Method and apparatus for decoding video, and method and apparatus for encoding video

A video encoding method comprising:

• obtaining a pixel value of a first pixel using first neighboring pixels determined based on a first motion vector of a current block in a first reference picture;
• obtaining a pixel value of a second pixel using second neighboring pixels determined based on a second motion vector of the current block in a second reference picture;
• obtaining a first gradient value of the first pixel by using third neighboring pixels of the first pixel;
• obtaining a second gradient value of the second pixel by using fourth neighboring pixels of the second pixel;
• determining a first displacement vector in a horizontal direction and a second displacement vector in a vertical direction;
• obtaining a prediction pixel value of the current block by using the pixel value of the first pixel, the pixel value of the second pixel, the first gradient value, the second gradient value, the first displacement vector and the second displacement vector;
• and
• generating a bitstream comprising information about the first motion vector and information about the second motion vector,
• wherein when a first intermediate value used for determining at least one of the first displacement vector and the second displacement vector is greater than a predetermined value, the at least one of the first displacement vector and the second displacement vector is determined by performing a clipping operation based on a first threshold value and a second threshold value to a second intermediate value which is derived from the first intermediate value, and
• wherein when the first intermediate value is smaller than or equal to the predetermined value, the at least one of the first displacement vector and the second displacement vector is determined as 0 without the clipping operation.

A non-transitory computer-readable medium for recording a program for generating a bitstream, the bitstream comprising:

• information about a first motion vector of a current block;
• and
• information about a second motion vector of the current block,
• wherein a pixel value of a first pixel is obtained using first neighboring pixels determined based on the first motion vector in a first reference picture, and a pixel value of a second pixel is obtained using second neighboring pixels determined based on the second motion vector in a second reference picture,
• wherein a first gradient value of the first pixel is obtained by using third neighboring pixels of the first pixel, and a second gradient value of the second pixel is obtained by using fourth neighboring pixels of the second pixel,
• wherein a first displacement vector in a horizontal direction and a second displacement vector in a vertical direction are determined,
• wherein a prediction pixel value of the current block is obtained by using the pixel value of the first pixel, the pixel value of the second pixel, the first gradient value, the second gradient value, the first displacement vector and the second displacement vector,
• wherein when a first intermediate value used for determining at least one of the first displacement vector and the second displacement vector is greater than a predetermined value, the at least one of the first displacement vector and the second displacement vector is determined by performing a clipping operation based on a first threshold value and a second threshold value to a second intermediate value which is derived from the first intermediate value, and
• wherein when the first intermediate value is smaller than or equal to the predetermined value, the at least one of the first displacement vector and the second displacement vector is determined as 0 without the clipping operation.