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Alex DeJesus 493 posts
Jul 25, 2008
Currently Being Moderated

Roto Brush only works for a few frames

May 29, 2012 11:26 PM

Tags: #rotobrush

CS6 After Effects. I am trying to remove the background behind a person in a shot about 1 1/2 minutes long. The roto brush tool does a good job of selecting the area. It replaces the background area with black. But it doesn't seem to want to propagate past the first few frames. I am working in the layer panel. I watched a couple of tutorials. 


I have to page down 3 to four times for it to advance one frame. After about the 6th frame it has stopped applying the roto brush. The background has reappeared in the frame. RAM preview plays the clip as if no effect is applied.


I have never done any rotoscoping, so I'm not sure if it is meant for this purpose or for this long a clip. In the tutorial, the clip used is only 11 seconds. Mine is 1 1/2 minutes


Addtn: Now I see that you have to drag the span slider across the timeline first. Now it seems to be rendering. However, the program is freezing after each ten frames or so. Looks like I'll let this one work overnight.

  • Currently Being Moderated
    May 29, 2012 11:32 PM   in reply to Alex DeJesus

    Screeenshots tell a lot... Manually having to set the spans is not the way it's designed to work and such excessive render times point to otehr issues.



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    May 30, 2012 11:18 PM   in reply to Alex DeJesus

    I'm afraid I have no answer for you. this sounds completely insane. I have rotobrushed 10 minute clips and the propagation would take at most twice that long, so having it sit there for hours on a one minute clip just isn't right. Anything specific to the footage? Have you tried with a completely different footage to compare results?



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    May 31, 2012 2:32 AM   in reply to Alex DeJesus

    Well, you info tells a lot. It would seem that AE is decoding your footage over and over to extract the current frame and produce the temp frame. I recommend you convert the file to something else. I'm sure things will work like a snap once you do.



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