Geometry with Opacity 0 casting shadow on SSS - Resolved Tweet

[rajib]

Hello Otoy team,

I would like to highlight a issue that I have noticed with multiple versions of Octane include the current 2019.1.5 and the 2020.1 XB1 / 2020.1 XB2.

The scene is a very simple scene with one cube that has SSS applied (Diffuse with Absorption node + Specular with Scatter node) and a plane (Diffuse) above it whose opacity is set to 0. If In the cube Diffuse I set transmission to 1, the invisible plane seems to cast an shadow even though in the shadow render pass there is no shadow.

MainWithDiffuseTransmission1.jpg

RenderPassWithDiffuseTransmission1.jpg

Now if I change the Diffuse transmission of the Cube material to 0, the shadow is not cast on the SSS or any of the render passes.

MainWithDiffuseTransmission0.jpg

RenderPassWithDiffuseTransmission0.jpg

So the question is why is diffuse transmission leading to a shadow being formed from an invisible geometry (Opacity is 0). In my opinion, there should not be any shadow being shown on the cube irrespective of whether the Diffuse Cube material node transmission is set to 0 or something else.

I have attached the test scene file for your reference. Hope it can be fixed.

Regards,
Rajib

[TRRazor]

I've had a similar issue and was advised to check my Coherent ratio settings in OctaneRender's settings tab.
Apparently, when using higher coherent ratio values, it takes a lot of samples to clear those opacity transparencies. In my example scene, it worked, but I'm having the same problem in another scene, where I can't solve it, since coherent ratio is set to "0" in that.

This is definitely a bug in the system.

[rajib]

I've had a similar issue and was advised to check my Coherent ratio settings in OctaneRender's settings tab.
Apparently, when using higher coherent ratio values, it takes a lot of samples to clear those opacity transparencies. In my example scene, it worked, but I'm having the same problem in another scene, where I can't solve it, since coherent ratio is set to "0" in that.

This is definitely a bug in the system.

Hi TRRazor,

Yup, did read your post and the solution given to you. For me I am already using 0 for the coherent. Also I can let it render for long and it will still not clear. I generally do around 3000 samples for all my renders. The shadow is only present in the SSS. All other render passes including the shadow pass has no shadow. But that shadow in the SSS does affect the main render. My issues was the invisible part of the hair casting the shadow. So I tried repeating it using the cube and plane as a sample test scene for Otoy to look at and it was easily repeatable. I too think this is a bug. I had encountered this in the earlier versions but with constant edits to my skin materials I could never full pin it down until now.

Regards,
Rajib

[TRRazor]

It seems that the issue can be isolated within the Universal and MIx Materials. I'm unable to reproduce it with Diffuse, Glossy, Specular materials and so on...still investigating

[rajib]

It seems that the issue can be isolated within the Universal and MIx Materials. I'm unable to reproduce it with Diffuse, Glossy, Specular materials and so on...still investigating

Yes, need to mix materials. Diffuse with absorption medium + transmission and specular with scattering medium. The denser the scattering medium, the more pronounced the shadow which should not be there in the first place. And for skin one needs to keep the density high in the mediums otherwise the light passes through the whole body and creates light bleeds and other artifacts for me via the SSS. If you download the test scene you will see the fairly simple material setup that reproduces the effect.

[wallace]

Just a note, I am currently investigating this issue, and will let you know once a fix is in place.

[rajib]

Just a note, I am currently investigating this issue, and will let you know once a fix is in place.

Thank you Wallace. Looking forward for it to be fixed.

[rajib]

Thank you Wallace / Otoy Team. I can confirm this has been resolved and working okay as of 2020.1 XB3. I tested in both Standalone and the Daz plugin.