School of Computer Science & Information Technology G6DPMM - Lecture 10 Analogue Video

Video Real world “movie” Real world “movie” Powerful communication media Powerful communication media Do you need it? Do you need it? The cost of video The cost of video IPR or filming costs IPR or filming costs Processing / editing costs Processing / editing costs Data budget costs Data budget costs Cognitive costs Cognitive costs

Digital or Analogue? Broadcasting industry and professional film making is still largely analogue. Broadcasting industry and professional film making is still largely analogue. Professional digital equipment is expensive. Professional digital equipment is expensive. Semi-pro / amateur digital equipment is much cheaper than analogue. Semi-pro / amateur digital equipment is much cheaper than analogue. Digital filming is becoming common for low budget and multimedia projects. Digital filming is becoming common for low budget and multimedia projects.

Movies Movie is a cognitive illusion created by a rapid sequence of still photographs (frames). Movie is a cognitive illusion created by a rapid sequence of still photographs (frames). Traditional film is chemical and projected at frames per second. Traditional film is chemical and projected at 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 more Charge Coupled Devices (CCD). Light is converted to an electronic signal by one or more Charge Coupled Devices (CCD). CCD output is processed into R G & B signals, and combined with a synchronisation pulse. CCD output is processed into R G & B signals, and combined with a synchronisation pulse. Types of video signal Types of video signal RGB - three separate signals, one for each of R G & B. RGB - three separate signals, one for each of R G & B. Component Video - two separate signals - one for chroma and one for brightness. Component Video - two separate signals - one for chroma and one for brightness. Composite Video - single signal containing all information. Composite Video - single signal containing all information.

Analogue Video Video signal (RGB, Component or Composite) is written to magnetic tape. Video signal (RGB, Component or Composite) is 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 synchronisation pulses. Control track at bottom of tape - contains synchronisation pulses.

Analogue Video Input to tape recorder by a “video in” connector Input to tape recorder by a “video in” connector Video signal (RGB, Component or Composite) is written to magnetic tape. Video signal (RGB, Component or Composite) is 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 synchronisation pulses. Control track at bottom of tape - contains synchronisation pulses. Output from tape recorder by modulation in the FM broadcast band Output from tape recorder by modulation in the FM broadcast 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, common for multimedia) High-8 / Highband U-matic tape (semi-pro, 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 NTSC NTSC PAL PAL SECAM SECAM HDTV HDTV

NTSC Standard National Television Standards Committee (1952) National Television Standards Committee (1952) US & Far East US & Far East 525 scan lines 525 scan lines 30 frames per second 30 frames per second Interlaced at 60Hz Interlaced at 60Hz

PAL Standard Phase Alternate Line Phase Alternate Line UK, most of Europe, Australia & South Africa UK, most of Europe, Australia & South Africa 625 scan lines 625 scan lines 25 frames per second 25 frames per second Interlaced at 50Hz Interlaced at 50Hz

SECAM Standard Sequential Colour and Memory Sequential Colour and Memory France & Russia France & Russia 625 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 PAL Colour model completely different from PAL

Conversion between analogue formats PAL / SECAM conversion is fairly easy (ie cheap) PAL / SECAM conversion is fairly easy (ie cheap) PAL & SECAM / NTSC conversion is much more complex (ie expensive) PAL & SECAM / NTSC conversion is much more complex (ie expensive) Low quality conversion is now cheap Low quality conversion is now cheap dual standard equipment dual standard equipment High quality conversion remains expensive High quality conversion remains expensive

Video Colour Models NTSC, PAL & SECAM use different colour models. NTSC, PAL & SECAM use different colour models. Certain colours may be “illegal” ie unavailable. Certain colours may be “illegal” ie unavailable. Not all RGB colours are available. Not all RGB colours are available. Filters can be used to convert between them (though there is a slight loss of quality). Filters can be used to convert between them (though there is a slight loss of quality).

Overscan & Underscan Broadcast TV images are usually slightly larger than will fit on screen. Broadcast TV images are usually slightly larger than will fit on screen. Overscan Overscan Computer images are slightly smaller than will fit on screen. Computer images are slightly smaller than will fit on screen. Underscan Underscan

Overscan

Underscan

Acquiring Analogue Movie Film Film View film moving View film moving Note time codes Note time codes Transfer to tape (“wet-gating”) Transfer to tape (“wet-gating”) Video Video Professional video usually stored on betacam Professional video usually stored on betacam Transfer to other formats Transfer to other formats Copying or transfer causes quality loss Copying or transfer causes quality loss Always use the highest available standard Always use the highest available standard Avoid VHS if at all possible Avoid VHS if at all possible Avoid editing with consumer equipment Avoid editing with consumer equipment