NTSC (1)

1. NTSC (1) • NTSC: 2:1 interlaced, 525 lines per frame, 60 fields per second, and 4:3 aspect ratio • horizontal sweep frequency, fl, is 525  30 = 15.75 kHz, 63.5 s to sweep each horizontal line. • horizontal retrace takes 10 s, that leaves 53.5 s ( )for the active video signal per line. • Only 485 lines out of the 525 are active lines, 40 (202) lines per frame are blanked for vertical retrace. • The resolvable horizontal lines, 485  0.7 = 339.5 lines/frame, where 0.7 is the Kell factor. • The resolvable horizontal lines, 339 4/3 (aspect ratio) = 452 elements/line. Course 2007-Supplement Part 1

2. NTSC (2) • NTSC: 2:1 interlaced, 525 lines per frame, 60 fields per second, and 4:3 aspect ratio. The bandwidth of the luminance signal is 452/(253.510-6) = 4.2 MHz. • The chrominance signals, I and Q can be low-pass filtered to 1.6 and 0.6 MHz, respectively, due to the inability of the human eye to perceive changes in chrominance over small areas (high frequencies). • Modulation: vestigial sideband modulated (VSB), quadrature amplitude modulated (QAM). Course 2007-Supplement Part 1

3. NTSC Video Signal Course 2007-Supplement Part 1

4. Digital Video • There is no need for blanking or sync pulses. • It has the aliasing artifacts due to lack of sufficient spatial resolution. • The major bottleneck of the use of digital video is the huge storage and transmission bandwidth requirements. • digital video coding: concerning the efficient transmission of images over digital communication channels. Course 2007-Supplement Part 1

5. Digital Video, CCIR601 • Sampling rate fs = fs,xfs,yfs,t = fs,xfl. • Two constraints: (1) x = y;(2)for both NTSC and PAL. • (1)  fs,x  IARfs,y, or fs = IAR(fs,y)2fs,t, which leads to fs  11 (NTSC) and 13 (PAL) MHz. So, fs = 858fl(NTSC) = 864 fl(PAL) = 13.5 MHz. Course 2007-Supplement Part 1

6. Fourier Analysis Course 2007-Supplement Part 1

7. Fourier Transform Pairs Course 2007-Supplement Part 1

8. Fourier Transform Pairs –Limited Bandwidth Course 2007-Supplement Part 1

9. Fourier Approximations Course 2007-Supplement Part 1

10. Sampling + Truncating Effect in FT (1) Course 2007-Supplement Part 1

11. Sampling + Truncating Effect in FT (2) Course 2007-Supplement Part 1

12. Simple Condition for DFT = FT • The signal h(t) must be periodic, and band-limited, • satisfying the Nyquist rate, and • the truncation function x(t) must be nonzero over exactly one period of h(t). Course 2007-Supplement Part 1

13. DFT VS. FT (1) • Difference arises because of the discrete transform requirement for sampling and truncation. • [Case 1]Band-limitedperiodic waveform: Truncation interval equal to period e.g. [-T/2, T0-T/2]. • They are exactly the same within a scaling constant. Course 2007-Supplement Part 1

14. Course 2007-Supplement Part 1

15. Course 2007-Supplement Part 1

16. DFT VS. FT (2) • [Case 2] Band-limited periodic waveform: Truncation interval NOT equal to period • The zeros of the sinf/f function are not coincident with each sample value. • Leakage: The effect of truncation at other than a multiple of the period is to create a periodic function with sharp discontinuities. The introduction of these sharp changes in the time domain results additional frequency components (a series of peaks, which are termed sidelobes.) Course 2007-Supplement Part 1

17. Course 2007-Supplement Part 1

18. DFT VS. FT (3) • [Case 3] Finite Duration Waveforms • N is chosen equal to the number of samples of the finite-length function, T = T0/N. • Errors introduced by aliasing are reduced by choosing the sample interval T sufficiently small. Course 2007-Supplement Part 1

19. DFT VS. FT (4) • [Case 4] General Waveforms • The time domain function is a periodic where the period is defined by the N points of the original function after sampling and truncation. • The frequency domain function is also a periodic where the period is defined by the N points whose values differ from the original frequency function by the error introduced in aliasing and truncation. • The aliasing error can be reduced to an acceptable level by decreasing the sample interval T. Course 2007-Supplement Part 1

20. periodic periodic Course 2007-Supplement Part 1

21. Leakage Reduction (1) • It’s inherent in the DIGITAL Fourier transforms because of the required time domain truncation. • If the truncation interval is chosen equal to a multiple of the period, the frequency domain sampling function is coincided with the zeros of the sin(f)/f function do not alter the DFT results. • If the truncation interval is NOT chosen equal to a multiple of the period, the side-lobe characteristics of the sin(f)/f frequencyfunction result additional frequency components (leakage) in DFT domain. Course 2007-Supplement Part 1

22. Leakage Reduction (2) • To reduce this leakage it is necessary to employ a time domain truncation function which has side-lobe characteristics that are of smaller magnitude. • The Hanning function: The effect is to reduce the discontinuity, which results from the rectangular truncation function. Course 2007-Supplement Part 1

23. Course 2007-Supplement Part 1

24. Course 2007-Supplement Part 1

25. Course 2007-Supplement Part 1

26. DCT VS. DFT • The spurious spectral phenomenon: Sampling in frequency domain results an implicit periodicity. The effect of truncation at other than a multiple of the period is to create a periodic function with sharp discontinuities. • To eliminate the boundary discontinuities, the original N-point sequence can be extended into a 2N-point sequence by reflecting it about the vertical axis. The extended sequence is then repeated to form the periodic sequence, this sequence may not have any discontinuities at the boundaries. • The symmetry implicit in the DCT results in two major advantages over the DFT: (1) less spurious spectral components, and (2) only real computations are required. Course 2007-Supplement Part 1