CN101404774A - Macro-block partition mode selection method in movement search - Google Patents

Abstract

The invention belongs to video encoding technology, in particular to an interframe fractional order movement searching method of H.264. The invention solves the technical problem that a selection method of a macro partition mode can rapidly partition a macro block in the movement searching. The selection method of the macro partition mode in the movement searching uses a threshold valve to judge SAD value of a partitioned block, thus judging matching degree of a block in the current mode; if the partitioned block has higher matching degree in the current mode, other modal partitions are not carried out on the partitioned block so as to reduce quantity of selection of the macro block partition mode; if the partitioned block has lower matching degree in the current mode, other modal partitions are carried out on the partitioned blocked so as to guarantee interframe precision of prediction. The invention can effectively reduce quantity of selection of the macro block partition selection mode and movement searching times of the block, thus improving arithmetic speed of an encoder.

Description

The system of selection of macro-block partition mode in the motion search

Technical field

The invention belongs to video coding technique, be specifically related to a kind of interframe mark level method for searching motion H.264.

Background technology

H.264/AVC be that (Joint Video Team JVT) formulates by joint video team.This standard provides technical support for the video technique of aspects such as broadcasting, memory device, dialogue service and wireless network, this standard is compared with standard in the past, for example: H.263, H.263+, H.263++ and MPEG-4, on video coding efficient, obtained very big raising, under same video quality, H.264 not only than H.263 having saved 50% code check, and Network Transmission had better support function with MPEG-4.H.264/AVC adopt many new technology, comprised the estimation of multimodal infra-frame prediction, FMO (flexible modular order), 1/4 pixel precision and motion compensation, multi-reference frame technology, loop filtering technology etc.These new technology not only make H.264 had better video compression performance, and allow video standard can be applied to different network environments more widely, more neatly.

Video source is made of sequence of video images, and video sequence is divided into different GOP (video image group), in the video image group, can be made of three kinds of different video frame images, is respectively I frame, P frame and B frame.The I frame is the infra-frame prediction frame, and its video image carries out compressed encoding by the image information in this frame, and the code efficiency of this pattern is often not high.The P frame is a MB of prediction frame, and it has adopted the inter motion compensation technology, promptly predicts present frame by the information of front coded frame.The B frame is the bidirectional interframe predictive frame, and it can utilize front coded frame or subsequent frame, perhaps uses the information of front and subsequent reconstruction frame to carry out inter prediction simultaneously.The P frame is compared the I frame with the B frame, only needs coded-bit seldom to come store image information, if the residual error of these information spinner inter predictions.

Inter prediction carries out compressed encoding by motion compensated prediction to video source.Macro block in the present frame predicts that by the macro block of seeking coupling in reference frame macro block position in its present frame and the macro block position difference in the reference frame are motion vector.The key component of inter prediction just is how to seek match block, i.e. motion search.The motion search accuracy affects the efficient of video compression and the quality of reconstruction, has adopted the method for searching motion of 1/4 pixel precision and multiple macro-block partition mode to carry out motion search in H.264.And in H.264, need to travel through every kind of partition mode of macro block, need a large amount of amounts of calculation like this.H.264 why carry out the motion search of different macro-block partition modes, purpose is for residual error that reduces motion search as far as possible and encoding motion vector bit number.The piece that macroblock partitions becomes is more little, and motion search can more accurately match the image in the reference frame, and the residual error of its inter prediction just can be few more.But the piece that macroblock partitions becomes is many more, and the motion vector of its required transmission is many more.Therefore how many optimum division patterns of macro block should (being determined by absolute error and (sum of absolute difference, SAD) decision) and the number of coded bits of encoding motion vector by residual error jointly.Because the schema category of macroblock partitions is a lot, macro block for 16 * 16 can be divided into 16 * 16,8 * 16,16 * 8 and 8 * 8 four kinds of patterns, as shown in Figure 1, and further, each piece of 8 * 8 can also be divided into 8 * 8,8 * 4,4 * 8 and 4 * 4 four kinds of patterns, as shown in Figure 2.Prior art is in motion search, and (16 * 16 macro blocks have first pattern 16 * 16, second pattern 8 * 16, three-mode 16 * 8, four-mode 8 * 8 to the various patterns of the macroblock partitions that the optimum macro-block partition mode of selection need travel through; 8 * 8 macro blocks have first pattern 8 * 8, second pattern 4 * 8, three-mode 8 * 4 and four-mode 4 * 4), obtain the motion vector of motion search under every kind of partition mode and residual error (absolute error and), calculate its matching error function, find out macro block and under each partition mode, have the partition mode of the pattern of minimum matching error function as this macro block.This needs a large amount of amounts of calculation, has influenced the speed of video coding, and especially when real time communication, this searching method is difficult to satisfy actual needs.

The matching error function calculation formula of each piece is as follows:

$J(\stackrel{\→}{\mathrm{MV}},{\mathrm{\λ}}_{\mathrm{MOTION}})=\mathrm{SAD}(s,c\left(\stackrel{\→}{\mathrm{MV}}\right))+{\mathrm{\λ}}_{\mathrm{MOTION}}\×R(\stackrel{\→}{\mathrm{MV}}-\stackrel{\→}{\mathrm{PMV}})$

Wherein the computing formula of SAD (absolute error and) is as follows:

$\mathrm{SAD}(s,c\left(\stackrel{\→}{\mathrm{MV}}\right))=\underset{x=1}{\overset{\mathrm{Bx}}{\mathrm{\Σ}}}\underset{y=1}{\overset{\mathrm{By}}{\mathrm{\Σ}}}\left|s\right[x,y]-c[x-{\mathrm{MV}}_x,y-{\mathrm{MV}}_y\left]\right|;$ Bx, By=16,8 or 4

Wherein, s is current initial data of encoding, and carries out the data of the reference frame of motion compensation and c is the term of coding and rebuilding;

Be candidate's motion vector,

Motion vector for prediction; λ _MOTIONBe Lagrangian constant;

The bit number of having represented the motion vector differential coding to expend; MV _xThe expression motion vector

In the axial size of x; MV _yThe expression motion vector

In the axial size of y.After obtaining the matching error function of each piece,, just obtain the matching error function of macro block under this partition mode with the matching error function addition of all pieces in the macro block.

Summary of the invention

Technical problem to be solved by this invention is that the system of selection that can divide the macro-block partition mode of macro block in a kind of motion search fast is provided.

The present invention solves the problems of the technologies described above the technical scheme that is adopted to be, the system of selection of macro-block partition mode in the motion search may further comprise the steps:

A, with first pattern as the current macro partition mode, macro block is carried out the motion search first time, obtain the residual matrix and the motion vector of the first mode block correspondence, calculate the sad value of dividing 4 four-mode pieces that obtain from first mode block;

B, select the four-mode piece that has maximum SAD in described 4 four-mode pieces, with the sad value addition of the sad value of this four-mode piece correspondence adjacent and vertical adjacent four-mode piece respectively at its level; Judge the four-mode piece adjacent with level the sad value addition value whether greater than with the value of the sad value addition of vertical adjacent four-mode piece, in this way, then with second pattern as the current macro partition mode, for the second time motion search is divided macro block with second pattern; As not, then with three-mode as the current macro partition mode, motion search is divided macro block with three-mode for the second time;

Under c, the calculating current macro partition mode, 2 second mode blocks that respectively division obtained or the sad value of three-mode piece and first threshold are relatively, whether the sad value of judging second mode block under the current macro partition mode or three-mode piece one by one is greater than first threshold, in this way, second mode block or three-mode piece greater than second threshold value are carried out the motion search second time, obtain the residual matrix and the motion vector of this second mode block or three-mode piece correspondence; As not, with residual matrix that the first time, motion search obtained and motion vector as second mode block or corresponding residual matrix that obtains of three-mode piece and motion vector;

D, according to the residual matrix that the second time, motion search obtained, calculate the sad value that second mode block or three-mode piece are divided the four-mode piece obtain;

E, judge that whether the sad value of each four-mode piece is greater than second threshold value one by one, in this way, divide macro block with four-mode, the four-mode piece greater than second threshold value is carried out motion search for the third time, obtain the residual matrix and the motion vector of this four-mode piece correspondence; As not, the residual matrix that obtains with last motion search and motion vector are as four-mode piece corresponding residual matrix and motion vector;

F, statistics macro block are at first pattern, second pattern and four-mode, perhaps first pattern, three-mode and four-mode descend corresponding residual matrix and motion vector, and calculate the matching error function of each pattern, with the macro-block partition mode of the matching error function correspondence of minimum partition mode as current macro.

Among the step e, described last motion search is specially, in second mode block or the sad value and first threshold judgement of three-mode piece in step c at this four-mode piece place, the second corresponding mode block or the sad value of three-mode piece are greater than first threshold, and the last motion search of this four-mode piece correspondence is the motion search second time so; Otherwise the last motion search of this four-mode piece correspondence is the motion search first time.

Residual matrix is the difference that current macro deducts match block in the reference frame, sad value has embodied the size of residual error, sad value is big more to show that the matching degree of current macro and reference frame is low more, among the present invention, adopt threshold value that the sad value of the piece after dividing is judged, thereby judge the matching degree of piece under the present mode, higher as piece matching degree under present mode of dividing, then this piece is no longer carried out the division of other pattern, to reduce the selected amount of macro-block partition mode; Piece matching degree under present mode as division is lower, in order to guarantee the inter prediction precision, then this piece is carried out the division of other pattern.

Described macro block is 16 * 16 or 8 * 8; When macro block was 16 * 16, the first corresponding mode block was 16 * 16, and second pattern is 8 * 16, and the three-mode piece is that 16 * 8, the four-mode piece is 8 * 8; When described macro block was 8 * 8, the first corresponding mode block was 8 * 8, and second pattern is 4 * 8, and the three-mode piece is that 8 * 4, the four-mode piece is 4 * 4.

The invention has the beneficial effects as follows, reduce the selected amount of macroblock partitions preference pattern and the motion search number of times of piece effectively, thereby improve the encoder algorithm speed.

Description of drawings

Fig. 1 is 16 * 16 macro-block partition modes;

Fig. 2 is 8 * 8 macro-block partition modes;

Fig. 3 is that the sad value of divided block in 16 * 16 macro blocks is represented;

Fig. 4 is that the sad value of divided block in 8 * 8 macro blocks is represented.

Embodiment

With the method to the selection of 16 * 16 macro-block partition modes is example, carries out 16 * 16 macro-block partition modes earlier and selects, and the partition mode of 8 * 8 macro blocks is selected again, and final macro-block partition mode normal root really determines according to the matching error function under the different partition modes.

Concrete implementation step of the present invention is as follows:

I. carry out the partition mode of 16 * 16 macro blocks and select, the sad value of each divided block as shown in Figure 3:

1) pattern (first pattern) of employing 16 * 16 is carried out motion search;

2), obtain the residual matrix and the motion vector of 16 * 16 correspondences, and calculate the sad value of 48 * 8 (four-mode pieces) according to motion search; This sad value of 48 * 8 is respectively SAD41, SAD42, SAD43 and SAD44, and their magnitude relationship is SAD41＞SAD42＞SAD43＞SAD44;

3) find out the piece (SAD41) that has maximum sad value in 48 * 8, with its SAD41 respectively at level adjacent 8 * 8 with vertical adjacent 8 * 8 sad value (sad value that level is adjacent 8 * 8 is SAD42, vertical adjacent 8 * 8 sad value is SAD43) addition, owing to, then adopt 8 * 16 (second mode blocks) as the current macro partition mode (SAD41+SAD42) greater than (SAD41+SAD43); SAD41 value and SAD42 addition obtain SAD21;

4) calculate another sad value of 8 * 16 under second pattern, SAD43 value and SAD44 addition obtain SAD22, whether the sad value (SAD21, SAD22) of judging these two pieces respectively is greater than the threshold value (TSAD23 of 8 * 16 partition modes, first threshold), SAD21 is greater than TSAD23, then 8 * 16 of SAD21 correspondence needs carry out once new motion search (with 8 * 16 patterns as the current macro partition mode), and obtain the residual matrix and the motion vector of these 8 * 16 correspondences; SAD22 is less than TSAD23, and 8 * 16 of the SAD22 correspondence then do not need to carry out new motion search, the result that this 8 * 16 motion vector and residual matrix still adopt 16 * 16 motion search to obtain;

5), obtain the sad value (SAD41 ', SAD42 ') of its 28 * 8 (four-mode pieces), SAD41 '＞SAD43＞SAD42 '＞SAD44 according to 8 * 16 new motion search that carry out of step 4) to the SAD21 correspondence;

6) judge SAD41 ', SAD42 ', SAD43 and SAD44 whether greater than the threshold value (TSAD4, second threshold value) of 8 * 8 partition modes, wherein, SAD41 '＞SAD43＞TSAD4＞SAD42 '＞SAD44; SAD41 ' and SAD43 be greater than TSAD4, and then 8 * 8 needs of SAD41 ' and SAD43 correspondence carry out once new motion search (with 8 * 8 patterns as current 8 * 16 piece partition modes), and obtain the residual matrix and the motion vector of these 8 * 8 correspondences; SAD42 ' and SAD44 are less than TSAD4, then do not need to carry out new motion search, the result that motion vector that SAD42 ' correspondence is 8 * 8 and residual matrix still adopt 8 * 16 motion search to obtain, and the result that the motion vector of 8 * 8 of SAD44 correspondences and residual matrix still adopt 16 * 16 motion search to obtain;

II. carry out in this macro block each partition mode of 8 * 8 and select, the sad value of each divided block as shown in Figure 4:

1) residual matrix and the motion vector of each that obtains 8 * 8 (first mode blocks), and calculate the sad value (SAD71, SAD72, SAD73 and SAD74) of 44 * 4 (four-mode pieces) in its each 8 * 8, SAD71＞SAD74＞SAD72＞SAD73;

2) find out the piece (SAD71) that has maximum sad value in 44 * 4, with its SAD71 adjacent and vertical adjacent 4 * 4 sad value (SAD72, SAD73) addition respectively at level, compare these two sad values that addition obtains, find out a maximum SAD and 4 * 4 integrated modes (macro-block partition modes of 4 * 8 (second patterns) or 8 * 4 (three-modes)) thereof, (SAD71+SAD73), show and to adopt 8 * 4 macro-block partition mode greater than (SAD71+SAD72); SAD71 value and SAD73 addition obtain SAD51;

3) sad value of calculating another piece under this macro-block partition mode, SAD74 and SAD72 addition obtain SAD52; Judge that respectively this SAD51, SAD52 are whether greater than the threshold value (TSAD56, first threshold) of this piece partition mode; SAD51＞TSAD56＞SAD52; 8 * 4 needs of SAD51 correspondence carry out once new motion search (with 8 * 4 patterns as current 8 * 8 piece partition modes), and obtain the residual matrix and the motion vector of these 8 * 4 correspondences; 8 * 4 of the SAD52 correspondence do not need to carry out new motion search, the result that the motion vector of this piece and residual matrix still adopt 8 * 8 motion search to obtain;

4) obtain wherein 24 * 4 sad value (SAD71 ', SAD73 ') according to 8 * 4 of SAD51 correspondence; SAD71 '＞SAD74＞SAD72＞SAD73 ';

5) judge that SAD71 ', SAD72, SAD73 ' and SAD74 are whether greater than the threshold value (TSAD7 of 4 * 4 macro-block partition modes, second threshold value), SAD71 '＞TSAD7＞SAD74＞SAD72＞SAD73 ', SAD71 ' is greater than TSAD7, then 4 * 4 needs of SAD71 ' correspondence carry out once new motion search (with 4 * 4 patterns as current 8 * 4 partition mode), and obtain the residual matrix and the motion vector of these 4 * 4 correspondences; SAD72, SAD73 ' and SAD74 are less than TSAD7,4 * 4 of their correspondences do not need to carry out new motion search, the result that the motion vector of its SAD73 ' corresponding blocks and residual matrix still adopt 8 * 4 motion search to obtain, and the result that the motion vector of SAD72 and SAD74 corresponding blocks and residual matrix still adopt 8 * 8 motion search to obtain;

III. go on foot the result who obtains according to I and II, count the motion vector and the residual error of motion search under every kind of partition mode of macro block, calculate its matching error function, find out macro block and under various partition modes, have the partition mode of the pattern of minimum matching error function as this macro block.

In the algorithm implementation procedure, the speed that being provided with of threshold value influenced algorithm and the precision of inter prediction.Often the threshold value setting is low more, the precision of inter prediction is high more, but the quantity of the macro-block partition mode that need travel through is many more, the quantity that needs simultaneously to carry out the motion search piece under different mode is also many more, its encoder speed is slow more, otherwise the precision of inter prediction is low more, but the quantity of the macro-block partition mode that need travel through is few more, the quantity that needs simultaneously to carry out the motion search piece under different mode is also few more, and its encoder speed is fast more.Generally speaking, the setting of its threshold value should not be too low, the purpose of doing like this is under the very little situation of the SAD of some pieces, again its piece is divided further that to reach the possibility that reduces SAD little with motion search, promptly enable to decrease, the degree of its reduction also can be very little, but but need more motion vector coded-bit, and the further division of piece is difficult to become optimum partition mode under these situations.

Claims (4)

1. the system of selection of macro-block partition mode in the motion search is characterized in that, may further comprise the steps:

A, with first pattern as the current macro partition mode, macro block is carried out the motion search first time, obtain the residual matrix and the motion vector of the first mode block correspondence, calculate the sad value of dividing 4 four-mode pieces that obtain from first mode block;

B, select the four-mode piece that has maximum SAD in described 4 four-mode pieces, with the sad value addition of the sad value of this four-mode piece correspondence adjacent and vertical adjacent four-mode piece respectively at its level; Judge the four-mode piece adjacent with level the sad value addition value whether greater than with the value of the sad value addition of vertical adjacent four-mode piece, in this way, then with second pattern as the current macro partition mode, for the second time motion search is divided macro block with second pattern; As not, then with three-mode as the current macro partition mode, motion search is divided macro block with three-mode for the second time;

Under c, the calculating current macro partition mode, 2 second mode blocks that respectively division obtained or the sad value of three-mode piece and first threshold are relatively, whether the sad value of judging second mode block under the current macro partition mode or three-mode piece one by one is greater than first threshold, in this way, second mode block or three-mode piece greater than second threshold value are carried out the motion search second time, obtain the residual matrix and the motion vector of this second mode block or three-mode piece correspondence; As not, with residual matrix that the first time, motion search obtained and motion vector as second mode block or corresponding residual matrix that obtains of three-mode piece and motion vector;

D, according to the residual matrix that the second time, motion search obtained, calculate the sad value that second mode block or three-mode piece are divided the four-mode piece obtain;

E, judge that whether the sad value of each four-mode piece is greater than second threshold value one by one, in this way, divide macro block with four-mode, the four-mode piece greater than second threshold value is carried out motion search for the third time, obtain the residual matrix and the motion vector of this four-mode piece correspondence; As not, the residual matrix that obtains with last motion search and motion vector are as four-mode piece corresponding residual matrix and motion vector;

F, statistics macro block are at first pattern, second pattern and four-mode, perhaps first pattern, three-mode and four-mode descend corresponding residual matrix and motion vector, and calculate the matching error function of each pattern, with the macro-block partition mode of the matching error function correspondence of minimum partition mode as current macro.

2. the system of selection of macro-block partition mode in the motion search according to claim 1, among the step e, described last motion search is specially, in second mode block or the sad value and first threshold judgement of three-mode piece in step c at this four-mode piece place, the second corresponding mode block or the sad value of three-mode piece are greater than first threshold, and the last motion search of this four-mode piece correspondence is the motion search second time so; Otherwise the last motion search of this four-mode piece correspondence is the motion search first time.

3. the system of selection of macro-block partition mode in the motion search as claimed in claim 1 or 2, described macro block is 16 * 16, and the first corresponding mode block is 16 * 16, and second pattern is 8 * 16, and the three-mode piece is that 16 * 8, the four-mode piece is 8 * 8.

4. the system of selection of macro-block partition mode in the motion search as claimed in claim 1 or 2, when described macro block was 8 * 8, the first corresponding mode block was 8 * 8, and second pattern is 4 * 8, and the three-mode piece is that 8 * 4, the four-mode piece is 4 * 4.

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