WO2017000222A1

WO2017000222A1 - Grouping bypass bins and improved sign data hiding for residual coding

Info

Publication number: WO2017000222A1
Application number: PCT/CN2015/082833
Authority: WO
Inventors: Han HUANG; Jicheng An
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2015-06-30
Filing date: 2015-06-30
Publication date: 2017-01-05
Anticipated expiration: 2017-12-30

Abstract

Method for grouping bypass bins and improved sign data hiding is proposed.

Description

GROUPING BYPASS BINS AND IMPROVED SIGN DATA HIDING FOR RESIDUAL 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, an example of 8x8 TU consisting 4 CGs is shown in Fig. 1. 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 by up to five scan passes. Each scan pass codes a syntax element within a CG, when necessary, as follows:

1) significant_coeff_flag: significance of a coefficient (zero/non-zero) .

2) coeff_abs_level_greater1_flag: flag indicating whether the absolute value of a coefficient level is greater than 1.

3) coeff_abs_level_greater2_flag: flag indicating whether the absolute value of a coefficient level is greater than 2.

4) coeff_sign_flag: sign of a significant coefficient (0: positive, 1: negative) .

5) coeff_abs_level_remaining: remaining value for absolute value of a coefficient level (if value is larger than that coded in previous passes) .

The bins in the first 3 passes are coded in regular mode (use context) , the bins in scan pass 4 and 5 are coded in bypass mode. Grouping bypass bins can increase the throughput of the entropy coder.

In current HEVC, residuals in a TU is coded in CG basis, the CGs are coded one by one. Therefore, although the bypass bins within a CG are grouped together, the regular mode bins and bypass bins in a TU are interleaved.

For each CG, depending on a criterion, coding the sign of the last non-zero coefficient is omitted when sign data hiding is applied. The sign value is derived by the parity of the sum of the levels of the CG, even corresponds to positive and odd corresponds to negative. The criterion is the distance in scan order between the first and last non-zero coefficients. If the distance is larger than a threshold, 4 in HEVC, then sign data hiding is applied.

SUMMARY

Methods of grouping bypass bins and improved sign data hiding are proposed. In which, the coeff_sign_flag and coeff_abs_level_remaining are coded in a separate (2^nd) CG scan pass, the CG size in the 2^nd CG scan pass can be independent of that in 1^st CG scan pass.

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.

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, coding of syntax elements coeff_sign_flag and coeff_abs_level_remaining are in a separate (2^nd) CG scan pass.

In one embodiment, 3 coefficient scan passes are performed within each CG to code the syntax elements significant_coeff_flag, coeff_abs_level_greater1_flag, and coeff_abs_level_greater2_flag in the first pass of CG scan, 2 coefficient scan passes are performed within each CG to code the syntax coeff_sign_flag and coeff_abs_level_remaining elements in the second pass of CG scan.

In another embodiment, the CG size in the second pass can be different from the CG size in the first pass. For example, the CG in the first pass corresponds to a 4x4 block size, but the CG in the second pass corresponds to a 4x2 or 2x4 block size. In this way, the sub-block size for significant flag coding and sign data hiding can be optimized separately.

In still another embodiment, the CG in the first pass corresponds to a 4x4, 4x2 or 2x4 block size depending on TU size, but the CG in the second pass corresponds to a fixed block size, 4x4 for example.

In still another embodiment, the CG in the second pass corresponds to N consecutive coefficients in a predefined scan order (the scan order used in the first pass) . The number N can be 4, 6, 8, 10, 12, 16, 24, 32, 64 et al.

In still another embodiment, the criterion for sign date hiding depends on the CG size in the second pass. For example, if the CG size in the second pass is 24, then the criterion is: when distance between the first and last non-zero coefficients in a CG is larger than 6 (or 8 et al) .

In still another embodiment, the CG sizes in the two passes are explicitly signaled independently.

The methods described above can be used in a video encoder as well as in a video decoder. Embodiments of grouping bypass bins and improved sign data hiding 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 grouping bypass bins and improved sign data hiding, containing:

coding of syntax elements coeff_sign_flag and coeff_abs_level_remaining are in a separate (2nd) CG scan pass； and

the size of CG in the separate (2nd) CG scan pass can be different from that in the (1st) CG scan pass coding syntax elements significant_coeff_flag, coeff_abs_level_greater1_flag and coeff_abs_level_greater2_flag.
The method as claimed in claim 1, 3 coefficient scan passes are performed within each CG to code the syntax elements significant_coeff_flag, coeff_abs_level_greater1_flag, and coeff_abs_level_greater2_flag in the first pass of CG scan, 2 coefficient scan passes are performed within each CG to code the syntax coeff_sign_flag and coeff_abs_level_remaining elements in the second pass of CG scan.
The method as claimed in claim 2, the CG size in the second pass can be different from the CG size in the first pass, the CG in the first pass corresponds to a 4x4 block size, but the CG in the second pass corresponds to a 4x2 or 2x4 block size.
The method as claimed in claim 2, the CG in the first pass corresponds to a 4x4, 4x2 or 2x4 block size depending on TU size, but the CG in the second pass corresponds to a fixed block size, 4x4 for example.
The method as claimed in claim 2, the CG in the second pass corresponds to N consecutive coefficients in a predefined scan order (the scan order used in the first pass) , the number N can be 4, 6, 8, 10, 12, 16, 24, 32, 64.
The method as claimed in claim 2, the criterion for sign date hiding depends on the CG size in the second pass, if the CG size in the second pass is 24, then the criterion is: when distance between the first and last non-zero coefficients in a CG is larger than 6 or 8.
The method as claimed in claim 1, the CG sizes in the two passes are explicitly signaled independently.