GGX Noise (white specs)

[pixelwerk]

Actually it's not really a VRay-only problem, MODO 901's physically based shader does the same and I've encountered the same in VRay for MAYA: When rendering, especially when lighting with an HDRI, materials with a higher roughness tend to have lot's of noise. Not a general grain i could live with, but small white specs i can't get rid of, no matter what sampling-level I increase. Once switching to another shading method like ward/blinn or modo's energy-conserving shading system the renders are smooth and clean and hardly any difference in the overall look.

Is this some general shading-system problem, since Vray and MODO use a similar Disney Microfacet GTR / GGX BRDF?

[vlado]

Can you post some images of what that looks like? In general though, the GGX BRDF is more difficult to sample than other models and tends to be more noisy.

Best regards,
Vlado

[pixelwerk]

I can imagine that it's more complex to sample. Here are some results. It's a quick scene, but i guess it illustrates what my "problem" is. Rendersettings are the same, only difference is changing from Physically to Energy Conserving, and two settings of Ray Max Intensity. One time it's set to 20 (default) the other is set to 1.





The results are more intense than I've thought in this example. Usually I'm mainly getting rid of these white freckles or i can paint them out in Photoshop later

[vladimir.nedev]

Do you have "Environment Important Sampling" enabled in these tests ? I guess you do, but just in case.
What happens if you render the scene in RT GPU ?

Greetings,
Vladimir Nedev

[vandigital]

Looks like its happening primarily in the fresnel reflections

[pixelwerk]

That's why i was asking if it's a GGX-related problem, since the biggest change with this shading model is the reflecting behaviors depending on the normals. Sorry for the long delay, was really busy the last weeks and actually i was not really saving the scene from my previous post.

To answer the questions: Yes, EIS was enabled with a value of 16 (it's on by default anyway) and when i render the scenes in VRay GPU-RT the results are quite different to the CPU-RT or the, i'll call it F9-Render-Version. I've created a new scene and tried to rebuild the previous one and got rid of most of this white dots but especially in the fresnel-regions they're still there, even after an hour of CPU-RT-rendering, not to speak of the "normal" rendered version. But take a look ->

[vladimir.nedev]

In RT GPU , the fresnel formula used for MODO's advanced material is not the same as the one used in RT CPU / Production rendering.
RT CPU / Production rendering use the actual Fresnel Schlick approximation that MODO uses, whereas RT GPU uses the non-approximated formula that V-Ray's own material uses.

But I don't think this is the reason for the difference in this case, as I could reproduce it with V-Ray's material as well, where the CPU/GPU fresnel formula is the same.
It seems to me it is related to the bump mapping.
You do have bump mapping in each of these scenes, right ?
Is it possible to send me the scene (together with the HDR and maps), as I could reproduce the problem, but not as good as your scene.

It seems on the CPU, the bump map is handled differently, and the edges of the object are much brighter, which cause the extreme fireflies.

Greetings,
Vladimir Nedev

[pixelwerk]

Did you geht the PN with the wetransfer link for the scene?

[vladimir.nedev]

Yes, thank you, sorry for not confirming. I haven't had the chance to look at it yet.

Greetings,
Vladimir Nedev

[chadstevens]

Any news on this problem? I have had the same problem multiple times and I generally solve it by switching from GGX to ward or blinn brdf which is not ideal as it doesn't have the same PBR shader qualities.

[vandigital]

you can even see it in the quick start tutorials where the scene is mostly clean except very visible white dots on the fresnel.

I hope this gets attention sooner than later.

[vladimir.nedev]

The nightly build from 2016.05.31 has the improvements Vlado made to the importance sampling of the GGX BRDF.

It will be nice to see the original scene retested with the improvements.

Greetings,
Vladimir Nedev

[pixelwerk]

As far as i can judge, all the problems areas are pretty much solved with the implemented improvements. No more white specs, not even with Depth-of-Field ON. Didn't even had to clamp the results. Awesome!

[NicoC]

I have to bump on this - we are still on v3.40.01, and we regularly get white dots here and there, only when using BF + LC, never when on IM + LC ...

EDIT: sorry, wrong thread ... I shouldn't have multiple threads open in multiple tabs ! my post should be in 3dsmax section - sorry again. I can't remove this post myself, right ?

[vlado]

I have to bump on this - we are still on v3.40.01, and we regularly get white dots here and there, only when using BF + LC, never when on IM + LC ...

EDIT: sorry, wrong thread ... I shouldn't have multiple threads open in multiple tabs ! my post should be in 3dsmax section - sorry again. I can't remove this post myself, right ?

Get me a scene to vlado@chaosgroup.com and I'll try to sort it out.

Best regards,
Vlado