Hair Shader is causing weird lighting variation

[Eddoron]

It actually is.
I think you'll find the solution in the illumination channel of the c4d hair material. reflection, translucency etc. are still turned on and affecting the look heavily.

It should also be mentioned that the c4d hair shader gives overbright results and the color has to be tweaked & toned down if you want it to look "properly" in Corona.(even with spec/backlight turned off)

[danielsian]

It actually is.
I think you'll find the solution in the illumination channel of the c4d hair material. reflection, translucency etc. are still turned on and affecting the look heavily.

It should also be mentioned that the c4d hair shader gives overbright results and the color has to be tweaked & toned down if you want it to look "properly" in Corona.(even with spec/backlight turned off)

You are misunderstanding the problem. Nothing that I change in Illumination tab fixes the BUG.
I'll try to explain again.

Key Light = top light, white color
Back Light = Left side, pink color

If I use only Key, nice result, top illumination, dark shadow.
If I use only Back Light, nice result, extreme left illumination drawing the silhouette on the left edge only.

If I use Both lights at the same time the Back Light cross the model and illuminates everything, like if the Key Light was pink.

Is this the expected result?
Of course not!

[TomG]

What is the result from other render engines? Wondering if this bug is with Corona, or with the C4D hair material (or hair system itself), so would be great to see comparisons. Thanks!

[Eddoron]

If the pink light still penetrates the mesh and colorizing the hair with a normal material, without the hair shader plugged in, then it's likely to assume that the hair shader is the problem.
As I mentioned, the shader wasn't constructed for this purpose, it was for c4d's renderer and using polygonal hair.
There are a lot of things that don't work well.
As for the illumination tab, things like translucency, reflection, even shading affects the colors. It might be that the light hits the roots of the hair somehow and those transmit the color all over the hair, together with the bounces, it might be even worse.

To be clear: I meant that you might find the solution in the hair materials illum. tab, not the shaders. (pic1)
You can decrease the colorization, not completely but to a certain level. A Rayswitch material could also help. It won't be perfect with the hair shader and I'd make use of some multipass channels to get rid of those.

2.pic: RS render with the c4d hair material connected to the RS hair.
If you want more RS examples, you'll have to wait until next week when I visit my gpu-buddy again.

[danielsian]

What is the result from other render engines? Wondering if this bug is with Corona, or with the C4D hair material (or hair system itself), so would be great to see comparisons. Thanks!

Using Physical Render we have a expected result. No surprises.

If you wanna check the file, see attached a Corona version and a Physical version.

So, I presume Corona is not being able to deal with Polygon Hair shader.

Thanks

[danielsian]

... the shader wasn't constructed for this purpose, it was for c4d's renderer and using polygonal hair.
There are a lot of things that don't work well.

Yes, I agree, all the shaders in Cinema 4D were constructed to work only in Cinema 4D.
And because of this, Corona is trying to adapt it´s code and fix every error and bug in order to have everything working fine, including Polygon Hair shader.

... As for the illumination tab, things like translucency, reflection, even shading affects the colors. It might be that the light hits the roots of the hair somehow and those transmit the color all over the hair, together with the bounces, it might be even worse.

As I said earlier, nothing in Illumination tab is going to fix the problem. It changes a little, but the problem is not fixed.

Thanks

[Eddoron]

Not solving the problem entirely, but it could make post easier.
BTw, What about just rendering the rim, key separately, maybe use light passes for that and then combining the image? That could go quickly.

[danielsian]

Not solving the problem entirely, but it could make post easier.
BTw, What about just rendering the rim, key separately, maybe use light passes for that and then combining the image? That could go quickly.

The dog is done already, everything alright thanks to post production.
To reduce the colorization I had to use only white lights. Then I fixed the remaining problem in Photoshop, and add the warmness  as I was looking for before to desaturate my lights.

But I have more animals to do so I need to have everything working well from my raw render.

[houska]

So I looked into the issue briefly and I cannot find out what the cause is. Indeed, the colorization should not be there, because your rim light is behind the object and thus should not appear on the "hair".

As I said earlier, we will be looking into C4D hair later. To fix your issue would mean understanding how C4D hair is done internally and that's non-trivial. When we do a more thorough investigation, we might as well implement the Corona hair already.

I'm sorry to be the bearer of bad news, but you'll have to wait for hair to appear in a Beta 2 daily build.

[danielsian]

Thanks houska

I'm looking forward to see the Corona's hair.