I don't know very well combustion, so I'm sure that is an error of mine. I've a character animated in a background, the camera doesn't move so for accelerate rendering times, I've rendered the background in 1 frame, and the character in a sequence of rpf files with the ground, for the final gather coloring the character, and an object wich receive shadows from the character, but this object is rendered with a matte shadow material, in order to keep just the shadows, because it is rendered with the background too. The character rendering sequence is in rpf with an obgect Id for the ground.
My problem is that, when I extract the ground with the gbuffer extract, the matted object turn black.... I don't understand because this object doesn't have any alpha channel, as it's a matte shadows material.
I know that my explanation si a little heavy to understand if it's necessary I will post a picture to illustrate my problem.
Thamkd a lot for your Help.