# US 11,451,783 B2 · Image decoding method using context-coded sign flag in image coding system and apparatus therefor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,783 B2 - Document ID: US11451783B2 - Status: Granted - Kind: B2 - Application number: 17/436,207 - Filed: 2020-03-04 - Published: 2022-02-10 - Granted: 2022-09-20 - Earliest claimed: 2019-03-04 - Assignees: LG Electronics Inc. - Applicants: LG Electronics Inc. - Inventors: Sunmi Yoo; Jin Heo; Jungah Choi; Seunghwan Kim - Web page: https://patentgrep.com/patent/US11451783B2 ## CPC - 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 19/91: Entropy coding, e.g. variable length coding [VLC] or arithmetic coding - H04N 19/159: Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction - H04N 19/176: the region being a block, e.g. a macroblock - H04N 19/196: being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters (processing of motion vectors H04N19/513) - H04N 19/70: characterised by syntax aspects related to video coding, e.g. related to compression standards - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract An image decoding method performed by a decoding device according to the present document comprises the steps of: deriving a context model for a sign flag of a current residual coefficient of a current block; and decoding the sign flag on the basis of the context model, wherein the context model for the sign flag is derived on the basis of a sign flag of a residual coefficient decoded before the current residual coefficient in the current block. ## Claims ### Claim 1 An image decoding method, performed by a decoding apparatus, comprising: receiving residual information for a current block; deriving a prediction sample of the current block; deriving a context model for a sign flag of a current residual coefficient of the current block; decoding the sign flag based on the context model; deriving the current residual coefficient based on the sign flag; deriving a residual sample based on the current residual coefficient; and generating a reconstructed picture based on the prediction sample and the residual sample, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient decoded prior to the current residual coefficient in the current block. ### Claim 2 (depends on 1) The image decoding method of claim 1, wherein when the current residual coefficient is a residual coefficient first decoded in the current block including the current residual coefficient, the context model for the sign flag of the current residual coefficient is derived as a context model 0. ### Claim 3 (depends on 1) The image decoding method of claim 1, wherein when a value of the sign flag of the residual coefficient decoded prior to the current residual coefficient is 0, the context model for the sign flag of the current residual coefficient is derived as a context model 0, and wherein when the value of the sign flag of the residual coefficient decoded prior to the current residual coefficient is 1, the context model for the sign flag of the current residual coefficient is derived as a context model 1. ### Claim 4 (depends on 1) The image decoding method of claim 1, wherein the context model for the sign flag is derived as one of a plurality of context models based on sign flags of a plurality of residual coefficients decoded prior to the current residual coefficient in the current block. ### Claim 5 (depends on 1) The image decoding method of claim 1, wherein when a current sub-block in the current block is not a sub-block decoded in the first order and the current residual coefficient is a residual coefficient decoded first in the current sub-block, the residual coefficient decoded prior to the current residual coefficient is derived as a residual coefficient decoded last in a sub-block decoded prior to the current sub-block. ### Claim 6 (depends on 1) The image decoding method of claim 1, wherein the residual coefficient decoded prior to the current residual coefficient is a residual coefficient adjacent to the current residual coefficient. ### Claim 7 (depends on 1) The image decoding method of claim 1, further comprising determining whether the sign flag is decoded based on the context model, based on whether transform of the current block is applied. ### Claim 8 (depends on 7) The image decoding method of claim 7, wherein when the transform is applied to the current block, the sign flag is bypass-decoded, wherein when the transform is not applied to the current block, the sign flag is decoded based on the context model. ### Claim 9 An image encoding method, performed by an encoding apparatus, comprising: deriving a residual sample of a current block; deriving a current residual coefficient of the current block based on the residual sample; deriving a context model for a sign flag of the current residual coefficient; encoding the sign flag based on the context model; and generating a bitstream including the sign flag, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient encoded prior to the current residual coefficient in the current block. ### Claim 10 (depends on 9) The image encoding method of claim 9, wherein when the current residual coefficient is a residual coefficient first encoded in the current block including the current residual coefficient, the context model for the sign flag of the current residual coefficient is derived as a context model 0. ### Claim 11 (depends on 9) The image encoding method of claim 9, wherein when a value of the sign flag of the residual coefficient encoded prior to the current residual coefficient is 0, the context model for the sign flag of the current residual coefficient is derived as a context model 0, and wherein when the value of the sign flag of the residual coefficient encoded prior to the current residual coefficient is 1, the context model for the sign flag of the current residual coefficient is derived as a context model 1. ### Claim 12 (depends on 9) The image encoding method of claim 9, wherein the context model for the sign flag is derived as one of a plurality of context models based on sign flags of a plurality of residual coefficients encoded prior to the current residual coefficient in the current block. ### Claim 13 (depends on 9) The image encoding method of claim 9, wherein when a current sub-block in the current block is not a sub-block encoded in the first order and the current residual coefficient is a residual coefficient encoded first in the current sub-block, the residual coefficient encoded prior to the current residual coefficient is derived as a residual coefficient encoded last in a sub-block encoded prior to the current sub-block. ### Claim 14 (depends on 9) The image encoding method of claim 9, further comprising determining whether the sign flag is encoded based on the context model, based on whether transform of the current block is applied. ### Claim 15 A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising: deriving a residual sample of a current block; deriving a current residual coefficient of the current block based on the residual sample; deriving a context model for a sign flag of the current residual coefficient encoding the sign flag based on the context model; and generating the bitstream including the sign flag, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient encoded prior to the current residual coefficient in the current block. ### Claim 16 A transmission method of data for image, the method comprising: obtaining a bitstream of image information including a sign flag of a current residual coefficient of a current block; and transmitting the data including the bitstream of the image information including the sign flag, wherein the current residual coefficient is derived based on a residual sample of the current block, wherein the sign flag is encoded based on a context model for the sign flag, and wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient encoded prior to the current residual coefficient in the current block.