WO2016183814A1

WO2016183814A1 - Coded block flag coding using cross-component correlation

Info

Publication number: WO2016183814A1
Application number: PCT/CN2015/079350
Authority: WO
Inventors: Han HUANG
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2015-05-20
Filing date: 2015-05-20
Publication date: 2016-11-24
Anticipated expiration: 2017-11-20

Abstract

Method for coding of CBF is proposed. CBF signaling for one color component depends on the number of significant coefficients in the other color components.

Description

CODED BLOCK FLAG CODING USING CROSS-COMPONENT CORRELATION

TECHNICAL FIELD

The invention relates generally to image and video processing. In particular, the presented invention relates to image and video coding.

BACKGROUND

In a typical hybrid video codec, e.g. H. 264 and HEVC, an image block is first intra/inter predicted, and then the residual signal is transform coded. In the transform coding stage, a coded block flag (CBF) is first signaled to indicate the significance of the entire transform block. If CBF is not zero, then the transform coefficients are coded； else, the transform coefficients are inferred to be all zero.

The CBF flag is usually independently signaled for each color component. A root CBF flag is used to indicate whether transform coefficients of all color components are zero. If root CBF is zero, then the CBF flags and transform coefficients of all color components are inferred to be zero. If root CBF is not zero, then it indicates that at least one CBF flag in one color component is not zero. So, for example, in YUV color format, if root CBF is not zero and CBF flag in U and V components are both zero, then the CBF flag for Y component is not explicitly coded and is inferred to be not zero. However, when U and V components are not both zero, the CBF flag for Y component should always be explicitly signaled.

When coding the CBF flag, usually arithmetic coding is adopted. Typically the Context Based Binary Arithmetic Coding (CABAC) is used.

SUMMARY

Methods of coded block flag (CBF) coding are proposed. In which, CBF signaling for one color component depends on the number of significant coefficients in the other color components.

Other aspects and features of the invention will become apparent to those with ordinary skill in the art upon review of the following descriptions of specific embodiments.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating an example of Y component CBF coding depending on the number of significant coefficients in U and V components.

DETAILED DESCRIPTION

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

In the proposed methods, CBF signaling for one color component depends on the number of significant coefficients in the other color components. Without loss of generality, the YUV format is used as example in the following description. The same methods can be applied to other formats as well. It also should be noted that the proposed methods can be applied to any transform method or transform skip. In the case of transform skip, the coefficients in a transform block are the quantized residual signal.

For simplicity, let CBF_Y, CBF_U, CBF_V denote the CBF of Y, U and V component, respectively. Also, let NumSig_Y, NumSig_U, NumSig_V denote the number of significant coefficients in Y, U and V component, respectively.

In one embodiment, coding of CBF_Y depends on NumSig_U and NumSig_V. For examples:

1) If NumSig_U > TH &&NumSig_V > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero.

2) If NumSig_U > TH || NumSig_V > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero.

3) If f (NumSig_U, NumSig_V) > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero. f () is a function of NumSig_U and NumSig_V, e.g. f (NumSig_U, NumSig_V) ＝ NumSig_U+NumSig_V.

In still another embodiment, coding of CBF_V depends on the NumSig_U. For examples:

1) If NumSig_U > TH, then CBF_V is not explicitly coded, and is inferred to be not zero.

2) If f (NumSig_U) > TH, then CBF_V is not explicitly coded, and is inferred to be not zero. f () is a function of NumSig_U

In still another embodiment, coding of CBF_U depends on the NumSig_V. For examples:

1) If NumSig_V > TH, then CBF_U is not explicitly coded, and is inferred to be not zero.

2) If f (NumSig_V) > TH, then CBF_U is not explicitly coded, and is inferred to be not zero. f () is a function of NumSig_V

In still another embodiment, context modeling in coding of CBF_Y depends on NumSig_U and NumSig_V. In other words, depending on different values of NumSig_U and NumSig_V, different context models are chosen for CABAC coding of CBF_Y. For examples:

1) If NumSig_U > TH &&NumSig_V > TH, use a predefined context model； Else, use other context models.

2) If NumSig_U > TH || NumSig_V > TH, use a predefined context model； Else, use other context models.

3) If f (NumSig_U, NumSig_V) > TH, use a predefined context model, Else, use other context models. f () is a function of NumSig_U and NumSig_V, e.g. f (NumSig_U, NumSig_V) ＝ NumSig_U+NumSig_V.

In still another embodiment, context modeling in coding of CBF_V depends on the NumSig_U. In other words, depending on different values of NumSig_U, different context models are chosen to code CBF_V. For examples:

1) If NumSig_U > TH, use a predefined context model； Else, use other context models.

2) If f (NumSig_U) > TH, use a predefined context model； Else, use other context models. f () is a function of NumSig_U.

In still another embodiment, context modeling in coding of CBF_U depends on the NumSig_V. In other words, depending on different values of NumSig_V, different context models are chosen to code CBF_U. For examples:

1) If NumSig_V > TH, use a predefined context model； Else, use other context models.

2) If f (NumSig_V) > TH, use a predefined context model； Else, use other context models. f () is a function of NumSig_V.

The number TH in the above description can be a predefined value in both encoder and decoder or can be signaled to decoder.

The methods described above can be used in a video encoder as well as in a video decoder. Embodiments of CBF coding according to the present invention as described above may be implemented in various hardware, software codes, or a combination of both. For example, an embodiment of the present invention can be a circuit integrated into a video compression chip or program codes integrated into video compression software to perform the processing described herein. An embodiment of the present invention may also be program codes to be executed on a Digital Signal Processor (DSP) to perform the processing described herein. The invention may also involve a number of functions to be performed by a computer processor, a digital signal processor, a microprocessor, or field programmable gate array (FPGA) . These processors can be configured to perform particular tasks according to the invention, by executing machine-readable software code or firmware code that defines the particular methods embodied by the invention. The software code or firmware codes may be developed in different programming languages and different format or style. The software code may also be compiled for different target platform. However, different code formats, styles and languages of software codes and other means of configuring code to perform the tasks in accordance with the invention will not depart from the spirit and scope of the invention.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art) . Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

A method of CBF coding, in which CBF signaling for one color component depends on the number of significant coefficients in the other color components.
The method as claim in claim 1, wherein CBF_Y signaling depends on the number of significant coefficients in U and V components, wherein

1) if NumSig_U > TH && NumSig_V > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero；

2) if NumSig_U > TH || NumSig_V > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero；

3) if f (NumSig_U, NumSig_V) > TH, then CBF_Y is not explicitly coded, and is inferred to be not zero； f is a function of NumSig_U and NumSig_V, e.g. f (NumSig_U, NumSig_V) ＝ NumSig_U+NumSig_V.
The method as claimed in claim 1, wherein context modeling in CABAC coding of CBF_Y depends on the NumSig_U and NumSig_V, wherein

1) NumSig_U > TH && NumSig_V > TH, use a predefined context model； Else, use other context models；

2) NumSig_U > TH || NumSig_V > TH, use a predefined context model； Else, use other context models；

3) If f (NumSig_U, NumSig_V) > TH, use a predefined context model, Else, use other context models； f () is a function of NumSig_U and NumSig_V, e.g. f (NumSig_U, NumSig_V) ＝ NumSig_U+NumSig_V.
The method as claim in claim 1, wherein CBF_V signaling depends on the number of significant coefficients in U component, wherein

1) if NumSig_U > TH, then CBF_V is not explicitly coded, and is inferred to be not zero；

2) if NumSig_U > TH, then CBF_V is not explicitly coded, and is inferred to be not zero；

3) if f (NumSig_U) > TH, then CBF_V is not explicitly coded, and is inferred to be not zero； f is a function of NumSig_U.
The method as claim in claim 1, wherein CBF_U signaling depends on the number of significant coefficients in V component, wherein

1) if NumSig_V > TH, then CBF_U is not explicitly coded, and is inferred to be not zero；

2) if NumSig_V > TH, then CBF_U is not explicitly coded, and is inferred to be not zero；

3) if f (NumSig_V) > TH, then CBF_U is not explicitly coded, and is inferred to be not zero； f is a function of NumSig_V.
The method as claimed in claim 1, wherein context modeling in CABAC coding of CBF_V depends on the NumSig_U, wherein

1) NumSig_U > TH, use a predefined context model； Else, use other context models；

2) If f (NumSig_U) > TH, use a predefined context model, Else, use other context models； f () is a function of NumSig_U.
The method as claimed in claim 1, wherein context modeling in CABAC coding of CBF_U depends on the NumSig_V, wherein

1) NumSig_V > TH, use a predefined context model； Else, use other context models；

2) If f (NumSig_V) > TH, use a predefined context model, Else, use other context models； f () is a function of NumSig_V.
The method as claimed in claim 2～ claim 7, the value TH can be predefined at both encoder and decoder.
The method as claimed in claim 2～ claim 7, the value TH can be coded at sequence level, view level, picture level, slice level, or other levels.
The method as claimed in claim 1, wherein one or more syntax elements can be used to signal whether the proposed CBF coding method is used； the syntax element can be coded.
The method as claimed in claim 10, wherein the syntax elements can be explicitly transmitted in the sequence level, view level, picture level, slice level, or other levels； for example, it can be coded in VPS, SPS, PPS, APS, slice header, LCU et al.