Creating Refraction Masks

Wrapped a project yesterday where I was doing alot of Photoshop retouching of renders.  One area they wanted to change the color of was seen through bunch of glassware.   So I figured I'd write up a quick how to.

Went into the scene and changed two materials.  The back area (green) and the bartop (red)  Standard Max material with either pure green or red in the diffuse.  Thats it.  Hit render.

After that I pulled the render into Photoshop and copied the red and green channels into their own layer

Added a Levels Adjustment layer and crushed the blacks and the whites.

After the Levels Adjustment.

Combined these with a mask of the glasses (Ivan Tepavicharov's RenderMask script - an awesome tool to create mattes of objects)

And that's it.  Now you can color correct materials behind glass.