Using externally generated mattes with the remove module

Hi, I’ve roto’d a mask for an element I want to remove from a shot in After Effects. It’s a nice, tight mask and I’d really like to use it with the remove module in Mocha to take out a pole and wire from a shot. I imported the footage (as a 16bpp TIFF seq) and the rendered mask sequence (as an 8bit TIFF seq).into a new mocha project. The footage is locked-off (no camera movement), so I drew an x-spline around the whole shot and called it “background”, then duplicated this layer, called it “FG element” and set the matte clip for this layer to use the mask sequence. This shows up correctly on screen (FG layer is masked by the alpha) but when I try to remove it, nothing happens.

Any idea where I’m going wrong here? TLDR: Is it possible to remove elements from footage using mattes created in other applications?

Actually, I think I might have cracked it. It appears that I have to track the background plate, even if there’s no movement in there. Once I did that, the remove module works.

PS. I’m having to use “interpolated” mode to render the removes - due to lighting changes. It works really well, but is really slow. I noticed in Activity monitor that the remove process only appears to be using a single core. It would be lovely to see some multithreaded optimisation in a future build!

Yes, you always have to track the background. I am glad that you have that sorted.

Also, less tight roto will get you better remove results usually, since motion blur can get left on the background with tight roto.

You might also get a better understanding of the remove module through these tutorials:

Please let me know if you have any more questions and I will be happy to help you.Cheers, Mary

Thanks Mary - I’ve already watched those tutorials, and have a pretty good understanding of the remove module (which is an amazing tool!)

The only confusion here came from the fact you have to track the background plate - even if there’s no movement- otherwise the remove module seems unable to calculate a remove. Now I’ve done that, I’ve almost finished doing the shot :slight_smile:

Exactly, the remove module doesn’t use the layer you’re trying to remove to calculate how to replace those pixels, it uses the BG tracks for that calculation. The remove layer just tells where to replace pixels, the BG tracks tell mocha how to replace the pixels, and any Foreground layers tell mocha what not to look at.