View Full Version : GI glowing spots appear randomly - LW 2015

03-19-2018, 03:31 AM
Hi forum,

I'm having an issue noticable with some HDR texture environments and hope you can help. I made this little test to try and solve it.

These two renders have the exact same settings on everything, yet random glowing spots appear in different places.

In general it's most noticable in scenes with a HDRI that's fairly dark and has pin lights, or something like a sunset. Limiting dynamic range has no effect. Been fiddling with most other GI settings and nothing really solved it either.
I think it's strange that it appears in random locations and at random intensity, despite it being identical renders.

On another note, "Enable Caustics" setting has absolutely no effect on my renders. Caustics in GI appear even if its off. And caustics do NOT appear in a ray traced non-GI scene no matter what.

03-19-2018, 06:25 AM
Did you try ISBG Sampling? (render settings) Also blur the hdri image can help...

From manual: Enables the importance sampled background (ISBG) samples below. This reduces noise when using an HDR backdrop image to illuminate the scene and also makes the illumination far more accurate. Specifically, it will examine very bright hot-spots to help generate more accurate lighting/shading from those hot-spots.

03-19-2018, 06:30 AM
LSR-LW Tools & Techniques - Backgrounds (clip)

03-19-2018, 07:01 AM
Thanks OjN,

ISBG was turned on, and at 1024 samples.
Increasing the samples to 5000 changed nothing, just the random location of the blotches.

I reduced the HDRI to 1k and gaussian blurred it 3%
Result is renders below:


The blotches are now fainter, but still as random in location in identical renders, as before. (Also, the caustics are kinda reduced to a smear because there's less light info)

03-19-2018, 07:21 AM
In the sIBL version of HDR you load the blurred HDR for global illumination, just as you seem to have done, but you also load a sharp HDR version under reflections in the Texture Editor and set it to Spherical Map I always assumed the BG image was solely for colour and illumination and the second for sharp highlights and reflections, don't know if that helps any but it's what I do

03-19-2018, 01:28 PM
Thanks Gerry. I only assumed that the caustics would be blurred if the IBL version was, so I didn't do a test with hi res maps on reflection/refraction, but now I tried it and it seems caustics are generated from the refraction sperical map, so the end result is kind of a compromise that works, with less blotches and better caustics. Reflections look a bit different in intensity in various spots compared to when they're drawn from the same map as backdrop, not sure why, but it's no big deal. Cheers.

03-19-2018, 01:36 PM
Thing with this setup though, if you rotate Texture Environment 90 degrees, you have to go into the shader and change the reflection and refraction map seam angles to -90, to line them up. At arbitrary angles it becomes a bit clumsy in terms of workflow. There doesn't seem to be a way to use reference object for all the maps to rotate them together.