US-12627793-B2 - Image encoding/decoding method, method of transmitting bitstream, and recording medium in which bitstream is stored

US12627793B2US 12627793 B2US12627793 B2US 12627793B2US-12627793-B2

Abstract

An image encoding/decoding method, a bitstream transmission method, and a computer-readable recording medium for storing a bitstream are provided. The image decoding method according to the present disclosure is an image decoding method performed by an image decoding device, and may comprise the steps of: deriving multiple direct mode (DM) candidates for a chroma block; determining one DM candidate among the multiple DM candidates on basis of first information; and performing intra prediction of the chroma block on the basis of the determined DM candidate, wherein default modes for the chroma block are modified on the basis of whether same are identical to the multiple DM candidates.

Inventors

Jangwon CHOI
Hyeong Moon JANG
Sunmi YOO
Jungah CHOI

Assignees

LG ELECTRONICS INC.

Dates

Publication Date: 20260512
Application Date: 20230102
Priority Date: 20220104

Claims (13)

1 . An image decoding method performed by an image decoding apparatus, the image decoding method comprising: deriving a plurality of direct mode (DM) candidates for a chroma block; determining any one mode of default modes and the plurality of DM candidates for the chroma block based on first information; and intra-predicting the chroma block based on the determined mode, wherein the default modes are modified based on whether the default modes are the same as the plurality of DM candidates.
2 . The image decoding method of claim 1 , wherein the default modes are modified to different prediction modes based on the order in which the default modes are determined to be the same as the plurality of DM candidates.
3 . The image decoding method of claim 2 , wherein a first default mode determined to be the same as the plurality of DM candidates is modified to intra prediction mode of 66 , and wherein a second default mode determined to be the same as the plurality of DM candidates is modified to intra prediction mode of 34 .
4 . The image decoding method of claim 3 , wherein a third default mode determined to be the same as the plurality of DM candidates is modified to intra prediction mode of 2 .
5 . The image decoding method of claim 4 , wherein a fourth default mode determined to be the same as the plurality of DM candidates is modified to intra prediction mode of 42 .
6 . The image decoding method of claim 1 , wherein the plurality of DM candidates are derived from intra prediction modes at different positions within a luma block corresponding to the chroma block.
7 . The image decoding method of claim 6 , wherein the plurality of DM candidates is derived from the default modes based on the number of DM candidates derived from the intra prediction modes being less than a predetermined number.
8 . The image decoding method of claim 7 , wherein the number of default modes used to derive the plurality of DM candidates among the default modes is the same as the predetermined number.
9 . The image decoding method of claim 6 , wherein the plurality of DM candidates are derived from intra prediction modes of different neighboring blocks of the chroma block, based on the number of DM candidates derived from the intra prediction modes being less than a predetermined number.
10 . The image decoding method of claim 9 , wherein the plurality of DM candidates are derived from the default modes, based on the number of DM candidates derived from the intra prediction modes and intra prediction modes of the neighboring blocks being less than a predetermined number.
11 . An image encoding method performed by an image encoding apparatus, the image encoding method comprising: deriving a plurality of direct mode (DM) candidates for a chroma block; determining any one mode of default modes and the plurality of DM candidates for the chroma block; and intra-predicting the chroma block based on the determined mode, wherein the default modes are modified based on whether the default modes are the same as the plurality of DM candidates, and wherein first information indicating the determined mode is encoded in a bitstream.
12 . A non-transitory computer-readable recording medium storing a bitstream generated by the image encoding method of claim 11 .
13 . A method of transmitting a bitstream generated by an image encoding method, the image encoding method comprising: deriving a plurality of direct mode (DM) candidates for a chroma block; determining any one mode of default modes and the plurality of DM candidates for the chroma block; and intra-predicting the chroma block based on the determined mode, wherein the default modes are modified based on whether the default modes are the same as the plurality of DM candidates, and wherein first information indicating the determined mode is encoded in a bitstream.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/KR2023/000045, filed on Jan. 2, 2023, which claims the benefit of Korean Patent Application No. 10-2022-0000907, filed on Jan. 4, 2022. The disclosures of the prior applications are incorporated by reference in their entirety. TECHNICAL FIELD The present disclosure relates to an image encoding/decoding method, a method of transmitting a bitstream, and a recording medium storing the bitstream, and relates to chroma intra prediction using a plurality of direct modes. BACKGROUND Recently, demand for high-resolution and high-quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields. As resolution and quality of image data are improved, the amount of transmitted information or bits relatively increases as compared to existing image data. An increase in the amount of transmitted information or bits causes an increase in transmission cost and storage cost. Accordingly, there is a need for high-efficient image compression technology for effectively transmitting, storing and reproducing information on high-resolution and high-quality images. SUMMARY An object of the present disclosure is to provide an image encoding/decoding method and apparatus with improved encoding/decoding efficiency. Another object of the present disclosure is to provide a method of deriving a plurality of direct modes. Another object of the present disclosure is to provide a method capable of using both default modes and a plurality of direct modes as a chroma intra prediction mode. Another object of the present disclosure is to provide a method of encoding direct modes. Another object of the present disclosure is to provide a method of eliminating overlap between default modes and a plurality of direct modes. Another object of the present disclosure is to provide a non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method according to the present disclosure. Another object of the present disclosure is to provide a non-transitory computer-readable recording medium storing a bitstream received, decoded and used to reconstruct an image by an image decoding apparatus according to the present disclosure. Another object of the present disclosure is to provide a method of transmitting a bitstream generated by an image encoding apparatus according to the present disclosure. The technical problems solved by the present disclosure are not limited to the above technical problems and other technical problems which are not described herein will become apparent to those skilled in the art from the following description. An image decoding method according to an aspect of the present disclosure is performed by an image decoding apparatus. The image decoding method may comprise deriving a plurality of direct mode (DM) candidates for a chroma block, determining any one mode of default modes and the plurality of DM candidates for the chroma block based on first information, and intra-predicting the chroma block based on the determined mode. The default modes may be modified based on whether the default modes are the same as the plurality of DM candidates. An image encoding method according to another aspect of the present disclosure is performed by an image encoding apparatus. The image encoding method may comprise deriving a plurality of direct mode (DM) candidates for a chroma block, determining any one mode of default modes and the plurality of DM candidates for the chroma block, and intra-predicting the chroma block based on the determined mode. The default modes may be modified based on whether the default modes are the same as the plurality of DM candidates, and first information indicating the determined mode may be encoded in a bitstream. A computer-readable recording medium according to another aspect of the present disclosure can store a bitstream generated by the image encoding method or apparatus of the present disclosure. A transmission method according to another aspect of the present disclosure may transmit a bitstream generated by the image encoding method or apparatus of the present disclosure. The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the detailed description below of the present disclosure, and do not limit the scope of the present disclosure. According to the present disclosure, it is possible to provide an image encoding/decoding method and apparatus with improved encoding/decoding efficiency. Additionally, according to the present disclosure, the performance of chroma intra prediction can be improved by more precisely deriving a plurality of direct modes. Additionally, according to the present disclosure, a plurality of direct modes can be derived while maintaining default modes corresponding to essential modes as ch