Encoding device, decoding device, encoding method, and decoding method for efficient coding

An encoding method, comprising:

• setting, by circuitry, an index that represents information of a reference image, a color difference weighting factor, and an offset of the color difference;
• setting, by the circuitry, a first value to the reference value, wherein the first value is equal to a value of the color difference weighting factor used when a difference of pixel value between the reference image and a target image is less than or equal to a specific value;
• setting, by the circuitry, a second value to the difference value, wherein the difference value is equal to a value of a difference between the color difference weighting factor and the reference value;
• encoding, by the circuitry, the difference value;
• multiplying, by the circuitry, a median value of a maximal brightness value of the color difference by the color difference weighting factor;
• determining, by the circuitry, a predicted value by using the median value of the color difference, a value obtained by multiplying the median value of the maximal brightness value of the color difference by the color difference weighting factor, and the offset;
• and
• encoding, by the circuitry, the predicted value.

A non-transitory computer readable medium storing computer executable instructions that, when executed by circuitry of a computer, cause the circuitry of the computer to:

• set an index that represents information of a reference image, a color difference weighting factor, and an offset of the color difference;
• set a first value to the reference value, wherein the first value is equal to a value of the color difference weighting factor used when a difference of pixel value between the reference image and a target image is less than or equal to a specific value;
• set a second value to the difference value, wherein the difference value is equal to a value of a difference between the color difference weighting factor and the reference value;
• encode the difference value;
• multiply a median value of a maximal brightness value of the color difference by the color difference weighting factor;
• determine a predicted value by using the median value of the color difference, a value obtained by multiplying the median value of the maximal brightness value of the color difference by the color difference weighting factor, and the offset;
• and
• encode the predicted value.