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Greetings all,
I have used Povray for some time now and yet never could quite
get the hang of Media (ie atmospheric effects) this has caused me a great
deal of annoyiance having seen some of the wonderfull examples of it's use
but being relativly unable to produce them myself. Can any here point me in
the right direction for a Tutorial or prehaps provide some tips? The effect
I'm looking for at the moment would resemble the mist caused by a heavy
rain. My thanks
From the Desk of Rigger Mortice Thanos
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"Rigger Thanos" <nomail@nomail> wrote in message
news:web.3e4c8d1b78321f62298dcb1c0@news.povray.org...
<snip>
Someone, someday, will write the definitive media tutorial, but I don't think
it's there yet.
Some general tips.
1. Test the 'shape' of your media-density using emitting media - much faster
than scattering
2. Unlike most aspects of POV, media is very sensitive to scale, but in general
the media colour/density will need to be a lot less than <1,1,1>. To get the
same thickness of media at different scales, divide the media colour by the new
scale.*
3. Use the defaults to start with.
4. Always try and use a container
5. Oh, and don't use rgbft 1 for your container's pigment - either rgbf 1 or
rgbt 1
* e.g.
sphere{
0,1
pigment{rgbf 1}
hollow
interior{
media{
method 3
scattering{1, 0.001}
}
}
}
Scaled up by 10 would be:
sphere{
0,1
pigment{rgbf 1}
hollow
interior{
media{
method 3
scattering{1, 0.001/10}
}
}
scale 10
}
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> 1. Test the 'shape' of your media-density using emitting media - much faster
> than scattering
True
> 2. Unlike most aspects of POV, media is very sensitive to scale, but in general
> the media colour/density will need to be a lot less than <1,1,1>. To get the
> same thickness of media at different scales, divide the media colour by the new
> scale.*
I'll come back to that later...
> 3. Use the defaults to start with.
True
> 4. Always try and use a container
True
> 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...
Now to that color...
I've come across a very nice method to model clouds etc (almost
any subsurface-scattering) with using rather high scattering values,
some high absorption values being the inverse of the scattering-color
(<1,1,1>-Scattering_Color) and then some high density values
(no color here, just rgb 5 or something), and get nice results. Playing
a little with the different values (once you know better what they're
supposed to do) gives you all kind of nice side-effects, which you can
either aim for or leave away.
The clouds in the Worldbowl of my ongoing project for 2003 are
made that way, they even use emission for some coloring...
If its only for a small effect, yes, low rgb-colors are needed, but if
you really want to make something "feel" solid, and still don't want
a bright patch of white, thats the approach I'm using since I've discovered
it.
(In case someone tries to download the Worldbowl-Sources on my
homepage: thats the old version, using stacked-planes for the clouds,
no media)
Regards,
Tim
--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmx de
>
> <snip>
>
> Someone, someday, will write the definitive media tutorial, but I don't think
> it's there yet.
>
> Some general tips.
>
> 1. Test the 'shape' of your media-density using emitting media - much faster
> than scattering
> 2. Unlike most aspects of POV, media is very sensitive to scale, but in general
> the media colour/density will need to be a lot less than <1,1,1>. To get the
> same thickness of media at different scales, divide the media colour by the new
> scale.*
> 3. Use the defaults to start with.
> 4. Always try and use a container
> 5. Oh, and don't use rgbft 1 for your container's pigment - either rgbf 1 or
> rgbt 1
>
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"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} ?
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> 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} ?
>
>
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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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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
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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/
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> > 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/
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