AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2006.09.15 12:38 "[Tiff] is there alpha component present in Grayscale or Palette color image", by Anurag Singh
2006.09.15 15:49 "Re: [Tiff] is there alpha component present in Grayscale or Palettecolor image", by Gerben Vos
2006.09.15 17:37 "Re: [Tiff] is there alpha component present in Grayscale or Palettecolor image", by Bob Friesenhahn
2006.09.15 17:46 "RE: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Grissom, Ed
2006.09.15 17:54 "RE: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Bob Friesenhahn
2006.09.16 09:58 "Re: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Anurag Singh
2006.09.18 11:23 "Re: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Gerben Vos
2006.09.16 20:01 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolor image", by Joris Van Damme
2006.09.16 20:47 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolor image", by Bob Friesenhahn
2006.09.16 21:50 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.16 22:00 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Toby Thain
2006.09.16 22:18 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.16 22:20 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Toby Thain
2006.09.16 22:38 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.17 02:07 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Graeme Gill
2006.09.17 08:49 "Re: [Tiff] is there alpha component presentin GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.17 09:03 "Re: [Tiff] is there alpha component presentin GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.17 10:39 "Re: [Tiff] is there alpha component presentin GrayscaleorPalettecolorimage", by Graeme Gill
2006.09.17 17:23 "Re: [Tiff] is there alphacomponent presentin GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.18 01:35 "Re: [Tiff] is there alphacomponent presentin GrayscaleorPalettecolorimage", by Graeme Gill
2006.09.18 09:40 "Re: [Tiff] isthere alphacomponent presentin GrayscaleorPalettecolorimage", by Joris Van Damme
2006.09.18 14:39 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Gerben Vos
2006.09.18 11:06 "Re: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Gerben Vos

2006.09.15 17:46 "RE: [Tiff] is there alpha component present in Grayscale orPalettecolor image", by Grissom, Ed

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.

Transparency and especially translucency are not always tied to the color of a pixel (which would be the effect of the extra column in the colortable), rather, it is often tied to position in the image (i.e. vignettes around the edges)

In that case, the advice for palette images would be the same as your advice for the greyscale images.

--
ed grissom
ed.grissom@intergraph.com

-----Original Message-----

From: tiff-bounces@lists.maptools.org [mailto:tiff-bounces@lists.maptools.org] On Behalf Of Gerben Vos

Subject: Re: [Tiff] is there alpha component present in Grayscale orPalettecolor image

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.