Invariance properties of integral transforms of images

In this paper previous results on invariance coding are extended in two ways: 1) by proving that there exists a formal relation between the kernel of an integral transform "invariant in the strong sense" and the eigenfunctions of the operator of the transformation 2) by showing that necessary and sufficient conditions for invariance with respect to one-parameter Lie transformation groups can hold for a class of two-parameters transformation groups, and by providing a procedure to compute an integral transform "invariant in the strong sense" with respect to these transformations.