Intra prediction method and device

An image encoding method performed by an encoding apparatus, the method comprising:

• determining an intra prediction mode of a current block;
• deriving neighboring reference samples of the current block;
• deriving filtered reference samples by performing filtering on the neighboring reference samples;
• and
• generating a predicted block based on the filtered reference samples,
• wherein for deriving the neighboring reference samples, an unavailable neighboring reference sample is substituted by using an available neighboring reference sample,
• wherein based on that a specific neighboring reference sample is located in a different slice from a slice to which the current block belongs, the specific neighboring reference sample is determined as the unavailable neighboring reference sample,
• wherein the filtering is performed based on the intra prediction mode and a size of the current block,
• wherein a distance variable is determined based on the intra prediction mode and a threshold value is determined based on the size of the current block,
• wherein the filtering is performed based on the distance variable and the threshold value,
• wherein for determining the threshold value based on the size of the current block,
• a first threshold value is set for a 4×4 block, a second threshold value is set for an 8×8 block, a third threshold value is set for a 16×16 block, a fourth threshold value is set for a 32×32 block, and a fifth threshold value is set for a 64×64 block,
• wherein the second threshold value for the 8×8 block is smaller than the first threshold value for the 4×4 block, the third threshold value for the 16×16 block is smaller than the second threshold value for the 8×8 block, the fourth threshold value for the 32×32 block is smaller than the third threshold value for the 16×16 block, and the fifth threshold value for the 64×64 block is not smaller than the fourth threshold value for the 32×32 block,
• wherein first threshold value for the 4×4 block has the greatest value among the threshold values.

A transmission method for image data, the method comprising:

• obtaining a bitstream generated based on an image encoding method, wherein the image encoding method comprises determining an intra prediction mode of a current block, deriving neighboring reference samples of the current block, deriving filtered reference samples by performing filtering on the neighboring reference samples, and generating a predicted block based on the filtered reference samples;
• and
• transmitting the image data comprising the bitstream,
• wherein for deriving the neighboring reference samples, an unavailable neighboring reference sample is substituted by using an available neighboring reference sample,
• wherein based on that a specific neighboring reference sample is located in a different slice from a slice to which the current block belongs, the specific neighboring reference sample is determined as the unavailable neighboring reference sample,
• wherein the filtering is performed based on the intra prediction mode and a size of the current block,
• wherein a distance variable is determined based on the intra prediction mode and a threshold value is determined based on the size of the current block,
• wherein the filtering is performed based on the distance variable and the threshold value,
• wherein for determining the threshold value based on the size of the current block,
• a first threshold value is set for a 4×4 block, a second threshold value is set for an 8×8 block, a third threshold value is set for a 16×16 block, a fourth threshold value is set for a 32×32 block, and a fifth threshold value is set for a 64×64 block,
• wherein the second threshold value for the 8×8 block is smaller than the first threshold value for the 4×4 block, the third threshold value for the 16×16 block is smaller than the second threshold value for the 8×8 block, the fourth threshold value for the 32×32 block is smaller than the third threshold value for the 16×16 block, and the fifth threshold value for the 64×64 block is not smaller than the fourth threshold value for the 32×32 block,
• wherein first threshold value for the 4×4 block has the greatest value among the threshold values.