CONSTRUCTION METHOD FOR INTRA BLOCK COPY

TECHNICAL FIELD

[0001] The invention relates generally to video processing. In particular, the presented invention relates to intra block copy.

BACKGROUND

[0002] In the current HEVC extension of screen content coding, Intra block copy (Intra BC) is being considered to reduce redundancy by prediction from reduplicated content within a same picture. As depicted in Fig.l, a reference block in the current picture is copied to the current block as the prediction if Intra BC 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.

[0003] As a coding efficiency improvement of Intra BC (IBC), an IBC merge mode was proposed. In the candidate list of the IBC merge mode as shown in Fig. 2, there are two BV candidates, including left and above BVs. If either of the left or above PU is not block copy PU, the corresponding BV candidate is set to the vector of (0, 0).

[0004] According to such a design, quite a few (0, 0) BV candidates will exist in the merge candidate lists of all IBC PUs. However, (0, 0) vector is not helpful at all for IBC PUs, since the predicted reference must have been reconstructed. This invention focuses on improving the coding efficiency of merge IBC by constructing a better merge candidate list.

SUMMARY

[0005] In light of the previously described problems, this invention proposes to prune the merge candidate list of IBC. Several default and effective candidates are also utilized and added into the list.

[0006] 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

[0007] The invention can be more understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

[0008] Fig. 1 is a diagram illustrating Intra block copy (IBC).

[0009] Fig. 2 is a diagram illustrating the current BV candidate list construction method of in the proposed IBC Merge.

[0010] Fig. 3 is a diagram illustrating the proposed block-copy vector (BV) candidate list construction process.

[0011] Fig. 4 is a diagram illustrating the examples for neighboring BV positions.

DETAILED DESCRIPTION

[0012] 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.

[0013] Several IBC merge candidate list construction methods are proposed to predict or encode BVs of IBC PUs more efficiently.

[0014] In 1 ^st embodiment, a pruning process is utilized to process the constructed list of BV candidates of IBC merge. In the pruning process, if there are candidates with the same BVs, these candidates are merged into one BV.

[0015] In 2 ^nd embodiment, a modification process is utilized to replace the zero BV in the candidate list by specially designed default BVs. The default BVs include (-W, 0), (-kxW,0), (0, -H), (0, -kxH) and previously decoded IBC BVs ect, where W is the width of the current CU, k is a fixed number and H is height of the current CU. Usually, when there are only two candidates in the IBC merge lists, both {(-W, 0), (-2W.0)} and {(-W, 0), (0,-H)} can be utilized as example default BVs. (-W,0) or and the most recently decoded IBC BV can have a higher priority.

[0016] In 3 ^rd embodiment, an adding process can be carried out to complement the candidate list. Take a maximum of 2 candidates in the list as example, if there is only

1 candidate (e.g. after pruning), the BV with highest priority among the default BVs, which is not equal to the existent candidate, is added into the candidate list.

[0017] In 4 ^th embodiment, maximum number of merge IBC candidates and which default BVs are utilized can be signalized in CU, slice or sequence level.

[0018] In 5 ^th embodiment, specified neighboring BV can be added into the list, including BVs of left, above, left below, left up, above left, above right, left-up corner and right-up corner PUs. The related positions are shown in Fig. 4.

[0019] In 6 ^th embodiment, when one upside PU of the current PU does not exist,

(-kxW, 0) is added into the candidate list for IBC merge.

[0020] In 7 ^th embodiment, when one left-side PU of the current PU does not exist,

(0, -kxH) is added into the candidate list for IBC merge.

[0021] In 8 ^th embodiment, when one upside PU of the current PU is not an IBC PU, (-kxW, 0) or (0, -kxH) is added into the candidate list for IBC merge.

[0022] In 9 ^th embodiment, when one left-side PU of the current PU is not an IBC PU, (-kxW, 0) is added into the candidate list for IBC merge.

[0023] In 10 ^th embodiment, when the default BV is added, it can be utilized to directly replace the zero or empty BV candidates.

[0024] In 11 ^th embodiment, the default BV is added after making all empty BV candidates in the list be after available BV candidate.

[0025] In 12 ^th embodiment, flags or symbols can be transmitted in CTU, CU, slice and sequence level in coding tree unit, coding unit, PPS and SPS to signalize the maximum number of BV candidates for merge IBC.

[0026] In 13 ^th embodiment, any combination of the 1 ^st to 12 ^h embodiments is utilized. An example is shown in Fig. 3, where the construction includes following steps:

Adding neighbor BV, if one specified neighboring BV exits, add the specified neighboring BV into the candidate list for IBC merge, otherwise, either a specified default BV or zero BV is added into the candidate list;

Pruning zero and same BVs by removing zero BV or so-called redundant BV which is the same with one BV in the candidate list;

Constructing a default BV list which includes horizontal BVs of (-kxW,0), vertical BVs of (0, -kxH) and recently decoded non-zero BVs, before ones in the candidate list has a higher priority; and

Adding default BV into the candidate list according to a default BV order in the default BV list.

[0027] 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.

[0028] 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.