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Abstract

The system encodes a high rate digital video signal conveying picture elements into a low rate digital signal conveying words representative of some picture elements. The system comprises a frame store, a movement detector for detecting the movement area in one frame with respect to the preceding frame, a predictor, a bit distributing circuit for selecting the picture elements to be transmitted, a PCM encoder which encodes the DPCM words of the selected elements according to a quantization law and an interpolating circuit. The number of bits NB allocated to each line in the low rate digital signal is made constant. The movement detector detects two ledge elements defining each line moving area and thereby deduces the maximum number NP and average number B of bits in the element words to be encoded and transmitted. The bit distributing circuit down-counts the bits which remain for allocation to the line and the element words which remain likely to be encoded and compares these down-count totals for selectively controlling the encoding of a moving area element word. A transmitted and encoded word represents the level number with respect to a quantization law associated with the line.

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First Claim