Image encoding method and apparatus using artifact reduction filter, and image decoding method and apparatus using artifact reduction filter

An image decoding method comprising:

• receiving a bitstream comprising information about whether to apply an artifact reduction filter after an in-loop filter is applied;
• reconstructing a picture by performing decoding on the bitstream;
• when the information indicates that the artifact reduction filter is to be applied after the in-loop filter is applied, applying the second artifact reduction filter to the reconstructed picture to which the in-loop filter has been applied;
• and
• when the information indicates that the artifact reduction filter is not to be applied after the in-loop filter is applied, outputting the reconstructed picture to which the in-loop filter has been applied.

An image encoding apparatus comprising:

• a first artifact reduction filter applier configured to generate a first picture reconstructed by using a residual picture and a predicted picture, and generate a second picture by applying a first artifact reduction filter to the first picture;
• a bit-rate distortion cost comparator configured to determine a picture having a smaller bit-rate distortion cost from among the first and second pictures by comparing a first bit-rate distortion cost of the first picture with a second bit-rate distortion cost of the second picture;
• a second artifact reduction filter applier configured to generate a third picture by applying an in-loop filter to the determined picture, and generate a fourth picture by applying a second artifact reduction filter to the third picture;
• a distortion comparator configured to evaluate subjective quality and objective quality of each of the third and fourth pictures so as to determine a first distortion of the third picture and a second distortion of the fourth picture and determine a picture having smaller distortion from among the third and fourth pictures by comparing the first distortion with the second distortion;
• and
• a bitstream generator configured to generate a bitstream comprising information about whether the second artifact reduction filter is applied,
• wherein the distortion comparator is further configured to evaluate the subjective quality of each of the third and fourth pictures based on a size of a display and a distance between the display and a viewer, and determine sharpness of each of the third and fourth pictures, based on sharpness of each of blocks in the third and fourth pictures.