Originally Posted by
DanK
One topic that I and a few others have posted about from time to time is that if you adjust tonality with RGB tools, like a curve in Lightroom or in Photoshop with a normal blend mode, you also change saturation. In fact, some time back, Manfred and I had a detailed thread comparing the two options in Photoshop for avoiding this link: working in the LAB color space, and working in an RGB space but using the luminosity blend mode.
I went back to this topic recently because a few of us are considering whiling away our hours of seclusion by offering online mini-seminars on specific postprocessing skills, and this is on the list. (I actually did one in an in-person meeting of a local photo club a year ago.) I realized that I can't explain why this happens. If one imposes a curve in an RGB color space, one is actually imposing curves in all three color channels. However, the curve is changing the distribution of luminosity in each channel.
Can anyone explain this or point me to a source I can read that explains it?
thanks very much.
Dan