VECTOR PREDICTION IN VIDEO COMPRESSION

FIELD OF INVENTION

The invention relates generally to video processing. In particular, the presented invention relates to intra block copy.

BACKGROUND OF THE INVENTION

In the current HEVC extension of screen content coding, Intra block copy (IBC) is being considered to reduce redundancy by prediction from reduplicated content within a same picture. A reference block in the current picture is copied to the current block as the prediction if IBC is applied. The reference block is located by applying a block-copy vector (BV). The samples in the reference block must have been reconstructed already before the current block is coded or decoded.

The intraBC technique was first proposed by TI (Texas Instrument) and then adopted to the RExt draft standard with Qualcomm's modifications in the 14 ^th JCT-VC meeting, in July 2013 in Vienna, AT. In the 15 ^th JCT-VC meeting in Oct. 2013, Geneva, CH, a variant of it, i.e. 2NxM IntraBC was proposed by NCTU (the National Chiao-Tung Univeristy, Taiwan). In the 16 ^th JCT-VC meeting in Jan. 2014, San Jose, CA, the prediction unit (PU) based IntraBC technique was adopted to the HEVC RExt standard. In the 17 ^th JCT-VC meeting in April. 2014, the above adopted proposals for IBC were removed from RExt but still in the HEVC-SCC platform to be further discussed and improved.

Following these, IBC AMVP (adaptive motion vector prediction) is proposed to improve the IBC vector prediction efficiency. Generally as in Fig. 1, IBC AMVP can select predicted IBC vector from a number of possible spatial block vector candidates in previously coded neighboring block positions. In Table I, these positions are described in details.

Table I: List of neighboring positions for BV prediction

5 left position of the top left corner of the current block

6 above position of the top left corner of the current block

Two candidate lists are constructed. For List 0, position 0 is checked first. If this the block in this position is IBC coded, then its block vector is selected to fill List 0; otherwise, position 1 will be checked. If this the block in this position is IBC coded, then its block vector is selected to fill List 0. If none of the above two positions are IBC coded, positions 2, 3, 4 will be checked one by one, the BV of first IBC coded block will be filled in List 0; if List 0 has been filled by either position 0 or 1, positions 2, 3, 4 will be checked one by one, the BV of first IBC coded block will be filled in List 1. For each IBC coded block, there are two B V prediction candidates from the above two lists (List 0 and List 1). A flag is used to indicate which of the two BV predictors is actually used for the prediction of the BV in the current block. Then the BV prediction difference is further entropy coded. There exits some other kinds AMVP methods for IBC which selects different candidate neighbouring blocks, and utilities different list-filling orders.

However, one common-used method used for IBC AMVP is to fill the unfilled AMVP list(s) with default vectors when there are no enough IBC coded blocks to fill the lists after checking the specified positions. This invention focuses on selecting better default BVs for the AMVP list construction procedures of IBC.

SUMMARY OF THE INVENTION

In light of the previously described problems, this invention proposes kinds of default IBC vectors for its AMVP procedures.

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 understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating the BV candidates utilized in the AMVP for Intra block copy;

Figs. 2(a) - 2(d) are diagrams illustrating the proposed default BVs of (-2xpW-pX,0) and

(0,-2 pH-pY) for different PU patterns. 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.

Several new kinds of default BVs are proposed for the AMVP list construction process of

IBC.

In a first embodiment, the horizontal or vertical coordinates of the current prediction unit (PU) in the current coding unit (CU) is utilized in the derivation of the default BVs.

In a second embodiment, default BVs are selected among the sets of vertical BVs and horizontal BVs. The horizontal set is defined as {(-j ^x cW-kxpW-txpX,0)| k,j,t are integer numbers} and vertical set is defined as {(0,-jxcW-kxpW-txpY)| k,j,t are integer numbers}, where pW and pH are the width and height of the current PU for IBC, cW and cH are the width and height of the current CU; (pX, pY) is the position of the current PU in the current CU.

In a third embodiment, among the selected default BVs for n specified AMVP lists, there must be BVs belonging to different sets (including horizontal set {(-jxcW-kxpW-txpX,0)| k,j,t are integer numbers} and vertical set {(0,-j ^x cW-kxpW-txpY)| k,j,t are integer numbers }).

In a fourth embodiment, (-cW,0) and (0,-cH) are included in the set of default BVs utilized for the IBC AMVP, when there are no-less-than two AMVP lists.

In a fifth embodiment, (-2xcW,0) and (0,-2 xcH) are included in the set of default BVs utilized for the IBC AMVP, when there are no-less-than two AMVP lists.

In a sixth embodiment, (-2xcW,0) and (0,-cH) are included in the set of default BVs utilized for the IBC AMVP, when there are no-less-than 2 AMVP lists.

In a seventh embodiment, (-2xpW,0) and (0,-2 xpH) are included in the set of default BVs utilized for the IBC AMVP, when there are no-less-than two AMVP lists.

In an eighth embodiment, as shown in Figs. 2(a) - 2(d), (-2xpW-pX,0) and (0,-2xpH-pY) are included in the set of default BVs utilized for the IBC AMVP, when there are no-less-than two AMVP lists.

In a ninth embodiment, any combination of the first to eighth embodiments is utilized. 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.