I ran more test on one of the characters. Maya keeps crashing even with the hair count as low as 1000 hairs.

Any ideas?

The first thing to make sure of, to avoid aliasing, is that the width of a hair should not be much less than a pixel.
This means the number of hairs on a character is a function of the size of this character on screen and varies with distance from the camera (assuming a perspective projection is used).

This is called level of detail (LOD). Any furry character you saw in any blockbuster in recent years uses this.  Otherwise you would need an insane number of pixel samples, on characters with dense fur.

I don't know Shave very well. If it doesn't support LOD, you can do per shot LOD yourself., manually.
An easy rule of thumb is to half the number of hairs and double the width. Quarter the number and quadruple the width, etc. In math lingo: multiply the width by the factor you divide the number of hairs by. Note that this factor doesn't need to be an integer!

In a fur system with continous LOD, hairs are faded out as the width of the remaining hairs is increased proportionally.

As far as shading rate & pixel samples go: shading rate is the shading quality. It does not help with antialiasing of geometric primitives. For fur that doesn't have much median detail, a good shading rate to start with is 20 (yes, twenty), Set this shading rate only on the fur, of course. Keep the global shading rate at around 1 for everything else (for a beauty render).
One thing beginners often miss is that shading rate is a local quality knob (per object/gprim). Pixe samples is a global one (per image, unfortunately).

Start with 10 pixel samples. 20-30 pixel samples are not rare with dense fur. Pixel samples are cheap, low shading rates are not!

But before tweaking those settings, definitely make sure your fur strands are not much smaller than a pixel in width.

Lasty, if you have a lot of lateral detail on the hair strands (along the width), 3Delight has an undocumented feature where you can force a lateral dicing on curves that is independent of shading rate.
This is an attribute called "dice:hair". Set this to the numbers >1 to force the resp. number of shading samples on the affected curves in the lateral direction.
This will only make sense when you use a complex shading model like Marschner et al. For Kaija & Kay (the shader baobao posted) or something equally simple, "dice:hair" should be 1.
In any case, the shading time spent on the fur is proportional to "dice:hair", when this is >0. Watch your render times for values >1 thus.

Hope some of this helps.

--Moritz

Last edited by Mauritius (2009-10-02 05:39:00)

Hi,
another thing to consider are deep shadow samples. I run all the fur jobs with a minimum of 9 samples to avoid flickering in shadows.

Andreas

Thank you so much for all your detailed answers. I'm working on styles at the moment.

Olivier, what do you mean by fine shading rate? And how do you set semi-transparency on fur? I am kind of running into the issue of having fine fur on the head of animals around the cut map, otherwise the wider width of the root it's too noticeable.

Mauritius - THANK YOU! IT'S GREAT!

Asyl - great advice!

baopao - thank you for shader. I will try to use it today!

It's the best forum I've ever visited.

nataimages wrote:

I ran more test on one of the characters. Maya keeps crashing even with the hair count as low as 1000 hairs.

Any ideas?

It can be many things :) There are some problems with the Shave API provided by the Shave and a Haircut package that we use. Using high number of segments can do that. Some cases of cut maps can also cause troubles.

Maybe you are already aware of this, but just in case: the following options have a direct effect on the amount of data required to represent the shave hair shape and thus should be kept as low as possible to minimize memory usage and render time:
- hair count
- hair segments (which is often set too pointlessly high)
- multi-strand count

….anyway, you can also attach to shave geometry the standard
maya Anisotropic shader and connect color input with
a RendermanCode node with this code:

in Shading Parameters:

output color o_color
output normal skin_N
shader_input uniform color rootcolor
shader_input uniform color tipcolor
shader_input uniform normal skin_normal
shader_output varying color aov_hair_msk

in Shading Code:

extern float v;
o_color = mix(rootcolor, tipcolor, v);
aov_hair_msk=1;
skin_N = skin_normal;

this one pass the color values of shave to the color of Anisotropic,
and you can use all other parameters in a "standard" mode (….aov too), ….for opacity you can use a ramp if you like, example for have a transparency in the tip and in the root also.

Anisotropic use  curves normal, if you want "skin_normal" (good for short fur) just connect skin_N to normalCamera of Anisotropic shader(…or phong, blinn etc.).

Add a secondary display and in the "user specified" write :   color aov_hair_msk   
you will have a mask of the hair, in the Advanced check "on" the Compute Alpha for this pass for have a opacity alpha.

RendermanCode is very powerful node of 3dfm and very simple to use for create custom shader, output aov_pass ect, try this and let me know if works.

a.

Last edited by baopao (2009-10-02 01:54:41)

hi
im trying this with maya hair (PFX)
i got a flat color render
which i suspect i can't directly assign anisotrphic shader to PFX.

any way to do this method on maya hair?

thanks a lot