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EP-3972254-B1 - METHOD FOR IMAGE CODING USING MOTION VECTOR

EP3972254B1EP 3972254 B1EP3972254 B1EP 3972254B1EP-3972254-B1

Inventors

  • PARK, Naeri
  • NAM, Junghak
  • JANG, Hyeongmoon

Dates

Publication Date
20260506
Application Date
20200615

Claims (3)

  1. An image decoding method performed by a decoding apparatus (300), the method comprising: obtaining (S1800) image information including prediction related information and residual information from a bitstream; deriving (S1810) an inter prediction mode for a current block based on the prediction related information; wherein the prediction related information includes inter prediction type information specifying that bi-prediction is applied to the current block and symmetric motion vector differences, SMVD, flag information specifying that SMVD is applied to the current block, deriving reference picture lists L0 and L1 for the current block; deriving reference picture indexes for the reference picture lists based on the prediction related information; constructing motion vector predictor, MVP, candidate lists based on neighboring blocks of the current block; deriving MVPs for the current block from MVP candidates indicated by an MVP index in the MVP candidate lists; deriving motion vectors for the current block based on symmetric motion vector differences, SMVD, for the current block and the MVPs; and generating (S1830) prediction samples for the current block based on motion information including reference picture indexes and motion vectors; generating (S1840) residual samples of the current block based on the residual information; and generating (51850) reconstructed samples of the current block based on the prediction samples and the residual samples, characterized in that a reference picture index of a first reference picture in the reference picture list L0 is derived as the reference picture index for L0 by checking the first reference picture being a short-term reference picture, a picture order count (POC) difference between a current picture including the current block and the first reference picture being greater than 0, and the POC difference between the current picture and the first reference picture being less than the POC difference between the current picture and other reference picture in the reference picture list L0, and wherein a reference picture index of a second reference picture in the reference picture list L1 is derived as the reference picture index for L1 by checking the second reference picture being the short-term reference picture, the POC difference between the current picture and the second reference picture being less than 0, and the POC difference between the current picture and the second reference picture being greater than the POC difference between the current picture and other reference picture in the reference picture list L1 .
  2. An image encoding method performed by an encoding apparatus (200), the method comprising: deriving (S1600) an inter prediction mode for a current block; deriving reference picture lists L0 and L1 for the current block; deriving reference picture indexes for the reference picture lists based on symmetric motion vector differences, SMVD; constructing motion vector predictor, MVP, candidate lists based on neighboring blocks of the current block; deriving MVPs for the current block based on the MVP candidate lists; generating information on an MVP index related to the MVP included in the MVP candidate lists; deriving motion information of the current block including motion vectors of the current block and reference picture indexes; deriving symmetric motion vector differences, SMVD, based on the MVPs and the motion vectors for the current block; generating (S1630) prediction related information related to the inter prediction mode, and generating information on the MVD; wherein the prediction related information includes inter prediction type information specifying that bi-prediction is applied to the current block and SMVD flag information specifying that SMVD is applied to the current block, generating (S1620) prediction samples of the current block based on the motion information; generating (S1640) residual information based on the prediction samples; and encoding (51650) image information including the prediction related information and the residual information, characterized in that a reference picture index of a first reference picture in the reference picture list L0 is derived as the reference picture index for L0 by checking the first reference picture being a short-term reference picture, a picture order count (POC) difference between a current picture including the current block and the first reference picture being greater than 0, and the POC difference between the current picture and the first reference picture being less than the POC difference between the current picture and other reference picture in the reference picture list L0, and wherein a reference picture index of a second reference picture in the reference picture list L1 is derived as the reference picture index for L1 by checking the second reference picture being the short-term reference picture, the POC difference between the current picture and the second reference picture being less than 0, and the POC difference between the current picture and the second reference picture being greater than the POC difference between the current picture and other reference picture in the reference picture list L1 .
  3. A transmission method of data for an image the method comprising: obtaining a bitstream for the image, wherein the bitstream is generated based on deriving an inter prediction mode for a current block, deriving reference picture lists L0 and L1 for the current block, deriving reference picture indexes for the reference picture lists based on symmetric motion vector differences, SMVD, constructing motion vector predictor, MVP, candidate lists based on neighboring blocks of the current block, deriving MVPs for the current block based on the MVP candidate lists, generating information on an MVP index related to the MVP included in the MVP candidate lists, deriving motion information of the current block including motion vectors of the current block and reference picture indexes, deriving symmetric motion vector differences, SMVD, based on the MVPs and the motion vectors for the current block, generating (S1630) prediction related information related to the inter prediction mode, and generating information on the MVD, wherein the prediction related information includes inter prediction type information specifying that bi-prediction is applied to the current block and SMVD flag information specifying that SMVD is applied to the current block, generating (S1620) prediction samples of the current block based on the motion information, generating (S1640) residual information based on the prediction samples, and encoding (51650) image information including the prediction related information and the residual information; and transmitting the data comprising the bitstream, characterized in that a reference picture index of a first reference picture in the reference picture list L0 is derived as the reference picture index for L0 by checking the first reference picture being a short-term reference picture, a picture order count (POC) difference between a current picture including the current block and the first reference picture being greater than 0, and the POC difference between the current picture and the first reference picture being less than the POC difference between the current picture and other reference picture in the reference picture list L0, and wherein a reference picture index of a second reference picture in the reference picture list L1 is derived as the reference picture index for L1 by checking the second reference picture being the short-term reference picture, the POC difference between the current picture and the second reference picture being less than 0, and the POC difference between the current picture and the second reference picture being greater than the POC difference between the current picture and other reference picture in the reference picture list L1.

Description

BACKGROUND OF THE DISCLOSURE Field of the disclosure The present document is related to a method and a device for image coding using motion vector. Related Art Recently, demand for high-resolution, high-quality image/video such as 4K or 8K or higher ultra high definition (UHD) image/video has increased in various fields. As image/video data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to the existing image/video data, and thus, transmitting image data using a medium such as an existing wired/wireless broadband line or an existing storage medium or storing image/video data using existing storage medium increase transmission cost and storage cost. In addition, interest and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content or holograms has recently increased and broadcasting for image/video is having characteristics different from reality images such as game images has increased. Accordingly, a highly efficient image/video compression technology is required to effectively compress, transmit, store, and reproduce information of a high-resolution, high-quality image/video having various characteristics as described above. Also, inter prediction in image/video coding may include a procedure for symmetric motion vector difference (SMVD) reference indices and/or a procedure for a merge motion vector difference (MMVD). Considering reference picture marking (for example, short-term or long-term reference), there is a discussion of technology performing the procedures. EP 3 912 357 A1 is a prior art document under Art. 54(3) EPC (published on 24 November 2021 and claiming the priority date of 20 February 2019) discloses a method of performing video coding using constraints on motion vector derivation for long-term reference pictures. In the method, the motion vector pointing to the long-term reference picture cannot be modified by signaled MVD in deriving SMVD candidates. A conventional method of integrating symmetrical mode for bi-prediction is discussed by CHEN (HUAWEI) H ET AL: "CE4: Symmetrical MVD mode (Test 4.5.1)", 124. MPEG MEETING; 20181008 - 20181012; MACAO; (MOTION PICTURE EXPERT GROUP OR ISO/IEC JTC1/SC29/WG11), no. JVET-L0370-v1; m44396 25 September 2018 (2018-09-25), pages 1-4. SUMMARY The invention is defined by the appended claims. ADVANTAGEOUS EFFECTS According to the present disclosure, the overall image/video compression efficiency may be improved. According to the present disclosure, signaling of information on motion vector differences may be performed efficiently. According to the present disclosure, L1 motion vector differences may be efficiently derived when bi-prediction is applied to a current block. According to the present disclosure, information used for deriving L1 motion vector differences may be signaled based on the types of reference pictures, and thus the complexity of a coding system may be reduced. According to one embodiment of the present disclosure, efficient inter prediction may be performed using short-term reference pictures for deriving a reference picture index of SMVD. The technical effects achieved through specific embodiments of the present disclosure are not limited to those described above. For example, various other technical effects may be obtained, which may be understood or derived from the present disclosure by a person having ordinary skills in the related art. Therefore, specific effects of the present disclosure are not limited to the embodiments disclosed explicitly in this document and may include various other effects that may be understood or derived from the technical characteristics of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an example of a video/image coding system to which the embodiments of the present document may be applied.FIG. 2 is a diagram schematically illustrating a configuration of a video/image encoding apparatus to which the embodiments of the present document may be applied.FIG. 3 is a schematic diagram illustrating a configuration of a video/image decoding apparatus to which the embodiment(s) of the present disclosure may be applied.FIG. 4 shows an example of a video/image encoding method based on inter prediction.FIG. 5 shows an example of a video/image decoding method based on inter prediction.FIG. 6 exemplarily shows an inter prediction procedure.FIG. 7 shows a method for constructing a merge candidate list according to the present disclosure.FIG. 8 shows a method for constructing an MVP candidate list according to the present disclosure.FIG. 9 is a diagram for describing symmetric motion vector differences (SMVD).FIG. 10 is a diagram for describing a method of deriving motion vectors in inter prediction.FIG. 11 illustrates an MVD derivation process of MMVD according to one embodiment of the present disclosure.FIG. 12 illustrates an MVD derivation process of MMVD according to another embodiment o