Image encoding/decoding method and recording medium therefor

A video encoding method, comprising:

• obtaining an intra predicted block of a current block by performing intra prediction for the current block;
• obtaining an inter predicted block of the current block by performing inter prediction for the current block;
• obtaining a residual block of the current block;
• and
• encoding information on a prediction mode of the current block, the prediction mode being determined as one of the intra prediction and the inter prediction,
• wherein in response to the prediction mode of the current block being the inter prediction, the method further comprises:
• determining which of a merge mode and a motion vector prediction mode is applied to the current block;
• and
• in response to the motion vector prediction mode being applied to the current block, encoding, into a bitstream, an inter prediction indicator for the current block, the inter prediction indicator indicating whether a uni-directional or bi-directional inter prediction is applied to the current block,
• wherein in response to the bi-directional inter prediction being applied to the current block, the inter predicted block is obtained based on a weighted sum of an L0 inter prediction block and an L1 inter prediction block, the L0 inter prediction block being obtained from an L0 reference picture based on an L0 motion vector of the current block, the L1 inter prediction block being obtained from an L1 reference picture based on an L1 motion vector of the current block,
• wherein an L0 motion vector difference is derived by subtracting an L0 motion vector candidate from the L0 motion vector,
• wherein an L0 motion vector candidate index specifying the L0 motion vector candidate from an L0 motion vector candidate list is encoded,
• wherein an L1 motion vector difference is derived by subtracting an L1 motion vector candidate from the L1 motion vector,
• wherein an L1 motion vector candidate index specifying the L1 motion vector candidate from an L1 motion vector candidate list is encoded,
• wherein the weighted sum is performed by applying a first weighting factor to the L0 inter prediction block and applying a second weighting factor to the L1 inter prediction block,
• wherein index information, which is used to determine the first weighting factor and the second weighting factor at a decoder side, are encoded into the bitstream,
• wherein the index information is encoded into the bitstream only when the inter prediction indicator of the current block is encoded with a value indicating that the bi-directional inter prediction is applied to the current block,
• wherein motion vector difference information is explicitly encoded only for the L0 motion vector difference but is not explicitly encoded for the L1 motion vector difference,
• wherein the index information specifies a weighting factor set candidate which corresponds to a pair of the first weighting factor and the second weighting factor, and
• wherein a plurality of pre-defined weighting factor set candidates comprise a candidate in which at least one of the first weighting factor and the second weighting factor is a negative value.

A non-transitory recording medium storing a bit stream generated by a video encoding method, wherein the method includes:

• obtaining an intra predicted block of a current block by performing intra prediction for the current block;
• obtaining an inter predicted block of the current block by performing inter prediction for the current block;
• obtaining a residual block of the current block;
• and
• encoding information on a prediction mode of the current block, the prediction mode being determined as one of the intra prediction and the inter prediction,
• wherein in response to the prediction mode of the current block being the inter prediction, the method further comprises:
• determining which of a merge mode and a motion vector prediction mode is applied to the current block;
• and
• in response to the motion vector prediction mode being applied to the current block, encoding, into a bitstream, an inter prediction indicator for the current block, the inter prediction indicator indicating whether a uni-directional or bi-directional inter prediction is applied to the current block,
• wherein in response to the bi-directional inter prediction being applied to the current block, the inter predicted block is obtained based on a weighted sum of an L0 inter prediction block and an L1 inter prediction block, the L0 inter prediction block being obtained from an L0 reference picture based on an L0 motion vector of the current block, the L1 inter prediction block being obtained from an L1 reference picture based on an L1 motion vector of the current block,
• wherein an L0 motion vector difference is derived by subtracting an L0 motion vector candidate from the L0 motion vector,
• wherein an L0 motion vector candidate index specifying the L0 motion vector candidate from an L0 motion vector candidate list is encoded,
• wherein an L1 motion vector difference is derived by subtracting an L1 motion vector candidate from the L1 motion vector,
• wherein an L1 motion vector candidate index specifying the L1 motion vector candidate from an L1 motion vector candidate list is encoded,
• wherein the weighted sum is performed by applying a first weighting factor to the L0 inter prediction block and applying a second weighting factor to the L1 inter prediction block,
• wherein index information, which is used to determine the first weighting factor and the second weighting factor at a decoder side, are encoded into the bitstream,
• wherein the index information is encoded into the bitstream only when the inter prediction indicator of the current block is encoded with a value indicating that the bi-directional inter prediction is applied to the current block,
• wherein motion vector difference information is explicitly encoded only for the L0 motion vector difference but is not explicitly encoded for the L1 motion vector difference,
• wherein the index information specifies a weighting factor set candidate which corresponds to a pair of the first weighting factor and the second weighting factor, and
• wherein a plurality of pre-defined weighting factor set candidates comprise a candidate in which at least one of the first weighting factor and the second weighting factor is a negative value.