Light Select Render Element

[Uniel]

Hi,

I'm trying to use the Light Select Render Element properly.
I've managed to render separate images for my different light. But here's where I'm stuck and a bit confused, pasted from the online guide:
"Type –
Full – Lights within the VRayLightSelect element provide full output for all information available in the scene such as GI, SSS, reflection, refraction, etc."

It specifically says that GI is supported under the Type "Full", but when I render my passes/elements there is absolutely no GI in my separate light renders. There's GI in the beauty pass, but none in the ligtht passes.
Further down the guide it reads:
"The examples below show how several Light Select Render Elements can be combined to give the same result as the Lighting render element, and combined with the Global Illumination render element to give the equivalent of the Total Lighting render element."
This suggests that you need a separate GI pass to have GI, which contradicts the info under the discription for the "Full Type", which states that GI is included in the Light Select Render Element. Which is it, please?
Also, if I need a render element for GI that is for ALL the lights combined, this pretty much beats the purpose of the Light Select Render Element, doesn't it?
Please explain.

Thank you!

[Uniel]

So, I'm replying to my own post, because I noticed something right after posting. I usually work with these GI engines:
Primary Bounces: Irradiance Map
Secondary Bounces: Light Cache

Now, if I change the Primary Bounces to Brute Force I seem to get GI in my Light Select renders (When set back to Irradiance Map I don't).
Is this a bug? Why doesn't Irradience Map work with the Light Select Render Element? This isn't something that is obvious or easy to figure out by your own.

[vlado]

The irradiance map doesn't work with the full light select. You are right, we should print a warning about this - I will make a note to look into it. Apologies for the confusion.

Best regards,
Vlado

[Uniel]

Hi Vlado,

Thanks for confirming that.
Now when using Brute Force instead, my separate light renders, when combined, give a result that is similar to the beauty pass. Everything in the scene looks the same, except for the objects where I've used the VrayFastSSS material. They differ a bit, I'm not quite sure how, but in the beauty pass they somehow receive more light, i.e. the areas of the material become brighter. I played around with the Multiple Scattering setting, but the result/difference is still the same.

[yolov]

Seems to work fine for me in a simple test. Can you get me an example where it doesn't composite back perfectly?

[Uniel]

Hi,
Thanks for your reply. Sorry for the delay, been busy. I've prepared a scene in which this is visible.
In the attached image I have drawn a red line at the middle. Top half is the beauty render, bottom half is the light select comp.
If you look closely at the cube (FastSSS2 material), where the red line would have been, had it continued over the cube, you will see that the different cube renders differ slightly in brightness where they meet:
I have also uploaded a zip file containing the Maya scene and a 32-bit Photoshop document with both the beauty render and the comp. If you hide/show the beauty layer in the PSD it's easier to see the difference to the comp.
Thank you.

[yolov]

This seems like a bug. My tests show that the whole thing comes from the diffuse amount of the SSS2 material. In other words - when the diffuse amount is larger than 0 (i.e. the diffuse color starts blending into the mix) the light selects compose back to a darker image.
I'll log a bug for the developers.

[Uniel]

Ok, excellent! Thank you.