Patent ID: 6741747
Filing Date: 2004-05-25
Classification: H04N

Abstract:
Data compression apparatus for compressing an input data unit to produce an output data unit in accordance with a desired data quantity of said output data unit, the degree of compression applied by said apparatus being determined by a compression control variable having a range of possible values;said apparatus comprising: (i) a trial encoder for compressing successive sections of said input data unit in accordance with a trial group of two or more values of said compression control variable, said trial group being a subset of the range of possible values of said compression control variable; (ii) a data quantity detector for detecting the trial data quantities generated by each trial encoding of said sections of said input data unit and for selecting a base compression control variable applicable to said input data unit on the basis of said detected trial data quantities, in order to comply with the desired data quantity; and (iii) an allocator for allocating a compression control variable for use in final-encoding each section of said input data unit to generate said output data unit, said allocator being operable to determine whether to use said base compression control variable or another possible value of said compression control variable for a current section by a comparison between (a) the increase in data quantity determined for compression of the current section using a next less harsh compression value from said trial group; and (b) the maximum possible increase in data quantity, while still complying with said desired data quantity, over that obtained if the remainder of said input data unit were compressed using said base compression control variable.