r.PostProcessing.PropagateAlpha

0 to disable scene alpha channel support in the post processing 0: disabled (default) 1: enabled in linear color space 2: same as 1, but also enable it through the tonemapper. Compositing after the tonemapper is incorrect, as their is no meaning to tonemap the alpha channel. This is only meant to be use exclusively for broadcasting hardware that does not support linear color space compositing and tonemapping.