No matter how much I may work a 3d piece to death, it's never finished until I spend an hour on it in Post. "Fixing in Post" is just a fancy way of saying you don't have to skills/time/patience/means to deal with an element during the piece's creation, and instead you address it post-process in a more hands-on program, like Photoshop.
It used to be that most 3d stills you'd see that contained anything pretty looking had been doctored in post, but nowadays more and more "post-process processes" are becoming integrated with the 3d Package. "Doctoring a still in Photoshop" is becoming less and less necessary. But in case your 3d Package doesn't include some of these processes, here's a tutorial on how to achieve some basic Post effects in Photoshop.
This Tutorial covers: Backgrounds(Alpha Channels), Glows, Depth-of-Field and Blurs, Noise and Color Adjustment. Along the way we'll explore Channels, Selection Tools, Masking, Blending Modes, Quick Masking, Adjustment Layers, and more.
This tutorial is intended for people familiar but novices with Photoshop, although it contains enough tricks and tips to make just about anyone feel like they've learned something. The example piece I'm using is going to jam in every trick to the fullest, so remember this as the 'Dante's Peak' of examples (If it can be added, it's going to be). I can't stress enough how most images don't need ALL of the following edits to their full effect and you should use your own discretion. Also, please note that there are a thousand ways to do anything in Photoshop, and my way may or may not necessarily be the best way. Learn to develop your own technique.
Here's the piece we're starting with, you can grab a .TGA of it here
Here's what we'll end up with, Photoshopped like crazy:
Before doing the tutorial
Render out your 3d piece to a bitmap format, preferably as a targa file (.tga). The Targa file format is high quality and usually incorporates an alpha channel (see below). If you don't have the option of saving an alpha channel, then click here for steps on making your own
Alpha Channels are basically saved selections. When you save out an alpha channel from a 3d program, a small black and white image is created that can be used to separate your object from the negative (surrounding) space. Usually the alpha channel is found as "alpha" under the Channels Palette in Photoshop, but I've seen a few times where a 3d application will save the "Alpha Channel" as it's own black and white bitmap file.
Now there are a lot of different things you can do to an image in Post. You can either click on one of the following steps to skip to it, or keep clicking next to follow this tutorial in order.