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List:       imagemagick-user
Subject:    Re: [magick-users] Problems flattening out an alpha channel
From:       Anthony Thyssen <anthony () griffith ! edu ! au>
Date:       2005-02-22 6:20:26
Message-ID: 200502220620.j1M6KQfD013840 () wumpus ! itc ! gu ! edu ! au
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Scott Tringali on  wrote...
| Hello,
| 
| I'm trying to convert a bunch of icons from png with full alpha channel, 
| to xpm (1-bit alpha).  But the default reduction of the alpha channel 
| leaves a bit to be desired.
| 
| I get better results, via gimp, if I do a Threshold Alpha of, say, 
| around 127.
| 
| Interestingly, I can get GIMP to behave identically to convert, by 
| setting a Threshold Alpha to 0.
| 
| But, I'd prefer to use "convert" so I can automate it a bit better.  Is 
| there a command line I can use to get identical results?
| 
| I can almost do it with -threshold on the opactiy argument, but I don't 
| see how to affect only the alpha channel.  No luck either with 
| "ordered-dither opacity".  Any ideas?
| 
See 'GIF Boolean Transparency'
   http://www.cit.gu.edu.au/~anthony/graphics/imagick6/formats/#trans

Specifically...

    convert a.png -channel A -threshold 50%   a_threshold.xpm

  Anthony Thyssen ( System Programmer )    <A.Thyssen@griffith.edu.au>
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       Sign on kite flying field --   ``Do not feed the trees''
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     Anthony's Home is his Castle     http://www.cit.gu.edu.au/~anthony/
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