How do I fix the "gray" backgrounds on studio photos?
I have a batch of photos I need to get ready for a print publication. They were all shot in a studio on a gray background. I see two problems:
1) the "gray" isn't really gray. In some shots it is purplish; in others it is yellowish. How do remove all hint of hue without changing the value (lightness/darkness) of the background? It looks perfect in that regard - I simply want to turn it into a perfectly neutral color.
2) in some places there is an unpleasant introduction into the background. Perhaps you can see it in this screen shot - about 25% of the way down from the top a band of greenish pixels appear. Is this what people call "noise"? How can I remove it?

