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Re: Sub-Surface Scattering

Posted: Wed Nov 04, 2020 7:37 pm
by B.Y.O.B.
MetinSeven wrote:
Wed Nov 04, 2020 3:28 pm
I was thinking: how come in real life certain materials have a certain light, almost glowing SSS, as if the light is perfectly scattered inside the volume without the surface or volume significantly decreasing the light strength.
Can you post some reference photos that show the effect you mean?

I have also considered you might mean fluorescence, but I'm not so sure. Fluorescence means that a material absorbs light of a certain wavelength and re-emits it on another wavelength. It is not really related to SSS, it's a different thing.

From wikipedia: https://en.wikipedia.org/wiki/Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region, which gives the fluorescent substance a distinct color that can be seen only when exposed to UV light.
A good example are warning vests: they absorb invisible UV light and re-emit it at a visible wavelength, leading to the impression of being brighter than they should be when viewed under daylight.

Re: Sub-Surface Scattering

Posted: Wed Nov 04, 2020 8:32 pm
by MetinSeven
That looks quite cool. I'll experiment with it, thanks.

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:11 am
by MetinSeven
This is my final SSS material setup in the pumpkin scene:
Halloween pumpkin by Metin Seven - Path and Sobol.png
But, very interestingly... I decided to switch from Path + Sobol + Light Tracing + Photon GI Cache + Caustic Light Cache to Bidir + Metropolis, just to see if there would be a noticeable difference. It turned out there are quite some differences:
Halloween pumpkin by Metin Seven - Bidir and Metropolis.png
I think Bidir + Metropolis looks noticeably better, and not only the SSS, also the metal shader of the knife looks a lot better.

I've been using Path + Sobol + Light Tracing + Photon GI Cache + Caustic Light Cache because of the SDS paths, but I guess I'll return to Bidir + Metropolis. Would it be possible to accelerate Bidir + Metropolis using the GPU?

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:30 am
by Dez!
what purpose do you pursue by uploading such huge images to the forum? They are simply too lazy to wait when they open in full size.
I also like the metal of the knife more in the version with BiDir

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:33 am
by MetinSeven
Dez! wrote:
Thu Nov 05, 2020 9:30 am
what purpose do you pursue by uploading such huge images to the forum?
Haha, no purpose. Just forgot to convert them to JPG. :)

It seems that all specular highlights are more prominent in the Bidir + Metropolis rendering, and the SSS also is a bit lighter, with a more gradual falloff.

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:48 am
by Sharlybg
Path + Sobol + Light Tracing + Photon GI Cache + Caustic Light Cache
Wonder if the caches and light tracing is helping anything here ?

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:53 am
by MetinSeven
I just figured to activate all settings that bring the Path engine closer to the Bidir + Mis result, for the best quality. But it turns out that Bidir + Mis still has the edge.

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:58 am
by CodeHD
Bidir + Metropolis can't do SDS caustics, so at least the Caustics light cache would be an "advantage" for Path. I'm also with Sharly as in I don't even see any obvious SDS paths there. Maybe in the knife reflection onto the pumpkin-eye carving, but there is only diffuse lighting arriving there.

Also again threre seems to be a systematic difference between the two images: I can't see the bump(?) texture on the skin? Did you make any other changes than just the render engine?

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 10:04 am
by MetinSeven
CodeHD wrote:
Thu Nov 05, 2020 9:58 am
Bidir + Metropolis can't do SDS caustics, so at least the Caustics light cache would be an "advantage" for Path. I'm also with Sharly as in I don't even see any obvious SDS paths there. Maybe in the knife reflection onto the pumpkin-eye carving, but there is only diffuse lighting arriving there.
Yeah, I guess the SDS caustics are only apparent in specific scenarios with visibly transparent materials.
Also again threre seems to be a systematic difference between the two images: I can't see the bump(?) texture on the skin? Did you make any other changes than just the render engine?
No, but good point about the bump map. It turned out I need to set the bump effect to a more prominent value when using Bidir + Mis.

Re: Sub-Surface Scattering

Posted: Thu Nov 05, 2020 9:22 pm
by MetinSeven
I'm wondering: is Bidir + Mis not able to render SDS paths at all, or is it able to do so if the light has some area or volume? (Not a distant sun or point light.)