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 of the input image and a Fourier magnitude of the input modified by the nonlinearity. For compression types of nonlinearity, 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 nonlinearity on the enhanced images. Analytical expressions for the enhanced images obtained by the nonlinear technique 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 and that it provides much better light efficiency when compared with the block spatial filtering technique.
© 1990 Optical Society of America
Bahram Javidi, Jack Ruiz, and Carol Ruiz, "Image enhancement by nonlinear signal processing," Appl. Opt. 29, 4812-4818 (1990)