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 Ed Grissom
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

2006.09.17 02:07 "Re: [Tiff] is there alpha component present in GrayscaleorPalettecolorimage", by Graeme Gill

challenge here is to somehow involve alpha in that scheme. Is RGBA (20,20,20,20) closest to RGBA (20,20,100,20), or is it closest to RGBA (20,20,20,100)? Put more generally, you need to weigh color difference against alpha difference, and it's not quite clear how to avoid making rather arbitrary weight decisions.

That doesn't seem that difficult. Assume the most sensitive situation (ie., against an opaque neutral background), and compute the RGB color that would result from that RGBA value. Convert color distance to a more visual metric if you like (L*a*b* maybe), and apply the usual color quantization algorithms in 4D, rather than 3D (I used to like the variance cut that I put in xli).

The main limitation would be that your palette may be rather small when measured against the 4D space you're trying to quantize, and the result may not be that visually appealing.

One trick that would help would be to scale the Alpha dimension so that it is quantized more coarsely, freeing up more palette entries for colors.

(This seems all rather similar to the types of things I do in arriving at an "optimal" CMYK test point set used for color profiling, the Alpha being analogous to K ....)

Graeme Gill.