Coherent deblurring techniques

Abstract

Experimental realization of Fourier plane filters for use in a coherent optical deblurring system for pictures affected hy space­ invariant blurs is discussed. Linear motion blur and defocusing are the two types of blurs considered. A method of developing phase­ inverting filters as diffraction gratings is given. The amplitude filters to go with the phase-inverting filters are developed as density variations on photographic films. The results of deblurring both linear motion blurred objects and out-of-focus pictures are presented and the degree of deblurring achieved is discussed. It is found that increasing the noise tenn in the amplitude filter results in loss of resolution in the deblurred output. Linear motion blurred object is then processed with an 'amplitude only' filter after subjecting the input object to a further blur of the same nature and amount as the original blur. Deblurring filters are also developed as binary holograms and the deblurred outputs presented and discussed. Loss of resolution in the output due to coarse amplitude quantization levels in a binary hologram filter is reduced by splitting the amplitude part of the filter into two halves and having only one of the halves encoded in the binary hologram filter while the other is produced as a photographic density variation. A simple optical method of enhancing the space-bandwidth product of the binary hologram filters helps to reduce plotting costs while processing large objects.