Re: Shading hair

["peter boeykens" <peter_b(at)skynet.be>]

 

WOW! So many answers! ;) It shows how much people get something out of hair! Geez! ;)

hm I'll pick up the gauntlet then?

 

this said, I have no experience with long hair, only fur and the like.

but still, some of it could be usefull.

FYI, I?ve played some more with MuHair. Getting better results as I tweak and tweak and change my lighting.

Compositing here and there does help a lot. Not perfect but what can I do?

a problem you run into with hair, is that it reacts differently than a surface does.

as a result, your carefully tweaked lighting setup for the surfaces will often produce undesired results for hair.

 

I think that has two reasons:

 

1) its a different shading model

if you use the geo_shader you can much more closely mimic the result of the underlying surface, as its using a very comparable shading model, so it will respond more predictable.

You used to be able to render the hair as geometry and assign any shader to it, and I cant help but think it was more easy to create a consistent result between hair and underlying geometry.

At a big performance cost, if I remember correctly.

 

2) the form (orientation, normals) is quite different than the surface underneath.

this is due to nature of the hair primitives: they're flat ribbons, oriented to the camera (like sprites), so the normals will hardly ever be oriented along the underlying surface normals.

so even with the same shading model, it will pick up light differently.

 

all this makes it quite hard to match fur to geometry.

 

allthough some things can help:

shadows from the hair on the geometry

transparency of the hair

tweaking the hair's gradients to adapt the roots

rendering a matte for the hair to tweak it seperately, and also rendering a hair gradient pass (eg flat blue for the roots and flat red for the tips) so you can tweak roots and tips independently

 

For lighting, the use of spotlights, shadowmaps and volumic shadowmaps can also help a lot in making the hair look better.

often I'd use shadowmaps for the selfshadowing of the hair, and raytraced shadows for dropshadow of the hair onto geometry.

 

To make things more involved, there's parameters all over the place to affect the look, some in the shader, some in the hair ppg, but also in the rendersettings.

Some to have a look at: hair quality and subdivisions, long hair and short hair shading model, flat shade parameters, normal blending,

The thickness also greatly affects the overall look.

And for rendersettings: rapid motion used to cope MUCH better with hair around v4, not just in terms of speed but also quality. you would get much less flickering, better drawn small lines, a smoother overall look. Gaussian filter also helps a lot for hair renders.

 

Texturing the hair can also help you further.

There's this tutorial out there, that uses the hair barycentric coordinates, in order to map an image to the hair.

But you can also use it with gradients or procedurals.

This way you can have more control, such as color variations along the hair's length or crosssection.

But also create transparency maps, to create irregularity.

 

So there you go. rendering hair is somewhere inbetween voodoo, art and chaostheory.

each time you think you got it nailed and learned a thing or two, but the very next time you have retry everything again.

 

There was this sequence on Barnyard, with the coyotes at night, and the setup had to be (lovingly) tweaked for every single shot to get it looking good and consistent over the sequence. and there was easily as much going on with the fur in the composite than in the 3D render...

 

Peter

 

 

 

Scratching me beard and doin? the hummmmmm?

 

MAC

 

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From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Marc-Andre Carbonneau
Sent: February 27, 2007 11:48 AM
To: XSI(at)Softimage.COM
Subject: RE: Shading hair

 

Hey Daniel,

 

Perhaps your shader is already good enough but I lack the ability to make it look the way I need?

 

I am trying to make ?dry? hair. Attached is an example.

 

What happens is that I get specular that is too harsh and all over the hair. If you look at the image, you notice how it?s really uneven.

 

I notice that the Muhair shader requires a light setup that is different than the one I use for my face?otherwise the colors are blown?

The volumic shadow maps don?t seem to work either. Is this a bug?(might be because Muhair was developed a while ago?)

 

I just did some test with a little comping and I?m getting closer but that?s with the Hair_geo_shader which takes long to render.

That?s why I?d prefer to use Muhair.

 

Thanks

MAC

 

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From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Daniel Rind
Sent: February 27, 2007 10:14 AM
To: XSI(at)Softimage.COM
Subject: Re: Shading hair

 

Well, post your wishes.

 

Ciao, Daniel!

 

2007/2/27, Alan Jones <skyphyr(at)gmail.com>:

I've messed around with a sprite shader with a mixer gradient using
the bary co-ordinates to drive the matte and using OrenNayaWolff for
the illumination and got some reasonable results - though it was a
long time ago. (Sorry for pimping my own warez)

Cheers,

Alan.

On 2/27/07, Kris Rivel < krisrivel(at)gmail.com> wrote:
>
>  Let this be a reminder how badly we need some better hair shaders and
> better hair control overall.
>
>
>
> Kris Rivel
>  3D Artist
>  kris(at)krisrivel.com
>  www.krisrivel.com
>
>
>  Marc-Andre Carbonneau wrote:
>
>
>
> Hi.
>
>
>
> I have a full head of hair to shade. It needs to be realistic. I'm using
> Muhair and I can't get something that looks convincing.
>
> I've been told it's way better and faster than XSI's hair shader and the
> hair_geo_shader.
>
>
>
> My character has short blondish hair that looks dry.
>
>
>
> Anybody got something real looking and could provide me with indications,
> light setup, shader tricks?
>
>
>
> We made hair before but it didn't have to look realistic so to speak?
>
>
>
> Thanks.
>
>
>
> MAC
>
>

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