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| p.1 #6 · Why essentially no discussion about CYMK? |
Needs based ... CMYK isn't as "needed" for most folks.
When I took my first printing class in 1980's ... the whole CMY think fried my brain, such that I just stuck with shooting chromes and skipped out on it altogether.
Fast forward to digital about three decades later, and several good FM'ers here had to straighten me out on RGB to get things started.
As a student (in recent years) of Dan Margulis' books that others reference, here are a few points that I've synthesized (i.e. my .02 perspective) along the way.
RGB ... Red (0,360), Green (120), Blue (240)
CMYK ... Cyan (180), Magenta (300), Yellow (60), Black
LAB ... Luminance, Green (120) / Magenta (300), Blue (240) / Yellow (60)
NOTE: ... LAB numbers are based on PS Color Checker equivalency, please correct if technically inaccurate.
From Dan's perspective, this represents 10 channels from which to work, and K is one of them ... but after having dedicated some time to learning to work in each, I find that they are all essentially taking the same 360 color circle and dividing them in different ways. As a result, working from RGB (120 degree separation) is the same as working with the reciprocal CMY (120 degree separation) ... just offset by 180 degrees.
So, if you are working in RGB you are basically working in CMY inversely anyway. Notice that many sliders are Cyan/Red, Magenta/Green, Yellow/Blue ... thus, there is little reason to convert to CMY(K) until you have specific needs for working with the K, GCR or ink volume aspect of CMYK vs. RGB, or want to specifically isolate the K channel.
LAB works from the same 360 color circle, but divides the degree of separation into a non- 120 degree trisection, thus differing from the RGB/CMY approach ... and has the luminance channel separate.
In that regard ... for many folks (in practical terms) CMY is only an inverse redundancy to RGB. For myself, if I want to use a Cyan channel, I just use the Red channel followed by Ctrl-I and "voila" I've got the Cyan channel (GCR/K notwithstanding) without ever going to CMYK space.
Dan's point @ 10 channels is pertinent to having multiple ways to slice/dice the 360 degree color wheel ... using whichever slicing paradigm that best suits your ability to isolate things to fit your practical/working needs.
So, to your question @ why not much FM press about CMYK ...
1) most folks don't live in the GCR/K/offset realm
2) those who are well versed in control of RGB, realize that it is simply the inverse of CMY anyway and use it accordingly
Some people will speak to doing some sharpening in the K channel of CMYK that is different from RGB offering, but I usually head for L (Luminance) channel of LAB if I want to go that route. Thus, for me it is mostly RGB (95%), followed by LAB (4.99%) and CMYK (0.01%) ... i.e. CMYK gets very little press, as it gets very little use.
CMYK used to be some magical, mystical thing that only people who really knew color knew CMYK, and I was in awe of it. Now, I just see it as the inverse of RGB (noting that K/GCR/ink volume is a pertinent distinction if needed for output variance) for color correction/pp purposes and printing instructions for those applications that require being told how much black ink to use (i.e. that can't convert from RGB to CMYK or you don't like their conversion process) ... if that makes any sense.