CN103414891A - Bottom-up fast quad-tree clipping algorithm for HEVC intra-frame coding - Google Patents

Abstract

The invention discloses a bottom-up fast quad-tree clipping algorithm for HEVC intra-frame coding. A coding unit partition method of a quad-tree structure is adopted in HEVC, and the fast algorithm is designed and realized according to characteristics of a quad-tree structure decision algorithm adopting bottom-up clipping. The process of mode decision on a coding unit on the current layer is self-adaptively and selectively skipped over through known coding information of a coding unit on the bottom layer of a quad-tree, therefore, unnecessary calculation can be avoided, and complexity of intra-frame coding can be reduced. The bottom-up fast quad-tree clipping algorithm can effectively shorten coding time without lowering coding efficiency.

Description

A kind of bottom-up quick quaternary tree trimming algorithm of HEVC intraframe coding

Technical field

The present invention relates to technical field of video coding, particularly the fast algorithm of the intraframe coding of a kind of efficient video coding standard HEVC.

Background technology

Efficient video coding mark standard (High Efficiency Video Coding, HEVC) is by the common video encoding standard of new generation of formulating of International Telecommunications Union's telecommunication standards tissue (ITU-T) Video coding expert group (VCEG) and moving images expert group of International Standards Organization/International Electrotechnical Commission (ISO/IEC) (MPEG).VCEG and MPEG have set up joint video coding work group (Joint Collaborative Team on Video Coding in January, 2010, JCTVC), and through discussion, research and the improvement of repeatedly JCTVC meeting, final ITU-T and ISO/IEC have formally issued the HEVC standard in January, 2013, namely ITU-T H.265 with MPEG-H Part2.Code check reduces half than previous H.264/MPEG-4AVC video encoding standard under the prerequisite of same application condition and video quality.

HEVC has adopted and the previous video encoding standard basic framework of the same hybrid coding H.264/MEPG-4AVC.While in conducting frame, encoding, a frame of video is divided into the code tree piece (Coding Tree Block, CTB) of non-overlapping copies, and each CTB can resolve into a plurality of encoding blocks (Coding Block, CB) by quaternary tree.The size of CB can be 64 * 64,32 * 32 or 16 * 16.While in conducting frame, predicting, a CB can be one or resolve into four prediction pieces (Prediction Block, PB) of cun chis on an equal basis; When carrying out transform and quantization, a CB can resolve into a plurality of transform blocks (Transform Block, TB) by quaternary tree again.For intraframe predictive coding, in HEVC, defined altogether 35 kinds of intra prediction modes, comprise Intra_Planar, Intra_DC and 33 kinds of directivity predictive mode Intra_Angular[i], i=2 ..., 34.This partitioned organization flexibly and more intra prediction mode make HEVC on code efficiency than H.264/MEPG-4AVC being greatly improved.Yet it has also greatly increased the computation complexity of coding simultaneously.

When carrying out the decision-making of partitioned organization, the reference software HM of HEVC has adopted a kind of bottom-up quaternary tree trimming algorithm.At first, a CTB is formed to a full quaternary tree, as shown in Figure 1.Wherein each node is a CB, and we from top to bottom, the position of each node of mark is (i, j) from left to right, i ∈ [0,3], j ∈ [0,4 ⁱ-1].If X _i,jCB while not decomposing for node (i, j), C _i,jFor the CB quad-tree structure of the optimum of node (i, j), the rate distortion costs of J () optimum during for a CB of coding.Bottom-up quaternary tree trimming algorithm travels through each node in full quaternary tree by the order of depth-first, when

The time, the subtree of cutting node (i, j), that is: the CB on this node does not carry out the quaternary tree decomposition.

Summary of the invention

For the problems referred to above, the invention provides a kind of bottom-up quick quaternary tree trimming algorithm of HEVC intraframe coding.In the situation that does not reduce code efficiency, can effectively reduce encoder complexity.Although bottom-up quaternary tree trimming algorithm is more effective than the partitioned organization of exhaustive every kind of CB, still has higher complexity.For a quaternary tree level, mostly be 4 CTB most, required quantity of carrying out the CB of frame mode search is Therefore, the present invention has designed a kind of quick quaternary tree trimming algorithm of novelty, thereby reaches by skipping some unnecessary nodes the purpose that reduces computation complexity.

For achieving the above object, the technical solution adopted in the present invention is:

Make Q ()=0 mean that a node does not decompose, and Q ()=1 mean to decompose downwards.If Q is (C _I+1,4j+k)=1, mean to contain comparatively complicated texture structure in the CB of k child node of node (i, j), need to resolve into less piece and carry out intraframe predictive coding, thereby can infer that present node also may need to decompose.Therefore, the present invention adopts As threshold value, determine whether skipping the frame mode search procedure of present node (i, j).Work as N _i,jDuring>=i+1, skip present node (i, j).As shown in Figure 2, node (1,1) is subtree, skips the pattern search process that node (0,0) is located.

Beneficial effect

The present invention realizes in HEVC reference software HM8.2, and adopt intra-frame encoding mode to 5 classifications of HEVC totally 20 cycle testss test.Encoder is set to acquiescence, and the quantization parameter of selection has 22,27,32 and 37.With mode decision algorithm original in HM8.2, compare the present invention saves on the scramble time percentage and distortion performance ^[6]As shown in Table 1.Can see, the present invention can reach the saving that surpasses scramble time of 20%, on code efficiency, only has average 0.46% code check to increase simultaneously.

The accompanying drawing explanation

Fig. 1 is full quaternary tree;

Fig. 2 is the Fast trim example schematic;

Fig. 3 is bottom-up trimming algorithm fast;

Embodiment

Embodiment 1

As shown in Figure 3, the bottom-up trimming algorithm fast carried of the present invention adopts a kind of mode of recurrence to carry out.Wherein D means maximum number of levels that quaternary tree allows.For the node of the bottom, directly carry out the frame mode search and obtain optimum rate distortion costs function, be designated as J (C _i,j).For the node (i, j) of other level, i<D-1, structure and the rate distortion costs of child node are known.If $\underset{k=0}{\overset{3}{\mathrm{\&Sigma;}}}Q\left(C_{i+1,4j+k}\right)\&GreaterEqual;i+1,$ $C_{i,j}={\&cup;}_{k=0}^3{C}_{i+\mathrm{1,4}j+k};$ If

Carry out the frame mode search and obtain optimum rate distortion costs function J (X _i,j), now, if

C _i,j=X _i,j, otherwise $C_{i,j}={\&cup;}_{k=0}^3{C}_{i+\mathrm{1,4}j+k}.$

The when increase of average bit rate of percentage that table 1 scramble time is saved

Finally it should be noted that: obviously, above-described embodiment is only for example of the present invention clearly is described, and is not the restriction to execution mode.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without also giving all execution modes.And the apparent variation of being amplified out thus or change still are among protection scope of the present invention.

Claims (2)

1. the bottom-up quick quaternary tree trimming algorithm of a HEVC intraframe coding is characterized in that:

Make Q ()=0 mean that a node does not decompose, and Q ()=1 mean to decompose downwards, as Q (C _I+1,4j+k)=1, mean to contain comparatively complicated texture structure in the CB of k child node of node (i, j), need to resolve into less piece and carry out intraframe predictive coding, infers that present node also needs to decompose.

2. algorithm according to claim 1 is characterized in that:

Adopt

As threshold value, determine whether skipping the frame mode search procedure of present node (i, j), work as N _i,jDuring>=i+1, skip present node (i, j).

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