Previous generalizations of the fractional Fourier transform to two di
mensions assumed separable kernels. We present a nonseparable definiti
on for the two-dimensional fractional Fourier transform that includes
the separable definition as a special case. Its digital and optical im
plementations are presented. The usefulness of the nonseparable transf
orm is justified with an image-restoration example. (C) 1998 Optical S
ociety of America.