The results of a feasibility study of some new methods for reducing the bandwidth required for transmission of commercial-quality television are described in this thesis. It is shown that television requires a wide transmission bandwidth because of the broad frequency spectrum obtained in scanning scenes which contain abrupt changes of brightness at edges. An efficient method of coding these edges is therefore sought. The properties of the Gabor-type hologram are studied and it is shown that holograms may be used advantageously to code the picture edge information. A two-channel system is proposed and its construction and testing described. The low-frequency information is transmitted in conventional form on one channel and the high-frequency information in hologram form on the other channel. The test results support the theoretical prediction that the system can transmit television pictures with reduced bandwidth. However, the system is shown to have practical disadvantages largely caused by the necessity of making electro-optical conversions which cannot be performed in real time. In one of the alternative systems proposed here, a reduced bandwidth is made possible by transmitting the low-frequency information conventionally, and the edge pattern is scanned in a vertical direction to transmit the high frequencies. In a practical test, the system gave a bandwidth compression ratio of 6:1. As a basis for another possible system it is shown that because the edge pattern of typical pictures occupies only a small fraction of the raster area and exhibits a high degree of spatial correlation, bandwidth compression could be achieved by transmitting only this edge information. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Call number: LD2668 .T4 1951 B83 / Master of Science

Call number: LD2668 .T4 1950 F85 / Master of Science

Optical signal processing is introduced as a tool for investigations in the field of television compression research. An optical signal processing system is designed, which performs the Fourier transform of a picture signal F[B(x,y)] and its reconstruction F⁻¹ {F [B(x,y)]} . Some basic optical filtering experiments are performed in the spatial frequency plane, and the optical analogue of the frequency sampling theorem is demonstrated. The Fourier transforms of test pattern pictures show large gaps which can be used for compression. Observation of complex spectra of continuous tone pictures is found to be impaired by noise effects. A physiological experiment is carried out, which investigates the relationship between tolerable flicker frequency and spatial frequency of a television picture. It is found that the tolerable flicker rate f decreases as the spatial frequency fx is increased, according to the empirical equation fc = fo exp(-kfx). fo and k are parameters depending on factors like contrast ratio, kind and size of picture, etc. Compression systems using the above results are found to have a limit of obtainable compression ratio of approximately 3 to 1. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Thesis (M.Sc.)--Chinese University of Hong Kong. / Bibliography: leaves 84-86.

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Jack Capon. / "May 25, 1955." "This report is based on a thesis submitted to the Department of Electrical Engineering, M.I.T., ... for the degree of Master of Science." / Bibliography: p. 53. / Army Signal Corps Contract DA36-039 sc-42607 Project 102B Dept. of the Army Project 3-99-10-022

R.D. Stuart ... [et al.]. / "July 6, 1953." / Bibliography: p. 10. / Army Signal Corps Contract No. DA36-039 sc-100 Project No. 8-102B-0 Dept. of the Army Project No. 3-99-10-022