This might be my most wonkish post ever. I don't think I've included diagrams before. But, as happens, I got to thinking on day.
Say we have some scene, a tree perhaps. When we look at the scene, we get a mental thing, a perception which is a fairly shoddy representation of whatever we're looking at. We, insofar as as we are even separate from the perception interact with that mental thing, our reactions and emotions affect, modify, the perception, there's a back-and-forth interaction here.
When we take a picture, we index the scene and create another viewable object, a photograph. A viewer, which might well be us, has exactly the same relationship with that object as we do with the original tree, the original scene.
Roughly speaking, we, at point A are trying to interact with a viewer at point F and to be blunt we're kind of a long way away. We're trying to spoon soup into someone's mouth, handling the spoon with tongs, which tongs we are manipulating with another set of tongs.
Most of the methods employed in photography can be viewed as trying to effectively shorten then length of the path from A to F
I think that an argument could be made that most gear acquisition is trying to shorten that index line, from C to D by making the photograph sharper, or more colormetrically precise, or whatever. Rules of Composition can be viewed as an attempt to jump the line directly from A to D from photographer to photograph in some partial sense, and they're usually justified by an appeal to the path from photograph to viewer with things like "people tend to find diagonal lines cooling" or similar rot.
Post-processing, which is not "photography" as such, places us into the position of the viewer, so we have a perception of the photograph, which we react to and so forth, but we add in another interaction in which we manipulate the photograph at D through photoshop, or by mashing the gum-bichromate, or painting on the print, or whatever. Again, we're jumping the line directly to point D in an effort to get closer to the ultimate viewer.
A consequence of post-processing of whatever sort, of these manipulations of the photograph, is that we extend the line labeled index in the first figure, the final print is farther and farther away from the original scene, farther away from our original perception, farther away from our original reaction to the scene. Now, the argument goes that in post we're actually trying to recapture our original perception of the scene, and to some extent or another that's true. But still, we've placed ourselves on the other side of the index line, so we are still in some sense both closer to the viewer (good) and farther from the original perception of the scene (bad). We are farther away from the original "selection" of whatever it was that was interesting.
I have argued in the past, and argue again here: photography is the bit on the first line of the first diagram above. It's the bit from A to C and extends along the index line a bit. It's the selecting part. Everything that happens after that could be done just as well to a drawing as a photo, and the result would still be a drawing, whereas without any of that a photo remains a photo.
This is not, as always, to suggest that post processing is evil or wrong, it's just not part of the essence of photography as such.
This is the Big Idea here: to shorten up that path from photographer to viewer, photographically, we need to shorten up the lines between A, B, and C.
Which is another way of talking about truly seeing, of actually perceiving what is in front of you.