More light -> more noise?

[alexthg]

This has really bugged me. Whenever I add more light (vraylights, vrayies lights), the more noisier the rendering.

So I've done a simple test
1. Scene 1 -> create a new scene, render a simple teapot with a single vraylight (default setting). No camera, everything in default vray setting (no GI, reinhard gamma 2.2, adaptive AA) -> rendered ok
2. Scene 2 -> added an enclosed box away from the teapot, away from the view, and put additional 50 vraylights INSIDE the box -> the teapot rendering look more noisy, even though the additional vraylights should have no effect on the teapot (they're enclosed in the box, and not visible from the view)
3. Scene 3 -> put 500 vraylights in the box -> rendering look terrible

is this a bug? or maybe i misses something? as far as i know it didn't happen when i was using vray 1.5 (i skipped directly to vray 3)

Vray 3.00.07, max 2014
max file is attached

[Pixelcon]

Do you have probabilistic lights enabled?

[alexthg]

so that's causing it! Probabilistic light

yes, it was enabled (default is enabled?). Turning it off solves the problem

thanks

anyway, according to vray documentation, shouldn't enabling the probabilistic light produce cleaner result with many lights? Why do i get more noise?

[Da_elf]

there is a probability that you probably will have problems with the probabilistic lights

[Lupaz]

I'm just guessing here, but if probabilistic light is checked, it would take into account those lights that you have in the box, while excluding some that you actually need (?).
If it counts the samples and not the lights themselves, it would use less samples from those lights outside the box, generating more noise.

[Pixelcon]

Which is my main problem with this feature. If I have 1000s of scattered lights around a massive scene, then this feature wont work. Come to think of it I can't think of many situations where it would work really well...

[Dariusz Makowski (Dadal)]

Can you try increasing subd on lights? I think you need more samples to get it to work properly. TBH its not in maya yet so I didn't test it. So I'm not 100% sure. But I'd like to think that probabilistic light need lights with enough samples so that it can then optimize the look. Also you might need more complex scene than a teapot. I think I read that somewhere.

[alexyork]

Yes this seems to be the problem. I was working on a scene the other day with about 420 lights or so and I was getting major noise issues around certain important lit areas. Turning off Probablistic Lights solved the issue because it forced Vray to sample them all on an equal footing, I guess.

Is the number value for PLs absolute? I.e. the actual number of lights to sample? In that case I struggle to understand the logic of a default value of 8 lights when the idea is apparently to use this in a scene with "many" lights. My idea of many lights is 50+, something you typically get in an exterior view with loads of landscape lighting and internal office lights, for example.

I think the danger with this setting is that you have zero control over *which* lights VRay should sample/prioritise. So those 8 (or however many) could all end up being very small, not important lights in the distance, rather than the important close-up ones that will naturally require greater sampling. I wonder if some kind of control is needed here? Maybe a simple Light Priority setting for lights? You could simply grab all of your main/important lights in the scene and allocate them a value of 1, then the rest set to 2 or 3 etc. Just thinking aloud...

[alexyork]

By the way, when using Probablistic Lights, are these lights chosen at random per-frame? This would not work for animation, then, because it would introduce random sampling. I feel like for almost all use cases it's best to leave this feature turned off so you can get totally reliable sampling control of your lights. The idea being to avoid the scenario where you whack up a light's samples to 400 because it's noisy nearby, but actually the Probablistic setting is totally ignoring this light, as part of its random-choice selection.

[Lupaz]

Can you try increasing subd on lights?.

I don't think this is a solution. The "probabilisitc light" algorithm should be checking for sample visibility automatically. If it doesn't, we better disable "probabilistic lights" all together.

[Dariusz Makowski (Dadal)]

I don't think this is a solution. The "probabilisitc light" algorithm should be checking for sample visibility automatically. If it doesn't, we better disable "probabilistic lights" all together.

Maybe because there is not enough visible samples the algorithm fail to produce good result?

What I mean. Give lights lots of samples so that probabilistic lights algorithm can subtract the samples he don't need and produce smooth effect. I think this effect is not meant to produce good results with low sampling. Quite opposite. Give it lots of samples so it can subtract it from light that don't matter etc etc? I dunno.

[Lupaz]

Yes, I get that problem too. I did the following test. Probabilistic lights on.

Many lights with boxes blocking most of them:



Deleting the lights previously blocked:

[RockinAkin]

Can confirm - Probablistic lights are a no-go as of it's current implementation, and it really bothers me that it's set to ON by default.

Even if it gets fixed it should set to OFF by default.

[Lupaz]

the question is...Did previous versions of V-ray had this behavior under the hood in some way? If we uncheck this, it renders much slower. Is this how V-ray was pre V3?

[RockinAkin]

The Probabilistic Lights setting was only introduced in 3.X. Its behavior isn't present in V-Ray 2.X or older.