interior: glossy reflection grain

# 1 02-07-2012 , 03:40 PM

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Join Date: Jan 2005

Location: vienna

Posts: 1,095

Hi guys,
I am working on my first interior scene, and I noticed that lighting & shading is quite a bit different from the usual product viz workflow.

scene:
- 4x32 FB
- openEXR
- IBL
- 4 areaLights in the windows connected with mia_portal_light
- all shaders are mia_material_x

first odd thing I noticed is blurry reflection quality - in specific when anisotropic is set to 0.1 to make metallic surfaces. (smoothness) quality is awefull.

I have added two pics. the object has applied a standard grey material_x. in first case it is not anisotropic, for 2nd pic the anisotropy is set to 0.1. in both cases glossyness is 0.4 and Glossy Samples are 64. additionally I plugged an envBlur into the shading group which makes no difference since most reflection comes from other object in the room. usually 64 samples is enough, but for this interior scene I´ve already cranked it up to 256 samples. unfortunately there is still grain! and - the more samples I give them glossy reflections the weaker the reflection color becomes, which btw is a major drawback. I´ve already talked about that somewhere else in this forum.

What I´ve tried so far and didn´t make any difference at all:

- increase IBL quality from default 0.2 to 0.5 (adding a string option in the miDefaultOptions)
- increasing AreaLight Samples from 20/1/10 to 60/60/60 (because at first I thought it is a shadowing artefact)
- increasing glossy samples until 256
- Shadows (renderGlobals) set to normal/sorted/segments
- FG filter 0, 1, 2

what made a difference but rendered for ages:
AA set to 1/3 and AA Contrast 0.02

because of resulting render time that low contrast setting really is no option.

my conclusion is:
imho it must have something to do with the glossy sampling...

any ideas?

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# 2 02-07-2012 , 05:01 PM

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Posts: 3,522

I find glossy reflections, when it comes to objects reflecting other objects is always expensive.

Have you tried unified sampling? I've been fiddling around with it and its gotten a lot better from 2012 to 2013.

- Genny
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# 3 02-07-2012 , 07:40 PM

The Nurb Herd
Join Date: Oct 2007

Location: London

Posts: 2,381

try an envBlur. :/

edit: ha, i should have read the thread. What are your UVs like?

Last edited by honestdom; 02-07-2012 at 07:43 PM.

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# 4 03-07-2012 , 04:39 AM

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Join Date: Jan 2005

Location: vienna

Posts: 1,095

thx for your input.

UV´s are laid out on every object nicely. I used to do a lot of modeling in the past for realtime renderers, so I am used to build my stuff clean and error free from start.

I read about unified sampling and thought it would be terribly interesting to play with it. unfortunately we run maya 2011 in the office, and since this software is so buggy I often thought about going back to maya 7 - in my opinion the last stable version. but my job is focused on rendering now, so that wasn´t an option.

everything starts and ends in the right place at the right time.

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# 5 05-07-2012 , 02:27 PM

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Join Date: Jan 2005

Location: vienna

Posts: 1,095

holy f** moly!

I think I figured it out finally.

the glossy reflection grain was a result of 2 (1/2) factors.

the first and minor thing was, I had areaLight samples set to max 20 which was too low and I needed around 50 samples. this made the material look about 20% cleaner.

secondly and that´s the big surprise for me, I was trying to fake a fresnel effect in the BRDF settings:

0 degree - 0.9
90 degree - 1.0
BRDFcurve - 30

where the material looked and behaved the same way (grain) when I was just checking on the fresnel effect. now, after lowering the BRDF curve back to 5 the grain is almost gone! glossy samples back to 64.

the only remaining thing is - it would be great to have an per object or per material override for the Anti Aliasing Contrast and the metal would look perfectly fine without effecting the whole sceene and increasing rendertime too much.

all best!

everything starts and ends in the right place at the right time.

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