COMPRESSION OF VIDEO SIGNALS

摘要

A digital video signal (component or composite) is compressed by spatial sub-bands filtering (12A or 12B) to form data sets constituting respective sub-bands (Fig.4) of the two-dimensional spatial frequency domain. The data sets for a field or frame of the signal are stored (28). A first sequencer (29A or 29B) controls writing, in accordance with a desired sequence, of the stored data to a quantiser (14-Fig.8) in which they are quantised in accordance with respective values (Fig.7), those values being such that the amount of quantisation of a data set constituting a sub-band to which dc luminance information of the signal is at least predominantly confined (and, in the case of a composite signal, also at least two of the data sets constituting sub-bands to which dc chrominance information of the signal is at least predominantly confined) is less than the average of the amounts of quantisation of the remaining data sets. The quantised data sets are then entropy encoded in an entropy encoder (16-Fig. 12) which has a first coding portion (64, 72) for coding quantised data representative of dc luminance information and a second coding portion (62) for coding quantised data representative of ac luminance information. A second sequencer (58), which may in fact be the same sequencer as the first sequencer (29A or 29B), controls the operation of the quantiser (14) so that each datum (sample) written thereto is appropriately quantised, and controls the operation of the entropy encoder (16) so that each quantised sample is directed to the appropriate one of the first (64, 72) and second (62) coding portions.