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From: Andreas Leitgeb <avl@logic.at>
Newsgroups: comp.lang.tcl
Subject: Re: is there an image package that doesn't require Tk ?
Date: Sun, 30 Jun 2024 16:58:00 -0000 (UTC)
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Andreas Leitgeb <avl@logic.at> wrote:
> Andreas Leitgeb <avl@logic.at> wrote:
>> I'd like it to open a .png file (screenshot from an android
>> phone) extract five rectangular regions from it, and convert
>> them to something similar to Tk's [$image data] - e.g. a list
>> of lists of colors
> Thanks to all who answered...
> Unfortunately, I haven't yet succeeded with any of the suggestions.

I didn't mean to make anyone "responsible" in any way for a suggestion
made - quite the opposite: I was happy for all suggestions.

In the end I went without tcl package, and merely invoke the 
imagemagick tool "convert" with a list of parameters such that
it writes out an uncompressed bmp3 in 16-colors (palette) mode,
which turned out pretty simple to parse from Tcl code (binary scan).

Given a "list-of-list-of-color", it is amazingly simple
to extract a sub-rectangle:

   proc rect {data x1 y1 x2 y2} {
      lmap row [lrange $data $y1 $y2] { lrange $row $x1 $x2 }
   }

Case closed ;-)