monitor and then when I contact the printer, ask them what profile(s) they print with?

                              From there, I'm assuming you would then convert your design to the necessary profile.

                              Am I correct or completely off?

                              Again, thanks for all the replies.

                              Comment

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