A little help with SSS

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AndreasResch
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Joined: Fri Jul 06, 2018 9:32 am

A little help with SSS

Post by AndreasResch » Wed Jul 11, 2018 5:21 pm

Hey.

I see why there are requests for artist friendly SSS settings :)

I watched the video with the dragon on Youtube and I understand that it takes a combination of a shader not and a volume to get an SSS effect. Here's what I don't understand yet. While the volume looks nice and soft, the shader on top, when the opacity is low, is razor sharp. I tried to increase Roughness but this only seems to affect the surface but not the translucency. With this behaviour the I can't get a soft material like wax or translucent plastic. And the shadows show the sharp faces as well.

Here's a render test that shows the problem.
Image

Unfortunately I can't find anything like a material library that I can use to get some insight. Does such a thing exist?

I've also attached the scene if somebody wants to look at the settings.

Cheers for now,
Andreas
Attachments
LuxRender_Test_01.blend
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Sharlybg
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Re: A little help with SSS

Post by Sharlybg » Wed Jul 11, 2018 6:05 pm

Upload a real world photography of the kind of shader you want. Will try to provide you the blend and the setup.
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Sharlybg
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Re: A little help with SSS

Post by Sharlybg » Wed Jul 11, 2018 9:58 pm

Or better if know how to do it with cycles give me the blend file with your cycles setup and i will convert it for you !
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AndreasResch
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Joined: Fri Jul 06, 2018 9:32 am

Re: A little help with SSS

Post by AndreasResch » Thu Jul 12, 2018 6:29 am

Hello.

Any standard glossy translucent material with SSS will do. Let's take candle wax for example, or with a little less SSS, a LEGO brick.

This example in the documentation will also do ... https://wiki.luxcorerender.org/LuxCoreR ... ranslucent

Cheers,
Andreas

TryToRemember
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Joined: Tue Jul 03, 2018 3:35 am

Re: A little help with SSS

Post by TryToRemember » Fri Jul 13, 2018 5:44 am

Hi.

So yea your scale is a bit drastic, that's what the problem is... material scaling is orders of magnitude off. At the current scene scale, try the volume absorption depth at 2µm, not 2cm, and try setting the scattering scale to 1200, not 12.

This example is 50µm absorption and 1800 scattering on the volume, with the matglossytranslucent specular set to .248 (don't go higher) absorption pure white and 0.50 absorption depth, material opacity also 0.50.

Image

Hope this helps get you on the right track.
Attachments
spikey ball thingie sss volume.jpg

AndreasResch
Posts: 16
Joined: Fri Jul 06, 2018 9:32 am

Re: A little help with SSS

Post by AndreasResch » Fri Jul 13, 2018 8:08 am

Hello.

Thanks for your reply and time. Your version still looked a little odd and nothing like wax or any other semi-translucent material. Your hint about higher scattering values was a good one though. So I worked with the material a little more and together with the recent post in the Development forum, I created a new scene that works better. I had to crank the Scattering Scale up to 500 or more to get a nice milky effect. With the Volume now filling most of the geometry, it's not problem to dial down the Opacity. The Absorption Depth isn't too much of a problem now. I can use a few millimeters as well as several centimeters and it doesn't look wrong any more.

Here's a test with two slighty different variations of the material.

Image

I've attached the scene if anybody wants to check it out.

Cheers,
Andreas

AndreasResch
Posts: 16
Joined: Fri Jul 06, 2018 9:32 am

Re: A little help with SSS

Post by AndreasResch » Fri Jul 13, 2018 9:14 am

Here's another test with a real model. Scattering Scale had to be cranked up to 3000 here. But it looks exactly as I wanted it now.

Image

Cheers,
Andreas

TryToRemember
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Joined: Tue Jul 03, 2018 3:35 am

Re: A little help with SSS

Post by TryToRemember » Fri Jul 13, 2018 4:54 pm

Hi.

Hey! I like it. That plasticky / soft stone feel makes it looked carved and looks great. A little stronger/shallower scattering and little less specular and you've got a soap carving, too. Like Sharlybg said, I wasn't sure what you were after, just wanted to show you scattering and obstruction in effect, with the internal structure being lit through the surface and reflecting back "up".

It matters because everything in lux is tied to scale, blender itself it way more forgiving and will help a person out, "artist friendly" indeed - I really wish lux could, but then issues comes in with the physical accuracy. (I would assume.)

One of the best materials design skills in lux? When something doesn't look like you think it should? Remember first that It's probably scale and/or some setting(s) related to scale. This is why in blender on the materials preview there is a very helpful zoom setting and a sphere relative size setting. Get in close and check that bump map or that dispersion, because chances are high it's not going to look like you want it on the first try, unless everything is the same as when you first made it. (this is part of the reason a materials library is tricky; everything is a starting point, not a handy ready-to-apply-with-a-click material.)

AndreasResch
Posts: 16
Joined: Fri Jul 06, 2018 9:32 am

Re: A little help with SSS

Post by AndreasResch » Fri Jul 13, 2018 5:08 pm

Yeah - I will fine-tune eventually. But at least I know which dials to turn to get the result I want. I don't mind to work in real scale and enter my values in metric values. My models are metric anyway.

I just tried to add the material to my Asset Management addon and it works, this is great. I can build a material library like that one day.

Cheers for now,
Andreas

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