WO2016205999A1

WO2016205999A1 - Adaptive coding group for image/video coding

Info

Publication number: WO2016205999A1
Application number: PCT/CN2015/082073
Authority: WO
Inventors: Han HUANG; Jicheng An
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2015-06-23
Filing date: 2015-06-23
Publication date: 2016-12-29

Abstract

Method for adaptive coding group is proposed.

Description

ADAPTIVE CODING GROUP FOR IMAGE/VIDEO CODING

TECHNICAL FIELD

The invention relates generally to image and video coding.

BACKGROUND

Transform coding is widely used in typical image/video coder. An image block, either original signal or prediction residual, is first transformed, scaled and quantized, and then the quantized transform coefficients are entropy coded.

In the High Efficiency Video Coding (HEVC) standard, the basic unit for transform coding is square size Transform Unit (TU) . A Coding Group (CG) is defined as a set of 16 consecutive coefficients in scan order. Given the scan order, a CG corresponds to a 4x4 subblock. A syntax element coded_sub_block_flag is signaled to indicate whether a subblock contains non-zero coefficients. If significant, then the coefficient significant flag, sign flag, and absolute level of the subblock are further coded.

SUMMARY

Methods of adaptive coding group are proposed. In which, the size of a CG is no long fixed to 4x4, but can be adaptive.

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 coding groups for 8x8 TU.

Fig. 2 is a diagram illustrating an example of coding groups for 8x4 TU.

Fig. 3 is a diagram illustrating an example of coding groups for 4x8 TU.

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, the size of CG is adaptive.

In one embodiment, the size of CG depending on TU size, non-square CG size is used for non-square TU. For example, 2x4 CG is used if TU height is larger than TU width, 4x2 CG is used if TU width is larger than TU height. Examples are show in Fig. 1, Fig. 2 and Fig. 3. For the square 8x8TU, 4x4 CG is used； for 8x4 TU, 4x2 CG is used； for 4x8 TU, 2x4 CG is used.

In still another embodiment, smaller CG is used for small TU. For example, 1x1 CG is used for 8x8 TU； in this case CG significant flag is not signaled.

In still another embodiment, CG partition is disabled for small TU. For example, CG partition is disabled for TU that is smaller than 8x8, i.e. 4x8 TU, 4x4 TU, 2x8 TU, 8x4 TU, 8x2 TU, et al.

In still another embodiment, the size of CG is signaled at slice header.

In still another embodiment, the size of CG is signaled at coding tree unit (CTU) level.

In still another embodiment, the size of CG is signaled at coding unit (CU) level.

In still another embodiment, the size of CG is signaled at TU level.

In still another embodiment, the size of CG is signaled at CTU level, and whether to signal the CG size at CTU level is control by a flag at slice header or other high level syntax.

In still another embodiment, the size of CG is signaled at CU level, and whether to signal the CG size at CU level is control by a flag at slice header or other high level syntax.

In still another embodiment, the size of CG is signaled at TU level, and whether to signal the CG size at TU level is control by a flag at slice header or other high level syntax.

In still another embodiment, a flag indicating whether to use adaptive CG size is signal at CTU level, if the flag is true, then a syntax element indicating the CG size is signaled at CU level.

In still another embodiment, a flag indicating whether to use adaptive CG size is signal at CU level, if the flag is true, then a syntax element indicating the CG size is signaled at TU level.

The methods described above can be used in a video encoder as well as in a video decoder. Embodiments of adaptive coding group 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

Method of adaptive coding group (CG) , containing:

1) The size of CG depending on TU size；

2) The size of CG is explicitly signaled.
The method as claimed in claim 1, non-square CG size is used for non square TU； for example, 2x4 CG is used if TU height is larger than TU width, 4x2 CG is used if TU width is larger than TU height.
The method as claimed in claim 1, smaller CG is used for small TU； for example, 1x1 CG is used for 8x8 TU； in this case CG significant flag is not signaled.
The method as claimed in claim 1, CG is disabled (i.e. , CG size is 1x1) for TU that is smaller than 8x8.
The method as claimed in claim 1, the CG size is signaled at TU level.
The method as claimed in claim 1, the CG size is signaled at CU level.
The method as claimed in claim 1, the CG size is signaled at CTU level.
The method as claimed in claim 5, whether to signal the CG size at TU level is control by a flag at slice header or other high level syntax.
The method as claimed in claim 6, whether to signal the CG size at CU level is control by a flag at slice header or other high level syntax.
The method as claimed in claim 7, whether to signal the CG size at CTU level is control by a flag at slice header or other high level syntax.
The method as claimed in claim 1, a flag is signaled in CTU level to indicate whether adaptive CG size is used in current CTU； if the flag is true, then another syntax element is further signaled to indicate which CG size is used for each CU.
The method as claimed in claim 1, a flag is signaled in CU level to indicate whether adaptive CG size is used in current CU； if the flag is true, then another syntax element is further signaled to indicate which CG size is used for each TU.
The method as claimed in claim 1, the CG size is signaled at slice header.