Method and device of coding a digital video signal for reproduction of pictures with a high quality even upon occurrence of a drastical change between the pictures

摘要

On subjecting a digital video signal representative of successive pictures to predictive coding by using correlation between two successive pictures, an estimated result is derived from the digital video signal to represent a degree of correlation between a current picture and a previous picture and is increased with a reduction of the degree. When the estimated result becomes greater than a predetermined threshold value as a result of a drastical change, such as a scene change, from the previous picture to the current picture, a control signal is produced. Furthermore, the digital video signal is separated into a preceding signal part ending at the previous picture and a succeeding part which begins at the current picture. The control signal controls the predictive coding so that the succeeding part be coded with an area of predictive coding of each picture gradually widened with time. The control signal may be supplied to a predictive coder. Alternatively, the control signal may be used to control a frame memory for supplying the digital video signal to the predictive coder with the area gradually widened for the succeeding part. A plurality of threshold levels may be used collectively as the predetermined threshold. The threshold levels are for use in selecting a rate of gradually widening the area.