School of Computer Science & Information Technology

School of Computer Science & Information Technology

G6DPMM - Lecture 10G6DPMM - Lecture 10

Analogue VideoAnalogue Video

Video

Real world “movie”Real world “movie”Powerful communication mediaPowerful communication mediaDo you need it?Do you need it?

The cost of videoThe cost of videoIPR or filming costsIPR or filming costsProcessing / editing costsProcessing / editing costsData budget costsData budget costsCognitive costsCognitive costs

Digital or Analogue?

Broadcasting industry and professional film Broadcasting industry and professional film making is still largely analogue.making is still largely analogue.

Professional digital equipment is expensive.Professional digital equipment is expensive.Semi-pro / amateur digital equipment is Semi-pro / amateur digital equipment is

much cheaper than analogue.much cheaper than analogue.Digital filming is becoming common for low Digital filming is becoming common for low

budget and multimedia projects.budget and multimedia projects.

Movies

Movie is a cognitive illusion created by Movie is a cognitive illusion created by a rapid sequence of still photographs a rapid sequence of still photographs (frames).(frames).

Traditional film is chemical and Traditional film is chemical and projected at 20-30 frames per second.projected at 20-30 frames per second.

Video is an electronic film substitute.Video is an electronic film substitute.

The Video Process

Light is converted to an electronic signal by one or Light is converted to an electronic signal by one or more Charge Coupled Devices (CCD).more Charge Coupled Devices (CCD).

CCD output is processed into R G & B signals, and CCD output is processed into R G & B signals, and combined with a synchronisation pulse.combined with a synchronisation pulse.

Types of video signalTypes of video signal RGBRGB - three separate signals, one for each of R G & B. - three separate signals, one for each of R G & B. Component VideoComponent Video - two separate signals - one for chroma - two separate signals - one for chroma

and one for brightness.and one for brightness. Composite VideoComposite Video - single signal containing all information. - single signal containing all information.

Analogue Video

Video signal (RGB, Component or Composite) is Video signal (RGB, Component or Composite) is written to magnetic tape.written to magnetic tape.

Audio track at top of tape (one or two channels).Audio track at top of tape (one or two channels).

Control track at bottom of tape - contains Control track at bottom of tape - contains synchronisation pulses.synchronisation pulses.

Analogue Video

Input to tape recorder by a “video in” connectorInput to tape recorder by a “video in” connector Video signal (RGB, Component or Composite) is Video signal (RGB, Component or Composite) is

written to magnetic tape.written to magnetic tape. Audio track at top of tape (one or two channels).Audio track at top of tape (one or two channels). Control track at bottom of tape - contains Control track at bottom of tape - contains

synchronisation pulses.synchronisation pulses. Output from tape recorder by modulation in the FM Output from tape recorder by modulation in the FM

broadcast bandbroadcast band

Media Standards

Laserdisk (rarely used).Laserdisk (rarely used).Betacam tape (professional broadcast).Betacam tape (professional broadcast).High-8 / Highband U-matic tape (semi-pro, High-8 / Highband U-matic tape (semi-pro,

common for multimedia)common for multimedia)S-VHS tape (amateur)S-VHS tape (amateur)VHS tape (domestic)VHS tape (domestic)Digital tape (DV Tape / Mini DV Tape)Digital tape (DV Tape / Mini DV Tape)

Broadcast Standards

NTSCNTSCPALPALSECAMSECAMHDTVHDTV

NTSC Standard

National Television Standards Committee National Television Standards Committee (1952)(1952)

US & Far EastUS & Far East525 scan lines525 scan lines30 frames per second30 frames per secondInterlaced at 60HzInterlaced at 60Hz

PAL Standard

Phase Alternate LinePhase Alternate LineUK, most of Europe, Australia & South UK, most of Europe, Australia & South

AfricaAfrica625 scan lines625 scan lines25 frames per second25 frames per secondInterlaced at 50HzInterlaced at 50Hz

SECAM Standard

Sequential Colour and MemorySequential Colour and MemoryFrance & RussiaFrance & Russia625 scan lines (as PAL)625 scan lines (as PAL)25 frames per second (as PAL)25 frames per second (as PAL)Interlaced at 50Hz (as PAL)Interlaced at 50Hz (as PAL)Colour model completely different from Colour model completely different from

PALPAL

Conversion between analogue formats

PAL / SECAM conversion is fairly easy PAL / SECAM conversion is fairly easy (ie cheap)(ie cheap)

PAL & SECAM / NTSC conversion is much PAL & SECAM / NTSC conversion is much more complex (ie expensive)more complex (ie expensive)

Low quality conversion is now cheapLow quality conversion is now cheapdual standard equipmentdual standard equipment

High quality conversion remains expensiveHigh quality conversion remains expensive

Video Colour Models

NTSC, PAL & SECAM use different NTSC, PAL & SECAM use different colour models.colour models.

Certain colours may be “illegal” ie Certain colours may be “illegal” ie unavailable.unavailable.

Not all RGB colours are available.Not all RGB colours are available.Filters can be used to convert between Filters can be used to convert between

them (though there is a slight loss of them (though there is a slight loss of quality).quality).

Overscan & Underscan

Broadcast TV images are usually Broadcast TV images are usually slightly larger than will fit on screen.slightly larger than will fit on screen.OverscanOverscan

Computer images are slightly smaller Computer images are slightly smaller than will fit on screen.than will fit on screen.UnderscanUnderscan

OverscanOverscan

UnderscanUnderscan

Acquiring Analogue Movie

FilmFilm View film movingView film moving Note time codesNote time codes Transfer to tape (“wet-gating”)Transfer to tape (“wet-gating”)

Video Video Professional video usually stored on betacamProfessional video usually stored on betacam Transfer to other formatsTransfer to other formats Copying or transfer causes quality lossCopying or transfer causes quality loss

Always use the highest available standardAlways use the highest available standard Avoid VHS if at all possibleAvoid VHS if at all possible Avoid editing with consumer equipmentAvoid editing with consumer equipment