I've learned a lot in this forum over the past year, thought I'd give something back finally that I haven't seen posted yet. Apologies if this has already been posted:
When sharpening in RGB (where most people sharpen) ... as PS increases the contrast of lines to make the image look more sharp, the contrast increase also boosts saturation considerably.
A friend of mine who works in LAB mode almost exclusively showed me a much better way to sharpen. The "L" in LAB stands for Luminocity. The luminocity channel in LAB has zero color information, so when you sharpen the L channel in LAB it doesn't affect color in any way.
To demonstrate, I opened up a photo I took over Christmas, twice. The exact same RAW conversion was done for each, and the exact same USM parameters was used for each. In the following photo, notice the various color overruns and casts that are created for the 100% crop on the right (RGB).
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The orange branch in the bottom left, the exhaggerated bright-blue areas on Piglet, there are lots of subtle color fluctions and this is not the best of examples. Sharpening the L channel in the LAB color space makes the image much cleaner.
I hope this is useful to someone.
Bill
