Thanks to all for some great responses to my original question. Thanks in particular to Messrs. McCormick-Goodhart and Segal. Your comments have both enlightened and confused me, and I appreciate both states. Makes me think.
Watching LAB values while working on skin tones in RGB mode is a new idea for me, and after a little practice I find it very intuitive. I've seen Mr. Rodney's argument against using CMYK and in favor of using RGB percentages in other forum threads, but I must admit I've never been able to adopt that mentality. The fact that LAB values stay consistent regardless of the RGB and CMYK working space seems a big advantage.
In hopes of "cutting to the chase", I'd like to ask what methods you actually use to increase saturation. As I mentioned before, I've learned several different methods, and continue to play with them. My experience has been that my preference is often image dependent. I'll prefer one method on a particular image, but then a different method on the next image. That's why I've been revisiting the saturation issue, trying to understand why that is. Trying to underestand how and why the methods vary depending on the hue, saturation, and brightness of the starting values.
Here are my methods, all in Photoshop. Would appreciate comments, critiques, alternatives.
METHOD 0: I use a saturation mask on all the methods below. I've learned several ways to generate saturation masks, and they vary widely. I use the old HBS/HSL filter to make my masks. Also, with each method I turn on soft proofing and gamut warning. Then I increase the saturation until the first gamut warning appears. Then I decrease from there to my personal taste. For my soft proof, I set the printer/paper combination I am most likely to use. Saturation adjustments are always the last step in my workflow. I don't do saturation (or vibrance) adjustments in the raw converter, because I can't use sat masks there, and until CS6 I could not soft proof there.
METHOD 1: The plain old Hue/Sat adjustment layer. Mostly discounted by "experts", but I still use it as a reference check.
METHOD 2: A Channel Mixer adjustment layer, with fairly strong boosts in each channel, then reduced with opacity. Example, I set the red channel to 190, green and blue to -45, and so on.
METHOD 3: The basic Margulis LAB method. I make a dupe of the document, flatten, convert to LAB, apply the "flat" or "linear inward shift" Curves adjustment (with sat mask and soft proof in place). Then flatten that and copy it back to the original as a new layer. I understand that when the LAB image is copied back to the original RGB image it goes through a profile conversion which further modifies color values. Usually, I will put a copy of the original RGB image in Hue blending mode on top of the LAB layer to counteract the Hue shift that occurs in LAB.
METHOD 4: Perform a separation of Luminosity from Color, creating two layers, one in Luminosity mode, one in Color Mode. Then apply (clip) an S-Curve adjustment to the color layer. This is a unique method I learned from a German that goes by the name of "JoansW" and "DerW" in the ModelMahem and RetouchPro forums. I have not seen it discussed much by others.
