“3D Compositing Guide – part1 ” by Simon Reeves
This should come earlier in the comp, I mainly use it to colour correct the diffuse pass before anything else is layered on top (so maybe earlier in this guide? But its a bit special so I thought I’d leave it till now). This is a very useful pass for making multiple matte’s (masks) in one pass.
By giving certain objects materials that are either, 100% Red, 100% Blue or 100% Green we can extract just one of these channels (R, G, or B) in post as a matte to do colour correction on specific objects or whatever you please. As you can see by this gif below, which cycles through the RGB, then Red, then Green, then Blue channels.
If you’re feeling fancy you can use the A channel too, currently the A channel will show the objects that are in the R,G,B channels (as they have an alpha of 1 / 100%), but if you assign everything else a black material with an alpha of 1, you could specifically assign some objects with a black material with alpha 0. Hope that made sense, don’t have any images for that at the moment. 
? Here is the final Graded shot:
If you want to watch the shot, and the film infact you can find it here: Diversion Film Website.
Hopefully I will write another part to this if its useful about the actually comping process, Multiplying/Adding/Over using ID mattes and so on. I personally use the FxTree within XSI but Shake/Nuke/Combustion are all the same principles so it shouldn’t be a problem. If you see any mistakes or have any comments please email me or use the comments thing on here – Cheers.
Thanks.
Simon Reeves ,www.simonreeves.com
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