The first time I started rotoscoping on the film I immediately went for the mask tool and began to mask out areas. After taking 4 mins to do one frame I decided I must give the new roto brush a go,
At times I found it frustrating and very slow, for example the rotobrush not automatically setting the footage you are working on to full resolution (if you have to work at full res then that just makes sense). It was also slow when using the rotobrushed layer many times in a comp as it has to 'propagate' ever time for each layer, instead of just once and placing that on each layer.. (I know what I'm on about :P)
Earlier on in my work-flow, long before any CGi started I used the new refine matte tool that is also integrated with the rotobrush. I found this very glitchy and unstable, often blurring the start and end frame of a scene. So I wasn't going to risk making that an integral part of my CGi.
Instead I used the rotobrush to cut out the layer that needed to obscure a CGi element, the characters arm in front of a projection for example. When this was done I would simply put this layer above the CGi layer and then set the CGi layer to alpha matte invert the rotobrushed layer.
Then I would add a fast blur to the roto layer and the whole thing would blend nicely. This also gave me the option when i need to edit, in the middle of a frame, to switch the track matte off, do the edit and switch it back on and not need to wait as it all propagates...
This technique has given me some great looking roto's that made the CGi elements blend in very well.
Here are some screen shots, that I hope explain this a little better than I can :)
Clean shot:
Rotoscoping with the roto brush tool:
Rotoscoped layer:
Track matte applied:
Fast blur applied:
Added to all layers that need it:
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