VFB masks. Use the alpha channel as a mask

[Ahmed Sharif]

Hi,

Is it possible to use the alpha element as a mask in the framebuffe? This would be really handy for exterior shots when you just wanna lower the exposure of the sky and colour correct it without affecting the rest of the image, and without having to use environment overrides.

Thank you

[matanov]

Hello,

That's doable now - you need to add VRayBackground render element before rendering and then in Composite - first subtract it from the RGB and then add it again with your corrections on top. The example is with a simple color mult, but you can apply everything on the respective layer - Color Balance, Curves etc.

[dlparisi]

Another workaround would be to put your VraySky or HDRI into a domelight and then mask it with a Cryptomatte in the VFB. No Composite necessary

[Ahmed Sharif]

Thank you matanov. I don't really want to use the Composite method. I work in a studio where projects get passed around sometimes and this method wouldn't suit a lot of the guys who prefer no framebuffer adjustments to begin with.

I hoped an Exposure layer masked with the existing alpha map would be simple enough.

dlparisi I always add the Sky in a dome light. But how would that work? Do I set the Cryptomatte to object mode instead of material?

[dlparisi]

Thank you matanov. I don't really want to use the Composite method. I work in a studio where projects get passed around sometimes and this method wouldn't suit a lot of the guys who prefer no framebuffer adjustments to begin with.

I hoped an Exposure layer masked with the existing alpha map would be simple enough.

dlparisi I always add the Sky in a dome light. But how would that work? Do I set the Cryptomatte to object mode instead of material?

Yeah, set it to node (the default).