Impurity? I have thought a lot about where to draw the line on post processing. I am a bit torn between approaching the original as a base to work with like Ansel Adams compared to the score and the finished product would be the performance to the more Puritan view.
At the moment I think it's up to every photographer to decide where to draw the line and what's feels right.
...this rocks..."in darkroom" in photoshop, same thing, doesn't matter to me how you arrived at this delightful end result...purity is in the mind of the beholder as far as I'm concerned.