First Impressions: Rotobrush

Following the (relatively quick) install of Production Premium CS 5, I imported the project files I used for producing my latest DVD into the new versions of Premier Pro, Encore and After Effects. All of them loaded fine and I saved out some CS5 versions for later use. I then jumped straight into After Effects to try and implement a shot using the new rotobrush I did not have the time and patience to do with manually controlled masks.
At one point in the show, the 2 leads are singing a duet, with a pretty full stage behind them. The problem is that to make things easier for the cameraman, and due to the camera positioning, the depth of field was pretty big. This was OK for most of the show, but in this one shot as the leads sing to one another, one of the background characters is right in the middle of the shot looking out from between them. Now I could have fixed this in CS4 if I had a lot of time. I could have created an adjustment layer and focus blurred the background, leaving the two leads in focus. This would mean manually masking out the two leads for each frame of the shot.
The shot is about 40 seconds long, that would mean manually drawing the mask for 960 frame!
With the release of CS5 the rotobrush was announced, and for me this was the decider as to whether I upgrade or not. I will be using this tool a lot.

The red will be blurred...

So I loaded up the clip, drew a stick figure over the two leads and "hey presto" they had a nice purple outline around them. It wasn't perfect, but it didn't take long to tidy up. I then hit play and watched as it process each frame in turn. When it went wrong, I corrected it then continued to play. After a while, however, it stopped tracking and simply played back, there was only a purple box around the whole screen. After some trial and error, it seemed that it would calculate 9 frames each time I made a change, then stop. In order to progress, I would make a minor change to the rotobrush area every 9 frames, while reading the manual in between.
It was some time before I realised what I was doing wrong. When the brush is used, it creates a base frame. All the changes are tracked from this frame for a limited time, so as to preserver resources. In the rotobrush view, there is a track under the timeline that highlights the base frame and displays the span (the frames that AE will rotoscope for you). By default the span was 9 frames. I simply had to click and drag the end of the span to where my effect would end and it would do it all for me. (The reason I had missed this before was than my source clip was much longer than the bit I was editing, so the track seemed to be showing a single dot when zoomed out.)
Unfortunately, due to the way it works, all changes are calculated from the base frame. Once that is set and the span extended for 40 seconds, when you click on the last frame of the span, all of the frames before that must be calculated for it to display. It still takes a long time to create the mask, but at least now it is my computer doing the work and now me!

Well, at least I know it's working in 64-bit now...