Warp schrieb:
>   IIRC, POV-Ray 3.5 mishandled alpha transparency against the background
> in that with antialiased edges and semi-transparent surfaces it blended
> the surface's color with the background color and then saved the resulting
> color with an alpha value. This caused object borders to have a pixel-wide
> halo of the wrong shade, and especially semi-transparent surfaces would have
> the wrong color.
> 
>   This was fixed in POV-Ray 3.6, where it's calculated correctly (iow. the
> background color has no effect on the pixel colors when using +UA).
> 
>   Last time I checked (it has been some time, though), the same problem had
> resurfaced in POV-Ray 3.7 beta. Someone had undone the fix in POV-Ray 3.6.
> 
>   Has this been corrected already?

No, apparently not - I just took the time to test it.

That means POV-Ray 3.7 /is/ actually doin' it plain wrong, as this 
behavior effectively constitutes writing premultiplied alpha. I don't 
know about TGA, but the PNG file format is explicitly specified to use 
/non/-premultiplied alpha. Which, when viewed with some piece of 
software that totally ignores the alpha channel, may look like crap for 
some scenes (e.g. a glass sphere on an opaque plane), but that's how the 
file format is specified.

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