fastsss2 - scale, scatter radius etc...

[phoenix4]

Hi Everyone,

Well I am still battling away, trying to create a realistic character render using fastsss2.
(Sad to say.. I am still a long way off)

Since there are so many variables involved, including lighting and render settings.

I was wondering, is the a way to actually calculate the scale and scatter radius parameters for your model?
As now, I just keep adjusting and going around in circles.. surely there must be a 'proper' approach to setting fastsss2 up correctly.

Thanks,
Adam

[vlado]

Since there are so many variables involved, including lighting and render settings.

There are really only 2 of them - the scale and the scatter radius, and you can normally lock down one of them and only play with the other. Choosing one of the presets to start with is probably the best way to go. Render settings don't have much influence on the appearance of the sss2 material, and it would be better to set up the material under neutral light.

I was wondering, is the a way to actually calculate the scale and scatter radius parameters for your model?

Yes, you need figure out how much scattering in terms of centimeters you want for the red, green and blue light components respectively. The presets contain realistic values for these parameters, provided that your geometry is modeled correctly with respect to the chosen scene units.

Best regards,
Vlado

[Deflaminis]

I too have terrible times trying to get vray to do SSS. It's still my favorite renderer by far and I love it, but SSS is a pain the butt. Any chance for diagnostic tools sort of like MR? (Or do they already exist and I'm missing it?)

In addition, I can seldom get my highlights/reflections to appear properly on skin shader with SSS2. It always seems so muted, even at 90 degree angles.

I've been working with Maxwell a bit lately to expand my overall understanding of lighting in general, and the transmittance in Maxwell has a 'half life' of sorts which I assume works the same way as the scatter radius. Is that correct? Or do they work differently?

I know it's a lot of questions but I've started to learn more about the other renderers to help me with vray SSS and my conclusion is that they haven't helped. :P

[MoonDoggie]

If it's helpful I did sss2 render and posted my settings in the thread.

http://www.chaosgroup.com/forums/vbu...3-Old-Man-Head

[JeffG2]

I know it's a lot of questions but I've started to learn more about the other renderers to help me with vray SSS and my conclusion is that they haven't helped. :P

Nope. That won't help a bit. The only way to learn about VrayFastSSS2 is to spend some days (or weeks) at it. Someone has made a good dvd tutorial - http://www.digitaltutors.com/11/training.php?pid=537

Also, your LFW has to be set up correctly and you need to use real world lighting and camera settings to get good results. An incorrect setup can severely affect the look of human skin.

[MoonDoggie]

The only way to learn about VrayFastSSS2 is to spend some days (or weeks) at it

Quoted for truth. Start with the skin preset and figure it out. I even wrote a script to help with the Skin shader by rendering out different settings. It's on my website and it's called "Tweaker"

[joconnell]

The only problem with the digital tutors stuff is that the end results never look any good - it's all fine to a point but it's never anything more than just an intro. I struggled to get the sss2 shader working nicely on a large ice wall scene I did and I found it really counter intuitive.

[3DMK]

As SSS is based on scattering rays by scene units...an incorrectly scaled scene will always give you problems

[Deflaminis]

I do in fact use real world scale, been for ages once I learned how important it is to vray. My setup is Max gamma 2.2, input 2.2. I use vray gamma 2.2 and "don't affect colors" to avoid the double gamma issues. I've tried max gamma 1.0 and vray gamma 2.2 with "don't affect colors" off as well. I also use real word camera settings...

I can't say I've spent weeks on it though, deadlines being what they are. I have probably spent over 50 hours trying however, and I don't think I've made any progress at all. I appreciate the heads up though.

Moondoggie your stuff looks really nice in there, impressive! Admittedly even with dramatic lighting, I never came close to that. Guess I'll have to keep trying or check out the dvd. I think what would help is a sort of process checklist. I never know which order to do things and I end up going between scale and scatter back and forth and back and forth and it just seems like I'm not doing it right. Then I'll think " well maybe reduce the diffuse amount"... and now I'm back and forth between scale and radius again. D'oh!

I've also had no luck bringing SSS objects into other scenes and having them work easily, though it generally does work easily with mental ray. Not bashing vray, I love it and have spent the past 6 years using it every day trying to get better and better, but SSS in all it's forms has always kicked my butt.

[vlado]

In addition, I can seldom get my highlights/reflections to appear properly on skin shader with SSS2. It always seems so muted, even at 90 degree angles.

There is a Fresnel falloff built into the reflection amount; if you don't need it, set the specular amount to 0.0 and layer a reflective material on top of the fastsss2 shader.

Then I'll think " well maybe reduce the diffuse amount"... and now I'm back and forth between scale and radius again. D'oh!

The diffuse amount should be pretty low anyways, usually best to leave it to 0.0. The scale and scatter radius do pretty much the same thing, so just make sure the scale is large enough for your scene and leave it at that. Then you only need to work with the scatter radius and probably the sub-surface color a bit. That leaves you with two colors to adjust - it doesn't get much simpler than that.

Best regards,
Vlado

[Morbid Angel]

There is a Fresnel falloff built into the reflection amount;

it would be really great to have the fresnel curve control available in the fast shader. I know you can layer stuff, but sometimes simple is best!

[Deflaminis]

There is a Fresnel falloff built into the reflection amount; if you don't need it, set the specular amount to 0.0 and layer a reflective material on top of the fastsss2 shader.

The diffuse amount should be pretty low anyways, usually best to leave it to 0.0. The scale and scatter radius do pretty much the same thing, so just make sure the scale is large enough for your scene and leave it at that. Then you only need to work with the scatter radius and probably the sub-surface color a bit. That leaves you with two colors to adjust - it doesn't get much simpler than that.

Best regards,
Vlado

I've been away for a week or two, but I really appreciate the heads up Vlado! Thank you and I'm pretty excited to get home and try some of this stuff. Thank you all for schooling me, I needed it.

[ruffstuff]

If it's helpful I did sss2 render and posted my settings in the thread.

http://www.chaosgroup.com/forums/vbu...3-Old-Man-Head

Any chance you can post an image of what your color map looked like?

[MoonDoggie]

Absolutely not, I would never ever ever give out trade secrets. In fact I'm ashamed you would even ask...

Here, however is a picture of my grandpa looking rather flat.


I was told at the end I put it in the wrong slot and it should go in the Scatter color slot? Still not sure. Good luck finding some other references of what someone's "overall map" would look like though.

-Colin