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September 2006
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2006.09.15 17:54 "Re: alpha in Grayscale or Palette", by Bob Friesenhahn
On Fri, 15 Sep 2006, Grissom, Ed wrote: > > 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 ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/