2005.03.10 10:46 "[Tiff] libtiff: Tiff Tag EXTRASAMPLES and TIFFRGBAImage",
by Daniel Sievers
Thread
2005.03.11 09:17 "[Tiff] Re: libtiff: Tiff Tag EXTRASAMPLES and TIFFRGBAImage", by Daniel Sievers
To make it more obvious why this seems strange:
In the code below, it is checked for extrasamples>1, but then the only item considered is sampleinfo[0].
For the case extrasamples==1 (the common case), img->alpha is never changed from the original initialization to 0. (Therefore later the alpha channel from the file is ignored.)
if (extrasamples > 1)
{
switch (sampleinfo[0]) {
case EXTRASAMPLE_UNSPECIFIED:
if (img->samplesperpixel > 3)
img->alpha = EXTRASAMPLE_ASSOCALPHA;
break;
case EXTRASAMPLE_ASSOCALPHA: /* data is pre-multiplied */
case EXTRASAMPLE_UNASSALPHA: /* data is not pre-multiplied */
img->alpha = sampleinfo[0];
break;
}
}