Subsurface scattering

Started by Dune, October 11, 2019, 10:39:45 am

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Dune

October 19, 2019, 03:06:55 am #45 Last Edit: October 19, 2019, 04:01:29 am by Dune
It's only a small part of the face, but the SSS-part can be seen in the light through the left (her right) nose hole wing (or whatever that's called), so it's there alright. I had to do this very subtly or it would have been too light. Decay depth is 0.017 I believe and density 2 with an unvaried medium reddish as color.

I believe the diffuse is also needed to give e.g. the lips its color. And I have added patches of dirt, skin variation, scratches and pimples, and such, and sometimes may even need body paint. Some procedural, some by image map. I also need bump maps for these low poly objects. I don't know if that really works now.
One can achieve a lot with just glass and roughness for variation (and maybe the skintone can be altered by using a darker reddish (blood) color), but I think there needs to be a way to add diffuse textures to the glass.
Also for things like icebergs; like (fake) rocks caught in/on the ice, strata lines (though the latter can probably be done through color input).

Dune

Some more experiments. Bump is obviously not taken well. Understandable, but a pity.

Matt

One of the useful characteristics of a shader that supports SSS is that the bump mapping can have a strong visible effect on the specular/glossy component while simultaneously having a much softer effect on the diffuse component (because the diffuse is caused by subsurface scattering instead of surface scattering). If you mix in a separate diffuse layer it stops looking like skin because the bump on the diffuse is hard. I would let SSS do its thing to soften the bumps and let the bumps show in the gloss instead.

In your tests there appears to be blueish light leaking through the model. If this is caused by SSS then then a reddish "decay colour" is needed to make this more realistic.

Changing the "Lighting method in PT" to "Subsurface scatter in all directions (BETA)" will do a better job of transmitting light through thin parts of the model. This will allow you to use smaller decay distances (or higher volume densities) and get a more realistic result.
Just because milk is white doesn't mean that clouds are made of milk.

Dune

I understand that you are saying that the total of diffuse and bump in the preceding shaders both act upon the glass shader. So the only thing that needs to be done is matching the colors in the glass to what I had in the pure PT render (dark skinned). How about the reflection settings from the default shader, are they passed on or should I mimic them in the glass shader?
And what about say red lips (especially in female models' face textures), will that be passed on?

Matt

October 19, 2019, 01:04:04 pm #49 Last Edit: October 19, 2019, 01:07:53 pm by Matt
Quote from: Dune on October 19, 2019, 12:20:10 pmI understand that you are saying that the total of diffuse and bump in the preceding shaders both act upon the glass shader.

Bump does, but figuring out how the diffuse comes through is more complicated.

I think it is going to be more complicated than it needs to be if you try to use a Default Shader and a Glass Shader together. For the skin and lips I would try to do everything with the Glass Shader, and follow it with a Displacement Shader (or Image Map Shader with displacement) to add the bump mapping. The face colour map should go into the "volume colour" input of the Glass Shader.

Dirt and body paint could be a separate layer that follows the Glass Shader, appropriately masked to not cover up the Glass Shader.
Just because milk is white doesn't mean that clouds are made of milk.

KyL

Quote from: Matt on October 19, 2019, 01:04:04 pmThe face colour map should go into the "volume colour" input of the Glass Shader
Actually this is the first thing I tried. However this doesn't seem to work. I plugged an image map shader set to Object UVs in the volume Colour function but it ends up black! Volume density does work though.

Matt

Quote from: KyL on October 19, 2019, 01:13:57 pm
Quote from: Matt on October 19, 2019, 01:04:04 pmThe face colour map should go into the "volume colour" input of the Glass Shader
Actually this is the first thing I tried. However this doesn't seem to work. I plugged an image map shader set to Object UVs in the volume Colour function but it ends up black! Volume density does work though.

OK, I'll take a look.
Just because milk is white doesn't mean that clouds are made of milk.

KyL


Dune

Thanks from me too, Matt. Off to try again...

Dune

Tried to do some bubbles in ice. The bubbles themselves are a bit grainy (samples 49 at AA6), but the effect is nice. I also tried to get bubbles only in the ice, and not on the ice surface (the hard white dots), so I masked them by a surface shader with max altitude. But that doesn't work. They are probably calculated starting from the top, and if that isn't there....
Too bad I don't have an X thread Threadripper (yet), as this took 1 hour.

The ice around the pole is a flattened sphere, btw. Iced too.

WAS

Quote from: Dune on October 21, 2019, 10:56:52 amTried to do some bubbles in ice. The bubbles themselves are a bit grainy (samples 49 at AA6), but the effect is nice. I also tried to get bubbles only in the ice, and not on the ice surface (the hard white dots), so I masked them by a surface shader with max altitude. But that doesn't work. They are probably calculated starting from the top, and if that isn't there....
Too bad I don't have an X thread Threadripper (yet), as this took 1 hour.

The ice around the pole is a flattened sphere, btw. Iced too.

I like that effect a lot actually. Even looks like they were trapped in motion. Maybe they're grainy due to noise roughness? Seems everything else is fairly smooth.

Matt

Quote from: KyL on October 16, 2019, 11:17:57 amtgout-014 03m18s v4.4.38.1.jpg

Do you have a version of the Lee Perry Smith head with vertex normals? I downloaded it from the source but it's faceted. I think it expects me to the use the normal map but Terragen doesn't support that yet.
Just because milk is white doesn't mean that clouds are made of milk.

digitalguru

Quote from: Matt on October 21, 2019, 05:27:57 pmDo you have a version of the Lee Perry Smith head with vertex normals?
Here you go

Dune

Another experiment; glass with bubbly. Forgot to set RDM to 1 though. It's not (yet) what I expected.

Matt

Quote from: digitalguru on October 21, 2019, 06:21:58 pm
Quote from: Matt on October 21, 2019, 05:27:57 pmDo you have a version of the Lee Perry Smith head with vertex normals?
Here you go

Thanks. I used this model to test and fix a bump mapping bug and also fix the UV texture mapping problem. You can grab the fixes in 4.4.40 frontier build which is available on Windows and Linux now. Mac version coming in a day or two.
Just because milk is white doesn't mean that clouds are made of milk.