Method for encoding/decoding image signal, and apparatus therefor

A video encoding method comprising:

• in case to derive a first prediction and a second prediction corresponding to a coding block, determining a partition type of the coding block;
• a
• deriving first motion information regarding the first prediction of the coding block and second motion information regarding the second prediction of the coding block;
• and
• acquiring a prediction sample of the coding block on the basis of the first motion information and the second motion information,
• wherein
• the first motion information regarding the first prediction is derived from a first merge candidate among a plurality of merge candidates included in a merge candidate list,
• the second motion information regarding the second prediction is derived from a second merge candidate among the plurality of merge candidates included in the merge candidate list, and
• first index information for specifying the first merge candidate and second index information for specifying the second merge candidate are respectively encoded;
• wherein when an index for indicating the second merge candidate is greater than an index for indicating the first merge candidate, the second index information is encoded with a value obtained by subtracting one from the index for indicating the second merge candidate.

A video decoder, comprising:

• a memory having stored instructions;
• a processor for executing the instructions to:
• in case to derive a first prediction and a second prediction corresponding to a coding block, determine a partition type of the coding block, derive first motion information regarding the first prediction of the coding block and second motion information regarding the second prediction of the coding block, and acquire a prediction sample of the coding block on the basis of the first motion information and the second motion information,
• wherein
• the first motion information regarding the first prediction is derived from a first merge candidate specified by first index information among a plurality of merge candidates included in a merge candidate list, and the second motion information regarding the second prediction is derived from a second merge candidate specified by second index information among the plurality of merge candidates included in the merge candidate list;
• wherein when a value of the second index information is greater than or equal to a value of the first index information, the second merge candidate is indicated by an index equal to the value of the second index information plus one.

A video encoder, comprising:

• a memory having stored instructions;
• a processor for executing the instructions to:
• in case to derive a first prediction and a second prediction corresponding to a coding block, determine a partition type of the coding block;
• derive first motion information regarding the first prediction of the coding block and second motion information regarding the second prediction of the coding block;
• and
• acquire a prediction sample of the coding block on the basis of the first motion information and the second motion information,
• wherein
• the first motion information regarding the first prediction is derived from a first merge candidate among a plurality of merge candidates included in a merge candidate list,
• the second motion information regarding the second prediction is derived from a second merge candidate among the plurality of merge candidates included in the merge candidate list, and
• first index information for specifying the first merge candidate and second index information for specifying the second merge candidate are respectively encoded;
• wherein when an index for indicating the second merge candidate is greater than an index for indicating the first merge candidate, the second index information is encoded with a value obtained by subtracting one from the index for indicating the second merge candidate.