WO2015096093A1

WO2015096093A1 - Simplified cabac contexts in 3dvc

Info

Publication number: WO2015096093A1
Application number: PCT/CN2013/090566
Authority: WO
Inventors: Kai Zhang; Yi-Wen Chen; Jian-Liang Lin; Jicheng An; Xianguo Zhang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2013-12-26
Filing date: 2013-12-26
Publication date: 2015-07-02

Abstract

A simplified CABAC contexts derivation method is proposed. In the proposed method, the above neighboring block is considered as unavailable if it is in a CTU different from the CTU of the current block. Thus the syntax elements above the current CTU need not to be stored.

Description

SIMPLIFIED CABAC CONTEXTS IN 3DVC

FIELD OF INVENTION

The invention relates generally to Three-Dimensional (3D) video processing. In particular, the presented invention relates to advanced residual prediction.

BACKGROUND OF THE INVENTION

In the current 3D-HEVC [1], illumination compensation (IC) [1] and advanced residual prediction (ARP) [2] was adopted. For each CU, the encoder determines to enable or disable the IC or ARP according to the rate-distortion optimization (RDO) criterion, and signals the control flag ic flag or arp flag, which is 0 or 1, in the bit-stream.

To code X flag, such as ic flag or arp flag in the CABAC way, a context model is utilized. In 3D-HEVC, there are 3 context models for X flag, denoted as X_model[0], X_model[l] and X_model[2]. For the current block, X_model[idx] is chosen to code X flag, where idx is calculated as

Idx = X_flag(A)+X_flag(B), if A and B are both available;

Idx = X flag(A), if A is available but B is unavailable;

Idx = X flag(B), if A is unavailable but B is available;

Idx = 0, if A and B are both unavailable;

where X flag(A) and X flag(B) represent X flag in the left and above neighbouring blocks respectively as depicted in Figure 1.

It is obvious that X flag in the neighbouring blocks must be stored. In the High Efficiency Video Coding (HEVC) or the extensions, such as 3D-HEVC, Coding tree unit (CTU) is the basic processing unit and conceptually corresponds in structure to macroblock units that were used in several previous video standards. CTU is also referred to as largest coding unit (LCU). Since the above neighbouring block is in a different CTU from the current CTU, a whole CTU line of X flags above the current CTU line must be stored.

SUMMARY OF THE INVENTION

In light of the previously described problems, a simplified CABAC contexts derivation method is proposed. In the proposed method, the above neighboring block is considered as unavailable if it is in a CTU different from the CTU of the current block. Thus X flags above the current CTU need not to be stored. 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 THE DRAWINGS

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

Fig. 1 is a diagram illustrating Neighboring blocks A and B of the current block C.

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.

To save the buffer required to select the context model, several methods are proposed. In one embodiment, the above neighboring block is considered as unavailable if it is in a

CTU different from the CTU of the current block or if it is located in the above CTU row.

In another embodiment, the left neighboring block is considered as unavailable if it is in a CTU different from the CTU of the current CTU.

In another embodiment, the above neighboring block is always considered as unavailable. In still another embodiment, the left neighboring block is always considered as unavailable.

In another embodiment, only two context models are required to codeX flag. For the current block, X_model[idx] is chosen to code X flag, where idex is calculated as Idx = X_flag(A) and X_flag(A) represents X_flag in the left neighbouring block.

In another embodiment, only two context models are required to codeX flag. For the current block, X_model[idx] is chosen to code X flag, where idex is calculated as Idx = X flag(B) and X flag(B) represents X flag in the above neighbouring block.

In another embodiment, only two context models are required to codeX flag. For the current block, X_model[idx] is chosen to code X flag. idex is calculated as Idx = X flag(B) and X flag(B) represents X flag in the above neighbouring block if the above neighbouring block is located in the current CTU row. Otherwise, ldx=0 (when the above neighboring block is located in the above CTU row).

In still another embodiment, we also propose a method of choosing CABAC context models to code a syntax element without referring to the information from the neighboring blocks for contexts selection. For simplicity, only one context is used to CABAC code this syntax element. Moreover, multiple contexts could also be used; given multiple contexts, the context can selected according to the CU splitting depth information, CU size of PU partitioning of current block.

The methods described above can be used in a video encoder as well as in a video decoder. Embodiments of disparity vector derivation methods 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.

REFERENCES

[1] G. Tech, K. Wegner, Y. Chen, S. Yea, "3D-HEVC Draft Text 1," Document of Joint Collaborative Team on 3D Video Coding Extension Development, JCT3V-F1001, Nov., 2013.

[2] H. Liu, J. Jiwook, J. Sung, etc., "3D-CE2.h: Results of Illumination Compensation for Inter- View Prediction", Doc. JCT3V-B0045, Oct. 2012.

[3] L. Zhang, Y. Chen, X. Li, M. Karczewicz, "CE4: Advanced residual prediction for multiview coding," Document of Joint Collaborative Team on 3D Video Coding Extension Development, JCT3V-D0177, April, 2013.

Claims

1. A method of choosing CAB AC context models to code a syntax element, wherein a neighboring block is considered as unavailable as specified.

2. The method as claimed in claim 1, wherein the syntax element is used to indicate whether IC is used or how IC is used in 3D-HEVC.

3. The method as claimed in claim 1, wherein the syntax element is used to indicate whether ARP is used or how ARP is used in 3D-HEVC.

4. The method as claimed in claim 2 and 3, wherein the syntax element is coded for per PU, CU, or CTU.

5. The method as claimed in claim 1, wherein the above neighboring block is considered as unavailable if it is in a CTU different from the CTU of the current block.

6. The method as claimed in claim 1, wherein the above neighboring block is considered as unavailable if it is located in the above CTU row.

7. The method as claimed in claim 1, wherein the left neighboring block is considered as unavailable if it is in a CTU different from the CTU of the current block.

8. The method as claimed in claim 1, wherein the above neighboring block is always considered as unavailable.

9. The method as claimed in claim 1, wherein the left neighboring block is always considered as unavailable.

10. The method as claimed in claim 1, wherein only two contexts are used to CABAC code the syntax element when context selection is only based on one neighboring block.

11. The method as claimed in claim 10, wherein the choosing of CABAC context depends on the coded syntax element (0 or 1) of the left neighboring block.

12. The method as claimed in claim 10, wherein the choosing of CABAC context depends on the coded syntax element (0 or 1) of the above neighboring block.

13. The method as claimed in claim 10, wherein the choosing of CABAC context depends on the coded syntax element (0 or 1) of the left neighboring block, a default CABAC context is used when the left neighboring block is located in left CTU.

14. The method as claimed in claim 10, wherein the choosing of CABAC context depends on the coded syntax element (0 or 1) of the above neighboring block, a default CABAC context is used when the left neighboring block is located in the above CTU row.

15. A method of choosing CABAC context models to code a syntax element, wherein no information from the neighboring blocks are used for contexts selection.

16. The method as claimed in claim 15, wherein the syntax element is used to indicate whether IC is used or how IC is used in 3D-HEVC.

17. The method as claimed in claim 15, wherein the syntax element is used to indicate whether ARP is used or how ARP is used in 3D-HEVC.

18. The method as claimed in claim 15, wherein only one context is used to CABAC code the syntax element.

19. The method as claimed in claim 15, wherein multiple contexts could be used to CABAC code the syntax element, the context is selected according to the CU splitting depth information.

20. The method as claimed in claim 19, wherein multiple contexts could be used to CABAC code the syntax element, the context is selected according to the CU size or PU partition structure.