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Old 01-08-2013, 10:56 AM   #1
patrickrowan
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Reflection noise & dots - Mentalray

Hey,

It's a long shot but I'm up against it and was looking for some suggestions.

I have a scene with some area lights and a simple HDR. Most of the reflections are coming from the lighting. My shaders are very glossy around 0.15 and glossy samples are 82. The problem is my reflection pass is slightly buzzing mostly around edges and there's bright dots running through it in the final renders.

My render settings are 1 and 16, contrast 0.05, Mitchell 3/3, maya 2012, no fg

If I want a baby smooth reflection pass should I just be putting up the glossy samples in the shader more? Or am I missing something?

There is a fine noise as a bump map and I think this might have something too do with it.

Anyone ever have similar issues dialling out reflection noise with mental ray?

Any help is welcome. Cheers
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Old 01-08-2013, 01:39 PM   #2
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Hey Paddy,

Long time!

So is it to do with over brights in the hdr? What you could do is try and clamp the hdr reflection so the brightest parts are not so bright. This could be done with a rayswitch and an low dynamic range reflection map.

You say you are using mitchell filter. You are probably better switching to gauss filter as it will soften things out. Mitchel introduces sharpening and can possible issues in animation.

Another option might be to use the mia_env_blur option for those very glossy materials. However I do think there is sometimes an issue using that in animation.

Another thing might be to try unified sampling. are you aware of this newer sampling method for mr? (know you have been using renderman and vray mainly so you might be out of the mr loop) To give you a quick idea I guess it is similar to vray DMC sampler. It can deal with glossy reflections a lot better than regular mr adaptive AA.

Elemental Ray can be your source for all new mental ray information.

Best,

Rich
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Old 01-08-2013, 02:31 PM   #3
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Dots in my reflections usually come from HDR's that have very high upper values. If it gives me trouble, I usually bring it into nuke and clamp its output to something like 5 or so and rerender out the hdr.
 
Old 01-08-2013, 03:05 PM   #4
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In my experience mental ray have a very hard time resolving very blurry reflections and highlights, at least by just increasing samples. I have an old thread here where I increased the samples to like 2000 and it was still very noisy. Vray on the other hand have no trouble at all, as it uses some kind of importance sampling in these cases.

Anyhow, maybe there is some way to solve it but it didnt come up in my thread. Cant remember if I tried unified sampling, maybe that is your ticket.
 
Old 01-08-2013, 11:17 PM   #5
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mental ray also uses importance sampling, but many people in Vray add a clamp to their HDR to resolve hotspots. mental ray assumes prepping your HDR in a 2D program best designed to handle it like Nuke. (Typically for VFX we process HDRs anyway, this is part of that process)

I would try Unified sampling and a lower reflection ray value. I would also use the Native IBL for lighting (NOT the Maya 'emit light option') Do a search on here for an explanation.

If hot spots persists, look at the values in the HDR, how high to they go?

I would also use gaussian filter 2.0 2.0 and not mitchell. Sinc filters have edge enhancing properties that can look like ringing or noise.
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Old 01-09-2013, 01:28 AM   #6
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hey Rich hows new york?

I ended up just sampling the living day lights out of it. thanks again for the tips guys!
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Last edited by patrickrowan : 01-09-2013 at 03:31 AM.
 
Old 01-09-2013, 09:18 AM   #7
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Did some tests with unified sampling on a reflected light sphere and must say I was impressed with how it resolved the noise Although I had to use what I guess are high values ( samp qual 3, min samp 2) it did a fine job. So maybe you can try that with your render, like bitter said.

Last edited by Ekenryd : 01-09-2013 at 10:03 AM.
 
Old 01-09-2013, 07:00 PM   #8
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Quality 3 isn't too high, especially if the surface has a wide gloss and no textural or bump detail (a perfect surface)

We typically render with Quality 1.5 min 1 max 200 for most scenes using brute force and Native IBL. This tends to render quickly even with motion blur. But very few of our surfaces are perfectly clean/lacking detail. In those cases we need more samples. This is the case for product shots.

Or we could just use iray for product renders.
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Old 01-09-2013, 10:28 PM   #9
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at glossy samples 512 and sampling 4/16,contrast 0.5 and gauss its pretty smooth other than some fine edges.

I looked into unified sampling by adding all the string options. 1/100 ,1 ,000

I found it did do a better job but took an extra 20mins a frame for some reason. also when I put the sample quality down for test 0.1 it didnt seem to change much. I still needed very high glossy samples and in the end just didnt have the time too get my head around it as im sure im doing something wrong. It looks great but I just need a bit of testing time
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Old 01-09-2013, 10:39 PM   #10
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Changing to 0.1 should make it look pretty low quality.

Take a look here: http://elementalray.wordpress.com/2...sampling-redux/

mental ray 3.10 and up should not need as high a quality as what is seen here since it was improved.
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Old 01-09-2013, 10:53 PM   #11
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I looked through elementalray. It was very helpful. For testing I put it too 0.1 but did not really see and difference in quality or render time. Hoping it would be quicker for testing. This was done in the string options.
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Old 01-09-2013, 10:56 PM   #12
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If you're still using a high sample rate on the reflection, then it won't help a lot to change the settings.

You want Unified to do the work for you.
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Old 01-09-2013, 11:30 PM   #13
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select miDefaultOptions;
int $idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name
"unified sampling";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "on";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "boolean";
$idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name "samples min";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "1.";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "float";
$idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name "samples max";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "100.";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "float";
$idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name
"samples quality";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "0.3";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "scalar";
$idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name
"sample error cutoff";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "0 0 0";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "color";
$idx = `getAttr -size miDefaultOptions.stringOptions`;
setAttr -type "string" miDefaultOptions.stringOptions[$idx].name
"samples per object";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].value "off";
setAttr -type "string" miDefaultOptions.stringOptions[$idx].type "boolean";

i used these string options.

Yeah I was thinking that was the case but I put my glossy samples down too 8 and it all went very noisy again. Render time went down a little but I didnt get a chance to see what sample level to put the glossy samples at for production quality.
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Old 01-10-2013, 12:01 AM   #14
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We typically use 1-4 for glossy samples.

What are you using to light? Is the HDR very contrasty? Very hot?
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Old 01-10-2013, 10:14 AM   #15
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Just a few area lights and a dosch hdr. I'm on a new scene now so I might test it out some more. Thanks
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