H16 Hair shader issue - fur is always gray

[Infinite Rave]

Hi Everyone,

I started to play with the new fur tool and it blows my mind. But I need a little help here with the fur shelf tool. I created a nice groom and everything works perfectly except the hairshader tints the whole fur with a gray color. I can not produce white fur at all, as it turns middle gray. I did a test file too where only a cube were in the scene and the same happened with fur color.

Any idea where I gone wrong?
 

Appreciate any help,

Francesco

 

 

 

 

Edited May 2, 2017 by Infinite Rave

[McNistor]

Hi,

Why does the Houdini's hair system blow your mind? I'm not implying that you're not justified to think so, I'm genuinely curious. I too like Houdini's hair tools, my past experience with a hair system being Softimage which I think is based on, by now infamous, Joe Alter's Shave&Haircut. What I like Houdini's hair tools is the versatility. What don't like is the performance - half the time (if not more) I'm waiting for chef Houdini to cook.

Regarding your issue - white hair is notoriously hard to simulate in 3d. I'm not an expert in Mantra shading/rendering, but as a general rule, you want to lower hair's transparency as well as influence its reflection (by not allowing it to reflect much of the env. map, but a white color) and use a more colorless HDR map.

Try these until you'll get a more edifying answer.

[Guest tar]

3 hours ago, McNistor said:

What I like Houdini's hair tools is the versatility. What don't like is the performance - half the time (if not more) I'm waiting for chef Houdini to cook.

Much better performance if you just work with guides. i.e. hide other objects in the viewport

[McNistor]

@martyThat works for viewport grooming, but there are cases in which I'm better off, for keeping a tighter control over guides, to apply process nodes to the hairgen instead of the groom node, like for example a Frizz. And then things get truly hairy...

Lowering the number of genhairs is a solution for improving performance, but you wouldn't want to work with a vastly different number from the final version, as you'd have the unpleasant surprise to end up with something else you had in mind.

@Infinite RaveNormally I'd suggest using a black/white version of the same hdr map just on the hair shader, but I don't know how you'd do that in Houdini. Google it up, maybe you'll find something. I'd do that now, but I'm turning in. So tomorrow...

[Guest tar]

yeah true - I'm thinking that later versions will be like the new muscle tools - chains of compiled openCL nodes to speed things up!

[Infinite Rave]

@McNistor Thanks for the advice, changing the HDRI to a B/W version solved the problem.

Houdini hair is so easy to understand and works as expected, experienced neither crashes nor rendering artifacts, no surprises whatsoever. Rendertimes are also reasonably short even with fairly large number of hairs. Thanks to these features it provides a very short learning curve. I could achieve literally anything came in my mind from simple bunnies to complex photoreal tigers or facial hairs. Very happy with it so far.

Luckily I did not face any speed issues on my HP Z820. But I'm not using the built in paint tools for the features, instead I'm painting them in PS. For me it's more straightforward and lighter on the pipeline.

 

@marty The only thing I don't like in Houdini fur is the guides visualization. The guides do not seem to represent correctly the fur generated by the _hairgen node so I can rely on them only as a rough estimation if at all.

 

Francesco

[McNistor]

@marty@Infinite Rave

Here's an attempt at creating convincing white hair. Funny trivia: polar bears are "actually" black - they have black skin and their fur strands are transparent. Multiple passes of light diffuse and refraction when it passes through each strand, makes the polar bear's fur look white.

Inspired by this fact, that white hair IRL is actually transparent hair without pigment, I went and set the transparency (opacity tab of the hairshader) to a very low value. Also enabled "transparent shadows". Keep in mind that these will increase render times. A lot.

The scene is lit with one direct light and an env. one. As soon as you add an hdr map, it will tint the color of the white hair. Ideally one would keep the original env. map for the entire scene and use a desaturated version of it (B&W is unrealistic) just for the hair. THis could be achieved in Houdini with light exclusions, but ideally one should be able to plug an env. map just for the hair material instead of using multiple lights. If this were Mentalray I'd tell you how to do that, alas it's Mantra and I don't know how or if it's at all possible. If Houdini wouldn't keep me way with its poor viewport and traditional modeling tools I'd probably be a lot more competent with Mantra too.

In the image to the right is the default hair shader with colors set to white only and to the left with all the other adjustments. The lighting and all other settings are identical. Make sure you don't miss the attached .rar file - I've included the .hdr map so you'll get exact same results and if after your own experimentation you get better looking results and render times, don't forget to post them here.

white_hairball.rar

[Infinite Rave]

@McNistor Very impressive, thanks a lot.

[McNistor]

@Infinite Rave No problem. Feel free to improve upon it and share it with us.