Loads of speckles when object reflects itself

[kosso_olli]

Hello,
I have a serious problem with speckles this time. Mostly, these are generated by HDRIs with values way above 1. In this case however, it is different. I have a car part with a silver metallic paint. The paint is using glossy reflections, reflection depth for the paint is 5, glossy subdiv is 56. Clamp output and subpixel mapping is on.

When I hit render, I get a lot of white speckles in all the areas where a car part is reflecting itself, let say the bumper for example. If I set reflection depth for the carpaint to 1, these areas are speckle-free, but I loose the self-reflection of course.

I tried all sorts of things: Setting the AA to 50 min and 100 max, no change. Setting subdivision for the metallic paint to 256, no change. Is there any workaround? This has been annoying me for months...



Thanks in advance

Oliver

[Morbid Angel]

go to options of your vray material and set the cutoff value to 0.001 and see if that helps.

[kosso_olli]

Dmitry,
thanks for the tip. Tried it, but it didn't help.

Regards

Oliver

[joconnell]

High AA will undermine your high material samples - for the laugh try setting your aa max to 12 and keep your really high material samples and see if it'll do it.

[Morbid Angel]

can you post a small part of your scene so we can have a look, just a part of this object is enough.

[kosso_olli]

I hope so, will have to ask. If not I can replicate it with some simple objects.

Regards

Oliver

[kosso_olli]

Here is the file. The speckles are visible in the metallic layer of the carpaint (see MtlSelect render element). I narrowed it down to one light in the scene. Increasing the subdivs of the metallic layer helps a bit, but I need that scene completely noise-free.

EDIT: wtf, file size limit for zip is 97kb? Come on... Please send a pm and I will mail the file to you. It is about 600 kilobytes

Regards and thanks for the help

Oliver

[Svetlozar Draganov]

Hello there,

We are sorry about the delay of this answer.
Could you please send this scene to vray@chaosgroup.com
Please include the link to this post , and mention what is the issue with the scene.

Thank you very much in advance.

[Morbid Angel]

Svetlozar, I have already forwarded this scene to your email a while ago. The issue was the directional parameter which he had used in his vray light, it caused the unresolvable noise. If you'd like I can resend it.

[t3dm]

had an issue similar to this... hdri on environment and vray dome light.. what was the directional parameter that was incorrect?

[vlado]

Another way to avoid the problem is to use the VRayOverrideMtl material and use a different and simpler material for the reflections.

There is no bug here, just the probability of a camera ray to go through the two reflections and hit the bright light source is very very small and happens very rarely. We must find another way to solve this issue, perhaps using some kind of multi-bounce adaptive sampling.

Best regards,
Vlado

[Morbid Angel]

I don't think dome light has a directional parameter. For this issue the rectangular light had a value of 0.75 if I remember correctly. Setting the dir value to 0 and making the light have no decay with value of 0 instead solved that current noise problem.

[vlado]

It can happen with any light; in your particular case that was a work-around, but we must find a general solution.

Best regards,
Vlado

[kosso_olli]

There is no bug here, just the probability of a camera ray to go through the two reflections and hit the bright light source is very very small and happens very rarely.

I feel that this also the case when using hdri's of sunlit locations in a dome light. The sun in these hdri's is often very bright, causing the same speckles. Single pixels in the framebuffer sometimes have 3-digit float values. That's the white speckles. I have a scene file for that problem, if that helps. It is quite large though, because of the hdri.

Regards

Oliver

[Svetlozar Draganov]

Hello Oliver,

You can send you scene to support@chaosgroup.com , if the scene is too large we can provide you our FTP server - just let us know in the email.