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J
Jan Renette
Participant
March 5, 2012
Question

"Black" in RGB versus CMYK colors

  • March 5, 2012
  • 2 replies
  • 28280 views

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

    This topic has been closed for replies.

    2 replies

    P
    p_d_f
    Participating Frequently
    March 7, 2012

    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.

    TheDigitalDog
    TheDigitalDog
    Inspiring
    March 5, 2012

    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.

    Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
    J
    Jan RenetteAuthor
    Participant
    March 5, 2012

    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

    TheDigitalDog
    TheDigitalDog
    Inspiring
    March 5, 2012

    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).

    Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
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