I use this declaration:

#declare intensite_r = 0.0000000;
#declare intensite_g = 0.0000000;
#declare intensite_b = 0.0000015;


media
 {
  intervals 5
  scattering { 1, rgb < intensite_r, intensite_g, intensite_b > }
  //samples 50, 100
  samples 35, 50
  confidence 0.99999
  variance 1/100
  ratio 0.9
 }

But the media remains coarse and grainy. Is there a way to
get smooth-looking fog like mist without pumping the sampling
rate to, say, 500 or something ?


Best,

    S.

----------------------------------------------------------
Steven Pigeon                     Ph. D. Student.
University of Montreal.
pig### [at] iroumontrealca           Topics: data compression,
pig### [at] jspumontrealca          signal processing,
ste### [at] researchattcom           non stationnary signals
                                  and wavelets.
----------------------------------------------------------
         http://www.iro.umontreal.ca/~pigeon

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Steven Pigeon wrote:
> 
> I use this declaration:
> 
> #declare intensite_r = 0.0000000;
> #declare intensite_g = 0.0000000;
> #declare intensite_b = 0.0000015;
> 
> media
>  {
>   intervals 5
>   scattering { 1, rgb < intensite_r, intensite_g, intensite_b > }
>   //samples 50, 100
>   samples 35, 50
>   confidence 0.99999
>   variance 1/100
>   ratio 0.9
>  }
> 
> But the media remains coarse and grainy. Is there a way to
> get smooth-looking fog like mist without pumping the sampling
> rate to, say, 500 or something ?
> 
> Best,
> 
>     S.

 Hi,

 Try adding extinction 0.1 to the scattering statement and drop your
intervals setting. Your intensity color level is much smaller than
anything I have ever tried and I am surprised you are getting anything.
The extinction may make this difference more visible once added. Also I
posted source yesterday on the images group for participating media you
might look at. The only reason it looks as rough as it does is because
I was in a hurry and used a very low max samples setting for that render.
I also doubt you need the min. samples as high as you have them and
they could probably be reduced to 10.


-- 
Ken Tyler

mailto://tylereng@pacbell.net

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Ken wrote:

>  Try adding extinction 0.1 to the scattering statement and drop your
> intervals setting. Your intensity color level is much smaller than
> anything I have ever tried and I am surprised you are getting anything.
> The extinction may make this difference more visible once added. Also I
> posted source yesterday on the images group for participating media you
> might look at. The only reason it looks as rough as it does is because
> I was in a hurry and used a very low max samples setting for that render.
> I also doubt you need the min. samples as high as you have them and
> they could probably be reduced to 10.

I used to use atmosphere in earlier versions and kind of figured out howto use
it correct. My first few tries with media aren't really sucesses so
far :-) Besides, I was trying to get very subtle hues...

I downloaded your source and I'm toying with it...

Thanks...

    S.

>
>
> --
> Ken Tyler
>
> mailto://tylereng@pacbell.net



--
----------------------------------------------------------
Steven Pigeon                     Ph. D. Student.
University of Montreal.
pig### [at] iroumontrealca           Topics: data compression,
pig### [at] jspumontrealca          signal processing,
ste### [at] researchattcom           non stationnary signals
                                  and wavelets.
----------------------------------------------------------
         http://www.iro.umontreal.ca/~pigeon

Post a reply to this message

Hmm, these settings _should_ give a rather smooth media. I think min_samples
could be dropped quite a bit, actually. You could try lowering variance to
1/256. Sometimes (I'm not sure, under what conditions) media looks very
grainy when the light_source is nearly anti-parallel to the camera. Have you
tried some mega-high sampling rate and does that solve the problem?
Like Ken suggests, the extinction should be lowered for fog (or any media
whose particles have a high albedo); 0.1 seems a bit extreme, though.
Dunno...
BTW, your scene must be truly huge, if such low-intensity media shows up at
all.

Margus

Steven Pigeon wrote in message <370F6DEA.F25FE695@iro.umontreal.ca>...
>
>
>I use this declaration:
>
>#declare intensite_r = 0.0000000;
>#declare intensite_g = 0.0000000;
>#declare intensite_b = 0.0000015;
>
>
>media
> {
>  intervals 5
>  scattering { 1, rgb < intensite_r, intensite_g, intensite_b > }
>  //samples 50, 100
>  samples 35, 50
>  confidence 0.99999
>  variance 1/100
>  ratio 0.9
> }
>
>But the media remains coarse and grainy. Is there a way to
>get smooth-looking fog like mist without pumping the sampling
>rate to, say, 500 or something ?
>
>
>Best,
>
>    S.
>
>----------------------------------------------------------
>Steven Pigeon                     Ph. D. Student.
>University of Montreal.
>pig### [at] iroumontrealca           Topics: data compression,
>pig### [at] jspumontrealca          signal processing,
>ste### [at] researchattcom           non stationnary signals
>                                  and wavelets.
>----------------------------------------------------------
>         http://www.iro.umontreal.ca/~pigeon
>
>

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I would say lose the scattering altogether, nothing but noise from it in
a open scene (non-container media) from what I've seen; try 'emission'
(absorption too if necessary) instead. Those other parameters don't need
to be so fine either execpt maybe upping the intervals (opposite of Kens
suggestion? Okay, so I'm different).


Margus Ramst wrote:
> 
> Hmm, these settings _should_ give a rather smooth media. I think min_samples
> could be dropped quite a bit, actually. You could try lowering variance to
> 1/256. Sometimes (I'm not sure, under what conditions) media looks very
> grainy when the light_source is nearly anti-parallel to the camera. Have you
> tried some mega-high sampling rate and does that solve the problem?
> Like Ken suggests, the extinction should be lowered for fog (or any media
> whose particles have a high albedo); 0.1 seems a bit extreme, though.
> Dunno...
> BTW, your scene must be truly huge, if such low-intensity media shows up at
> all.
> 
> Margus
> 
> Steven Pigeon wrote in message <370F6DEA.F25FE695@iro.umontreal.ca>...
> >
> >
> >I use this declaration:
> >
> >#declare intensite_r = 0.0000000;
> >#declare intensite_g = 0.0000000;
> >#declare intensite_b = 0.0000015;
> >
> >
> >media
> > {
> >  intervals 5
> >  scattering { 1, rgb < intensite_r, intensite_g, intensite_b > }
> >  //samples 50, 100
> >  samples 35, 50
> >  confidence 0.99999
> >  variance 1/100
> >  ratio 0.9
> > }
> >
> >But the media remains coarse and grainy. Is there a way to
> >get smooth-looking fog like mist without pumping the sampling
> >rate to, say, 500 or something ?
> >
> >
> >Best,
> >
> >    S.
> >
> >----------------------------------------------------------
> >Steven Pigeon                     Ph. D. Student.
> >University of Montreal.
> >pig### [at] iroumontrealca           Topics: data compression,
> >pig### [at] jspumontrealca          signal processing,
> >ste### [at] researchattcom           non stationnary signals
> >                                  and wavelets.
> >----------------------------------------------------------
> >         http://www.iro.umontreal.ca/~pigeon
> >
> >

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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Bob Hughes wrote in message <370FC807.D9F96872@aol.com>...
>I would say lose the scattering altogether, nothing but noise from it in
>a open scene (non-container media) from what I've seen; try 'emission'
>(absorption too if necessary) instead. Those other parameters don't need
>to be so fine either execpt maybe upping the intervals (opposite of Kens
>suggestion? Okay, so I'm different).
>



I also have to agree with Bob - scattering is not necessery for basic media
use - it just sounds tempting in the docs. Stick to emission and absorbtion,
leave sampling at the defaults and up intervals to something decent - I tend
to use about 20 - 30 for final renders and about 10 for test renders.

See my post "intervals vs samples" in this thread for my best guess as to
why intervals are more important than samples, but basically samples control
the accuracy of a media, whereas intervals control the detail quality.

Post a reply to this message

Margus Ramst <mar### [at] peakeduee> wrote in message news:370f8245.0@news.povray.org...
> Hmm, these settings _should_ give a rather smooth media. I think min_samples
> could be dropped quite a bit, actually. You could try lowering variance to
> 1/256. Sometimes (I'm not sure, under what conditions) media looks very
> grainy when the light_source is nearly anti-parallel to the camera. Have you
> tried some mega-high sampling rate and does that solve the problem?
> Like Ken suggests, the extinction should be lowered for fog (or any media
> whose particles have a high albedo); 0.1 seems a bit extreme, though.
> Dunno...

Well, I'm far from expert in these matters, but to get a light fog type effect, I use
the
following:

{
intervals 40
samples 5, 15
scattering { 1, 0.05 extinction 0}
}

leaving all other settings at their defaults. I find that using anything other than
extinction 0 ( in an uncontained media ) doesn't allow the background / sky_sphere etc
to
show.

But then again, what do I know? ;-)

----------------------
Andy
------------------------------------------------------------------------------------------
-
--The Home Of Lunaland--
--visit my POV-Ray gallery--
--listen to my music--
www.acocker.freeserve.co.uk

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