A whiter shade of fur - VrayHairMtl can't get white enough

[windowlicker]

I'm trying to create two things - a polar bear like fur and a white wool carpet.

The bear fur is a rather matte kind of fur, which hardly ever shows any distinct highlights, unlike human hair. The bear's fur is made up of rather fine and straight hairs.
The wool carpet is made of yarn which is thick (around 2-5mm) and has extremely diffused highlights. Since the yarn is cut, the carpet has a very fuzzy finish, which catches the light and distributes it evenly.
I included a style sheet so you know what I'm aiming for.

I thought translating this into the world of vray - with the use of VrayFur and VrayHairMtl - would be simple enough, but I can't seem to get it right. The problem appears to be that light will not travel deep enough into the fur, and instead I get a dull gray finish. What I find rather weird is that the shorter the fur gets, the more dull it gets. Fine hairs do a somewhat better job, but takes longer to render and doesn't give the right look for the carpets. In the renders I included, I used 1mm fur thickness at the most and around 0,15mm as a minimum. All the objects in the scene have the same material, and even though some of them look ok from one direction of viewing they look absolutely horrible from another; the "carpet" on the wall and floor being the most obvious one.

The scene setup is fairly simple. A light gray (220 RGB) box which is open to three sides, a vray sun/sky where the sun is at 0.75 intensity. BF/LC and no AO. Scene gamma 2.2, linear multiply color mapping, no clamping

The material uses 255 white in all slots. I've tried all kinds of combinations of glossiness and transmission, and these are the settings that gave me the "best" result... which still is far from the desired whiteness.

Does anyone here have any experience with this kind of problem, or some other solution they know of? I have tried disabling shadows (which gave the fur an extremely burnt out look) and boosting the GI for the fur objects (resulting in bright light blotches).
Maybe there's something I've overlooked completely? Some simple solution? Some other shader I should use perhaps (even though I like HairMtl, since it renders fast, and gives a nice "hairy" look)? Right now, I'm thinking some kind of "ambient light" parameter in the material would work great, but unfortunately there is none. I guess the whole problem is based on the way light is diffused in white hair, and that vray has to use a simpler model for the diffusion of the light.

Any ideas?

[vlado]

What are your GI settings?

Best regards,
Vlado

[windowlicker]

I'm including a picture of the render settings for the renders in the previous post.
The spot3d-page ( http://www.spot3d.com/vray/help/200R...mtl_params.htm ) suggests BF as primary, and LC as secondary. However, I got better "whiteness" switching them around, using LC as primary and actually lowering the secondary bounce to 0.5... even though those settings are not physically correct.
Using BF as primary and LC as secondary and using a multiplyer of 1 on both of them, makes the fur even darker. I've tried changing a whole lot of parameters, but without any major impact on the way the fur renders. I'll include the file aswell if anyone feels like really looking into this.

I thought it could be a unit issues, since my scene is 1unit=10mm. A quick test using 1=1 made no difference either.

http://www.mediafire.com/?r43sbjol9i12v7a

[windowlicker]

Soo... Did anyone succeed in making better white fur?
I got some time today to look more into it, and I built a new scene from scratch, this time with IR/LC for the GI, since that is what I use the most. (I want the fur to be able to transfer into various scenes, and not be bound by any particular GI setup.)

Results however are more or less the same with the hair material, as they were in the other GI setup.

I tried using FastSSS2 which gave a better result, but took a lot longer to render. I'll see if I can make some more attempts next week, but I'm not sure what to try next.

Adding the renders I made today.
FastSSS2: HairMtl: :/

[Neilg]

Would it help to consider that polar bears fur is transparent, hollow tubes?
It's not going to do your render times any good though...

[windowlicker]

Well, yes. Of course.. in a way. The polar bear's fur is made to channel light into its dark skin, so it absorbs the little heat it gets... but there are other furs which are equally white, with just normal hairs.

I think you would have to consider (dense) furs in general more like objects with sub surface scattering, though the scattering takes place in between the hairs. I guess there's also SSS going on inside the actual hair. The whiter the hair gets, the more pronounced the scattering effect. I would expect the hair shader took that into consideration, but I simply can't get it to work.
Seems kind of logical now that the FastSSS2 would be a better material to use here. Looking at the renders, it is pretty close to what I want to achieve. With a bit of tweaking I'm sure I can reach some decent render times, too.

I'll look at it a bit more soon, but I'd be very happy if someone would give it a shot and succeed! (And tell me how! hehe)

[Dubbie99]

The problem is is that with that sort of thick white transparent hair, a major component of the look is internal scattering which isn't modeled by Vray. As far as I know, the only renderer that does this is Mitsuba. It's not a production render, just a research renderer, so you're kinda out of luck if you're hoping for some sort of plug and play solution. You're going to have to fake it somehow.

[wxyz]

How about a VRay light material to fake the internal scattering?

[stevesideas]

I was about to suggest the same thing. Probably a composite material with the base colour and then a vray light mat blended in to the desired amount. I've used it before to adjust the shadows darkness and it works quite well.

Is your scene using 2.2 gamma because that would lighten the shadows also.

edit: sorry, i mean vrayblend material, not composite material....not in front of 3dsmax at the moment.

[Neilg]

Light mtl is the way to go.
Very difficult to get rid of the blotches, but if I was willing to turn my settings up more I reckon they'd slip away.

It's a vray material, diff 251, ref 230, fresnel ref. on at an IOR of 4. highlight glossy .65, ref glossy .85, max depth 1.
This is inside a 2 sided material, which is inside a blend material along with a vray light mat (blend at 40) which is white with a strength of 1.

higher res crop:

[windowlicker]

That looks great, cubiclegangster! Only problem with having a vraylightmaterial is that it will never go completely dark. It will always have sort of a glow to it, even if it is in a completely dark scene. However, it is a good solution for brightly lit scenes!
A 2-sided material inside a blend material.... how did it render? Feels like it would take a rather long time, no? I'd love to take a look at that scene though.

I spent a full 5 minutes modelling a polar bear, applied a simple vray fur to it and did two renders: One with the vrayhairmtl and one with a fastSSS2 material. The fastSSS2 one only took 15% longer to render, which is completely ok with me. It won't be very noticable unless the fur is a major scene element. Getting rid of the speculars is another way of making it render faster.
It feels like the fastSSS is doing a fairly good job at dispersing light within the fur. Right now, I'm definitely leaning towards using it in my scene. It will be interesting taking the fur from this testing environment into a proper scene with a more difficult lighting situation. I'll post more renders when I get around to that.

Really appreciate the help!

HairMtl:

FastSSS2:

[Neilg]

A 2-sided material inside a blend material.... how did it render? Feels like it would take a rather long time, no? I'd love to take a look at that scene though.

Very slowly... Mostly the fault of the IR/LC though. Maybe the 2 sided was causing the problems - this is an old scene I was trying to get a white fur in ages ago, so I took what I had before and put it in a blend to instantly fix my results. Before it was much darker & blotchier...
I also didnt use fur - It's multiscatter and geometry strands.

Check the scene here:
If you dont have multiscatter, the material is on the base geo at least. The hdri is missing, so it'll look different too. Throw one in the dome light and it'll be ok.
studio-fur.zip

[möbius]

Well, white thin fur is really hard stuff for a raytracer. Could you tell me if you plan to make an animation or do you need the fur for stills, depending on that there are several thing you could try out.

Here is a test i made with VrayHairMtl an Bruteforce+LightCache, i don't know if this the look you try to achive.


Another one with more and thinner Hair


And a really fluffy one


But actually i've only created a VrayAmbient Light (additionally to my scene lighting) and included only the Hair Object to it and switched it to only affect the GI rays. I gues this is kinda similar to using a self illumination material but at least you can use the VrayHairMtl for shading.

[windowlicker]

Ah, that's pretty clever! I'll give it a try sometime (or look at your scene, should you ever post a link to it ). I guess that one will render pretty fast though, since it has a very simple setup.

I will use the material mainly for stills, but on occasion it will be animated. My firm works with architectural visualization, so you get a bit of both. In the ideal situation, I would like to create a material for fur that works in any scene under any lighting conditions. We have built our own library of furniture and accessories, so being able to merge a ready-made object into any scene is the goal.