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Broadcast Basics

Broadcast Basics

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Broadcast Basics

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  1. Broadcast Basics Week 13 ICS 620

  2. BROADCAST BASICS ICS 620 Week 13

  3. Introduction • Video Basics (Analog Systems) • Transmission Systems • Wireless (terrestrial) • Wired (cable television) • Digital Video (Two Weeks)

  4. Video Standards • Standards and Principals • Persistence of Vision The rapid presentation of frames of video information to give you the illusion of smooth motion.

  5. Frequency StandardsFrame Frequency • 16 Frames per Second (fps) Black and White • 24 fps SOF • Continuity of Action • Problem of Flicker • The gross alteration of light and dark

  6. Frame Frequency x 2 Continuity of Illumination Frequency StandardsField Frequency

  7. Film Vs. Video • Film - Project a complete picture • Video - Scan, line by line, at a high rate of speed - 6 million bits per second

  8. How do we describe a picture? • A picture element (“pel” or “pixel”) one at a time • For each pel we need to somehow describe: • Brightness (luminance) • Hue (phase, “tint”) • Saturation (color intensity, “chroma”)

  9. Vertical Resolution • The picture quality associated with the number of dots (pixels) used to construct the picture. • 367,000 dots • on 525 rows (vertical)

  10. Film vs. NTSC Specs Aspect Ratio

  11. Camera Tubes

  12. Early Camera Tubes

  13. Image Orthicon

  14. Electronic Scan (Camera Pickup Tube) Object Lens Target Electron Beam Video Signal

  15. Scanning • Progressive • Interlace/Offset Interlace Example NTSC: 525 lines, 30 frames/sec, 60 fields/sec

  16. Picture Tube

  17. Picture Tube

  18. Picture Tube

  19. Scanning a Focused Image

  20. Progressive Scanning

  21. Interlace Scanning

  22. Sync Pulses

  23. Differences Between Horizontal and Vertical Synch Pulses RateDuration Vertical 59.94/sec 1:3 Horizontal 15,734.264/sec 3:1

  24. Waveform Sketch of a Video Signal

  25. A simple videowaveform One Line

  26. Waveform of Sync Pulses

  27. IRE Measurement Scale

  28. Vertical Blanking Interval (VBI) • Lines 1-21 of each field • Vertical Interval Test Signal (VITS) • Vertical Interval Reference Signal (VIRS) • Lines 1-9 V-sync and Equalizing Pulses • Lines 12-14 SMPTE Time Code • Lines 17-19 VITS and VIRS • Line 20 Network Source Code (field 1) • Line 21 Closed captioning (field 1)

  29. Kell Factor The Ratio of effective resolution to the theoretical resolution is known as the Kell Factor.

  30. Vertical Resolution Summary • Max Lines/Frame = 525 • Lost for Vertical Blanking = 42 (21 lines per field) • Visible = 525-42 = 483 • Kell Factor = 72.5% • Effective Resolution = 350 lines

  31. Horizontal Resolution Summary (4.2 MHz Video Bandwidth) = 4.2 cycles per microsecond x 52 microseconds (active scan) x 2 pixels per cycle = 436 pixels per line

  32. Television Transmission • Picture Information • Blanking pulses • Sync pulses • Audio information

  33. What about Color?

  34. Component Nature of Color R G B

  35. Video Color Palette

  36. Color Television R = Red G = Green B = Blue B + G = Cyan G + R = Yellow B + R = Magenta

  37. NTSC Color Bars

  38. Block Diagram of Color Camera

  39. Gamma G A measurement of contrast, gamma correction is required because the brightness output of a camera does not correspond to the brightness recognition of the human eye.

  40. Composite Color • Y = Luminance Signal Y =30% red + 59% green + 11% blue • C = Chrominance Signal C = I Q Matrix

  41. Color Matrix • Saturation = Amplitude of the I and Q signals • Hue = Phase developed by the difference in amplitude between the I and Q signals

  42. Transmitter Tube

  43. Color TV Transmitter

  44. TV Frequency Allocations 2 - 4 VHF-Lo 54 MHz - 72 MHz 5 - 6 VHF-Lo 76 MHz - 88 MHz 7 – 13 VHF-Hi 174 MHz – 216 MHz 14 – 59 UHF 470 MHz – 746 MHz NOTE: Natural breaks occur between channels 4 and 5; channels 6 and 7; and channels 13 and 14. Each channel is 6 MHz wide.

  45. NTSC Bandpass Characteristics (Black and White)

  46. Color TV Signal

  47. NTSC Bandpass Characteristics(Color)

  48. Color TV Signal

  49. Worldwide Standards • National Television System Committee - NTSC (1953) • Phase Alternation Line -PAL (1967) • Sequentiel Couleur Avec Memoire - SECAM (1967)

  50. World TV Standards