CS4624 Text - Ch 5

Video Technology

This chapter has a great deal of important material. Some will be considered again during the unit on compression. Some, such as about analog artifacts, is somewhat beyond the scope of this course, except to help you critique compression schemes. But the rest should be read several times, since video plays a key role in multimedia systems.

5.1 Raster Scanning Principles

• scanning
• raster
• video signal
• horizontal blanking interval
• frame

• length of scanning line: vertical coverage
• TV is 4:3, movies may be 2:1

• same relative time for sender/receiver
• separate cable or send during blanking interval

• ability to resolve fine details

• 400 lines means can resolve 200 each of B and W alternating
• leads to high freq; 1MHz/80 lines horiz. resolution so N. American 4.5 MHz bandwidth yields 360 lines

• no. of scanning lines per frame
• 525 in N. America and Japan, 625 in Europe
• 40 lines go to vertical blanking interval

• interlace to reduce flicker on TV; not used on computers
• Broadcast TV uses 2 fields/frame, 30fps
• artifacts: jagged edges on moving objects, flicker on fine horiz. edges

• vacuum tube pickup
• CCD

• additive (used in video): RGB lights yield white
• subtractive paint uses magenta (RB = minus green), cyan (BG = minus red), yellow (minus blue)

• registration of 3 colors
• each sensed separately because of filters

• luminance (brightness) - chrominance (2 color differences)
• hue (color) - saturation (deep color) - value (luminance) = HSV or h-s-intensity (HSI)
• bandwidth reduction of chrominance of 2-4 vs. luminance

• 3.579545 MHz color carrier
• YIQ
• Y uses 4.5 MhZ, I uses 1.5, Q uses 0.5
• color subcarrier has saturation (color) as amplitude and hue (tint) as phase

• YUV
• 1.5 MHz for both color dimensions

• vertical, horizontal lines converging (resolution wedge)

• gamma correction
• drive CRT whose brightness vs. voltage characteristic is not linear

• signal-to-noise (S/N) in dB
• want 200:1 or 46 dB

• NTSC color bars, video waveform, vectorscope

• snow
• random horizontal streaks, large streaks of varying color

• vertical bars moving slowly across picture
• diagonal or vertical lines, pattern of horiz. bars

• loss of saturation or even all color
• sharpness of vertical edges

• to the right

• bright object
• shifting brightness across image at vertical location of bright object

• edges have colors not originally present
• from registration errors

• different levels on RGB
• set zero to white region, fix grayscale steps too

• due to phase problems

• incorrect high-freq. response

• sync problem at top of picture

• random motion from left to right
• from time-base errors - use TBC (time-base corrector)

• broadcast vs. professional vs. consumer

• broadcast+prof.: 3 sensor
• consumer uses CCD and may couple recorder too (camcorder)

• 3:2 pulldown for film 24 fps to video 30 fps
• artifacts: jerkiness, wagon wheels spinning backwards
• telecine for film to video but need color correction on faded film, excessive gamma due to CRT needs vs. film's dark regions

• tape by modulating FM carrier with video signal
• SMPTE time code
• handle generations of editing
• one-inch Type C, half-inch Betacam SP, 3/4 inch U-matic
• consumer 8mm, VHS and better versions Hi-8 and S-VHS

• broadcast: match monitors, several thousands
• consumer: snow, ghosts

• scanning, timing parameters
• color matrix equations

• color modulation parameters
• burst

• start analog, never perfect, distortions may accumulate
• broadcast, professional, consumer - cost/quality