Originally posted by flippedgazelle I was wondering that myself. Properly done PP improves image quality.
He may be talking about reprocessing a JPG, which with multiple edit/save generations, Can and does degrade quality. With 12 and 15Mp sensors though, I think you have to go a long way for that to happen.
Re PF/CA: I've said it before, I'll say it again. I can make every single lens I own, Purple Fringe (in the generic sense), Including my Limited lenses. With some it's easier that others. We all know and love (or hate) the Tamron 70-300 that is especially well known for this..
Taken at 300mm f5.6 (wide open) K7
The photo is actually pretty sharp, not perfect but passable. PF, seems to really pronounce itself in the fuzzy edges in a slightly out of focus photo, such as the one above (click it for the peeper version).
I work in CS4 so the solution may be different for others but basically what I do, is fix the color balance, adjust the exposure, fill, contrast, etc until most of the PF is gone. All the while, trying to leave the photo looking natural. I often find that the PF tool in ACR while correcting Purple or blue fringe, will introduce red or green or some combo. So the sliders for that adjustment are set just at the point where one type almost disappears, and the other type starts. Then I'll play around with the Hue/Sat/Luminance sliders for each color to minimize the fringing. Have to be careful though not to destroy the colors of the photo that belong there. The same photo after a trip through ACR. Go ahead, click to peep....
Still not quite perfect but certainly much better. There is a bit of a trade off in this case. Some loss of color around the tree buds, where most of the real fringing was. For a shot of a couple black birds at the top of a tree, still a workable photo. Or at least I think so...