Abstract

Image addition and subtraction in real time are very useful techniques for image processing, permitting the compilation of composite images from a number of separate inputs via addition, and correction or modification of images via subtraction. The time constant associated with photorefractive materials that dictates the time required to write and erase holographic gratings can be used to integrate or accumulate image information that is written into the crystal. By multiplexing the desired number of inputs to a photorefractive device such as the double phase conjugate mirror or a two-beam coupling configuration, multiple images can be combined as the photorefractive BaTiO₃ crystal integrates the information by constructive interference in the holographic gratings that are formed. Similarly, image subtraction can be achieved by introducing a π phase shift¹ between multiplexed inputs to create a destructive interference condition that selectively erases image information. (Earlier information is erased by the new inputs to the crystal.)

© 1987 Optical Society of America