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Digital Television

Digital Television. Dr. Nikos Desypris ndessipris@yahoo.com nikolaos.desypris@bronet.gr Feb. 2010 Postgraduate course University of Athens. 3 rd Lecture on Digital TV. Standards Bodies related to Broadcast Television field The structure of the video standard

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Digital Television

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  1. Digital Television Dr. Nikos Desypris ndessipris@yahoo.com nikolaos.desypris@bronet.gr Feb. 2010 Postgraduate course University of Athens

  2. 3rd Lecture on Digital TV • Standards Bodies related to Broadcast Television field • The structure of the video standard • Reference data related to the video standard

  3. Standard bodies • International bodies • ITU (part of United Nations –UN) • ITU-R • ITU-T • ISO and how it is related to national members • Bodies at regional level • EBU • ETSI • SMPTE • FCC

  4. International bodies ITU is the former CCIR: International Radio Consultative Committee Branch of ITU (International Telecommunications Union), part of the United Nations (UN) Organisation • ITU-R: Radiocommunications sector of ITU (new name of CCIR in 1993). • ITU-R Study Group 11 deals with Television and issues Recommendations and Reports, containing explicit information in reasonably general form (implementation variants are allowed). ITU-R documents related to broadcast television have the prefix BT

  5. International bodies • ITU-T: ITU Telecommunication Standardisation Sector, a permanent organ of ITU, responsible for studying technical, operating and tariff questions and issuing Recommendations aiming at developing world-wide standards on a world wide basis

  6. International bodies ISO: International Organisation on Standardisation. • ISO issues standards through its branches International Electrotechnical Commission (IEC), International Illumination Commission (CIE). ISO issues Publications containing detailed descriptions. • National bodies, members of ISO and IEC participate in the development of Standards though technical committees. ISO and IEC technical Committees collaborate and draft international standards that are circulating to national bodies for voting. Publication of an international standard requires at least 75% from national bodies

  7. National level bodies • EBU: European Broadcasting Union EBU issues EBU Technical Documentations which are in fact obligatory for its members. EBU is the world’s largest professional association of national broadcasters. Founded in 1950, it merged with East – European International Radio and television Organisation (OIRT) and todayit has 74 active members, from 56 countries in and around Europe and 36 associate members around the world reaching an audience of 650 million weekly. • ETSI: European Telecommunications Standard Institute, an intergovernmental organisation issuing European Telecommunications Standards

  8. National level bodies • ETSI: European Telecommunications Standard Institute, an intergovernmental organisation issuing European Telecommunications Standards • Society of Motion Picture and Television Engineers (SMPTE) started activity in North America, but is now an international Organisation, linking broadcasters, manufacturers and academicians. Issues SMPTE Recommended Practice, SMPTE Standards and SMPTE Engineering Guidelines. •  FCC: Federal Communications Commission, the national government agency of the US

  9. The video standards and convergence • video = I see (in latin) • In this course when we are talking of video signals, we are referring to TV broadcast environment • Convergence: demands harmonisation of terminologies and technologies • What is a Standard? Set of rule or characteristics defining a particular system or product. Some are mandatory but most, including TV signals are voluntary.

  10. Broadcast Colour TV standards • Today we have three quite different colour TV standards: • NTSC (National television Standard Committee), • PAL (Phase Alternating Lines) and • SECAM (Sequence de Couleur a Memoire). • Broadcast standards not only define the video signal parameters, but many others such as those related to modulation. In reality they are not three, but many more although many have small differences.

  11. Broadcast TV systems: NTSC-M

  12. Broadcast TV systems: PAL

  13. Broadcast TV systems: SECAM

  14. Broadcast Colour TV standards The table below presents the characteristics of radiated monochrome and colour signal (analogue terrestrial) in broadcast TV systems

  15. The structure of the video standard • The several (major) parts of a video standard • The scanning standard • Aspect Ratio • Colour Information representation • Accompanying audio • Capturing video : Video cameras with 1 and 3 CCD arrays

  16. The parts of the video standard • Scanning standard determines: • How the picture is scanned in space and time (no lines/picture, no pictures /second) including interlace • Colour Information Representation: • Component (for production) and composite (for broadcasting, i.e. NTSC, PAL, SECAM) • Aspect Ratio: • how a signal fits in a screen of a particular proportion • The signal levels: • in analogue domain and in digital domain • Format: • agreed way of packaging the picture information for transmission or recording

  17. Scanning standard Scanning standard determines: • Number of Lines per frame • Frame Rate • Interlace Ratio • Line Rate, Field Rate result from the above • What is Progressive Scanning • Short specification of the scanning standard : • no of lines/frame rate/Interlace video i.e. ‘625/50/2:1’

  18. Scanning standard

  19. Scanning standard

  20. Scanning standard Interlaced scanning • If the TV picture is interlaced, the frame is broken into fields. • Odd and even number of lines are scanned as different fields • The field rate is obtained by multiplying the frame rate by the interlace ratio Progressive scanning • Scanning without interlace • Spatially adjacent TV frame lines are consecutively captured, stored or displayed • The interlace ratio is 1:1

  21. Scanning standard Short form of scanning standard • no of lines/frame rate/Interlace video i.e. ‘625/50/2:1’, or ‘625/50’ or ‘625’ • We have the 50Hz and 60 Hz countries Historically interlaced remained due to: • Backward compatibility • Low frequency beating between lighting pulsation and TV camera fields

  22. Scanning standard HDTV and relevant standards • Any video signal above 1000 lines • 1125/60 (USA, Japan and others) • 1250/50 (Europe and others) • easy conversion to 625/50 Multi-standard productions become commonplace: • Backward compatibility • Low frequency beating between lighting pulsation and TV camera fields

  23. Scanning standard Typical production procedure is multistandard • signal from HD camera • Down-converted • Transferred to a format compatible with storage media

  24. Aspect Ratio • Ratio of width of an object to its height • Defined as a two integer number (i.e. 4:3) or as a single number (i.e. 1.33) • Difference between Screen Aspect Ratio and Picture Aspect Ratio

  25. Aspect Ratio

  26. Aspect Ratio • Early films were shot with aspect ratio 4:3 • HDTV and EDTV have different aspect ratio to 4:3 • Cinematography from 1.333 (early films) to 2.35 (CinemaScope) and 2.77 in Dynavision widescreen 3D format • Note: Aspect Ratio is independent of the scanning parameters. As a result we can have video signals with exactly the same scanning parameters but different aspect ratios

  27. Aspect Ratio Widescreen 16:9 and 4:3 productions are incompatible • 4:3 -> 720 samples/active line @13.5 MHz (Rec. CCIR 601, Part A) • 16:9 -> 960 samples/active line @18 MHz (Rec. CCIR 601, Part B) i.e. to keep the same no of vertical lines we increase the horizontal resolution

  28. Colour Information representation • RGB (Red, Green, Blue) • Component : Luminance and colour difference signals • Luminance signal derivation • Y = 0.299 R + 0.587 G +0.114 B • Analogue component signals • Luminance and colour difference signals (YPrPb) • Pr =0.71327 (R-Y) • Pb = 0.56433 (B-Y) • Composite video (figure next page)

  29. Colour Information representation

  30. Video signal formats

  31. Accompanying audio • In digital TV the AES/EBU digital audio interface was specified as a result between Audio Engineering Society and the European Broadcasting Union, resulting in the AES3 (ANSI4.40) document, entitled: • ‘AES recommended practice for digital audio engineering – Serial transmission format for two-channel linearly represented digital audio data.’ • AES3 offers a lot of flexibility: • Support word-lengths from 16 to 24 bits • Fixed sampling rates of 32, 44.1 and 48 kHz • Support dynamic sampling rate • May synchronize the audio sampling rate to the video line rate • Standard line impedance at 75 Ohm and signal level to 1 Volt

  32. Accompanying audio • Additionally according to ITU-T the use of six streams of audio information is a desirable feature on all new DTV systems, known as multichannel 3/2+1 • Mono: one channel • Stereo: left, right • Dolby surround: left, right center • Surround 5.1: left right, left surround, right surround and a low frequency effect stream, a fraction of the others

  33. Sampling • 4:2:2 format (625 /50 13.5 MHz standard TV signal)

  34. Sampling • 4:2:2 format (625 /50 13.5 MHz 16:9 TV signal)

  35. Sampling grid (4:2:2)

  36. Sampling grid (4:1:1)

  37. Sampling grid (4:2:0) • 4:2:0 sampling grid (horizontal chrominance half the standard) Chrominance samples shifted vertically by one quarter of the field (down in the top field and up in the bottom field)

  38. Quantisation of the input signal Non-uniform quantisation is usually employed

  39. Quantisation: Uniform

  40. Quantisation: non - uniform

  41. Quantisation: compression/expansion

  42. Capturing video signals Videocamera with • 1CCD array (consumer) • 3 CCD arrays (professional, prosumer)

  43. Capturing video signals (1 CCD array)

  44. Capturing video signals (3CCD arrays)

  45. Capturing video signals (3CCD arrays)

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