Chaos Scatter Bug?

[hunter_williams]

I did a render using some proxy trees and Chaos Scatter and I get these random dots in my render:

https://drive.google.com/file/d/1WyS...ew?usp=sharing

If I turn off Chaos Scatter they are not there. The Denoise render element helps sometimes but not guaranteed.

I'm using Maya 2022.4 with V-Ray (v6.10.00) on Windows 10.

[hunter_williams]

Here are my render settings:



I've tried increasing the subdivisions but that doesn't seem to help.

[Morbid Angel]

Hey Hunter, it may be a few things in your scene. The bright dot is likely a result of reflection/specular on the leaves of your trees. If you are rendering at this distance there is really no real reason to use true reflections and sharp reflection/specular. I would suggest checking your tree model to make sure the reflection trace is off and specular glossiness is not .9 or something like that. More rough specular will ensure smoother highlight.

For the render settings it self, 1/6 at 0.01 is really low setting. Unfortunately for trees at a distance you want to sample the scene really really high to make sure there are no artifacts. We recently rendered a forest scene similar to this and our settings were as high as 4/32 at 0.007

[hunter_williams]

Thanks for the info about disabling the reflection/specular. I disabled those and did a test render sequence and it's not as bad as before.

[Twist]

Thanks for the info about disabling the reflection/specular. I disabled those and did a test render sequence and it's not as bad as before.

the fireflies are propably in the spec pass. But look through the various passes and locate the culprit. Then you have a better understanding of where to possibly tweak Settings.

[hunter_williams]

I actually tried Dmitry's render setting of 4/32 at 0.007 and that seems to eliminate it. Not too long of a render time if I render out just the terrain render layer.

Someday I will actually learn about those settings.

[Morbid Angel]

Hehe glad it worked but I think with forest it will take much longer.

If you ever see a bright dot load up sample rate element, in that element it will show up as full red most likely. It just means that for that given pixel there was not enough samples (max subdivs), so you just have to raise the max subdivs until the red becomes greener or blue. Lowering the noise threshold essentially ensures that in dark areas of the image there are still many many samples (subdivs) applied.

If you sample the pixels in the vray buffer you can actually see their RGB value (how bright they are) and most images are quite dark so the darker the area like your trees, the less samples it gets. If you have a setting of min 1 max 6, then in all dark areas it will get 1 sample (very very low).
Setting the min sample to 4, it can be set to lower however with thin lines, or small dots like little details in your geometry if you have it set to subdiv of one and the object is so far away that it's size can become less then 1 pixel, then the renderer can miss that object for a given frame, then on next frame it can hit that object thus create a flickering effect. Setting min subdivs to 4 or a high value, ensures that all objects will not be missed (thus no flickering). Some renders we have, for example an airplane flying past camera then far into distance, means that its lights become so small they start to flicker the further away it gets from us.

Those kind of renders we have to set min subdivs to a really high value like 15-20, sometimes 30 to ensure stability.

[SonyBoy]

Out of curiosity, at what point did 15-20 max subdivs become considered "really" high. Presumably at some point something about the way Vray works changed (I can't remember), but I recall often putting that value as high as 128 in versions of Vray 3 and 4.

[Morbid Angel]

Sonyboy I was talking about min subdivs not max )

[SonyBoy]

Oops, misread that. Well, 15-20 for MIN samples would indeed be really high. However, my question still sorta stands as it seems it's now common to have max subdivs set as low as 12 for production renders and I remember it being necessary to bump this as high as 50 just as a starting point for final quality. Something to do with adaptive sampling in Vray, presumably.