Introduced a cast(T) method into the ImageUtils template functor to allow code reading images to handle casting from source data to a form that a user can use more conviently

examples/osgvolume/osgvolume.cpp

@@ -132,7 +132,7 @@ struct ScaleOperator
     inline void rgba(float& r,float& g,float& b,float& a) const { r*= _scale; g*=_scale; b*=_scale; a*=_scale; }
 };
 
-struct RecordRowOperator
+struct RecordRowOperator : public osg::CastAndScaleToFloatOperation
 {
     RecordRowOperator(unsigned int num):_colours(num),_pos(0) {}