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Thread: After Effects CS5 - Rotobrushed Jpeg only stays masked for 1 second in comp

  1. Default After Effects CS5 - Rotobrushed Jpeg only stays masked for 1 second in comp

    Hi, I've got an issue with After Effects CS5 when I rotobrushed a still image (jpeg) the mask that the brush make seems to disappear after 1 second and all the background that I initially rotobrushed out comes back.

    Does anyone know why it is doing this please?


  2. #2


    Sorry I can't help you as I don't use the rotobrush. I prefer to get accurate rotowork with trackers and masks, for me the roto brush isn't quite there yet. But your question has got me curious, whether rotoscoping with masks or with the rotobrush the purpose is to animate. Your doing this with a still image, there is no animation.

    If you just draw a mask you will get your desired results with greater accuracy.


  3. #3



    David makes an excellent point about using the Roto Brush on a still image being a bit strange.

    That said, what you're encountering is that the Roto Brush effect operates on a "span". See this page. The Roto Brush is supposed to be used on moving images, and the idea is that you'll apply corrective strokes every now and then. Each time you apply a corrective stroke, the span extends a little bit. If you're just operating on one frame, thei isn't going to happen automatically. But you can extend the span manually.

    Leaping into using the Roto Brush without reading the documentation and watching the tutorials is a bad idea. It's not a beginner feature, and it has a lot of... shall we say... quirks.



    I find that almost everyone who doesn't like the Roto Brush a) hasn't read/watched the materials that we provide for learning it and/or b) is expecting it to to precise rotoscoping---which is not what it is designed to do. It's a great tool for getting you 90% of the way to a precise matte; it's a great tool for creating a rough matte for such things as secondary color correction or garbage matting. It's not adequate by itself to do precise compositing. We don't claim that it is.

    The very worst thing that people can do is to try to use it assuming that their experience with actual rotoscoping will help. For example, drawing strokes right along an edge makes it work worse, whereas a conventional rotoscoper is used to drawing masks right around an edge. Also, conventional roto usually involves hopping from beginning to end to middle, setting keyframes at various middle points between extremes of movement---whereas the Roto Brush relies on a progression in one direction outward from a base frame, with corrective strokes being made along the way as necessary.
    Todd Kopriva, Adobe Systems Incorporated
    After Effects Help and Support
    Premiere Pro Help and Support

  4. #4


    Hi Todd and thanks for the info on the rotobrush, it certainly all makes sence. I did look into it when it first appeared, as I do with anything that looks like it could be a potential speed up to roto work. But fair play, I certainly never gave it a great deal of time.

    What I did find relates exactly to what you say in relation to going into it with the mindset of a rotoscoper, not drawing directly on the edges was the first thing that never felt right for me. Generaly I found it felt very "wrong" even though at the time I was fully aware that it's not, it's just "different". A bit like a right hander writing left handed or if you gave a cyclist one of those bikes that you need to peddle backwards and steer in the opposite direction.

    For me, when it comes to less accurate roto work, which as you know is very useful, there is no real need for a faster tool. It only takes an uncomplex mask or two and the odd keyframe. Perhaps if I gave the rotobrush more time this I would find different, but to be honest when I did look into it I actually found it more of a hindrance than anything else, but perhaps.

    As for getting 90% of the way to a precice matte, I have a real strong feeling that I would spend more time getting to this 90% matte with the rotobrush, then cleaing it up with what I do anyway, than I would completing the job without. But it does interest me, when I get a chance I'll definately give it some time and get back to you.


    Last edited by david walsh; 01-04-2011 at 12:45 PM.

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