Am 30.04.2016 um 16:59 schrieb Simon J. Cambridge:
> I have been trying for ages to get satisfactory results with subsurface (both
> POV 3.7 and Samuel Benge's fastSSS). I imagine I am doing it wrong in some way
> as I can never get the results that I want! So I got to debating with myself as
> to the whichness of the why and tried using Irid instead. After various tests I
> came up with the following, ramping Irid up (2), using low lighting (fade
> distance) and a small thickness (0.05). The results are as you see (but be
> advised these are all very much works in progress!)
> 
> One thing of note. It is very much faster than SubSurface. Also, I was wondering
> whether there was any mileage in being able to use a colour component for the
> strength, eg Irid <1, 0.7, 0.5>.

Subsurface Light Transport and Iridescence are two entirely unrelated
phenomena in nature, and entirely unrelated mechanisms in POV-Ray.

If you find that the `irid` mechanism "kind of" does what you want,
you're likely in for much frustration if you try to coax it into doing
_exactly_ what you want, because it is probably designed to do something
entirely different.

Of course, figuring out what is _really right for you requires to get a
clear grasp of what you actually want to achieve.


SSLT is designed to make skin (and other materials, like wax, soap, or
even milk) look less "hard" than the results you can get from classic
rendering, to the point that it may look a little bit translucent.

I'd like to point out that your attempts at employing `irid` for more
realistic skin utterly fail in this respect (and inevitably so, for some
very fundamental reason); your people still look like made from some
hard plastic or plaster or something, and always will no matter how hard
you try with `irid`. There are other fast cheats that might do the trick
depending on the lighting conditions, but iridescence simulation is
certainly none of them.


If, on the other hand, what you're really after is just making the skin
look a little bit more "oily", then you're on the right track after all.
That's an effect that SSLT is unfit to simulate (so in that case it's no
surpsise you're getting nowhere with that mechanism), while `irid` is
indeed perfectly tailored for it.


As for allowing to modulate the `irid` effect on a per-colour basis,
that would be physically nonsensical, as iridescence _generates_ colour
effects, and it does so based on some very fundamental laws of nature.

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