Using After Effects 14, i masked out a moving person using the rotobrush tool, but its still imperfect.
So i want to know, if its possible to edit the rotobrush mask frame by frame afterwards without changing the whole mask or combining it with an ordinary mask?
Thank you already for your help.
the way Rotobrush works is that you set a proper base frame, use propagation method that will do the hard work for you. and only then work frame by frame with the brush strokes. if you did a bad job, you should correct your strokes and not add or subtract information with another method. there is a learning curve and a lot of practice. read everything here (it's a lot)
having said that - there are cases were there very small adjustment that can be made without redoing your work and you can do those by using the paint tool in AE - set it to Alpha and Single frame and use black or white alternatively to add or erase information from your image. use with caution - frame by frame roto is only in those cases where you have very fast movement or something interrupts your image for a brief moment, or painting and erasing RGB or ALPHA when motion blur is not looking so good (smeared hands... aghhh) or maybe fix some matte issues manually.
you can find that advice under "Tips for working with the Roto Brush and Refine Edge tools" in the link above:
"When you've gotten everything as good as you can with the Roto Brush & Refine Edge effect, you can touch up the matte further using other compositing features in After Effects—such as by painting on the alpha channel. "