Patent ID: 8204327

Claim:
A method of coding using a coding apparatus, the method comprising: for an ordered series of quantized transform coefficients of a block of image data, the ordering from low to high spatial frequency according to the transform, the series having a most likely-to-occur amplitude, and at least one other amplitude, including a next-to-most likely-to-occur amplitude, for a first region which could be the whole series: encoding the position of events in the first region that include one quantized coefficient having other than the most likely-to-occur amplitude or a cluster of at least one quantized coefficient having other than the most likely-to-occur amplitude, the encoding using a plurality of predetermined variable length code (VLC) mappings, including initially selecting an initial position VLC mapping, and later switching between position VLC mappings according to one or more position VLC selection criteria, including at least one context-based position VLC selection criterion; and if the position coding of the events leaves any amplitude values other than the most likely-to-occur amplitude to be encoded, encoding the amplitudes of the to-be-encoded amplitude values in the reverse order of the original ordering of the series or cluster of events includes a cluster, the encoding according to one of a plurality of pre-selected amplitude VLC mappings, including initially selecting an amplitude VLC mapping, and switching between the plurality of amplitude VLC mappings according to one or more amplitude VLC selection criteria, including at least one context-based amplitude VLC selection criterion, wherein by a context-based selection criterion is meant a criterion that during encoding is known or derivable from one or more previously encoded items of information.