To: bug### [at] povrayorg
From: Christoph Hormann <chr### [at] gmxde>
-----------------------------------------------------------------

Rendering certain scenes with alpha channel output (+UA) leads to 
incorrect results in POV-Ray 3.6.1.

The source of the problem is the function Compensate_For_Alpha_AA() in
renderio.cpp which does not handle color values larger than 1.0
properly.

A minimal test scene can be found in:

-------- Original Message --------
Subject: Problem with option +ua
Date: Tue, 11 Jan 2005 22:27:25 +0100
From: Nicolas Rougier <non### [at] nonefr>
Newsgroups: povray.binaries.images



Hi Guys,

I'm trying to re-make an old scene with a transparent background and
after trying different things, I realised that I was not getting the
same output depending on the use of the +ua option or not. I attached
a
minimal scene with the two images.

Do you get the same ? Is it the expected behaviour ? And if so, what
is
the explanation please ?


Nico


// povray +Iscene.pov +fn      +oscene.png
// povray +Iscene.pov +fn +ua  +oscene-ua.png

camera {
    location  <0,0,-3>
    look_at  0
    direction 1.5*z
    right     x*image_width/image_height
}

#macro Glow(Color)
    media {
      emission 1
      density {
        spherical
        poly_wave 5
        density_map {
          [0 rgb 0]
          [1 rgb Color]
        }
      }
      method 3
    }
#end


box {-10, 10 hollow}

sphere {
    0, 1
    hollow on
    pigment {rgbt 1}
    interior {Glow(<1.0, 0.1, 0.2>*44)}
}


Christoph

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