V-ray Next 4.30.02 - Extreme "dancing" white pixels on any material at a distance with glossy reflections

[kosso_olli]

Shouldn't all the frames be the same result?.

They are when you lock the noise pattern in the render settings. However, this only works if the camera is standing still. As soon as you move the camera or the car even slightly, the highlights are starting to dance again.
Still do not know what to do, really. To me it seems finding the sun disc or any other small light source is pure chance from frame to frame. Even with blurred glossiness.
I could bet it does happen on a range of teapots with glossy materials as well. Geometry or normals are not the cause of this it seems.

[kosso_olli]

Does it happen on just that car paint shader? Or if you assign say, a gloss black / piano black shader, does it still happen?

It does happen on every shader with high gloss reflections. Piano-black plastics, the clear-coat covered rims etc.

[Vizioen]

Well there's definitely something weird going on. I tested a similar setup because I also have problems (mostly with cars) with dancing highlights. So I made a test setup with 4 cars, that should have more or less proper geometry. All settings at default for animation, nothing is animated even (animated camera or whatnot has same results though). Shouldn't all the frames be the same result?

Granted it's a small resolution: (1000x700):

(20 frames in a loop)


But a bigger resolution (2000x1400 but scaled back to 1000x700 because the forum can't handle files bigger than 10MB ) produces similar results too, albeit less bad:



The weird thing is it even flickers in the glass at lower resolution, I always thought it was just the carpaintMTL.

[seandunderdale]

Does it happen on just that car paint shader? Or if you assign say, a gloss black / piano black shader, does it still happen?

[kosso_olli]

Here are two little images showing the current state after the informative exchange with Lele.
Geo is all welded, with no more open edges or coincident vertices. Clearcoat glossiness is set to 0.9, which already is way too blurry for car paint. Yet, still randomly appearing bright pixels around the door handle and at the shut line between the hood and front fender.

[kosso_olli]

So to close the topic: the issue was with geometric normals.
V-Ray was doing what it could with what it was given.
Geo fixed, issue gone.

Nope. It is not. Just did not have the time to tell you, I am still testing. In the full scene, the issue is still there.

[^Lele^]

Unwelded, coincident vertex normals.
Analogous to z-fighting, but for normals, essentially.
Usually it doesn't matter as all the unwelded vertex normals point the same way, but if even just one does not, the random seed across frames may mean a different one is picked.
Combined with the scene's specific lighting angle, it produced the unwanted result.
It's a tricky one to spot as well, because visual inspection of the mesh does not show *big* issues, and if viewed as diffuse, or inside a normals RE, it may just look OK.
One has to get up close, and try things, to notice.

[Vizioen]

So to close the topic: the issue was with geometric normals.
V-Ray was doing what it could with what it was given.
Geo fixed, issue gone.

What exactly was wrong the normals?

[^Lele^]

So to close the topic: the issue was with geometric normals.
V-Ray was doing what it could with what it was given.
Geo fixed, issue gone.

[kosso_olli]

Sure, eMail was sent right now. Thank you very much!

[^Lele^]

Ahah, no i meant email address, for you to send me over the scene so i can check it, and in case ameliorate it, or pass it to the devs to test the advancements we'd need.

[kosso_olli]

Did you send one? Seems I missed it, I can not find it :/
Could you please send it again?

[^Lele^]

do you still have my email, Olli?

[kosso_olli]

Okay guys,
I am stuck with this. It is impossible to get a clean-looking sequence out of V-Ray.

[kosso_olli]

Are you making a still or an animation? You could also try it without the lock nosie pattern, but then average a bunch of frame together. Of course that increases the render time linearly.

We are doing an animation where the camera is moving very slightly. And all those highlights are dancing around like crazy. Keeping the camera static and having the highlights in different positions for consecutive frames just seemed strange and we discovered it while debugging the scene.
As I said in the last post, having the noise pattern locked only helps when the camera is static. As soon as it moves, you will get the randomly placed highlights again. I still did not find a cure for this.