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CN-122027801-A - Image decoding method, image encoding method, and image data transmitting method

CN122027801ACN 122027801 ACN122027801 ACN 122027801ACN-122027801-A

Abstract

The present disclosure provides an image decoding method, an image encoding method, and an image data transmitting method. An image decoding method performed by a decoding apparatus according to this document includes the steps of deriving a value of a variable indicating whether all picture storage buffers within a decoded picture buffer DPB are emptied without output based on whether a current picture is a first picture of a current AU of an access unit CVSS AU that is started as an encoded video sequence that is not the access unit AU 0, updating the DPB based on the variable, and decoding the current picture based on the updated DPB.

Inventors

  • Henry Henry
  • JIN SHENGHUAN
  • S. Paluli

Assignees

  • LG电子株式会社

Dates

Publication Date
20260512
Application Date
20210504
Priority Date
20200518

Claims (15)

  1. 1. An image decoding method performed by a decoding apparatus, the image decoding method comprising the steps of: Deriving a value of a variable indicating whether all picture storage buffers in the decoded picture buffer DPB are emptied without output, based on whether the current picture is a first picture of the current access unit AU, the current AU being an encoded video sequence start AU other than AU 0, i.e., a CVSS AU, the AU 0 being the first AU in the bitstream; updating the DPB based on the variable, and Decoding the current picture based on the updated DPB, Wherein the value of the variable is derived after parsing a slice header for the current picture.
  2. 2. The image decoding method of claim 1, wherein when the value of the variable is 1, all picture storage buffers in the DPB are emptied without output, and DPB fullness is set equal to 0.
  3. 3. The image decoding method of claim 2, wherein when the value of the variable is 0, a picture storage buffer including a specific picture in the DPB is emptied without output, and a concave-convex process is performed on a non-empty picture storage buffer in the DPB, and Wherein the specific picture is a picture marked as not needed for output and not used for reference.
  4. 4. The image decoding method of claim 1, wherein the step of deriving the value of the variable comprises: When the current picture is the first picture of the current AU, which is the CVSS AU other than the AU 0, it is determined whether at least one of parameters for the current AU is different in decoding order from parameters of a previous AU for the current AU, Wherein when said at least one of the parameters for said current AU is different from the parameters for said previous AU, the value of said variable is set equal to 1, and Wherein when the parameters for the current AU are the same as the parameters for the previous AU, the value of the variable is set equal to the value of the syntax element signaled for the variable.
  5. 5. The image decoding method of claim 4, wherein the parameters for the current AU include a parameter for a maximum picture width, a parameter for a maximum picture height, a parameter for an available chroma format, a parameter for a maximum bit depth, and a parameter for a maximum DPB size for the current AU.
  6. 6. The picture decoding method according to claim 1, wherein the step of updating the DPB comprises: When the current picture is not the first picture of the current AU, which is the CVSS AU other than the AU 0, a specific picture satisfying a first condition and a second condition is removed from the DPB, Wherein the first condition is that the particular picture is a picture marked as unused for reference, Wherein the second condition is that the specific picture has a picture output flag equal to 0 or a DPB output time of the specific picture is less than or equal to a CPB removal time of a first decoding unit DU of the current picture.
  7. 7. The image decoding method of claim 1, wherein, when the current picture is not the first picture of the current AU that is the CVSS AU other than the AU 0, a picture storage buffer including a specific picture in the DPB is emptied without output, and Wherein the specific picture is a picture marked as not needed for output and not used for reference.
  8. 8. An image encoding method performed by an encoding apparatus, the image encoding method comprising the steps of: Deriving a value of a variable indicating whether all picture storage buffers in the decoded picture buffer DPB are emptied without output, based on whether the current picture is a first picture of the current access unit AU, the current AU being an encoded video sequence start AU other than AU 0, i.e., a CVSS AU, the AU 0 being the first AU in the bitstream; updating the DPB based on the variable, and Encoding image information for the current picture, Wherein the value of the variable is derived after encoding a slice header for the current picture.
  9. 9. The image encoding method of claim 8, wherein when the value of the variable is 1, all picture storage buffers in the DPB are emptied without output, and DPB fullness is set equal to 0.
  10. 10. The image encoding method of claim 9, wherein when the value of the variable is 0, a picture storage buffer including a specific picture in the DPB is emptied without output, and a concave-convex process is performed on a non-empty picture storage buffer in the DPB, and Wherein the specific picture is a picture marked as not needed for output and not used for reference.
  11. 11. The image encoding method of claim 8, wherein deriving the value of the variable comprises: When the current picture is the first picture of the current AU, which is the CVSS AU other than the AU 0, it is determined whether at least one of parameters for the current AU is different in encoding order from parameters of a previous AU for the current AU, Wherein when said at least one of said parameters for said current AU is different from the parameters for said previous AU, said value of said variable is set equal to 1, Wherein when the parameter for the current AU is the same as the parameter for the previous AU, the value of the variable is set equal to the value of the syntax element for the variable, and Wherein the image information includes the syntax element.
  12. 12. The image encoding method of claim 11, wherein the parameters for the current AU include a parameter for a maximum picture width, a parameter for a maximum picture height, a parameter for an available chroma format, a parameter for a maximum bit depth, and a parameter for a maximum DPB size for the current AU.
  13. 13. The image encoding method of claim 8, wherein the step of updating the DPB comprises: When the current picture is not the first picture of the current AU, which is the CVSS AU other than the AU 0, a specific picture satisfying a first condition and a second condition is removed from the DPB, Wherein the first condition is that the particular picture is a picture marked as unused for reference, Wherein the second condition is that the specific picture has a picture output flag equal to 0 or a DPB output time of the specific picture is less than or equal to a CPB removal time of a first decoding unit DU of the current picture.
  14. 14. The image encoding method of claim 8, wherein, when the current picture is not the first picture of the current AU that is the CVSS AU other than the AU 0, a picture storage buffer including a specific picture in the DPB is emptied without output, and Wherein the specific picture is a picture marked as not needed for output and not used for reference.
  15. 15. A method for transmitting data for image information, the method comprising the steps of: Deriving a value of a variable based on whether a current picture is a first picture of a current access unit AU, the current AU being an encoded video sequence start AU other than AU 0, i.e., a CVSS AU, the AU 0 being a first AU in a bitstream, the variable indicating whether all picture storage buffers in a decoded picture buffer DPB are emptied without output, the value of the variable being derived after encoding a slice header for the current picture; Updating the DPB based on the variable; encoding image information for the current picture to generate the bitstream, and Transmitting the data including the bit stream.

Description

Image decoding method, image encoding method, and image data transmitting method The present application is a divisional application of the application patent application No. 202180035728.6 (International application No. PCT/KR2021/005601, application day: 2021, 5/4, title of the application: image decoding method and apparatus for the same). Technical Field The present disclosure relates to image encoding techniques, and more particularly, to an image decoding method and apparatus for performing a DPB management process in an image encoding system. Background Recently, in various fields, demand for high-resolution, high-quality images such as HD (high definition) images and UHD (ultra high definition) images is growing. Since image data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or stored using an existing storage medium, its transmission cost and storage cost increase. Therefore, there is a need for an efficient image compression technique for efficiently transmitting, storing, and reproducing information of high-resolution high-quality images. Disclosure of Invention Technical problem The present disclosure provides methods and apparatus for improving image coding efficiency. Another technical challenge of the present disclosure is to provide a method and apparatus for performing a DPB management process. Technical proposal According to an embodiment of the present disclosure, there is provided an image decoding method performed by a decoding apparatus. The method includes deriving a value of a variable based on whether a current picture is a first picture that is a current access unit (CVSS AU) of an encoded video sequence start access unit (CVSS AU) other than Access Unit (AU) 0, updating the DPB based on the variable, and decoding the current picture based on the updated DPB. The variable indicates whether all picture store buffers in a Decoded Picture Buffer (DPB) are empty and not output. According to another embodiment of the present disclosure, there is provided a decoding apparatus for performing image decoding. The decoding apparatus includes a DPB for deriving a value of a variable based on whether a current picture is a first picture that is a current picture of a coded video sequence start access unit (CVSS AU) other than Access Unit (AU) 0 and updating the DPB based on the variable, and a predictor for decoding the current picture based on the updated DPB. The variable indicates whether all picture store buffers in a Decoded Picture Buffer (DPB) are empty and not output. According to another embodiment of the present disclosure, there is provided an image encoding method performed by an encoding apparatus. The method includes deriving a value of a variable based on whether a current picture is a first picture of a current picture that is a coded video sequence start access unit (CVSS AU) other than Access Unit (AU) 0, updating the DPB based on the variable, and coding image information of the current picture. The variable indicates whether all picture store buffers in a Decoded Picture Buffer (DPB) are empty and not output. According to another embodiment of the present disclosure, a video encoding apparatus is provided. The encoding apparatus includes a DPB for deriving a value of a variable based on whether a current picture is a first picture that is a current access unit (CVSS AU) of an encoded video sequence start access unit (CVSS AU) other than Access Unit (AU) 0 and updating the DPB based on the variable, and an entropy encoder for encoding image information of the current picture. The variable indicates whether all picture store buffers in a Decoded Picture Buffer (DPB) are empty and not output. According to another embodiment of the present disclosure, there is provided a computer-readable digital storage medium having stored therein a bitstream including image information causing an image decoding method to be performed. In a computer-readable digital storage medium, the image decoding method includes deriving a value of a variable based on whether a current picture is a first picture of a current picture that is a coded video sequence start access unit (CVSS AU) other than Access Unit (AU) 0, updating the DPB based on the variable, and decoding the current picture based on the updated DPB. The variable indicates whether all picture store buffers in a Decoded Picture Buffer (DPB) are empty and not output. Technical effects According to the present disclosure, whether to perform the process of removing pictures in the DPB without outputting them may be determined before decoding only the first picture of the CVSS AU other than AU 0, rather than before decoding all pictures of the CVSS AU other than AU 0. By doing so, the DPB status affecting all layers in the CVS may not be changed