LuxCoreRender Forums

B.Y.O.B. wrote: Tue Nov 03, 2020 10:01 am Have you read this? https://wiki.luxcorerender.org/Subsurface_Scattering
It explains some of the fundamental principles of using SSS in LuxCore.

MetinSeven wrote: Tue Nov 03, 2020 6:12 am I used Random Walk SSS in Cycles, which is the same algorithm as LuxCore uses, unless I'm mistaking.

This is correct.

MetinSeven wrote: Tue Nov 03, 2020 9:15 am Slightly closer again, using a Heterogeneous Volume now, and turned down Glossy Translucent material transparency a bit further...

Some notes about your last setup:

• You might want to leave the transmission color of the glossy translucent material white. Then you can control the color inside the volume solely via the absorption color.
• On the same topic, you might want to leave the scattering color of the volume white, so only the absorption color influences the color.
• Only use a heterogeneous volume if you need to texture volumetric properties with a spatially varying texture. If the properties are constant over the whole volume, it is better to use a homogeneous volume since it has much better performance.
• Because the glossytranslucent material does not refract light rays, the volume IOR does not matter here. It only really matters in combination with a glass material.

About the testscene:

It would be good to have a simple testscene that looks absolutely identical between Cycles and LuxCore when using a diffuse shader, and only looks different when using the SSS shader. Then we can iterate on it until they look identical with SSS.
You could use the LuxBall scene from here as a starting point, it already shows the same result between Cycles and Lux when using a diffuse/matte shader:

Thanks! I'll look into everything and report back.

OK, tried to match the advice in the Luxcore Wiki SSS page some more, but when I leave both the Glossy Translucent material's Transmission color and the Volume's Scattering value white, colors become very faint, and the bump map starts looking like artifacts: Darkening the Diffuse and Absorption colors also doesn't work out. And no matter what I do, changing materials, volumes and light strengths, I can't get the glowy light depth like in Cycles, as if Cycles has a different Random Walk implementation than Luxcore.

Concluding after all my attempts, I think Luxcore SSS is too hard to control compared to Cycles. I think that's a pity, as SSS is an important factor to create lively materials for characters. In just about every other aspect I like Luxcore's results better: overall shading, light response on surfaces, shadow crispness and more.

MetinSeven wrote: Tue Nov 03, 2020 11:06 am Darkening the Diffuse and Absorption colors also doesn't work out.

Without access to the scene, it's just guessing, but have you tried lowering the absorption depth in the volume, instead of darkening the absorption color?

I've tried just about everything, but I'm happy to send the scene to you in a PM.

Maybe this video can help: https://www.youtube.com/watch?v=79V_ySn5ZoY

Thanks, I know the video. Good tips, but despite that knowledge I can't get Luxcore SSS to behave as Cycles Random Walk SSS.

MetinSeven wrote: Tue Nov 03, 2020 2:35 pm I can't get Luxcore SSS to behave as Cycles Random Walk SSS

therein lies the mistake.
don't try to do it like in Cycles. Do as in Luxcore.
Make a cube, or some simple shape, and practice on it. Learn how volumes work. You can create any materials.

Yeah, but I love the gradually diminishing, glowy light as surface depth progresses in Cycles. I tried all advice I've read and viewed, and just don't succeed in achieving that effect in Luxcore. Either the whole surface gets lighter or light doesn't penetrate a surface enough.

But I've sent my scene to B.Y.O.B.. He knows a lot more of Luxcore SSS than I do, so I'm hopeful.

I recently did this for epoxy.
easily done. there depends on the color and intensity

MetinSeven wrote: Tue Nov 03, 2020 3:47 pm Yeah, but I love the gradually diminishing, glowy light as surface depth progresses in Cycles. I tried all advice I've read and viewed, and just don't succeed in achieving that effect in Luxcore. Either the whole surface gets lighter or light doesn't penetrate a surface enough.

But I've sent my scene to B.Y.O.B.. He knows a lot more of Luxcore SSS than I do, so I'm hopeful.

Can you just make a simpe scene of your Cycles SSS applied to luxball so that we can just convert it to Lux for you ?