Analogue Video: Powerful Communication Media or Costly Choice?

1. G6DPMM - Lecture 10 Analogue Video

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

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

4. Movies • Movie is a cognitive illusion created by a rapid sequence of still photographs (frames). • Traditional film is chemical and projected at 20-30 frames per second. • Video is an electronic film substitute.

5. The Video Process • 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. • Types of video signal • RGB - three separate signals, one for each of R G & B. • Component Video - two separate signals - one for chroma and one for brightness. • Composite Video - single signal containing all information.

6. Analogue Video • Video signal (RGB, Component or Composite) is written to magnetic tape. • Audio track at top of tape (one or two channels). • Control track at bottom of tape - contains synchronisation pulses.

7. Analogue Video • Input to tape recorder by a “video in” connector • Video signal (RGB, Component or Composite) is written to magnetic tape. • Audio track at top of tape (one or two channels). • Control track at bottom of tape - contains synchronisation pulses. • Output from tape recorder by modulation in the FM broadcast band

8. Media Standards • Laserdisk (rarely used). • Betacam tape (professional broadcast). • High-8 / Highband U-matic tape (semi-pro, common for multimedia) • S-VHS tape (amateur) • VHS tape (domestic) • Digital tape (DV Tape / Mini DV Tape)

9. Broadcast Standards • NTSC • PAL • SECAM • HDTV

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

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

12. SECAM Standard • Sequential Colour and Memory • France & Russia • 625 scan lines (as PAL) • 25 frames per second (as PAL) • Interlaced at 50Hz (as PAL) • Colour model completely different from PAL

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

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

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

17. Overscan

18. Underscan

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