First attempt with the Roto Brush tool

As mentioned previously, I spent some time today trying to get to grips with the Roto Brush tool with varied results. Mostly bad.

From what I understand of the Roto Brush tool so far, it works very similarly to the quick selection tool in Photoshop, by applying what is effectively an additive mask to the area that you paint over. It uses a fairly intuitive edge detection system that allows you to paint very vaguely around your object and still get a relatively accurate selection. Once you've got the selection around your object you can then go in with a smaller brush and further refine the edges to get as accurate a selection as possible.

By holding Alt the cursor changes and the lines you paint become red. This is a subtractive brush and basically tells After Effects which parts of the background to ignore.

You're basically "training" After Effects to learn parts of each frame to keep, and what to exclude. Once you've created your starting point, After Effects uses the information to track the object you've selected as it moves in each frame.

My first attempt at using the roto brush tool was fairly disastrous. In theory I should have been able to create my selection and then scrub through, frame by frame, and make minor alterations to my selection. For some reason it just didn't work — when I painted over a layer, absolutely nothing was happening. The selection stayed exactly the same. None of the video tutorials I read gave me any indication as to what I was doing wrong, nor could I find anybody else online with a similar problem.

I can only assume that the problem was with the way I was brushing my selection initially. From what I can gather I may have been giving After Effects too much information on my selection — I was probably using too many brush strokes to define my edges (the trick is to get as accurate a selection in as few strokes as possible). I was probably too specific with the additive and subtractive brushes, leading to conflicting information until eventually there was nothing left to work with. You can see above the selection shrinks and jumps about until eventually all I'm left with is a couple of black splotches, because that was the only part of the image that I hadn't brushed.

Still, failed experiments are still valid! I'm going to go back and look at some more tutorials on the tool to see if I can better get to grips with it.