Image enhancement by nonlinear techniques in the Fourier domain
Bahram Javidi · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1990
We present a nonlinear joint transform processor that can perform image enhancement. Image enhancement results are obtained for different degrees of nonlinearity applied to the joint power spectrum. The first order harmonic term at the output plane produces the enhanced image which has the exact Fourier phase information of the input image and a Fourier magnitude of the input modified by the nonlinearity. For compression types of nonlinearities the thresholding will redistribute the energy in the Fourier magnitude of the image by increasing the magnitude of the higher spatial frequencies. Thus the fine details of the image that are contained in the high spatial frequencies of the joint power spectrum are enhanced. We investigate the effects of various types of nonlinearities on the enhanced images. Analytical expressions for the enhanced images obtained by the nonlinear techniques will be provided. Computer simulations of the nonlinear processor for image enhancement are presented to study the performance of the system. We show that the nonlinear technique produces reasonably good results. II.