Image predict coding method, image predict coding device, image predict coding program, image predict decoding method, image predict decoding device, and image predict decoding program

An image predictive decoding method executed by an image predictive decoding device, the image predictive decoding method comprising:

• inputting a compressed target block and an encoded prediction mode syntax including a flag and either an index or a REM mode;
• generating a candidate prediction mode list listing intra-prediction modes used to predict blocks neighboring the target block, the candidate prediction mode list containing no duplicate prediction modes therein;
• responsive to a determination that the flag carries a first value, selecting an intra-prediction mode in the candidate prediction mode list which is identified by the index;
• decompressing the target block using the intra-prediction mode selected from the candidate prediction mode list;
• responsive to a determination that the flag carries a second value different from the first value, setting a variable equal to a value of the REM mode and recursively performing a round of mode restoration process on a respective intra-prediction mode listed in the candidate prediction mode list sequentially from an intra-prediction mode of a smallest value through an intra-prediction mode of a highest value in the candidate prediction mode list, wherein a respective round of mode restoration process comprises comparing a value of the variable with a value of an intra-prediction mode in the candidate prediction mode list and, if the value of the variable is greater than or equal to the value of the intra-prediction mode, incrementing the value of the variable, or otherwise keeping the value of the variable unchanged, to provide a next value of the variable for comparison in a next round with a next intra-prediction mode in the candidate prediction mode list;
• and
• decompressing the target block using an intra-prediction mode whose value is equal to a final value of the variable derived after performance of the rounds of mode restoration process.

An image predictive decoding method executed by an image predictive decoding device, the image predictive decoding method comprising:

• inputting a compressed target block and an encoded prediction mode syntax including a flag and either an index or a REM mode;
• generating a candidate prediction mode list listing intra-prediction modes used to predict blocks neighboring the target block, generating a candidate prediction mode list comprising comparing the intra-prediction modes of the neighboring blocks, to identify any duplicate intra-prediction modes included among the intra-prediction modes, and listing intra-prediction modes in the candidate prediction mode list without duplication of intra-prediction modes;
• responsive to a determination that the flag carries a first value, selecting an intra-prediction mode in the candidate prediction mode list which is identified by the index;
• decompressing the target block using the intra-prediction mode selected from the candidate prediction mode list;
• responsive to a determination that the flag carries a second value different from the first value, setting a variable equal to a value of the REM mode and recursively performing a round of mode restoration process on a respective intra-prediction mode listed in the candidate prediction mode list sequentially from an intra-prediction mode of a smallest value through an intra-prediction mode of a highest value in the candidate prediction mode list, wherein a respective round of mode restoration process comprises comparing a value of the variable with a value of an intra-prediction mode in the candidate prediction mode list and, if the value of the variable is greater than or equal to the value of the intra-prediction mode, incrementing the value of the variable, or otherwise keeping the value of the variable unchanged, to provide a next value of the variable for comparison in a next round with a next intra-prediction mode in the candidate prediction mode list;
• and
• decompressing the target block using an intra-prediction mode whose value is equal to a final value of the variable derived after performance of the rounds of mode restoration process.