US-12621456-B2 - Image coding method based on secondary transform and apparatus therefor

US12621456B2US 12621456 B2US12621456 B2US 12621456B2US-12621456-B2

Abstract

An image decoding method according to the present document comprises the steps of: receiving a quantized transform coefficient for a target block and a transform index for a non-separable secondary transform; dequantizing the quantized transform coefficients to derive transform coefficients; deriving modified transform coefficients on the basis of a matrix operation of a transform kernel matrix in a transform set indicated by the transform index and a transform coefficient list corresponding to the magnitude of dequantized transform coefficients; clipping the modified transform coefficients to a predetermined range of values; and deriving residual samples for the target block on the basis of an inverse primary transform with respect to the modified transform coefficients clipped.

Inventors

Moonmo KOO
Seunghwan Kim
Jaehyun Lim

Assignees

LG ELECTRONICS INC.

Dates

Publication Date: 20260505
Application Date: 20240604

Claims (4)

1 . An image decoding method performed by a decoding apparatus, the method comprising: obtaining quantized transform coefficients for a target block and a transform index for a non-separable transform; deriving transform coefficients by dequantizing the quantized transform coefficients; deriving modified transform coefficients based on a matrix operation of a transform kernel matrix related to the transform index in a transform set and a transform coefficient list corresponding to a size of the transform coefficients; deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients; and deriving reconstructed samples for the target block based on prediction samples of the target block and the residual samples, wherein the modified transform coefficients of top-left 4×4 region, top-right 4×4 region and the bottom-left 4×4 region in the 8×8 region are derived by applying the transform kernel matrix to the transform coefficients of the top-left 4×4 region in the 8×8 region of the target block, wherein the transform set is determined based on a mapping relationship according to an intra prediction mode of the target block, wherein the modified transform coefficients are clipped to values within a predetermined range, and wherein intermediate samples, for deriving the residual samples, on which the inverse primary transform of a vertical direction is performed for the modified transform coefficients are clipped to values within a predetermined range.
2 . An image encoding method performed by an image encoding apparatus, the method comprising: deriving transform coefficients by dequantizing quantized transform coefficients; deriving modified transform coefficients based on a matrix operation of a transform kernel matrix in a transform set and a transform coefficient list corresponding to a size of the transform coefficients; and deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients, wherein the modified transform coefficients of top-left 4×4 region, top-right 4×4 region and the bottom-left 4×4 region in the 8×8 region are derived by applying the transform kernel matrix to the transform coefficients of the top-left 4×4 region in a 8×8 region of the target block, wherein the transform set is determined based on a mapping relationship according to an intra prediction mode of the target block, wherein the modified transform coefficients are clipped to values within a predetermined range, and wherein intermediate samples, for deriving the residual samples, on which the inverse primary transform of a vertical direction is performed for the modified transform coefficients are clipped to values within a predetermined range.
3 . A non-transitory computer readable storage medium storing encoded information generated by the image encoding method of claim 2 .
4 . 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 transform coefficients by dequantizing quantized transform coefficients, deriving modified transform coefficients based on a matrix operation of a transform kernel matrix in a transform set and a transform coefficient list corresponding to a size of the transform coefficients, and deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients; and transmitting the data comprising the bitstream, wherein the modified transform coefficients of top-left 4×4 region, top-right 4×4 region and the bottom-left 4×4 region in the 8×8 region are derived by applying the transform kernel matrix to the transform coefficients of the top-left 4×4 region in a 8×8 region of the target block, wherein the transform set is determined based on a mapping relationship according to an intra prediction mode of the target block, wherein the modified transform coefficients are clipped to values within a predetermined range, and wherein intermediate samples, for deriving the residual samples, on which the inverse primary transform of a vertical direction is performed for the modified transform coefficients are clipped to values within a predetermined range.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 18/104,450, filed on Feb. 1, 2023, which is a continuation of U.S. application Ser. No. 17/587,910, filed on Jan. 28, 2022, now U.S. Pat. No. 11,632,551, which is a continuation of U.S. application Ser. No. 17/349,215, filed on Jun. 16, 2021, now U.S. Pat. No. 11,284,082, which is a continuation pursuant to 35 U.S.C. § 119 (e) of International Application PCT/KR2020/001533, with an international filing date of Jan. 31, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/800,384, filed on Feb. 1, 2019, the contents of which are hereby incorporated by reference herein in their entirety. TECHNICAL FIELD The present disclosure relates generally to an image coding technology and, more particularly, to an image coding method based on a transform in an image coding system and an apparatus therefor. RELATED ART Nowadays, the demand for high-resolution and high-quality images/videos such as 4K, 8K or more ultra high definition (UHD) images/videos has been increasing in various fields. As the image/video data becomes higher resolution and higher quality, the transmitted information amount or bit amount increases as compared to the conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or image/video data is stored using an existing storage medium, the transmission cost and the storage cost thereof are increased. Further, nowadays, the interest and demand for immersive media such as virtual reality (VR), artificial reality (AR) content or hologram, or the like is increasing, and broadcasting for images/videos having image features different from those of real images, such as a game image is increasing. Accordingly, there is a need for a highly efficient image/video compression technique for effectively compressing and transmitting or storing, and reproducing information of high resolution and high quality images/videos having various features as described above. SUMMARY A technical aspect of the present disclosure is to provide a method and an apparatus for increasing image coding efficiency. Another technical aspect of the present disclosure is to provide a method and an apparatus for increasing transform efficiency. Still another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus which are based on a clipping of a transform process. Yet another technical aspect of the present disclosure is to provide a method and an apparatus for increasing the efficiency of a secondary transform by changing the array of transform coefficients according to an intra prediction mode. Still another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus for increasing the efficiency of a secondary transform by optimizing the transformation kernel matrix applied to the secondary transform. Still another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus which are based on a transform set for increasing coding efficiency. According to an embodiment of the present disclosure, there is provided an image decoding method performed by a decoding apparatus. The method may include: receiving quantized transform coefficients for a target block and a transform index for a non-separable secondary transform; deriving transform coefficients by dequantizing the quantized transform coefficients; deriving the modified transform coefficients based on a matrix operation of a transform kernel matrix in a transform set related to the transform index and a transform coefficient list corresponding to a size of dequantized transform coefficients; clipping the modified transform coefficients to values within a predetermined range, and deriving residual samples for the target block based on an inverse primary transform for clipped modified transform coefficients. The method may further clip the residual samples to values within a predetermined range. According to another embodiment of the present disclosure, there is provided an image encoding method performed by an encoding apparatus. The method may include: deriving prediction samples based on an intra prediction mode applied to a target block; deriving residual samples for the target block based on the prediction samples; deriving transform coefficients by applying a primary transform to the residual samples; deriving an input transform coefficient size related to a length of the transform coefficients to which a non-separable secondary transform is applied, an output transform coefficient size related to a length of modified transform coefficients to which the non-separable secondary transform has been applied, and a transform set mapped to an intra mode for the target block based on the non-separable secondary transform being applie