I was thinking of making an effect where the game environment is black and white, but the player’s are in full color. Is there some sort of way of masking tonemapping for objects with specific materials?
I think this should be easy: You can use the stencil buffer (for that, I think you must set “Custom Depth-Stencil Pass” to “Enabled with Stencil” in Project Settings>Engine>Rendering>Postprocessing) and enable custom depth on the player mesh, then setting the stencil value (set it to something greater than 0 just in case; keep reading for details) so you can make a postprocessing material that looks for pixels with the stencil value you put on the mesh (I am not sure it will work if you set that value to 0), and colors those normally, while making everything else black or white,as you said.
Is there any way to Mask for postprocessing without using depth?
By just using an alpha channel, which is used from the shader of an actor?
(like know features from standard render passes in other software)
I have flat objects, easy to determine by their contained alpha channels (image planes), but I need to get a mask out from these alpha channels, which I can use to mask the postprocessing.