Encoder which generates prediction image to be used to encode current block
An encoder includes circuitry and memory connected to the circuitry. The circuitry, in operation: derives, as a first parameter, a total sum of absolute values of sums of horizontal gradient values respectively for pairs of relative pixel positions; derives, as a second parameter, a total sum of absolute values of sums of vertical gradient values respectively for the pairs of relative pixel positions; derives, as a third parameter, a total sum of horizontal-related pixel difference values respectively for the pairs of relative pixel positions; derives, as a fourth parameter, a total sum of vertical-related pixel difference values respectively for the pairs of relative pixel positions; derives, as a fifth parameter, a total sum of vertical-related sums of horizontal gradient values respectively for the pairs of relative pixel positions; and generates a prediction image to be used to encode the current block using the first, second, third, fourth, and fifth parameters.
1. A decoding method comprising:
generating a prediction image in order to decode a current block based on a first parameter, a second parameter, a third parameter, a fourth parameter, and a fifth parameter that are derived in a bi-directional optical flow (BDOF) process, wherein
the first parameter is derived based on the following expression:
Σ [i,j]∈Ω abs( I x 1 +I x 0 ); [Math. 1]
the second parameter is derived based on the following expression:
Σ [i,j]∈Ω ( I y 1 +I y 0 ); [Math. 2]
the third parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I x 1 +I x 0 )×( I 0 −I 1 )); [Math. 3]
the fourth parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I y 1 +I y 0 )×( I 0 −I 1 )); and [Math. 4]
the fifth parameter is derived based on the following expression,
Σ [i,j]∈Ω (sign( I y 1 +I y 0 )×( I x 0 −I x 1 )), [Math. 5]
where:
Ω indicates a set of relative pixel positions;
[i, j] indicates a relative pixel position in the set 22 defined by a horizontal position i and a vertical position j;
I x 0 indicates a horizontal gradient value at a first pixel position in a first gradient image, and I x 1 indicates a horizontal gradient value at the first pixel position in a second gradient image, the first pixel position being determined based on a relative pixel position [i, j], the first gradient image and the second gradient image corresponding to the current block;
I y 0 indicates a vertical gradient value at the first pixel position in the first gradient image, and I y 1 indicates a vertical gradient value at the first pixel position in the second gradient image;
I 0 indicates a pixel value at the first pixel position in a first interpolated image corresponding to the current block;
I 1 indicates a pixel value at the first pixel position in a second interpolated image corresponding to the current block;
the abs function outputs an absolute value of an argument; and
the sign function outputs a sign of an argument which is −1, 0, or 1.
2. An encoding method comprising:
generating a prediction image in order to encode a current block based on a first parameter, a second parameter, a third parameter, a fourth parameter, and a fifth parameter that are derived in a bi-directional optical flow (BDOF) process, wherein
the first parameter is derived based on the following expression:
Σ [i,j]∈Ω abs( I x 1 +I x 0 ); [Math. 1]
the second parameter is derived based on the following expression:
Σ [i,j]∈Ω ( I y 1 +I y 0 ); [Math. 2]
the third parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I x 1 +I x 0 )×( I 0 −I 1 )); [Math. 3]
the fourth parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I y 1 +I y 0 )×( I 0 −I 1 )); and [Math. 4]
the fifth parameter is derived based on the following expression,
Σ [i,j]∈Ω (sign( I y 1 +I y 0 )×( I x 0 −I x 1 )), [Math. 5]
where:
Ω indicates a set of relative pixel positions;
[i, j] indicates a relative pixel position in the set 22 defined by a horizontal position i and a vertical position j;
I x 0 indicates a horizontal gradient value at a first pixel position in a first gradient image, and I x 1 indicates a horizontal gradient value at the first pixel position in a second gradient image, the first pixel position being determined based on a relative pixel position [i, j], the first gradient image and the second gradient image corresponding to the current block;
I y 0 indicates a vertical gradient value at the first pixel position in the first gradient image, and I y 1 indicates a vertical gradient value at the first pixel position in the second gradient image;
I 0 indicates a pixel value at the first pixel position in a first interpolated image corresponding to the current block;
I 1 indicates a pixel value at the first pixel position in a second interpolated image corresponding to the current block;
the abs function outputs an absolute value of an argument; and
the sign function outputs a sign of an argument which is −1, 0, or 1.
3. A method of transmitting a bitstream, the bitstream comprising a prediction parameter which indicates a prediction process among prediction process candidates and which is read by a decoder to decode a current block provided in the bitstream, the prediction process candidates including a bi-directional optical flow (BDOF) process in which a first parameter, a second parameter, a third parameter, a fourth parameter, and a fifth parameter are used to generate a prediction image of the current block, wherein
the first parameter is derived based on the following expression:
Σ [i,j]∈Ω abs( I x 1 +I x 0 ); [Math. 1]
the second parameter is derived based on the following expression:
Σ [i,j]∈Ω ( I y 1 +I y 0 ); [Math. 2]
the third parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I x 1 +I x 0 )×( I 0 −I 1 )); [Math. 3]
the fourth parameter is derived based on the following expression:
Σ [i,j]∈Ω (−sign( I y 1 +I y 0 )×( I 0 −I 1 )); and [Math. 4]
the fifth parameter is derived based on the following expression,
Σ [i,j]∈Ω (sign( I y 1 +I y 0 )×( I x 0 −I x 1 )), [Math. 5]
where:
Ω indicates a set of relative pixel positions;
[i, j] indicates a relative pixel position in the set ( 2 defined by a horizontal position i and a vertical position j;
I x 0 indicates a horizontal gradient value at a first pixel position in a first gradient image, and I x 1 indicates a horizontal gradient value at the first pixel position in a second gradient image, the first pixel position being determined based on a relative pixel position [i, j], the first gradient image and the second gradient image corresponding to the current block;
I y 0 indicates a vertical gradient value at the first pixel position in the first gradient image, and I y 1 indicates a vertical gradient value at the first pixel position in the second gradient image;
I 0 indicates a pixel value at the first pixel position in a first interpolated image corresponding to the current block;
I 1 indicates a pixel value at the first pixel position in a second interpolated image corresponding to the current block;
the abs function outputs an absolute value of an argument; and
the sign function outputs a sign of an argument which is −1, 0, or 1.