Using external matte in BCC Primatte

My shot is dust (FG plate) layered onto footage of a character (BG Plate). The dust needs to look like it is behind the character so an inside mask applied to the FG plate would accomplish that.

I’m using BCC Primatte in Resolve to key out the green screen from the FG plate. I also used Mocha Pro to create the roto shape and exported a b/w matte as a video file. This part of the process is good.

The trouble is that I need to somehow apply the roto shape or the b/w matte video file to be used as an addition to the keyer’s matte in the Primatte plugin.

Things I’ve considered:

  1. I can’t use the mocha tool inside Primatte for the inside mask because the source object for the mask is coming from the background clip.
  2. Since Mocha is only supported in Fusion, I can’t use Mocha Pro plugin on the color page as a mask source and from what I can tell, the Primatte plugin does not have the ability to use the effect mask input unless you’re in AE.
  3. In BCC, I can’t import the roto project created in the Mocha instance from the BG plate clip because each plugin instance is necessarily a separate project. (Is there another shape import method?)

Aside from Mocha Pro and Silhouette plugins, I also have standalone that I can use as hosts for BCC if that allows a better workflow.

Hi there,

So the FG dust is part of a green screen that you’ve keyed out with primatte. Great. Now you need to punch a hole in this keyed shot so that it appear behind a BG element that you’ve roto’d with mocha.

Here are steps that you can follow to accomplish that task :

  1. export the roto shape from the mocha project to the desktop
  2. go to the color tab in resolve
  3. the FG dust shot is keyed out there with primatte and is the current selection
  4. if you have not already done so, add alpha out from primatte so that you’re seeing the keyed dust over the BG
  5. add a bcc pixelchooser node and set the primate node outputs (image and alpha) to the corresponding inputs in the pixelchooser node and from the pixelchoser to image and alpha out
  6. in the pixelchooser node parameter controls, set the output to multiply alpha
  7. in the pixelchooser matte control group, set the channel to none
  8. in the pixelchooser mocha group, launch mocha and import the roto from the desktop
  9. in the pixelchoser mask group, you might need to enable the invert mask option

I think that should do it for you - please let me know if it helps.


Awesome. I now see the merge projects option and that seems to be working to bring in the shape.

Alternatively, in step #1, are you referring to a .mov export of the roto or maybe an sfx file?

Thanks a bunch.


Hi Blake,

Glad you found that useful.

For step 1, we’re exporting the tracked Mocha spline shapes that you generated to the desktop so that we can merge them back into the pixelchooser.


So I see the export dialog with two options, 1)export rendered shape 2)export shape data. Option 1 is the linear video file method so I’m assuming we want option 2, is that right?

If so, what is the preferred format.

Also, In the plugin, I don’t see an import option.