Glossiness values of 0 and close to 0, ignore object normals and become faceted.

[irwit]

Hi all

The title explains the question really. I have been doing some tests and when taking reflective materials glossiness to 0 the test object has lost its normal information and becomes faceted. However when rendered without reflections the normals behave correctly and it is nice and smooth.

The object has no subdivisions or anything like that.

I'm using nightly build from 4.10.10 incase its a beta issue.

If needed I will post pics.

Any advice appreciated.

Thanks

Will.

[irwit]

I retested on just a sphere to make sure it wasnt my geometry and the same thing happens. This is quite an issue or have I gone wrong somewhere ?

The material is a new Vray material with reflection set the white and the glossiness set to 0,0.5 and 1.

To my knowledge nothing in the render settings are very far from default.

It is reflection a sphere with a surface shader with a gradient applied.

[vlado]

In recent versions there is an option "Fix dark edges" in the VRayMtl material, which may help a bit, but in general occlusion is not a smooth function over polygonal meshes, since the polygons of the mesh get in the way. Remeber that smoothed normals are a cheat to produce a smooth-looking surface from geometry that is not in fact smooth. In many cases this cheat works well, in others it fails to hide the true shape of the underlying geometry. Increasing the tesselation usually helps to get a better result too.

Best regards,
Vlado

[irwit]

Hi Vlado,

Thanks for the reply.

I am however left confused.

Firstly you talk about occlusion but I am taking about reflections ? Do you mean the glossy reflections are calculated in an occlusion type method?

Secondly, glossy reflections are a major thing and I have never had this issue using mental Ray, Brazil or Renderdrive. Surely there must be a way to keep the objects smoothed normal information when using glossy reflections? If not is it something that can be looked into as obviously this is quite a big issue for people using collapsed CAD data who cannot simply increase the subdivision settings.

Thanks again for the reply.

Will.

[irwit]

Just another update.

I have tried the "fix dark edges" and that didn't help the problem.

I have also spoke to a friend who uses Vray for Max and he doesn't see any facets on the objects he renders that have glossiness set to near 0 so Vray can render glossy reflections and still respect the objects smoothed normals, it just isn't doing it in Vray for Maya. I'll post some example pics when I get a chance.

[vlado]

I can easily get the same effect in 3ds Max as well...

Best regards,
Vlado

[irwit]

Ok, well I'm only going off what I was told, sorry if it was bad information. I had asked him for a similar render as above from him from 3dmax but there's obviously no need if its the same in max so I wont.

So just to confirm, are there any plans to resolve the issue or find a way to mask it better ? I'm putting a case together at the moment to go from Mental Ray to Vray and this has caught me off guard as this is a fairly serious issue I need to resolve or find a better way of masking before I continue pushing for Vray.

I can post pics of the mental ray glossy reflections if it helps, obviously they are noisy compared to Vray ones but they keep the objects smoothed normals.

Any more help on this is much appreciated as upping the resolution of the models is impossible for collapsed CAD data so I'm sure you can see my issue here.

Thanks again for the reply

Will.

[irwit]

Hi again

My friend sent the examples rendered in 3dmax2010 and Vray and there doesn't seem to be the faceting issue. The glossiness values go from 1, 0.5 and 0.

Would you like me to upload Maya and 3dMax files if that would help?

Does this not confirm that it is a Maya issue?

[vlado]

This is what I get in 3ds Max - it still has some faceting. Also two images with mental ray and a V-Ray material with similar settings, showing the same artifacts.

Best regards,
Vlado

[ultrasonic]

Hey vlado,

i also think that this behaviour is a little bit strange....we also talked about it in my occlusion thread over here -> http://www.chaosgroup.com/forums/vbu...see-poly-edges

Wouldn't it be possible to introduce the "distribution" parameter to the vraymtl as well?

As irwit mentioned before this is a real issue in terms of imagequality since we also make heavy use of glossy reflections. It is no permanent issue, but everytime i see objects with that problem we need to cheat in post, which is never a good solution

hope you guys can help us out...

cheerio
Oli

[vlado]

Wouldn't it be possible to introduce the "distribution" parameter to the vraymtl as well?

It's already there but it's called "glossiness"

There aren't too many things to do about that; will try to think of something, but I can't promise anything.

Best regards,
Vlado

[irwit]

These are my original comparison renders. This is rendered from Maya 2011.

Both are 100 percent reflection materials, one an mia_x_passes the other a vray with glossiness set to 0.

The left render is mental ray and there are no faceting issues. The left is Vray with obvious faceting issues.

[vlado]

When you set the mia material glossiness to 0.0 it is switched to a perfectly diffuse reflector and not to a glossy BRDF anymore. You need to do any comparisons tests with a small positive value like 0.001 for the glossiness. This roughly corresponds to Ward BRDF with glossiness about 0.64 in V-Ray. mia material does not allow you to get lower than that.

Best regards,
Vlado