Le_Forgeron <jgr### [at] freefr> wrote:
> What if SSLT, if it does not fit finish, was an additional (or two ? does SSLT have
a
> meaning to have a different "value" from outside/inside ?) piece of data ?

Again you're not following discussions in these newsgroups.

I already mentioned that I do think it is most suited to be considered an
"interior" attribute.

Its key parameters - aside from index of refraction - are the "(reduced)
scattering coefficient" and "absorption coefficient", both representing the
probability per unit of distance (in this case normalized to per-mm) that a
photon is scattered or absorbed, respectively, as it travels through the
material.

Note that these parameters are basically equivalent to absorbing / scattering
media density (except that media gives proper results only for low-scattering
substances, whereas SSLT is designed for highly-scattering materials).

Surface events are involved as well, but they play only a secondary role; the
main coefficients, at least, do not describe properties of an interface between
materials, but of one material only.


There might be reason to consider it a pigment property, as in real life the
events involved in subsurface scattering *cause* the pigment color, and the
SSLT mechanism supersedes the classic pigment&diffuse thing. But in my opinion,
this only shows that pigment is at the wrong place, at least from a theoretical
point of view.

An additional point is that pigment might still represent an additional surface
coating, which is too opaque to be worth modelling with an added layer of
SSLT-enabled material.


From your musings, I must assume you have no idea what SSLT actually does. I
recommend reading the original 2001 Siggraph paper "A Practical Model for
Subsurface Light Transport" by Jensen, Marschner, Levoy and Hanrahan.

I also wonder whether you have any idea what a "surface normal" is, that you
think SSLT could fit anywhere near.


> last note: should we keep using sslt, or a proper noun (simpler) could be used ?

I for one think "subsurface" is quite a good keyword to use. The proper
technical term is "Subsurface Light Transport" (SSLT), while some refer to it
as "Subsurface Scattering" (SSS), so "subsurface" fits both.

Also note that I'm not in the mood to discuss the whole smash with you. You may
ask me questions, and I may answer those. And you may make comments, and I may
be inspired by those. But I'm positively *NOT* going to *consult* you on how to
implement SSLT, what SDL statements to use, etc.

Honestly, there are lots of other people on these newsgroups I'd ask first.

I feel treated by you as if I had not much of an idea of what I'm doing, or
where to go from where SSLT currently is - and I know for sure that I do NOT
like to be treated that way. If that is really not the case, then I must ask
you to make more effort to convey your true attitude.

Otherwise, any further discussion about SSLT between the two of us ends right
here.

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