Am 08.05.2010 12:38, schrieb Warp:

>    The image on the left uses no alpha channel, and it's just a gradient
> from black to white, going through green. The image on the right uses
> alpha channel and goes from opaque black to transparent green.
>
>    There is no visible difference. You can't even tell where the border
> between the two images is.

(1) Yes, we can - see attched screenshot from IE8. It is not easy to 
distinguish, but it is there (measure in photoshop if you can't see it). 
With a gradient from fully-opaque green to fully-transparency green the 
effect would be more pronounced and thus a bit better visible.

(2) Try again with assumed_gamma=1.0, which does give you the proper 
mixing of colors in POV-Ray, and you /will/ see.

What happened in your test images is that the gamma issues almost (but 
not quite) canceled out the effect of the premultiplied alpha.

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