Maya: Mental Ray: Softening harsh shadows in Mental Ray final gather only.

 

This is a quick work around for harsh shadows using Final Gathering (FG) only (i.e., Global Illumination (GI) off).

For example, a scene with FG and no GI has two physical lights - looks pretty good except for some harsh shadows on areas hidden from both lights. Normally, you would turn on GI and add some bounced light into the area.

Without GI, you might boost ambient shading or use an ambiet light, but this is rarely satisfactory.

 

Thus you can thin the shadow in Mental Ray (MR) by attaching a "mib_shadow_transparency" shader to the material's downstream Shader Group (SG) node. Look for the shadow shader connection in the Mental Ray Custom Shaders section of the Shader Group.

 

For "mib_shadow_transparency", manually set mode to 3 (no light dependency), and increase transparency sufficiently to result in a lighter shadow.

If your object has multiple materials (exterior/interior), turn shadows off on all top-level transform nodes except one - usually an exterior.

 

f you don't want to spend countless hours getting GI and FG to work together and can live with FG only, then this technique can help eliminate the solid black areas in shadow that remain even after softening all raytrace shadows (i.e., area lights and increased shadow rays).