Re: Bug with B&W conversion

On Fri, 7 Jan 2011, Andrew Stonewall wrote:
> 
> "c:\Program Files\GraphicsMagick-1.3.12-Q16\gm.exe" convert -monochrome -format bmp original.bmp error.bmp
> 
> on the attached ZIP-ed BMP files you'll see that you get a blank image - these images have no compression or
> alpha channels - just plain 24-bit BMP.

Hmmm.  I am able to recreate this issue here.  This time I don't have 
an answer (yet) for why the issue occurs but it clearly has something 
to do with using the color reduction algorithm and some property of 
the input image.

This permutation works but only uses simple thresholding (key is to 
add +dither):

   gm convert original.bmp +dither -type bilevel crap.bmp

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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