View Full Version : Dirtmap V FG/GI?

01 January 2005, 06:04 AM
Hi, I'm looking for a nice setup to render out some high res model turntables. Some textured, some not.

I want an ambient occlusion look, since it shows off the nooks and crannys of the model. Someone recommended the Dirtmap mental ray shader which Im playing with now. But tbh I'm neither seeing nor understanding the difference between a mental ray FG render and a non FG render with dirtmap as a material node. Can anyone explain the difference to me? Or is it simply that Dirtmap is controllable at the shader level as opposed to the scene level?

01 January 2005, 11:49 AM
Dirtmap computes ambient occlusion, final gather computes indirect illumination from object to object. Depending on your lighting setup, the difference may be hard to spot.

The main difference which you should notice is that ambient occlusion should be faster

01 January 2005, 06:44 PM
To add a bit to what's already been explained:
Dirtmap just computes the plain, static occlusion of your objects and doesnt care about the lighting setup.
Gi and fg compute the actual lighting situation of your scene.
For example: You have a well lit edge of a wall. With dirtmap, the edge would become dark and darker toward the border, because the overall occlusion increases the closer you get to the corner, no matter how much light hits the wall. With gi/fg the edge would look bright, maybe even brighter than the other parts of the wall, depending on how directly the illumination hits the corner.
Although in 'ambient' (not lit by direct illumination) situations the dirtmap does a very good job.

01 January 2005, 07:33 PM
Great. Makes sense. Thanks guys.

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