Imagemagick >= 6.8.9-10

Imagemagick < 6.8.9-10

Fixes memory management w/ PixelIterator (im >= 6.8.9)

Fixes memory management w/ PixelIterator (im < 6.8.9)

Memory Management (ImageMagick >= 6.8.9)

Memory Management (Imagemagick < 6.8.9)

ImageMagick support: >= 6.8.9

ImageMagick support: >= 6.8.9

ImageMagick support: < 6.8.9

Update README regarding version compat.