Method and apparatus for encoding/decoding a video signal based on weighted prediction, and a recording medium storing a bitstream

Abstract

An image decoding method and apparatus according to the present disclosure may determine an inter prediction mode of a current block, derive motion information of a current block according to the inter prediction mode, obtain a first prediction block of the current block based on the motion information, and obtain a second prediction block of the current block by applying at least one of a weight, an offset, or a first variable for explicit weighted prediction to the first prediction block.

1 . A method of decoding an image, comprising:
 determining an inter prediction mode of a current block;   deriving motion information of the current block according to the determined inter prediction mode;   obtaining a first prediction block of the current block based on the derived motion information; and   obtaining a second prediction block of the current block by applying at least one of a weight, an offset, or a first variable for explicit weighted prediction to the first prediction block,   wherein the weight and the offset are derived based on weighted prediction information for the explicit weighted prediction,   wherein the weighted prediction information includes at least one of common weight information, weight number information, a first flag indicating whether a weight exists, weight delta information, or offset information, and   wherein the first variable is a variable derived based on the common weight information.   
     
     
         2 . The method of  claim 1 , wherein the current block performs only one of L0 prediction or L1 prediction. 
     
     
         3 . The method of  claim 2 , wherein obtaining the second prediction block of the current block is performed without considering whether the first variable is less than a predetermined threshold value. 
     
     
         4 . The method of  claim 3 , wherein whether the explicit weighted prediction is applied is determined based on at least one of a predetermined second flag or a weight index for default weighted prediction, and
 wherein the second flag is set based on a slice type of a slice to which the current block belongs.   
     
     
         5 . The method of  claim 4 , wherein when the slice to which the current block belongs is a P slice, the second flag is set as a value of a flag specifying whether the explicit weighted prediction is applied to the P slice, and
 wherein when the slice to which the current block belongs is a B slice, the second flag is set based on at least one of a third flag specifying whether the explicit weighted prediction is applied to the B slice or a fourth flag specifying whether a mode for improving a pre-derived motion vector in an image decoding apparatus is applied.   
     
     
         6 . The method of  claim 5 , wherein a value of the fourth flag is determined by considering at least one of the inter prediction mode of the current block, whether bi-prediction is applied to the current block, a location/type of a reference picture of the current block, the weight index for the default weighted prediction, whether the reference picture of the current block has a weight for the explicit weighted prediction or a size of the current block. 
     
     
         7 . The method of  claim 6 , wherein the weight index for the default weighted prediction is information specifying any one of a plurality of weight candidates pre-defined in the image decoding apparatus, and
 wherein the plurality of weight candidates include at least one of {4, 4}, {3, 5}, {5, 3}, {−2, 10}, or {10, −2}.   
     
     
         8 . A method of encoding an image, comprising:
 determining an inter prediction mode of a current block; and   deriving motion information of the current block according to the determined inter prediction mode,   wherein a first prediction block of the current block is obtained based on the derived motion information,   wherein a second prediction block of the current block is obtained by applying at least one of a weight, an offset, or a first variable for explicit weighted prediction to the first prediction block,   wherein weighted prediction information for the explicit weighted prediction is encoded based on the weight and the offset,   wherein the weighted prediction information includes at least one of common weight information, weight number information, a first flag indicating whether a weight exists, weight delta information, or offset information, and   wherein the first variable is a variable derived based on the common weight information.   
     
     
         9 . The method of  claim 8 , wherein the current block performs only one of L0 prediction or L1 prediction. 
     
     
         10 . The method of  claim 9 , wherein obtaining the second prediction block of the current block is performed without considering whether the first variable is less than a predetermined threshold value. 
     
     
         11 . The method of  claim 10 , wherein whether the explicit weighted prediction is applied is determined based on at least one of a predetermined second flag or a weight index for default weighted prediction, and
 wherein the second flag is set based on a slice type of a slice to which the current block belongs.   
     
     
         12 . The method of  claim 11 , wherein when the slice to which the current block belongs is a P slice, the second flag is set as a value of a flag specifying whether the explicit weighted prediction is applied to the P slice, and
 wherein when the slice to which the current block belongs is a B slice, the second flag is set based on at least one of a third flag specifying whether the explicit weighted prediction is applied to the B slice or a fourth flag specifying whether a mode for improving a pre-derived motion vector in an image decoding apparatus is applied.   
     
     
         13 . The method of  claim 12 , wherein a value of the fourth flag is determined by considering at least one of the inter prediction mode of the current block, whether bi-prediction is applied to the current block, a location/type of a reference picture of the current block, the weight index for the default weighted prediction, whether the reference picture of the current block has a weight for the explicit weighted prediction or a size of the current block. 
     
     
         14 . The method of  claim 13 , wherein the weight index for the default weighted prediction is information specifying any one of a plurality of weight candidates pre-defined in the image decoding apparatus, and
 wherein the plurality of weight candidates include at least one of {4, 4}, {3, 5}, {5, 3}, {−2, 10}, or {10, −2}.   
     
     
         15 . A non-transitory computer-readable medium for storing data associated with an image signal, comprising:
 a data stream encoded by an encoding method,   wherein the encoding method comprises:   determining an inter prediction mode of a current block; and   deriving motion information of the current block according to the determined inter prediction mode,   wherein a first prediction block of the current block is obtained based on the derived motion information,   wherein a second prediction block of the current block is obtained by applying at least one of a weight, an offset, or a first variable for explicit weighted prediction to the first prediction block,   wherein weighted prediction information for the explicit weighted prediction is encoded based on the weight and the offset,   wherein the weighted prediction information includes at least one of common weight information, weight number information, a first flag indicating whether a weight exists, weight delta information, or offset information, and   wherein the first variable is a variable derived based on the common weight information.