In this video i show how to composite render passes (diffuse, shadow etc) to get combined pass (beauty pass). I show the way how i do it ,if You have any suggestions how do that better, please emial me.
You maybe ask Yourself for what this technique can be usefull ?(I already has combined pass ,and why i should even spend more time on it!) For everything () Starting from a simple color correction, and ending in relight the scene .Another example You AO doesn't look like You want ,no problem ! You don't realy need to rerender all the scene, render only Ao and make change in node's (here can be usefull to add a overall material to all object's in scene ,see the render layer's panel and "mat" input)And bunch off other stuff. I think also to make part 2 of this tutorial ,and show a example for that what I write above .So keep patience, cheers!