Video encoding apparatus, video decoding apparatus, and video decoding method for performing intra-prediction based on directionality of neighboring block

A video encoding method performed by a video encoding apparatus, the method comprising:

• determining a current intra prediction mode associated with a current block;
• performing intra-prediction according to the current intra prediction mode associated with the current block to generate a prediction block associated with the current block;
• determining a neighboring intra prediction mode associated with a neighboring block, the neighboring block being adjacent to the current block;
• encoding the current intra prediction mode associated with the current block based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not;
• obtaining a residual block associated with the current block by using the prediction block and the current block;
• transforming the residual block to generate transform coefficients using a discrete cosine transform;
• quantizing the transform coefficients to generate quantized transform coefficients;
• encoding the quantized transform coefficients,
• wherein the encoding the current intra prediction mode associated with the current block comprises:
• encoding the current intra prediction mode associated with the current block according to a first set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has no directionality,
• encoding the current intra prediction mode associated with the current block according to a second set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has directionality,
• wherein the second set of two or more mathematical expressions is different from the first set of two or more mathematical expressions, and
• the neighboring block includes a left block adjacent to the current block.

A non-transitory computer-readable recording medium storing a bitstream that is received by an image decoding apparatus and used to reconstruct a current block included in an image,

• wherein the bitstream comprises information on a neighboring intra prediction mode associated with a neighboring block and information on a residual block associated with the current block, the neighboring block being adjacent to the current block,
• the information on the neighboring intra prediction mode associated with the neighboring block is decoded and used to reconstruct a neighboring intra prediction mode associated with the neighboring block,
• the neighboring intra prediction mode associated with the neighboring block is used to determine a current intra prediction mode associated with the current block based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not,
• the current intra prediction mode associated with the current block is used to perform intra-prediction to generate a prediction block associated with the current block;
• the information on the residual block associated with the current block is decoded and used to obtain a residual block associated with the current block,
• the prediction block and the residual block are used to reconstruct the current block,
• wherein when the neighboring intra prediction mode associated with the neighboring block has no directionality, the current intra prediction mode associated with the current block is determined according to a first set of two or more mathematical expressions,
• when the neighboring intra prediction mode associated with the neighboring block has directionality, the current intra prediction mode associated with the current block is determined according to a second set of two or more mathematical expressions,
• wherein the second set of two or more mathematical expressions is different from the first set of two or more mathematical expressions,
• the neighboring block includes a left block adjacent to the current block, and
• an intra prediction mode having no directionality includes a planar mode or a DC mode.