Page 1 of 2

Indirect lighting through subsurface diffusion

Posted: Sun Sep 13, 2015 12:41 pm
by franz
Hi,

Here is a render made with appleseed's upcoming raytraced subsurface scattering implementation:

Image

Image

Direct links to full resolution images:
https://raw.githubusercontent.com/apple ... direct.png
https://raw.githubusercontent.com/apple ... mosaic.png

The left room receives all its lighting via diffusion through the translucent object connecting the two rooms.

I would love to see how other renderers (V-Ray, Arnold, RenderMan, Mitsuba, Cycles, LuxRender...) perform in this situation.

The geometry for the scene (in .obj format) is available here:
https://www.dropbox.com/s/vx6nirxape51m ... t.zip?dl=0

Franz

Re: Indirect lighting through subsurface diffusion

Posted: Tue Sep 15, 2015 9:16 am
by Dade
franz wrote: I would love to see how other renderers (V-Ray, Arnold, RenderMan, Mitsuba, Cycles, LuxRender...) perform in this situation.
I'm going to try to replicate the test with LuxRender (as soon as I find the time). This would give access to few test cases: Path tracing, BiDir, Path+Metropolis, BiDir+Metropolis, Path tracing on GPUs, etc.

LuxRender uses brute force to render volumes: a path can be scattered when traveling inside a volume, if it is, the scattering point becomes a new path vertex (like a new surface hit). How AppleSeed is rendering volumes ?

Re: Indirect lighting through subsurface diffusion

Posted: Tue Sep 15, 2015 11:43 am
by franz
Hey Dade, very cool, looking forward to the test.

appleseed doesn't support volume rendering yet. For subsurface scattering, we use the diffusion approximation and have implemented most of the standard diffusion profiles, old and new, with the highest care possible.

Re: Indirect lighting through subsurface diffusion

Posted: Mon Sep 21, 2015 3:59 pm
by toxie
Here the scene rendered with iray. Materials do only match so much though, as we couldn't really match the look of your picture.
So material parameters would help tweaking this.
sss-indirect.png
sss-indirect.png (852.29 KiB) Viewed 13989 times

Re: Indirect lighting through subsurface diffusion

Posted: Mon Sep 21, 2015 4:25 pm
by franz
Hey Carsten,

Very nice! Is this based on the diffusion approximation, or is this volume rendering? If the former, what is the diffusion profile? What was the render time?

Some details about the appleseed render:

I used a Normalized Diffusion profile; pure translucency, no BSDF (I should redo it with a BSDF to get reflections, they look pretty good in your render). The diffuse surface reflectance is set to 0,178,89 (sRGB). The diffuse mean free path is set to 0.6 m. The index of refraction of the sphere is 1.8. The light radiance is 2 W.m^2.sr^-1. The final image is converted to sRGB.

Franz

Re: Indirect lighting through subsurface diffusion

Posted: Mon Sep 21, 2015 5:10 pm
by toxie
Ah, that will help a lot.. Will post another one with these settings tomorrow i guess..

And its brute force volume rendering, not even using the advanced samplers. Rendertime was around ~10mins i think.

Re: Indirect lighting through subsurface diffusion

Posted: Mon Sep 21, 2015 5:24 pm
by toxie
sss-indirect2.png
sss-indirect2.png (1.02 MiB) Viewed 13968 times
that matches better.. :)

Re: Indirect lighting through subsurface diffusion

Posted: Tue Sep 22, 2015 8:34 am
by franz
Very nice. Is that GPU or CPU rendering?

I did another render with the addition of a reflection component, just for fun...

The sphere is probably better treated as an actual volume rather than a diffuse translucent approximation, given how big the mean free path is... By the way, do you have diffuse approximations to translucency in Iray?

Franz

Re: Indirect lighting through subsurface diffusion

Posted: Fri Sep 25, 2015 4:00 am
by beason
Cool! Looks good, franz and toxie.

Re: Indirect lighting through subsurface diffusion

Posted: Tue Feb 02, 2016 3:04 pm
by rouncer
god everyones renders look so sterilized like a hospital!
max resolution + simplified scene.

Surface scratches and some more light sources would definitely help the issue a bit.