course 2007-supplement part 11 ntsc (1) ntsc: 2:1 interlaced, 525 lines per frame, 60 fields per...

Course 2007-Supplement Part 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 (202) 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.

'lT

',max KIAR ysff


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/(253.510-6) = 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).

'',max 2/KIAR lys Tff


NTSC Video Signal


Digital VideoThere 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.


Digital Video, CCIR601Sampling rate fs = fs,xfs,yfs,t = fs,xfl.

Two constraints: (1) x = y; (2)for both NTSC and PAL.

(1) fs,x IAR fs,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.


Fourier Analysis


Fourier Transform Pairs


Fourier Transform Pairs –Limited Bandwidth


Fourier Approximations


Sampling + Truncating Effect in FT (1)


Sampling + Truncating Effect in FT (2)


Simple Condition for DFT = FT

The signal h(t) must be periodic, and band-limited,satisfying the Nyquist rate, andthe truncation function x(t) must be nonzero over exactly one period of h(t).


DFT VS. FT (1)

Difference arises because of the discrete transform requirement for sampling and truncation.

[Case 1] Band-limited periodic waveform: Truncation interval equal to period

e.g. [-T/2, T0-T/2]. They are exactly the same within a

scaling constant.


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.)


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.


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.


periodic periodic


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 frequency function result additional frequency components (leakage) in DFT domain.


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.


DCT VS. DFTThe 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 11 ntsc (1) ntsc: 2:1 interlaced, 525 lines per frame, 60 fields per...

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