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RICH BLACK, K=100, please!

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While 0,0,0 for black is correct for RGB (screen, additive) work, this would be incorrect for using CMYK, which is a printing (subtractive) standard.

RGB and CMYK have completely different uses and should not be compared. If you are not intending your output to go to print, do not use CMYK.


Printing a dark ("rich") black commercially usually requires a mix of the coloured (CMY) inks in addition to the K (black) ink in order to produce a darker black colour on paper than you can get using only black (K) ink, which will usually only show on paper as a dark grey (true black printed inks are very difficult to achieve in practice with wet ink, ignoring powder/laser ink which has different issues). This why the printing industry uses the term rich black rather than true black (although you might see CMYK 0,0,0,100 as "plain black" - something commercial print customers might not be satisfied with on paper).

With some papers (especially coated paper), producing a rich black on paper (without wetness problems) will require noticeably less than 100% K ink and a mix of the other C,M,Y inks.


This does not translate exactly to RGB on screen, but in practice the CMYK you are seeing as RGB 32, 32, 32 on screen will produce a darker ("rich") black on paper than CMYK 0,0,0,100 (because of the practical lack of real-world true-black wet inks).

Exact mixes of CMYK for "rich black" on paper will vary according to printer, ink, and especially type of paper used (which is why CMYK swatches in software usually specify the paper type) - consult your commercial print expert.


As a subtractive (printing) process, the theoretically darkest mix with real-world ink would be CMYK 100,100,100,100 rather than CMYK 0,0,0,100 - however, in practice with real-world paper, this would be far too wet for the paper (with wet ink) and produces other issues with powder/laser ink. CMYK 100,100,100,100 is used for thin-line registration marks (the small marks and thin lines avoid the wetness problems) and is known as "registration black" - it will also show up any problems with CMYK alignment.


Software that uses  CMYK 0, 0, 0, 100 for printing "rich black" on paper (rather than "plain black") is telling lies about real-world printing conditions and real-world inks, and should stick to on-screen RGB where it is telling the truth.

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I suspect this probably already is, but if not, it should be determined by the color profiles assigned to the document.

Displays work in RGB, so in order to show any given CMYK color value, it needs to be translated to an RGB color - a straight conversion of 0,0,0,1 (100%/255) to RGB would give 0,0,0 but this does not account for the color profile(s) involved.  Real printer ink at 0,0,0,1 is *not* a true black, which is why on a color printer, some small amount of color ink is added when printing black colors coming from RGB documents or a "rich" black when selected, in order to further darken the black ink on the page.

What specific color and how much of it will vary depending on the composition of the ink, which is why color management profiles should become involved in determining how that translation takes place in order to give a more true on-screen representation of the actual printed color.

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