24-04-2014, 01:07 PM
Basic Monochrome Television System
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The frame rate must be larger enough to reduce flicker to an acceptable level.
It is also needed to be multiple or submultiple of the primary power frequency so that the
“humming” effect resulting from imperfect filtering of the power source are minimum.
6MHz Standard US TV broadcast channel
It has two carriers, the visual carrier 1.25 MHz above the lower channel edge and the aural carrier 4.5
MHz above the visual. The visual carrier is amplitude-modulated by the video signal. The aural
carrier is frequency-modulated with a pick deviation of ±25kHz (compared to ±75kHz for FM
broadcasting).
Basic Image Quality Criteria
Image definitionthe distinctness of the outlines in the image; the degree to
which the image appears to be “in-focus”; a measure of the sharpness of the
transitions or edges between its dark and light areas.
In the high-definition system, these edge must be very sharp.
This quality criterium is where the High Definition TV gets its name.
It is closely related to visual acruity, the smallest angular separation at
which individual lines can be distinguish.
Gray scalespecified by three parameters:
highlight brightnessthe brightness of the brightest area of the image
contrast ratiothe ratio of the brightness of the brightest area to
that of the darkest, expressed in dB.
gammathe slope of the image brightness as a function of the scene
brightness.