Picture coding supporting block partitioning and block merging

An encoder configured to encode a picture into a bitstream, the encoder being configured to:

• signal, within the bitstream, one of supported partitioning patterns for a current block of the picture;
• and
• if the signaled one of the supported partitioning patterns specifies a subdivision of the current block into a plurality of sub-blocks,
• determine coding parameter candidates for a current sub-block of the plurality of sub-blocks,
• check whether a total number of the determined coding parameter candidates is equal to a predetermined number of coding parameter candidates needed to complete a set of coding parameter candidates for the current sub-block, and
• based on an indication from the check that the total number of the determined coding parameter candidates is not equal to the predetermined number of coding parameter candidates, provide one or more ancillary coding parameter candidates including a zero motion vector parameter to the set of coding parameter candidates to complete the set, wherein:
• the current sub-block is not a first sub-block of the plurality of sub-blocks in a coding order, and
• a coding parameter candidate associated with any candidate sub-block is excluded from the set of coding parameter candidates for the current sub-block if the candidate sub-block, when being merged with the current sub-block, results in one of the supported partitioning patterns.

A method for decoding a data stream, comprising:

• obtaining, in the data stream, data signaling one of supported partitioning patterns for a current block of a picture;
• determining that the signaled one of the supported partitioning patterns specifies a subdivision of the current block into a plurality of sub-blocks;
• determining coding parameter candidates for a current sub-block of the plurality of sub-blocks;
• checking whether a total number of the determined coding parameter candidates is equal to a predetermined number of coding parameter candidates needed to complete a set of coding parameter candidates for the current sub-block;
• and
• based on an indication from the check that the total number of the determined coding parameter candidates is not equal to the predetermined number of coding parameter candidates, providing one or more ancillary coding parameter candidates including a zero motion vector parameter to the set of coding parameter candidates to complete the set, wherein:
• the current sub-block is not a first sub-block of the plurality of sub-blocks in a coding order, and
• a coding parameter candidate associated with any candidate sub-block is excluded from the set of coding parameter candidates for the current sub-block if the candidate sub-block, when being merged with the current sub-block, results in one of the supported partitioning patterns.

A method for encoding a picture into a data stream, comprising:

• signaling, within the data stream, one of supported partitioning patterns for a current block of the picture;
• and
• if the signaled one of the supported partitioning patterns specifies a subdivision of the current block into a plurality of sub-blocks,
• determining coding parameter candidates for a current sub-block of the plurality of sub-blocks,
• checking whether a total number of the determined coding parameter candidates is equal to a predetermined number of coding parameter candidates needed to complete a set of coding parameter candidates for the current sub-block, and
• based on an indication from the check that the total number of the determined coding parameter candidates is not equal to the predetermined number of coding parameter candidates, providing one or more ancillary coding parameter candidates including a zero motion vector parameter to the set of coding parameter candidates to complete the set, wherein:
• the current sub-block is not a first sub-block of the plurality of sub-blocks in a coding order, and
• a coding parameter candidate associated with any candidate sub-block is excluded from the set of coding parameter candidates for the current sub-block if the candidate sub-block, when being merged with the current sub-block, results in one of the supported partitioning patterns.