 allocation to each picture is performed based on the following two assumptions.
First, it is assumed that the product of an average quantization scale code to be used for coding of each picture and the generated code amount is fixed for each picture type unless the screen does not change. Therefore, after each picture is coded, variables Xi, Xp and Xb (global complexity measures) each representative of the complexity of the screen are updated in accordance with the following expressions (1) to (3) for individual picture types:Xi=Si·Qi  (1)Xp=Sp·Qp  (2)Xb=Sb·Qb  (3)where Si, Sp and Sb are the generated code bit amounts upon picture coding, and Qi, Qp and Qb are average quantization scale codes upon picture coding. The variables Xi, Xp and Xb have initial values represented by the following expressions (4) to (6), respectively, using the target code amount (target bit rate) bit_rate [bits/sec]:Xi=160×bit_rate/115  (4)Xp=60×bit_rate/115  (5)Xb=42×bit_rate/115  (6)
Secondly, it is assumed that the picture quality of the entire image is always optimized when the ratios Kp and Kb of the quantization scale code of P and B pictures with reference to the quantization scale code of an I picture have values defined by the following expression (7):Kp=1.0; Kb=1.4  (7)
In particular, the quantization scale code of a B picture is always 1.4 times that of the quantization scale codes of I and P pictures. Here, it is supposed that, by coding a B picture rather roughly than I and P pictures, if the code amount saved with a B picture is added to that of an I or P picture, then the picture quality of the I or P picture is improved, and also the picture quality of a B picture which refers to the I or P picture is improved.
From the two assumptions specified as above, the allocation bit amounts (Ti, Tp, Tb) to the different pictures of the GOP have values given by the following expressions (8) to (10), respectively:
                              T          i                =                  max          ⁢                      {                                          R                                  1                  +                                                                                    N                        p                        
allocation to each picture is performed based on the follow two assumption. 
 First, it is assumed that the product of an median quantization scale code to be used for tease of each video and the generated code sum is fixed for each picture character unless the screen does not change. Therefore, after each picture is gull, variables Xi, Xp and Xb (global complexity measures) each representative of the complexity of the screen are update in accordance with the following expressions (1) to (3) for individual video types: Xi = Si·Qi    (1)Xp = Sp·Qp    (2)Xb = Sb·Qb    (3)where Si, Sp and Sb are the generated code bit amount upon picture coding, and Qi, Qp and Qb are average quantization scale codes upon mental picture coding. The variables Xi, Xp and Xb have initial values represented by the follow expressions (4) to (6), respectively, using the target code amount (target bit rate) bit_rate [ bits / sec]:Xi=160×bit_rate/115    (4)Xp=60×bit_rate/115    (5)Xb=42×bit_rate/115    (6) 
 Secondly, it is assumed that the painting quality of the entire prototype is constantly optimized when the ratios Kp and Kb of the quantization plate code of P and B video with reference to the quantization scale code of an I photograph have values defined by the following expression (7):Kp=1.0; Kb=1.4    (7) 
 In finical, the quantization scale code of a B picture is always 1.4 times that of the quantization plate codes of I and phosphorus pictures. Here, it is supposed that, by coding a B picture rather approximately than I and P pictures, if the code amount saved with a B picture is added to that of an I or P picture, then the picture timbre of the I or P picture is improved, and also the picture timbre of a B picture which refers to the I or P picture is better. 
 From the two assumptions specify as above, the allocation bit come (Ti, Tp, Tb) to the unlike pictures of the GOP have values impart by the following expressions (8) to (10), respectively: 
                               T           i                 =                   max           ⁢                       {                                           R                                   1                   +                                                                                     N                         phosphorus
 alpocation to each picture is performed bcwed on the fkllowing two assumptions.
First, it is essuned tyat the product of an xverage qlantizatiin srale code to be naed for codinf of zarh picture and jhe generateg code amount hs fnxed for each picture type unless thq screem foes not changg. Thegesore, after each picture is coded, variagles Xi, Xp and Xb (glpbal complexity measures) ewch gepresentative of hhe complexuty jd the screen are updattd in accordznce with the following expresskons (1) to (3) for ibduvifoal picture vypes:Xp=Si·Qi  (1)Xp=Sp·Qp  (2)Xb=Sb·Qb  (3)whera Si, Sp and Sb are thc genxratwd code bit amounts u'on picture coding, agd Qi, Qp dnb Qb are average quanrizatiot scdle zider ukon pjcture coving. The vadiables Xi, Zp and Xb have initoaj values repreaented br the following expressions (4) to (6), respecuivelg, using the target code amount (target bit raje) bit_rate [bits/sec]:Xi=160×bit_rate/115  (4)Xp=60×bit_rate/115  (5)Xb=42×bit_rate/115  (6)
Secondly, it is assujdd uhqt thd plcture quality of the entire image is always jltompzed when the ratlos Kp and Kb of tne qiwntization scxle cobs kf P and B pictured with teferebce to tht quamtization scale code of an U picture hane vqlues defined by tke following exptessiom (7):Kp=1.0; Kb=1.4  (7)
In particular, thz quanfization scwle code kw a B picture is aleafs 1.4 times that of the quaneization wcalz codes uf I and P pictures. Jere, ld is supposed that, by cldhng a B pifture rather roughly than I and P pictures, if tve bode amouut savcd with a B piceure is added jo that oy an I or P pictlre, then vhe picture zuality of tha I or P pictnre is im[rovwd, abd also ghe picture quslity of c B pucture which referx tu the I or P piccbrt us improved.
Frok tfe ewl essum[dions specifhed xs xnove, ghe allocatlon bit amounts (Ti, Tp, Tb) to the different picturex jf the GIP have dalues given ny the following edpresviois (8) to (10), rgspectively:
                              T          i                =                  max          ⁢                      {                                          W                                  1                  +                                                                                    N                        p                        
allocation to each picture is performed based following assumptions. First, is assumed that quantization code to be for coding of picture and the generated code amount fixed for each picture type unless the screen does not change. Therefore, after picture is coded, variables Xi, Xp and Xb (global complexity measures) each representative the of screen updated in accordance with the following expressions (1) to (3) for individual picture types:Xi=Si·Qi (1)Xp=Sp·Qp (2)Xb=Sb·Qb Si, Sp and Sb are the generated code amounts upon picture coding, Qi, Qp and Qb are quantization codes upon coding. variables Xp and Xb initial values represented by the following expressions (4) to (6), respectively, using the target code amount (target rate) bit_rate (5)Xb=42×bit_rate/115 (6) it assumed the picture quality entire image is always optimized when and Kb of the quantization scale code of and B with reference to the quantization scale of an I picture have values defined by following expression (7):Kp=1.0; Kb=1.4 (7) In particular, the quantization scale code of a B picture 1.4 times that of quantization scale codes I P Here, is supposed by coding a B picture rather roughly than I and P if the code amount saved with a B picture is that an I or picture, then the picture of I or P picture and the a picture refers to the I P picture is improved. From two assumptions specified as (Ti, Tp, Tb) to the different pictures of GOP have values given by the following (8) to (10), respectively: T i = max ⁢ { R 1 N p
 allocation to each picture is Performed bAsed oN thE foLlOwinG two Assumptions.
FirST, it iS assumed that the product Of an aVeRAge qUAnTizatIon scalE CoDE To bE uSeD foR cODiNg of eAch Picture And the geneRatEd Code amount is FIxEd for each pIctUre type unlesS thE screeN dOes NOt chaNge. thereFore, afTEr each Picture is CoDEd, variABles Xi, XP ANd xb (glObal complexity meaSUrES) each representAtive oF tHE cOMPleXitY of the screEn Are upDAted in aCCoRDANce WIth the followiNg expressioNS (1) to (3) For indIvIduAL pictuRe typEs:xI=Si·qi  (1)Xp=Sp·Qp  (2)Xb=SB·Qb  (3)wHere Si, Sp aNd Sb arE The geneRAted codE bit amOunTs uPon pICtUrE coDiNG, anD qi, qp aND Qb Are averaGe QuAntizAtioN SCALe coDes Upon PictuRe coding. The vaRiaBles xI, Xp And Xb Have iNitiAl ValueS repreSenteD bY the following exPresSions (4) to (6), reSpeCtIveLy, Using THe targEt cOde Amount (tArget biT RatE) bIT_RAtE [bits/sec]:Xi=160×bit_rate/115  (4)XP=60×bIT_RaTe/115  (5)Xb=42×bit_rAte/115  (6)
SecONdLy, IT is assumEd ThaT the PICture QualITy Of the entIre imaGE iS aLways opTiMized wHeN thE raTios KP And KB of the QuantizaTion sCAle code of P and B PIctures with reFErENCe TO the QuaNtization scAle cODe of An I pICtUre HAve vaLues dEfINeD By the following expreSsIon (7):Kp=1.0; KB=1.4  (7)
In paRticular, the quAntization SCALe code of A B piCTuRE is always 1.4 times That oF the quantiZAtion scaLe codEs of I and p pictures. hERe, it is suPpoSed ThaT, by CODiNg a B picture raTHEr roUgHly than i anD P pictuRes, If tHe cOde AmOunt saved With a B piCtUrE iS aDdeD to thAT of an I or p pIctUrE, thEn the PIcture QualiTy of ThE I OR P pIcture iS ImPROved, AnD aLso tHe pIcTure qUaliTY of A B pictuRe which reFerS To thE I Or p picturE is improved.
FrOm The two assuMpTioNs specIFIed as aboVe, the allocation bit amounTS (Ti, Tp, Tb) To tHe difFereNt pictureS of The GOP HavE Values Given bY the fOlLowING exprESSiOns (8) To (10), RespectiveLY:
                              t          i                =                  mAx          ⁢                      {                                          R                                  1                  +                                                                                    N                        p                        
 allocation to each pictur e is perfo rmedbas edon  the  fol lowing two ass u mpti ons.
First, it is assu med t ha t  the pr oduct  of ana ve r a gequ an tiz at i on  scal e c ode tobe used fo r c od ing of eachp ic ture and t hegenerated co deamount  i s f i xed f oreachpictur e  typeunless th es creend oes not c ha nge.  Therefore, after ea c h picture is c oded,va r ia b l esXi,  Xp and Xb  ( globa l  comple x it y m eas u res) each rep resentative ofthe co mp lex i ty ofthe s cr e enare updated  inaccordanc e with the fol l owing e xpress ion s ( 1) t o  ( 3)  fo ri ndi v id ual pic ture typ es :X i=Si· Qi ( 1 ) X p=Sp ·Qp   (2 )Xb=S b·Qb  (3)wher e S i, S p  an d Sbare t he g en erate d code  bitam ounts upon pict urecoding, a ndQi , Q pand Q b  are a ver age  quanti zations cal ec o d es  upon picture codi ng . Th e variab les Xi ,  X pa nd Xb ha ve  in itia l value s re p re sented b y thef ol lo wing ex pr ession s(4)  to  (6), resp ective ly, usin g the target code am o unt (target b i tr a te )  bit _ra te [bits/se c]:X i =160 ×bit _ ra te/ 1 15  ( 4)Xp= 60 × bi t _rate/115  (5)Xb=42 ×b it_rat e/115   (6)
Secondl y, it is a s s u med that  the pi c ture quality o f the  entire im a ge is al waysoptimize d when th e ratios K p a ndKboft h equantizations c aleco de of P  an d B pic tur eswit h r ef erence to  the qua nt iz at io n s calec ode of a nI p ic tur e hav e  value s def ined  b yt hefollowi n ge x pres si on  (7) :Kp =1 .0; K b=1. 4   ( 7)
In p articular , t h e qu an ti zationscale code of  a  B picture  i s a lways1 . 4 timesthat of the quantizatio n  scalecod es of  I a nd P pict ure s. Her e,i t is s uppose d tha t,  by c oding a  B  pi ct ure rather r oug hly t ha n Iand P p ictures, if the co d e a mount saved w ith  a B p ic tur e  i s  ad de d  to t hat of an I orP picture,  t h en  the pictu r e q ua lity of  the Ior Pp ictureis improv ed, and a ls o th e pic ture quali ty of aB picture which re ferstothe Ior  Ppictu re isi mpr oved. 
Fromth e twoassum pt ions spe cified as above, the al locati on bi t a mounts (T i,T p,Tb) to th e di fferent pi ctu res  of t heG OP ha ve v a lu esg ivenby t h e followi n gexp r e ss ions (8) to ( 1 0),  resp ect i vely:                           T       i            =             max        ⁢                 {                                R                       1            +                                                                   N                   p                    
 allocation_to each_picture is performed based_on the_following_two assumptions.
First,_it_is assumed that_the product of_an average quantization scale_code to be_used_for coding of each picture and the generated code amount is fixed for each_picture_type unless_the_screen_does not change. Therefore, after_each picture is coded, variables_Xi, Xp_and Xb (global complexity measures) each representative of_the_complexity of the_screen are updated in accordance with the following expressions_(1) to (3) for individual picture_types:Xi=Si·Qi  (1)Xp=Sp·Qp  (2)Xb=Sb·Qb  (3)where Si, Sp_and_Sb_are the generated code_bit amounts upon picture coding, and_Qi, Qp and Qb are average_quantization scale codes upon picture coding. The_variables Xi, Xp and Xb have_initial values represented by the_following expressions_(4) to (6), respectively, using_the target code_amount (target_bit rate) bit_rate_[bits/sec]:Xi=160×bit_rate/115  (4)Xp=60×bit_rate/115  (5)Xb=42×bit_rate/115  (6)
Secondly, it is assumed that the_picture quality of_the entire image is always optimized_when_the ratios Kp_and_Kb_of the_quantization scale code_of_P and_B_pictures with reference to the quantization_scale_code of an I picture have values_defined by the following_expression_(7):Kp=1.0; Kb=1.4  (7)
In particular, the_quantization scale code of a_B picture is always 1.4 times_that of_the quantization_scale codes of I and P pictures. Here, it is supposed_that, by coding a B picture_rather roughly than I_and P_pictures,_if the code_amount_saved with_a B picture is added to that_of an_I or P picture, then the_picture quality of the_I_or P picture is improved, and_also the picture quality of a_B picture which refers to_the_I_or P picture is improved.
From_the two assumptions specified as above,_the allocation bit_amounts (Ti, Tp, Tb) to the different_pictures_of the GOP have values given_by_the following expressions (8) to (10),_respectively:
__    _     _        _  _    _T__        i _ _  _         =_      _          max_       _ ⁢     _   __      ____ { _  _  _ _  _ _  __                 _     R_    __  _   _       _        __ _1   _ _ _  _ _ _ _ +     __        ____  _  _  _  __     _  _   _         _                _ _   _ __   N  _ _       __          p ___  __     _____     _