An encoding technique called multilevel block truncation coding that preserves the spatial details in digital images while achieving a reasonable compression ratio is described. An adaptive quantizer-level allocation scheme which minimizes the maximum quantization error in each block and substantially reduces the computational complexity in the allocation of optimal quantization levels is introduced. A 3.2:1 compression can be achieved by the multilevel block truncation coding itself. The truncated, or requantized, data are further compressed in a second pass using combined predictive coding, entropy coding, and vector quantization. The second pass compression can be lossless or lossy. The total compression ratios are about 4.1:1 for lossless second-pass compression, and 6.2:1 for lossy second-pass compression. The subjective results of the coding algorithm are quite satisfactory, with no perceived visual degradation.>

A color-image data compression technique based on block truncation coding (BTC) is described. BTC is first implemented to encode a weighted trichromatic image. The bit map generated is then used to compress each of the R, G, and B signals separately, removing the intercolor correlations. The weighted trichromatic signal is generated by properly weighting R, G, and B signals so that the reconstructed R, G, and B signals have minimum mean square error (MSE). Another approach using a bit-wise majority rule on the R, G, and B BTC bit maps is also discussed. The algorithm preserves the spatial details in the image content and has low computational complexity. An 8:1 compression can be achieved.>

A hybrid BTC-VQ-DCT (block truncation coding, vector quantization, and discrete cosine transform) image coding algorithm is presented. The algorithm combines the simple computation and edge preservation properties of BTC and the high fidelity and high-compression ratio of adaptive DCT with the high-compression ratio and good subjective performance of VQ, and can be implemented with significantly lower coding delays than either VQ or DCT alone. The bit-map generated by BTC is decomposed into a set of vectors which are vector quantized. Since the space of the BTC bit-map is much smaller than that of the original 8-b image, a lookup-table-based VQ encoder has been designed to 'fast encode' the bit-map. Adaptive DCT coding using residual error feedback is implemented to encode the high-mean and low-mean subimages. The overall computational complexity of BTC-VQ-DCT coding is much less than either DCT and VQ, while the fidelity performance is competitive. The algorithm has strong edge-preserving ability because of the implementation of BTC as a precompress decimation. The total compression ratio is about 10:1.>

This paper presents a review of the distribution of broad-band visual signals in urban areas on cable television systems. Following a brief introduction, the early history of cable distribution in the U.S., U.K., and Canada is described. The architecture of wide-band visual distribution networks is presented, based on developments in Canadian cable systems which have formed the model for North American development. The present status of fiber optics in cable systems in reviewed. The paper concludes with a summary of probable development directions. The paper includes an extensive bibliography covering cable television.

Real-time processing of video waveforms has been implemented for the purpose of analyzing image dynamics. A digital preprocessor yields data sets that describe the difference between selected fields of an input video signal in both the spatial and temporal domains. Further reduction and analysis of the acquired data can provide several measures of image activity such as the frame-to-frame correlation, the frame-difference signal (FDS), and statistics of scene lengths. The results of a series of measurements of the dynamics of typical broadcast television programs are presented. It is demonstrated that image activity is separable into two distinct classes, one caused by image and camera movement, and the other by scene switches.

This paper describes a laboratory facility and the multidisciplinary research that has been carried out in it relevant to the application of communications technology in such areas as teleconferencing and education. This facility at Carelton University, Ottawa, Canada, provides multichannel multipoint audio and video communications, and information storage and control facilities to simulate a wide variety of uses. The research program, conducted by communication technologists, systems engineers, and social psychologists, is outlined and the results of a number of teleconferencing and educational experiments are presented. The forthcoming communications technology satellite (CTS) Stanford-Carleton Universities Curriculum-Sharing Experiment is described, as are the preparations for a project in the educational applications of communications technology.