Encoding device, decoding device, encoding method, and decoding method

An encoding device comprising:

• memory;
• and
• a circuit having access to the memory,
• wherein in operation, the circuit:
• for each of faces forming a three-dimensional mesh, encodes a connection type regarding a connection relationship between the face to be processed and a face not yet processed, in reverse order of processing order in which the connection type is defined;
• and
• in encoding a current connection type that is the connection type to be encoded, encodes, as the current connection type, information for identifying the current connection type among a candidate set defined according to a previous connection type, the previous connection type being the connection type encoded before the current connection type,
• when the previous connection type is a left type or an end type, the candidate set does not include a corner type,
• when the previous connection type is neither the left type nor the end type, the candidate set includes the corner type,
• the corner type is a type in which, along a path to the face to be processed in the processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed,
• the left type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is not connected to the left side of the face to be processed, and a face not yet processed is connected to the right side of the face to be processed, and
• the end type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is connected to neither the left side nor the right side of the face to be processed.

A decoding device comprising:

• memory;
• and
• a circuit having access to the memory,
• wherein in operation, the circuit:
• for each of faces forming a three-dimensional mesh, decodes a connection type regarding a connection relationship between the face to be processed and a face not yet processed, using arithmetic decoding based on a context;
• in decoding a current connection type that is the connection type to be decoded, selects the context to be applied to the arithmetic decoding from a plurality of contexts, using a first previous connection type, the first previous connection type being the connection type decoded before the current connection type;
• and
• selects the context according to a total number of one or more corner types when the first previous connection type is a corner type, the one or more corner types being each the corner type and being consecutively decoded up to the first previous connection type, and
• the corner type is a type in which, along a path to the face to be processed in processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed.

A decoding device comprising:

• memory;
• and
• a circuit having access to the memory,
• wherein in operation, the circuit:
• for each of faces forming a three-dimensional mesh, decodes a connection type regarding a connection relationship between the face to be processed and a face not yet processed, in reverse order of processing order in which the connection type is defined;
• and
• in decoding a current connection type that is the connection type to be decoded, decodes, as the current connection type, information for identifying the current connection type among a candidate set defined according to a previous connection type, the previous connection type being the connection type decoded before the current connection type,
• when the previous connection type is a left type or an end type, the candidate set does not include a corner type,
• when the previous connection type is neither the left type nor the end type, the candidate set includes the corner type,
• the corner type is a type in which, along a path to the face to be processed in the processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed,
• the left type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is not connected to the left side of the face to be processed, and a face not yet processed is connected to the right side of the face to be processed, and
• the end type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is connected to neither the left side nor the right side of the face to be processed.

An encoding method comprising:

• for each of faces forming a three-dimensional mesh, encoding a connection type regarding a connection relationship between the face to be processed and a face not yet processed, using arithmetic encoding based on a context;
• in encoding a current connection type that is the connection type to be encoded, selecting the context to be applied to the arithmetic encoding from a plurality of contexts, using a first previous connection type, the first previous connection type being the connection type encoded before the current connection type;
• and
• selecting the context according to a total number of one or more corner types when the first previous connection type is a corner type, the one or more corner types being each the corner type and being consecutively encoded up to the first previous connection type,
• wherein the corner type is a type in which, along a path to the face to be processed in processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed.

An encoding method comprising:

• for each of faces forming a three-dimensional mesh, encoding a connection type regarding a connection relationship between the face to be processed and a face not yet processed, in reverse order of processing order in which the connection type is defined;
• and
• in encoding a current connection type that is the connection type to be encoded, encoding, as the current connection type, information for identifying the current connection type among a candidate set defined according to a previous connection type, the previous connection type being the connection type encoded before the current connection type,
• wherein when the previous connection type is a left type or an end type, the candidate set does not include a corner type,
• when the previous connection type is neither the left type nor the end type, the candidate set includes the corner type,
• the corner type is a type in which, along a path to the face to be processed in the processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed,
• the left type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is not connected to the left side of the face to be processed, and a face not yet processed is connected to the right side of the face to be processed, and
• the end type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is connected to neither the left side nor the right side of the face to be processed.

A decoding method comprising:

• for each of faces forming a three-dimensional mesh, decoding a connection type regarding a connection relationship between the face to be processed and a face not yet processed, using arithmetic decoding based on a context;
• in decoding a current connection type that is the connection type to be decoded, selecting the context to be applied to the arithmetic decoding from a plurality of contexts, using a first previous connection type, the first previous connection type being the connection type decoded before the current connection type;
• and
• selecting the context according to a total number of one or more corner types when the first previous connection type is a corner type, the one or more corner types being each the corner type and being consecutively decoded up to the first previous connection type,
• wherein the corner type is a type in which, along a path to the face to be processed in processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed.

A decoding method comprising:

• for each of faces forming a three-dimensional mesh, decoding a connection type regarding a connection relationship between the face to be processed and a face not yet processed, in reverse order of processing order in which the connection type is defined;
• and
• in decoding a current connection type that is the connection type to be decoded, decoding, as the current connection type, information for identifying the current connection type among a candidate set defined according to a previous connection type, the previous connection type being the connection type decoded before the current connection type,
• wherein when the previous connection type is a left type or an end type, the candidate set does not include a corner type,
• when the previous connection type is neither the left type nor the end type, the candidate set includes the corner type,
• the corner type is a type in which, along a path to the face to be processed in the processing order, two faces not yet processed are connected to both a left side and a right side of the face to be processed, and all of a plurality of faces connected to a vertex of the face to be processed are not yet processed, the plurality of faces including the two faces not yet processed,
• the left type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is not connected to the left side of the face to be processed, and a face not yet processed is connected to the right side of the face to be processed, and
• the end type is a type in which, along the path to the face to be processed in the processing order, a face not yet processed is connected to neither the left side nor the right side of the face to be processed.