UBC Theses and Dissertations
Video bandwidth compression using hologram technique Akhtar, Sayed Amin-u-Daulah
This thesis is part of a feasibility study concerned with the application of the Gabor Hologram to a proposed method of bandwidth compression of television (video) signals obtainable by scanning a restricted class of two tone pictures: the experimental work consists of producing and improving on the Gabor type Holograms and demonstrating the reconstruction. The proposed television system will employ two channels. One channel would be used to transmit the signal obtained by scanning the picture normally; the bandwidth allowed for this channel, though, would be much less than the normal bandwidth: the other channel of equally reduced bandwidth would be used to transmit the signal obtained, again by normal scanning, from the Hologram. At the receiver, optical superposition of the two pictures obtained from the two channels would be made. For a certain restricted class of two tone pictures the distortion produced at the receiver by this method of picture transmission is anticipated to be negligible. The Fourier transform property of the Hologram is specially developed in order to complement the two channel television system. Considering the transform point of view it has been shown theoretically that the reconstruction lens suggested by Gabor is not necessary for the two step imaging process and a lensless system has been developed. It is demonstrated that better quality results can be obtained by using the modified process. In the experimental setup a positive lens necessary to widen the laser beam is used. The effect of the noisy Airy rings created by this lens is studied and a pinhole method of removing the noise has been suggested and its effectiveness demonstrated experimentally. Finally some examples of two step imaging using the modified lensless system are given. The detailed account of the experimental work is given to facilitate future work.
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