Coherent optical image deblurring with computer generated fourier plane filters

Abstract

This thesis deals with the fabrication techniques of optical filters for use in a coherent optical processor for correcting images that are degraded by space-invariant blurs. In particular, techniques wherein one can utilize a digital computer are emphasized. The blurs considered are linear motion and out-of-focus blurs. Inverse filtering as well as Wiener filtering are studied for these blurs. The desired complex deblurring filters are realized in two ways: The first is by developing separately the phase and the amplitude filters and sandwiching them together, and the second is by developing the deblurring filters as computer-generated binary holograms. The phase filters are produced with the aid of a Calcomp plotter. The design criteria for an optimum performance of phase filters are discussed in detail. Amplitude filters for the linear motion blur were fabricated using a cylindrical lens imaging system and for the out-of-focus blur using a photomechanical method. The binary objects for these imaging systems were also realized with the help of the Calcomp plotter. The results obtained and the conclusions drawn are presented in the thesis. Double phase holograms (DPH), which are a type of computer-generated binary holograms, are studied and deblurring filters are fabricated as double phase holograms. Both the amplitude as well as the phase quantization errors in a DPH are analyzed and a way to reduce the amplitude quantization error in a DPH deblurring filter is suggested. A circular overflow correction, which has been previously used for Lohmann holograms, is applied to the DPHs so as to improve diffraction efficiency. The generated DPH filters are used to deblur motion-blurred objects in an optical deblurring experiment. The results are compared with the ones obtained with the Vasu-Rogers deblurring filter. If the original Hsueh-Sawchuk coding scheme with the circular overflow correction is implemented, it is found to result in a high quantization error in coding the phase, as compared to the Vasu-Rogers scheme. A suggestion to improve the performance of the DPH deblurring filter is given.