Patent ID: 7324699

Claim:
A method of decoding a bitstream that includes codewords, the method comprising: (a) determining a plurality of codewords from the bitstream, wherein the codewords are formed by a method of encoding an ordered series of quantized transform coefficients of an image block, each quantized transform coefficient having an amplitude from the amplitude set consisting a first subset of values and a second subset of values, the first subset of values including the most common amplitude and at least one other amplitude, the method to reduce the amount of data used to represent the digital quantized transform coefficients and to form the codewords of the bitstream, the method of encoding including: forming a codeword for each event of a set of events, each event being any preceding run of quantized transform coefficients having the most common amplitude followed by a run of one or more identical sequences of a predefined set of sequences, the case of no such preceding run of quantized transform coefficients having the most common amplitude being indicated by a preceding runlength of 0, each sequence in the predefined set of sequences being either a single quantized transform coefficient having an amplitude from the second subset of amplitudes or a sequence of one or more quantized transform coefficients each having amplitude from the first subset of amplitudes, starting with an amplitude other than the most common amplitude, and providing with the codewords information indicative of the sign of any amplitude other than the most common amplitude in the events, such that relatively short codewords represent events that are relatively more likely to occur, and relatively long codewords are formed to represent events that are relatively less likely to occur; (b) determining a respective event represented by each codeword; and (c) determining the sub-series of coefficients of each determined event until all coefficients in the block are determined, until all coefficients of a block of image data have been determined.