In article <3A2FAB0A.D4918A9A@peak.edu.ee>, Margus Ramst 
<mar### [at] peakeduee> wrote:

> Well, in MegaPOV the default gray_threshold is 0, which  in most 
> cases makes the radiosity lighting look too saturated IMHO. In 
> regular POV the default is 0.5, but perhaps people still set it too 
> low to make the rad effects more conspicuous.

I think gray_threshold 0 is supposed to be the most realistic, it is a 
way to artificially limit the saturation of the color blending in the 
image.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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Chris Huff wrote:
> 
> I think gray_threshold 0 is supposed to be the most realistic, it is a
> way to artificially limit the saturation of the color blending in the
> image.
> 

Perhaps, although it should also help counteract the effects of a limited number
of samples and recursion levels.
And for example radiosity lit "blue sky" outdoor scenes do tend to look
unrealistically blue IMO, so despite my limited knowledge of physics I must
assume there is some aspect of natural light behaviour not provided for here.

-- 
Margus Ramst

Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg
Home page http://www.hot.ee/margusrt

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Margus Ramst wrote:
> 
> And for example radiosity lit "blue sky" outdoor scenes do tend to look
> unrealistically blue IMO, so despite my limited knowledge of physics I must
> assume there is some aspect of natural light behaviour not provided for here.
> 

It's probably right that a blue sphere/sky_sphere is not a good physical
representation of a real sky.  NTL, don't forget that the sunlight is
usually far from being 'white' so there is some kind of compensation.  

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
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Margus Ramst wrote:

>And for example radiosity lit "blue sky" outdoor scenes do tend to look
>unrealistically blue IMO, so despite my limited knowledge of physics I
>must assume there is some aspect of natural light behaviour not
>provided for here. 
>

In the real world there is no direct "colour-bleeding" from the blue sky. 
It where nice if it was possible to switch off the lolour of the bleeding 
from the "sky_sphere" in POV.

Photorealism: these blue pictures look as if an outdoor scene was 
photographed with a film suitable for artificial light.


Ingo

-- 
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In article <3A3### [at] peakeduee>, Margus Ramst 
<mar### [at] peakeduee> wrote:

> Perhaps, although it should also help counteract the effects of a 
> limited number of samples and recursion levels.

This is true for some cases...


> And for example radiosity lit "blue sky" outdoor scenes do tend to look
> unrealistically blue IMO,

The human eye can compensate for color casts...try messing with the 
color temperature of your monitor, for example. At first it will look 
red or blue, but after a while it looks white again. POV doesn't do 
this, it simulates the effect of a "perfect" film camera. If someone did 
a post_process filter to simulate different types of film, you could set 
it up to use an outdoor film and lessen that effect while still using 
accurate radiosity settings.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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In article <Xns### [at] povrayorg>, ing### [at] homenl (ingo) 
wrote:

> In the real world there is no direct "colour-bleeding" from the blue sky. 

I believe you are mistaken...most of the illumination in the shade comes 
from scattered light. And things lit with sky light *do* have a blue 
cast, but your eyes usually adjust to it.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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On 10 Dec 2000 11:46:40 -0500, ingo wrote:
>Margus Ramst wrote:
>
>>And for example radiosity lit "blue sky" outdoor scenes do tend to look
>>unrealistically blue IMO, so despite my limited knowledge of physics I
>>must assume there is some aspect of natural light behaviour not
>>provided for here. 
>
>In the real world there is no direct "colour-bleeding" from the blue sky. 

There is, but see below:

>It where nice if it was possible to switch off the lolour of the bleeding 
>from the "sky_sphere" in POV.
>
>Photorealism: these blue pictures look as if an outdoor scene was 
>photographed with a film suitable for artificial light.

Exactly. Sunlight is a lot more blue (or less red) than artificial
light. The human eye adapts to these differences, but film - or povray -
cannot. Therefore you need different films for indoors and outdoors to
get lighting, which "looks right". Similarly, would need different
settings in povray to simulate the adaptation of the human eye to
different lighting.

	hp

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Chris Huff wrote:
> 
> In article <Xns### [at] povrayorg>, ing### [at] homenl (ingo)
> wrote:
> 
> > In the real world there is no direct "colour-bleeding" from the blue sky.
> 
> I believe you are mistaken...most of the illumination in the shade comes
> from scattered light. And things lit with sky light *do* have a blue
> cast, but your eyes usually adjust to it.

Agreed.  Look at shadows on fresh snow.

-- 
Francois Labreque | Rimmer: "Let's go to red alert!"
    flabreque     | Kryten: "Are you sure, Sir?  You realize it
        @         |          actually means changing the bulb!"
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Francois Labreque wrote:

>Look at shadows on fresh snow.

The snow in the shadows has a bluish tint, the rest of the snow is 
"white". The general lightning is white, due to atmospheric scattering the 
shadow is blue.
When radiosity rendering with a blue sky_sphere it is as if the light is 
blue. The snow and the shadow are blue.

This is why I stated: "In the real world there is no direct "colour-
bleeding" from the blue sky", probably needed to put more emphasis on 
"direct".



Ingo

-- 
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Margus Ramst <mar### [at] peakeduee> wrote:
: And for example radiosity lit "blue sky" outdoor scenes do tend to look
: unrealistically blue IMO

  That's probably because people tend to make their skies unrealistically
blue and bright.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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