On Wed, 16 Jul 2003 00:40:05 +0200, "Gilles Tran" <git### [at] wanadoofr> wrote:


>> Many thanks. Excellent service. This newsgroup looks ripe for
>privatisation.
>
>True enough, I can't wait to have our first POV-Ray accidents once the
>development is subcontracted to the lowest bidders/highest bribers using
>temporary and expandable workers with prior expertise in fruit picking  ;)
>
That told him :-}

Regards
        Stephen

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"Gilles Tran" <git### [at] wanadoofr> wrote in message
news:3f145c58@news.povray.org...
> Try the code below. Left sphere is with subsurface scattering.
> Note that it shows one problem I had with the ISS image when I used this
on
> the kid's arm, which is that the dark (densest) parts tend to be quite
black
> and do not react to radiosity.

So to compensate the lack of radiosity (on this object), would you just use
a light_group to give it ambient light?

...Chambers

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In article <3f124882$1@news.povray.org>, "Slime" <slm### [at] slimelandcom> 
wrote:

> I can see the difference when dense media is used within an object, but is
> this really the same exact effect?

Not exactly the same effect, but very close. POV media doesn't simulate 
secondary scattering...a bright light scatters light to the camera, but 
not to other media. Something like photons may make this possible, or 
have scattering media use radiosity, but you can guess at the CPU 
requirements...anyway, for most purposes, media will work fine. Since 
subsurface scattering is usually limited to the near-surface, you might 
get render time and quality improvements by using an opaque core with a 
media shell.


> And why would human skin have it? *My*
> skin certainly isn't very transparent.

Your skin is perfectly opaque? You should probably see a doctor about 
that...
Flesh is normally fairly translucent. You can see veins under it, softer 
terminator lines on shadows, and reddish coloration of light filtering 
through it. There are images demonstrating this pretty well...an image 
without subsurface scattering looks like the skin is coated with a layer 
of paint when compared to one with subsurface scattering. Or like 
really, really thick makeup.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Check out this picture of three glasses of milk
http://graphics.ucsd.edu/~henrik/images/imgs/milk.jpg.  The one on the far
right has no subsurface scattering, and looks like thick paint.  But the two
on the left do have this effect and replicate the look of milk almost
perfectly.

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In article <3f17203a$1@news.povray.org>, mon### [at] stinet says...
> Check out this picture of three glasses of milk
> http://graphics.ucsd.edu/~henrik/images/imgs/milk.jpg.  The one on the far
> right has no subsurface scattering, and looks like thick paint.  But the two
> on the left do have this effect and replicate the look of milk almost
> perfectly.
> 
> 
> 

I have been thinking about this some. And media just won't do what is 
really needed for this. What you need is something like:

texture {
  pigment {Flesh}
  Subsurface {
    Pigment {
      ...
    }
    Scattering .5
    Depth .1
  }
}

Why? Because you can't get veins and things to show through properly. 
Anything like that you mapped to it would end up on the surface, but you 
want those sorts of things to be the 'subsurface' and have the light 
bounce back from there. It 'may' be possible to make a model that has two 
layers, one for the surface skin and a second for the subsurface and 
stuff media in between them, but this is hardly efficient and imho is 
outright impractical with a complex model. There is also the other 
factor, in the case of something like the milk you are talking about, it 
is literally impossible to make a media that is 'thick' enough (or my one 
attempt to fiddle with it failed to produce such anyway) so as to mask 
things behind it. Maybe in a very large container, but definitely not in 
something small.

A real method to do this would be very useful.

-- 
void main () {

    call functional_code()
  else
    call crash_windows();
}

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I have been able to with milk make it very thick.  Changing the transparency
of the main pigment and also the brightness of the scattering pigment ( i
make it something like 4 or 5), I can produce milk that cannot be seen
through at all but has the scattering below the surface that makes it look
real.  If you want I can post a picture of it on the pov binaries images.

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In article <3f186b18@news.povray.org>, mon### [at] stinet says...
> I have been able to with milk make it very thick.  Changing the transparency
> of the main pigment and also the brightness of the scattering pigment ( i
> make it something like 4 or 5), I can produce milk that cannot be seen
> through at all but has the scattering below the surface that makes it look
> real.  If you want I can post a picture of it on the pov binaries images.
> 
> 
> 

Rather see the code. lol Having fiddled with trying to do something of 
the sort a bit, I got quite annoyed. Though I suspect you are still not 
doing what I meant. I.e. you are having the surface of the media 
container define 'part' of the 'substance' of the media. This works, but 
isn't quite what I was experimenting to achieve. It also doesn't solve 
the other issue with having a real texture 'beneath' the layer in which 
the scattering, or media, needs to be active. Thus it works great for 
milk, but basically fails with something like skin. Which doesn't exactly 
help me much in the long run. ;) lol

However, to give you an idea of what I was trying to manage in this case. 
The concept was to take a sphere, fill it with the densest red colored 
media I could, then shave the side of the sphere off (differencing a 
transparent block from it). The expected result was a thick soupy 
interior that significantly obscured the other side of the sphere and 
made the inside 'seem' semi-solid. I suspect that part of the problem was 
the sphere being way to small, but I also suspect that it is simply 
impossible to make media 'thick' enough to obscure objects at relatively 
short distances without resorting to something like what you seem to be 
talking about doing for the milk. However, I could have simply screwed up 
the settings. ;) I am pretty much flying blind here and experimenting 
with something I never used before. lol

-- 
void main () {

    call functional_code()
  else
    call crash_windows();
}

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Patrick Elliott wrote:
> I suspect that part of the problem was the sphere being way to small, but I also
suspect that it is simply 
> impossible to make media 'thick' enough to obscure objects at relatively 
> short distances without resorting to something like what you seem to be 
> talking about doing for the milk.

You know, the 'scale' keyword works for media densities too...perhaps
that will help with making the relatively short distances less of a
problem.

-- 
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean

-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------

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In article <3f19b4f6@news.povray.org>, Tim Cook <z99### [at] bellsouthnet> 
wrote:

> You know, the 'scale' keyword works for media densities too...perhaps
> that will help with making the relatively short distances less of a
> problem.

The scale keyword only scales the pattern. You have to scale the density 
manually.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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In article <MPG.19835f5a3e611a0798983b@news.povray.org>,
 Patrick Elliott <sha### [at] hotmailcom> wrote:

> I suspect that part of the problem was 
> the sphere being way to small, but I also suspect that it is simply 
> impossible to make media 'thick' enough to obscure objects at relatively 
> short distances without resorting to something like what you seem to be 
> talking about doing for the milk. However, I could have simply screwed up 
> the settings. ;) I am pretty much flying blind here and experimenting 
> with something I never used before. lol

To make it thicker, you just need to increase the density. To get the 
same results at half the scale, you need to double the density. It 
sounds like you think there is some limit to how dense you can make 
media, or that high densities are somehow a "last resort".

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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