METHOD AND APPARATUS FOR ENCODING A DIGITAL IMAGE SIGNAL

摘要

A digital image signal is encoded for recording by placing in a sync block approximately an integer number of macro blocks representing orthogonally transformed image data for a certain portion of the image. When a sync block is reproduced at high speed, the reproduced data therein corresponds to a displayable portion of the image including DC components and both low and high frequency AC components. Also, each sync block contains fixed length areas for the orthogonal transform coefficient data according to the 4:1:1 (or 4:2:0) format in which four blocks of luminance coefficients and two blocks of color difference coefficients represent a certain portion of an image, and also contains at least one fixed length overflow area for the high frequency coefficients which exceed the capacity of the fixed length coefficient areas. An error in the low frequency coefficients in the fixed length areas does not harm the high frequency coefficients since they are in separately addressed areas. Before a set of macro blocks is compressed into variable length encoded data, with the amount of encoded data for each set being kept within a target value so as to fit into fixed length recording tracks, the macro blocks are shuffled so that the central portions of an image are at the beginning of the set for reducing the noticeability of errors in a reproduced image.