Combining Intraframe and Frame-to-Frame Coding for Television

Abstract

A method of frame-to-frame coding is proposed in which the changes from one frame to the next are first detected and then transmitted as an intraframe coded signal rather than as frame-to-frame differences. A coder was constructed to test the proposal using DPCM for the intraframe encoding. Three aspects of the coder design presented particular problems. They were: (i) Movement detection (as a result of the increase in frame-to-frame noise caused by the intraframe coding). (ii) Smooth reduction of bit-rate and picture quality so as to take advantage of the reduction in spatial quality that a viewer tolerates when areas are moving fast. (iii) Control strategy for linking the operation of the buffer, the movement detector, and the operating state of the coder. The coder gave good picture quality at a transmission rate of 1.5 megabits per second (0.75 bit per picture element), except in extreme situations where the moving area covered almost the entire screen. The performance is described in detail at bit rates of 2.0, 1.5, and 0.5 megabits per second. The experimental coder has a number of desirable properties from an overall systems point of view when compared with transmission of frame differences. These include high tolerance to transmission errors and small frame storage requirements.