I have a relatively simple video clip of an object rotating. Its shot straight on, no fancy moves or anything just rotating. I've rotobrushed it and it looks good on a plain white background. I'm animating a color shift such that as the object rotates its top 1/3rd part changes colors. The area changing colors has crinkly edges but I've used rotobrush to isolate that as well, no problems there. I duplicated the original clip, rotobrushed the duplicate to separate it from the background. The original clip fades into pure white leaving the rotobrushed layer visible. I duplicated the original again, rotobrushed the top 1/3rd in the same way. I created a new layer with just a color adjustment effect and used the rotobrushed top 1/3rd as a track-mask for the animated color adjustment layer.
What I want to do is run a color gradient that shifts colors same as the top part but bleeds into the lower part that does not change colors.
So, is it possible to use a regular mask for the gradient and do a difference operation with the rotobrush of the object so the gradient only effects the area below the top 1/3rd which changes color ? I know I can do it with regular masks, but I can't figure out how to do it with rotobrush masks. I want to be able to do intersections and unions.
any pointers would be greatly appreciated. Thanks
Wrong thinking. You need to get away from masks vs. Rotobrush. In the end, all you do is create matte channels and therein lies the answer - any channel can be mangled with effects, possibly requiring to be extracted and isolated first by pre-rendering or pre-comping. RB and masks are just means to an end/ tools, nothing more.