Bi-prediction coding method and apparatus, bi-prediction decoding method and apparatus, and recording medium

A bi-prediction decoding method for decoding bi-prediction coded data by using a plurality of reference pictures, the method comprising the steps of:

• (a) determining whether or not a current block to be decoded is a bi-prediction coding mode by analyzing the coded data;
• (b) recovering a decoding target motion vector by decoding the coded data in a case where it is determined that the current block is the bi-prediction coding mode;
• (c) calculating a non-decoding target motion vector corresponding to a second reference picture based on the recovered decoding target motion vector, a temporal distance between a current picture to which the current block belongs and a first decoding reference picture corresponding to the decoding target motion vector and a temporal distance between the current picture and a second decoding reference picture;
• and
• (d) recovering the current block based on a generated prediction block by generating the prediction block for the current block based on the recovered decoding target motion vector and the calculated non-decoding target motion vector,
• wherein the decoding target motion vector, which is recovered by decoding the coded data, and the non-decoding target motion vector, which is calculated based on the decoding target motion vector, are related to the identical current block.

A bi-prediction coding apparatus using a plurality of reference pictures, the apparatus includes:

• a first motion vector selecting unit selecting first selected motion vectors corresponding to a plurality of first reference pictures within a predetermined motion search range based on a current block to be coded from the plurality of first reference pictures;
• a first motion vector calculating unit calculating first calculated motion vectors corresponding to the first selected motion vectors based on the first selected motion vectors and second reference pictures corresponding to the first selected motion vectors;
• a first coding cost calculating unit calculating first prediction coding costs corresponding to the first selected motion vectors based on the first selected motion vectors, the first calculated motion vectors, first selected motion prediction blocks corresponding to the first selected motion vectors, and first calculated motion prediction blocks corresponding to the first calculated motion vectors;
• a first coding cost choosing unit choosing first representative prediction coding cost that satisfies a predetermined condition by comparing the calculated plurality of first prediction coding costs corresponding to the first selected motion vectors with each other;
• a second motion vector selecting unit selecting second selected motion vectors corresponding to second reference pictures from the second reference pictures;
• a second motion vector calculating unit calculating the second selected motion vectors and second calculated motion vectors corresponding to the second selected motion vectors based on the first reference pictures corresponding to the second selected motion vectors;
• a second coding cost calculating unit calculating second prediction coding costs corresponding to the second selected motion vectors based on the second selected motion vectors, the second calculated motion vectors, second selected motion prediction blocks corresponding to the second selected motion vectors, and second calculated motion prediction blocks corresponding to the second calculated motion vectors;
• a second coding cost choosing unit choosing second representative prediction coding cost that satisfies a predetermined condition by comparing the calculated plurality of second prediction coding costs corresponding to the second selected motion vectors with each other;
• a motion vector choosing unit choosing any one of the first selected motion vectors corresponding to the first representative prediction coding cost as a coding target motion vector if the first representative prediction coding cost is smaller than the second representative prediction cost and any one of the second selected motion vectors corresponding to the second representative prediction coding cost as the coding target motion vector if the second representative prediction coding cost is smaller than the first representative prediction coding cost;
• and
• a motion vector coding unit coding the coding target motion vector,
• wherein the coding target motion vector, which is meant to be coded, and non-coding target motion vector, which is not meant to be coded, are calculated with respect to the identical current block.

A bi-prediction decoding apparatus for decoding bi-prediction coded data by using a plurality of reference pictures, the apparatus includes:

• an entropy decoding unit decoding the coded data;
• a decoding controlling unit determining whether or not a current block to be decoded is coded through a bi-prediction coding mode by analyzing the decoded data;
• a decoding target motion vector recovering unit recovering a decoding target motion vector from the decoded data if the current block is determined by the decoding controlling unit to be coded in the bi-prediction coding mode;
• a non-decoding target motion vector unit calculating a non-decoding target motion vector corresponding to a second reference picture based on the recovered decoding target motion vector, a temporal distance between a current picture to which the current block belongs to and a first reference picture corresponding to the decoding target motion vector and a temporal distance between the current picture and the second reference picture;
• a motion compensating unit generating at least one prediction block based on the recovered decoding target motion vector and the calculated non-decoding target motion vector;
• and
• a current block recovering unit recovering the current block based on the recovered data and the prediction block,
• wherein the decoding target motion vector, which is recovered by decoding the coded data, and the non-decoding target motion vector, which is calculated based on the decoding target motion vector, are related to the identical current block.