When rendering the following scene, I don't understand the results:

If I use "media_interaction on" in the light_source, I got a red touch 
on the image (as expected due to the red scattering media).

Whereas if I use "media_interaction off", I got a blue touch on the 
image. Where does this blue come from? I'd expect the image to look like 
no media was present at all when using "media_interaction off" on the 
only light_source in the scene (as scattering media only works when 
light is shining on it).

Here's the scene:
<POV>
sphere {
     0,1 hollow
     pigment { uv_mapping checker rgb 0 rgb 1 scale 0.01  }
     interior {
         media {
             scattering { 1,rgb <1,0,0> }
             density { rgb 1 }
         }
     }
}
camera { location 0 look_at -z }
light_source { 0, rgb 1 media_interaction off }
</POV>

Thanks for your help,
Florian

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Scattering media also filters the scenery behind it. Thus, red scattering
media will filter red and you get a soft blue/cyan touch. That'd be my
explanation for it. Try "extinction 0" in the scattering-block (but I'm not
too sure about that, its just a quick first thought).

-- 
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>
Email: tim.nikias (@) nolights.de

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	Well, scattering media also absorbs the light coming from behind it. So
my guess is that the bule is one of your white checkers as seen once the
red has been scattered out of the way of the camera.

		Jerome

Florian Brucker wrote:
| When rendering the following scene, I don't understand the results:
|
| If I use "media_interaction on" in the light_source, I got a red touch
| on the image (as expected due to the red scattering media).
|
| Whereas if I use "media_interaction off", I got a blue touch on the
| image. Where does this blue come from? I'd expect the image to look like
| no media was present at all when using "media_interaction off" on the
| only light_source in the scene (as scattering media only works when
| light is shining on it).
|
| Here's the scene:
| <POV>
| sphere {
|     0,1 hollow
|     pigment { uv_mapping checker rgb 0 rgb 1 scale 0.01  }
|     interior {
|         media {
|             scattering { 1,rgb <1,0,0> }
|             density { rgb 1 }
|         }
|     }
| }
| camera { location 0 look_at -z }
| light_source { 0, rgb 1 media_interaction off }
| </POV>
|
| Thanks for your help,
| Florian
|
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>     Well, scattering media also absorbs the light coming from behind it. So
> my guess is that the bule is one of your white checkers as seen once the
> red has been scattered out of the way of the camera.

You're both right. Here's the text from the docs:
"The scattering effect is only visible when light is shining on the 
media from a light source. [...] In addition to reflecting light, a 
scattering media also absorbs light like an absorption media."

I just missed this last sentence when reading the docs :(

And Tim's tip (extinction 0) does work like a charm :)

Thanks for your help,
Florian

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