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Roto Brush - Refining the Matte

Apr 11, 2012 12:05 PM



I’ve been having a problem trying to finish a Project I’ve made using the roto brush tool. I’ve created the segmentation using the roto brush tool, I’ve froze it and then I´ve used the regular brush tool to touch it up.


So far all went ok, I’ve put a good amount of hours in making the effect, and to finish I just needed to Reffine the matte using “Effect controls tab”, and that’s whem things went bad.


As soon as I’ve selected the “Refine Matte” box I’ve lost the segmentation on some frames. The segmentation was not lost completely, whem I look on the alpha chanel for example, instead of having the “black and white” contrast between the person I’ve selected and the background, all the background turns to gray.


Whem I see previews of the clip in the timeline, those frames where the background turned to gray get some kind of weird blur with the colors of the person’s clothes.


Here are some screenshots comparing the good and bad frames.



Good frame


Alpha Good.jpg


Bad frame


Alpha Bad.jpg



Good frame


Preview Good.jpg


Bad frame


Preview Bad.jpg


It’s possible to see in the images that the touch ups I’ve made with the regular brush tool are there. I’ve also tested and I can erase the “gray/blur” areas using the regular brush, but that way I’ll have to go thru the video frame by frame again, and I’m hoping there’s a better way to do this.

I really need this help, and I appreciate any tip that can help me with this.


Thanks for the time and good will!

  • Currently Being Moderated
    Apr 11, 2012 6:06 PM   in reply to Fevmac

    Nothing wrong, I'd say. The Alpha was never clean in the first place and refining the matet simply responds to some artifact that you may not see, but technically are already there like tiny fractions of non-transparent pixels with just 0.1% opacity or something. You could try and render the raw clip out to a format which supports Alpha. The forced quantization might eradicate the offending pixel garbage and you can then apply any refinements to the re-imported clip. The same could be done by pre-composing teh Rotobrush result. and naturally, you might consider adding some garbage mattes/ masks somewhere in there to prevent stray pixels influencing your result. It's realyl just a workflow problem...



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