Glossy noissier and slower than I remember

[Lupaz]

Hi,

I seem to be having a problem with glossy reflections. They used to be faster and smoother with these settings, and with older computers!

Please see image:


This is a reflective surface with 0.75 glossy reflections and 16 subdivisions.
No GI.
Noise threshhold 0.005
AA DMC - Catmull


The bright object is a box with a white vraylight material. The same happens with a vray light.
It doesn't seem to be a problem of the computer (I tested it in more than one)
I'll send the file upon request.

Thanks.

[Fekta.studio]

Can you PM with the file, I'll try to play with it a bit.. let me see if I can help you.

[vlado]

I don't see anything wrong with that, but keep in mind that sharpening AA filters like Catmull-Rom tend to increase the apparent noise in the image.

Best regards,
Vlado

[Lupaz]

Andro, Thanks. I'll pm the file ASAP.

Vlado, It just seemed strange that this simple rendering takes 10 seconds with no GI, simple geometry and no lights. And yet I'd need more subdivs tu get a smooth result. Area filter gave the same result.
But I created this scene to see if I could replicate a problem I'm having in another scene. Please see below.

This is a region render of a surface with glossy 0.65 with 32 subdivs



This is a region render with interpolation with 128 interpolation samples


This is a region render with "affect reflections" off in every light.


This is a brief description of the scene




I never took subdivisions so high.
Could it be because my lights are 50mm x 50mm and intensity 8000?
The only thing I can think of is that it's reflecting a very bright white object.

Taking lights subdivisons to 24 gives the same result
These region renderings took 2:24 minutes each.

Thanks so much.

[Lupaz]

Anyone? Vlado?

I reduced the scene with the problem into the scene you can find in the following link.
Just click on render.

https://www.yousendit.com/download/a...YWJsUi92Wmc9PQ

Thanks!

[Lupaz]

Chaosgroup guys,

I really think you should take a look here. I tested this at work and at home. I can replicate the problem very easily just by placing a reflective glossy surface next to a mirror and a few vraylights. The reflection of the lights on the mirror looks very noisy on the glossy surface and it seems there's nothing I can do about it.

Am I missing something??

Please download the following file.
https://www.yousendit.com/download/a...aytoeVkwTVE9PQ

A rendering with the problem:



Thanks.

[vlado]

The rendering looks correct; the chance that a glossy ray will be reflected from the left surface, hit the mirror, get reflected and hit one of the small lights is really quite small. For one-bounce reflections, V-Ray can also use direct lighting to calculate the hilight, but for reflections in reflections there isn't much to do, except add more subdivisions.

Best regards,
Vlado

[Lupaz]

I added 400 subdivions to the glossy material (I never thought I'd have to take subdivisions so high!) and checked interpolation and it helps a lot. Rendering times go crazy of course.

It seems strange I never ran into this or never noticed it before.

Thanks for your time Vlado.

[Lupaz]

Even better in case someone is interested:
128 subdivisions + 128 interpolation samples. rendering time and quality are very good.

[Neilg]

I've seen one of the guys here take his subdivisions to 150 before, but I never knew why...

[dlparisi]

I added 400 subdivions to the glossy material (I never thought I'd have to take subdivisions so high!) and checked interpolation and it helps a lot. Rendering times go crazy of course.

I would think that once interpolation was checked the subdivisions would be basically ignored since it's using the sampling rates of the interpolation settings. A quick test shows identical renders and times with interpolation checked and subdivisions set to 1 and then 200.

[Lupaz]

Really? Not in my case. When I change subdivisions both time and quality change. I'm sure there's some thread that discuss this somewhere in the forum.

This is according to the manual in spot3d. I have no idea how it really works though:
Use interpolation - V-Ray can use a caching scheme similar to the irradiance map to speed up rendering of glossy reflections. Check this option to turn caching on. See the Reflection interpolation section for more details.