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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Audio Visual Engineering B RGB TO YUV B/W Luminance Y B/W Chrominance U, V B/W

Audio Visual Engineering . RGB to YUV transform Y = 0.3R + 0.59G + 0.11B U = B - Y V = R - Y YUV to RGB transform R = V + Y G = (Y - 0.3R - 0.11B)/0.59 B = U + Y

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

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?

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

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

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

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

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

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

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

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 )

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

= 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

Error Free phasor diagram Correct CV CU + CV  CU

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

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

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

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

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

PAL Error Compensation Implications in video signal fH 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

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

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

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

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

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

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

Line n-1 Line n-1 Line n Line n Line n+1

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

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