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

1. An image encoding device that carries out a block based coding process on each of coding blocks of an inputted image, each of the coding blocks being a unit for coding process, the image encoding device comprising:

a distortion remover to carry out a filtering process on a decoded image obtained by adding a prediction image to a decompressed image into which compressed data of a difference image, which is a difference between the inputted image and the prediction image, is decompressed, and to remove a block distortion at a boundary between adjacent transform blocks of the decoded image, the transform block being for transforming the difference image; and

a data encoder to encode the compressed data of the difference image and an offset,

wherein the distortion remover determines whether a vertical edge or a horizontal edge of the coding block overlaps the boundary, and determines filtering strength for a part where the vertical edge or the horizontal edge overlaps the boundary, and derives a value of a parameter specifying the filtering strength as a default value for the offset, wherein the offset is added to the value of the parameter to produce a value that identifies a filtering process to be selected from different filtering processes.

2. An image encoding method that carries out a block based coding process on each of coding blocks of an inputted image, each of the coding blocks being a unit for coding process, the image encoding method comprising:

carrying out a filtering process on a decoded image obtained by adding a prediction image to a decompressed image into which compressed data of a difference image, which is a difference between the inputted image and the prediction image, is decompressed, and removing a block distortion at a boundary between adjacent transform blocks of the decoded image, the transform block being for transforming the difference image; and

encoding the compressed data of the difference image and an offset,

wherein the filtering process determines whether a vertical edge or a horizontal edge of the coding block overlaps the boundary, and determines filtering strength for a part where the vertical edge or the horizontal edge overlaps the boundary, and derives a value of a parameter specifying the filtering strength as a default value for the offset, wherein the offset is added to the value of the parameter to produce a value that identifies a filtering process to be selected from different filtering processes.

3. 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, the image decoding device comprising:

a coded data decoder to decode the coded data to acquire compressed data of a difference image associated with each of coding blocks and an offset; and

a distortion remover to carry out a filtering process on a decoded image obtained by adding a prediction image to the difference image, and to remove a block distortion at a boundary between adjacent transform blocks of the decoded image, the transform block being for transforming the difference image,

wherein the distortion remover determines whether a vertical edge or a horizontal edge of the coding block overlaps the boundary, and determines filtering strength for a part where the vertical edge or the horizontal edge overlaps the boundary, and derives a value of a parameter specifying the filtering strength as a default value for the offset, wherein the offset is added to the value of the parameter to produce a value that identifies a filtering process to be selected from different filtering processes.

4. 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, the image decoding method comprising:

decoding the coded data to acquire compressed data of a difference image associated with each of coding blocks and an offset; and

carrying out a filtering process on a decoded image obtained by adding a prediction image to the difference image, and removing a block distortion at a boundary between adjacent transform blocks of the decoded image, the transform block being for transforming the difference image,

wherein the filtering process determines whether a vertical edge or a horizontal edge of the coding block overlaps the boundary, and determines filtering strength for a part where the vertical edge or the horizontal edge overlaps the boundary, and derives a value of a parameter specifying the filtering strength as a default value for the offset, wherein the offset is added to the value of the parameter to produce a value that identifies a filtering process to be selected from different filtering processes.

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

compressed data of a difference image; and

an offset,

wherein the compressed data of the coded data, when read by a processor, enables the processor to carry out a filtering process on a decoded image obtained by adding a prediction image to the difference image, and to remove a block distortion at a boundary between adjacent transform blocks of the decoded image, the transform block being for transforming the difference image, and

wherein the compressed data enables the processor to determine whether a vertical edge or a horizontal edge of the coding block overlaps the boundary, and determine filtering strength for a part where the vertical edge or the horizontal edge overlaps the boundary, and derive a value of a parameter specifying the filtering strength as a default value for the offset, wherein the offset is added to the value of the parameter to produce a value that identifies a filtering process to be selected from different filtering processes.