I haven't tried ImageScience yet, but it is possible to use ImageMagick without RMagick. MiniMagick is one option but if you only need simple operations, you can do it directly in your code. See http://atomgiant.com/2007/01/22/dead-simple-image-processing-with-imagemagick/ as a starting point and ImageMagick commands documentation for further possibilities...
-- bobes
