sss_fast shader: specular (map) settings?

[AndrewRaZ]

hoo boy, that's a loaded question.

ok, first of all, i recommend reading through as many tutorials and articles as you can. most of the stuff i've learned about SSS and advanced shaders has been learned through that and experience, and i'm still very very green on all of it.

some very good resources:
if you can understand the Mental Ray documentation, that's a great place to start. it's very technical, however, and generally regarded as pretty confusing and poorly written. however, it's from the engineers who wrote the system.
grepper (http://forums.cgsociety.org/showthread.php?t=214189) wrote a very good introduction to the shader
jozvex (http://www.highend3d.com/maya/tutorials/rendering_lighting/shaders/135-2.html) also wrote one, which is very in-depth, and should teach you everything you need about setting it up initially.
Lamrug (http://www.lamrug.org/resources/skintips.html) (LA Mental Ray Users Group) has quite a bit of info on this, and most of them know what they're doing with the system. the link goes to the non-physical SSS tips page.
this Deathfall walkthrough (http://www.deathfall.com/tutorials.php?op=showcontent&id=82) has a pretty good overview of one guy's results.
Rich Fallat (http://richfallatjr.com/SSS_tutorial/sss_tutorial.htm) wrote a walkthrough of his girl's shader, and it has proven a darned good resource. note that i used his techniques quite a bit, and for the still, it worked quite well, but when the lighting or camera changed, there weren't enough variations in the maps for the results to be convincing. he cites the book below as a reference.
Ballistic Publishing (http://www.ballisticpublishing.com/books/dartiste_character_modeling/) has a book out called d'Artiste: Character modeling, which has a couple tutorials from Fransisco Cortina on SSS, as well as tutorials from Pascal Blance and Steven Stahlberg. A great resource to have, and now that they ship from the US, there's no excuse not to have it, i say.
and of course, i would be remiss to not mention the misss tests topic (http://forums.cgsociety.org/showthread.php?t=163360&page=1&pp=15), which i think should be stickied in bold lettering with flashing neon icons. it's a *lot* of reading, but pretty much everything you would want to know is in there. if you've wondered it, it has probably been answered in there.


workflow:
some people prefer different ways of working, so you might just have to play around and see what works best for you. myself, i like to work in attribute groups to start, without any maps assigned, and get things looking good in that area, and then move on. for instance, i'll work with the overall and diffuse colors first, get them *roughly* where they should be, then start adding the SSS attributes and tuning those, but without any maps assigned to the weight or colors. then i'll move on to the bump, which usually doesn't take long, but takes some tweaking with the spec, which i estimate without using maps again. then i go into photoshop and/or zbrush and start creating my maps to control the different attributes. i usually have one of the two specular attributes with a lower, but more smooth levels map, and turn the shininess down, to get a more diffuse specular highlight. the other specular channel will be a tighter and more shiny highlight, which i get by putting a high-frequency noise layer in the map, turning the shininess up, and playing with the levels. i have found that i do have to add a map into the overall specular levels attribute if there are areas that aren't supposed to recieve specular highlights. otherwise, i tend to get bright highlights along edges on areas that aren't supposed to recieve highlights.

i've also been finding that layering shaders gives me a lot of control, so many times i'll actually do that instead. for instance, i will create a mix8layer node, put a grey blinn shader in the base, a black lambert over with its transparency tied into the UV map, then i'll put the SSS Skin shader above that with the specular turned off, and then either another SSS skin shader or SSS specular into the next shader, with the diffuse turned to black, and the blending mode set to screen. this way, i can render the grey model with and without wireframe, the SSS skin, and specularity layers by themselves just by turning a couple layers off. if you really want to be a control freak, you could even separate the diffuse/overall color from the SSS effect and all that, and even add reflection layers and such, to whatever degree of complexity you need.

i'm sure all of this should be plenty for you to get started. good luck!

[zenonithus]

hey Andrew, I forgot I posted this thread! :) I put the sss shader on hold as I started experimenting with displacement maps, but it's the next big task on my list.
There's some really great info you've posted here. good tutorials and tips, I will definately look into these. Thanks for taking the time to write this stuff down, I'm sure it will help others as well as myself.

cheers mate

Ed

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