(12) Patent Application Publication (10) Pub. No.: US 2013/ A1

Transcription

1 (19) United Sttes US A1 (12) Ptent Appliction Publiction (10) Pub. No.: US 2013/ A1 HUANG et l. (43) Pub. Dte: Sep. 12, 2013 (54) RATE-DISTORTION OPTIMIZED (52) U.S. Cl. TRANSFORMAND QUANTIZATION SYSTEM USPC /240.18; 375/E (75) Inventors: Tsung Yu HUANG, Tipei (TW); Homer H. CHEN, Tipei (TW); Po-Yen SU, Tipei (TW); Chieh Ki KAO, (57) ABSTRACT Tipei (TW); TAO-SHENG OU, Tipei (TW) The present invention is directed to rte-distortion opti (73) Assignee: NATIONAL TAIWAN UNIVERSITY, mized (RDO) trnsform nd quntiztion system. A frme Tipei (TW) clssifiction unit clssifies n input frme s either key frme or non-key frme. A rte model updte unit genertes (21) Appl. No.: 13/413,598 t lest one model prmeter of rte model ccording to 22) Filed: Mr. 6, 2012 trnsform coefficient nd bitrte resulted from n encoded (22) File r. 0, key frme. An RDO trnsform nd quntiztion unit pro Publiction Clssifiction cesses the input frme, thereby generting quntized trns form coefficient ccording to the model prmeter. A frme (51) Int. Cl. buffer is used to store previous frme, ccording to which H04N 7/30 ( ) the bitrte is estimted. O Frme clssifiction unit RDO trnsform nd X quntiztion unit Rte model updte unit model prmeter

2 Ptent Appliction Publiction Sep. 12, 2013 Sheet 1 of 4 US 2013/ A1

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6 US 2013/ A1 Sep. 12, 2013 RATE-DISTORTION OPTIMIZED TRANSFORMAND QUANTIZATION SYSTEM BACKGROUND OF THE INVENTION Field of the Invention 0002 The present invention generlly reltes to video cod ing, nd more prticulrly to system of rte-distortion opti mized (RDO) trnsform nd quntiztion Description of Relted Art The high performnce of H.264 video coding is ttributed to, mong others, the doption of rte-distortion optimiztion (RDO) frmework, which ttins good blnce between distortion nd bitrte for mode decision nd rte control Moreover, some methods hve recently dopted the rte distortion optimiztion frmework for nother importnt component of video encoder quntiztion. However, common drwbck of these methods is the high comput tionl overhed due to, for exmple, n exhustive serch nd redundnt entropy coding process to determine the quntized trnsform coefficients with lowest rte-distortion cost, s dis cussed in Rte distortion optimiztion for H.264 interfrme coding: generl frmework nd lgorithms, by E.-H. Yng nd X. Yu, IEEE Trns. Imge Process. Vol. 16, no. 7, July 2007, nd Rte distortion optimized quntiztion. by M. Krczewicz, Y.Ye nd I. Chong. VCEG-AH21, Jnury For the reson tht the trnsform nd quntiztion of H.264 only considers the distortion between originl nd reconstructed video s the cost of compression, nd conven tionl methods perform distortion optimiztion with high computtionl overhed, need hs thus risen to develop novel Scheme with high efficiency nd low computtionl complexity for video coding process. SUMMARY OF THE INVENTION In view of the foregoing, it is n object of the embodiment of the present invention to provide system of rte-distortion optimized (RDO) trnsform nd quntiztion tht llow the bitrte of quntized trnsform coefficient to be efficiently estimted. Another object of the embodiment of the present invention is to provide closed-form solution for the rte-distortion optimized (RDO) quntized trnsform coefficient, mking the optimiztion process computtionlly trctble According to one embodiment, the rte-distortion optimized (RDO) trnsform nd quntiztion system includes frme clssifiction unit, rte model updte unit, nd n RDO trnsform nd quntiztion unit. The frme clssifiction unit is configured to clssify n input frme s either key frme or non-key frme. The rte model updte unit is configured to generte t lest one model prmeter of rte model ccording to trnsform coefficient nd bitrte resulted from n encoded key frme. The RDO trnsform nd quntiztion unit is configured to process the input frme, thereby generting quntized trnsform coefficient ccord ing to the model prmeter. A frme buffer is configured to store previous frme, ccording to which the bitrte is estimted. BRIEF DESCRIPTION OF THE DRAWINGS 0009 FIG. 1 shows block digrm of rte-distortion optimized (RDO) trnsform nd quntiztion system ccord ing to one embodiment of the present invention; 0010 FIG. 2 shows n exemplry curve illustrtive of reltionship between bitrte nd quntized trnsform coeffi cient; 0011 FIG. 3 illustrtes the reltionship mong n input signl, residul signl, quntized trnsform coefficient, reconstructed residul signl, predicted signl nd bitrte; nd 0012 FIG. 4 shows detiled block digrm of the RDO trnsform nd quntiztion (RDOTO) unit in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION 0013 FIG. 1 shows block digrm of rte-distortion optimized (RDO) trnsform nd quntiztion system ccord ing to one embodiment of the present invention. The embodi ment illustrted below my be dpted to, but not limited to, H.264 coding stndrd. The shown blocks of the system my be performed by processor (e.g., digitl imge processor), softwre or their combintion In the embodiment, n input frme is first clssified s key frme or non-key frme by frme clssifiction unit 10. Generlly speking, the first frme of whole video sequence my be clssified s key frme, nd the first frme of sub-sequence in the video sequence my lso be clssi fied s key frme. The frmes other thn the key frme in the whole video sequence or the Sub-sequence re clssified s non-key frmes. It is noted tht the frmes in Sub-sequence my hve similr R-D chrcteristics, nd different sub-se quences my hve distinct R-D chrcteristics, due to, for exmple, high motion or scene chnge The clssified key frme is encoded by conventionl trnsform (e.g., discrete cosine trnsform (DCT)) nd qun tiztion. In the specifiction, the term "conventionl trns form nd quntiztion mens tht the trnsform nd qunti ztion considers only distortion rther thn both the distortion nd bitrte. The resulting bitrte nd trnsform coefficients re used, by rte model updte unit 12, to obtin model prmeter(s) of rte model. The model prmeter(s) my be stored in memory 14. Bsed on the obtined model prm eter(s), the key frme is Subjected to trnsform nd quntiz tion by RDO trnsform nd quntiztion (RDOTO) unit 16, resulting in quntized trnsform coefficient X. Finlly, the quntized trnsform coefficient X is subjected to coding (e.g., entropy coding) by coding unit 18. For non-key frme, it is subjected to trnsform nd quntiztion by the RDO trns form nd quntiztion unit 16 directly using the existing (or updted) model prmeter(s) provided by the memory With respect to the rte model updte, rte model clled p-model is dopted with modifiction in the embodi ment to estimte the bitrte ccording to previous frme stored in frme buffer 13, in order to minimize the rte distortion. Detils of p-model my be referred to A liner source model nd unified rte control lgorithm for DCT video coding. entitled to Zhihi He et l., IEEE Trns. Cir cuits Syst. Video Technol. Vol. 12, no. 11, November 2002, the disclosure of which is incorported herein by reference In the embodiment, the bitrte B my be pproxi mted by liner model round given quntiztion prm eter (QP): B(X)=C X+B (1) where C. nd fre model prmeters, X is one norm of the quntized trnsform coefficient X, which is defined s the sum of the bsolute vlues of ll elements in X.

7 US 2013/ A1 Sep. 12, FIG. 2 shows n exemplry curve illustrtive of reltionship between bitrte B nd the one norm of the qun tized trnsform coefficient X. The prmeter C. is the slope of the liner model t the given QP. To obtin C. t given QP, the frme is encoded twice using QP-EA respectively s the qun tiztion prmeter vlues, where A is smll vlue, therefore resulting in two points in the curve of FIG. 2. The slope C. my then be obtined by fitting the two points. It is noted tht nother model prmeter B does not ffect the process in minimizing the rte-distortion In the embodiment, both the rte nd distortion re to be minimized, nd my be formulted s: X = rgmin(d(r,r) + AB) (2) where B is the bitrte obtined by performing coding (e.g., entropy coding) on the quntized trnsform coefficient X, Wis the Lgrnge multiplier defined by the cost function J-D+). B. R is residul signl obtined by Subtrcting n (intr/ inter) predicted signl from n input signl (e.g., n input bsic unit), nd R is reconstructed residul signl obtined by inversely quntizing nd inversely trnsforming X. The reltionship mong the input signl, R. X. R, the predicted signl nd B is shown in FIG In the embodiment, the sum of squred error (SSE) is used to mesure the distortion nd the rte model described by (1) my be rewritten s X = rgmin (DIR-RI) + A x.) (3) O X = rgmin (D(AQX- RI) + A X 1). (4) where Q is n inverse quntiztion mtrix, nd A is n inverse trnsform mtrix, wherein denotes two norm, which is defined s sum of squred vlues of ll elements therein The minimiztion expressed in (4) is known s lest bsolute shrinkge nd selection opertor (LASSO), which hs the effect of shrinking the coefficients towrd Zero. According to one spect of the embodiment, closed-form solution my be derived from (4) s Xi (5) O, t - s () 2(II(AQ); II) round. - sign(i) rou) 2( (AQ),I)?) otherwise where X, is n element of X, t, is n element of quntized trnsform mtrix T defined by T-Q'A'R, wherein Q is quntiztion mtrix, A' is trnsform mtrix, nd ign(ii) entil Aoi, 2 is n djustment term. (0022. With respect to (5), it is shown in FIG. 4 the detiled block digrm of the RDO trnsform nd quntiztion (RDOTO) unit 16 (FIG. 1). Specificlly, the residul signl R is obtined by Subtrcting the (intr/inter) predicted signl from n input signl of the input (key/non-key) frme vi subtrctor 161. The residul signl R is processed by trns form unit 162, nd then quntiztion unit 163, resulting in the quntized trnsform signl T. The quntized trnsform signl T is then djusted with the djustment term by n djustment unit 164, therefore resulting in n djusted signl. Finlly, the djusted T is rounded by rounding unit 165, such tht the rte-distortion optimized (RDO) quntized trnsform coefficient X my be constrined to n integer According to the embodiment discussed bove, the coding performnce of the entire coding system cn be Sub stntilly improved over the conventionl scheme tht con siders only distortion, or consider none of the distortion nd bitrte. By using the rte model, the bitrte cn be estimted, nd closed-form solution (e.g., (5)) is derived for the RDO quntized trnsform coefficient X. This considerbly reduces the mount of computtions required to mke the rte-distor tion optimiztion process computtionlly trctble, in con trst to the conventionl method tht performs itertive com puttions, which incurs high computtionl overhed Although specific embodiments hve been illus trted nd described, it will be pprecited by those skilled in the rt tht vrious modifictions my be mde without deprting from the scope of the present invention, which is intended to be limited solely by the ppended clims. Wht is climed is: 1. A rte-distortion optimized (RDO) trnsform nd qun tiztion system, comprising: frme clssifiction unit configured to clssify n input frme s either key frme or non-key frme; rte model updte unit configured to generte t lest one model prmeter of rte model ccording to trns form coefficient nd bitrte resulted from n encoded key frme; n RDO trnsform nd quntiztion unit configured to process the input frme, thereby generting quntized trnsform coefficient ccording to the model prmeter; nd frme buffer configured to store previous frme, ccord ing to which the bitrte is estimted. 2. The system of clim 1, wherein the bitrte B is estimted by liner model round given quntiztion prmeter where C. nd fre the model prmeters, X is one norm of the quntized trnsform coefficient X, which is defined s sum of bsolute vlues of ll elements in X. 3. The system of clim 2, wherein the key frme is encoded twice using QP-EA respectively s the quntiztion prm eters, thereby resulting in two points in curve representing reltionship between the bitrte B nd the quntized trns form coefficient X, wherein the model prmeter C. is obtined by fitting the two points. 4. The system of clim 2, wherein the RDO trnsform nd quntiztion unit performs closed-form opertion s

8 US 2013/ A1 Sep. 12, 2013 Xi round - sign(i) 2ICAO)12 O - so is 0 otherwise rounding unit configured to round the djusted signl such tht the RDO quntized trnsform coefficient is constrined to n integer. 7. The system of clim 6, wherein the djustment term is obtined by minimizing rte-distortion ccording to where X, is n element of X, t, is n element of quntized trnsform mtrix T defined by T-Q'A'R, wherein Q' is quntiztion mtrix, A' is trnsform mtrix, ign(ii) entil Aoif. is n djustment term, nd W is Lgrnge multiplier defined by cost function J-D+ B, wherein D is distortion. 5. The system of clim 1, further comprising: memory configured to store sid t lest one model prmeter; nd coding unit configured to encode the quntized trnsform coefficient, thereby generting the bitrte; wherein the coding unit performs entropy coding on the quntized trnsform coefficient. 6. The system of clim 1, wherein the RDO trnsform nd quntiztion unit comprises: Subtrctor configured to generte residul signl by Subtrcting predicted signl from n input signl of the input frme; trnsform unit configured to trnsform the residul sig nl; quntiztion unit configured to quntize the trnsformed residul signl, thereby resulting in quntized trns form signl; n djustment unit configured to djust the quntized trns form signl with n djustment term, thereby resulting in n djusted signl; nd X = rgmin (D(R,R) + AB) where B is the bitrte obtined by performing coding on the quntized trnsform coefficient X, W is Lgrnge multiplier defined by cost function J-D+ B, D is distortion, R is residul signl obtined by Subtrcting predicted signl from n input signl of the input frme, nd R is recon structed residul signl obtined by inversely quntizing nd inversely trnsforming X. 8. The system of clim 7, wherein the RDO trnsform nd quntiztion unit performs closed-form opertion s Xi round - sign(ii). O ti- s O t; 2(I(AQ), II)? otherwise where X, is n element of X, t, is n element of quntized trnsform mtrix T defined by T-Q'A'R, wherein Q' is quntiztion mtrix of the quntiztion unit, A' is trns form mtrix of the trnsform unit, Sign(ii) ignit) "2 - IAoi, A 2 is the djustment term of the djustment unit, nd C. is the model prmeter of the rte model. k k k k k