8 Replies Latest reply on Mar 13, 2012 1:12 AM by Gernot Hoffmann

    "Black" in RGB versus CMYK colors

    Jan Renette

      More a question than a discussion.

      Just started with ADOBE INDESIGN 5.5 and created a document of 160 pages in 30x30 com format to be printed with Blurb later on. My images are in sRGB (or ADOBE-RGB) where the color "Black" is defined as RGB 0-0-0 (and translated into C91 M79 Y62 K97 in InDesign).

      As background for the image in full spread in InDesign, I use the swatch "Black", defined as C0 M0 Y0 K100. However, when I print the document for proof in PDF, the CMYK background is "grey" and the RGB image really black. What is the reason???

       

      I went somewhat further in my test to find out the reason...When I open the PDF proof document in Adobe Photoshop 5.1 and I check the colors, the swatch Black C0M0Y0K100 (added InDesign)  has been translated into R34 G34 B33 / C75 M65 Y62 K82.

      So I have two blacks, the C91 M79 Y62 K97 (R0 G0 B0) from the placed image,  and

                                           C75 M65 Y62 K82 (R34 G34 B33) from the background Swatch.

       

      I changed one of the backgrounds in InDesign into RGB colors (RGB 0-0-0) and then everything is OK on the PDF output. Does this mean that for consistent "Black" in printed book pages, you have always to work either in RGB or in CMYK, not at all in both combination. And is this the same for text defined in CMYK??

       

      Thanks for your help.

      Jan RENETTE

       

      http://j.renette.free.fr

        • 1. Re: "Black" in RGB versus CMYK colors
          thedigitaldog MVP & Adobe Community Professional

          Adobe treats process black (which is what you are getting with the CMYK conversion) versus Rich Black (for say type) where the later is always 100% K with zero CMY.

          • 2. Re: "Black" in RGB versus CMYK colors
            Jan Renette Level 1

            Thanks Andrew,

             

            Practically, what does this mean for me...????

            Do I have to translate all background BLACKS in INDesign to R0G0B0, or create in Photoshop a "background photo R0G0B0 (Black swatch)", which I place on each page where I need a black background???

             

            Thanks for your help. I am a little lost with black, rich black etc. For me, there is Pure Black and Pure White, with tints between, beeing 256 tints of grey in 8bit..

            Jan

            • 3. Re: "Black" in RGB versus CMYK colors
              thedigitaldog MVP & Adobe Community Professional

              The question becomes, do you want black to be defined as 100% K only or using the process the profile describes for black? For type, you’d probably want 100% K only and that is what should happen in ID. But for an image, not necessarily the case. You’ll get black assuming the profile correctly defines the CMYK process (for process black).

              1 person found this helpful
              • 4. Re: "Black" in RGB versus CMYK colors
                Jan Renette Level 1

                Feminite-pages140-141.jpg

                Thanks Andrew,

                Here one of the spreads in the book. At the left side and part of the right page, the sRGB image from Photoshop with black border around as RGB 0/0/0. At the right ( under the text part) background color from InDesign, defined as 100%K. Difficult to see on this reduced image, but the right part is "gray" (in reality (R34 G34 B33), the left border "black", so color difference. I need a consistent background color over the whole spread. That means in my opinion that I have to create a different swatch color black  RGB 0/0/0 for all the backgrounds, and use the 100%K only for the text when having white backgrounds. Do you agree with this???

                Thanks a lot for your help...and hope that it will help also others, because I found a lot of equal questions on the forum. Again, thanks a lot.

                Jan from Toulouse, France

                • 5. Re: "Black" in RGB versus CMYK colors
                  Gernot Hoffmann Level 3

                  Jan, you may proceed as follows.

                   

                  1) Ask the printer, which CMYK profile is most appropriate for his offset process.

                  2) Most common in Europe is Iso Coated v2 (ECI).

                  3) Choose this profile in Photoshop for CMYK and synchronize all programs by Bridge.

                  4) Choose either sRGB or AdobeRGB as RGB-profile, but don't change it later for the

                      same document.

                  5) Optimize all RGB images and embed always the profile.

                  6) Verify by View > Proof Setup (Iso Coated v2 (ECI) > Proof colors / Gamut Warning

                     that the RGB image is printable without change of appearance.

                     Eventually apply modifications (often a saturation reduction).

                  7) Finally convert to CMYK and save as a new version.

                  8) Editing in CMYK is a matter for experts. One can easily get too much ink

                     (Total Ink Limit violation).

                  9) Make the InDesign file. This does not have a global RGB or CMYK mode.

                      Both types can coexist (opposed to Illustrator). Just this is the problem.

                  10) Create a swatch for Rich Black in ID. That's the darkest printable black.

                      Define in Photoshop R0G0B0 or L0a0b0 and read (for Iso Coated):

                      C88M79Y64K93. Use these values for the swatch.

                  11) Use the Rich Black Swatch for your background, if you like.

                  12) Place your CMYK images.

                  13) Type text by C0M0Y0K100 = K-only. Overprinting, unless the size is very large.

                  14) Export as PDF/X1a. Colors unchanged. No profiles embedded. But Output Intent

                     Iso Coated v2 (ECI).

                  15) Check by Photoshop. Open as CMYK file (!!). Your Rich Black Swatch and all

                     the other swatches in CMYK will have the defined values (the will not, if you open

                     the file as RGB file). Verify by values in the Info Panel.

                  16) Verify PDF/X1a compatibility by Acrobat Professional > Print Production > Preflight.

                   

                  There are here and there alternatives.

                   

                  About Rich Black:

                  http://en.wikipedia.org/wiki/Rich_black

                   

                  Best regards --Gernot Hoffmann

                  1 person found this helpful
                  • 6. Re: "Black" in RGB versus CMYK colors
                    p_d_f Level 2

                    You're printing with Blurb. That's a digital press. You HAVE to specify your background colors as CMYK process - percentages of Cyan, Magenta, Yellow and Black. Then you have to make sure that whatever your black background of your image is in cmyk is and use exactly the same build in Indesign.

                     

                    It looks like you've got white type, but if you did have black you never want what Andrew calls a "rich" black, because in the inevitable event of plate misregistration, your type would have color fringes from the cyan, magenta and yellow plates. Not pretty. Black type is virtually always spec'd as 100% K for that reason.

                     

                    But back to your problem. This is the reason you have to design projects like this in CMYK, no matter how many people tell you it can all be done in RGB. It can't, unless you know for sure that your blacks from your different design elements will end up with exactly the same cmyk build percentages. And you'd be surprised at how little deviation it takes to actually see it in print. Enough that you should even turn the dithering off in the convert to profile dialog, as that alone can cause a visible change.

                    1 person found this helpful
                    • 7. Re: "Black" in RGB versus CMYK colors
                      Jan Renette Level 1

                      Thanks a lot Gernot,

                      I learned a lot of wikipedia..Thanks a lot for this link. It recognized the C91 M79 Y62 K97 (the R0G0B0 in photoshop, translated into CMYK in Adobe Indesign) as Rich Black FOGRA39 coated paper standard)...

                      You mentioned "C88M79Y64K93" in your responce..Why this difference?

                      I am working on your answer, to practice this and I will keep you informed of the results. Thanks again.

                      Jan

                      .

                      • 8. Re: "Black" in RGB versus CMYK colors
                        Gernot Hoffmann Level 3

                        Jan

                         

                        you're welcome. The percentages of the four inks depend on the profile,

                        that's to say on the specific printing process. That's the reason for

                        different 'mixtures'.

                        Using exactly the same mixture as indicated by Photoshop for a profile

                        with input L=0,a=0, b=0 (same result for R=0,G=0,B=0) would deliver a

                        background black which matches exactly the darkest black in images

                        nearby.

                        Using for instance C=70, M=70, Y=0, K=100 would deliver a Rich Black

                        as well, e.g. for a page background without special reference to images,

                        here with a reduced amount of total ink coverage.

                        By the way: adding ink Y can make the appearance lighter instead of

                        darker.

                        For offset printing we have (or had?) in Europe two standard profiles:

                        Isocoated_v2_eci.icc

                        Isocoated_v2_300_eci.icc

                        These are the official filenames. The first profile has 320% or 330%

                        total ink coverage, the second 300%.

                         

                        Best regards --Gernot Hoffmann