CN103581682A - Fast mode decision algorithm for HEVC intra-frame coding and application thereof - Google Patents

Abstract

The invention discloses a fast mode decision algorithm for HEVC intra-frame coding and application thereof. 35 intra-frame prediction modes are defined in HEVC. According to the result of rough mode decision, a filtering method for predictive coding is designed and achieved in order to reduce the number of candidate patterns in the rate distortion optimization mode decision process and reduce the complexity of the intra-frame coding. The fast mode decision algorithm effectively shortens coding time on the condition that coding efficiency is not reduced.

Description

A kind of fast mode decision algorithm and application thereof of HEVC intraframe coding

Technical field

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

Background technology

The common video encoding standard of new generation of formulating of efficient video coding mark standard (High Efficiency Video Coding, HEVC) Shi You International Telecommunications Union telecommunication standardsization 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 HEVC standard in January, 2013, ITU-T H.265 with MPEG-H Part2.Under the prerequisite of same application condition and video quality, code check reduces half than previous H.264/MPEG-4AVC video encoding standard.

HEVC has adopted and the previous video encoding standard basic framework of the same hybrid coding H.264/MEPG-4AVC.During coding, first an encoding block passes through infra-frame prediction in conducting frame, and then prediction residual is carried out entropy coding after by change quantization and joined in bit stream.In HEVC, defined altogether 35 kinds of intra prediction modes, comprised Intra_Planar, Intra_DC and 33 kinds of directivity predictive mode Intra_Angular[i], i=2 ..., 34, as shown in Figure 1.How to select rapidly optimum pattern very important to the computation complexity of reduction intraframe coding.

The reference software HM of HEVC has adopted a kind of scheme of two step search.First, choose J in 35 kinds of intra prediction modes _sHADthe m of value minimum as candidate pattern; Secondly, choose J in m candidate pattern _rDa predictive mode that conduct is optimum of value minimum, that is: the mode decision of rate-distortion optimization.Wherein,

d _sHADfor the absolute value of prediction residual after Hadamard transform (Hadamard transform) and, R _modefor the needed bit number of coded prediction mode index, λ is Lagrange multiplier; J _rD=D+ λ R, the image block that distortion D is reconstruct and the variance of original picture block and, R is coding current block needed total bit number, comprises the index, residual error coefficient of predictive mode etc.Owing to calculating J _rDneed to carry out the operations such as transform and quantization, than calculating J _sHADmuch complicated, therefore, adopt the scheme of two step search more effective fast than the mode decision method of full rate-distortion optimization.Meanwhile, due to J _sHADj _rDeffectively approximate, the scheme of two steps search very approaches the method for full rate-distortion optimization in distortion performance.

Summary of the invention

The object of the invention is for the problems referred to above, a kind of fast mode decision algorithm of HEVC intraframe coding is provided.The present invention can reduce encoder complexity effectively in the situation that does not reduce code efficiency.

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

In the reference software of HEVC, by calculating J _sHADthe quantity of the candidate pattern of choosing is that 8 * 8 and 4 * 4 are fixed as respectively 3,3,8 and 8 according to the size 32 * 32,16 * 16 of prediction piece.In the present invention, the quantity of candidate pattern is according to 8 of minimum J _sHADmean value determine.8 the minimum J that obtain in the note first step _sHADmean value be μ, only have J _sHADvalue be less than μ pattern just as candidate pattern, that is: by average value mu, filter out some J _sHADlarger pattern.This side's ratio juris is J _sHADthe pattern that is greater than average value mu is not optimum conventionally, or its distortion performance and J _sHADthe pattern that is less than μ is similar.The quantity of the pattern that note is selected by μ is m', experiment showed, general m'≤4.Therefore, the present invention can reduce more amount of calculation than the scheme of two original step search, keeps identical distortion performance simultaneously.If m'≤m is set, the complexity of coding can access further and be reduced.

Beneficial effect

The present invention realizes in HEVC reference software HM8.2, and adopt intra-frame encoding mode to 5 of HEVC classifications totally 20 cycle testss test.Encoder is set to acquiescence, and the quantization parameter of selection (QP) has 22,27,32 and 37.Compare with intra prediction mode decision making algorithm original in HM8.2, the percentage that the present invention saves on the scramble time and distortion performance are as shown in Table 1.Can see, the present invention can reach the saving of the scramble time of 18% left and right, only has average 0.25% code check increase simultaneously in code efficiency.

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

Accompanying drawing explanation

Fig. 1 is the directivity predictive mode in HEVC.

Embodiment

Embodiment 1

1) a given encoding block, calculates J to all intra prediction modes _sHAD;

2) according to the J obtaining in previous step _sHAD8 patterns finding out its intermediate value minimum, are designated as Cand _i, i=0,1 ..., 8;

3) calculate J _sHAD(Cand _i) mean value, be designated as μ;

To pattern Cand _i, i ∈ { i|J _sHAD(Cand _i)≤μ, i<m}, calculates J _rD, select a pattern of its intermediate value minimum to be set to the intra prediction mode of this encoding block.

Finally it should be noted that: obviously, above-described embodiment is only for example of the present invention is clearly described, and the not 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 are still among protection scope of the present invention.

Claims (6)

1. a fast mode decision algorithm for HEVC intraframe coding, is characterized in that: during the decision-making of conducting frame internal schema, first by coarse mode decision-making, calculated the cost function J of 35 kinds of patterns _sHAD, and to them by sequence from small to large, front m' pattern after sequence be as candidate pattern, 0 < m'≤35.

2. algorithm according to claim 1, is characterized in that: the quantity m' of described candidate pattern is according to 8 of minimum J _sHADmean value determine.

3. algorithm according to claim 2, is characterized in that: minimum front 8 J that obtain _sHADmean value be μ, J _sHADvalue be less than μ pattern just as candidate pattern, that is: by average value mu, filter out some J _sHADlarger pattern.

4. algorithm according to claim 3, is characterized in that: the quantity of the pattern of selecting by μ is m', m'≤4.

5. algorithm according to claim 4, is characterized in that: m'≤m, and the complexity of coding can access further and be reduced, and prediction piece is of a size of 32 * 32, and 16 * 16,8 * 8 and 4 * 4 o'clock, the value of m was respectively 3,3, and 8 and 8.

6. the application of method described in claim 5, is characterized in that, step is as follows:

1) a given encoding block, calculates J to all intra prediction modes _sHAD;

2) according to the J obtaining in previous step _sHAD8 patterns finding out its intermediate value minimum, are designated as Cand _i, i=0,1 ..., 8;

3) calculate J _sHAD(Cand _i) mean value, be designated as μ;

To pattern Cand _i, i ∈ { i|J _sHAD(Cand _i)≤μ, i<m}, calculates J _rD, select a pattern of its intermediate value minimum to be set to the intra prediction mode of this encoding block.

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