GI on matte objects

[FSGFX]

Hi!

I am currently rendering an outdoor setting with VRay Sun.
I need to split up the background and the characters.

Therefore I render the background elemnts and then the characters with all background objects set to be matte objects in their vray properties with these settings:

Matte objects: on
Alpha contribution: -1
Shadows: on
Affect alpha: on

Now I am getting strange colored GI on the background mattes when rendering the character.


The alpha of this imahge look like this.


When compositing the character on to the background in Fusion these GI colors look totally wrong.
It looks perfectly right when I "post-multiply" the character footage in Fusion, but this leads to the typical black edges around the character.

I don't wanna turn off receive GI on the matte objects, as this leads to pitch black shadows.

Is there a way to fix this without making a seperate shadow pass?

Thanks,
Flo

[vlado]

When calculating the GI for matte objects, V-Ray will compare the GI values against the scene environment; this means that you must match the scene GI environment color to the ambient color in your plates.

Best regards,
Vlado

[Morbid Angel]

well in this case I would treat gi which is cast from the character back on to the ground a part of the background and not the character. If you think about it this way, then you can render this in 3 stages: 1 background with the character not visible to camera (thus casting gi on the backplate). 2 character, with the background set as not visible to camera ( thus casting gi onto the character) and 3 alpha where the background is set to be black and character is set to be white for occluding objects.

[FSGFX]

Hi Vlado!

Unfortunately I don't get it.

For my matte renderings I usually turn off the "Use Map" option in the Max environment tab and set the background color to pitch black.
Then I instance the VraySky into the GI and reflection slots under the VRay environment tab.

Which color should I match then??