-posterize: near white colors replaced by green/brown
Posted: 2010-12-26T12:25:59-07:00
-posterize with more than 40 levels replaces near white colors with wrong colors.
$ convert -size 32x128 gradient: -posterize 32 test0.png
test0.png is correct. The bug doesn't affect posterizing to 32 levels.
$ convert -size 32x128 gradient: -posterize 64 test1.png
In test1.png the near white colors are replaced by green and brown tints.
$ convert -size 32x128 gradient:red-black -posterize 64 test2.png
test2.png is correct. This image doesn't contain light colors.
$ convert -size 32x128 gradient:white-red -posterize 64 test3.png
Again the near white colors turn green and brown.
$ convert magick:logo -posterize 64 test4.png
The white background on the logo and the beard turn brown, with green in the near-white regions.
$convert -version
Version: ImageMagick 6.6.6-7 2010-12-26 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP
$ convert -size 32x128 gradient: -posterize 32 test0.png
test0.png is correct. The bug doesn't affect posterizing to 32 levels.
$ convert -size 32x128 gradient: -posterize 64 test1.png
In test1.png the near white colors are replaced by green and brown tints.
$ convert -size 32x128 gradient:red-black -posterize 64 test2.png
test2.png is correct. This image doesn't contain light colors.
$ convert -size 32x128 gradient:white-red -posterize 64 test3.png
Again the near white colors turn green and brown.
$ convert magick:logo -posterize 64 test4.png
The white background on the logo and the beard turn brown, with green in the near-white regions.
$convert -version
Version: ImageMagick 6.6.6-7 2010-12-26 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP