Picture coding device, picture coding method, picture coding program, picture decoding device, picture decoding method, and picture decoding program

1. A picture decoding device that performs intra prediction decoding of a picture signal including a luma signal and a chroma signal in units of blocks by decoding information relating to an intra prediction mode, the picture decoding device comprising:

a luma intra prediction mode derivation unit that is configured to derive a value of a luma intra prediction mode; and

an intra prediction mode derivation unit that is configured to derive a value of a chroma intra prediction mode from a conversion table representing a value of the chroma intra prediction mode having a chroma format of 4:2:2 based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal, which is derived by the luma intra prediction mode derivation unit, in a case where the chroma format is 4:2:2 and derive a value of the chroma intra prediction mode based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal without using the conversion table in a case where the chroma format is not 4:2:2,

wherein the conversion table shows at least values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing ½ times scaling horizontally for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are horizontally aligned and values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing two-times scaling vertically for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are vertically aligned.

2. A picture decoding method for performing intra prediction decoding of a picture signal including a luma signal and a chroma signal in units of blocks by decoding information relating to an intra prediction mode, the picture decoding method comprising:

deriving a value of a luma intra prediction mode; and

deriving a value of a chroma intra prediction mode from a conversion table representing a value of the chroma intra prediction mode having a chroma format of 4:2:2 based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal, which is derived in the deriving of a value of the luma intra prediction mode, in a case where the chroma format is 4:2:2 and deriving a value of the chroma intra prediction mode based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal without using the conversion table in a case where the chroma format is not 4:2:2,

wherein the conversion table shows at least values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing ½ times scaling horizontally for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are horizontally aligned and values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing two-times scaling vertically for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are vertically aligned.

3. Non-transitory recording medium in which a picture decoding program causing a computer to execute performing intra prediction decoding of a picture signal including a luma signal and a chroma signal in units of blocks by decoding information relating to an intra-prediction mode is stored, the picture decoding program causing the computer to execute: deriving a value of a luma intra prediction mode; and deriving a value of a chroma intra prediction mode from a conversion table representing a value of the chroma intra prediction mode having a chroma format of 4:2:2 based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal, which is derived in the deriving of a value of the luma intra prediction mode, in a case where the chroma format is 4:2:2 and deriving a value of the chroma intra prediction mode based on a value of the luma intra prediction mode of a prediction block located at a same position as the position of a prediction block of the chroma signal without using the conversion table in a case where the chroma format is not 4:2:2, Wherein the conversion table shows at least values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing ½ times scaling horizontally for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are horizontally aligned and values representing a plurality of chroma intra prediction modes having prediction directions that are respectively closest to a plurality of directions derived by performing two-times scaling vertically for prediction directions of a plurality of the luma intra prediction modes in which reference destinations are vertically aligned.