Two-dimensional variable length coding of runs of zero and non-zero transform coefficients for image compression

A carrier medium carrying machine readable code including instructions for performing, when executed by a processor, a method for processing an ordered series of digital signals that each have an amplitude from a finite set of amplitudes consisting of the most likely-to-occur amplitude and at least one other amplitude, the processing to reduce the amount of data used to represent the digital signals and to form codewords such that the more likely-to-occur values or sequences of values of digital signals are represented by relatively short codewords and the less likely-to-occur values or sequences of values of digital signals are represented by relatively long codewords, the method comprising:

• for a first contiguous region in the series:
• identifying events that each includes a run of consecutive coefficients of the most likely-to-occur amplitude, preceding a run of one or more consecutive signals having any value other than the most likely-to-occur amplitude, including a run of no coefficients of the most likely-to-occur amplitude, preceding a run of one or more consecutive coefficients having other than the most likely-to-occur amplitude;
• for each identified event, jointly encoding the run lengths of the preceding run of the most likely-to-occur amplitude and the following run of other than the most likely-to-occur amplitude with a codeword, such that for at least some events, relatively more likely-to-occur pairs of runlengths are encoded by a shorter codeword than relatively less likely-to-occur runlengths;
• for each identified event, encoding each amplitude in the run of consecutive signals having other than the most likely-to-occur amplitude, the encoding according to an amplitude coding method,
• such that relatively short codewords are formed to represent values or sequences of values that are relatively more likely-to-occur, and relatively long codewords are formed to represent values or sequences of values that are relatively less likely-to-occur.

An apparatus for processing an ordered series of digital signals that each have an amplitude from a finite set of amplitudes consisting of the most likely-to-occur amplitude and at least one other amplitude, the processing to reduce the amount of data used to represent the digital signals and to form codewords such that the more likely-to-occur values or sequences of values of digital signals are represented by relatively short codewords and the less likely-to-occur values or sequences of values of digital signals are represented by relatively long codewords, the apparatus comprising:

• means for identifying events in a first contiguous region in the series, each event including a run of consecutive coefficients of the most Likely-to-occur amplitude, preceding a run of one or more consecutive signals having any value other than the most likely-to-occur amplitude, including a run of no coefficients of the most likely-to-occur amplitude, preceding a run of one or more consecutive coefficients having other than the most likely-to-occur amplitude;
• means for jointly encoding, for each identified event, the run lengths of the preceding run of the most likely-to-occur amplitude and the following run of other than the most likely-to-occur amplitude with a codeword, such that for at least some events, relatively more likely-to-occur pairs of runlengths are encoded by a shorter codeword than relatively less likely-to-occur runlengths;
• and
• means for encoding, for each identified event, each amplitude in the run of consecutive signals having other than the most likely-to-occur amplitude, the encoding according to an amplitude coding method,
• such that relatively short codewords are formed to represent values or sequences of values that are relatively more likely-to-occur, and relatively long codewords are formed to represent values or sequences of values that are relatively less likely-to-occur.

An apparatus including a processing system, the apparatus to accept an ordered series of digital signals that each have an amplitude from a finite set of amplitudes consisting of the most likely-to-occur amplitude and at least one other amplitude, the apparatus to perform a method for processing an ordered series of digital signals to reduce the amount of data used to represent the digital signals and to form codewords such that the more likely-to-occur values or sequences of values of digital signals are represented by relatively short codewords and the less likely-to-occur values or sequences of values of digital signals are represented by relatively long codewords, the method comprising:

• for a first contiguous region in the series:
• identifying events that each includes a run of consecutive coefficients of the most likely-to-occur amplitude, preceding a run of one or more consecutive signals having any value other than the most likely-to-occur amplitude, including a run of no coefficients of the most likely-to-occur amplitude, preceding a run of one or more consecutive coefficients having other than the most likely-to-occur amplitude;
• for each identified event, jointly encoding the run lengths of the preceding run of the most likely-to-occur amplitude and the following run of other than the most likely-to-occur amplitude with a codeword, such that for at least some events, relatively more likely-to-occur pairs of runlengths are encoded by a shorter codeword than relatively less likely-to-occur runlengths;
• for each identified event, encoding each amplitude in the run of consecutive signals having other than the most likely-to-occur amplitude, the encoding according to an amplitude coding method,
• such that relatively short codewords are formed to represent values or sequences of values that are relatively more likely-to-occur, and relatively long codewords are formed to represent values or sequences of values that are relatively less likely-to-occur.