SubSurface Scattering (for Grievous Modelers)

Just thought I'd mention this, since I came across it today whilst fiddling with Grievous's mask.

This is for LW, I don't know how it works in MAX.

I noticed that, in order for SSS to work properly, the model must be "solid". For example, ArtooRo's model can't use it, since the mask is only one poly thick, and has no "back side". Steve Wishart's works, but it's not as accurate.

At the moment, the methods I'm using are both "fake" SSS. I'm actually using a combination of two surface shaders, each simulates one aspect of SSS. "Ska" does the translucency effects (i.e. light shining through the surface from behind), while "TB_FakeSkin" simulates the internal-diffuse look of SSS. By themselves, neither quite does the trick, but they work quite well together. FakeSkin has zero impact on render times.. Ska is fairly slow, but not too much so.. much faster than OGO_Hikari, which is the only "real" SSS shader for LW that I'm aware of. The other bonus is that Ska and FakeSkin are both free.

I'm just mentioning the "solid" thing because it may affect how the plugins work. As I said, I've no idea about MAX, but it wouldn't surprise me if it works the same way. The head I'm currently toying with is JeneralJarJar's, which is wonderfully accurate. It was only partially "solid", though, so I ended up patching up the back of the head and Mirroring the "ears" to solidify them (they looked really funky with SSS prior to that, which furthers the "solid" argument).

Does SSS work that way in MAX, as well? Does it require a "solid" object? That might be something to consider for those still working on the model (Ravenger, Brandeni.. hehe). (and yes, Zoo, the SSS does make QUITE a difference in how he looks.. hehe)

I might be able to post a pic tonight of what I've got so far with SSS in LW (unless I go see a movie or something), but I want to fine-tune the textures first. The bone itself looks fine, but the cracks around the eyes look like ass, so it's back to the drawing board for those.. hehe. Thank heavens for multi-layer Photoshop files, eh?

 

Alright, let's see if I can get the damn markup codes working...

Eh, screw it.. always have the damndest time with ImageShack's thumbnails on this forum, so here's a direct link:

CLICKIE

That's what I've got so far. Still needs a little tweaking on the SSS, especially in the shadow areas. There are NO scene changes at all with those two images, the ONLY thing that changed was the addition of the surface shaders. The orange-ish color is from the SSS, and is fully adjustable.

 

Oooo I like.

Thats a good job on the Fake SSS. I've noticed that in Lightwave myself, tried an experimental project a while back with it and became very frustrated, because the way I model I don't model "solidly", and cut a few corners to save the poly count. I might have to revisit this project now seeing the way you were able to fake that.

I haven't used max in a while, but I'll do a quick check to see how SSS is done in Max. I'm not sure exactly how conclusive my results will be, but I'll go my best.

 

Looks good, Jedi. I messed around with SSS in max last night, and I got two very different results between "open" and "closed" meshes. I suppose that makes sense if the SSS calculates how light enters and exits the mesh. Or does SSS only affect the faces that are directly targeted by light? I'm not entirely sure how exactly it works. Maybe someone like Dr Jones knows?

 

True subsurface scattering does a variety of things. Most people look at the simple part of it, where it affects tranclucency of backlit objects (light shining through an ear, for example.. a popular example). That's more of a side-effect than anything else, though..

The main purpose of subsurface scattering is exactly what it's name implies. It calculates how light enters an object and bounces around beneath the surface. Take the following pic for example:

[image=http://www.asahi-net.or.jp/~pq1a-ogs/sk3.jpg]

You'll notice that there's only one main light source, coming from above. The model is NOT backlit, and yet we can still see the translucency. Make special note of the part of the "lozenge" that's in the shadow of the sphere. You can actually see the light scattering around inside it, without SSS, that area is completely black with shadow.

The trick is to find the right mid-ground.. so that you get some of the effects, without it looking like wax. I'll be fiddling with it some more today, maybe try some other plugins or techniques. Need to fix the textures, too.. they're planar UV, so there's a little bit of stretching on the sides.

 

I know what it does, just not how it does it

I did a few Google searches (imagine that - it actually works!) and came up with a couple things for people interested in a read:
LA mental ray user group
An informative Lightwave tutorial
Henrik Wann Jensen, the guy who did the big research on SSS
This is the SIGGRAPH paper from the last site ^ It's full of mathematical jargon but if you just look at the pictures you can get a sense of how it works.

 

I saw something on this last year I think as being a new feature of Maya, it's also a feature that can be used in MAX with mental ray... I've never messed with it, mainly cuz I just have a demo of MAX 7 and the time ran out on the demo before I got to it... oh well

Darksteps...

 

I know what it does, just not how it does it

Well the concept of what it means is just light dispersal in translucent and scattering media. If you mean in practical terms, it depends. The original Jensen paper used what is called the dipole technique, mainly it used a point light in the interior of the surface to simulate the SSS (after all light scatters and goes back out so in essesnce it's like having a light inside). Other techniques are even more accurate and physically correct, in particular photon maps ones where photos are traced to the interior of surfaces. There have also been aproximate methods, the original dipole method required a raytracer but for production ILM and Weta used a technique based on shadow buffers (which in rough terms are like depth maps from the POV of lights so basially you are determining the depth of materials where light scatters) to get an aproximate solution. There was also a subsequnt paper by Jensen and Juan Buehler of PDI to speed it up and since then there have been a few ways to fake it or aproximate it.

I saw something on this last year I think as being a new feature of Maya,

When Maya introduced Mental Ray they later provided real and aproximate SSS via the Bonus Tools, which were a free download. At least for Maya 6 but it's included in 6.5. In theory you wouldn't need to add anything since you could do it with Mental Ray but in most cases you would have to write a shader for it, so it's good that it's already included in most major packages.

 

Update:

http://img283.imageshack.us/img283/4003/render2sss1hm.jpg

More action-oriented pose.. hehe. Tweaked the SSS some more, got rid of the overt "glowy wax" look of the previous render. Also got it down to just one plugin (Ska). Some surface tweaks allow it to perform the same "full" SSS that FakeSkin was faking. I was fiddling with Ska vs Hikari, and realized that Hikari's models rendered better with Ska.. they have a similar "inside" surface (like the "air" layer of glass) that, for whatever reason, allow Ska to work much better than it does with a standard double-sided surface.

Probably try it with OGO_Hikari next, but that plugin's a pain, and it's slower than molasses to render. Not sure if it's worth it.

 

Hey Jedi2016....my hat's off to you...amazing texturing work so far. That is about as close as ILM's as I have seen on any of the models so far!



Later
Steve

 

jedi by that pic you posted you convinceed me to rebuild the mask i have for my model and that texture looks awsome

 

Ravenger posted on 7/4/05 3:30pm

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[b]jedi by that pic you posted you convinceed me to rebuild the mask i have for my model[/b] and that texture looks awsome
[hr][/blockquote]
Thanks.. I think.. hehe. :)

The texture was surprisingly easy.. I've never considered myself that good at texturing. It's a planar UV map, from the front.. so there IS some texture stretching on the sides and top, but I can fix that later. The texture was created in Photoshop.. the base layer was the beige with some splotches of pink, then overlaid with a plethora of grunge maps from DVGarage's Surface Toolkit. The cracks were hand-painted by literally tracing over the Visual Dictionary pic.. hehe. The black "stripes" I made just by filling in the UV wireframe of that section with the Paint Bucket tool. Handy, since it's a UV map, it automatically "snaps" to the right points once the texture is applied.

Still needs a few tweaks on the base surfaces.. things like specularity, etc. The mask is fairly shiny, since the bone is polished. It's getting there, though. It's given a good idea of where I'd need to go if or when I texture up the full monty, at least as far as the bone texture goes.

 

That's freakin' awesome Jedi2016.

 

Top-notch effort thus far Jedi2016!

 

"Thus far", huh? I'm fresh out of model, though... JarJar didn't make any more.. lol.

*Looks at Ravenger*

 

I said that because I knew you'd want to continue working on it.

Best of luck!

 

dunno how much good it will be to you i made it in maya
if i can export it
i asume your using max if so if your willing you can create the max version of my model
and i'll do the maya version

 

Ravenger posted on 7/5/05 1:08am

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dunno how much good it will be to you i made it in maya :P
if i can export it
i asume your using max if so if your willing you can create the max version of my model
and i'll do the maya version
[hr][/blockquote]
On the contrary.. I am one of SF3D's rare LightWave users.. hehe. LW and Maya get along rather well as I understand it.. OBJ was originally an Alias format, and LW can also import them natively. So long as it exports with quads intact (and no smoothing/subpatching, since I can do that in LW and it keeps the poly-count down), I'm golden. :)

No hurry, though, I know you're not done with it yet.. :)

 

ok and sweet

one problem tho ive been having problems exporting it lately i seem to only be able to export it as a completly combined mesh
and when i try to seperate the individual meshes maya just crashes

dunno if thats a problem?

 

Wow the last test looks really good. I'm trying to learn how to use real SSS with Brazil on my current project, but it's pretty hard to find the correct settings

 

Ravenger posted on 7/5/05 3:43am

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ok and sweet

one problem tho ive been having problems exporting it lately i seem to only be able to export it as a completly combined mesh
and when i try to seperate the individual meshes maya just crashes

dunno if thats a problem?
[hr][/blockquote]
Depends on how you mean.. I'll admit I know very little about Maya itself, though. I know OBJ supports layers, so it should, in theory, simply export it the way it's been built. Or by "combined mesh" do you mean that it collapses it into a single layer?

 

hmm how can i explain this

when i click on any part of the mesh it selects all the mesh pieces as if it was one mesh

 

Not a clue.. As I said, I don't have Maya to play with, so it's hard to make that determination. Even if it selects all the parts, as long as it still recognizes them as individual parts, it should export them that way. LW doesn't require separate object files for every piece (they fixed that years ago), it works on the same layer-based approach that most other apps work on.

Do you have something else you could "test-export" on? Perhaps a simpler, but still multi-layered file that selects in the same way the good General does? You could export it and throw it up somewhere, and I could see about getting it into LW.

 

i'll try

PM me with your contact details so we can work a little better hehe if you wish

 

Im putting Real SSS on my greivous, I changed the helmet so it IS solid, unlike the original version of artoo's


I might get that done in the next couple of days, im on vacation now so im kinda busy. Going to have to start over with the mask mabe now that I have refrences! lol what i have now is pretty much all done by using Ravenger as a reference on some parts, and my memory. Now I have some good stuff to work with.