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DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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Y’UV<br />

(or Y’IQ)<br />

CHROMA<br />

MODULATE<br />

CHROMA<br />

DE-<br />

MODULATE<br />

Chroma subcarrier<br />

Y’<br />

C<br />

Y’<br />

C<br />

Phase (encodes Hue)<br />

Amplitude<br />

(encodes Saturation)<br />

Analog<br />

LINE<br />

n–1<br />

LINE<br />

n<br />

LUMA /CHROMA<br />

COMBINE<br />

LUMA /Ł<br />

CHROMA<br />

SEPARATE<br />

106 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES<br />

∑<br />

Digital<br />

(4fSC NTSC)<br />

n–1 Y’–C<br />

n Y’+C<br />

ADD:<br />

Chroma cancels,<br />

Luma averages<br />

SUBTRACT: Luma cancels,<br />

Chroma averages<br />

NTSC<br />

Figure 12.1 NTSC chroma modulation and frequency interleaving are applied, successively, to<br />

encode luma and a pair of color difference components into NTSC composite video. First, the two<br />

color difference signals are modulated onto a color subcarrier. If the two color differences are interpreted<br />

in polar coordinates, hue angle is encoded as subcarrier phase, and saturation is encoded as<br />

subcarrier amplitude. (Burst, a sample of the unmodulated subcarrier, is included in the composite<br />

signal.) Then, modulated chroma is summed with luma. Frequency interleaving leads to line-byline<br />

phase inversion of the unmodulated color subcarrier, thence to the modulated subcarrier.<br />

Summation of adjacent lines tends to cause modulated chroma to cancel, and luma to average.

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