Image encoding method and image decoding method

1 . An image encoding method for encoding an image, comprising:

generating a prediction image by a plurality of types of prediction image generating processing, the plurality of types of prediction image generating processing include an intra prediction, an inter prediction, and a synthesis prediction, wherein the synthesis prediction performs synthesis processing of synthesizing a prediction image of an inter prediction and a prediction image of an intra prediction to an encoding-target block; and

encoding a difference between the prediction image generated in the prediction image generation and a pixel value of an image of the encoding-target block, wherein

types of predictions that can be used in prediction image generation include a first prediction mode and a second prediction mode,

synthesis processing includes weighting processing performed to the prediction image of the inter prediction and the prediction image of the intra prediction, and

processing states of weighting processing include setting a smallest weighting for the prediction image of the intra prediction while the type of the intra prediction is the first prediction mode, wherein

the first prediction mode is an intra prediction mode that includes generating a prediction image based on a first linear interpolation and a second linear interpolation, the first linear interpolation uses pixel values of a first pair of reference pixels, a first reference pixel of the first pair of reference pixels is located outside the encoding-target block and a second reference pixel of the first pair of reference pixels is located inside the encoding-target block, and the second linear interpolation uses pixel values of a second pair of reference pixels, a first reference pixel of the second pair of reference pixels is a reference pixel located outside the encoding-target block and a second reference pixel of the second pair of reference pixels is a reference pixel located inside the encoding-target block, and

the second prediction mode is an in-screen block copy mode, wherein

checking processing for checking both whether an available adjacent block exists immediately above the encoding-target block or not, whether an available adjacent block exists immediately on the left of the encoding-target block or not, are conducted for the weighting processing, are conducted for the weighting processing, and

the weighting processing is further based on a combination of prediction modes of a block adjacently immediately above the encoding-target block and a block adjacently immediately on a left of the encoding-target block, the combination of prediction modes including whether each of the adjacent blocks is unavailable, in an inter prediction mode, or in an intra prediction mode.

2 . An image decoding method for decoding an encoded image, the image decoding method comprising:

generating a prediction image by a plurality of types of prediction image generating processing, the plurality of types of prediction image generating processing include an intra prediction, an inter prediction, and a synthesis prediction, wherein the synthesis prediction performs a synthesis prediction by performing synthesis processing of synthesizing a prediction image of an inter prediction and a prediction image of an intra prediction to a decoding-target block; and

generating a decoded image based on the prediction image generated in the prediction image generation and a difference image of the decoding-target block, wherein

types of predictions that can be used in the prediction image generation include a first prediction mode and a second prediction mode,

synthesis processing includes weighting processing performed to the prediction image of the inter prediction and the prediction image of the intra prediction, and

processing states of weighting processing include setting a smallest weighting for the prediction image of the intra prediction while the type of the intra prediction is the first prediction mode, wherein

the first prediction mode is an intra prediction mode that includes generating a prediction image based on a first linear interpolation and a second linear interpolation, the first linear interpolation uses pixel values of a first pair of reference pixels, a first reference pixel of the first pair of reference pixels is located outside the decoding-target block and a second reference pixel of the first pair of reference pixels is located inside the decoding-target block, and the second linear interpolation uses pixel values of a second pair of reference pixels, a first reference pixel of the second pair of reference pixels is a reference pixel located outside the decoding-target block and a second reference pixel of the second pair of reference pixels is a reference pixel located inside the decoding-target block, and

the second prediction mode is an in-screen block copy mode, wherein

checking processing for checking both whether an available adjacent block exists immediately above the decoding-target block or not, whether an available adjacent block exists immediately on the left of the decoding-target block or not, are conducted for the weighting processing, and

the weighting processing is further based on a combination of prediction modes of a block adjacently immediately above the decoding-target block and a block adjacently immediately on a left of the decoding-target block, the combination of prediction modes including whether each of the adjacent blocks is unavailable, in an inter prediction mode, or in an intra prediction mode.

3 . An image encoding method for encoding an image, comprising:

generating a prediction image by a plurality of types of prediction image generating processing, the plurality of types of prediction image generating processing include an intra prediction, an inter prediction, and a synthesis prediction, wherein the synthesis prediction performs synthesis processing of synthesizing a prediction image of an inter prediction and a prediction image of an intra prediction to an encoding-target block; and

encoding a difference between the prediction image generated in the prediction image generation and a pixel value of an image of the encoding-target block, wherein

types of predictions that can be used in prediction image generation include a first prediction mode and a second prediction mode,

synthesis processing includes weighting processing performed to the prediction image of the inter prediction and the prediction image of the intra prediction, and

processing states of weighting processing include setting a smallest weighting for the prediction image of the intra prediction while the type of the intra prediction is the first prediction mode, wherein

the first prediction mode is an intra prediction mode that includes generating a prediction image based on a first linear interpolation and a second linear interpolation, the first linear interpolation uses pixel values of a first pair of reference pixels, a first reference pixel of the first pair of reference pixels is located outside the encoding-target block and a second reference pixel of the first pair of reference pixels is located inside the encoding-target block, and the second linear interpolation uses pixel values of a second pair of reference pixels, a first reference pixel of the second pair of reference pixels is a reference pixel located outside the encoding-target block and a second reference pixel of the second pair of reference pixels is a reference pixel located inside the encoding-target block, and

the second prediction mode is an in-screen block copy mode, wherein

checking processing for checking both whether an available adjacent block exists immediately above the encoding-target block or not, whether an available adjacent block exists immediately on the left of the encoding-target block or not, are conducted for the weighting processing, and

wherein both a result of checking whether an available adjacent block exists immediately above the encoding-target block or not, and a result of checking whether an available adjacent block exists immediately on the left of the encoding-target block or not, effect a result of the weighting processing.

4 . An image decoding method for decoding an encoded image, the image decoding method comprising:

generating a prediction image by a plurality of types of prediction image generating processing, the plurality of types of prediction image generating processing include an intra prediction, an inter prediction, and a synthesis prediction, wherein the synthesis prediction performs a synthesis prediction by performing synthesis processing of synthesizing a prediction image of an inter prediction and a prediction image of an intra prediction to a decoding-target block; and

generating a decoded image based on the prediction image generated in the prediction image generation and a difference image of the decoding-target block, wherein

types of predictions that can be used in the prediction image generation include a first prediction mode and a second prediction mode,

synthesis processing includes weighting processing performed to the prediction image of the inter prediction and the prediction image of the intra prediction, and

processing states of weighting processing include setting a smallest weighting for the prediction image of the intra prediction while the type of the intra prediction is the first prediction mode, wherein

the first prediction mode is an intra prediction mode that includes generating a prediction image based on a first linear interpolation and a second linear interpolation, the first linear interpolation uses pixel values of a first pair of reference pixels, a first reference pixel of the first pair of reference pixels is located outside the decoding-target block and a second reference pixel of the first pair of reference pixels is located inside the decoding-target block, and the second linear interpolation uses pixel values of a second pair of reference pixels, a first reference pixel of the second pair of reference pixels is a reference pixel located outside the decoding-target block and a second reference pixel of the second pair of reference pixels is a reference pixel located inside the decoding-target block, and

the second prediction mode is an in-screen block copy mode, wherein

checking processing for checking both whether an available adjacent block exists immediately above the decoding-target block or not, whether an available adjacent block exists immediately on the left of the decoding-target block or not, are conducted for the weighting processing, and

wherein both a result of checking whether an available adjacent block exists immediately above the decoding-target block or not, and a result of checking whether an available adjacent block exists immediately on the left of the decoding-target block or not, effect a result of the weighting processing.