WO2015143603A1

WO2015143603A1 - An improved method for temporal motion vector prediction in video coding

Info

Publication number: WO2015143603A1
Application number: PCT/CN2014/073949
Authority: WO
Inventors: Kai Zhang; Jicheng An; Xianguo Zhang; Han HUANG
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2014-03-24
Filing date: 2014-03-24
Publication date: 2015-10-01

Abstract

A method is proposed to improve the derivation of temporal motion vector prediction. Some special methods are further proposed for MVC,SVC,and3DVC.

Description

AN IMPROVED METHOD FOR TEMPORAL MOTION VECTOR

PREDICTION IN VIDEO CODING

FIELD OF INVENTION

The invention relates generally to video processing. In particular, the presented invention relates to temporal motion vector prediction in video coding.

BACKGROUND OF THE INVENTION

In video coding, temporal motion vector prediction (TMVP) is utilized as a kind of motion prediction. In TMVP, the motion vector predictor (MVP) is derived from the motion information of a collocated block in a collocated picture as depicted in Fig. 1.

The collocated picture is a temporal reference picture for the current picture. The collocated picture can be derived implicitly at decoder as specified in H.264/AVC, or it can be signaled explicitly from the encoder to the decoder as specified in H.265/HEVC.

The collocated block and the current block are at the same relative position in the collocated picture and in the current picture respectively. The motion vector (MV) in the collocated block is named as collocated MV.

TMVP is derived by scaling the collocated MV according to the time distances. Time distance (or named POC distance, POC difference) for a MV specifies the time distance between the picture the MV belonging to and the picture the MV pointing to. Herein POC represents picture order count.

The time distance for the collocated MV is available since the collocated MV has been determined when the collocated picture is encoded/ decoded. The time distance for the TMVP is determined by determining the reference picture of the TMVP. In HEVC, the reference for TMVP is signaled explicitly for a block coded with advanced motion vector prediction (AMVP) mode, while the reference for TMVP is determined implicitly for a block coded with merge mode.

If the collocated block possesses only one MV, it should be treated as the collocated MV directly. If the collocated block possesses more than one MV, e.g., two MVs with one from reference list 0 and the other from reference list 1, the collocated MV should be selected as follows as specified in clause 8.5.3.2.8 in HEVC.

1. If DiffPicOrderCnt( aPic, currPic ) is less than or equal to 0 for every picture aPic in every reference picture list of the current slice, the collocated MV should be chosen as the one in the reference list the same as the reference list in which the reference for TMVP is.

2. Otherwise, the collocated MV should be chosen as the one in the reference list with the same value as collocated from lO flag, which is signaled in slice header.

Suppose the time distance of the collocated MV, cMV, is cD and the time distance of the TMVP, tMVP, is tD, then tMVP should be calculated as tMVP = (cMV * tD )l cD. In practical implementation such as HEVC, some more sophisticated methods are used to guarantee the division can be done with limited bit-width. In the example of Fig. 1, the time distance of the collocated MV is 2 and the time distance of the TMVP is 1, thus tMVP should be equal to cMV/2.

A motion compression is applied to reduce the storage required by MVs. In H.265/HEVC, a 16: 1 compression is applied after a picture is encoded /decoded.

There are several extensions for video coding, such as Multi-view video coding (MVC), 3D video coding (3DVC) and scalable video coding (SVC). In MVC and 3DVC, an inter-view reference picture can be inserted into the reference list as a special reference picture for a picture on a dependent view. In SVC, a low-quality reference picture can be inserted into the reference list as a special reference picture for a picture on a high-quality layer. Still in SVC, an up-sampled low-resolution reference picture can be inserted into the reference list as a special reference picture for a picture on a high-resolution layer.

Since these special reference pictures are in the reference list, it is possible to treat the special reference picture as the collocated picture for the current picture when the special reference picture is available. In such a case, the POC of the current picture and that of the collocated picture will be the same. The collocated MV selection method specified in clause 8.5.3.2.8 in HEVC will be inefficient. SUMMARY OF THE INVENTION

In light of the previously described problems, methods are proposed to improve the MV selection method for TMVP in some cases.

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 and examples with references made to the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating TMVP in video coding; Fig. 2 is a diagram illustrating to use the interview reference picture as the collocated picture in MVC or 3DVC;

Fig. 3 is a diagram illustrating to use the corresponding texture picture as the collocated picture in MVC or 3DVC with depth;

Fig. 4 is a diagram illustrating to use the inter-quality-layer picture as the collocated picture in SVC;

Fig. 5 is a diagram illustrating to use the inter-spatial-layer picture as the collocated picture in SVC;

Fig. 6 is a diagram illustrating a general paradigm for virtual collocated picture.

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.

It is proposed to select the collocated MV from the reference list 0 or reference list 1 in a different way, if the collocated block possesses more than one MV, and the POC of the current picture and that of the collocated picture are the same.

In one embodiment, the judgment 'If DiffPicOrderCnt( aPic, currPic ) is less than or equal to 0 for every picture aPic in every reference picture list of the current slice' is not executed if the POC of the current picture and that of the collocated picture are the same.

In another embodiment, the collocated MV should be chosen as the one in the reference list the same as the reference list in which the reference for TMVP is, if the collocated block possesses more than one MV, and the POC of the current picture and that of the collocated picture are the same. For example, if the POC of the current picture and that of the collocated picture are the same, the reference for TMVP is in the reference list 0, and the collocated block possesses two MVs from reference list 0 and reference list 1 respectively, then the MV from reference list 0 should be chosen as the collocated MV. In another example, if the POC of the current picture and that of the collocated picture are the same, the reference for TMVP is in the reference list 1, and the collocated block possesses two MVs from reference list 0 and reference list 1 respectively, then the MV from reference list 1 should be chosen as the collocated MV.

In still another embodiment, the POC of the current picture and that of the collocated picture are the same in the following cases:

1. The inter- view reference picture is treated as the collocated picture used in TMVP in MVC, such as H.264 MVC extension or MV-HEVC, or 3DVC such as 3D-HEVC.as depicted in Fig. 2.

2. The corresponding texture picture is treated as the collocated picture used in TMVP to code a depth picture in MVC, such as H.264 MVC extension or MV-HEVC, or 3DVC such as 3D-HEVC with depth coding as depicted in Fig. 3.

3. The inter-quality-layer reference picture is treated as the collocated picture used in TMVP to code a picture in SVC, such as H.264 SVC extension or HEVC SVC extension as depicted in Fig. 4.

4. The upsampled or scaled inter-spatial-layer reference picture is treated as the collocated picture used in TMVP to code a picture in SVC, such as H.264 SVC extension or HEVC SVC extension as depicted in Fig. 5.

5. A virtual or a created which holds the same POC as the current picture is treated as the collocated picture used in TMVP as depicted in Fig. 6.

In still another embodiment, the proposed collocated MV selection method does not change the CU level design of HEVC. Only slice level or picture level changes are required.

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.

Claims

1. A method of obtaining temporal motion vector prediction (TMVP), comprising:

selecting a collocated motion vector (MV) according to properties of a current picture and a collocated reference picture; and

applying encoding or decoding based on the selected collocated MV.

2. The method as claimed in claim 1, wherein the collocated MV from reference list 0 or reference list 1 is selected in different ways depending on whether a picture order count (POC) of the current picture and that of the collocated picture are the same or not.

3. The method as claimed in claim 1, wherein a judgment 'If DiffPicOrderCnt( aPic, currPic ) is less than or equal to 0 for every picture aPic in every reference picture list of a current slice' is not executed if a POC of the current picture and that of the collocated picture are the same.

4. The method as claimed in claim 1, wherein the collocated MV is chosen as the one in a same reference list as the one in which the reference for TMVP is, if the collocated block possesses more than one MV, and a POC of the current picture and that of the collocated picture are the same.

5. The method as claimed in claim 2, wherein the POC of the current picture and that of the collocated picture are the same if an inter- view reference picture is treated as the collocated picture used in TMVP in multi-view video coding (MVC) or three-dimensional video coding (3DVC).

6. The method as claimed in claim 2, wherein the POC of the current picture and that of the collocated picture are the same if a corresponding texture picture is treated as the collocated picture used in TMVP to code a depth picture in MVC or 3DVC with depth coding.

7. The method as claimed in claim 2, wherein the POC of the current picture and that of the collocated picture are the same if an inter-quality-layer reference picture is treated as the collocated picture used in TMVP to code a picture in scalable video coding (SVC).

8. The method as claimed in claim 2, wherein the POC of the current picture and that of the collocated picture are the same if an upsampled or scaled inter-spatial-layer reference picture is treated as the collocated picture used in TMVP to code a picture in SVC.

9. The method as claimed in claim 2, wherein the POC of the current picture and that of the collocated picture are the same if a virtual or a created which holds the same POC as the current picture is treated as the collocated picture used in TMVP.

10. The method as claimed in claim 2, wherein the method does not change the coding unit (CU) level design of HEVC, and only slice level or picture level changes are required.