Abstract: Disclosed is a digital image compression and decompression method and apparatus for dividing a supplied digital image signal into blocks of predetermined size, performing variable-length coding of the signal, separating the signal with respect to principle information and remaining information, and controlling the record format so that each type of information is alternately recorded on a recording medium in an equal interval whenever recording the compressed information and decompressing the information, according to the reverse order, during decoding. Also, the function for extracting an activity in two steps during coding and then controlling the permitted number of bits of the variable length coding is provided. Accordingly, the coding efficiency is improved and the circuitry is simplified so that the price of the end product can be lowered.

Abstract: A fixed bit rate compression encoding method for dividing a two-dimensional video signal into DCT blocks and encoding the transform coefficients of each DCT block at a certain compression rate. The DC coefficient of each DCT block is scalar-quantized by l bits, each DCT block is classified into m classes according to its edge direction, AC coefficients of the classified DCT blocks are approximated to n representative vectors set for each class and are vector-scalar-quantized by p-bit indices of each representative vector, and the number B of encoding bits per block is generated at a fixed bit rate according to the expression: B=l+log.sub.2 m+n.times.p.