CN-122027792-A - Image decoding method, image encoding method, and bit stream transmission method

CN122027792ACN 122027792 ACN122027792 ACN 122027792ACN-122027792-A

Abstract

The application relates to an image decoding method, an image encoding method and a bit stream transmitting method. An image encoding/decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus according to the present disclosure includes determining a quantization parameter of a current block based on whether color space conversion is applied to residual samples of the current block, determining a conversion coefficient of the current block based on the quantization parameter, determining residual samples of the current block using the conversion coefficient, and resetting values of the residual samples based on whether color space conversion is applied.

Inventors

ZHAO JIE
JIN SHENGHUAN
Henry Henry
S. Paluli

Assignees

LG电子株式会社

Dates

Publication Date: 20260512
Application Date: 20201028
Priority Date: 20191028

Claims (14)

1. An image decoding method performed by an image decoding apparatus, the image decoding method comprising the steps of: determining a current block by dividing a picture; Determining a tree type of the current block; deriving quantization parameters for the current block based on a color space transform of residual samples for the current block; deriving transform coefficients of the current block based on the quantization parameter; Deriving the residual samples of the current block based on the transform coefficients, and Based on the application of the color space transform, modifying the values of the residual samples, Wherein the quantization parameter is derived by a clipping operation based on a value of a transform skip flag of the current block, Wherein the clipping operation includes adjusting a value of the quantization parameter to be within a range from a predetermined lower limit value to a predetermined upper limit value, wherein the range includes the predetermined lower limit value and the predetermined upper limit value, Wherein the predetermined upper limit value is derived based on a sum of a quantization parameter range offset and a predetermined constant value, Wherein whether to apply the color space transform for the residual samples of the current block is derived based on a tree type of the current block, Wherein, based on the tree type of the current block not being a single tree, the color space transform is not applied, Wherein the predetermined lower limit value is derived as a minimum allowable quantization parameter for a transform skip mode based on the transform skip flag indicating that the transform is not applied to the current block, and Wherein the predetermined lower limit value is derived to 0 based on the transform skip flag indicating that the application of a transform to the current block is determined by other syntax elements.
2. The image decoding method of claim 1, Wherein the predetermined constant value is 63.
3. The image decoding method of claim 1, Wherein the quantization parameter is derived based on an initial quantization parameter derived from a color component of the current block.
4. The image decoding method of claim 1, Wherein the quantization parameter is derived based on a quantization parameter offset derived from a color component of the current block.
5. The image decoding method according to claim 4, Wherein the size of the quantization parameter offset is derived to-5 based on the color component of the current block being a luma component and the color space transform being applied.
6. The image decoding method according to claim 4, Wherein the size of the quantization parameter offset is derived to be 3 based on the color component of the current block being a chroma Cr component and the color space transform being applied.
7. The image decoding method according to claim 4, Wherein a result of the subtraction based on the magnitude of the first value of the quantization parameter offset and the magnitude of the second value of the quantization parameter offset is 2, Wherein, based on applying the color space transform, the first value is derived based on the quantization parameter offset for the color component of the current block being a chroma Cr component and the second value is derived based on the quantization parameter offset for the color component of the current block being a chroma Cb component.
8. The image decoding method of claim 1, Wherein the predetermined lower limit value is derived based on the transform skip flag of the current block.
9. The image decoding method of claim 1, Wherein the predetermined lower limit value is derived as a minimum allowable quantization parameter for a transform skip mode based on the transform skip flag indicating that the transform is not applied to the current block.
10. The image decoding method of claim 1, Wherein the predetermined lower limit value is derived to 0 based on information about the application of the transform indicating that the application of the transform to the current block is determined by other syntax elements.
11. The image decoding method of claim 1, Wherein the value of the quantization parameter range offset is derived based on syntax elements for the bit depth of the current block.
12. An image encoding method performed by an image encoding apparatus, the image encoding method comprising the steps of: determining a current block by dividing a picture; Determining a tree type of the current block; Deriving values of residual samples of the current block based on applying a color space transform; deriving transform coefficients of the current block based on the residual samples of the current block; determining quantization parameters of the current block based on applying the color space transform, and Encoding the transform coefficients based on the quantization parameter, Wherein the quantization parameter is derived by a clipping operation based on a value of a transform skip flag of the current block, Wherein the clipping operation includes adjusting a value of the quantization parameter to be within a range from a predetermined lower limit value to a predetermined upper limit value, wherein the range includes the predetermined lower limit value and the predetermined upper limit value, Wherein the predetermined upper limit value is derived based on a sum of a quantization parameter range offset and a predetermined constant value, Wherein it is determined whether to apply the color space transform for the residual samples of the current block based on a tree type of the current block, Wherein, based on the tree type of the current block not being a single tree, the color space transform is not applied, Wherein the predetermined lower limit value is derived as a minimum allowable quantization parameter for a transform skip mode based on the value of the transform skip flag being determined to be 1, and Wherein the predetermined lower limit value is derived to 0 based on the value of the transform skip flag being determined to be 0.
13. The image encoding method according to claim 12, Wherein the predetermined constant value is 63.
14. A method of transmitting a bitstream, the method comprising the steps of: performing the image encoding method according to claim 12 to generate a bitstream, and And transmitting the bit stream.

Description

Image decoding method, image encoding method, and bit stream transmission method The present application is a divisional application of the application patent application (International application number: PCT/KR2020/014844, application date: 10/28/2020, title of the application: method and apparatus for encoding/decoding an image using color space conversion and method for transmitting a bitstream) of the original application number 202080090629.3. Technical Field The present disclosure relates to an image encoding/decoding method and apparatus. More particularly, the present disclosure relates to an image encoding/decoding method and apparatus using color space conversion (or transformation) and a method of transmitting a bitstream generated by the image encoding method/apparatus of the present disclosure. Background Recently, demands for high resolution and high quality images, such as High Definition (HD) images and Ultra High Definition (UHD) images, are increasing in various fields. As the resolution and quality of image data improves, the amount of information or bits transmitted increases relatively as compared to existing image data. An increase in the amount of transmission information or the amount of bits results in an increase in transmission costs and storage costs. Therefore, an efficient image compression technique is required to efficiently transmit, store, and reproduce information about high resolution and high quality images. Disclosure of Invention Technical problem The present disclosure is directed to an image encoding/decoding method and apparatus having improved encoding/decoding efficiency. In addition, the present disclosure is directed to an image encoding/decoding method and apparatus for improving encoding/decoding efficiency by performing selective color space conversion. In addition, the present disclosure is directed to a method for transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure. In addition, the present disclosure is directed to a recording medium storing a bitstream generated by the image encoding method or apparatus according to the present disclosure. In addition, the present disclosure is directed to providing a recording medium storing a bitstream received, decoded, and used for reconstructing an image by an image decoding apparatus according to the present disclosure. Those skilled in the art will understand that technical objects to be achieved by the present disclosure are not limited to the above technical objects, and other technical objects not described herein will be clearly understood from the following description. Technical proposal According to an aspect of the present disclosure, there is provided an image decoding method performed by an image decoding apparatus, the method including determining a quantization parameter of a current block based on whether color space conversion is applied to residual samples of the current block, determining a transform coefficient of the current block based on the quantization parameter, determining residual samples of the current block using the transform coefficient, and resetting values of the residual samples based on whether color space conversion is applied. Herein, the step of determining the quantization parameter may be performed by performing clipping on the quantization parameter such that the value of the quantization parameter has a value less than or equal to a predetermined upper limit value and greater than or equal to a predetermined lower limit value. In addition, according to another aspect of the present disclosure, there is provided an image decoding apparatus including a memory and at least one processor configured to determine a quantization parameter of a current block based on whether color space conversion is applied to residual samples of the current block, determine a transform coefficient of the current block based on the quantization parameter, determine residual samples of the current block using the transform coefficient, and reset values of the residual samples based on whether color space conversion is applied. Herein, the processor may be configured to perform clipping on the quantization parameter such that the value of the quantization parameter has a value less than or equal to a predetermined upper limit value and greater than or equal to a predetermined lower limit value. In addition, according to another aspect of the present disclosure, there is provided an image encoding method performed by an image encoding apparatus, the method including resetting residual samples based on whether color space conversion is applied, determining transform coefficients using the reset residual samples, determining quantization parameters based on whether color space conversion is applied, and encoding the transform coefficients based on the quantization parameters. Herein, the step of determining the quantization parameter may be per