Moving picture coding method and moving picture decoding method

A image decoding apparatus coupled to a memory and comprising processing circuitry, wherein the decoding apparatus, in operation:

• decodes a coded image signal to obtain:
• first reference indices that identify first reference images for blocks to be decoded, the first reference indices and the first reference images used for a slice;
• second reference indices that identify second reference images, the second reference indices and the second reference images used for the slice;
• weighting coefficient sets used for the slice;
• and prediction error;
• designates, based on a reference index obtained through decoding a current block, a reference image for the current block, wherein the reference index is one of the first reference indices, the reference image is one of the first reference images, and the current block is one of the blocks;
• specifies, based on the reference index, a weighting coefficient set for the current block from among the weighting coefficient sets;
• generates a predictive image by performing a prediction on the current block, using the specified weighting coefficient set, on pixel values of a reference block obtained from the designated reference image, the prediction comprising (i) scaling the pixel values of the reference block with a first part w1 of the specified weighting coefficient set and (ii) offsetting the scaled pixel values of the reference block by a second part c1 of the specified weighting coefficient set;
• and
• generates a reconstructed image from the predictive image and the prediction error,
• wherein at least two reference indices among the first reference indices are assigned to one reference image among the first reference images, and at least two weighting coefficient sets among the weighting coefficient sets are assigned to the one reference image, and
• wherein both (i) a first index among the first reference indices and (ii) a second index among the second reference indices are used for the prediction when the current block refers to two reference blocks, and one of (i) a first index among the first reference indices and (ii) a second index among the second reference indices is used for the prediction when the current block refers to a single reference block.