Flickering shadows...

[evanerichards]

So I have a render. The beauty pass looks great (I put the shadows on the background in a separate render layer). When I look at the matte shadow layer rendered from the render layer that contains only shadows it is very flickery. It's not noisy as if the subdivisions hadn't been turned up enough or as if the threshold was too high, but it's flickery as if it's a bad time-lapse where each frame is being hit with a slightly different intensity light. I only have two lights in the scene. A dome light with with flat white color (no HDR or image maps) and a rectangular directional light. I'm using GI but using a double brute force method.

The only thing I can think is that the rectangular light is quite large. Could the size of the light be causing the shadows to flicker for some reason?

Thanks!

[evanerichards]

I've narrowed it down to the dome light.
Strange thing is, even with 128 subdivs with all the default settings and a straight white color (no images mapped to it) it flickers like crazy.

[vlado]

Can you show me?

Best regards,
Vlado

[evanerichards]

Yes, sorry, I'm putting together a video and a scene file but its taking longer than I expected.

[evanerichards]

Here's is a 10 frame video. You can see it most on the cylinder on the wall.
I'll be posting a scene too, but I'm trying to strip all the extra geometry etc. out of it so it will be small enough to post.

I'd also point out that is SEEMS to only be happening in the matteshadow pass but not in the beauty pass.

Thanks

FlickeringShadow.zip

[evanerichards]

Here's the scene file.
It happens on the "Shadow Only" render layer and as far as I can tell may only happen to the "MatteShadow" render layer.

flickertest_v3.zip

[vlado]

I can reproduce this. Looking into it now.

Best regards,
Vlado

[evanerichards]

Any word on what might be the cause of this flickering?

[vlado]

The actual reason is a bug... I hope to have a fix for next week.

Best regards,
Vlado

[bennyboy]

did this ever get fixed? I'm having the same issue.

[vlado]

For the moment, you can turn off the animated noise pattern in the DMC sampler and it should stabilize. The proper solution turned out quite a bit more complicated.

Best regards,
Vlado

[simonreeves]

I've just ran into this issue (glad I found this post)

Any updates per chance?

[vlado]

No, it's not fixed yet; the issue in the original scene is that the DMC samples get stratified in a very specific way that causes the sub-pixel samples for matte/shadow element to have slightly different values between the frames. I have to look into it in more detail.

In any case you can reconstruct the matte/shadow element from the "lighting" and "shadow" elements: matteShadow=white-(lighting/(lighting+shadow)) - since this would be applied on the final pixel values, it should be more stable.

It's one of the cases where QMC sampling would have been useful

Best regards,
Vlado

[simonreeves]

I will looking to that other method, might be good to have those passes for control too.

[vance3d]

I just ran into this exact issue in vray next 1.2 and the lock animated noise checkbox in dmc settings is the only thing that fixed it

Is this still a known issue?