On Mon, 23 Apr 2001 20:17:43 -0400, Lothar Esser wrote:
>Hi,
>
>  is there a way to keep the alpha value for a partially transparent
>object ?
>Regarding my earlier question, a transparent background color works
>well  together with the +UA switch but if any object
>has a transparency < 1.0 it will get the appropriately mixed color
>(object(s) + background color) and appears to have a final
>transparency of 0. 

I don't see this.  If I render this:

box {<-1,-1,0> <1,1,.01> pigment {rgbt <1,0,0,.5>} finish {ambient 1}}
camera {location -5*z look_at 0}

using command-line options +fn +ua, I get a PNG image with a red square
in it.  Loading that into Photoshop 6, I see that the red square has a
color of 191 (bad, because as you said that is mixed with the black 
background, which doesn't seem right) but a transparency of .5 (which
also probably isn't right, since it should represent the cumulative
transparency along the ray, or .25)  The latter problem will definitely
be fixed in 3.5, which will generate an image with a transparency
of .25, but the former problem, if it is a problem, appears unchanged
in the current development build.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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