[magick-users] Dithering in transparent GIFs

[Anthony Thyssen]

Che Burashka on  wrote...
| Hi,
| 
| I didn't realise I had to use ordered dither. It now
| works perfectly. Thanks!
| 
| Andrey.
| 
The latest IMs (v6.3) saw a major expansion to the order-dither function
that I spent a month working on to get right, and as a direct result of
a new technique developed in IM Examples.
  DIY Dither Patterns
    http://www.cit.gu.edu.au/~anthony/graphics/imagick6/quantize/#diy_dither

As a result of this...

You can list the available ordered dither threshold maps, and their
backward compatibility alias name...

   convert -list threshold

You can now define your own personal ordered dither maps!!!
For example a diagonal shadowing map for GIF...
  http://www.cit.gu.edu.au/~anthony/graphics/imagick6/quantize/#thresholds_xml

and you can use a posterized, or mathematical color table, for
generallized ordered dithering of images.

  http://www.cit.gu.edu.au/~anthony/graphics/imagick6/quantize/#od_posterize

For animations this type of dithering is much better than the error
correctly dithering, as it does not generate large areas of color
differences, for a small change (even a single pixel change) to an
image.  See

Error Correction Dithering problems...
  http://www.cit.gu.edu.au/~anthony/graphics/imagick6/quantize/#dither_error

I have not however gotten around to updating GIF animation pages with
this discussion and techniques as I am concentrating on some other
things.  As such GIF animation color optimizations are a little output
date now.

  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
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    If your going to have delusions, you might as well go for the
    really satisfying ones.                   -- Marcus, Babylon 5
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     Anthony's Home is his Castle     http://www.cit.gu.edu.au/~anthony/