VRayLightSelect of lights that are off in the beauty pass?

[Laserschwert]

Would it be possible to add a way to render a VrayLightSelect element for lights that are actually turned off? I wouldn't actually mind if some kind of substraction happens under the hood, but we are still working in 8-bit, and usually substracting a LightSelect element from the beauty pass in post doesn't give a clean result.

The idea is to render extra lights that I can "turn on and off" in post, when needed.

[vlado]

There's no way to do this right now. You will have to render with the light on, and then subtract it from the beauty... or add up all the other lights without the one that needs to be off.

Best regards,
Vlado

[Laserschwert]

or add up all the other lights without the one that needs to be off

The problem with this is, this won't look identical to what the beauty pass with only those lights would look like. Stuff like environment reflections are missing from the LightSelect element. Now, if there was a render element which stores ONLY the environment reflections, then at least that could be added on top of the LightSelect element (or add a checkbox to the VRayLightSelect element "include environment reflections"). But right now I'm not sure if there might be other aspects missing in the LightSelect element...

[Laserschwert]

Thinking about it, I guess environment GI is missing from the LightSelect element as well, even when set to "Full", right? Would it be possible to have a "include beauty pass elements" or "inlcude environment" checkbox in the LightSelect element, so that it DOES basically render like a beauty pass with only the selected lights turned on?

[vlado]

I guess environment GI is missing from the LightSelect element

The way to do it is to put your environment map into a V-Ray dome light; then you can add it to any number of light select elements.

Best regards,
Vlado

[Laserschwert]

The way to do it is to put your environment map into a V-Ray dome light; then you can add it to any number of light select elements.

Would this look identical to having that environment map in both the Environment GI and the Reflection Environment slots?

[vlado]

Would this look identical to having that environment map in both the Environment GI and the Reflection Environment slots?

I think so...

Best regards,
Vlado

[Laserschwert]

Mh... just tried it, and it's not working as I'd like. First of all, VRayLightSelect on the dome light doesn't include its GI when GI is set to irradiance map. It only works with BF and LC. Also any light that's "excluded" in the LightSelect element still causes visible changes in image noise on objects, probably because even when they aren't visible, they are still affecting the sampling.

To be fair, I'm still on 3.60.01, so maybe this has been fixed by now?

EDIT: Another thing I've noticed, lights that are excluded in the VRayLightSelect element still show up in reflections, albeit as black (even when the light is set to invisible). Turning off "affect reflections" fixes this, but of course this also turns off their reflections in the elements where they are INCLUDED. But at least for flat lights (i.e. not spherical lights) this can be fixed with using a VRayColor with an alpha value of 0 as the light's texture.

[vlado]

Mh... just tried it, and it's not working as I'd like. First of all, VRayLightSelect on the dome light doesn't include its GI when GI is set to irradiance map. It only works with BF and LC.

The full light select mode doesn't work with the irradiance map, no matter what light it is. This is somewhere on the "to do" list for V-Ray 4 to implement.

Also any light that's "excluded" in the LightSelect element still causes visible changes in image noise on objects, probably because even when they aren't visible, they are still affecting the sampling.

You will have to bump up the min. AA subdivs if you want more even sampling.

To be fair, I'm still on 3.60.01, so maybe this has been fixed by now?

No, there aren't changes in that regard.

EDIT: Another thing I've noticed, lights that are excluded in the VRayLightSelect element still show up in reflections, albeit as black (even when the light is set to invisible).

This is normal - lights typically block GI/reflection rays based on their transparency. A work-around, as you have found out, is to use a texture with black alpha.

Best regards,
Vlado