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2005.03.11 15:36 "unassociated v associated alpha", by Chris Losinger

just curious...

in tif_getimage.c, the putRGBUAcontig8bittile function (8-bit packed 
samples => RGBA w/ unassociated alpha) appears to be treating the alpha 
data as if it's been pre-multiplied:

...
    a = pp[3];
    r = (pp[0] * a) / 255;
    g = (pp[1] * a) / 255;
    b = (pp[2] * a) / 255;
    *cp++ = PACK4(r,g,b,a);
...

while the putRGBAAcontig8bittile function (8-bit packed samples => RGBA w/ 
associated alpha) simply copies the pixel data to the output, without doing 
any alpha calculations.

are these reversed ? seems to me you'd want to multiply the "associated" 
data, but copy the "unassociated" data.

or, am I confused... ? :)

-c
__________________________
Chris Losinger
Smaller Animals Software, Inc.				
http://www.smalleranimals.com