# US 11,451,821 B2 · Image coding method and apparatus using motion vector > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,821 B2 - Document ID: US11451821B2 - Status: Granted - Kind: B2 - Application number: 17/559,417 - Filed: 2021-12-22 - Published: 2022-04-14 - Granted: 2022-09-20 - Earliest claimed: 2019-06-24 - Assignees: LG Electronics Inc. - Applicants: LG Electronics Inc. - Inventors: Naeri Park; Junghak Nam; Hyeongmoon Jang - Web page: https://patentgrep.com/patent/US11451821B2 ## CPC - H04N 19/52: by predictive encoding - H04N 19/105: Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction - H04N 19/109: among a plurality of temporal predictive coding modes - H04N 19/132: Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking - H04N 19/139: Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability - H04N 19/159: Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction - H04N 19/172: the region being a picture, frame or field - H04N 19/176: the region being a block, e.g. a macroblock - H04N 19/573: Motion compensation with multiple frame prediction using two or more reference frames in a given prediction direction - H04N 19/577: Motion compensation with bidirectional frame interpolation, i.e. using B-pictures - H04N 19/70: characterised by syntax aspects related to video coding, e.g. related to compression standards - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract According to embodiments according to the present document, merge mode motion vector differences (MMVD) and symmetric motion vector differences (SMVD) may be performed on the basis of reference picture types and, in particular, short-term reference pictures may be used. Accordingly, prediction performance and coding efficiency in an inter prediction mode may be increased. ## Claims ### Claim 1 An image decoding method performed by a decoding apparatus, the method comprising: receiving image information including prediction related information and residual information from a bitstream; deriving an inter prediction mode for a current block in a current picture based on the prediction related information; deriving motion information for the current block based on the inter prediction mode; generating prediction samples based on the motion information; generating residual samples based on the residual information; and generating reconstructed samples of the current picture based on the prediction samples and the residual samples, wherein the prediction related information includes inter prediction type information specifying whether bi-prediction is applied to the current block, wherein the prediction related information further includes symmetric motion vector difference flag information specifying whether symmetric motion vector difference reference is applied, based on the inter prediction type information, wherein based on the symmetric motion vector difference reference flag information, symmetric motion vector difference reference indices are derived from reference indices indicating short-term reference picture, wherein the motion information includes motion vectors for the current block and the symmetric motion vector difference reference indices, and wherein the prediction samples are generated based on the motion vectors and the symmetric motion vector difference reference indices. ### Claim 2 (depends on 1) The image decoding method of claim 1, wherein the symmetric motion vector difference reference indices are derived based on picture order count (POC) differences between each of the short-term reference pictures and the current picture. ### Claim 3 (depends on 2) The image decoding method of claim 2, further including configuring a reference picture list L0 for L0 prediction and a reference picture list L1 for L1 prediction, wherein the short-term reference pictures include a short-term reference picture L0 included in the reference picture list L0 and a short-term reference picture L1 included in the reference picture list L1, wherein the POC differences include a first POC difference between the short-term reference picture L0 and the current picture and a second POC difference between the short-term reference picture L1 and the current picture, wherein the symmetric motion vector difference reference indices include a symmetric motion vector difference reference index L0 and a symmetric motion vector difference reference index L1, wherein the symmetric motion vector difference reference index L0 is derived based on the first POC difference, and wherein the symmetric motion vector difference reference index L1 is derived based on the second POC difference. ### Claim 4 (depends on 3) The image decoding method of claim 3, wherein the first POC difference is identical with the second POC difference. ### Claim 5 (depends on 2) The image decoding method of claim 2, further including configuring a reference picture list L0 for L0 prediction, wherein the short-term reference pictures include a first short-term reference picture L0 and a second short-term reference picture L0 included in the reference picture list L0, wherein the POC differences include a third POC difference between the first short-term reference picture L0 and the current picture and a fourth POC difference between the second short-term reference picture L0 and the current picture, wherein the symmetric motion vector difference reference indices include a symmetric motion vector difference reference index L0, and wherein a reference picture index specifying the first short-term reference picture L0 is used as the symmetric motion vector difference reference index L0 based on a comparison between the third and fourth POC differences. ### Claim 6 (depends on 5) The image decoding method of claim 5, wherein when the third POC difference is smaller than the fourth POC difference, a reference picture index specifying the first short-term reference picture L0 is used as the symmetric motion vector difference reference index L0. ### Claim 7 (depends on 1) The image decoding method of claim 1, wherein the image information include information about motion vector differences (MVD), wherein the motion information includes motion vectors (MVs), wherein MVDL0 for L0 prediction is derived based on the information about the MVD, wherein MVDL1 for L1 prediction is derived based on the MVDL0, and wherein the MVs are derived based on the MVDL0 and the MVDL1. ### Claim 8 (depends on 7) The image decoding method of claim 7, wherein a size of MVDL1 is identical with a size of MVDL0, and wherein a sign of the MVDL1 is opposite to a sign of the MVDL0. ### Claim 9 An image encoding method performed by an encoding apparatus, comprising: deriving an inter prediction mode for a current block in a current picture; deriving reference pictures for the inter prediction mode; deriving motion information for prediction of a current block based on the inter prediction mode; generating prediction samples based on the motion information; generating prediction related information including the inter prediction mode; generating residual information based on the prediction samples; encoding image information including the prediction related information and the residual information, wherein the prediction related information includes inter prediction type information specifying whether bi-prediction is applied to the current block, wherein the prediction related information further includes symmetric motion vector difference flag information specifying whether symmetric motion vector difference reference is applied, based on the inter prediction type information, wherein the reference pictures include short-term reference pictures, wherein based on the symmetric motion vector difference reference flag information, symmetric motion vector difference reference indices are derived from reference indices indicating the short-term reference picture, wherein the motion information includes motion vectors for the current block and the symmetric motion vector difference reference indices, and wherein the prediction samples are generated based on the motion vectors and the symmetric motion vector difference reference indices. ### Claim 10 (depends on 9) The image encoding method of claim 9, wherein the symmetric motion vector difference reference indices are derived based on picture order count (POC) differences between each of the short-term reference pictures and the current picture. ### Claim 11 (depends on 10) The image encoding method of claim 10, further including configuring a reference picture list L0 for L0 prediction and a reference picture list L1 for L1 prediction, wherein the short-term reference pictures include a short-term reference picture L0 included in the reference picture list L0 and a short-term reference picture L1 included in the reference picture list L1, wherein the POC differences include a first POC difference between the short-term reference picture L0 and the current picture and a second POC difference between the short-term reference picture L1 and the current picture, wherein the symmetric motion vector difference reference indices include a symmetric motion vector difference reference index L0 and a symmetric motion vector difference reference index L1, wherein the symmetric motion vector difference reference index L0 is derived based on the first POC difference, and wherein the symmetric motion vector difference reference index L1 is derived based on the second POC difference. ### Claim 12 (depends on 11) The image encoding method of claim 11, wherein the first POC difference is identical with the second POC difference. ### Claim 13 (depends on 10) The image encoding method of claim 10, further including configuring a reference picture list L0 for L0 prediction, wherein the short-term reference pictures include a first short-term reference picture L0 and a second short-term reference picture L0 included in the reference picture list L0, wherein the POC differences include a third POC difference between the first short-term reference picture L0 and the current picture and a fourth POC difference between the second short-term reference picture L0 and the current picture, wherein the symmetric motion vector difference reference indices include a symmetric motion vector difference reference index L0, and wherein a reference picture index specifying the first short-term reference picture L0 is used as the symmetric motion vector difference reference index L0 based on a comparison between the third and fourth POC differences. ### Claim 14 (depends on 13) The image encoding method of claim 13, wherein when the third POC difference is smaller than the fourth POC difference, a reference picture index specifying the first short-term reference picture L0 is used as the symmetric motion vector difference reference index L0. ### Claim 15 (depends on 9) The image encoding method of claim 9, wherein the image information include information about motion vector differences (MVD), wherein the motion information includes motion vectors (MVs), wherein MVDL0 for L0 prediction is derived based on the information about the MVD, wherein MVDL1 for L1 prediction is derived based on the MVDL0, and wherein the MVs are derived based on the MVDL0 and the MVDL1. ### Claim 16 (depends on 15) The image decoding method of claim 15, wherein a size of MVDL1 is identical with a size of MVDL0, and wherein a sign of the MVDL1 is opposite to a sign of the MVDL0. ### Claim 17 A non-transitory computer readable storage medium storing a bitstream generated by a method, wherein the method comprising: deriving an inter prediction mode for a current block in a current picture; deriving reference pictures for the inter prediction mode; deriving motion information for prediction of a current block based on the inter prediction mode; generating prediction samples based on the motion information; generating prediction related information including the inter prediction mode; generating residual information based on the prediction samples; encoding image information including the prediction related information and the residual information to output the bitstream, wherein the prediction related information includes inter prediction type information specifying whether bi-prediction is applied to the current block, wherein the prediction related information further includes symmetric motion vector difference flag information specifying whether symmetric motion vector difference reference is applied, based on the inter prediction type information, wherein the reference pictures include short-term reference pictures, wherein based on the symmetric motion vector difference reference flag information, symmetric motion vector difference reference indices are derived from reference indices indicating the short-term reference picture, wherein the motion information includes motion vectors for the current block and the symmetric motion vector difference reference indices, and wherein the prediction samples are generated based on the motion vectors and the symmetric motion vector difference reference indices.