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DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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numerical parameter having a value of about 0.5 (or in some<br />

systems, about 1 ⁄2.2).<br />

Production aperture In a video scanning standard, the active samples: The pixel array,<br />

comprising S AL columns and L A rows.<br />

Progressive A scanning standard in which spatially adjacent picture lines are<br />

associated with consecutive periodic (or identical) instants in<br />

time. Examples are 1080p24 and 720p60. Distinguished from<br />

Interlace. See also PsF, below.<br />

PsF Progressive segmented frame: An interface scheme for progressive<br />

scanned video whereby lines are rearranged to interlaced<br />

order for transmission or recording. Unlike true interlace, the first<br />

and second fields are sampled during the same time interval, and<br />

no vertical filtering is necessary. See also 24PsF, on page 610.<br />

PSF Point spread function.<br />

QAM Quadrature amplitude modulation: A modulation system wherein<br />

two information signals independently modulate two subcarriers<br />

that are in quadrature (that is, offset in phase by 90°), which are<br />

then summed to form the modulated subcarrier. An analog<br />

version of QAM, usually called just quadrature modulation,<br />

combines two color difference components onto a color subcarrier<br />

in NTSC and PAL composite video. A digital version of QAM is<br />

used for RF modulation in some digital television transmission<br />

systems (e.g., 16-QAM, 64-QAM), particularly for cable television.<br />

QCIF Quarter common intermediate format: In the ITU-T Rec. H.261<br />

standard for videoconferencing, a progressively scanned raster<br />

with 4:2:0 chroma subsampling having 176×144 luma samples at<br />

29.97 frames per second. QCIF image data is ordinarily subsampled<br />

from SDTV. See CIF, common intermediate format, on<br />

page 618.<br />

QPSK Quadrature phase-shift keying: A modulation system wherein<br />

a signal alters the phase of a carrier (or subcarrier). In video,<br />

digital QPSK is used for RF modulation.<br />

Quantization The process of assigning a discrete, numbered level to each of two<br />

or more intervals of amplitude of a sample. (In video or audio,<br />

there are typically hundreds or thousands of intervals.) In the<br />

usual uniform quantization, the steps between levels have equal<br />

amplitude.<br />

Quasi-interlace Term in consumer electronics denoting progressive segmented<br />

frame; see PsF, on page 642.<br />

Quincunx sampling A misleading term for offset sampling; see page 640. The term<br />

stems from the arrangement of club, diamond, heart, or spade<br />

symbols on a playing card of value five. The term is misleading<br />

because the sampling structure has nothing to do with the<br />

number 5.<br />

642 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES

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