BACKGROUND

Field

The present disclosure relates to a method and apparatus of encoding and decoding video, and more particularly, to a method and apparatus of encoding and decoding an intra prediction mode using a plurality of candidate intra prediction modes.

Discussion of the Background

Needs for high resolution, high quality video, such as HD (High Definition) and UHD (Ultra High Definition) video, are increasing in various application areas. Higher resolution, higher quality video inevitably causes increase in the amount of data compared with the existing video data; therefore, when video data are transmitted by using a medium, such as the existing wired or wireless broadband system, or video data are stored by using the existing storage media, costs for transmission and storage also increase. To address the above mentioned problems caused by a widespread use of high resolution, high quality video data, high efficient video compression technologies may be employed.

Various technologies may be employed for video compression: inter prediction technology for predicting pixel values of a current picture from the picture encoded before or after the current picture, intra prediction technology for predicting pixel values of a current picture by using pixel information within the current picture, an entropy encoding method for assigning symbols of short length to those values appearing more frequently while assigning symbols of long length to those values appearing less frequently, and so on. By using the video compression technologies as introduced above, video data can be more efficiently compressed for the transmission or the storage of the video data. However, there is a need for more improved compression technologies SUMMARY

Exemplary embodiments of the present invention provide a method of encoding and decoding an intra prediction mode for a current block.

Exemplary embodiments of the present invention provide an apparatus carrying out a method of encoding and decoding an intra prediction mode for a current block.

Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.

Exemplary embodiments of the present invention provide a method of decoding an intra prediction mode of a current block comprising: determining whether a first intra prediction mode derived from a first neighboring block located at the left side of the current block is identical to a second intra prediction mode derived from a second neighboring block located at the upper side of the current block; in response to a determination that the first intra prediction mode is not identical to the second intra prediction mode, deriving a first candidate intra prediction mode from the first intra prediction mode and deriving a second candidate intra prediction mode from the second intra prediction mode; and based on priority of order among a planar mode, a DC mode, and a vertical mode, deriving an intra prediction mode different from the first candidate intra prediction mode and the second candidate intra prediction mode into a third candidate intra prediction mode. The deriving of the intra prediction mode comprises deriving the planar mode into the third candidate intra prediction mode if the first candidate intra prediction mode and the second candidate intra prediction mode are not the planar mode; deriving the DC mode into the third candidate intra prediction mode if one of the first candidate intra prediction mode and the second candidate intra prediction mode is the planar mode and the other is not the DC mode; and deriving the vertical mode into the third candidate intra prediction mode if one of the first candidate intra prediction mode and the second candidate intra prediction mode is the planar mode and the other is the DC mode. The first neighboring block corresponds to a current block including a pixel positioned at (x−1, y) when the position of a pixel in the upper left side of the current block is (x, y); and the second neighboring block corresponds to a current block including a pixel positioned at (x, y−1) when the position of a pixel in the upper left of the current block is (x, y), where the x and y are an integer value. The method of decoding an intra prediction mode of a current block may comprise decoding information indicating whether one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block; and if one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block, deriving an intra prediction mode of the prediction mode based on the identical one from among the three candidate intra prediction modes. The method of decoding an intra prediction mode of a current block may comprise decoding information indicating whether one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block; and if the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode are not the same as an intra prediction mode of the prediction mode, deriving an intra prediction value of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. In the method of decoding an intra prediction mode, the deriving of the intra prediction mode of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode if the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode are not the same as an intra prediction mode of the prediction mode may further comprise deriving an intra prediction mode of the current block by comparing the remaining intra prediction mode with the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode.

Exemplary embodiments of the present invention provide a method of decoding an intra prediction mode comprising: determining whether a first intra prediction mode derived from a first neighboring block located at the left side of the current block is identical to a second intra prediction mode derived from a second neighboring block located at the upper side of the current block; in response to a determination that the first intra prediction mode is identical to the second intra prediction mode and the first intra prediction mode is a planar mode or a DC mode, deriving a first candidate intra prediction mode into the planar mode; deriving a second candidate intra prediction mode into the DC mode; and deriving a third candidate intra prediction mode into a vertical mode. The method of decoding an intra prediction mode of a current block may comprise decoding information indicating whether one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block; and if one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block, deriving an intra prediction mode of the current block based on the one of the three candidate intra prediction modes. The method of decoding an intra prediction mode of a current block may comprise decoding information indicating whether one of the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode is identical to an intra prediction mode of the current block; and if the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode are not the same as an intra prediction mode of the current block, deriving an intra prediction mode of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. In the method of decoding an intra prediction mode, the deriving an intra prediction value of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode if the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode are not the same as an intra prediction mode of the current block may further comprise deriving an intra prediction mode of the current block by comparing the remaining intra prediction mode with the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. The first neighboring block corresponds to a current block including a pixel positioned at (x−1, y) when the position of a pixel in the upper left side of the current block is (x, y); and the second neighboring block corresponds to a current block including a pixel positioned at (x, y−1) when the position of a pixel in the upper left of the current block is (x, y), where the x and y are an integer value.

Exemplary embodiments of the present invention provide an image decoding apparatus comprising: an entropy decoding unit configured to decode information indicating whether one candidate intra prediction mode from among a first candidate intra prediction mode, a second candidate intra prediction mode, and a third candidate prediction mode is identical to an intra prediction mode of a current block, the first, second, and third candidate intra prediction modes being three intra prediction modes for the current block; and a predictor configured to derive an intra prediction mode of the current block based on the information, wherein, if a first intra prediction mode derived from a first neighboring block located at the left side of the current block is not identical to a second intra prediction mode derived from a second neighboring block located at the upper side of the current block, the first candidate intra prediction mode is derived from the first intra prediction mode; the second candidate intra prediction mode is derived from the second intra prediction mode; and, based on priority of order of a planar mode, a DC mode, and a first mode, an intra prediction mode different from the first candidate intra prediction mode and the second candidate intra prediction mode is derived into the third candidate intra prediction mode. The third candidate intra prediction mode is derived into the planar mode if the first candidate intra prediction mode and the second candidate intra prediction mode are not the planar mode; the third candidate intra prediction mode is derived into the DC mode if one of the first candidate intra prediction mode and the second candidate intra prediction mode is the planar mode and the other is not the DC mode; and the third candidate intra prediction mode is derived into the vertical mode if one of the first candidate intra prediction mode and the second candidate intra prediction mode is the planar mode and the other is the DC mode. The first neighboring block corresponds to a current block including a pixel positioned at (x−1, y) when the position of a pixel in the upper left side of the current block is (x, y); and the second neighboring block corresponds to a current block including a pixel positioned at (x, y−1) when the position of a pixel in the upper left of the current block is (x, y), where the x and y are an integer value. The predictor, if one of the three candidate intra prediction modes is identical an intra prediction mode of the current block, derives an intra prediction mode of the current block based on the one of the three candidate intra prediction modes; and if none of the three candidate intra prediction modes is not identical to an intra prediction mode of the current block, derives an intra prediction mode of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. The predictor, if none of the three candidate intra prediction modes is identical to an intra prediction mode of the current block, derives an intra prediction mode of the current block by comparing the remaining intra prediction mode with the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode.

Exemplary embodiments of the present invention provide an image decoding apparatus comprising: an entropy decoding unit configured to decode information indicating whether one candidate intra prediction mode from among a first candidate intra prediction mode, a second candidate intra prediction mode, and a third candidate prediction mode is identical to an intra prediction mode of a current block, the first, second, and third candidate intra prediction modes being three candidate intra prediction modes for the current block; and a predictor configured to determine whether a first intra prediction mode derived from a first neighboring block located at the left side of the current block is identical to a second intra prediction mode derived from a second neighboring block located at the upper side of the current block, wherein, if the first intra prediction mode is identical to the second intra prediction mode and the first intra prediction mode is a planar mode, a first candidate intra prediction mode is derived as the planar mode and a second candidate intra prediction mode is derived as a DC mode and a third candidate prediction mode is derived as a vertical mode. The predictor, if one of the three candidate intra prediction modes is identical to an intra prediction mode of the current block, is configured to derive an intra prediction mode of the current block based on the one of the three candidate intra prediction modes; and if none of the three candidate intra prediction modes is identical to an intra prediction mode of the current block, the predictor is configured to derive an intra prediction mode of the current block based on the remaining intra prediction mode different from the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. The predictor, if none of the three candidate intra prediction modes is identical to an intra prediction mode of the current block, is configured to derive an intra prediction mode of the current block by comparing the remaining intra prediction mode with the first candidate intra prediction mode, the second candidate intra prediction mode, and the third candidate intra prediction mode. The current block is such that the first neighboring block corresponds to a current block including a pixel positioned at (x−1, y) when the position of a pixel in the upper left side of the current block is (x, y); and the second neighboring block corresponds to a current block including a pixel positioned at (x, y−1) when the position of a pixel in the upper left of the current block is (x, y), where the x and y are an integer value.

According to aspects of the present invention, a method of encoding and decoding an intra prediction mode by using a plurality of candidate intra prediction modes and an apparatus using the method can represent an intra prediction mode of a current block by using a short codeword and predict an intra prediction mode of a current block based on a plurality of candidate intra prediction modes, thereby improving video encoding efficiency.

It is to be understood that both forgoing general descriptions and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

