Image encoding method

A coded picture signal generated using a picture coding method of coding a plurality of pictures included in a picture signal in the following manner:

• coding each of predetermined pictures as an entry picture without reference to another picture;
• and coding each of the pictures other than the entry pictures with reference to another coded picture,
• wherein the picture coding method comprises:
• a first reference restriction step of restricting, in a target access unit to be processed, so that a post-entry picture located after the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in coding order;
• and a pre-entry picture which is located before the entry picture in display order and refers to a picture located before the entry picture in coding order;
• and
• a second reference restriction step of restricting, in an access unit immediately following the target access unit, so that a pre-entry picture located before the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in the target access unit in coding order;
• and a pre-entry picture included in the target access unit, which refers to a picture located before the entry picture in the target access unit in coding order.

A program for coding a plurality of pictures included in a picture signal for generating a coded picture signal in the following manner:

• coding each of predetermined pictures as an entry picture without reference to another picture;
• and coding each of the pictures other than the entry pictures with reference to another coded picture,
• wherein the picture signal is processed per access unit which is made up of a plurality of pictures including the entry picture, and
• the program causes a computer to execute the following:
• a first reference restriction step of restricting, in a target access unit to be processed, so that a post-entry picture located after the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in coding order;
• and a pre-entry picture which is located before the entry picture in display order and refers to a picture located before the entry picture in coding order;
• and
• a second reference restriction step of restricting, in an access unit immediately following the target access unit, so that a pre-entry picture located before the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in the target access unit in coding order;
• and a pre-entry picture included in the target access unit, which refers to a picture located before the entry picture in the target access unit in coding order.

A recording medium storing a program for coding a plurality of pictures included in a picture signal for generating a coded picture signal in the following manner:

• coding each of predetermined pictures as an entry picture without reference to another picture;
• and coding each of the pictures other than the entry pictures with reference to another coded picture,
• wherein in the program, the picture signal is processed per access unit which is made up of a plurality of pictures including the entry picture, and
• the recording medium causes a computer to execute the following:
• a first reference restriction step of restricting, in a target access unit to be processed, so that a post-entry picture located after the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in coding order;
• and a pre-entry picture which is located before the entry picture in display order and refers to a picture located before the entry picture in coding order;
• and
• a second reference restriction step of restricting, in an access unit immediately following the target access unit, so that a pre-entry picture located before the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in the target access unit in coding order;
• and a pre-entry picture included in the target access unit, which refers to a picture located before the entry picture in the target access unit in coding order.

A picture coding apparatus for coding a plurality of pictures included in a picture signal for generating a coded picture signal in the following manner:

• coding each of predetermined pictures as an entry picture without reference to another picture;
• and coding each of the pictures other than the entry pictures with reference to another coded picture,
• wherein the picture signal is processed per access unit which is made up of a plurality of pictures including the entry picture, and
• the apparatus comprises:
• a first reference restriction unit operable to restrict, in a target access unit to be processed, so that a post-entry picture located after the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in coding order;
• and a pre-entry picture which is located before the entry picture in display order and refers to a picture located before the entry picture in coding order;
• and
• a second reference restriction unit operable to restrict, in an access unit immediately following the target access unit, so that a pre-entry picture located before the entry picture in display order refers to another picture except for the following pictures:
• a picture located before the entry picture in the target access unit in coding order;
• and a pre-entry picture included in the target access unit, which refers to a picture located before the entry picture in the target access unit in coding order.