2006.09.15 17:54 "RE: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Bob Friesenhahn

Gerben -

For palette images, is an alpha channel explicitly forbidden by the spec

?

What I am thinking is an extra data plane, not an extra column in the color table.

Right. An interesting issue is that libtiff requires that all samples be the same size so Pallete images using a small bits per sample for the index impose the same bits per sample restriction on the alpha channel. For an 8 bits per sample image, this is not usually a restriction, but it becomes more so for 2 or 4 bits per sample.

Associated alpha makes no sense since Pallete entries are not related to pixel position but associated alpha is related to pixel position.

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