1. Audio Visual Engineering
Television - the art of image transmission and reception
CAMERA
TELEVISION

2. Audio Visual Engineering
Early days, camera adopted line scanning
Vidicon -
line scanning
Electronic signals in PAL, NTSC standards
TELEVISION

3. Audio Visual Engineering
No scanning required now, standard remains the same
CCD - solid state image recording
Electronic signals in PAL, NTSC standards
TELEVISION

4. Audio Visual Engineering
Figure 1
J.S. Zarach and Noel M. Morris, Television principles & practice

5. Audio Visual Engineering
Frequency
Modulator
Audio
Signal MY
Amplitude
Modulator RF
Modulator
Video
Signal Y
(I.F.)
Syn. Pulses
Generator
Figure 2

6. Audio Visual Engineering
Resolution:
The smallest distance that can exist between two points
Maximum number of points that can exist in an area x
Figure 3

7. Audio Visual Engineering
B/W Y
B/W R
B/W + Y G
Weighted sum
B/W B
Figure 4a

8. Processing of Illuminance
in TV Systems Y
Negative AM
Camera MY
fY - I.F. Carrier
D.C.
fY +
5.5MHz fY
5.5MHz Y
LSB
USB
Figure 4b

9. Audio Visual Engineering
D.C. fY
fY + 5.5MHz
Signal
LSB
USB fY
D.C.
Filter
Passband
D.C. fY
fY + 5.5MHz
SSB
Signal
Figure 5a

10. Audio Visual Engineering
D.C. fY
fY + 5.5MHz
Signal
LSB
USB fY
D.C.
Filter
Passband
D.C. fY
fY + 5.5MHz
VSB
Signal
VSB
USB
Figure 5b

11. Audio Visual Engineering
What about Color?
Straightforward approach
fR+
5.5MHz
fG+
5.5MHz
fB+
5.5MHz
D.C. fR fG fB
But this will require THREE TIMES the bandwidth
Figure 6

12. Art of Frequency Interleaving
Time
Spectrum A
S1(t)
freq T1 1 T1 A
S2(t)
freq T2 1 T2
Figure 7

13. Art of Frequency Interleaving
THREE important findings for repetitive signals
a. Frequency spectrum is not continuous
b. Frequency components can only occur in
regular spaced slots
c. The positions of the slots are determined by
the smallest repetitive frequency of the signal

14. Art of Frequency Interleaving
TWO important findings for continuous sine wave
e. For a continuous sine wave (i.e. infinite duration), the frequency spectrum is a single impulse.
f. The position of the impulse of a continuous sine wave is dependent only on the frequency

15. S1 f1 S2 f2 f2 freq A 1st cycle 3rd cycle 2nd cycle 4th cycle T1
(Enlarged
Frequency
Scale) A f2
freq 1 T1
Figure 8a

16. S1 f1 S3 f2 f2 freq A 1st cycle 3rd cycle 2nd cycle 4th cycle T1
(Carrier) f2 A f2
freq 1 T1
Figure 8b

17. Art of Frequency Interleaving
Can RGB components be interleaved? fR fG fB
freq
Answer: No
Figure 8c

18. Art of Frequency Interleaving
The 3 color components are only roughly periodic R G B
freq
Result: Partial Overlapping between components
Distortion is very prominent in smooth region
Figure 8d

19. Audio Visual EngineeringB
RGB TO
YUV
B/W
Luminance Y
B/W
Chrominance
U, V
B/W

20. Audio Visual Engineering.
RGB to YUV transform
Y = 0.3R G B
U = B - Y
V = R - Y
YUV to RGB transform
R = V + Y
G = (Y - 0.3R B)/0.59
B = U + Y

21. Characteristics of Y, U and V
Y - Luminance (intensity information)
U and V - Chrominance (color information)
Y - Wide band (5.5 MHz)
U and V - Narrow band (about 2MHz)
The Eye is not sensitive to
Lumninance at high frequency (e.g. texture)
Chrominance, as compare with Luminance

22. Interleaving Y, U and V Chroma at 4.43 MHz Sound at 6 MHz VSB f
Note: Y and UV are separated by interleaving, what about U and V?

23. Audio Visual Engineering
Quadrature Modulation (QM)
cos  c t CU U AM Y + S V AM CV
Note: Y and UV are separated by interleaving
cos ( c t + 90o)
Figure 9

24. Audio Visual Engineering
Phasor representation of Quadrature Modulation
CU +CV CV  CU
Color (hue) defined by 

25. Line frequency = 1/T = 15.6kHz
YUV Spectrum after QM
Line duration = T = 64s
Line frequency = 1/T = 15.6kHz
Color Subcarrier frequency fsc = 283.5/T = 4.43MHz
1/T
freq Y
1/2T
fsc U
284/T V
Figure 26

26. Quadrature Demodulation
cos  c t (LO) X
LPF U
S-Y X
LPF V
cos ( c t + 90o) (LO)
Figure 10

27. Quadrature Demodulation
CU cos c t = U cos2 c t
= U (cos 2 c t + cos (0))
= U after LPF
CU cos( c t + 90o)
= U cos c t cos( c t + 90o)
= U (cos (2 c t+90) + cos (90o))
= 0 after LPF

28. Quadrature Demodulation
CV cos( c t+90) = V cos2( c t+90o)
= V (cos (2 c t+180o) + cos (0))
= V after LPF
CV cos c t
= V cos c t cos( c t + 90o)
= V (cos (2 c t+90) + cos (90o) )
= 0 after LPF

29. Problems with QM
1. The two quadrature carrier signals are not sent
to the receiver
2. Phase error in demodulation +d
CU +CV CV
- d  CU

30. Problems with QM
The two quadrature carrier signals are regenerated in the receiver with a short burst of sine wave
The regenerated carrier signals may contain error
Consider an error ‘d ’ in the regenerated carrier
The carrier (LO) changes from:
cos( c t) to cos( c t+ d ) , and
cos( c t+90o) to cos( c t+ 90o+d )

31. CU cos( c t+ )= U cos c t cos( c t+ )
Phase Distortion in QM
CU cos( c t+ )= U cos c t cos( c t+ )
= U (cos (2 c t+  ) + cos ( ))
= U cos ( ) after LPF
CU cos( c t + 90o + )
= U cos c t cos( c t + 90o + )
= U (cos (2 c t+90 + ) + cos (90o + ))
= Ucos (90o + ) after LPF

32. = V (cos (2 c t+90o + ) + cos (90o + ))
Phase Distortion in QM
CV cos( c t+ )
= V (cos (2 c t+90o + ) + cos (90o + ))
= V cos (90o + ) after LPF
CV cos( c t+90+ )
= V (cos (2 c t+180o + ) + cos ( ))
= V cos ( ) after LPF

33. Error Free phasor diagram
Correct CV
CU + CV  CU

34. Error phasor diagram
Note: distortion is similar between adjacent lines
Error
Correct CV
Every line is subject to distortion  CU

35. Color Distortion Audio Visual Engineering Distorted (anticlockwise
Original
Distorted (clockwise)
Figure 11

36. PAL Error Compensation
1. Odd lines:
U modulated by cos( c t)
V modulated by cos( c t+90o)
2. Even lines:
U modulated by cos( c t)
V modulated by cos( c t-90o)
Under Error Free condition U and V are fully recovered with quadrature demodulation

37. PAL Error Compensation
Error Free Signal
Odd Lines
Even Lines CV
- 
Correct
CU + CV  CV CU

38. PAL Error Compensation
Error Free Signal CV
Line 1 CU CU
Line 2 CV CV
Line 17 CU CU
Line 18 CV

39. PAL Error Compensation Implications in video signalfH Y
Line 1
Line 2
Line 3
Line 4 fH U
Line 1
Line 2
Line 3
Line 4
fH/2 V
Line 1
Line 2
Line 3
Line 4
fH=15.625kHz is the line frequency

40. PAL Error Compensation
LO with Error ‘d ’
Odd Lines
Even Lines CV
-  CU
Error
CU + CV d d
Correct
CU + CV  CV CU

41. PAL Error Compensation
LO with Error ‘d ’
Odd Lines
Even Lines (inverted) CV CV
Error
Error
CU + CV
CU + CV d d   CU CU

42. PAL Error Compensation
LO with Error ‘d ’
Odd Lines (delayed)
Even Lines (inverted) CV CV
Error
Error
CU + CV
CU + CV + d d   CU CU

43. PAL Error Compensation
LO with Error ‘d ’
Phasor addition
Error Free Resultant
Error (odd) CV CV
Correct
CU + CV
CU + CV
Error (even) = d   CU CU

44. Audio Visual Engineering
PAL Color Compensation - Graphical illustration
Original
Distorted
Figure 12a

45. Audio Visual Engineering
PAL Color Compensation
Original
Distorted
Compensated
Figure 12b

46. Line n-1
Line n-1
Line n
Line n
Line n+1

47. Recovering Chrominance Signals in PAL System
PAL Compensation by averaging consecutive lines: 1st case
Subscript “D” denotes delay by 64 us

48. Recovering Chrominance Signals in PAL System
PAL Compensation by averaging consecutive lines: 1st case
PAL Compensation by averaging consecutive lines: 2nd case
Subscript “D” denotes delay by 64 us