Hair Shader is causing weird lighting variation

[danielsian]

Hi guys

EDIT: please see the project file attached

I'm working in a character with hair/fur and I'm experiencing a weird problem with Polygon Hair shader.
It's hard to explain so I'm attaching some images to show the problem.

I did 2 sets of render tests, the first using a standard Corona material with off-white color only. Everything works as expected.
Then I just applied another material with Polygon Hair shader in my Hair object. The result you can see, looks like there is a reflector bouncing the light on my model, and resulting in a wrong lighting and funny colorization.

I suppose this is a bug not hard to address a solution.
I'd be glad if it's possible to fix this so I can proceed with my project without issues.

Thanks

[Eddoron]

Did you disable the specularity in the c4d hair material? (if you're using that as source)
It doesn't create correct highlights(no traced reflections) if the native or flat hair is not used.
The highlights are also way to bright.
Those things could affect the overall look and the problems you've described.

[danielsian]

I made a lot of tests before to post here, so I'm sure this is something I can't control.

I tried also turn off all the channels, leaving only Diffuse, but the same problem happens.

If you are happy to test by yourself, the project file is attached. Maybe you have a new idea and can find a different solution.

Thanks for your help!

[Eddoron]

So from what I can see, the undesired color comes from the spherical light with the light yellowish tone. It disappears when you decrease the saturation.
I also did a test with another renderer, placed lights at the same place, same colors etc. and the result was pretty much the same.
So it doesn't stem from the material but the color of the light.(40°,14%,100%)

[danielsian]

yes, I agree the problem is related with light. To be precise, colored light.
I've tried already to change all the lights, but the result is the same, so there is no relation with the shape, but only color.

I have another light just illuminating a different object in my scene, far away from my dog and with Include option on, just to illuminate that specific object. But even in that case that light is affecting the hair and makes the colorization more visible.

I'm proceeding with my project without colors in my illumination just to avoid problems. I'll try to put some warm temperature in post because it's the only way to attenuate the problem. Once the hair receive any ray other than white, we start to see a weird result.
So, I'm using white lights (the same settings as the sample I shared earlier) but I still can see a wrong colorization in the shadows (attached image). Probably it's related to non-white rays from bounces.

I'll try to make another test and making the problem more evident.

Thanks

[Eddoron]

Yes, I think Post would be the best to get rid of those areas.
However, I noticed that the yellow color affects the fur overall, it's just more prominent in the shadowed areas.
For me, it looks like as if someone added an ambient light. (Same result in AR too)
You could try a darker light with the same degree&saturation or switch to a more directionalized area light.
Another thing would be to add some grayish-white color to the translucency which could absorb some of the yellow.
Also, before going to post, maybe you'll find the answer in one of the multipass channels.

[danielsian]

I have rendered already, and I can see the yellowish color only on Indirect pass.
I'm surprised you can see the problem in AR as well.

[Eddoron]

I used the preset color first, then a neutral fill and at last a bluish tone.

[danielsian]

Just to make the problem more evident I'm using a pinky rim light.

This rim light is supposed to illuminate only the left edge, but as we can see, is coloring overall in a wrong way.

Please, anyone from development team, help me to fix this problem?

Thanks

[houska]

I don't know man...

First of all - we are going to add support for hair in Beta 2, so nothing can be guaranteed right now.

That said, I tried your scene and I must say I was a little bit confused by the stack of materials on the Hair object. What are you trying to achieve?

[danielsian]

I'm trying to use a color map to paint the hair based on UV, like the first example.

As you know if we apply a color map on Diffuse channel, this texture will be repeated for every single hair and this is not what I need.

I hope I was clear in my explanation.
Thanks

[danielsian]

... I was a little bit confused by the stack of materials on the Hair object. What are you trying to achieve?

Forget the stacking. I left both tags there just to help tests.

[danielsian]

... First of all - we are going to add support for hair in Beta 2, so nothing can be guaranteed right now.

I'm following the Road Map and I'm looking forward to have a Corona's Hair shader.
But I presume it is interesting to have an alternative until Beta 2 arrive. And this is the way to go once we dont have a Corona hair shader.

This technique, using Cinema 4D's Hair Shader inside a Corona Material, is awesome because makes possible to have some access to parameters normally unreachable in Hair material, like Color.

Currently there is no option to colorize the hair based on UV unless we use Hair Shader.
Don't forget this technique looks like is the unique way to render Hair properly with Corona if you need color in it, and it's working already with limitations.

Should be simple to fix this, isn't?

[Eddoron]

I don't see what there is to fix.

[danielsian]

I don't see what there is to fix.

Did you see the pink version I posted above?
Is that normal for you?