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Let me preface this by disclaiming it is the first time I try using this shader, although I've had plenty of experience with SSS materials. I've been using Vray since 2012, and before this MR and Renderman. Also have extensive production experience with Redshift. I'm familiar with the shading model for Alsurface, as it is modeled after an old SIGGRAPH paper for skin shading. I'm trying to control the SSS component with the shader applied on a simple sphere, lit with one rec light. Basic test setup.
It appears that I cannot dissociate the diffuse component from the SSS components. If you start by setting a simple color into the diffuse value, and set the diffuse strength to 1, and set the SSS strength to 1 for the SSS components, you will see the diffuse color component mixed in to the SSS AOV. It should be completely separate. To see this, set your "SSS mix" attribute to 1. According to the docs, this attribute is "Mix between the Diffuse component and the SSS component.". This is very vague. Does it mean it mixes in the Diffuse component to contribute to the SSS? Or does it mean it is an exclusive value to toggle between diffuse OR SSS in the final shading math? If I set SSS mix to 0, I get no values in the SSS AOV, as predicted. Now, try to set SSS mix to1, and Diffuse strength to 0, to remove contribution from the diffuse component of the shader. If you do this, you'll find that the SSS AOV gets no values at all, regardless of what value is set under SSS mix. It seems that SSS output is inextricably tied to Diffuse Strength. It also seems that diffuse color is passed into the SSS AOV.
None of this makes sense from a logic perspective, nor is it useable for look development. The shading math should be implemented as Diffuse+SSS1+SSS2+SSS3, with each component having dials for strength independent of one another. Also, the SSS AOV should not be getting contributions from the diffuse channel. How do you build a beauty back from AOVS?. I understand the SSS Mix is there to act as a fader control between diffuse contribution and SSS, but it confuses the whole shader math a bit, although it's useable if properly implemented. Right now, I'm seeing my diffuse color in my SSS AOV, and it's not at all what I would expect. Also, I cannot have any SSS values unless that diffuse strength is set to 1. This seems patently wrong to me.
Perhaps I need some clarification, or maybe there is a bug with this particular version of Vray/Maya... Your feedback is appreciated.
It appears that I cannot dissociate the diffuse component from the SSS components. If you start by setting a simple color into the diffuse value, and set the diffuse strength to 1, and set the SSS strength to 1 for the SSS components, you will see the diffuse color component mixed in to the SSS AOV. It should be completely separate. To see this, set your "SSS mix" attribute to 1. According to the docs, this attribute is "Mix between the Diffuse component and the SSS component.". This is very vague. Does it mean it mixes in the Diffuse component to contribute to the SSS? Or does it mean it is an exclusive value to toggle between diffuse OR SSS in the final shading math? If I set SSS mix to 0, I get no values in the SSS AOV, as predicted. Now, try to set SSS mix to1, and Diffuse strength to 0, to remove contribution from the diffuse component of the shader. If you do this, you'll find that the SSS AOV gets no values at all, regardless of what value is set under SSS mix. It seems that SSS output is inextricably tied to Diffuse Strength. It also seems that diffuse color is passed into the SSS AOV.
None of this makes sense from a logic perspective, nor is it useable for look development. The shading math should be implemented as Diffuse+SSS1+SSS2+SSS3, with each component having dials for strength independent of one another. Also, the SSS AOV should not be getting contributions from the diffuse channel. How do you build a beauty back from AOVS?. I understand the SSS Mix is there to act as a fader control between diffuse contribution and SSS, but it confuses the whole shader math a bit, although it's useable if properly implemented. Right now, I'm seeing my diffuse color in my SSS AOV, and it's not at all what I would expect. Also, I cannot have any SSS values unless that diffuse strength is set to 1. This seems patently wrong to me.
Perhaps I need some clarification, or maybe there is a bug with this particular version of Vray/Maya... Your feedback is appreciated.
