Larry, 1. "If using luminance leads to better results, should we be doing that by default, and only do it for each channel separately if some other flag is set (perchan=1)?"
I see two options. Option 1: this is what I was going for, apply contrast to all channels separately, even for 3-channel images. It does not produce that bad results for RGB images. Example: http://postimage.org/image/d5d0v6y6d/ http://postimage.org/image/irqldypvl/ http://postimage.org/image/aer0niy41/ http://postimage.org/image/o7n5qqykl/ But when it does produce a bad result, the user can tell us it is RGB image and we can try a better solution, that is apply contrast to the luminance channel for the RGB image. Option 2: Apply contrast separately to all channels if the image has channels different than 3, and if it has 3 then assume it is RGB and apply contrast to the luminance channel. If the image has 3 channels, but it is not RGB, then you can say perchan=1 and contrast will be applied to all channels. 2. "And I'm assuming that contrast leaves any designated alpha channels untouched? " I wanted to ask you what to do about alpha and Z channels. Really not sure how to handle this stuff, we will have to deal with it for all the other operations too. That is why I wanted to solve channels masks early on. 3. "Can the contrast be a color as well as a float? For example, can you oiiotool in.png --contrast 1.5,1.5,0.8,1 -o out.png and would that add contrast to R and G, reduce it a bit in B, and leave the alpha channel alone?" Yep that is what those numbers would do. This is a very good idea, to be able to set contrast per channel.
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