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.

An interframe coding system is described which is capable of transmitting a 4-MHz National Television System Commission (NTSC) color television signal. 6.3 Mbit/s transmission gives acceptable picture quality for video telephone or conference TV use. The NTSC color television signal is converted into a timedivision multiplex (TDM) signal which is composed of time-compressed chrominance and luminance signal in sequence. This signal is encoded using a frame-difference coder of the kind that has been used for black-and-white television signals. A field-repeating technique is introduced into the coder, to prevent a buffer memory from overflowing and to improve picture quality. Statistical investigations show that the presence of the timecompressed chrominance signal gives less than 10 percent increase in the amount of information generated by picture movements; this increase scarcely affects the picture quality.

Edge busyness in delta modulation (AM) is analyzed theoretically and a method of reducing edge busyness is presented. By assuming a simple model for quantizing error waveforms, a theoretical signal-to-edge noise ratio is derived as a function of signal slope. It is shown that more than 10-dB edge-busyness reduction can be achieved by limiting input signal slope to about 80 percent of the\DeltaMoverload slope prior to\DeltaM. The performance is verified through computer simulation and experimentation.

A digital differential pulse-code modulation (DPCM) codec based on ΔM/DPCM and DPCM/ΔM digital conversions is presented as an equivalent replacement of a conventional DPCM codec for TV signals by using digital processing technology. A generalized model and equivalent circuit are shown for the digital DPCM codec, and transfer characteristics and quantizing noises are analyzed. The digital DPCM codec is designed for 1-MHz TV signals and the performance is verified by experiments. By the use of double integration ΔM and digital filter technology, it is shown that at the ΔM sampling rate of 16 MHz the overall SNR performance is sufficiently good for use as a conventional DPCM codec, and the digital code converters can be realized with commercially available transistor-transistor-logic (TTL) medium-scale-integrated (MSI) circuits and low-power emitter-coupled-logic (ECL) integrated circuits (IC's).