Three-dimensional data decoding method, three-dimensional data encoding device, and three-dimensional data decoding device

1 . A three-dimensional data decoding method comprising:

selecting, from among contexts, a first context for an encoded first information item to be processed; and

arithmetic-decoding the encoded first information item to be processed, using the first context, to generate a first information item to be processed,

wherein encoded first information items including the encoded first information item to be processed are included in a bitstream generated by encoding an information item about positions of three-dimensional points,

the encoded first information items are generated by arithmetic-encoding first information items including the first information item to be processed,

each of the three-dimensional points is assigned to one of a plurality of reference positions,

each of the reference positions contains a first direction component and a second direction component,

each of the reference positions is a reference position to which no three-dimensional point is assigned or a reference position to which one or more three-dimensional points are assigned, and

the first information items each correspond to a different one of the reference positions and indicate whether a three-dimensional point assigned to a reference position corresponding to the first information item is present.

2 . The three-dimensional data decoding method according to claim 1 ,

wherein in the selecting of the first context, the first context is selected based on an information item about a reference position corresponding to a decoded three-dimensional point among the reference positions.

3 . The three-dimensional data decoding method according to claim 2 ,

wherein the information item about the reference position corresponding to the decoded three-dimensional point is a first information item corresponding to the reference position corresponding to the decoded three-dimensional point.

4 . The three-dimensional data decoding method according to claim 1 ,

wherein the information item about the positions of the three-dimensional points expresses each of the positions using a distance component, the first direction component, and the second direction component.

5 . The three-dimensional data decoding method according to claim 4 ,

wherein in the selecting of the first context, the first context is selected based on an information item about a first reference position that corresponds to a decoded three-dimensional point and contains a first direction component having a same value as a first direction component contained in a second reference position corresponding to the first information item to be processed.

6 . The three-dimensional data decoding method according to claim 5 ,

wherein first information items corresponding to reference positions are arithmetic-decoded in an order based on the first direction component in a processing unit composed of the first information items, the reference positions containing second direction components having a same value.

7 . The three-dimensional data decoding method according to claim 6 ,

wherein the first direction component is a vertical component,

the second direction component is a horizontal component, and

the first information items are arithmetic-decoded in the order based on the vertical component.

8 . The three-dimensional data decoding method according to claim 4 ,

wherein the first information item to be processed indicates a first difference between a value of the first direction component of a three-dimensional point to be processed and a value of the first direction component contained in a first reference position corresponding to the three-dimensional point to be processed.

9 . The three-dimensional data decoding method according to claim 4 ,

wherein the first information item to be processed indicates a third difference that is a difference between a first difference and a second difference,

the first difference is a difference between a value of the first direction component of the three-dimensional point to be processed and a value of the first direction component contained in a first reference position corresponding to the three-dimensional point to be processed, and

the second difference is a difference between a value of the first direction component of a decoded three-dimensional point and a value of the first direction component contained in a second reference position corresponding to the decoded three-dimensional point.

10 . The three-dimensional data decoding method according to claim 1 ,

wherein the reference positions correspond to sampling positions in a sensor for generating the three-dimensional points.

11 . The three-dimensional data decoding method according to claim 1 ,

wherein when intra prediction is applied to a three-dimensional point to be processed, the first context is selected by a first method, and

when inter prediction is applied to the three-dimensional point to be processed, the first context is selected by a second method that is different from the first method.

12 . The three-dimensional data decoding method according to claim 11 ,

wherein in the second method, the first context is selected by reference to a processed frame that is different from a frame to be processed that includes the three-dimensional point to be processed.

13 . A three-dimensional data encoding device comprising:

a processor; and

memory,

wherein using the memory, the processor:

determines, from among reference positions, a reference position corresponding to each of a plurality of three-dimensional points, wherein each of the three-dimensional points is assigned to one of the reference positions;

generates first information items each of which corresponds to a different one of the reference positions and indicates whether a three-dimensional point assigned to a reference position corresponding to the first information item is present;

selects, from among contexts, a first context for a first information item to be processed that is included in the first information items; and

arithmetic-encodes the first information item to be processed, using the first context,

each of the reference positions contains a first direction component and a second direction component, and

each of the reference positions is a reference position to which no three-dimensional point is assigned or a reference position to which one or more three-dimensional points are assigned.

14 . A three-dimensional data decoding device comprising:

a processor; and

memory,

wherein using the memory, the processor:

selects, from among contexts, a first context for an encoded first information item to be processed; and

arithmetic-decodes the encoded first information item to be processed, using the first context, to generate a first information item to be processed,

encoded first information items including the encoded first information item to be processed are included in a bitstream generated by encoding an information item about positions of three-dimensional points,

the encoded first information items are generated by arithmetic-encoding first information items including the first information item to be processed,

each of the three-dimensional points is assigned to one of a plurality of reference positions,

each of the reference positions contains a first direction component and a second direction component,

each of the reference positions is a reference position to which no three-dimensional point is assigned or a reference position to which one or more three-dimensional points are assigned, and

the first information items each correspond to a different one of the reference positions and indicate whether a three-dimensional point assigned to a reference position corresponding to the first information item is present.