In this video for 3ds max well talk about rendering passes with VRay and how to use it in compositing to have better control over rendered images.

In Working with passes with VRay well see which passes we can export with VRay to re-construct the beauty pass with Fusion. Then well see step by step how to configure the passes in the Render Elements panel and how it works in rendering. Well take a deeper look at Ambient Occlusion to understand how to catch it without the need to activate its calculation in GI just using the VRayTex element. Well see how to import all passes in Fusion to obtain back the beauty pass and how to tweak passes to control image look depth of field simulation and color grading. Well see how to use multi matte elements to create custom masks to access to meshes in comp to change illumination and color correction.

http://cgcookie.com/max/2014/01/17/working-passes-vray/