Patent ID: 7742528
Filing Date: 2010-06-22
Classification: H03M,H04N

Abstract:
1. A decoding method for arithmetic decoding a bit stream which is obtained by arithmetic coding, on a block basis, coefficients of a two-dimensional array of frequency components in a predetermined scanning order starting at a high frequency component toward a low frequency component, the coefficients being generated by frequency transformation performed on picture data of a block which has a predetermined size of pixels, the decoding method comprising: an arithmetic decoding step of arithmetic decoding the bit stream into a first bit of binary data corresponding to each absolute value of the coefficients, on a block basis, according to a predetermined scanning order starting at a high frequency component toward a low frequency component by using a plurality of probability tables; and a switching step of switching between the plurality of probability tables, from a current probability table for the first bit of the binary data corresponding to a first coefficient to be decoded, to a new probability table for the first bit of the binary data corresponding to a second coefficient to be decoded, based on a result of a comparison between an absolute value of the first coefficient to be decoded and a predetermined threshold value, wherein, in the switching step, the switching between the plurality of probability tables is performed in a predetermined one direction within each block such that each of the probability tables, which has been used for performing arithmetic decoding on the first bit of the binary data corresponding to an already decoded coefficient before switching to the new probability table, is not used within each block after switching to the new probability table, and the switching is not performed in the direction opposite to the predetermined one direction regardless of said result of the comparison, and wherein, within each block, if a predetermined one of the plurality of probability tables has been used to perform arithmetic decoding, the switching between the plurality of probability tables is not performed regardless of said result of the comparison.