13 Replies Latest reply on Jun 19, 2008 9:19 PM by (g_ballard)

    Why do I need to use a CMYK profile?

      Hi all,

      I am new to these forums, but have some theoretical and a bit of practical knowledge on Color Management. I know what a dot gain, color space, true black vs composite black, etc are, yet I struggle to build the big picture of the whole thing. I am actually doing design work, where we are going to print a brochure. I have done the Illustrator artwork, it has an embedded image and I am trying to make it ready for a good precise print.

      My question is, why do I need a CMYK profile at all??

      As I understand it, my document IS CMYK already, i.e. it uses component C, M, Y and K numbers for artwork primitives, and as far as I can understand the whole point of working with CMYK instead of RGB (which is for additive colorimetry - i.e electron guns and LCDs) is the fact that it is suitable for printers. If Cyan, Magenta, Yellow and BlacK inks get input from the CMYK numbers, then the print should look the same on all ink-utilizing devices, should it not?

      That said, I understand the point of RGB-to-CMYK conversion and vice versa, since obviously i have to preview my art on my monitor before it gets into printing. But since CMYK profiles exist, does it mean printers printing the same CMYK values get different results? (disregarding issues of different paper weights and dot gains)

      Thanks. This has been bugging me, and I am not THAT much into printing yet as to buy the Real World Color Management book i ve been hearing so much about.
        • 1. Re: Why do I need to use a CMYK profile?
          (Marco_Ugolini) Level 1
          Armen Michaeli wrote:

          >...as far as I can understand the whole point of working with CMYK instead of RGB (which is for additive colorimetry - i.e electron guns and LCDs) is the fact that it is suitable for printers. If Cyan, Magenta, Yellow and BlacK inks get input from the CMYK numbers, then the print should look the same on all ink-utilizing devices, should it not?

          Armen,

          No, there is no one CMYK that suits all printing scenario. Each printing scenario requires different CMYK numbers to produce an appearance similar to what is printed on other presses with another set of CMYK numbers.

          That's why color management is helpful, because a profile embeds into the image file a precise description of the final printing environment on which the image will end up being printed.

          In other words, what a set of CMYK numbers ends up looking like changes depending on which press ends up printing them. That is why CMYK is described as a
          b device-dependent
          color mode.

          With color management, not only you can precisely describe the intended printing environment, but you can also convert a set of CMYK numbers that are good for printing environment A to another set of numbers that will produce a similar look in printing environment B.

          >But since CMYK profiles exist, does it mean printers printing the same CMYK values get different results?

          Exactly.

          >This has been bugging me, and I am not THAT much into printing yet as to buy the Real World Color Management book i ve been hearing so much about.

          I strongly advise that you take the time to read that book. It will be time well spent, and will provide a comprehensive introduction to this topic.

          Best of luck.
          • 2. Re: Why do I need to use a CMYK profile?
            (Aandi_Inston) Level 1
            >That said, I understand the point of RGB-to-CMYK conversion and vice versa, since obviously i have to preview my art on my monitor before it gets into printing.

            What you may not realise is that the CMYK profile is use for the
            screen conversion. So there has to be one. To get accurate colour this
            has to be the profile matching your intended output conditions
            (printer, ink, etc.)

            >But since CMYK profiles exist, does it mean printers printing the same CMYK values get different results?

            Absolutely, certainly. There is no standard "Cyan" that everyone uses.
            Think of CMYK as a recipe, not a colour. The recipe says how much of
            each ink to mix, but does not define a colour. To define a colour you
            need the recipe AND you need to know the ink colours (which is in the
            profile).

            >As I understand it, my document IS CMYK already, i.e. it uses component C, M, Y and K numbers for artwork primitives,
            >and as far as I can understand the whole point of working with CMYK ...is the fact that it is suitable for printers.

            Not exactly. There are many reasons
            * old-fashioned workflows where RGB can't be converted accurately or
            at all
            * workflows where the rules forbid RGB (e.g. PDF/X-1a)
            * the opportunity to design directly into ink channels. For example,
            to control overprinting, rich black, ink density. All of these are
            lost in RGB. They are ALSO lost if converted to a different CMYK, so
            great care is needed to make sure the right CMYK is chosen, and that
            further onward conversion is avoided.

            Aandi Inston
            • 3. Re: Why do I need to use a CMYK profile?
              Level 1
              Thank you VERY much everybody. Your precise answers have been of great help. I think I get it now. The CMYK profile part, at least.

              I am about to order the book :-)
              • 4. Re: Why do I need to use a CMYK profile?
                Level 1
                I have a followup question :-)

                What exactly is the purpose of "Preserve RGB numbers" option when choosing a Proof Colors setup? Obviously i want to see what the colors look like when the artwork comes out on an output device. I do not really care for the NUMBERS, do I?

                Thank you in advance. And FYI, i have ordered the book, 2nd edition, through Amazon.com. It should be in my hands saturday latest.
                • 5. Re: Why do I need to use a CMYK profile?
                  (Marco_Ugolini) Level 1
                  >What exactly is the purpose of "Preserve RGB numbers" option when choosing a Proof Colors setup?

                  "Preserve [RGB or CMYK] numbers" is meant to show you what your image would look like on the destination device if you sent the file to it as is, without converting it to that device's profile.

                  Most of the time it shows you how bad that would look, but some rare times the results may conceivably be good enough not to necessitate a conversion. But those would be very rare instances indeed.

                  Most of the time (99% of the time, if I were to put a number on it) the "Preserve..." option should remain
                  b unchecked.
                  • 6. Re: Why do I need to use a CMYK profile?
                    Adding to Marco's comments about Preserve Numbers:

                    It's the same Assign Profile. The numbers remain the same, the look changes to reflect the new output conditions.
                    • 7. Re: Why do I need to use a CMYK profile?
                      (Marco_Ugolini) Level 1
                      That's exactly right.
                      • 8. Re: Why do I need to use a CMYK profile?
                        Level 1
                        If I may add,

                        The ONLY times most of us need to embed an ICC profile in a CMYK file are:

                        1) We want to PROOF it faithfully on a hardware-calibrated monitor (Photoshop reads the embedded profile and Converts it to Monitor RGB).

                        2) We want to PROOF it faithfully on any other hardware-calibrated printer that uses a different Target color space (Photoshop reads the embedded profile and Converts it to the specific target profile). (Or the workflow ignores my Source Profile and Converts to target proofing space based on the wrong working space).

                        3) We need to CONVERT it to another profile (Photoshop reads the embedded profile and Converts it to a new target space/profile).

                        PERSONALLY, when I deliver CMYK it is already Converted to the correct CMYK (directly from my 16-bit Adobe RGB file), and I do not want anyone downstream dinking around with My Color.

                        The old Quark did this task nicely -- simple place the tif and print the job.

                        Today's pdf and color-managed layout programs make understanding and implementing this instruction much more confusing and hazardous (how to send 'the numbers' straight through).

                        If I trust the print shop 100%, I will hand them my 8-bit Adobe RGB and let them do the Conversion to their press CMYK.

                        Otherwise, send [my] CMYK 'numbers' straight through. Period.

                        +++++++

                        The problems with people who do not understand HOW ICC profile work is they will strip my profile (knowingly or unknowingly) and Assign-Apply-Assume their own profile -- effectively -- hosing my color.

                        This problem is easy to see in Photoshop by Assign profile.

                        The classic real-world example is the old-school print shop's clueless "color expert" who ignores our embedded profile, because he says, he has turned "color management off" and "doesn't use profiles." He tells us our file is bad because his print is bad, and he will try to correct our bad color and print another round of proofs.

                        Does this sound familiar?

                        What the cave man actually did was strip our embedded file of its profile, and/or he Applied-Assumed-Assigned his own working space to our file then he takes a sledgehammer and beats our color up into his closed workflow (and he is probably working on an uncalibrated monitor to boot).
                        • 9. Re: Why do I need to use a CMYK profile?
                          (Aandi_Inston) Level 1
                          >The ONLY times most of us need to embed an ICC profile in a CMYK file are...

                          Or when mandated by the print provider/publisher. This is a
                          requirement for many PDF/X formats, for example.

                          Aandi Inston
                          • 10. Re: Why do I need to use a CMYK profile?
                            Level 1
                            Yes, that's my point (I don't understand HOW to make all that happen through today's many PDF/X formats)...
                            >>GB) Today's pdf and color-managed layout programs make understanding and implementing this instruction much more confusing and hazardous (how to send 'the numbers' straight through).

                            It comes down to knowing what you are doing (or working with people who do), trouble is I've been burned too many times by so-called color experts.

                            I can wholeheartedly agree that if a shop proves to know how to use profiles and the many PDF/X formats, then my approach is based on old-school lessons learned the hard way, but still correct in basic theory.

                            I would still get a red flag by anyone whose workflow needs to Convert my CMYK into theirs -- simply tell me what CMYK to send (or accept my tagged RGB and do your own ONE good Conversion)...
                            • 11. Re: Why do I need to use a CMYK profile?
                              >The ONLY times most of us need to embed an ICC profile in a CMYK file are...

                              Well, in a truly color-managed world, you should ALWAYS embed your profiles. I understand completely how including a profile with a CMYK image sent to someone who doesn't understand color management can result in disaster, and I've experienced exactly the sort of thing you are talking about. For years it was our shop policy to leave our CMYK untagged.

                              However, if the person downstream IS color management savvy, then including the profile can be extremely helpful. It serves as an "output intent" and tells them what print condition you separated to. Many printers like to re-separate images so they can get uniform GCR and/or ink savings, and it is very helpful to know the source profile.

                              Sure, in a TRULY color-managed world we could just release RGB images and let the printer separate to the correct seps, just as you suggest. However, we don't always have such close communication with the final printer. Often images are released to clients who give them to their clients who give them to their licensees who them pass them on to a printer. The profile provides useful information that might not get passed on any other way.

                              Hard learned real world lessons are hard to let go of, but if we are going to move forward we sometimes have to try. If I receive an untagged CMYK image and a proof that has no indication of what target it is emulating (GRACoL_coated1, SWOP_Coated3, FOGRA39L, etc.), I request either tagged CMYK or RGB. I don't want to play guessing games trying to figure out HOW this image made this proof. I don't want to have to make 3 or 4 test proofs to see which one is 'closest' to theirs so I can figure out their output intent. Why should I guess when that information is readily available?
                              • 12. Re: Why do I need to use a CMYK profile?
                                Level 1
                                Thanks again everybody. The book will be delivered to my door tomorrow. And I will take all read here into strong consideration.
                                • 13. Re: Why do I need to use a CMYK profile?
                                  Level 1
                                  >>> if the person downstream IS color management savvy

                                  Good good good, [I] wouldn't bet my paycheck on that being the case, though.

                                  Here is a link to Bruce Fraser's articles page:
                                  http://www.creativepro.com/articles/author/127446