Spectral Rendering & SSS Settings

magog_a4eb71ab

I've been following a guide and using the settings given and the results I'm getting are a bunch of black specks. I only applied the settings to the torso of the character. Am I doing something wrong or were these settings pulled out of a unicorn's butt? I like to think its something that I'm either missing or maybe a couple of settings were listed incorrectly in the guide. I know I've had similar problems before with other skins, which I had narrowed down to Transmitted Measurement Distance(TMD) vs. Scattering Measurement Distance(SMD) settings and/or Transmitted Color vs. SSS Color. It just doesn't seem to work setting the Transmitted Color to 254 254 254. Given the approximate 85% reduction in light with spectral rendering, I had increased the environment intensity from my usual 0.25 to 1.67, and the two spotlights I used were set to 700,000 lumens. Besides a screenshot of a spot render, I've also included the PDF file that I'm following in the attachment. Its a free guide and can be freely distributed without any issues.

barbult

Given the approximate 85% reduction in light with spectral rendering

What? I've never seen any overall reduction of light with spectral rendering. I assume you are talking about Iray. 

Fishtales

I personally don't agree with everything in that PDF but if it works for those that try it then I wont say it is wrong. As @barbuilt has said I have never seen a reduction in light and I use Spectral Rendering all the time in renders. I also think your problem is too much light hitting the character.

Padone

Spectral rendering works fine with the faithful conversion. While the natural conversion has issues with photometric lights, though hdri and sky work fine. Then the settings used in that guide are a strong simplification of sss since volume absorption is not used. It may produce "beautiful" images with some light setups but it's not general purpose nor physically correct.

see

https://www.daz3d.com/forums/discussion/comment/5743051/#Comment_5743051

https://www.daz3d.com/forums/discussion/comment/5766991/#Comment_5766991

TheKD

I stopped using spectral a while back, as turning it on would make seams in character texture maps visible in my renders sometimes. 

magog_a4eb71ab

Such a shame that its a broken feature. I actually liked how the skin appeared with some of the settings, but the black or green specks just ruin it. No, its not an issue of too much light as I tried adjusting it up & down, using HDRI lighting ONLY vs Spotlight(sphere) ONLY. If you're not seeing a reduction in light without the need to increase the lumens dramatically, then either you're not using Iray or you're not using the same spectral rendering settings. Its all there in the PDF. SSS chromatic appears to be another one of those settings that isn't based on what makes sense, but relies on playing around with it for hours until it "looks right", which varies with each skin. Some of the default settings I find used on some skins for transmitted measurement distance & scattering measurement distance makes me wonder why they even bother using chromatic.

magog_a4eb71ab

Padone said:

Spectral rendering works fine with the faithful conversion. While the natural conversion has issues with photometric lights, though hdri and sky work fine. Then the settings used in that guide are a strong simplification of sss since volume absorption is not used. It may produce "beautiful" images with some light setups but it's not general purpose nor physically correct.

see

https://www.daz3d.com/forums/discussion/comment/5743051/#Comment_5743051

https://www.daz3d.com/forums/discussion/comment/5766991/#Comment_5766991

Yeah, I'm thinking its a load of [nonsense] to be honest. There's probably a lot of important stuff left out of the PDF since those settings just don't work, regardless of the lighting & surface settings I try. I read a couple of pages from the one thread, some of which I was already aware of with regards to seams in spectral rendering. Lots of banter, lol.

magog_a4eb71ab

TheKD said:

I stopped using spectral a while back, as turning it on would make seams in character texture maps visible in my renders sometimes. 

Would screwed up Normal/Bump maps contribute to this? If so, there are a LOT of them that either don't match at the seams or they match the seams in such a way that they don't match the rest of the textures. Usually its not noticeable using a character's default skin settings or with minor tweaks, but if you make more dramatic changes, these "minor" inconsistencies really start to show.

TheKD

I never really troubleshooted what caused it, I just noticed that turning it off fixed it, so I stopped turning it on lol.

lilweep

magog_a4eb71ab said:

Padone said:

Spectral rendering works fine with the faithful conversion. While the natural conversion has issues with photometric lights, though hdri and sky work fine. Then the settings used in that guide are a strong simplification of sss since volume absorption is not used. It may produce "beautiful" images with some light setups but it's not general purpose nor physically correct.

see

https://www.daz3d.com/forums/discussion/comment/5743051/#Comment_5743051

https://www.daz3d.com/forums/discussion/comment/5766991/#Comment_5766991

Yeah, I'm thinking its a load of [nonsense] to be honest. There's probably a lot of important stuff left out of the PDF since those settings just don't work, regardless of the lighting & surface settings I try. I read a couple of pages from the one thread, some of which I was already aware of with regards to seams in spectral rendering. Lots of banter, lol.

The skin shader "works".  I have followed the guide and not had issues you are experiencing.  Granted, Padone's comments are valid.