I just did a quick google through the newsgroups but couldn't find an answer 
to this. Here's a really simple scene, with fog turned off the cylinder 
appears solid black, because it's a black & transparent checker containing a 
dense black media. But with fog turned on the media parts become lighter 
*regardless of how dense the media is*.

fog {
 fog_type 1
 rgb x
 distance 3
}

background { rgb z }

cylinder {
 -y, y, .3
 translate z*2
 hollow on
 pigment {
  checker
  rgb 0,
  rgbt 1
  scale <.3,.3,100>
 }
 interior {
  media { //media so dense that without fog it looks identical to the opaque 
bits.
   absorption 1
   density { rgb 100 }
  }
 }
}

Try increasing the media density, you'll see it doesn't get any darker.

Is this a known bug with media & fog? Is there any solution? It's screwing 
up the smoke in my volcano image :(

-- 
Tek
http://evilsuperbrain.com

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And this time, with a picture (doh!)
You shouldn't be able to see those checks, and increasing the media density 
doesn't make them darker.

-- 
Tek
http://evilsuperbrain.com

"Tek" <tek### [at] evilsuperbraincom> wrote in message 
news:43f78692@news.povray.org...
>I just did a quick google through the newsgroups but couldn't find an 
>answer
> to this. Here's a really simple scene, with fog turned off the cylinder
> appears solid black, because it's a black & transparent checker containing 
> a
> dense black media. But with fog turned on the media parts become lighter
> *regardless of how dense the media is*.
>
> fog {
> fog_type 1
> rgb x
> distance 3
> }
>
> background { rgb z }
>
> cylinder {
> -y, y, .3
> translate z*2
> hollow on
> pigment {
>  checker
>  rgb 0,
>  rgbt 1
>  scale <.3,.3,100>
> }
> interior {
>  media { //media so dense that without fog it looks identical to the 
> opaque
> bits.
>   absorption 1
>   density { rgb 100 }
>  }
> }
> }
>
> Try increasing the media density, you'll see it doesn't get any darker.
>
> Is this a known bug with media & fog? Is there any solution? It's screwing
> up the smoke in my volcano image :(
>
> -- 
> Tek
> http://evilsuperbrain.com
>
>

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Attachments:
Download 'fog-media-bug-test.jpg' (11 KB)

Preview of image 'fog-media-bug-test.jpg'

No solution, but you have made me aware of a (possible) problem.
In my Alien Cliff scene, I have added a media for simulating the spray at
the base of the waterfall. The image is (still) rendering (off and on), but
I have the feeling that something similar to you is happening... Maybe there
is an incompatibility, indeed?

Thomas

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This is an image (like Tek's) showing what is happening when media and fog
interact.

The container is, however, hardly or not visible when in front or
intersecting a textured surface/object. In my Alien Cliff image, I cannot
see it against the cliff.

Thomas

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Attachments:
Download 'Media_mist_test.jpg' (20 KB)

Preview of image 'Media_mist_test.jpg'

"Thomas de Groot" <t.d### [at] internlnet> wrote in message 
news:43f970b9@news.povray.org...
> This is an image (like Tek's) showing what is happening when media and fog
> interact.
>
> The container is, however, hardly or not visible when in front or
> intersecting a textured surface/object. In my Alien Cliff image, I cannot
> see it against the cliff.

Transparent objects mixing with fog is an old issue. It could be remedied, 
somewhat, by increasing the transmit or filter value a little beyond 1.0. 
Unfortunately, now I can't remember if that is really a solution at all. If 
anything, an imperfect one probably. Wish I could say more about it with 
more assurance as to what or how it was dealt with in the past or in the 
current version(s).

The original question here is apparently more an issue of the fog being in 
front of the media container object. That 'distance 3' causes the camera to 
see that fog color between it and the cylinder, which is at <0,0,0> and 
<0,0,2> (less 0.3 radius) respectively.

Hope that is of some help.

Bob H

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"Bob Hughes" <omniverse@charter%net> wrote in message 
news:43f9a13a$1@news.povray.org...
> "Thomas de Groot" <t.d### [at] internlnet> wrote in message 
> news:43f970b9@news.povray.org...
>> This is an image (like Tek's) showing what is happening when media and 
>> fog
>> interact.
>>
>> The container is, however, hardly or not visible when in front or
>> intersecting a textured surface/object. In my Alien Cliff image, I cannot
>> see it against the cliff.
>
> Transparent objects mixing with fog is an old issue.

Hey Thomas, I tried a test render in both 3.6 and the latest beta of 3.7 
just to make sure I was on the right track about my reply to you. The media 
container is invisible amid fog, also not seen in ground type, so I'm 
wondering if you could have rendered that from version 3.5 or something 
other than POV for Windows which I am using here. Just wasn't sure with 
absolute certainty if that had changed in the later versions.

Anyway... I still think I was right about Tek's (AKA evil super brain) media 
container being obscured by the fog between the camera and cylinder. It 
could never be completely black with a red fog color there, right? Not 
unless the container object surface is next to the camera, or the camera 
within it.  ;)

Bob H

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"Bob Hughes" <omniverse@charter%net> schreef in bericht
news:43f9c077$1@news.povray.org...
>
> Hey Thomas, I tried a test render in both 3.6 and the latest beta of 3.7
> just to make sure I was on the right track about my reply to you. The
media
> container is invisible amid fog, also not seen in ground type, so I'm
> wondering if you could have rendered that from version 3.5 or something
> other than POV for Windows which I am using here. Just wasn't sure with
> absolute certainty if that had changed in the later versions.
>
I used MegaPOV 1.21 (which uses 3.6.1) for Windows.

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Perhaps I should include the used code:

The fogs:
fog {
  fog_type   2
  distance   15
  color      rgb 0.6 // gray
  fog_offset 0.05   // below this level the fog is constant
  fog_alt    0.29   // halving distance
  turbulence 1
}

fog {
  fog_type   2
  distance   800
  color      rgb <0.8, 0.8, 0.8>
  fog_offset 0.1   // below this level the fog is constant
  fog_alt    15.00   // halving distance
  turbulence 0.1
}

And the media:
#declare Scattering =
sphere {
  0, 10
  texture {
    pigment { rgbt 1 }
  }
  interior {
    media {
      samples 10, 100
      scattering {1, <0.9, 0.9, 0.9, 0.0, 0.9> extinction 3} // higher
extinction = more transparant media
      intervals 1
      density {
        spherical
        poly_wave 5
        scale 2
        warp { turbulence <T,T/2,T/1> }
        scale 2
        warp { turbulence <T,T/2,T/2> }
        scale 2
        warp { turbulence <T,T/2,T/3> }
        scale 2
        warp { turbulence <T,T/2,T/4> }
      }
      scale 0.3*exp(pow(T,0.5))/(1+T)
    }
  }
  hollow
  scale <1,1,1>
}

object {Scattering
  scale <0.3, 0.6, 0.3>
  translate <1.75, 0, 2.0>
}

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Maybe an important issue:
I have used tone_mapping.inc, and then: Clip_Colors()  in the
global_sttings, for tone mapping for antialiasing like in version 3.5
(smoother transitions)

I shall test without this to see if there is a difference

Thomas

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Actually that's different to my problem, my media container is invisible but 
the smoke media from my volcano gets more fogged than the top of the volcano 
does at the same distance.

I've managed to work round the problem by an extremely elaborate means:

First, I tried using a global media instead of the fog, but that did exactly 
the same thing. So then I replaced it with a huge box of media in front of 
the camera, differenced with the smoke-media's container. And I added a copy 
of the air-media to the inside of the smoke media's container. All of this 
meant that pov finally got the message and gave me the result I was after, 
though it's a ludicrously elaborate work-round.

-- 
Tek
http://evilsuperbrain.com

"Thomas de Groot" <t.d### [at] internlnet> wrote in message 
news:43f970b9@news.povray.org...
> This is an image (like Tek's) showing what is happening when media and fog
> interact.
>
> The container is, however, hardly or not visible when in front or
> intersecting a textured surface/object. In my Alien Cliff image, I cannot
> see it against the cliff.
>
> Thomas
>
>
>

Post a reply to this message