Digital Image Processing by Means of Generalized Scale-Invariant Filters

A 2-D linear system is said to be a generalized scale-invariant filter if its weighting function is such that the effect of a scale change of the input image is merely a (generally different) scale change of the output. This property cannot be satisfied by shift-invariant systems. After a discussion on the use of such filters in the framework of scale-independent pattern recognition, the most general class of generalized scale-invariant shift-variant 2-D systems is presented and two different implementation techniques are described, one based on the use of the Mellin transform and the other one exploiting suitable coordinate transformations in conjunction with linear shift-invariant systems.