Analog Video

The following figures (Fig. 6.27 and 6.28) are from A.M. Tekalp, Digital video processing, Prentice Hall PTR, 1995.

Raster Scanning

NTSC Signal

NTSC Video

• 525 scan lines per frame, 30 frames per second (or be exact, 29.97 fps, 33.37 msec/frame)

• Aspect ratio 4:3

• Interlaced, each frame is divided into 2 fields, 262.5 lines/field

• 20 lines reserved for control information at the beginning of each field (Fig. 6.29)
  • So a maximum of 485 lines of visible data
  • Laserdisc and S-VHS have actual resolution of 420 lines
  • Ordinary TV - 320 lines

• Each line takes 63.5 microseconds to scan. Horizontal retrace takes 10 microseconds (with 5 microseconds horizontal synch pulse embedded), so the active line time is 53.5 microseconds.

  

  Digital Video Rasters

• Colour representation:
  • NTSC uses YIQ colour model.
  • composite = Y + I cos(Fsc t) + Q sin(Fsc t), where Fsc is the frequency of colour subcarrier
  • Eye is most sensitive to Y, next to I, next to Q. In NTSC, 4 MHz is allocated to Y, 1.5 MHz to I, 0.6 MHz to Q.

PAL Video

• 625 scan lines per frame, 25 frames per second (40 msec/frame)

• Aspect ratio 4:3

• Interlaced, each frame is divided into 2 fields, 312.5 lines/field

• Colour representation:
  • PAL uses YUV (YCbCr) colour model
  • composite = Y + 0.492 x U sin(Fsc t) + 0.877 x V cos(Fsc t)
  • In component analog video, U and V signals are lowpass filtered to about half the bandwidth of Y.