Rotobrush and Rendering

Report · Dec 11, 2020

Hello, I seem to be having trouble with the rendering of my rotobrush. I select with my rotobrush and it renders 20 or 19 frames ahead instead of the whole clip. I have selected the work area to be the whole clip excluding some of the already selected frames I have already used my rotobrush on in hopes of that helping, but it hasn't. I have rendered turned on, yet once I get to a clip far enough from a frame I hand edited with the rotobrush, it seems to select the whole image. These pictures are one frame apart.

Now that it has selected the whole image, I will go in and fix it so it selects just the person in the clip.

As you can see, now that I have fixed the clip, I will begin to cycle through the next few frames to make sure everything is okay. Usually about 19 or 20 frames in, it will then select the whole image again.

This is my first time using rotobrush and it's for a short film I'm producing for my school. I have limited time left to edit and I'd like to not have to cycle through every 20 or so frames of this only minute long clip. Help appreciated!

Report · Dec 11, 2020

Nothing unusual there. People simply have a wrong understanding and wrong expectetions how RB works. All it does is try to detect distinct features across time and in your case that is simply not going to work very well due to the woodboard background and the overblown lighting. It makes the footage "flat" in technical terms (you would likely see this even in e.g. the Lumetri effect's scopes) and simply doesn't give the algorithms enough to work with. similarly, there may in fact not be enough motion to synthesize a motion field for the advanced, AI-bolstered mode. So there you have it: RB is not Thor's magical hammer and you see it's limitations. Either you keep on chewing through the footage bit by bit as you currently do or you switch to conventional, mask-based rotoscoping. This would still be a lot of work, but it may ultimately be quicker than forever trying to correct RB's automated results...

Mylenium