Specular Banding on thin lights

[dlparisi]

I have a scene where I'm getting very visible banding in the specular components of reflected vray lights. The lights in question are very thin, just a 1/2" wide. The lights reflect fine on the walls, but at the floor I've tried lots and lots of things but the only thing that works is making them wider (around 2" the banding goes away). Cutoff on both the lights and the materials set to 0.0. I've attached the rgb, specular and a crop along with the scene. Anyone have any ideas on how to resolve this or what's causing it? BTW-VRay 3.40.02

[Morbid Angel]

I took a look at your scene, the issue happens even with 3.55 nightly, it appears to be a bug.

[dlparisi]

Thanks for taking a look at it. I'm not sure what you tried but other things I tried (that I can remember at least):
-raising the msr to ~100
-BF/BF
-linear color mapping vs. reinhard
-different BRDF's
-sub-pixel/clamping
-turn off max ray intensity
-turn embree off

I didn't expect most of those to do anything really but it was easy enough to check.

[Morbid Angel]

Right it looks like an issue with light size in particular. Even scaling the scene up does not change it...so it seems to be related to how big the light is in screen..Only devs will be able to say for sure...

[Alan Iglesias]

Hmmm...interesting that the problem seems to disappear in RT/GPU...



-Alan

[dlparisi]

But not in RT/CPU unfortunately...

[Alan Iglesias]

But not in RT/CPU unfortunately...

True that...but perhaps it will help give the Devs something to go on...

-Alan

[dlparisi]

Agreed. Clearly makes it seem more like a bug than some weird setting somewhere.

[svetlozar.draganov]

It looks like a bug indeed - it's already added into the system.
Will keep you posted for any updates.

[vlado]

Set the light cutoff to 0.0 and see if it helps.

Best regards,
Vlado

[Morbid Angel]

Set the light cutoff to 0.0 and see if it helps.

Best regards,
Vlado

its mentioned earlier that cutoff did not solve the issue, I've confirmed this as well.

[vlado]

Ok, sorry - I missed that part. Looking into it...

Best regards,
Vlado

[dlparisi]

Very, very late update on this.... I was able to correct this my swapping the "plane" light for a "mesh" light with the same dimensions. Seems the sampling is better on the mesh light or something. BTW, this is on VRay 6 so the bug is still present. I've got a current job that's using a very similar setup so needed to find a workaround.

[dlparisi]

Another update...I just tried it in VRay 7 Beta (as of 10/29/24) and the bug is still present. I can still do the mesh light workaround but it adds to the render time a bit. Can this be fixed/compensated or does it kill any sampling efficiencies and just make it take the same time to render as the mesh light?

[hermit.crab]

Another update...I just tried it in VRay 7 Beta (as of 10/29/24) and the bug is still present.

I've asked the product manager to bump its priority.