The Grails part is straight forward as documented. As for the Windows environment make sure that you have the jmagick.dll in your <JDK>/jre/bin directory and the jmagick.jar in the <JDK>/jre/lib directory. Also make sure that the core_rl_magick_.dll is installed on your system. You can do so by downloading and installing an ImageMagick version that contains the dlls, e.g. ImageMagick-6.3.9-0-Q16-windows-dll.exe.