CODING DISTORTION REMOVAL METHOD, VIDEO ENCODING METHOD, VIDEO DECODING METHOD, AND APPARATUS AND PROGRAM FOR THE SAME

1 . An image coding and decoding system which includes an image coding apparatus for coding an image and an image decoding apparatus for decoding a coded image, the coded image being generated by coding the image,

wherein said image coding apparatus comprises:

a coding unit which codes an input image segmented into a plurality of blocks on a block basis with a quantization parameter for each block, to obtain a first coded image;

a first decoding unit which decodes the first coded image on a block basis, to obtain a reconstructed image;

a determining unit which determines a first filter setting parameter for the input image, wherein the first filter setting parameter sets a threshold value for each quantization parameter, the threshold value being used to judge whether a filter for coding distortion removal is to be applied to a block of the reconstructed image;

a first comparing unit which compares a difference of pixel values between a pixel in a first block of the reconstructed image and a pixel in a second block of the reconstructed image adjacent to the first block, with the threshold value; and

a first removing unit which removes a coding distortion in an area disposed on both sides of a block boundary between the first block and the second block, by applying the filter for coding distortion removal based on a result of said first comparing unit,

wherein, in said first removing unit,

the coding distortion removal is not conducted when the difference of pixel values is greater than the threshold value, and

the coding distortion removal is conducted by applying the filter when the difference of pixel values is smaller than the threshold value, and

wherein said image decoding apparatus comprises:

an obtaining unit which obtains a second filter setting parameter by decoding the coded image, wherein the second filter setting parameter is used to set a threshold value for a quantization parameter and the threshold value is used to judge whether a filter for coding distortion removal is to be applied to a block;

a second decoding unit which decodes the coded image to obtain a reconstructed image;

a second comparing unit which compares a difference of pixel values between a pixel in a first block of the reconstructed image and a pixel in a second block of the reconstructed image adjacent to the first block, with the threshold value set by the second filter setting parameter; and

a second removing unit which removes a coding distortion in an area disposed on both sides of a block boundary between the first block and the second block, by applying the filter for coding distortion removal based on the result of said second comparing unit,

wherein, in said second removing unit,

the coding distortion removal is not conducted when the difference is greater than the threshold value, and

the coding distortion removal is conducted by applying the filter when the difference is smaller than the threshold value.

2 . The image coding and decoding system according to claim 1 ,

wherein the first filter setting parameter changes the threshold value in correlation with each quantization parameter in said image coding apparatus, and

the second filter setting parameter changes the threshold value in correlation with each quantization parameter in said image decoding apparatus.