Cryptomatte and Brightness/contrast

[Tedri_Mark]

So I’m trying to use a brightness/contrast node on a renderlayer which then goes through a cryptomatte node, and I’d expect that only the objects picked through cryptomatte should be visible, just with the adjusted brightness, but instead, the brightness seems to be visible in areas which should be masked.

Hard to describe, but the vidwer node is connected to the output of the cryptomatte, which shows just the objects I’ve got added to the mask, affected by the brighgtness node, but then in the render result you can see that when composited with an alpha over, the area where the plane is is affecting the brightness too:

The viewer node

[vklidu]

On “Alpha Over” node use Cryptomatte’s “Matte” output as Factor and enable “Convert Premium”.

You can use also “Mix” node, but with “Allpha” icon (next to Mix text) enabled.

[Tedri_Mark]

i think it might have been a bug, as the same setup now provides more of an expected result:

EDIT: I spoke too soon, composited over the backplate as before I get the same thing, but by checking “Convert Premul” as you suggested it produced the result I expect.