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September 2006
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2006.09.15 17:37 "Re: alpha in Grayscale or Palette", by Bob Friesenhahn
On Fri, 15 Sep 2006, Gerben Vos wrote: > Anurag Singh wrote: > > I'm trying to handle tiff images with alpha component, so i want to > > know that any tiff image which is Grayscale or Palette color can have > > alpha component. > > It is possible for greyscale, just use the ExtraSamples tag as defined > in section 18 of the TIFF spec. It is not possible for palette images; > the ColorMap tag uses a fixed format with exactly three values per > entry. I would not go so far as to say it is not possible to have an alpha channel with a Palette-based image. It does seem to be quite possible, albeit rather inconvenient/senseless if associated alpha is used. I don't recall if I have ever written such an image and I have certainly never seen one in the real world. It is correct that the color Palette itself can not contain the alpha information. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/