Gmagick

In WordPress 3.5 all of the GD functionality has been abstracted out and with that power Imagick has been including to WordPress 3.5 too. Gmagick needs to wait a little bit more but with this plugin you can already use it.

If you want to know a little bit more about the changes you can look at:
* https://make.wordpress.org/core/2012/12/06/wp_image_editor-is-incoming/
* http://markoheijnen.com/wordpress-new-image-manipulation/
* http://www.slideshare.net/markoheijnen/image-manipulation-in-wordpress-35