"Tim Nikias" <tim### [at] gmxde> wrote in message
news:3e4cea83$1@news.povray.org...

> > 5. Oh, and don't use rgbft 1 for your container's pigment - either rgbf 1 or
> > rgbt 1
>
> I'm curious, why? I'm always using rgbt...
>

rgbt is fine, so is rgbf - it's rgbft that's a problem - see:

http://news.povray.org/povray.binaries.images/30422/
and
http://news.povray.org/povray.general/30421/

btw, you mention density{rgb 5} - funnily enough I came across this the other
day(putting a rgb val into a density block). The docs don't really mention that
this syntax is okay, and I'm slightly mystified as to what it is doing.

is scattering{1, 5} any different from scattering{1,1} density{rgb 5} ?

Post a reply to this message

> btw, you mention density{rgb 5} - funnily enough I came across this the other
> day(putting a rgb val into a density block). The docs don't really mention that
> this syntax is okay, and I'm slightly mystified as to what it is doing.
>
> is scattering{1, 5} any different from scattering{1,1} density{rgb 5} ?

It is different!
If the volume is denser, this should have different effects, like being
absorbed faster, but since we've got more "particles" to light, it also
gets brighter. Hence I use absorption to compensate for that.
Its quiet difficult to explain, actually, and you should experiment with
it. Here's a code snippet for you to start with (its just the media),
you might want to place it in a sphere on a plane... :-)
And then just fumble with the settings, and modify the code.

//SubSurfaceScattering
#local SSS=2;
#local SSS_Color=<1,0,0>;
#local Extra_Absorb=1.5;

#local SSS_Media=
  media{
   scattering{2,vnormalize(SSS_Color)*SSS}
   absorption (vnormalize(<1,1,1>-SSS_Color)*SSS+Extra_Absorb)
   emission Extra_Absorb*vnormalize(SSS_Color)
   density{rgb SSS_Cloud}
   method 3 intervals 1 samples 10,30
   }



--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde
"Tom Melly" <tom### [at] tomandlucouk> schrieb im Newsbeitrag
news:3e4cfaac@news.povray.org...
> "Tim Nikias" <tim### [at] gmxde> wrote in message
> news:3e4cea83$1@news.povray.org...
>
> > > 5. Oh, and don't use rgbft 1 for your container's pigment - either rgbf 1 or
> > > rgbt 1
> >
> > I'm curious, why? I'm always using rgbt...
> >
>
> rgbt is fine, so is rgbf - it's rgbft that's a problem - see:
>
> http://news.povray.org/povray.binaries.images/30422/
> and
> http://news.povray.org/povray.general/30421/
>
> btw, you mention density{rgb 5} - funnily enough I came across this the other
> day(putting a rgb val into a density block). The docs don't really mention that
> this syntax is okay, and I'm slightly mystified as to what it is doing.
>
> is scattering{1, 5} any different from scattering{1,1} density{rgb 5} ?
>
>

Post a reply to this message

Tim, 
Thanks much for this information! I have never been able to get scattering media
to work well for me in other than one unit containers - yes, I divided the
density by the scale. The trouble is always that the media gets far too bright
at settings I 'think' should be perfect. When I adjust the scattering to get the
brightness right, the media looked simply awful. I never thought to try
adjusting the absorbtion to dim the media! I'll have to play with this later
today. 
Regards, Bill P.  

> 
> It is different!
> If the volume is denser, this should have different effects, like being
> absorbed faster, but since we've got more "particles" to light, it also
> gets brighter. Hence I use absorption to compensate for that.
> Its quiet difficult to explain, actually, and you should experiment with
> it. Here's a code snippet for you to start with (its just the media),
> you might want to place it in a sphere on a plane... :-)
> And then just fumble with the settings, and modify the code.
> 
> //SubSurfaceScattering
> #local SSS=2;
> #local SSS_Color=<1,0,0>;
> #local Extra_Absorb=1.5;
> 
> #local SSS_Media=
>   media{
>    scattering{2,vnormalize(SSS_Color)*SSS}
>    absorption (vnormalize(<1,1,1>-SSS_Color)*SSS+Extra_Absorb)
>    emission Extra_Absorb*vnormalize(SSS_Color)
>    density{rgb SSS_Cloud}
>    method 3 intervals 1 samples 10,30
>    }
>

Post a reply to this message

Always glad to help!

I came up with this system whilst trying to create "Treasure", in which
I've made my first attempt at subsurface-scattering for realistic hands
and a woman (see my website's gallery), and fumbling with density,
absorption and scattering I found the combination these can make. Its
become very useful for me since then, I don't know of any other approach
which is quiet as flexible and (for me at least) intuitive.

I might put this on my "Hints" section, cause subsurface-scattering
seems to pop up now and then on the newsgroups...


--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

> Tim,
> Thanks much for this information! I have never been able to get scattering media
> to work well for me in other than one unit containers - yes, I divided the
> density by the scale. The trouble is always that the media gets far too bright
> at settings I 'think' should be perfect. When I adjust the scattering to get the
> brightness right, the media looked simply awful. I never thought to try
> adjusting the absorbtion to dim the media! I'll have to play with this later
> today.
> Regards, Bill P.
>
> >
> > It is different!
> > If the volume is denser, this should have different effects, like being
> > absorbed faster, but since we've got more "particles" to light, it also
> > gets brighter. Hence I use absorption to compensate for that.
> > Its quiet difficult to explain, actually, and you should experiment with
> > it. Here's a code snippet for you to start with (its just the media),
> > you might want to place it in a sphere on a plane... :-)
> > And then just fumble with the settings, and modify the code.
> >
> > //SubSurfaceScattering
> > #local SSS=2;
> > #local SSS_Color=<1,0,0>;
> > #local Extra_Absorb=1.5;
> >
> > #local SSS_Media=
> >   media{
> >    scattering{2,vnormalize(SSS_Color)*SSS}
> >    absorption (vnormalize(<1,1,1>-SSS_Color)*SSS+Extra_Absorb)
> >    emission Extra_Absorb*vnormalize(SSS_Color)
> >    density{rgb SSS_Cloud}
> >    method 3 intervals 1 samples 10,30
> >    }
> >

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Tom Melly wrote:
>"Rigger Thanos" <nomail[at]nomail> wrote in message
>news:web.3e4c8d1b78321f62298dcb1c0[at]news.povray.org...
>
><snip>
>
<one good snip deserves another>

Thank you all very much, especially for the hint as to scale. I typically
model on a very fine scale ie 1 pov unit = 1 mm (virtually) and usually
wind up with either, no light or all white as a result of using media, I'll
play with the settings as you suggest and perhaps let you all see the
results when I get what I'm looking for, Cheers.



From the Desk of Rigger Mortice Thanos

Post a reply to this message

In article <3e4cfcb9@news.povray.org>, "Tim Nikias" <tim### [at] gmxde> 
wrote:

> It is different!

It is the same. Should be, anyway.


> If the volume is denser, this should have different effects, like being
> absorbed faster, but since we've got more "particles" to light, it also
> gets brighter. Hence I use absorption to compensate for that.

The color value given is a multiplier for the total density value. The 
closest thing to "number of particles" is samples.

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

Post a reply to this message

> > If the volume is denser, this should have different effects, like being
> > absorbed faster, but since we've got more "particles" to light, it also
> > gets brighter. Hence I use absorption to compensate for that.
>
> The color value given is a multiplier for the total density value. The
> closest thing to "number of particles" is samples.

I'm not so sure about that, I may be wrong. As I understand it,
samples/intervals/method are an approach on how to calculate the
actual media, they don't represent "particles" of the media
itself.

An you may be right about that density being just a multiplier, though
I'm not quiet sure if different densities don't have a different effect
than just multiplying the scattering/absorption/emission values...

Does someone have true insight into this (since you wrote "Should be,
anyway", I assuming you're not quiet sure about this either)?


--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

>
> > It is different!
>
> It is the same. Should be, anyway.
>
>
> > If the volume is denser, this should have different effects, like being
> > absorbed faster, but since we've got more "particles" to light, it also
> > gets brighter. Hence I use absorption to compensate for that.
>
> The color value given is a multiplier for the total density value. The
> closest thing to "number of particles" is samples.
>
> --
> Christopher James Huff <cja### [at] earthlinknet>
> http://home.earthlink.net/~cjameshuff/
> POV-Ray TAG: chr### [at] tagpovrayorg
> http://tag.povray.org/

Post a reply to this message

In article <3e4fdd8e$1@news.povray.org>,
 "Tim Nikias" <tim### [at] gmxde> wrote:

> I'm not so sure about that, I may be wrong. As I understand it,
> samples/intervals/method are an approach on how to calculate the
> actual media, they don't represent "particles" of the media
> itself.

There are no particles, media only considers total density over a ray. 
The closest thing to a "particle" is a single media sample. Intervals 
and sampling methods simply control number and location of samples.


> An you may be right about that density being just a multiplier, though
> I'm not quiet sure if different densities don't have a different effect
> than just multiplying the scattering/absorption/emission values...

Multiple medias add together, multiple densities multiply. That part of 
the code is quite simple and clear, and the documentation backs it up.


> Does someone have true insight into this (since you wrote "Should be,
> anyway", I assuming you're not quiet sure about this either)?

The media code is a bit messy..."tangled" would be a good way to 
describe it. Lots of stuff in there for things like the different 
sampling methods, it is not always easy to figure out the exact effects.

But the only places those values are used are as multipliers for the 
density, the only place the density is used is where it is multiplied by 
those values, and I am certain that was what was intended. If the 
results are not the same (you implied you had tried it and got different 
results), it most likely is a bug caused by something I'm not seeing.

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

Post a reply to this message

> There are no particles, media only considers total density over a ray.
> The closest thing to a "particle" is a single media sample. Intervals
> and sampling methods simply control number and location of samples.

Thats what I thought. Probably misunderstood what you were saying
about samples.

> Multiple medias add together, multiple densities multiply. That part of
> the code is quite simple and clear, and the documentation backs it up.

No argueing about that one. I was thinking if it doesn't change in effect
if I have e.g.
scattering{1,1} emission 1 and density{rgb 5} versus
scattering{1,5} emission 5 and density{rgb 1}.

> But the only places those values are used are as multipliers for the
> density, the only place the density is used is where it is multiplied by
> those values, and I am certain that was what was intended. If the
> results are not the same (you implied you had tried it and got different
> results), it most likely is a bug caused by something I'm not seeing.

Hm, so you ARE the guy with insight, eh? :-)
I'm not sure if there was something I actually felt as "difference in
look" or if it was more like "my idea of an intuitive approach to
subsurface-sampling" that became my combination of scattering/absorption/
emission/density.
I guess I should make some quick tests for that...


--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

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Yup, you're right. Density only acts as multiplier.
Now I'm wondering where I came up with that idea?

Regards,
Tim

--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

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