Image coding device, image decoding device, image coding method, and image decoding method

1. An image decoding device that carries out a decoding process on a coded data obtained by performing a block based coding process on an image, said image decoding device comprising:

a coded data decoder to decode the coded data to acquire compressed data of a difference image and a coding mode associated with each of coding blocks, the coding mode indicating a prediction mode and prediction blocks in each of the coding blocks;

a prediction image generator to carry out a prediction process for each of the coding blocks according to the coding mode to generate a prediction image of each of coding blocks;

a decoded image generator to add a decompressed difference image to the prediction image for each of the blocks to generate a decoded image; and

an image distortion remover to carry out a filtering process on the decoded image to remove a block distortion occurring at a boundary between adjacent prediction blocks of the decoded image,

wherein the image distortion remover derives a parameter specifying filtering strength according to a set of conditions including whether the coding mode corresponding to at least one of the adjacent prediction blocks to which the filtering process is to be applied is intra prediction mode, and a value of the parameter is used in a process of selecting from different filtering processes.

2. An image decoding method that carries out a decoding process on a coded data obtained by performing a block based coding process on an image, said image decoding method comprising:

decoding the coded data to acquire compressed data of a difference image and a coding mode associated with each of coding blocks, the coding mode indicating a prediction mode and prediction blocks in each of the coding blocks;

carrying out a prediction process on each of the coding blocks to generate a prediction image;

adding a decompressed difference image to the prediction image for each of the coding blocks to generate a decoded image; and

carrying out a filtering process on the decoded image to remove a block distortion occurring at a boundary between adjacent prediction blocks of the decoded image,

wherein, when removing said block distortion occurring in said decoded image, a parameter specifying filtering strength is derived according to a set of conditions including whether the coding mode corresponding to at least one of the adjacent prediction blocks to which the filtering process is to be applied is intra prediction mode, a value of the parameter being used in a process of selecting from different filtering processes.

3. A non-transitory computer readable medium comprising coded data for each of a plurality of coding blocks, said coded data including:

information specifying a coding mode; and

compressed data of a difference image,

wherein the information of the non-transitory computer readable medium, when read by a processor, enables said processor to carry out a filtering process on a decoded image to remove a block distortion occurring at a boundary between adjacent prediction blocks of the decoded image, the decoded image being obtained by adding a decompressed difference image generated from the compressed data to the prediction image generated based on the coding mode for each of the blocks,

wherein, when removing the block distortion occurring in the decoded image, a parameter specifying filtering strength is derived according to a set of conditions including whether the coding mode corresponding to at least one of the adjacent prediction blocks to which the filtering process is to be applied is intra prediction mode, and a value of the parameter is used in a process of selecting from different filtering processes.