"Peter J. Holzer" wrote:
> 
> On Fri, 29 Sep 2000 19:24:45 +0200, Vahur Krouverk wrote:
> >Why not use "associated alpha" approach instead, which is used in
> >RenderMan (R) renderers (shaders actually): it premultiplies opacity
> >with color and outputs "dimmed" colors.
> 
> This is exactly what povray does with a black background, if I
> understood the discussion correctly. The problem is that this is wrong
> for PNG files, which require non-premultiplied RGB values (See RFC 2083,
> Sections 2.4 and 12.8).
> 

In this case I've lost point... Due to lack of time I read messages
"diagonally" and probably missed this description. Next time I try to
spend more time reading before jumping in.
Thanks for the clearance about PNG files, I've tried to search
information, how alpha is used in various formats but found only
information about TIFF format (it supports both associated and
unassociated alphas). Does anyone know, is TGA used with masking
transparency or associated alpha? (I guess that first is used)

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