Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
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I think it's the dither operation that's very slow when I create certain images with one very large dimension. The time it takes seems to be exponential (correction: quadratic)
based on image's larger dimension, and jumps way up at each power of 2(?). Maybe there is a legitimate reason for this, but I'm reporting it because it seems wrong.
Steps to reproduce:
Code: Select all
$ convert logo: -resize '640x1!' -resize '32767x1!' test32767.ppm
$ convert logo: -resize '640x1!' -resize '32768x1!' test32768.ppm
$ time convert test32767.ppm test.pbm
user 0m8.664s ←
$ time convert test32768.ppm test.pbm
user 0m32.996s ←
$ time convert test32768.ppm +dither test.pbm
user 0m0.020s ←
$ convert -version
Version: ImageMagick 7.0.5-5 Q16 x86_64 2017-05-01 http://www.imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC
Features: Cipher DPC HDRI OpenMP
Delegates (built-in): jng jpeg png zlib
Last edited by Jason S
on 2017-05-02T07:30:15-07:00, edited 1 time in total.
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You may find that FloydSteinberg gives as good results as Riemersma, as is much faster.