Dust Busting with embedded Alpha Matte

Need to use the remove module for dust busting. The footage has an embedded alpha dust map. I was told that each matte shape in the alpha can be converted into a matte shape in Mocha but can’t find info in the manual. How do I setup the embedded dust map?

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You need to make a shape using any of the spline tools, then in layer properties go to the matte clip dropdown menu and click “import.” You can then load in a black and white matte of your preference. Depending on the version of Mocha, you should see the matte on your layer once you import it. We have been seeing a bug where the matte doesn’t import properly, so if that happens let us know what version of Mocha you are on.


Thanks Mary. I’ll give it a try.

Hi Mary,
So I tried to find a way to export a traveling matte from Resolve but can’t find a way to do that. It may be a function that was available in the past but I can’t seem to find that option in the deliver page. Is there a way to tell Mocha Pro to look at the Alpha for the matte?

In Mocha, when I choose “show matte” and turn off “show RGB”, the whole screen turns white.

So technically we haven’t given Resolve the “supported” stamp of approval. I’d go to Mocha File>Export Rendered shapes and render out a matte from Mocha and bring that into Resolve. We are still working with the resolve team to get Mocha to render properly to the timeline in real time. Sorry for the inconvenience, we were hoping to have a solution to this by now but are working hard to make that happen.

Ok. That’s good to know.

It looks like I have no shapes in the Alpha channel, which would be a problem with the footage. Once I get that sorted out, I’ll try your suggestion.

I see you released 2019.5. Sales told me that this version would have support for Resolve but I don’t see that in the release notes. Will that be added as a 2019 dot release?


2019.5 was meant to support Resolve, unfortunately, we are still waiting for a resolution to a timeline compatibility issue that is outside of our control. As soon as it works, I promise, we will be delightedly shouting it from the proverbial rooftops.

Ok, thx

Hi Mary,
After several months of coordinating with the film lab, I now have an RGBA matte file that will import into Mocha AVX with conversion to 8 bit Greyscale. This was imported as a matte file on my one shape that I created with the spline tool. I can see the IR dirt map as black specks and if I have the color space set to log, I can tweak the dirt map to be more or less “aggressive.” So now that I’ve gotten that part figured out, how do I use it to do the remove?

The bug for the import should be fixed… but the workflow is the same. Make sure you have a background track to remove over. And that should be it.

The dirt map is what I need to use as the track. This is basically to eliminate the need to roto-scope as the film scanner has already identified the problem pixels.

Right, you don’t even need to track that layer. Just make a new shape, go to the matte clip section in layer properties, import the matte. It shouldn’t need to be tracked.

Yes, as I was saying, I’ve done that. I don’t understand your earlier response -

“… but the workflow is the same. Make sure you have a background track to remove over. And that should be it.”

What does this mean? Usually when I do a remove the shapes that are assigned to a layer identify which pixels are to be removed. But, after the matte import, there are no shapes, just a matte file that I can look at in the viewer. How do I create the shapes that are designated by the black spots in the matte file?

Oh! I see where the disconnect is. The matte does not convert into shapes, it’s just the matte overlay. But that’s all Mocha needs for the remove or for holdouts.

The shape you make just makes a new layer, importing the matte clip replaces the shape on that layer with your matte.

That’s all you need. Please let me know if you have any other questions and I will be happy to help you further.

Oh. Nice!

So I’m having some crashing issues when I try to launch Mocha or when I close out and go back to the host timeline, but lets put that aside for now. I was able to apply the matte file and took a screen shot of the Mocha interface and the input viewer (see attached.) You can see that a loop shaped scratch (that was part of the matte file) has been subtracted from the red overlay. This is where I got lost. Shouldn’t mocha have to render the remove to fill in the pixels from surrounding frames? All this was greyed out.

It looks like you might need to invert the matte colors before import, because your whole screen looks like it has a red overlay.

And you must have a background track where the matte crosses various planes, you need a track per plane. You have to have at least two layers for a remove. The object to be removed and below that, tracks of the planes that move behind the object to be removed.

But the object to be removed is physically independent of the image, i.e. dust and scratches that do not correspond to objects that can be tracked. And the dust/scratches happen at random across the entire image raster so, the entire frame is the thing that is behind the objects to be removed. So what would I track?

Unfortunately, if you have nothing to track for the dust spots and they appear randomly where there’s not good data then the remove module won’t work.

However, before we give that up as a bad idea, You could try to track the floor and wall and expand those shapes and see if you get passable results but if there’s a ton of parallax then that won’t work either. Or, if there is parallax, you could shorten the frames before and frames after to be only a few frames (2 or 3 if the dust pops on and off) to counteract the movement of the shot.

If that didn’t work… You’d have to track the table top, side of the table, planes of the rocking chair, etc. The remove tool has to have tracks to remove objects.

So then, is this track on the same layer as the matte, or on a new background layer?

Is there a good video that explains the idea of parallax?

The spots only last for 2 or 3 frames but there are lots of them. Does Mocha see each matte spot as a separate remove instance?

Mocha will see the matte layer as one remove layer, so no, it doesn’t separate out that matte into many mattes.

You need the tracks on the new background layer.

Have you watched our remove module overview videos? They really help understand what Mocha needs for a solid remove. The best tutorials for remove are the following, we have a video series on the basics of the remove tool, part 1, 2, and 3 (the principles are the same regardless of if it is 2D or 360):

For this type of complex remove, we have a complex remove tutorial: https://borisfx.com/videos/mocha-pro-solving-complex-object-removes/

Please have a look at those.