Rendering Discussion: "Edges" Tips and Tricks
I wrote this up as part of a reply to this thread, but I thought it was worth reposting here.
Edge basics 101:
There is a scale of edges, just as there is a scale of values. It goes from hard>firm>soft>lost. Just as with value, you can use the whole scale in one picture or just a piece of it. The careful manipulation of edges is one of the most overlooked, but most important, tools an artist can use to create form, atmosphere, and believability.
In general, edges are:
Harder in the light, softer in the shadow
Harder in bright light, softer in dim light
Harder in focused light, softer in diffused light
Harder in the foreground, softer in the background
Harder on smooth forms, softer on textured forms
Harder on hard forms, softer on soft forms (Duh, but really)
Harder on flat forms, softer on rounded forms
Harder on thin forms, softer on thick forms
Harder on still forms, softer on forms in motion (on moving forms they are harder on the leading edge and softer on the trailing edge)
Harder at the center of interest, softer as you move away
The above are additive. So a kitten, far away, in the dark, would be really soft.
Of course, any of these guidelines can be ignored/modified for pictorial effect.