Image encoding device, image decoding device, image encoding method, and image decoding method for generating a prediction image

An image decoding device comprising:

• a decoder for decoding coding mode information and an intra prediction parameter;
• and
• an intra predictor for, when the coding mode information associated with a coding block is an intra coding mode, carrying out an intra-frame prediction process on each block which is a unit for prediction of the coding block to generate a prediction image, wherein
• when the intra prediction parameter indicates an average prediction, the intra predictor carries out a filtering process on target pixels of the intra prediction located at an upper end and a left end of the block based on an intermediate prediction value, which is an average value of adjacent pixels of the block, and at least one adjacent pixel of the target pixel, and wherein
• the intra predictor sets a filter coefficient to ¾, associated with the intermediate prediction value for a target pixel at the left end of the block other than the target pixel at an upper left corner of the block, and sets a filter coefficient to ¼, associated with the adjacent pixel adjacent to the left side of the target pixel at the left end of the block.

An image encoding method comprising:

• carrying out an intra-frame prediction process on each block which is a unit for prediction of a coding block to generate a prediction image, when a coding mode corresponding to the coding block into which an inputted image is divided is an intra coding mode;
• and
• encoding coding mode information and an intra prediction parameter indicating an average prediction, wherein
• when the average prediction is carried out, a filtering process is carried out on target pixels of the intra prediction located at an upper end and a left end of the block which is a unit for prediction of the coding block, the filtering process using an intermediate prediction value, which is an average value of adjacent pixels of the block, and at least one adjacent pixel of the target pixel, and wherein
• the filtering process sets a filter coefficient to ¾, associated with the intermediate prediction value for a target pixel at the left end of the block other than the target pixel at an upper left corner of the block, and sets a filter coefficient to ¼, associated with the adjacent pixel adjacent to the left side of the target pixel at the left end of the block.

An image decoding method comprising:

• decoding coding mode information and an intra prediction parameter;
• and
• carrying out an intra-frame prediction process on each block which is a unit for prediction of a coding block to generate a prediction image, when the coding mode information associated with the coding block is an intra coding mode, wherein
• when the intra prediction parameter indicates an average prediction, a filtering process is carried out on target pixels of the intra prediction located at an upper end and a left end of the block which is a unit for prediction of the coding block, the filtering process using an intermediate prediction value, which is an average value of adjacent pixels of the block, and at least one adjacent pixel of the target pixel, and wherein
• the filtering process sets a filter coefficient to ¾, associated with the intermediate prediction value for a target pixel at the left end of the block other than the target pixel at an upper left corner of the block, and sets a filter coefficient to ¼, associated with the adjacent pixel adjacent to the left side of the target pixel at the left end of the block.

A non-transitory computer readable medium comprising coded data for each of coding blocks, the coded data including:

• coding mode information causing a decoder to determine a type of coding mode, and causing the decoder to carry out an intra-frame prediction process on each block which is a unit for prediction of a coding block to generate a prediction image, when the coding mode information associated with the coding block indicates an intra coding mode;
• and
• an intra prediction parameter causing the decoder to determine a type of intra prediction, wherein
• when the intra prediction parameter indicates an average prediction, a filtering process is carried out on target pixels of the intra prediction located at an upper end and a left end of the block which is a unit for prediction of the coding block, the filtering process using an intermediate prediction value, which is an average value of adjacent pixels of the block, and at least one adjacent pixel of the target pixel, and wherein
• the filtering process sets a filter coefficient to ¾, associated with the intermediate prediction value for a target pixel at the left end of the block other than the target pixel at an upper left corner of the block, and sets a filter coefficient to ¼, associated with the adjacent pixel adjacent to the left side of the target pixel at the left end of the block.