Encoding device, decoding device, encoding method, and decoding method for coding efficiency
According to an embodiment, an encoding device includes a deriving unit and an encoding unit. The deriving unit is configured to derive a first reference value based on fixed point precision representing roughness of a weighting factor that is used for multiplying a reference image. The encoding unit is configured to encode a first difference value that is a difference value between the weighting factor and the first reference value and the fixed point precision. The weighting factor is included in a first range of predetermined bit precision having the first reference value at approximate center. The first difference value is in the predetermined range.
1. An encoding method, comprising:
encoding a first denominator for a luma weighting factor;
encoding a first difference value that is equal to a value of a difference between the first denominator and a second denominator for a chroma weighting factor;
encoding a second difference value of the luma weighting factor, wherein the second difference value is equal to a value of a difference between the luma weighting factor and a first reference value, and the first reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the first denominator, and the second difference value is in a fixed range of −128 to +127 regardless of the first denominator;
encoding a third difference value of the chroma weighting factor, wherein the third difference value is equal to a value of a difference between the chroma weighting factor and a second reference value, the second reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the second denominator, and the third difference value is in a fixed range of −128 to +127 regardless of the second denominator; and
encoding a fourth difference value of a chroma offset, wherein the fourth difference value is equal to a value of a difference between the chroma offset and a third reference value, the fourth difference value is in a fixed range of −2n to +2n−1, n being an integer value according to a bit precision of the chroma offset, and the third reference value is equal to a value obtained by subtracting a value obtained by both multiplying a median value of a maximum pixel value by the chroma weighting factor and shifting to right for the at least one binary digit specified by the second denominator, from the median value, wherein
the first reference value is equal to a value of the luma weighting factor set when a luma component of a reference image and a luma component of a target image are equal, and
the second reference value is equal to a value of the chroma weighting factor set when a chroma component of the reference image and a chroma component of the target image are equal.
2. A decoding method, comprising:
inputting encoded data;
decoding a first denominator for a luma weighting factor from the encoded data;
decoding a first difference value that is equal to a value of a difference between the first denominator and a second denominator for a chroma weighting factor from the encoded data;
decoding a second difference value of the luma weighting factor from the encoded data, wherein the second difference value is equal to a value of a difference between the luma weighting factor and a first reference value, and the first reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the first denominator, and the second difference value is in a fixed range of −128 to +127 regardless of the first denominator;
decoding a third difference value of the chroma weighting factor from the encoded data, wherein the third difference value is equal to a value of a difference between the chroma weighting factor and a second reference value, the second reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the second denominator, and the third difference value is in a fixed range of −128 to +127 regardless of the second denominator; and
decoding a fourth difference value of a chroma offset from the encoded data, wherein the fourth difference value is equal to a value of a difference between the chroma offset and a third reference value, the fourth difference value is in a fixed range of −2n to +2n−1, n being an integer value according to a bit precision of the chroma offset, and the third reference value is equal to a value obtained by subtracting a value obtained by both multiplying a median value of a maximum pixel value by the chroma weighting factor and shifting to right for the at least one binary digit specified by the second denominator, from the median value, wherein
the first reference value is equal to a value of the luma weighting factor set when a luma component of a reference image and a luma component of a target image are equal, and
the second reference value is equal to a value of the chroma weighting factor set when a chroma component of the reference image and a chroma component of the target image are equal.
3. A storage device, comprising:
one or more processors configured to generate encoded data in which
data of a first denominator for a luma weighting factor is encoded;
data of a first difference value is encoded, the first difference value being equal to a value of a difference between the first denominator and a second denominator for a chroma weighting factor;
data of a second difference value of the luma weighting factor is encoded, wherein the second difference value is equal to a value of a difference between the luma weighting factor and a first reference value, and the first reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the first denominator, and the second difference value is in a fixed range of −128 to +127 regardless of the first denominator;
data of a third difference value of the chroma weighting factor is encoded, wherein the third difference value is equal to a value of a difference between the chroma weighting factor and a second reference value, the second reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the second denominator, and the third difference value is in a fixed range of −128 to +127 regardless of the second denominator; and
data of a fourth difference value of a chroma offset is encoded, wherein the fourth difference value is equal to a value of a difference between the chroma offset and a third reference value, the fourth difference value is in a fixed range of −2n to +2n−1, n being an integer value according to a bit precision of the chroma offset, and the third reference value is equal to a value obtained by subtracting a value obtained by both multiplying a median value of a maximum pixel value by the chroma weighting factor and shifting to right for the at least one binary digit specified by the second denominator, from the median value; and
a memory configured to store the encoded data, wherein
the first reference value is equal to a value of the luma weighting factor set when a luma component of a reference image and a luma component of a target image are equal, and
the second reference value is equal to a value of the chroma weighting factor set when a chroma component of the reference image and a chroma component of the target image are equal.
4. A transfer device, comprising:
one or more processor configured to generate encoded data in which:
data of a first denominator for a luma weighting factor is encoded;
data of a first difference value is encoded, the first difference value being equal to a value of a difference between the first denominator and a second denominator for a chroma weighting factor;
data of a second difference value of the luma weighting factor is encoded, wherein the second difference value is equal to a value of a difference between the luma weighting factor and a first reference value, and the first reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the first denominator, and the second difference value is in a fixed range of −128 to +127 regardless of the first denominator;
data of a third difference value of the chroma weighting factor is encoded, wherein the third difference value is equal to a value of a difference between the chroma weighting factor and a second reference value, the second reference value is equal to a value obtained by left shift of 1 by at least one binary digit specified by the second denominator, and the third difference value is in a fixed range of −128 to +127 regardless of the second denominator; and
data of a fourth difference value of a chroma offset is encoded, wherein the fourth difference value is equal to a value of a difference between the chroma offset and a third reference value, the fourth difference value is in a fixed range of −2n to +2n−1, n being an integer value according to a bit precision of the chroma offset, and the third reference value is equal to a value obtained by subtracting a value obtained by both multiplying a median value of a maximum pixel value by the chroma weighting factor and shifting to right for the at least one binary digit specified by the second denominator, from the median value; and
transfer circuitry is configured to transfer the encoded data, wherein
the first reference value is equal to a value of the luma weighting factor set when a luma component of a reference image and a luma component of a target image are equal, and
the second reference value is equal to a value of the chroma weighting factor set when a chroma component of the reference image and a chroma component of the target image are equal.