Compositing Ambient Occlusion and channel based lighting.
By Tahl Niran.



Hi this is another in a series of my shake tutorials. Although I am using big words in the tut name, what I am really interested in covering here is a workflow for relighting and tweaking the lighting of 3d CGI in a comopositing environment. As such I will show you all some of the �lighting� techniques which I rely on in compositing!

A quick note for those reading who don�t have lots of cash and studio experience.. I am using two fairly popular applications in this tut. Alias� Maya and Apple�s Shake, but this should be achievable in nearly any 3d app:

For Xsi users: this should be very easy to implement as the shader �Dirtmap� is compiled and works almost identically in XSI.

For 3dsMax users: ver 7 of max contains a full implementation of this technique in its new mental ray shaders. Maybe someone will be nice enough to extend this section as I don�t have a copy of max to check out the specifics.



This exciting episode we will be covering the following techniques:

Ambient occlusion compositing in shake: This technique is loosely based on some techniques used by some large studios, it may not be technically the �ILM� way to do things but it gives good result fast! I have whipped up a quick example of ambient occlusion (for the sake of brevity this referred to as ambOcc or AO from now on) using Alias� Maya v6 and metal ray v3.3.

Channel lighting in shake: An old favourite technique which I am using here to further extend the flexibility of this technique. This is a basic technique achievable in nearly any 3d/compositing app.

�Light Wrapping�: One of the most basic image integration techniques, but one that I see done wrong or ignored all together in a lot of people�s work. Learn it and then its there for ever. Again this is a compositing technique which can be used in nearly any app !

and a little bit on

Depth Of field: I got a LOT of requests for more on this after my last tut. I know there is a huge rift in the shake user community about how to use this. Here is one technique