US-12621443-B2 - Encoder, encoding method, decoder, and decoding method

US12621443B2US 12621443 B2US12621443 B2US 12621443B2US-12621443-B2

Abstract

An encoder that encodes a current block in a picture includes circuitry and memory. Using the memory, the circuitry: determines whether to use intra prediction for the current block; and when determining to use intra prediction, (i) performs a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients; and (ii-1) performs a second transform on the first transform coefficients using a second transform basis to generate second transform coefficients and quantizes the second transform coefficients, when an intra prediction mode of the current block is a predetermined mode or when the first transform basis is same as a predetermined transform basis; and (ii-2) quantizes the first transform coefficients without performing the second transform when the intra prediction mode is different from the predetermined mode and the first transform basis is different from the predetermined transform basis.

Inventors

Masato Ohkawa
Hideo Saitou
Tadamasa Toma
Takahiro Nishi
Kiyofumi Abe
Ryuichi KANOH

Assignees

PANASONIC INTELLECTUAL PROPERTY CORPORATION OF AMERICA

Dates

Publication Date: 20260505
Application Date: 20240926

Claims (4)

1 . An encoder that encodes a current block in a picture, the encoder comprising: circuitry; and memory, wherein using the memory, the circuitry: determines whether to use intra prediction for the current block; performs a transforming process when determining to use intra prediction for the current block; and quantizes transform coefficients generated by the transforming process; wherein the transforming process includes: (i) performing a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients and performing a second transform on the first transform coefficients using a second transform basis to generate second transform coefficients, with an intra prediction mode of the current block being different from a predetermined mode and the first transform basis being same as a predetermined transform basis; and (ii) performing a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients, with the intra prediction mode of the current block being different from the predetermined mode and the first transform basis being different from the predetermined transform basis, and wherein the residual signal is a luminance signal.
2 . A decoder that decodes a current block in a picture, the decoder comprising: circuitry; and memory, wherein using the memory, the circuitry: determines whether to use intra prediction for the current block; and performs an inverse transforming process when determining to use intra prediction for the current block; wherein the inverse transforming process includes: (i) performing a second inverse transform on inverse quantized coefficients of the current block using a second inverse transform basis to generate second inverse transform coefficients and performing a first inverse transform on the second inverse transform coefficients using a first inverse transform basis to generate a residual signal, with an intra prediction mode of the current block being different from a predetermined mode and the first inverse transform basis being same as a predetermined inverse transform basis; and (ii) performing the first inverse transform on the inverse quantized coefficients of the current block using the first inverse transform basis to generate a residual signal without performing the second inverse transform, with the intra prediction mode of the current block being different from the predetermined mode and the first inverse transform basis being different from the predetermined inverse transform basis, and wherein the residual signal is a luminance signal.
3 . An encoding method for encoding a current block in a picture, the encoding method comprising: determining whether to use intra prediction for the current block; performing a transforming process when determining to use intra prediction for the current block; and quantizing transform coefficients generated by the transforming process; wherein the transforming process includes: (i) performing a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients and performing a second transform on the first transform coefficients using a second transform basis to generate second transform coefficients, with an intra prediction mode of the current block being different from a predetermined mode and the first transform basis being same as a predetermined transform basis; and (ii) performing a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients, with the intra prediction mode of the current block being different from the predetermined mode and the first transform basis being different from the predetermined transform basis, and wherein the residual signal is a luminance signal.
4 . A decoding method for decoding a current block in a picture, the decoding method comprising: determining whether to use intra prediction for the current block; and performing an inverse transforming process when determining to use intra prediction for the current block; wherein the inverse transforming process includes: (i) performing a second inverse transform on inverse quantized coefficients of the current block using a second inverse transform basis to generate second inverse transform coefficients and performing a first inverse transform on the second inverse transform coefficients using a first inverse transform basis to generate a residual signal, with an intra prediction mode of the current block being different from a predetermined mode and the first inverse transform basis being same as a predetermined inverse transform basis; and (ii) performing the first inverse transform on the inverse quantized coefficients of the current block using the first inverse transform basis to generate a residual signal without performing the second inverse transform, with the intra prediction mode of the current block being different from the predetermined mode and the first inverse transform basis being different from the predetermined inverse transform basis, and wherein the residual signal is a luminance signal.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 18/368,140, filed Sep. 14, 2023, which is a continuation of U.S. application Ser. No. 17/350,640, filed Jun. 17, 2021, now U.S. Pat. No. 11,800,093, which is a continuation of U.S. application Ser. No. 16/733,774, filed Jan. 3, 2020, now U.S. Pat. No. 11,076,150, which is a U.S. continuation application of PCT International Patent Application Number PCT/JP2018/026114 filed on Jul. 11, 2018, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/532,116 filed on Jul. 13, 2017, the entire contents of which are hereby incorporated by reference. BACKGROUND 1. Technical Field The present disclosure relates to encoding and decoding of an image/video on a block-by-block basis. 2. Description of the Related Art A video coding standard known as High-Efficiency Video Coding (HEVC) is standardized by the Joint Collaborative Team on Video Coding (JCT-VC). SUMMARY An encoder according to an aspect of the present disclosure is an encoder that encodes a current block in a picture. The encoder includes: circuitry; and memory. Using the memory, the circuitry: determines whether to use intra prediction for the current block; when determining to use intra prediction for the current block, (i) performs a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients; and (ii-1) performs a second transform on the first transform coefficients using a second transform basis to generate second transform coefficients and quantizes the second transform coefficients, when an intra prediction mode of the current block is a predetermined mode or when the first transform basis is same as a predetermined transform basis; and (ii-2) quantizes the first transform coefficients without performing the second transform when the intra prediction mode of the current block is different from the predetermined mode and the first transform basis is different from the predetermined transform basis. Note that these general or specific aspects may be implemented by a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or by any combination of systems, methods, integrated circuits, computer programs, or recording media. BRIEF DESCRIPTION OF DRAWINGS These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. FIG. 1 is a block diagram illustrating a functional configuration of an encoder according to Embodiment 1; FIG. 2 illustrates one example of block splitting according to Embodiment 1; FIG. 3 is a chart indicating transform basis functions for each transform type; FIG. 4A illustrates one example of a filter shape used in ALF; FIG. 4B illustrates another example of a filter shape used in ALF; FIG. 4C illustrates another example of a filter shape used in ALF; FIG. 5A illustrates 67 intra prediction modes used in intra prediction; FIG. 5B is a flow chart for illustrating an outline of a prediction image correction process performed via OBMC processing; FIG. 5C is a conceptual diagram for illustrating an outline of a prediction image correction process performed via OBMC processing; FIG. 5D illustrates one example of FRUC; FIG. 6 is for illustrating pattern matching (bilateral matching) between two blocks along a motion trajectory; FIG. 7 is for illustrating pattern matching (template matching) between a template in the current picture and a block in a reference picture; FIG. 8 is for illustrating a model assuming uniform linear motion; FIG. 9A is for illustrating deriving a motion vector of each sub-block based on motion vectors of neighboring blocks; FIG. 9B is for illustrating an outline of a process for deriving a motion vector via merge mode; FIG. 9C is a conceptual diagram for illustrating an outline of DMVR processing; FIG. 9D is for illustrating an outline of a prediction image generation method using a luminance correction process performed via LIC processing; FIG. 10 is a block diagram illustrating a functional configuration of a decoder according to Embodiment 1; FIG. 11 is a flow chart illustrating transform and quantization processing performed by an encoder according to Embodiment 2; FIG. 12 is a flow chart illustrating inverse quantization and inverse transform processing performed by a decoder according to Embodiment 2; FIG. 13 is a flow chart illustrating transform and quantization processing performed by an encoder according to Embodiment 3; FIG. 14 is a flow chart illustrating inverse quantization and inverse transform processing performed by a decoder according to Embodiment 3; FIG. 15 is a flow chart illustrating transform and quantization processing performed by an encoder according to Embodiment