Method for encoding/decoding image signal and device therefor

A video encoding method comprising:

• obtaining a first triangular prediction unit and a second triangular prediction unit according to a coding block;
• deriving a merge candidate list for the coding block;
• deriving first motion information for the first triangular prediction unit from a merge candidate, and deriving second motion information for the second triangular prediction unit from another merge candidate;
• wherein the merge candidate is determined based on first index information and a first merge candidate in the merge candidate list, and the another merge candidate is determined based on second index information and a second merge candidate in the merge candidate list, and the second merge candidate is different from the first merge candidate;
• encoding the first index information and the second index information, wherein when an index of the second merge candidate of the second triangular prediction unit is equal to or greater than an index of the first merge candidate of the first triangular prediction unit, the second index information is encoded using a value obtained by adding 1 to the index of the second merge candidate of the second triangular prediction unit;
• and
• obtaining a prediction sample in the coding block based on the first motion information and the second motion information,
• wherein a maximum number of merge candidates that the merge candidate list includes is determined based on whether the first triangular prediction unit and the second triangular prediction unit are obtained.

A video decoding apparatus comprising an inter prediction part configured to:

• obtain a first triangular prediction unit and a second triangular prediction unit according to a coding block;
• derive a merge candidate list for the coding block;
• derive first motion information for the first triangular prediction unit from a merge candidate, and derive the second motion information for the second triangular prediction unit from another merge candidate;
• wherein the merge candidate is determined based on first index information and a first merge candidate in the merge candidate list, and the another merge candidate is determined based on second index information and a second merge candidate in the merge candidate list, and the second merge candidate is different from the first merge candidate;
• wherein the first index information and the second index information are decoded from a bitstream, and when a value of the second index information is equal to or greater than a value of the first index information, the value of the second index information is obtained by adding 1 to the value of the second index information;
• and
• obtain a prediction sample in the coding block based on the first motion information and the second motion information,
• wherein a maximum number of merge candidates that the merge candidate list includes is determined based on whether the first triangular prediction unit and the second triangular prediction unit are obtained.

A video encoding apparatus, comprising an inter prediction part, configured to:

• obtain a first triangular prediction unit and a second triangular prediction unit according to a coding block;
• derive a merge candidate list for the coding block;
• derive first motion information for the first triangular prediction unit from a merge candidate, and derive second motion information for the second triangular prediction unit from another merge candidate;
• wherein the merge candidate is determined based on first index information and a first merge candidate in the merge candidate list, and the another merge candidate is determined based on second index information and a second merge candidate in the merge candidate list, and the second merge candidate is different from the first merge candidate;
• and
• encode the first index information and the second index information, wherein when an index of the second merge candidate of the second triangular prediction unit is equal to or greater than an index of the first merge candidate of the first triangular prediction unit, the second index information is encoded using a value obtained by adding 1 to the index of the second merge candidate of the second triangular prediction unit;
• and
• obtain a prediction sample in the coding block based on the first motion information and the second motion information,
• wherein a maximum number of merge candidates that the merge candidate list includes is determined based on whether the first triangular prediction unit and the second triangular prediction unit are obtained.