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Jack K. Video demystified (2001)(T)(783s).djvu |
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Size 4.6Mb Date Nov 26, 2004 |
staircase test signal, the maximum peak-to-
peak measurement of the subcarrier
(expressed in IRE) during active video is used
to specify the residual subcarrier relative to
the burst amplitude...
Another genlocking option allows adjust-
adjustment of the subcarrier phase so it can be
matched with other video sources at the mix-
mixing or processing point...
AGC Options
For some pro-video applications, such as if the
video signal levels are known to be correct, if
all the video levels except the sync height are
correct, or if there is excessive noise in the
video signal, it may be desirable to disable the
automatic gain control...
Q is obtained by multiplying the chromi-
chrominance data by [2 sin rot], and I is obtained by
multiplying by [2 cos rot]:
((Q sin rot) + (I cos rot)) B sin rot)
= Q - (Q cos 2rot) + (I sin 2rot)
((Q sin rot) + (I cos rot)) B cos rot)
= I + (I cos 2rot) + (Q sin 2rot)
The 2rot components are removed by low-
pass filtering, resulting in the I and Q signals
being recovered...
As shown in Figure 9.23 with an ideal
color of green, two adjacent lines of the display
have a hue error (towards yellow), the next
two have the complementary hue error
(towards cyan), and so on...
Frequency Spectra for NTSC Digital Chrominance Demodulation (Fs = 13.5 MHz, Fsc
= 3.58 MHz), (a) Modulated chrominance, (b) Color subcarrier...
Genlocking
The purpose of the genlock circuitry is to
recover a sample clock and the timing control
signals (such as horizontal sync, vertical
sync, and the color subcarrier) from the video
signal...
Distortion of sync edges,
resulting in the locking point being slightly
shifted, is minimized by the lowpass filtering,
effectively shaping the sync edges prior to pro-
processing...
As shown in
Figure 8.5, at the beginning of field 1, the sub-
carrier phase is ideally 0° relative to sync; at
the beginning of field 3, the subcarrier phase is
ideally 180° relative to sync...
Although the crosstalk problem cannot be
solved entirely at the decoder, more elaborate
Y/C separation minimizes the problem...
Since the phase shift through the 284 Tsc
delay line is a function of frequency, the sub-
subcarrier sidebands are not phase shifted exactly
90°, resulting in hue errors on vertical chromi-
chrominance transitions...
Thus, vertical chrominance resolution after
processing usually will be better than that
obtained from the circuits for general viewing...
Both attenuation and
amplification may occur, so differential gain is
expressed as the largest amplitude change
between any two levels, expressed as a per-
percentage of the largest chrominance amplitude...
Although this parameter is included within the
differential gain and phase parameters, it is tra-
traditionally specified independently...
Using a modulated pedestal test signal, or
the modulated pedestal portion of the combi-
combination test signal, the largest difference
between the decoded 50 IRE luminance level
and the decoded luminance levels specifies the
chrominance-to-luminance intermodulation,
expressed in IRE or as a percentage...
H.261
ITU-T H.261 was the first video compression
and decompression standard developed for
video conferencing...
The procedures for computing the trans-
transforms are not defined, but the inverse trans-
transform must meet the specified error tolerance...
Tvoe Information (МТУРЕ)
MTYPE is a variable-length codeword contain-
containing information about the macroblock and data
elements that are present...
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