Patent ID: 9686552
Date: 2017-06-20
CPC Classifications: H04N

Claim:
1. A decoding method for decoding a B frame on a block-by-block basis by adaptively switching between frame decoding and field decoding, the decoding method comprising: obtaining, from a bit stream, a first maximum number of first frame indices and a second maximum number of second frame indices, the first maximum number indicating a maximum number of the first frame index for frame decoding and the second maximum number indicating a maximum number of the second frame index for frame decoding; obtaining, from the bit stream, first commands and second commands, the first commands indicating correspondence between the first frame indices and first reference frames, each of the first frame indices being an index for designating the first reference frame for a current block to be decoded and the second commands indicating correspondence between the second frame indices and second reference frames, each of the second frame indices being an index for designating the second reference frame for the current block to be decoded; determining a maximum number of first field indices for field decoding to be double a value of the first maximum number of the first frame indices, and determining a maximum number of second field indices for field decoding to be double a value of the second maximum number of the second frame indices; adaptively switching, on a block-by-block basis, between frame decoding and field decoding; extracting, from the bit stream, a first reference index and a second reference index for the current block to be decoded; (i) specifying a first reference frame corresponding to the extracted first reference index and a second reference frame corresponding to the extracted second reference index when frame decoding is performed for the current block to be decoded, the first and second reference frames being referred to when the current block is decoded through motion compensation using frame decoding, and (ii) specifying a first reference field corresponding to the extracted first reference index and a second reference field corresponding to the extracted second reference index when field decoding is performed for the current block to be decoded, the first and second reference fields being referred to when the current block is decoded through motion compensation using field decoding; and decoding a prediction error for the current block to be decoded to obtain a recovered current block, wherein said specifying of a first reference field corresponding to the extracted first reference index and a second reference field corresponding to the extracted second reference index includes: