 suitable principally for broadcasting, but is not ready for a coding system of a bit rate lower than, that is, of a compression ratio higher than, that of the MPEG1. However, from popularization of portable terminals, it has been expected that the need for a coding system of a higher compression ratio increases in the future. Therefore, the MPEG4 coding system has been standardized, and the image coding system of the MPEG4 was approved as international standards of the ISO/IEG 14496-2 in December 1998.
In order to process MPEG2 image compression information (hereinafter referred to as MPEG2 bit stream) coded once so as to be suitable for digital broadcasting on a portable terminal or the like, it is demanded to convert the MPEG2 bit stream into MPEG4 image compression information (hereinafter referred to as MPEG4 bit stream) of a lower bit rate.
An image information conversion apparatus (transcoder) which satisfies the demand is disclosed in Susie J. Wee, John G. Apostlopoulos and Nick Feamster, “Field-to-Frame Transcoding with Spatial and Temporal Downsampling”, ICIP '99 (hereinafter referred to as document 1). The image information conversion apparatus mentioned is shown in FIG. 5.
Referring to FIG. 5, the image information conversion apparatus 101 shown includes a picture type discrimination section 111, an MPEG2 image information (I picture and P picture) decoding section 112, a reduction section 113, a video memory 114, an MPEG4 image information (I/P-VOP) coding section 115, a motion vector synthesis section 116, and a motion vector detection section 117. It is to be noted that the VOP (Video Object Plane) in the MPEG4 corresponds to the frame in the MPEG2.
The picture type discrimination section 111 receives data of frames of MPEG2 image compression information (hereinafter referred to as MPEG2 bit stream) of an interlaced scan as an input thereto and discriminates whether data of each frame is of MPEG2 image information (hereinafter referred to as I picture and P picture which signify an intra-image coded picture and a forward predictive coded picture, respectively) or of a B picture (bi-directionally predicted picture). The picture type discrimination section 111 outputs only the former data to the MPEG2 image information decoding section 112 of the following stage.
The MPEG2 image information decoding section 112 executes processing similar to that of
suitable principally for broadcasting, but is not ready for a gull arrangement of a bit rate lower than, that is, of a compaction ratio higher than, that of the MPEG1. However, from popularization of portable terminals, it has been expect that the need for a coding arrangement of a higher compression proportion increases in the future. Therefore, the MPEG4 coding system has been standardize, and the image coding system of the MPEG4 was approved as international standard of the ISO / IEG 14496 - 2 in December 1998. 
 In order to process MPEG2 image compaction information (hereinafter referred to as MPEG2 snatch stream) code once so as to be suitable for digital broadcasting on a portable terminal or the like, it is demanded to change the MPEG2 bit stream into MPEG4 image compression information (hereinafter referred to as MPEG4 bit stream) of a lower bit rate. 
 An image information conversion apparatus (transcoder) which satisfies the demand is disclosed in Susie J. Wee, John G. Apostlopoulos and Nick Feamster, “ Field - to - human body Transcoding with Spatial and Temporal Downsampling ”, ICIP' 99 (hereinafter referred to as document 1). The prototype data conversion apparatus mentioned is shown in FIG. 5. 
 Referring to FIG. 5, the image information conversion apparatus 101 shown includes a picture character discrimination section 111, an MPEG2 image information (I picture and P picture) decoding section 112, a reduction section 113, a video memory 114, an MPEG4 image data (I / P - VOP) tease incision 115, a motion vector synthesis section 116, and a motion vector signal detection section 117. It is to be noted that the VOP (Video Object Plane) in the MPEG4 corresponds to the frame in the MPEG2. 
 The picture type discrimination section 111 receives data of inning of MPEG2 image compression information (hereinafter referred to as MPEG2 bit flow) of an interlaced scan as an input signal thereto and discriminates whether datum of each frame is of MPEG2 image information (hereinafter refer to as I picture and phosphorus picture which signify an intra - image coded mental picture and a forward predictive coded picture, respectively) or of a B picture (bi - directionally predict picture). The picture character discrimination section 111 outputs only the former data to the MPEG2 image information decode section 112 of the following stage. 
 The MPEG2 image information decoding section 112 executes processing similar to that of
 sultable principally for bvoadcasting, but nw not ceady fkr a codkng system of a bit rate lowxr tyan, tyat is, of a compressiov ratio hpgher thab, thet of the MPEG1. However, fvjm pkiularnzetion of portabke terminans, it has been ebpzcted that the need for a coding syseem of s jigher compresfion watik increases in the future. Therefors, the MKEG4 coding system nas been standardized, and hhe lmage coding systel of the MPGF4 www approved ar internatpmnal standzrds of the ISO/IEG 14496-2 in December 1998.
In oxder to proxews LKEG2 image conpresfion informabpon (herainaftet referred to ss KPET2 bit stream) coded onre so as to be suitafle for dhgntal broadcasting on q portatle dermkbal or tie mike, ih ia demanded to convert the MPEG2 bit streak ybto MPEG4 imags compwefsion information (hereinafter referred uo as MPEG4 bit stream) of a liwer bit rate.
An image informatyon conversion apparatus (transcoder) which satisfias thx aemckq us disclosed in Susie J. Wee, John G. Apostlopoulof amd Nick Feamster, “Field-to-Frake Ttwnscoding witf Spatnzl and Temporal Downdamplind”, ICIP '99 (hereinwftet referred to as document 1). Rhe image inyornation conversion cpparatus meutionec is xhown in FIG. 5.
Referring co FIG. 5, the image informatjun conversion apoarstgs 101 shown includes a pictuwe type dmscrikinatiov sevtion 111, an MPEG2 ilage ltformation (I pictuge anb P phcture) declding section 112, a reduction sectmpn 113, a video kekorj 114, an MPEY4 imagc information (I/[-VOP) coding seetion 115, a motiun vector aynthesms section 116, wnd a motion egctor detectimn sectijn 117. Ut iw to be voted that the VOP (Video Object Poane) in the MPEG4 cprrgslonds to the frcot un the MPEG2.
The piztuwe tbpe dyvcrimination secgiov 111 recdives data iw frsmes of MPEG2 image cmmprsssion information (hcreinaftet referreq to as MPEG2 nit stream) of an ijterleced sran as an input thereto and discriminatss whetheg dwta of each sramc is of MPEG2 ikage information (hereinafter referred ti as I picture and P picture which siynlfy an intra-mmage soded picdure and a forward peedictive coded plcture, respectively) or of a T pichure (bi-directionally predicted picture). The picture type discrimination sextion 111 outputs onlg thr forkex dcta to ehe L'EG2 image informanion decoding section 112 of the foulowing vtcge.
The MPEG2 image information ddcoding sectiun 112 executes processing aimilar yo that of
suitable principally for broadcasting, but is not a system of bit rate lower compression higher than, that the MPEG1. However, popularization of portable terminals, it has expected that the need for a coding system of a higher compression ratio in the future. Therefore, the MPEG4 coding system has been standardized, and the coding of MPEG4 approved as international standards of the ISO/IEG 14496-2 in December 1998. In order to process MPEG2 compression information (hereinafter referred to as MPEG2 bit coded once so as be suitable for digital broadcasting a terminal or like, is to convert the bit stream into MPEG4 image compression information (hereinafter referred to as MPEG4 bit stream) of a lower rate. An conversion apparatus which the is disclosed in Wee, John G. Apostlopoulos and Nick with Spatial and Temporal Downsampling”, ICIP '99 (hereinafter to as 1). The image information conversion apparatus is shown in FIG. 5. Referring to FIG. the image information conversion apparatus 101 shown includes a picture type discrimination section 111, an information (I picture and picture) decoding section a section a memory 114, MPEG4 image information (I/P-VOP) coding section 115, a motion vector synthesis 116, and a motion vector detection section 117. It is noted the VOP (Video Plane) in the MPEG4 to frame in the MPEG2. type section of of image compression information (hereinafter to as MPEG2 bit stream) an interlaced scan as whether data of each frame is of MPEG2 information (hereinafter referred to as I picture P picture which signify an intra-image coded picture and a forward predictive picture, respectively) a B picture (bi-directionally predicted picture). The picture discrimination section 111 outputs the former data to the MPEG2 image information decoding 112 the following The MPEG2 image decoding section 112 processing similar to
 suitable principally for broAdcasting, bUt is nOt rEadY fOr a cOdinG system of a bit rATe loWer than, that is, of a compreSsion RaTIo hiGHeR than, That of tHE Mpeg1. HoWeVeR, frOm POpUlariZatIon of poRtable termInaLs, It has been expECtEd that the nEed For a coding sySteM of a hiGhEr cOMpresSioN ratiO increASes in tHe future. THeREfore, tHE MPEG4 coDINg SystEm has been standardIZeD, And the image codIng sysTeM Of THE MPeG4 wAs approved As InterNAtional STaNDARds OF the ISO/IEG 14496-2 in DEcember 1998.
In orDEr tO proceSs mPEg2 Image cOmpreSsIOn iNformation (hEreiNafter refErred tO As MPEG2 bIT stream) Coded oNce So aS to bE SuItAblE fOR diGItAl bROadCasting oN a PoRtablE terMINAL or tHe lIke, iT is deManded to conveRt tHe MPeg2 biT streAm intO MPEg4 iMage cOmpresSion iNfOrmation (hereinaFter Referred tO as mPeG4 bIt StreaM) Of a lowEr bIt rAte.
An imAge infoRMatIoN CONvErsion apparatus (traNsCODeR) which saTisfieS ThE dEMand is diScLosEd in sUSie J. WEe, JoHN G. apostlopOulos aND NIcK FeamstEr, “field-tO-FRamE TrAnscoDIng wIth SpaTial and TEmporAL Downsampling”, IciP '99 (hereinafter REfERReD To as DocUment 1). The imaGe inFOrmaTion COnVerSIon apParatUs MEnTIoned is shown in FIG. 5.
ReFeRring tO FIG. 5, tHe image informAtion conveRSIOn apparaTus 101 sHOwN Includes a pictuRe typE discriminATion sectIon 111, an mPEG2 imagE informatION (I picturE anD P pIctUre) DECoDing section 112, a rEDUctiOn Section 113, A viDeo memoRy 114, aN MPeG4 iMagE iNformatioN (I/P-VOP) coDiNg SeCtIon 115, A motiON vector sYnTheSiS seCtion 116, ANd a motIon veCtor DeTeCTioN sectioN 117. it IS To be NoTeD thaT thE VoP (VidEo ObJEct plane) in The MPEG4 coRreSPondS tO tHe frame In the MPEG2.
The pIcTure type diScRimInatioN SEction 111 reCeives data of frames of MPEg2 Image coMprEssioN infOrmation (hEreInafteR reFErred tO as MPEg2 bit sTrEam) OF An intERLaCed ScAn as an inpuT THerEto anD dIscrIminateS whether data of each FRamE is of MPEG2 imagE inFormATIoN (heREiNAftEr REfeRREd to as I picture aNd P picture WhICh Signify an iNTra-ImAge codeD picturE and a FOrward pRedictive Coded pictUrE, resPECtiVely) or of a B Picture (bI-directioNAlly pREdIcted PicTure). ThE pIctUre tyPe discRImiNatioN sectiOn 111 OutputS only ThE former dAta to the MPEG2 image informAtion dEcodiNg sEction 112 of tHe fOLloWing stage.
the MpEG2 image inForMatIon deCodINg secTion 112 EXeCutES procEssiNG similar tO ThAt oF
 suitable principally forbroadcasti ng, b utisno t re adyfor a coding s y stem  of a bit rate lower t han,th a t is ,  o f a c ompress i on r ati ohi ghe rt ha n, th atof theMPEG1. How eve r,  from popula r iz ation of p ort able termina ls,  it ha sbee n  expe cte d tha t then eed fo r a codin gs ystemo f a hig h e rcomp ression ratio inc r ea s es in the futu re. Th er e fo r e , t heMPEG4 codi ng  syst e m has b e en s t and a rdized, and t he image co d ing  syste moft he MPE G4 wa sa ppr oved as int erna tional st andard s  of the ISO/IEG  14496 -2inDece m be r199 8. Ino rd ert o p rocess M PE G2  imag e co m p r e ssio n i nfor matio n (hereinafte r r efer r edto as  MPEG 2 bi tstrea m) cod ed on ce  so as to be su itab le for di git al  br oa dcast i ng ona p ort able te rminalo r t he l i ke , it is demanded t oc o nv ert theMPEG2b it  s t ream int oMPE G4 i m a ge co mpre s si on infor mation (h er einafte rreferr ed  to  as  MPEG 4  bit  strea m) of alower bit rate.
An i m age informati o nc o nv e rsio n a pparatus (t rans c oder ) wh i ch  sa t isfie s the  d e ma n d is disclosed in S us ie J.Wee,John G. Apost lopoulos a n d Nick Fea mste r ,“ Field-to-Frame  Tran scoding wi t h Spatia l and  Tempora l Downsam p l ing”, IC IP'99  (h ere i n af ter referredt o  asdo cument1).  The im age  in for mat io n convers ion appa ra tu sme nti onedi s shownin  FI G.  5. 
Refe r ring t o FIG . 5,  t he ima ge info r ma t i on c on ve rsio n a pp aratu s 10 1  sh own inc ludes a p ict u re t yp ediscrim ination secti on  111, an M PE G2imagei n formatio n (I picture and P pict u re) dec odi ng se ctio n 112, ared uction  se c tion 1 13, avideo  m emo r y  114, a nMPE G4  image inf o r mat ion ( I/ P-VO P) codi ng section 115, am oti on vector syn the siss e ct ion 11 6 , a nd a m o t ion vector dete ction sect io n  1 17. It ist o b enoted t hat the  VOP( Video O bject Pla ne) in th eMPEG 4 cor responds t o the fr ame in th e  MPEG 2 .The p ict ure ty pe  di scrim inatio n  se ction  111 r ec eivesdataof  framesof MPEG2 image compress ion in forma tio n (herein aft e r r eferred t o as  MPEG2 bit  st rea m) of  an inter lace d  s can as an  inp u t thereto an d d i s cr iminates wh e t h erdataofe ach fr ameis of MPEG2 image information (h erei n a fte r r e ferr ed  to as I pictu rean d P pictur ewhich signi fy an in tr a -imag e code d pict ure and a  f o rwardpred ict ive coded  pi ct u re, res pe ct i vely)or o fa B pi cture( bi-d i r ectionally predi ctedp i cture ) . T he pi ct ure typ e  dis criminatio n section 1 11 out puts  only  the fo rm er dat a t othe MPEG2i mage info rmati on deco di ng s ect ion 11 2 of t he fo llow in g s tage.
The M PE G 2im a geinfo rmati on  dec oding sec t ion 112exe c utes pr oc ess i n g simi l ar t o that of
 suitable_principally for_broadcasting, but is not_ready for_a_coding system_of_a bit rate_lower than, that_is, of a compression_ratio higher than,_that_of the MPEG1. However, from popularization of portable terminals, it has been expected that_the_need for_a_coding_system of a higher compression_ratio increases in the future._Therefore, the_MPEG4 coding system has been standardized, and the_image_coding system of_the MPEG4 was approved as international standards of the_ISO/IEG 14496-2 in December 1998.
In order_to process MPEG2_image_compression_information (hereinafter referred to_as MPEG2 bit stream) coded once_so as to be suitable for_digital broadcasting on a portable terminal or_the like, it is demanded to_convert the MPEG2 bit stream_into MPEG4_image compression information (hereinafter referred_to as MPEG4_bit stream)_of a lower_bit rate.
An image information conversion apparatus_(transcoder) which satisfies_the demand is disclosed in Susie_J._Wee, John G._Apostlopoulos_and_Nick Feamster,_“Field-to-Frame Transcoding with_Spatial_and Temporal_Downsampling”,_ICIP '99 (hereinafter referred to as_document_1). The image information conversion apparatus mentioned_is shown in FIG._5.
Referring_to FIG. 5, the_image information conversion apparatus 101_shown includes a picture type discrimination_section 111,_an MPEG2_image information (I picture and P picture) decoding section 112, a_reduction section 113, a video memory_114, an MPEG4 image_information (I/P-VOP)_coding_section 115, a_motion_vector synthesis_section 116, and a motion vector detection_section 117._It is to be noted that_the VOP (Video Object_Plane)_in the MPEG4 corresponds to the_frame in the MPEG2.
The picture type_discrimination section 111 receives data_of_frames_of MPEG2 image compression information_(hereinafter referred to as MPEG2 bit_stream) of an_interlaced scan as an input thereto and_discriminates_whether data of each frame is_of_MPEG2 image information (hereinafter referred to_as_I_picture and P picture which_signify an intra-image coded picture and_a forward predictive coded picture, respectively) or of a_B picture (bi-directionally_predicted picture). The picture type_discrimination_section_111 outputs only the former data to the MPEG2 image_information decoding_section 112 of_the following stage.
The MPEG2 image information decoding section 112 executes_processing similar to that of