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

An image decoding apparatus comprising:

• an entropy decoding unit for receiving an encoded bit stream of a current picture to be decoded and entropy decoding the encoded bit stream of the current picture;
• a first motion vector recovering unit for recovering a first motion vector from the current picture to a first decoding reference picture based on the entropy decoded bit stream of the current picture, the first decoding reference picture being different from the current picture;
• a second motion vector calculating unit for calculating a second motion vector from the current picture to a second decoding reference picture by scaling the first motion vector based on a first temporal distance between the current picture and the first decoding reference picture and a second temporal distance between the current picture and the second decoding reference picture, the calculated motion vector being used for inter prediction of a current block belonging to the current picture, the second decoding reference picture being different from the first decoding reference picture;
• a motion compensating unit for generating a prediction block relating to the current block in the current picture, based on the second motion vector;
• a residual data decoding unit for generating a residual block relating to the current block through a residual data decoding process based on the entropy decoded bit stream;
• and
• a current block recovering unit for recovering the current block based on the prediction block and the residual block,
• wherein the residual data decoding unit performs inverse-quantization for entropy decoded transform coefficients to generate the residual block.