Contrast enhancement of underwater images with coherent optical image processors.

The use of coherent optical processors for improving the quality of degraded underwater images is discussed, and a holographic filter suitable for the enhancement of contrast in underwater images is described. The filter is a modified matched spatial filter, and it performs a nonlinear local contrast enhancement. The theory of the operation of the coherent optical image processor with this new filter is presented and experimentally verified. The removal of the backscattered light from underwater images is demonstrated under laboratory conditions. The results show an improvement in the overall image contrast.