Use Background checkbox in the ai Shadow Matte shader?

[excentriPMNA2]

what do the attribute activate?
that is, Background Color in ai Shadow Matte shader or background color in the Camera shape node?

[lee_griggs]

"If enabled, the background color is used to determine the overall indirect diffuse contribution in the scene. Otherwise, the color defined in the Diffuse color is used."

Here is a quick test showing the difference with Use Background enabled and disabled. Indirect Diffuse has also been enabled and so the indirect diffuse green color is evident in the floor from the emissive green sphere with Use Background disabled.

[mishominas]

it not transparent when i have no bg at all

how we can fix that