Back at the beginning of this thread, Antea made some good comments about 2D tasks associated with modeling/rendering in 3D. I thought I'd yak a tad about what I use and what I use it for.

1. Terrain creation - Terragen/Bryce/Vue (and other programs) allow you to import a 2D bitmap in black/white/grays to create a terrain from scratch. You can paint away in your 2D application and then bring that into your 3D app terrain editor, and end up with some very cool stuff. Check your 3D application to see, but usually black = low, white = high, grays are in between.

2. Texture map creation - Bryce and Vue both let you bring in texture maps to put on terrains and objects. You can draw/paint a brick wall, for example, in your 2D app, make a grayscale copy as a bump map, and bring that into the texture/material editor in your 3D app. Terragen doesn't quite work like this; if I could figure that out, I'd let you know for sure! Very cool, though; you can even take an existing texture map and put stuff on it, like moss, for example, or layer texture maps in your 2D application and create transparencies. You can also create seamless tiles in some 2D applications, which are idea for textures you want to apply to a large surface, like a terrain.

3. You can render separate images with masks, and composite them in your 2D application. This helps if you have huge, polygon intensive scenes that are slowing your machine to a crawl.

4. After the render, you have the option to save in several different image types; I usually save in bmp format. Then you can open your image in your 2D application and do any amount of postwork you desire, like cloning/smudging, painting in plants, hair, or other items, play with the contrast, saturation, levels, or hide or correct mistakes. I am not a purist; I use postwork in some of my images for various things. Some folks are devoted to using only the result of the 3D render, and don't care for postwork in any form. To each their own, I say!

5. Finally, you use your 2D app to crop/resize your image as you like (if you will resize it smaller, I recommend sharpening the image first so you don't lose all your detail), and then optimize it. This can take the form of exporting as a jpg, or saving for web; these have various option for file size. Remember, all folks who will see your image aren't on DSL; some of us poor slobs are still on dialups (sob!), so if an image is too huge, we won't see it for a while!

Some of the 2D applications I use include PhotoShop, Paint Shop Pro, and Painter. There are also some freebies and demos out there; I think Gimp is one of them. (Onions, you use Gimp, right?) But a 2D application is a must for image processing, that's for sure. Paint Shop Pro is a great application and very inexpensive.

Hope this little summary helps!