2008.04.17 21:48 "Re: [Tiff] a question about creating transparency of the image in TIFF", by Bob Friesenhahn

There are 2 types of alpha in TIFF: associated (transparency) and unassociated (undefined extra channels).

Also, the TIFF spec. states that images with associated alpha (transparency) must be premultiplied.

The TIFF specification does not prevent a colormapped file with transparency but the colors in the colormap would then need to be premultiplied, which could be a challenge to surmount. As a result, no one does this.

Popular software like Photoshop does not place any interpretation on unassociated alpha, so such channels are just "extra" channels that only a Photoshop expert could figure out.

Bob
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Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/