Video coding device, video coding method, video decoding device, and video decoding method

A video decoding device that decodes a decoding-target picture included in encoded video data, the video decoding device comprising:

• a region determination circuit configured to determine, for a first block to which a bidirectional prediction mode has been applied for a first component of a pixel value from among a plurality of blocks resulting from dividing the decoding-target picture, a partial region to which a unidirectional prediction mode is to be applied for a second component of a pixel value;
• a prediction circuit configured to generate a prediction block for the second component by applying a unidirectional prediction mode to the partial region in the first block and by applying a bidirectional prediction mode to a region that is not the partial region in the first block;
• and
• a decoder configured to generate the second component of each pixel in the first block by adding a value of a corresponding pixel of the prediction block to a prediction error for the second component between corresponding pixels belonging to the first block and the prediction block included in the encoded video data.

A video coding method that encodes a coding-target picture included in video data, the video coding method comprising:

• determining, by a video coding device and for a first block encoded by referring to a first prediction block generated by applying a bidirectional prediction mode for a first component of a pixel value from among a plurality of blocks resulting from dividing the coding-target picture, a partial region to which a unidirectional prediction mode is to be applied for a second component of a pixel value on the basis of a difference value for the first component between corresponding pixels belonging to the first prediction block and the first block;
• generating, by the video coding device, a second prediction block for the second component by applying a unidirectional prediction mode to the partial region in the first block and by applying a bidirectional prediction mode to a region that is not the partial region in the first block;
• calculating, by the video coding device, a prediction error for the second component between corresponding pixels belonging to the first block and the second prediction block;
• and
• encoding the prediction error by the video coding device.

A video decoding method that decodes a decoding-target picture included in encoded video data, the video decoding method comprising:

• determining, by a video decoding device and for a first block to which a bidirectional prediction mode has been applied for a first component of a pixel value from among a plurality of blocks resulting from dividing the decoding-target picture, a partial region to which a unidirectional prediction mode is to be applied for a second component of a pixel value;
• generating, by the video decoding device, a prediction block for the second component by applying a unidirectional prediction mode to the partial region in the first block and by applying a bidirectional prediction mode to a region that is not the partial region in the first block;
• and
• generating, by the video decoding device, the second component of each pixel in the first block by adding a value of a corresponding pixel of the prediction block to a prediction error for the second component between corresponding pixels belonging to the first block and the prediction block included in the encoded video data.

A non-transitory computer-readable recording medium having stored therein a video-encoding computer program that causes a computer to execute a process comprising:

• determining, for a first block encoded by referring to a first prediction block generated by applying a bidirectional prediction mode for a first component of a pixel value from among a plurality of blocks resulting from dividing a coding-target picture included in video data, a partial region to which a unidirectional prediction mode is to be applied for a second component of a pixel value on the basis of a difference value for the first component between corresponding pixels belonging to the first prediction block and the first block;
• generating a second prediction block for the second component by applying a unidirectional prediction mode to the partial region in the first block and by applying a bidirectional prediction mode to a region that is not the partial region in the first block;
• calculating a prediction error for the second component between corresponding pixels belonging to the first block and the second prediction block;
• and
• encoding the prediction error.

A non-transitory computer-readable recording medium having stored therein a video-decoding computer program that causes a computer to execute a process comprising:

• determining, for a first block to which a bidirectional prediction mode has been applied for a first component of a pixel value from among a plurality of blocks resulting from dividing a decoding-target picture included in encoded video data, a partial region to which a unidirectional prediction mode is to be applied for a second component of a pixel value;
• generating a prediction block for the second component by applying a unidirectional prediction mode to the partial region in the first block and by applying a bidirectional prediction mode to a region that is not the partial region in the first block;
• and
• generating the second component of each pixel in the first block by adding a value of a corresponding pixel of the prediction block to a prediction error for the second component between corresponding pixels belonging to the first block and the prediction block included in the encoded video data.