Still learning Blender here, coming from Houdini and Maya. I’ve just figured out how to set up light groups, but I can’t figure out how to get the individual AOVs for each light group (diffuse direct, indirect, color, glossy direct, &c.)–I get the combined AOVs for everything, the AOVs for all lights combined, but then I just get the combined pass for each light group. How do I get that set up?
Thanks!
You can separate each light by collection and specify it.
Please refer to the video.
I saw that video, but he never appears to render to an EXR, which is what I need so I can composite in Nuke (unless I’m missing that part). Most of the tutorials I’ve seen along these lines are only compositing within Blender, which doesn’t help me.
I tried subtracting the diffuse color from the combined pass of my light group, which should theoretically remove all color and just give me the lighting info, but it doesn’t appear to work–the color info remains in my light group combined pass.
I don’t think this is the function you want.
As far as I know, it is not a function to store pure lighting information.
Add…
Please refer to the video below.
This is an image that uses stored exr in other software.
Unfortunately, it’s just the combined passes again, which I have no problem getting. So is this just one of the places Blender hasn’t caught up yet, and the only way to get lighting-only information of a light group is to actually render it as a second file/sequence?
What I am trying to do is add a flickering light–and I’ll be controlling and tinting the flickering light in comp–so all I want is the lighting-only info for that light group–no color information–so I can do my grading and then just plus it on top of the main render (lit by the HDR and some targeted spots and area lights). But it looks like that might not be doable in Blender? (I’m ending that seemingly-declarative sentence with a question mark, hoping someone will gently come to the rescue and I don’t have to triple my number of renders, since I have two different flickering lights.)
It’s been a long time since this feature was made, but it doesn’t seem to be used much.
I rarely use it either.
I think it’s possible in a different way…? I don’t know the answer. 
Yes, Blender doesn’t yet support the shader passes for each light group—each light group only gives you a Combined pass.
I tried subtracting the diffuse color from the combined pass of my light group
Do you mean divide? Division would be the operation to get raw lighting: raw light is multiplied by color to get the beauty, so dividing the beauty by color would give you raw light. (Although since specular color is separate, dividing the whole image, glossy and diffuse alike, by the single diffuse color, won’t give you the correct raw light mathematically, but could still be workable for your needs.)
That said, are you sure that’s actually what you’re looking for in this case? If you’re intending to add light to your scene, the correct pass is indeed the Combined, which contains the exact illumination that light contributes to the scene: multiplying that light-group render by a color is mathematically equivalent to adjusting the color of that light. ( RGB = lightColor * surfaceColor, so newColor * RGB is the same as newColor * lightColor * surfaceColor, which is what would happen if you changed the light color inside the rendered scene.) Plusing only the raw light on top of a beauty render would be incorrect if you want a match to what would happen in 3D.
Here’s extracting the light group, tinting it, and adding it to the other lights:
Comparison between that result (left) and a render with the light’s color changed in the scene (right):
And here’s dividing the light group by the diffuse color to get a pseudo-“raw light,” tinting it, and adding that result to the other lights:
And here’s the comparison for that one—comp left, render right:
Without the colors present to attenuate the effects of the “raw” lighting info, the values are wrong. Raw light needs to be multiplied by raw color before it can be added into the scene.
If the former is all you’re trying to do, the Combined pass is all you need. Are you hoping to tint only the light’s diffuse or spec, instead of changing the color of the light entirely, the way it would if you adjusted it inside the 3D scene?
