Default Settings, Light Cache, Noise Limit - upping those, I still cannot get rid of noise / fireflies etc.

[JezUK]

Discloser: I haven't been using 3DS Max / V-Ray in quite a while....

Yet I find that some of my renders, I simply cannot get rid of noise / fireflies.

I use GPU rendering, I'm using Cosmos HDRI, I'm upping the Subdivs from default 1000 to 3000, I'm upping the Noise Limit from default 0.01 to 0.005 and sometimes even lower, Denoiser from default to Strong - yet the crazy fireflies are still there.

In one case I had to remove the Cosmos HDRI I preferred and try something else to get rid of some bad noise.

I'm doing GPU rendering, setting to Light Cache - do I go Brute Force (and then my render times go absolutely crazy from 5 minutes with LC, to over an hour with BF)?

I know I could upload a scene to here but then I'd have to strip stuff out first to send it (as the textures cannot be uploaded as they are purchased ones).

Any ideas what it could be and what I can do about it?

Here's an example image I'm talking about..... effectResult and also showing the Cosmos 034 Daytime Lightsource RE where this noise seems to show up amongst all the REs.

[vladimir_krastev]

Hi, thanks for posting. I am afraid we can not help much without the scene. Please send it trough the support contact form and put a link to this thread in the description. Your assets will be used only for the purpose of trouble shooting. We have a secure place to keep them and the policy about confidential information is maintained very well throughout the company. Other than that you could check this thread and this article.

[JezUK]

Thanks Vladimir, that's a great plan, I'll do that asap.

Many thanks.

[^Lele^]

In GPU those are samples, not subdivs.
So, with a sample setting of 1000, you're actually using a subdivs of ~31, which for GPU rendering is most definitely very low.
GPU uses a fixed MSR of 1, whereas CPU uses an MSR of 6. GPU then traces 2 rays per sample (one camera ray, one secondary one) whereas for the same settings CPU traces 7 (one camera ray, six secondary rays).
Try setting max samples to 10k, and a noise threshold, and let it run.
Regardless, add a sampleRate RE, and check it: if there's red, up the samples without touching noise threshold.
How much to up them by? Double them each time, as in the worst case, the sampler will stop it at the noise threshold.

This, ofc, assuming the scene has no other issues that are raising noise levels "artificially".

[JezUK]

Hi Lele,

Many thanks.

Unless I'm misunderstanding, it is called Subdivs in Render Settings - here are my current settings (or are we talking about something else here?). These settings are working for me (thank you for your guidance), but I do have to use a "Strong" Denoiser to get rid of all fireflies/noise - I'd like to get away with not so much denoising if I can.

Any ideas what other settings I should change?

Many thanks.

PS if I up the Subdivs to anything more than 10,000 I get an error "[GPU light cache] Could not allocate buffer of size 22857MB!" (I have 2 x RTX 3090 each with 24Gb)

[^Lele^]

I didn't mean the LC subdivs!
Reset the LC to the default settings for subdivs and sample size.
I meant the "Samples limit" value, at the very top of the settings, in the screenshot set to 2500.
Try for example 10000, and a noise threshold of 0.01.
Remember to add the sampleRate RE so we'll be able to tell what is actually going on in the scene.

[JezUK]

Thanks Lele,

Here's another scene, no matter what i do with settings in the Render Settings Dialog box, I cannot get a nice clean render.




Samples Limit is set to 30,000 (and no matter how high I make that, there is no improvement).

Also the SampleRate RE is literally all blue.

[^Lele^]

Samples Limit is set to 30,000 (and no matter how high I make that, there is no improvement).
Also the SampleRate RE is literally all blue.

Hey Jez!
When the behaviour is as you described, and the image is as you see it, with noise everywhere, and the samplerate is all blue, it means the noise threshold is too high, and V-Ray stops sampling very early.
In theory, all you'd need to do here (with a high samples limit) is to lower noise threshold.

You can mail me the scene if you have trouble, and i'll take a look.

edit: you may want to check this post: the sampling logic hasn't changed since then, and it applies to both the CPU and the GPU engine.

[JezUK]

Thanks Lele, I'd like to take you up on that kind offer but won't be able to until the weekend, and during then I'll try and fathom it out as well.

In the meantime, please can you enlighten me, as to what I should be looking for in the SampleRate RE exactly, I did study this years ago (with Grant Warwick training videos) but I need a refresher regarding how to optimize my scene. So, if I've gone too high on the Samples Limit, do I keep reducing it until I see that noise going? (and what should I be looking for in that RE exactly?).

Once upon a time I used to be able to leave VRay to render at default settings (I think back then I used to use Brute Force and CPU) and just adjust the noise levels to taste. Now I'm finding that I have to do more than just that with several of the known settings I was familiar with having disappeared entirely (eg Subdivs in materials etc). Sorry, I don't use V-Ray much at the moment.

Many thanks, as always, for your help.

[^Lele^]

It's all in the link to that old post.

[JezUK]

Sorry Lele, I didn't see that link

Yikes.... that's post is 17 pages (though I guess most of what I need will mostly be at the beginning) - I now know what I'll be doing this weekend

Many thanks

[^Lele^]

The cheatsheet alone should be enough.

[JezUK]

Hi Lele,

I've just sent you the scene via WeTransfer to your email address - I appreciate your kind offer and look forward to hearing your conclusion

Many thanks.