flickering highlights of ies-lights in high glossy reflecting and refracting surfaces

[Robert1977]

Dear all,

since last year I have spotted some problems with renderings when I use ies-lights together with materials like glass, chrome and other high glossy materials. In still images it occurs as well but is not so evident. Since ies-lights cannot be part of the irradiance map (store with irradiance map), they seem to be always rendered "hard", so are their highlights, they look like sharp white pixels without any smoothing to their borders. In an animation you see an evident and disturbing flickering like white spots that are dancing.
I assume this is because the ies-light is like a light source emitting from a point that has no dimension like an area light.
Does anybody have a solution that is different from the following?

-clamping the images so that it doesn't contain hdr-information anymore
-exclude the glasses from the ies-light-source
-decrease the level of highlight glossiness (from 1.0 to 0.95 for example).

Thank you very much

Robert

[vlado]

Can you post some images or animations to show the problem?

Best regards,
Vlado

[Robert1977]

Dear Vlado,

sorry for the long time of no reply. Have been off for some weeks and had projects.

Here is a screenshot of the white spots. If I look at them in the frame buffer, I often see high values of hdr-intensity on these pixels, while they are not smoothed against the background. In animations they are dancing, not being fixed to a place. Clamping the hdr-image in color settings of vray helps, but this is not what i want due to color corrections after the rendering.

Best regards

Robert

[Robert1977]

Dear all, since an animation better shows the problems, I have here an animation showing the flickering highlights. Did anybody have the same problems? It seems to occur just with ies-lights.

Best regards

Robert Reimann

http://kgh.untergrund.net/renderartefact.gif

[vlado]

Unfortunately it's a tough problem to solve as the IES light does not have a geometric shape in rendering at the moment; you could disable speculars from the IES light and put a self-illuminated plane for the reflections, or else use a VRayLight.

Best regards,
Vlado

[Robert1977]

Thank you much, Vlado. My former workaround was to increase the highlight glossiness of the materials to avoid the flickering but this is not so perfect since the material is changed.

Best regards

Robert

[Robert1977]

Dear Vlado, I switched the ies-lights off, and the flicker problem remains. I just have small diffusors illuminating the scene, basically small geometry with a self-illuminating material with pure white and an intensity of 3.0. Is this a sampler issue, that for some frames the pixels occur, for others not? How could I avoid this?

Thanks

Robert

[vlado]

How are those diffusers illuminating the scene? Through a VRayLightMtl material with direct illumination enabled?

Best regards,
Vlado

[Robert1977]

It is a VrayLightMtl without direct illumination enabled. The diffusers are only enabled to see them in the rendering, since the illumination normally comes from the VrayArealights or IES-lights. But for testing, I just used them for illlumination. The pixels are not so strong anymore, but still there.

[vlado]

In that case, you could make them invisible to reflection/refraction. Other than that, it would take really a lot of AA samples to reduce the flicker.

Best regards,
Vlado

[Robert1977]

Yes, you are right, this is what I tried today, so the flicker is gone but the lights are not visible anymore in the refraction.
Thanks

Robert