Line numbering and synchronization in digital HDTV systems

Transcription

1 Lie umberig ad sychroizatio i digital HDTV systems D. (VURT) I cotrast to aalogue televisio systems where lie umberig is covetioally liked to the vertical sychroizatio, digital televisio offers the possibility of icorporatig lie by lie umberig embedded withi the data stream. The article proposes a ew umberig sequece for digital HDTV, based o the active lies. The scheme offers several advatages, i particular i respect of the time take to achieve sychroizatio i digital equipmet.. Itroductio Oe of the basic characteristics of ay televisio system is the lie umberig associated with the picture sigal. Covetioally, the umberig has always bee coected i some way to the field sychroizatio ad it provides a meas of distiguishig the active lies formig the picture from the lies of the field blakig itervals which cotai o picture iformatio. I iterlaced scaig systems, the lie umberig also disti guishes betwee the lies of the first ad secod fields. These covetios have bee carried over from covetioal 4:3 aalogue televisio to the aalogue HDTV systems (250/50/2: ad 25/60/2:), where the field sychroizig pulse of the first field marks the start of the sequece (Figs. ad 2). The iclusio of permaet lie umberig embedded withi the data stream is ot, so far, beig cosidered for digital televisio, although lie umbers may be trasmitted as acillary data i the lie blakig iterval. The structure of the digital picture sigal is depedet o the aalogue sigal which is still i use i display hardware. Digital sychroizatio is based o the trasmissio of three sychroizatio bits [, 2]: H which distiguishes betwee the start ad the ed of the active lie; V which idicates the field blakig iterval; F which distiguishes betwee the first ad secod fields. Two of these sychroizatio bits, V ad F, are uambiguously related to the lie umber, so if the lie umbers are icluded as a permaet feature of the picture data stream, this might ifluece techiques for digital sychroizatio, as discussed below. Autum

2 Start of first field V blakig 49 lies 32 s Start of secod field V blakig 48 s 49 lies Existig lie umbers, based o frame sychroizatio Figure Lie umberig for aalogue ad digital HDTV 250/50/2: system Active lies Aomaly Proposed lie umbers, based o start of active picture 24 Autum 993

3 Start of first field V blakig 5 lies 45 lies Start of secod field V blakig 45 lies 5 lies Existig lie umbers, based o frame sychroizatio Active lies Proposed lie umbers, based o start of active picture Figure 2 Lie umberig for aalogue ad digital HDTV 25/60/2: system. Autum

4 2. Lie umberig i digital systems Lie umberig ca be itroduced i various ways. With the developmet of solid state scaig ad diplay devices, the time is drawig ear whe the cocept of electro beam flyback, ad the cosequet eed for lie ad field blakig itervals, will loose their origial meaigs. I a all digital world, it would seem irratioal to have a umberig sequece that begis i the vertical blakig iterval. If digital techologies were beig developed without the back drop of the aalogue past, it would be more coveiet to start with the first active lie i the field. Two basic ways of umberig for 625/50/2: ad 525/60/2: digital televisio were proposed i [3]. With a view to harmoizig the various systems i use, ay such chage implies also makig chages to the covetioal practices i aalogue televisio ad this is o doubt oe of the mai reasos why a ew lie umberig sequece has ot yet bee adopted i the 4:2:2 covetioal televisio systems. The umberig cocept proposed for digital HDTV is based o a sequece of lies i the whole televisio frame, i the order i which they are displayed o the receiver scree. Apart from the beefits of clarity, this method has the merit of distiguishig simply betwee iterlaced ad progressive scaig, a requiremet of decisive importace i moder systems where coversio from iterlaced to progressive scaig, ad vice versa, may be required. I progressively scaed sigals the lie umbers icrease steadily from oe lie to the ext whereas i iterlaced scaig the umbers of successive lies i the trasmitted sigal differ by two ad the parity of the lie umber (eve, odd) defies uambiguously the first ad secod fields. I additio, the choice of the poit of origi of the coordiate system of the active picture (upper left corer) is of great importace, otably i video effects systems ad bit rate reductio systems. If there is a requiremet to shift the poit of origi to a differet positio (for example, to the cetre of the picture), it is ecessary merely to apply a simple coordiate trasformatio. The relatioship betwee the origial lie umbers ad the ew umbers, for the 250/50/2: system is show i Fig.. The upper part of the figure shows the sigals i the regio of the field blakig itervals, while the lower part shows idividual lies i the aalogue scaig raster. The relatioships betwee the old ad ew systems ca be expressed mathematically: = 2+62 for 44 = 2 89 for = for = (+89)/2 for 249 odd = (+338)/2 for 2 62 eve = ( 62)/2 for eve The old ad ew umberig i the 25/60/2: system is show i Fig. 2 ad the relatioships are as follows: = for 40 = 2 80 for = for Mr. Dusa graduated from the Czech Techical Uiversity i Prague durig 959. Sice 960 he has bee workig as a specialist i aalogue ad digital televisio sigal processig at the Radio ad Televisio Research Istitute (VURT) i Prague. I 979 he defeded his post graduate thesis o televisio clampig circuits. Sice 990 he has bee Head of the Video Departmet ad Deputy Director of the VURT. Mr. is a member of EBU Workig Party V (ew systems ad services) ad of Specialist Group V/HDTV. = (+205)/2 for 045 odd = ( 045)/2 for odd = (+80)/2 for 2 24 eve It is evidet from Figs. ad 2 that the ew lie umberig is more lucid tha the old oe. A aomaly occurs i the regio of the blaked aalogue lies followig after the field sychroizig pulse (Fig. lies 6 to 250) where, i the absece of suitable precautios, the eve ad odd lies will overlap. I iterlaced scaig the first aalogue field i fact has lies ad the secod field lies; these details are isigificat i the digital domai. 26 Autum 993

5 3. Lie umber trasmissio ad sychroizatio i digital HDTV systems If lie umbers are to be carried i the digital video data stream, they must evidetly be iserted i the lie blakig itervals. The trasmissio of lie umbers as acillary data, however, is of o practical sigificace; the iformatio must be preset permaetly ad must be easily accessible. The acillary data decoder will be a multi purpose uit ad its direct utilizatio for lie umber extractio would ot be ecoomical. or would it be ecoomical to use a special acillary data extractor which would be uecessarily complicated ad would offer oly limited protectio. The most coveiet solutio is therefore either to place the lie umber immediately after the sychroizig sigal EAV (ed of active video) [3], or its icorporatio withi the EAV ad SAV (start of active video) sigals. The iformatio F ca be derived simply from the lie umber, assumig the whole of the followig field blakig iterval is associated with the active lies of the respective field. I these circumstaces the iformatio F is idetical with the uits bit of the lie umber (LSB eve/odd). Similarly, the V iformatio ca be derived as follows: if > 52 the V = 0 for 250/50/2: if > 035 the V = 0 for 25/60/2:. EAV SAV D P D6 0 0 F 9 P F D5 0 0 V 8 P V D4 0 0 H 7 P. 0 0 H D3 0 0 P3 6 P P3 D2 0 0 P P2 D 0 0 P P D0 0 0 P P0 EAV SAV D7 0 0 P4 0 D6 0 9 P3 0 D5 0 8 P2 0 D4 0 7 P 0 D3 0 6 P0 0 D D D EAV SAV D D8 0 0 H. 0 0 H D7 0 9 P P5 D6 0 8 P P4 D5 0 7 P P3 D4 0 6 P P2 D3 0 5 P. 0 5 P D2 0 4 P P0 D D a) 8 bit video, prefix FF h, 00 h,00 h b) 8 bit video, prefix FF h, 00 h c) 0 bit video, prefix FF h, 00 h Figure 3 Examples of the isertio of bit lie umbers i EAV ad SAV. For reasos of uiformity it is logical to associate the whole of the lie blakig iterval with the active part of the precedig lie. If that is doe, it is ecessary to trasmit the umber of the ext followig lie i each blakig iterval. It is ecessary to code the lie umbers with at least eleve iformatio bits ( < ) i the curretly proposed HDTV systems. If the exteded Hammig code (6,) is applied, a oe bit error ca be corrected ad a two bit error detected i every codeword. The lie umber trasmissio therefore requires a 6 bit code, either after the EAV or directly after the preamble (FF h, 00 h, 00 h or FF h, 00 h ). Examples of potetial arragemets of lie umber trasmissio i the digital sychroizig sigals, for 8 bit ad 0 bit digital video, are show i Fig. 3. The choice of a agreed method will deped o particular coditios ad the cosesus of all the parties ivolved. Further studies will be eeded to this ed ad cosideratio will also have to be give to protectio of the preamble trasmissio carried i the EAV ad SAV sigals. 4. Coclusios If the iclusio of lie umberig i digital HDTV systems as outlied here is adopted iteratioally, the ew structure should be reflected also i chages to the umberig of aalogue HDTV systems. The basis of the ew approach is the umberig of lies i the order i which they appear o the scree; this is ot just for the sake of chage the ew structure is clearer ad more logical ad if the umbers are used for sychroizatio the lock- Autum

6 ig up of digital equipmet may be achieved more rapidly ad with o trasiet effects. I effect, almost immediately after ay cut to a o sychroized sigal (i.e. at the begiig of the first complete lie) it will be possible to store the icomig sigal directly i the correct memory locatio, usig the lie umber as a memory address. Makig the umberig sequece start with the first lie of the active picture also simplifies some forms of sigal processig, such as video effects: for example, a simple traformatio is sufficiet to displace the origi of the coordiates to the cetre of the active picture area. The proposed scheme is simpler tha those begiig i the field blakig iterval ad does ot require the use of a sig bit. A questio that remais ope is the most coveiet time to implemet such a fudametal chage. It would seem best to do it whe ew systems are itroduced ad from this poit of view the preset time would appear suitable. The future advatages should richly compesate for the difficulties i the trasitio period. Bibliography [] EBU Techical Recommedatio R76 993: Iterlaced versio of the 250/50 HDTV productio stadard [2] EBU documet Tech 327 (993): Iterlaced versio of the 250/50 HDTV productio stadard [3], D. et al: Lie umberig i the digital televisio systems OIRT cotributio to CCIR documet TK 29 77/B, February 988. Writig for the The Review welcomes articles from broadcastig orgaizatios, broadcast research istitutes ad the broadcast maufacturig idustry. Our readers are iterested i theoretical studies, explaatios of ew techiques, descriptios of major egieerig developmet projects, reports o the broadcast coverage of large scale evets, etc. The is distributed to the egieerig divisios of all the EBU Active ad Associate Member orgaizatios throughout Europe ad the rest of the world. It also has a wide circulatio amog broadcast equipmet maufacturers, uiversities ad other specialist istitutios. To obtai a copy of the Guidelies for authors, please cotact: The Editor EBU Techical Review Case postale 67 CH 28 Grad Sacoex (GE) Switzerlad fax: or after December 993: Autum 993