View Full Version : GI + Shadow Catcher

01-24-2014, 09:13 PM
Is there a way to get GI "shadows" to be included in a Shadow Catcher-generated alpha?

I'm rendering an object that sits on a ground plane object with Shadow Catcher Node applied. It is black (color 0,0,0, 100% diffuse, and recv shadows only - but color doesn't appear to matter as it is not rendered in rgb pixels, only alpha). Surrounding the scene is a sphere mapped with an LDR 360 pano image (sky/ground). It is set unseen by camera, so only reflective surfaces and GI see it. Camera backdrop is default black. The scene has one raytraced Sphere light and uses 2 bounce Interp. Monte Carlo GI.

In order to get the desired shadow density for compositing, the ground plane object is dissolved 70%, so the client can add a gradient background in a Photoshop comp. (supplying the client with 32-bit PNGs).

What is lacking in the Shadow Catcher produced alpha channel of the rendered image is the characteristic GI contact "shadows." I assume this is because such is a change in pixel color value, not transparency.

What additional nodes do I need to add to my simple Shadow Catcher-only node tree in order to capture the subtle GI shading as a change in alpha transparency?