I've read a web page: "A Practical Model for Subsurface Light Transport" by
Wann Jensen, Marshner, Levoy, Hanrahan. The page can be found at the
following place:
http://www.cc.gatech.edu/~sarah/a_practical_model_for_subsurface.html

The article seems talking about single scattering and diffuse scattering and
there is also some example code.

At the end of the article is written "We have modified the open source ray
tracer POV-Ray. The only files that we modified inside it are lighting and
render. The rest can be downloaded from POV-Ray's site.".

Maybe it could be a way to implement sub-surface scattering in Povray...
Maybe the proposed code could be merged to Povray code... Maybe we are far
from BSSRDF...

Do you have any details about this argument? Do you think sub-surface
scattering would be a good improvement in Povray? I think so. Someone dont
agree with me, but he could have his reasons...

Best regards.

Antonio Ferrari

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Antonio Ferrari wrote:
> I've read a web page: "A Practical Model for Subsurface Light Transport" by
> Wann Jensen, Marshner, Levoy, Hanrahan. The page can be found at the
> following place:
> http://www.cc.gatech.edu/~sarah/a_practical_model_for_subsurface.html
> 
> The article seems talking about single scattering and diffuse scattering and
> there is also some example code.
> 
> At the end of the article is written "We have modified the open source ray
> tracer POV-Ray. The only files that we modified inside it are lighting and
> render. The rest can be downloaded from POV-Ray's site.".

That page says they developend a patch for this technique but does not 
provide that patch.  What's even more strange is that it's on the 
website of a student (Sarah Tariq) but contains only the names you 
mentioned (which are the authors of a Siggraph paper with the same name).

> Maybe it could be a way to implement sub-surface scattering in Povray...
> Maybe the proposed code could be merged to Povray code... Maybe we are far
> from BSSRDF...
> 
> Do you have any details about this argument? Do you think sub-surface
> scattering would be a good improvement in Povray? I think so. Someone dont
> agree with me, but he could have his reasons...

This has been covered several times already but once again - POV-Ray 
already has the means to simulate subsurface scattering effects through 
its scattering media simulation.  This is not limited in accuracy 
compared to techniques like described on that page, the main possible 
disadvantage is that it can be quite slow.  Note however that the render 
times given for the test renders there are quite slow as well.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 01 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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In article <dblsu5$c3u$1@chho.imagico.de>, chr### [at] gmxde says...
> Antonio Ferrari wrote:
> > I've read a web page: "A Practical Model for Subsurface Light Transport" by
> > Wann Jensen, Marshner, Levoy, Hanrahan. The page can be found at the
> > following place:
> > http://www.cc.gatech.edu/~sarah/a_practical_model_for_subsurface.html
> > 
> > The article seems talking about single scattering and diffuse scattering and
> > there is also some example code.
> > 
> > At the end of the article is written "We have modified the open source ray
> > tracer POV-Ray. The only files that we modified inside it are lighting and
> > render. The rest can be downloaded from POV-Ray's site.".
> 
> That page says they developend a patch for this technique but does not 
> provide that patch.  What's even more strange is that it's on the 
> website of a student (Sarah Tariq) but contains only the names you 
> mentioned (which are the authors of a Siggraph paper with the same name).
> 
Too bad. Would have been interested in seeing such a patch.

> > Maybe it could be a way to implement sub-surface scattering in Povray...
> > Maybe the proposed code could be merged to Povray code... Maybe we are far
> > from BSSRDF...
> > 
> > Do you have any details about this argument? Do you think sub-surface
> > scattering would be a good improvement in Povray? I think so. Someone dont
> > agree with me, but he could have his reasons...
> 
> This has been covered several times already but once again - POV-Ray 
> already has the means to simulate subsurface scattering effects through 
> its scattering media simulation.  This is not limited in accuracy 
> compared to techniques like described on that page, the main possible 
> disadvantage is that it can be quite slow.  Note however that the render 
> times given for the test renders there are quite slow as well.
> 
And once again, the existing method, while more accurate, is impractical, 
complicated and incomprehensible to most people for any reasonable 
application they might want to try it with. Even the people that have 
experimented with it so far have yet to get it to work as easily as it 
would need to be for a newbie to employ it. As someone that doesn't spend 
all my free time trying things in POV-Ray, that includes me. lol And, as 
you point out, its quite likely slower, which also makes it impractical 
for some uses.

-- 
void main () {

    call functional_code()
  else
    call crash_windows();
}

Post a reply to this message

Patrick Elliott wrote:
> 
> And once again, the existing method, while more accurate, is impractical, 
> complicated and incomprehensible to most people for any reasonable 
> application they might want to try it with. Even the people that have 
> experimented with it so far have yet to get it to work as easily as it 
> would need to be for a newbie to employ it. As someone that doesn't spend 
> all my free time trying things in POV-Ray, that includes me. lol And, as 
> you point out, its quite likely slower, which also makes it impractical 
> for some uses.
> 

What exactly makes you think that any such patch is easier to use?  On 
the contrary - a patch that takes a less universal approach than a full 
scattering media simulation to gain faster results most likely requires 
additional controls to be set.

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 01 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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Christoph Hormann <chr### [at] gmxde> wrote:
> Patrick Elliott wrote:
> >
> > And once again, the existing method, while more accurate, is impractical,
> > complicated and incomprehensible to most people for any reasonable
> > application they might want to try it with. Even the people that have
> > experimented with it so far have yet to get it to work as easily as it
> > would need to be for a newbie to employ it. As someone that doesn't spend
> > all my free time trying things in POV-Ray, that includes me. lol And, as
> > you point out, its quite likely slower, which also makes it impractical
> > for some uses.
> >
>
> What exactly makes you think that any such patch is easier to use?  On
> the contrary - a patch that takes a less universal approach than a full
> scattering media simulation to gain faster results most likely requires
> additional controls to be set.
>
> Christoph

Mmmh... I also think that an universal method is better, and media
functionality in Povray seems complete. Some time ago I also tried to
implement sub-surface scattering trough povray language, after reading some
articles posted in these news. I encountered two problems:

1 - poor results: the quality reached has never been like the one seen in
the image seen for example in the articles about real sub-surface
scattering.

2 - it's very complicated to reach a good approximation/simulation of sss in
povray.

The problem stands for generic objects. It's easy to apply density to a
simple object (a sphere, a box, etc.) but for a generic or complex objects
things change: the only way I found was the construction of a density file
ad-hoc, using macros that scanned the interior of an object and calculated
a particular density in strata near the outer surface. It's not easy to
explain this idea. It was just an idea; my job doesnt allow me to find the
necessary time to implement it... :(

Maybe there are simpler methods. Can anyone find a macro or a method to
simulate sss for a generic object using povray media? This is not the
correct place to ask this question, but the answer could definitevely close
the question if a patch can be discussed or not, I think...

Thanks

AF

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Antonio Ferrari wrote:
> 
> Maybe there are simpler methods. Can anyone find a macro or a method to
> simulate sss for a generic object using povray media? This is not the
> correct place to ask this question, but the answer could definitevely close
> the question if a patch can be discussed or not, I think...

Not aware of media, but my fake subsurface scattering shader in POVMan 
could work for some cases, if you want something like this:
 >http://news.povray.org/povray.binaries.images/thread/%3C3ec7d192@news.povray.org%3E/?ttop=189070&toff=1000

Shader itself along with POVMan could be found from my homepage 
http://www.aetec.ee/fv/vkhomep.nsf/pages/POVMAN2/
(it's old version, based in previous version of MegaPOV).

Post a reply to this message

Antonio Ferrari wrote:
> 
> 1 - poor results: the quality reached has never been like the one seen in
> the image seen for example in the articles about real sub-surface
> scattering.

As already said the scattering media simulation in POV-Ray is more 
realistic than most subsurface scattering techniques.

> 2 - it's very complicated to reach a good approximation/simulation of sss in
> povray.
> 
> The problem stands for generic objects. It's easy to apply density to a
> simple object (a sphere, a box, etc.) but for a generic or complex objects
> things change: the only way I found was the construction of a density file
> ad-hoc, using macros that scanned the interior of an object and calculated
> a particular density in strata near the outer surface. It's not easy to
> explain this idea. It was just an idea; my job doesnt allow me to find the
> necessary time to implement it... :(

Using media is not restricted in any way - you can use it for 
arbitrarily complex surfaces.  In most cases constant density is 
perfectly sufficient (and i am pretty sure most examples you see in 
subsurface scattering demonstration use constant density as well).

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.tu-bs.de/~y0013390/ (Last updated 01 Jul. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

Post a reply to this message

In article <dbngn5$265$1@chho.imagico.de>, chr### [at] gmxde says...
> Patrick Elliott wrote:
> > 
> > And once again, the existing method, while more accurate, is impractical, 
> > complicated and incomprehensible to most people for any reasonable 
> > application they might want to try it with. Even the people that have 
> > experimented with it so far have yet to get it to work as easily as it 
> > would need to be for a newbie to employ it. As someone that doesn't spend 
> > all my free time trying things in POV-Ray, that includes me. lol And, as 
> > you point out, its quite likely slower, which also makes it impractical 
> > for some uses.
> > 
> 
> What exactly makes you think that any such patch is easier to use?  On 
> the contrary - a patch that takes a less universal approach than a full 
> scattering media simulation to gain faster results most likely requires 
> additional controls to be set.
> 
Ok. The major problem I see is the memory, parse time and complexity 
needed. Now, with media, its probably impossible to 100% fix the render 
time. However, what about something simpler? Like:

subsurface {[image "blah"]
           [image map]
           depth <blah>
}

In other words, instead of having to stuff a skull or skeleton into the 
model, simple have a second 'skin' generated inside the object, which 
automatically creates an internal structure, where ever it can fit one? 
See, that is the advantage fake SSS has, the ability to arbitrarily 
define the 'depth' of the media and what ever physical characteristics 
the bones, etc. add, without having to make an entire model 'just for 
those things', and in the process maybe tripling the parsing time, 
quadrupling the memory used, etc. That's why 'bad' solutions, even if not 
realistic, are more useful. You don't have to spend 2-3 times as much 
time building a 'subsurface' for the light to actually scatter off of as 
you do designing the original model, which is the current problem. 
Without it, the media method doesn't work well and even with it, it still 
can't entirely approximate what is needed.

-- 
void main () {

    call functional_code()
  else
    call crash_windows();
}

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Hrmmm. This site -- http://rise.sourceforge.net/cgi-bin/makepage.cgi?Home --
has a render engine that can implement sub-surface scattering for arbitrary
meshes, and claims it's code is "lucid and readable". Anyone interested in
adding sss to POV might want to take a look. I don't know if it helps,
since it doesn't use media to simulate it. I'm just throwing the link out
there.


"Antonio Ferrari" <nomail@nomail> wrote:
>
> Mmmh... I also think that an universal method is better, and media
> functionality in Povray seems complete. Some time ago I also tried to
> implement sub-surface scattering trough povray language, after reading some
> articles posted in these news. I encountered two problems:
>
> 1 - poor results: the quality reached has never been like the one seen in
> the image seen for example in the articles about real sub-surface
> scattering.
>
> 2 - it's very complicated to reach a good approximation/simulation of sss in
> povray.
>
> The problem stands for generic objects. It's easy to apply density to a
> simple object (a sphere, a box, etc.) but for a generic or complex objects
> things change: the only way I found was the construction of a density file
> ad-hoc, using macros that scanned the interior of an object and calculated
> a particular density in strata near the outer surface. It's not easy to
> explain this idea. It was just an idea; my job doesnt allow me to find the
> necessary time to implement it... :(
>
> Maybe there are simpler methods. Can anyone find a macro or a method to
> simulate sss for a generic object using povray media? This is not the
> correct place to ask this question, but the answer could definitevely close
> the question if a patch can be discussed or not, I think...
>
> Thanks
>
> AF

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"Sleazy Saint" <Oll### [at] aolcom> wrote:
> Hrmmm. This site -- http://rise.sourceforge.net/cgi-bin/makepage.cgi?Home --
> has a render engine that can implement sub-surface scattering for arbitrary
> meshes, and claims it's code is "lucid and readable". Anyone interested in
> adding sss to POV might want to take a look. I don't know if it helps,
> since it doesn't use media to simulate it. I'm just throwing the link out
> there.

Hi! I read your article only now. I don't know if someone will want to
develop a patch for SSS or BSSRDF in Povray. Maybe will be simply necessary
to add a shortcut in the grammar (plus little develop I suppose, since media
already simulate scattering) instead of making complex calculations using
media and density. Let's hope to see this feature implemented in the
future. AF

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