Hsph. subdivs and Samples Ratio

[inevitableavoidance]

The blotchiness i had came from emissive materials I had, but the settings you gave me really sped things up, while still maintaining quality!

I can now render a 128MP image withing 3 hours, without any light leaks or blotches!

Thank you very much, again.

[MoonDoggie]

Awesome. I'm having long render times myself for my GI Calc. And I'm getting some blotches on a render I'm doing right now too. There's no perfect setting. Best way to approach this problem at the beginning of every render seems to be this:

1. Turn on the separate VRayGlobalIllumination render element to isolate the problem (I usually add VRayLighting, VRayReflection as well to see if noise is coming from my direct light or reflection, helps fight noise). Noise in the VRayLighting channel? Turn up the light subdivs, reflection? bump up your material subdivs or AA.

2. Turn your GI settings way down, and slowly turn them up, examining the GI each step till you get a good result. The key is starting with bad settings. (I start -5/-3)

[inevitableavoidance]

That's a great tip! I'll definitely start using that method.

[andybot_cg]

Ok, you're getting large blotches for your GI. It looks like you aren't getting decent sampling from the windows. Do this for me real quick. I apologize if they aren't clear because they aren't vfsu specific.

Select all your windows and turn them off to GI.
Place VRayLights just outside the windows, the same size as the windows (slightly bigger), set them to "Skylight Portal" and "Simple".

Re-render using the same settings and let's see.

Thanks for the suggestions. Since I never really saw any issue with the final rendering, I never thought to look at the GI solution by itself. With the textures and the semi-glossy finishes, plus the direct lighting (I have two point lights with about 10cm radius shadows), there's not much of the splotchiness that is visible in the final render.

But in the interests of learning and improvement, I tried your suggestion of doing the light portals. With the glass though, there is no ability to specify vray properties per object, only per material. I tried the light portal test with and without the glass layer turned on. I did find that the glass I had was not 100% transparent, and it was reducing the exposure inside. Trying the test with fully transparent glass, and with and without the light portals showed identical results.

Here is the result with 100% transparent - solution is identical with and without light portals.


What did make a difference was the overall exposure - the greater the exposure, the smoother the rawGI pass (more light = more samples = higher quality) In a similar vein, I did some tests with a clay render and with lighter material values, and found wherever there was greater exposure, the GI solution was smoother. I also did one run with Brute Force, and it gives the image a very different feel, absolutely no splotchiness, but much more grainy (I didn't have the patience to run higher subdivisions.)

material changes (you can see the GI splotchiness is now in the dark beams)



And here's the BF solution



I guess bottom line for me is that the splotchiness of the GI solution doesn't really come through when there's direct light sources and materials that obscure it. When I do see it in the final render, upping my hsph subdivs works fine without much of a hit in render times.

[MoonDoggie]

Awesome, thanks for the excellent images showcasing the differences. I'll refer to this later. I'd say with a better GI solution you should be able to get better shadow definition from an Irradiance map solution. Looks great though.

[MoonDoggie]

The BF looks so good, it's just obviously not really attainable on more projects. My goal is always trying to get as close to a BF solution as possible with IMAP.