When I say "post processing" I don't mean fixing obvious technical faults like chromatic abberation, vignetting, sensor dust, lens distortion, etc. etc. - even though we may start to argue which is just a "fix", and which is an alteration of reality.
When I say "post processing" I don't mean replacing entire parts of an image with another image either, like "foreground of image A and background of image B" - even though we may start to argue what HDR and exposure blending/fusion is in that case. From a purists point of view, HDR may already be cheating, because it does something that the camera can't do (which IMHO is a big pile of nonsense).
By describing what I don't mean and which objections some may already have at that point, its clear that the discussion about digital post processing has reached philosophical dimensions today. So, what do I mean when I say post processing and the discussion about it?
I mean the people who worry about perfect white balance - and sacrifice natural hues of warm morning and evening light, cold blue shadows, the distinct green tint of the sunlight through the leaves of a forest on a sunny day for it. I mean people discussing tonemapped to death-by-chewing-gum HDR, and photos that obviously lack post processing when everything is pale and without contrast. I mean the discussion about "naturally" reproducing "reality".
Now, we live our linear existence in a three dimensional world, and try to capture what we see with two eyes by opening the shutter of a camera for a more or less short time. There are the two problems of photography: 1. lack of "3D" on a "2D" photo, to say so, and 2. lack of the ability to capture time/movement (we have movies for that). So, can this be a natural reproduction of reality? I don't think so - what we see with our own eyes is so much different from what the camera can capture. And besides that, what the camera captures is also lacking environmental sensations like temperature, wind, sound, smell, etc.
Therefore, I think it is only natural that we want to intensify the captured image - it is simply an effort to transport the moment (that made us release the shutter first place) to a possible beholder that was not there "in reality" when we took the photo.
I think its good to interrupt the large amount of babbling with a photo. Here's what the camera saw on March 16th, 2007 when I made the ascend to the Zwiesel:
"Blue Mountains" (Nikon D70 + 28-80mm AF-Nikkor on program automatic, JPEG out of cam)
Aha? Now, if you say that this is not very impressive, I'm with you... but on with the text, and on to the meat of things.
One of the most wonderful things I got from my girlfriend as a christmas present (ever!) is John Szarkowski's "Ansel Adams at 100" biography and fine art print book. And there is one paragraph in the book that sums "it" all up:
[...] as Adams stood on a granite shelf four thousand feet above the floor of Yosemite Valley, facing the motif that he later titled "Monolith, the Face of Half Dome" [...] it came to Adams that the finished print might more closely match his sense of the emotional power of the experience if he revised the tonal relationships of the picture by exposing his negative through a red filter, which would deepen the tone of the sky almost to black. Adams remembered the occasion because he had, for the first time, consciously applied a specific technical solution to an aesthetic problem. He used the red filter not by rote, or because dark skies were good, but because a dark sky was necessary for the picture he envisioned. [...]Thats it. A technical solution to an aesthetic problem. And it doesn't matter if you attach a filter in front of your lens or work on the contrast and color on the computer IMHO.
So... if post processing in the digital domain helps you to better express what you saw (or wanted to see), you should do it. You have to take the risk that no one else but you will like the result (but given the sheer amount of cheering comments for completely over-the-top HDR images it seems to be a small risk); the important thing is that you have done what you think is right (or what was right, at that time - I mean: our perception and our sense of how and if and why a certain photo may or should work - or not - changes all the time). The response from the public, from your family and friends will quickly tell you if it was good (and different people have different tastes, of course).
This should not be mistaken as some religious finding-your-spiritual-self workshop style thing like "just play around with it, whatever the outcome may be, its OK" (but of course, there will always be someone out there who finds a crap experiment with wrong white balance "quite interesting" as long as you serve hip beverages).
The key is our own vision. And just like filters, post processing can be used to lessen the difference between that what we see with our own eyes, our own vision, and what the camera is able to capture, to transport the "real" beauty of a scenery - and I'm writing "real" here (with the doublequotes) because that may very well be a more or less artificial rendition. Just like Ansel Adams' photo of Half Dome with the black sky.
And after that, there's only one mistake you can make: show the photo before and after post processing. :-) So here's the post processed version of the photo shown above:
"Blue Mountains" (Nikon D70 + 28-80mm AF-Nikkor on program automatic, post processed with Lightroom)
And you can be quite sure that what I saw on that day where these silhouttes of the mountains disappearing in the blue haze - and not the white muddy foggy blurb like on the first photo. :-) I still remember that day and that scene and picked this one as an example, because another man with a camera who was already on the descend passed me by when I made this photo - and he said: "its not a good day for making photos"...