Option cast to CGBitmap info to avoid Xcode 5 warning
See: http://stackoverflow.com/questions/18831179/cgbitmapcontextcreate-method-causes-compiler-warning-xcode-5-not-xcode-4
and: http://stackoverflow.com/questions/18921703/implicit-conversion-from-enumeration-type-enum-cgimagealphainfo-to-different-e