This paper proposes a DPCM algorithm to be deployed for broadcast quality transmission of composite NTSC color TV signal at DS-3 rate (45 Mb/s). Recently, many algorithms have been proposed for TV coding and most of them are based on orthogonal transform such as DCT. DCT is appropriate for high compression. On the other hand, DPCM is the best candidate for highest quality transmission, though it might need a comparatively high transmission rate. DPCM can be directly applied to composite NTSC signal without separation/synthesis of chrominance and luminance components before/after the compression. In case of cascaded connection, no accumulation of coding noise can be achieved unlike transform coding. It has been confirmed, using a complete codec running at DS-3 rate, that the proposed adaptive DPCM is very effective even for composite NTSC signals including the CCIR standard sequences. This adaptive DPCM contributes to rapid progress of a digital broadcast TV transmission network using a high speed medium such as SONET as well as DS- 3 service.

Entropy coding has been investigated for motion-compensated interframe (MC) prediction followed by two-dimensional discrete cosine transform (DCT) for prediction error. In particular, variable word length coding methods for motion vector and transform coefficients have been discussed assuming low bit rate such as 384 kbits/s for transmission of videoconference sequences. For motion vector information, it is advantageous to employ a one-dimensional code set common to both horizontal and vertical components of motion vectors. The code set can be obtained using a combined distribution of the two components. In order to encode transform coefficients, different methods are applied to significant and insignificant blocks. Run-length coding is adequate for representing clusters of insignificant blocks. In encoding transform coefficients in significant blocks, a zone coding method which encodes transform coefficients within a minimum area enclosing all nonzero coefficients is suitable. Simulation of video sequences shows that a combination of the coding methods described here can achieve high coding efficiency for videoconference sequences.

This paper proposes a new adaptive prediction algorithm which exclusively selects, on a pel-by-pel basis, either intraframe or motion-compensated interframe prediction. Prediction selection is made referencing previous samples, thus transmission of the selection information is not needed. Compared with motion-compensated interframe coding, it has been shown that coding performance is improved to a great extent, by about 40% for pictures with very fast motion, which is beyond motion compensation capability, and by 50% for scene change where motion compensation is, in principle, of no use.

This paper desribes an objective evaluation for coding performance of an interframe encoder (NETEC-22H). Also described is the coding performance improvement by an adaptive bit sharing multiplexer (ABS-MUX) in which transmission bit rate is dynamically allocated to several channels. Measurements made for actual broadcast TV programs over a time of 36 h show that an SNR of higher than 50 dB unweighted is obtained by this coding equipment for 99 percent of the time for broadcast TV programs at the transmission bit rate of 30 Mbits/s and for 93 percent of the time at 20 Mbits/s. The residual 1 percent at 30 Mbits/s or 7 percent at 20 Mbits/s is transmitted with a slightly lower SNR. The picture quality difference between the 20 and 30 Mbit/s transmission is about 6 dB in SNR on the average. It is also shown that a three-channel ABS-MUX (20 Mbits/s per channel on the average) reduces probability of coarse quantization by a factor of 5-10 compared with the fixed bit rate transmission at 20 Mbits/s.