A Fast and Efficient Predictive Block Matching Motion Estimation

Transcription

1 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 33 A Fat and Eicient Predictive Bock Matching Motion Etimation V.S.Kmar Reddy Somnath Sengpta Y. Madhaveeatha 3 IIT, Kharagpr, India IIT, Kharagpr, India JTUniverity, Hyderabad, India Smmary Thi paper decribe a nove and at approach to F Search Bock Matching () empoying prediction o earch region, baed on the amped tatitic o Sm-o-Abote Dierence (SAD) ditribtion. The motion vector i predicted to beong to either o two region, repreenting ong-motion and hort-motion, with imited amont o overap between the two. The propoed prediction i tatiticay vaidated with more than 98% ccee or dierent video eqence. Experimenta ret revea that the propoed Predicted (P) agorithm ave p to 89% o comptation, a compared to and the etimation accracy i very coe to that o. The P approach ha been ccey teted with integer, a we a ha-pe accracy. It perormance ha been compared with three-tep earch () and or a variety o tet video eqence and the ret are encoraging. Key word: Motion Etimation, Video Coding, Predictive Search,, Sb-pixe Etimation.. Introdction Motion etimation i the one o the key eement to achieve video compreion by expoiting tempora redndancy o video data. For mot o the practica appication on video coding, motion etimation i baed on bock matching (BM). The impet and mot eective method o motion etimation i to exhativey compare each x macro-bock o the crrent rame with a the candidate bock in the earch range deined with in the previo proceed rame and ind the bet matching poition with the owet ditortion, thi i caed earch bock matching agorithm (). The ditortion meare i ay the Mean o Abote Dierence (MAD) or it impicity, in which the candidate bock with the minimm amont o ditortion i conidered a the bet match. The ditortion or the candidate bock at the dipaced poition (, ) and the motion vector v are given by SAD - - ( i, j, x, x ) = å å ( x + i + k, x + j + ) -r( x + k, x + ) k= = v = arg min SAD(,, x, x ) - p, p () Where, X i the bock ize, (x, x ) i the top-et pixe poition o the reerence bock with repect to the rame coordinate; r(i, j) and (i+, j+ ) are the minance vae o the reerence bock and the candidate bock repectivey and p i the earch range in both vertica and horizonta direction. A earch bock-matching proce with a earch range p ha a earch window o ize (p+) x (p+) pixe and a tota o (p+) x (p+) candidate bock in the reerence rame or each bock o the crrent rame. The ditortion vae are compted or each o the candidate bock and it minimm vae i ond rom the et o (p+) candidate bock. Athogh, F Search Bock Matching () obtain gobay optima ret, thi er rom high comptationa compexity. To aeviate thi, evera at bock-matching agorithm, ch a three tep earch [], nove or-tep earch agorithm [], the cro earch [3], the diamond earch agorithm [4], the hexagon-baed earch agorithm [5], bock-baed gradient decent earch agorithm [6] etc., have been propoed. Thee agorithm are not optima in the ene that intead o exhative earch, ony ome ixed poition are earched. Any error in motion prediction may ead to wrong motion vector, reting in high Mean Sqare Error () o the motion-compenated rame. To achieve a bet trade-o between the comptationa compexity o and degraded PSR o motion compenated rame ing ater agorithm, recenty ome reearcher have invetigated redction o comptationa compexitie o, withot caing any igniicant redction o PSR. Hang et a [7] preented a predictive ine earch, baed on the mean vae o motion vector o the caa neighbor macro-bock. Chng et a [8] preented a new predictive earch area approach, in which predicted earch area can be obtained rom b area o the neighboring bock. Mohnyaga [9] preented a () Mancript received December 5, 7 Mancript revied December, 7

2 34 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 modiied, where the nmber o comptation i or time ewer than thoe o. Thi work on a data-driven threhod, which pdate according to the pictre variation. Yang et a [] preented another comptation redction agorithm where the motion vector can be determined baed on contant and reerence threhod. Brnig et a [] preented another variant o in which the ower bond o the matching criteria or bdivided bock are evaated in order to redce the nmber o earch poition. In or approach, it i poibe to redce the comptationa compexity o rther by empoying a predicted region -earch. The tota earch range i divided into two overapping region. The overap enre that the motion vector coe to the bondary o the two region can be determined rom either o thee two region, even i wrong prediction happen at the bondary. Or propoed prediction o region ha been vaidated with more than 98% cce or the tandard tet video eqence. Uing or approach, reerred to a Predicted F Search Bock Motion (P) hereater, the comptationa aving are o the order o 89% a compared to. The o the motion compenated rame are coe to thoe o. The P approach ha been ccey teted with integer, a we a hape accracy [] or a variety o tet video eqence and the ret are encoraging. The remainder o thi paper i organized a oow. Section preent the propoed earch area prediction mechanim and it tatitica vaidation. Section 3 dice the comptationa compexity, perormance anayi and comparion with ome popar agorithm. Section 4 preent the imation ret on the tet video eqence. Section 5 concde the paper with direction or rther work.. Propoed Search Area Prediction (, ) Î R i p ³ where, p <, ³ p (4) p to aow ome overapping, ch that (, ) Î R and R i p, p Intead o earching or the motion vector over the entire earch area R, we ave comptation by earching over either R or R, baed on or prediction. I the candidate poition correponding to the acta motion vector beong to R, the SAD vae at the crrent bock poition (i.e. zero motion vector) i expected to be ower than what it wod be, i it beong to R. Thi i baed on the obervation that becae o patia correation o video rame, the SAD vae increae owy a we move away rom the poition o the minima. A typica SAD ditribtion proie i hown in Fig (,)... Fig.. Search area prediction within the earching window R R (5) In or propoed approach, the compete earch region R i divided into two b-region R and R, correponding to ma motion and arge motion repectivey, a hown in igre. The earch range o ma motion region i taken a ± p and that o arge motion region i ± p (ower imit) to ± p (pper imit). A candidate bock with dipacement (, ) with repect to the crrent bock poition beong to thee two region according to the oowing deinition: (, ) Î R i p ³, ³ (3) ditortion earch range y earch range x Fig : A typica SAD ditribtion in a rame o Foreman, eqence 5

3 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 35 To predict a earch region, we irt take ampe o SAD vae at regar interva within the entire earch region R and then take the average, which may be expreed a SADav = å SAD(, ) T (, ) ÎS (6) where, SAD (, ) i the SAD vae compted at the candidate bock poition (, ) with repect to the crrent bock, S i the et o amped poition and T i the tota nmber o ampe. Or earch-area prediction hypothei i ormated a: v Î i ( ) av R, SAD, < SAD v Î R otherwie (8) Since, the SAD vae compted at ony one bock poition (,) may be in error, we made ome modiication to the above hypothei by conidering a ma neighborhood region R S arond (,). I majority o the SAD vae in the region R S have vae ower than SAD av, the conidence with which we can ay that the motion vector beong to the region R improve. To keep an accmated cont CP o the nmber o bock poition within the range -, (i.e. ma neighborhood region R S ), or which the SAD(, ) vae are ower than SAD av, we deine a binary qantity C(, ) a oow: ì i SAD(, ) < SADav C(, ) = í î otherwie (9) Hence, CP = C(, ) å -, () Or modiied earch-area prediction hypothei i ormated a: v Î R, i CP > CPth v Î R otherwie. (7) () () where C th i a threhod baed on the majority o bock poition within R S. where v motion vector o the bock. Uing the above hypothei, the earch area, caiied a ma motion (R ) and ong motion (R ) can be predicted. We vaidated or prediction hypothei experimentay ing a arge nmber o rame o tandard video eqence. The cce rate wa oberved to be a high a 98%, and wa vaidated with ive tet eqence.. Sb-Pixe Motion Etimation Sb-pixe motion compenation ha become a main ingredient in many modern video compreion tandard de to it abiity to provide accrate motion prediction. We are expoiting the advantage o b-pixe motion etimation to or agorithm to improve the perormance rther. Thi proce i generay imited to a ma area arond the integer pixe motion vector in order to keep comptationa compexity ma [], a hown in Fig. 3. X X X X X X X + X + X X X X X X X X X X X X X X X X Fig. 3. Sb-pixe motion etimation proce: X denote bet-matched point in the integer pixe accracy, + denote earch point in the ha-pe accracy. 3. Perormance Evaation and Ret Or P agorithm i deigned toward achieving better prediction, meared in term o a we a redced comptationa compexity. We irt preent a comptation compexity anayi o the agorithm, oowed by it qaity meare in term o. 3.. Comptationa compexity anayi To anayze the comptationa compexity o the agorithm, we deine the oowing qantitie: F earch range: ± p pixe Tota nmber o bock per rame: B. o. o candidate bock within earch window:

4 36 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 = (p+) o. o candidate bock within ma motion window: o. o candidate bock within arge motion window: Probabiity o the motion vector beonging to the ma motion window: P The tota nmber o comptation CC invoved with may be expreed a CC = B = ( p + ) ( p) B (3) Likewie, the tota nmber o comptation CC p invoved with the P i given by CC p = ( P + ( - P )) B (4) We deine a Comptationa Saving Index (CSI) reative to the a CC - CC p CSI = CC (5) Uing eqation (3) and (4) in eqation (5), we obtain - [ P + ( - P ) ] CSI = (6) For P = (i.e, when a motion vector beong to ma motion region), - CSI = = - (7) and or P = (i.e, when a motion vector beong to ong motion region), - CSI = = - Typicay, < and hence, (8) æ ö æ ö ç - ç - CSI è ø è ø (9) The above ineqaity how the pper and ower bond o the CSI. From eqation (7) and (8), it i evident that the eqence having predominanty ma motion oer more comptationa aving a compared to the eqence having predominanty ong motion. Experimenta ret revea that the propoed Predicted (P) agorithm ave p to 75% o comptation, a compared to and the etimation accracy i very coe to that o. Tabe-I how the Comptationa Saving Indice (CSI) obtained or ive tandard video eqence. It may be noted that in addition to the earch range prediction o P, or impementation tiized eary jmp-ot trategy [3], to achieve rther comptationa aving. Tabe I. CSI obtained or dierent tet eqence Seqence CSI Foreman.86 Szie.85 Car-phone.86 Mi-America.8 Mother Perormance anayi Athogh the redction o comptationa compexity i one o the main motivation in the deign o P, thi redction hod not be at the cot o degraded prediction perormance, a i the cae with ome o the b-optima agorithm ch a three-tep earch. It i worth noting that P achieve the perormance o, a ong a the bock ha a hit (cce) in prediction. In cae o bock having a mi, the perormance degrade. We compare the perormance o P with and, baed on the mean qared error. The o a predicted bock k at the poition (, ) may be expreed a K = åå - - ( i +, j + ) - r( i +, j + ) i= j= () where, i the ize o the bock, ( i +, j + ) i the predicted image and r ( i +, j + ) i the reerence image. The overa o the rame i given by = B å - K = K () Let ppoe that h i the hit-ratio o the earch prediction in P. Then, the average o a P predicted rame may be expreed a

5 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 37 = h + ( - h) P mi () where, i the average mean-qare-error o the predicted rame and mi i the average mean qare error o the mi-predicted bock in P. We introdce a new meare, caed Qaity Improvement Factor (QIF) to expre the prediction perormance o P over the earch trategy and we deine thi a - P QIF = - (3) where, i the average o the ame qare motion compenated ing. Sbtitting rom eqation () in (3), we P obtain QIF = - ( - h) mi - - (4) we away have mi > and >. A h, we away have QIF. A ong a P ha a better than, QIF i away poitive. A h approache nity, QIF approache nity, indicating perormance very coe to that o. 4. Simation Ret The eiciency o the propoed agorithm i teted with ive tandard video eqence. The meare o the predicted rame or Foreman and Carphone eqence i hown in Fig.4. and 4.. The perormance o P i qite coe to that o. Tabe II how a comparative perormance o P with and or dierent tandard video eqence. perormance are mch better with ha-pe accracy, a hown in Tabe-III. We oberve that the eqence, where ony ma motion are invoved, ch a Mi-America and Mother, the perormance o a the agorithm are very coe to each other. On the other hand, or arge motion eqence ch a Foreman, Szie and Carphone, P otperorm igniicanty and i very coe to the ret o. Tabe II. perormance (integer pixe accracy) Carphone Mother Mi-America Tabe III. perormance (ha- pe accracy) Seqence P Foreman Szie Car-phone Mother Mi-America > Frame mber > '-ore' '-ore' 'P-ore' Fig. 3.. Foreman video eqence Seqence P QIF Foreman Szie

6 38 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December > Frame mber > '-car' '-car' 'P-car' FIG. 3.. CARPHOE VIDEO SEQUECE 5. Concion A new, at and eicient predicted earch agorithm ha been propoed. De to adaptive adjtment o earch area, the agorithm ave p to 89% o tota operation reqired by the, withot acriicing the etimation accracy. The perormance o the propoed agorithm in term o, QIF and CSI are evaated and compared with and. The crrent impementation e ixed ize window or the ma and arge motion region. It i poibe to make the window ize adaptive baed on the motion content. Reerence [] R. Li, B. Zeng, and M.L. Lio A new three tep earch agorithm or bock motion etimation, IEEE Tranaction on CSVT, vo.4, pp , Oct. 994 [] L.M. Po and W.C. Ma, A nove or-tep earch agorithm or at motion etimation, IEEE Tranaction on Circit and Sytem or Video Technoogy, pp.33-37, Jne 996 [3] M. Ghanbari, The cro-earch agorithm or motion etimation, IEEE Tranaction on Commnication, vo. 38, pp , Jy 99 [4] S. Zh and K.K. Ma, A new diamond earch agorithm or at bock matching motion etimation, IEEE Trana ction on Image Proceing, vo. 9, pp. 87-9, Feb.. [5] Ce Zh, Xiao Lin, and Lap-Pi Cha, Hexagon-Baed Search Pattern or Bock Motion Etimation IEEE Tran. on Circit and Sytem or Video Tech., vo., no. 5, May. [6] L.K. Li and E. Feig, A bock-baed gradient decent earch agorithm or at bock motion video coding, IEEE Tranaction on CSVT, vo.6, pp. 49-4, Ag. 996 [7] Y-Wen Hang, Shyh-Tih Ma, Chn-F Shen and Liang- Gee Chen, Predictive Line Search: An Eicient Motion Etimation Agorithm or MPEG-4 Encoding Sytem on Mtimedia Proceor IEEE Tranaction on Circit and Sytem or Video Technoogy, vo. 3, no., Jan. 3. [8] Ko-Liang Chng and Lng-Chn Chang, A ew Predictive Search Area Approach or Fat Bock Motion Etimation, IEEE Tranaction on Image Proceing, vo., no. 6, Jne 3. [9] Vaiy G. Mohnyaga A ew Comptationay Adaptive Formation o Bock-Matching Motion Etimation IEEE Tranaction on Circit and Sytem or Video Technoogy, vo., no., Jan.. [] Jar-Ferr Yang, Shih-Cheng Chang, and Chin-Yn Chen, Comptation redction or Motion Search in Low Rate Video Coder, IEEE Tranaction on Circit and Sytem or Video Technoogy, vo., no., Oct.. [] Michae Brnig and Wogang iehen, Fat F-Search Bock Matching, IEEE Tranaction on Circit and Sytem or Video Technoogy, vo., no., Feb.. [] Krit Panopone and David M. Bayon, An Anayi and Eicient Impementation o Ha-Pe Motion Etimation, IEEE Tranaction on Circit and Sytem or Video Technoogy, vo., no.84, Ag. [3] H.C Hang and Y.P. Hng, Adaptive Eary Jmp-Ot Techniqe or Fat Motion Etimation in Video coding, Graphica Method and Image Proceing, vo. 59, no 6. pp ov V.S.K.Reddy born on Jne 967, gradated rom S.V. Univerity, Tirpathi India, and Pot Gradation rom JT Univerity, Hyderabad. Hi Doctora Reearch rom Indian Intitte o Technoogy, Kharagpr in the area o VLSI Signa Proceing. He ha been working at Sreenidhi Intitte o Science and Technoogy ince 998. Hi reearch interet are Image and Video Proceing, TCP/IP etwork and Protoco, VLSI Architectre or Signa Proceing. Somnath Sengpta, Doctora Reearch rom Indian Intitte o Technoogy, Bombay. He ha been working a a Proeor, Eectronic & Eectrica Commnication Engineering, IIT Kharagpr, India. He i ao Chairman, Kapana Chawa Space Technoogy Ce. He joined in the Intitte in 99. Hi peciaized ied are Compter Viion and Mtimedia, era etwork appication to Image/Video Proceing.

7 IJCSS Internationa Jorna o Compter Science and etwork Secrity, VOL.7 o., December 7 39 Y.Madhaveeatha, born on Janary, 97, competed her Gradation and Pot Gradation rom JT Univerity, Hyderabad. She ha been working at G.arayanamma Intitte o Science and Technoogy, JT Univerity, Hyderabad ince Sept.. Her reearch interet incde Image and Video proceing, Mtimedia Sytem Deign. Crrenty pring Ph.D at JT Univerity, Hyderabad in the area o Image and Video Proceing.