Large image dimension causes slow dithering
Posted: 2017-05-01T07:52:08-07:00
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:
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
real 0m11.681s
user 0m8.664s ←
sys 0m0.056s
$ time convert test32768.ppm test.pbm
real 0m36.347s
user 0m32.996s ←
sys 0m0.068s
$ time convert test32768.ppm +dither test.pbm
real 0m0.087s
user 0m0.020s ←
sys 0m0.012s
$ convert -version
Version: ImageMagick 7.0.5-5 Q16 x86_64 2017-05-01 http://www.imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenMP
Delegates (built-in): jng jpeg png zlib