This extension works best with GraphicsMagick version 1.4+ and PHP 5.1.3+. Gmagick should work with earlier versions up to GraphicsMagick 1.2.6 but some features and formats are not supported for these versions. Windows version of GraphicsMagick is available from the GraphicsMagick website. To read about the difference between ImageMagick and GraphicsMagick, check this out: » FAQ .
Note: The official name of this extension is gmagick.
For Windows, the build of the Gmagick extension is available » here