POV-Ray : Newsgroups : povray.beta-test : Problem scattering media (beta4) and error in the documentation : Problem scattering media (beta4) and error in the documentation Server Time: 27 Mar 2017 08:27:20 GMT
  Problem scattering media (beta4) and error in the documentation  
From: Warp
Date: 7 May 2005 11:07:15
There's a problem with scattering media in pov3.7beta4.

  Try the following scene with pov3.6. The shadow of the cylinder
is basically perfect.
  Try it with pov3.7beta4. The shadow is full of sampling artifacts.
Also the media looks darker.

-------8<-------8<-------8<-------8<-------8<-------8<-------8<-------
background { rgb 1 }
camera { location <3,4,-5>*.8 look_at 0 angle 35 }
light_source { <20,40,10>, 1 }
box
{ <-1.5,-1.01,-1.5>, <1.5,-1.2,1.5>
  pigment { checker rgb .75, rgb .25 scale .2 }
}

box
{ -1,1 pigment { rgbt 1 } hollow
  interior
  { media
    { scattering { 1, .5 }
    }
  }
}
cylinder
{ <.9,-1,.7>, <.9,.9,.7>, .5
  pigment { rgb <1,.9,.7> }
}
-------8<-------8<-------8<-------8<-------8<-------8<-------8<-------


  The documentation gives some default values for scattering media.
I was wondering if it was the source of the problem (ie. pov3.7beta
using different default values than pov3.6). The mentioned default
values are the following:

      samples 1,1
      intervals 10
      aa_level 4 aa_threshold 0.1
      variance 1/128 confidence .9
      method 3

  However, it soon became clear that those are *not* the default values
for scattering media in pov3.6. If I add them to the media block in
the example code above, the rendering time (with pov3.6 at 640x480 +a +am2)
increases from 13s to 1m 21s.
  If I render the same scene (ie. with those values explicitly added) with
pov3.7beta4 the rendering time is equivalent and the image looks about
equal (except that the media is a bit darker).

  The actual default values used by pov3.6 are excellent because they
give high-quality scattering media very fast. However, the documentation
lists at least some of them wrongly. I think that pov3.7 should use these
same default values and the documentation should be updated.

  Making some tests it seems that the documentation has mixed the
default intervals value with the default min and max samples value.
If specify these values, the rendering time with pov3.6 keeps the
same (ie. about 13s) and the image looks the same:

      samples 10,10
      intervals 1
      aa_level 4 aa_threshold 0.1
      variance 1/128 confidence .9
      method 3

  However, if I render that with pov3.7beta4 the artifacts are still
there (and the render time is 24s).

  So it may be that pov3.7beta4 is using the same default values
as pov3.6 but the artifacts are caused by something else.

-- 
                                                          - Warp


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