Rendering Object Buffer or Alpha Channel of Asset in Sequencer

I’m trying to create an alpha channel of an animated character that’s been shot in sequencer to further composite it outside of Unreal. The closest thing I can find is to enable CustomDepthPass in the Render Settings of the SkeletalMeshActor but I can’t get it to render a black and white matte of the character. Any ideas?

you need to add a custom stencil to an object / character
and render out a custom stencil pass

you’re gonna have issues with any kind of translucency
may have to check other passes that contain the black and white from translucent objects and mix and match passes in comp

Thanks YuuJin,

I have a SkelatalMeshActor in a Level sequence, in sequencer. When I enable CustomDepth Stecil Write Mask to Default and have “render CustomDepthPass” turned on for the SkelatalMeshActor, the resulting file written to the “CustomStencil” file is just black.


you may have to google some tutorials on it

you have to put a random number in the CustomDepth Stencil Value (ie. 7)
you have to adjust the engine content custom stencil shader to remove the numbers that show up in the shader so they don’t show up on the stencil pass itself, you’ll know when you see it

Thanks for pointing me in the right direction…I’m half way there. I can get the custom stencil to render the object buffer, but 2 things happen when doing so. The CustomStencil number is written in to the file, in my case the number “2” and it also is not rendering motion blur for the Stencil that is in the sequencer final render. ObjectBufferExample.JPG

It looks like motion blur and matting has been a long time issue, in the latest 4.22 is there any new developments on this? For certain workflows I would love to use unreal as a render engine. But it needs to be able to properly matte objects for use in compositing in something like After Effects, Fusion, or Nuke.

yah, I dont think stencils come with motion blur, i think without an engine coder to manipulate the engine itself to run the same blur on the stencil passes, you wouldn’t be able to render out a mask for the object,

in 4.22 there’s a velocity pass.
which while I haven’t tested it, may be the gbuffer that has motion vector information. if it’s not, then I have no idea what it is.
so technically if it is as such, you could spit out the velocity pass, the stencil mask, then mask out the final render and then motion blur it in post with something like rsmb pro with a motion vector pass

Modify the material /Engine/BufferVisualization/FinalImage.FinalImage