Need Help Getting Maya Fur To Take Light Properly In Mental Ray

[sean-montgomery]

I'm working on a production where a bunch of furry characters that were previously done in XSI are being ported over to Maya. On that prior production, there was a whole hair/fur team...but now there are just a couple of us, and we don't have a ton of expertise in this area. We have been wasting a lot of time trying to get the fur to match the previously approved look, without success. The problem we're having is that Maya Fur does not take light well when rendered in Mental Ray with Shadow Maps (which renders far faster than the Software renderer, so I would prefer to go this route). We want characters to have some dimensionality and shading, but can't get it. A key light placed to the right of them will cast shadows properly, but will illuminate the entire front surface of the fur evenly (there is no sense of a bright side or dark side). To make just one side brighter, the key has to be moved to behind the character, which is not an acceptable solution. I've been doing searches through message boards and can't see anyone else reporting this behavior..has no one else experienced something like it?

Futhermore, the spotlights do not seem to respect surfaces that they hit. A rim light behind the character will contribute to the intensity of the lighting on the front surface. Is this just how Maya Fur is? Is there some material attribute we can apply to the fur that will help solve it?

In addition, we are seeing some areas of fur on a character render as a flat colour...you cannot see any fur definition at all (even though there's plenty of it there, and it will look fine from a different angle). We've tried adjusting the Equalization map, so that parts of the underlying geo surface show through, but this only partially works, and isn't a very elegant solution.

Finally, has anyone experienced an issue with Maya fur rendering differently on a Linux render node than when rendered locally in Windows?

[sean-montgomery]

I find it amusing that there have been almost 200 hits on this posting, but no replies.

Well, it seems that the simplest answer to this question is 'forget about Maya Fur, especially with Mental Ray....use Shave and a Haircut". Rendering fur with raytraced shadows looks better, but results in predictably unacceptable render times.

The answer to the 'flat areas' of colour problem was that there was insufficient contrast between the fur root and fur tip colours. We had attempted to use the same colour maps that had been on the characters in XSI, but this made the fur go red. So then we used just the tip colour map, but it was too close to the colour of the roots. Blowing the maps away entirely solved the problem.

Another issue we have found is Mental Ray generating black pixels on fur passes. The only solution that works here is to use directional lights instead of spot lights. Switching to 'Rapid Fur' seemed to work, but it makes the alpha channel dissapear.

Anyone else care to share Maya Fur war stories?

[christopher-richard-bernal]

I have been trying to use Maya Software to render fur for the past week. Every time I come across a solution, another problem presents itself. Adjusting the base width too much relative to the tip width, and global scale causes the fur to freak out and become little blocks of color.

Using a spotlight, the recommended way to light fur, results in dark patches 'false shadows' in the areas tangent to the light. The two recommended solutions don't work in my case. Polar noise just makes the fur messy, and I am already using ambient colors in the fur.

The more I look online the more I suspect that the people that have the solutions don't feel like sharing. I hope some proves me wrong.

[deusdk]

Mental Ray generating black pixels on fur passes.

Have you tried changing the Fur shader in mental ray settings(Fur render settings) from 'hair primitives' to 'volume' and then rendering...let me know if it works...

[noizfactory]

QUOTE(Sean_Montgo @ 05/04/07, 11:46 PM) [snapback]265470[/snapback]
I find it amusing that there have been almost 200 hits on this posting, but no replies.

Well, it seems that the simplest answer to this question is 'forget about Maya Fur, especially with Mental Ray....use Shave and a Haircut". Rendering fur with raytraced shadows looks better, but results in predictably unacceptable render times.

The answer to the 'flat areas' of colour problem was that there was insufficient contrast between the fur root and fur tip colours. We had attempted to use the same colour maps that had been on the characters in XSI, but this made the fur go red. So then we used just the tip colour map, but it was too close to the colour of the roots. Blowing the maps away entirely solved the problem.

Another issue we have found is Mental Ray generating black pixels on fur passes. The only solution that works here is to use directional lights instead of spot lights. Switching to 'Rapid Fur' seemed to work, but it makes the alpha channel dissapear.

Anyone else care to share Maya Fur war stories?

Hi Sean,

I had a hard time rendering fur with Mental Ray too. The lighting never matches the fur renders you get from Maya Scanline (which, on its own, is just about ok). However, having scourged through countless forums, it has dawned upon me that the Rasterizer mode of rendering in mental ray is a preferred option for rendering scenes with large volumes of fur and hair, etc, etc. Read up on the rasterizer here: http://www.lamrug.org/resources/rastips.html

And these two threads, though quite old, might help too:
http://forum.lamrug.org/viewtopic.php?t=33...ight=rasterizer
http://forum.lamrug.org/viewtopic.php?t=21...ight=rasterizer

I might add that so far, PRMan (and any Renderman based renderer) renders fur and hair stuff the best and fastest. I have used SiTex Air and rendered tonnes of Maya Fur and Shave And A Haircut stuff with it. It hardly crashed and renders looked really good too. Until, of course, I got my hands on RenderMan for Maya 2.0 eval and I realised that the real thing renders even better. Just try the evaluation version and you'll see. The default setting itself, without any deep shadows, look so beautiful! But I digress.

Cheers,
Sachin

[noizfactory]

QUOTE
I have been trying to use Maya Software to render fur for the past week. Every time I come across a solution, another problem presents itself. Adjusting the base width too much relative to the tip width, and global scale causes the fur to freak out and become little blocks of color.

Hey Falseye,

Are you rendering fur too close to the camera? And by what factor are you globally scaling the fur? Too high a value makes the fur blocky, especially evident when the furred object is closer to the camera. Try a different technique of getting the fur volume you want, by balancing the global scale, the fur's length and root/tip widths. If you could expand more on the exact problems you are facing with a description of your scene setup and the current renders as well, I might try to help you out.

QUOTE
Using a spotlight, the recommended way to light fur, results in dark patches 'false shadows' in the areas tangent to the light. The two recommended solutions don't work in my case. Polar noise just makes the fur messy, and I am already using ambient colors in the fur.

When you say "the recommended" way, I guess you mean the spotlights with tight cone angles, high quality shadow maps and a manually set dmap focus size, right? A screen grab of your render could really clear up things here. In general, fur reacts differently to lights than your regular geometry. Results often seem better when the lights are at an angle greater than they normally would be in a non-fur scene. So, its best to have separate light set-ups for just your characters or objects and a separate set-up for their respective fur. Rendering them out in separate layers always helps. Usually, the fur lights' position wouldn't be too drastic as compared to the characters' lights. So an obvious method would be to light your character first and after you are happy with that setup, duplicate it and go about tweaking it for the fur layer.

QUOTE
The more I look online the more I suspect that the people that have the solutions don't feel like sharing. I hope some proves me wrong.

Its more about looking in the right places with the right keywords, dude. I have had so many issues and problems but I have actually never posted any query on any forum. I just searched on various forums for similar problems other people might have faced and always ended up finding a solution. And eventually, if you do have to post our problems, always make sure you give a comprehensive run through of the situation, like, screen grabs of your scene setups/renders, software you are using etc. etc..

And like they say, Google is your friend

Cheers!
Sachin