ADAPTIVE ENTROPY ENCODING/DECODING

摘要

The blocks of coefficients are divided into a plurality of zones best fitting the energy distribution of the transform. The coefficients in these zones are then group into triplets comprising of run, level and next symbols. The run symbol indicates the number of consecutive zero coefficients prior to the non-zero coefficients in the scanning order. The level indicates the value of the non-zero coefficient. The next symbol indicates the state of the zone. Each zone has a plurality of states. These states are classified based on the subsequent coefficients in the scan. A separate table is designed for the entropy coding of the triplets in each of the state. Depending on the state of the zone, the appropriate table to use for the variable length coding of the next triplet. Since the state of the zone prior to the decoding of the first triplet is unknown, it is necessary to insert into the bitstream a symbol that indicates the initial state of the zones, which is the Initial State Pattern. The Initial State Pattern indicates the state and the table to be used for the decoding of the first triplet in each zone.