Hideo Kuroda

An Interframe Coding System for Video Teleconferencing Signal Transmission at a 1.5 Mbit/s Rate

This paper describes the interframe coding system (TRIDEC 1.5) used for NTSC color television signal transmission at a 1.5 Mbit/s rate. TRIDEC 1.5 is developed with the intention of making video teleconferencing service more economical. The system utilizes the following highly efficient coding techniques: 1) interframe combinational difference coding 2) temporal subsample coding 3) noise reduction 4) demand refreshing to protect against channel errors, which makes periodic forced refreshing unnecessary. In addition, new coding parameter control methods have been devised to prevent buffer memory overflow. The subjective evaluation test results make it clear that the encoded picture quality is good enough for teleconferencing use.

Transmitting 4-MHz TV Signals by Combinational Difference Coding

An interframe coding system is described which is capable of transmitting both 4-MHz videotelephone signals and NTSC color TV signals at an average rate of 6.312 Mbits/s. The coding system takes as much advantage as possible of in-frame correlation, in addition to interframe correlation, by coding pel-to-pel difference of interframe difference (combinational difference). Variable-length word coding is effectively used to reduce the number of bits to be transmitted. In order to prevent buffer overflow, luminance and spatial resolutions are controlled. To control luminance resolution, interframe difference is multiplied by a coefficient \alpha \leq 1 , so that value approaches zero when violent motion causes the buffer to fill. Though multiplication with small α results in temporal resolution reduction in moving areas, quality degradation is not too marked. Spatial resolution control is achieved by using subsample and subline coding modes.

Uncovered Background Prediction in Interframe Coding

Various interframe coding methods have been devised to reduce the cost of television signal transmission. Some degradation still remains, however, because prediction efficiency is lowered in uncovered background areas which appear behind moving objects. This paper proposes an uncovered background predictive coding algorithm, which increases prediction efficiency. Prediction efficiency is evaluated by using a simple signal model and real television signals. Experimental results show that the information generation rate is reduced to 78 percent as compared to that of previous frame predictive coding when the displacement is 10 pels/frame.