UBC Theses and Dissertations
Some television bandwidth-compression systems using edge coding Farr, Peter
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.