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2-4-3. White Balance
Matrix
•
The 2R-G and G-28 signals obtained by MPX are corre
lated with Y (=Yo+Y1 ) to generate the r, g and b signals as
mentioned in 2-1 -3. Later on, the white balance is adjusted .
Adjusting the white balance means that when shooting a
white subject, the r and b levels are controlled so that the
chroma signals after sub-carrier modulation become zero.
In fact, they are controlled so that
r=g and b=g.
The white balance is adjusted by the voltages at Pin @
and @ of IC91 1 (MSM6524GS) and VR931 and VR932,
and is automatically controlled by the PWM output of Pin ®
and @ of IC932 (S87C51 FC).
After white balance compensation is carried out, the r, g
and b signals are limited to the bandwidth required for the
chroma signal by LPF, and the low level noise component is
eliminated by the slicing circuit. Then appropriate gamma
compensation is performed by the gamma (
In the R-Y and B-Y matrix, HUE and GC circuits, R-Y and
B-Y are generated using the gamma-compensated r, g and
b signals, and hue adjustment is done by the HUE circuit
using the following formulas :
± a
/3
(R-Y) ' = (R-Y)
(B-Y)
(B-Y)' = (B-Y) ±
(R-Y)
The GC circuit adjusts the levels of (R-Y)' and (B-Y)'.
®
The hue and level are adjusted by the voltage of Pins@) ,@ ,
and ® of IC91 1 (MSM6524GS).
2-4-4. YH Processing
The F3 signal (YH) fed to Pin (§ of IC91 4 (CXA 1 391 R) is
clamped and compensated for proper gamma. The gamma
characteristics are determined by the voltage of Pin @ . The
signal is AE corrected by the PWM output of Pin @ of
IC932 (S87C51 FC).
The gamma-compensated YH is fed to Pin ® (YH 1 ) through
Pin @ , Pin CD of IC91 9 (YHo), Pin @ of IC91 9, 091 60, T9040
and T9041 . I C91 9 is a broad band 1 H delay line driven at
1 4 M Hz. The clock signal is fed from Pin @) of IC91 6 to Pin
® of IC91 9. T9040 and T9041 are LPFs that eliminate clock
leakage and unnecessary high band component. After
being fed to Pin ® , the signal is passed through a clamping
circuit and is level adjusted by the voltage of Pin ® of
IC91 1 , and is then output from Pin ® .
Gamma Compensation
•
r
) circuit.
2-5. IC91 2 (Fig. 2-1 1 )
2-5-1 . Y Signal Processing
The YH signal is fed to Pin @ via DL for H aperture
correction (T9020, delay time t=approx. 83 nsec) at 1 kQ of
output impedance. Since DL is terminated at high im
pedance, a reflection wave is generated as shown in Fig.
2-1 2. and superimposed onto YH (Pin @ ) .
The signals at Pins @ and @ are differentially amplified
inside the IC and become the H aperture signal (HAP).
The HAP level is given by the voltage at Pin ® . The level is
suppressed by the increase in the AGC voltage at Pin
IC91 7 (CXA1 390AR) when AGC gain is high. After slicing
the low level component, the HAP signal is added to the Y
signal at Pin @ and the VAP signal at Pin @ .
Thus, the aperture-corrected Y signal is gain adjusted by
the voltage at Pin @ of IC91 1 (MSM6524GS), and the
attenuation level is determined by the FADE control voltage
simultaneously input to Pin @ .
The setup level is added to the Y signal, which then passes
through the white clip in order to limit high luminance, and is
then fed from Pin @ to the VTR as CAM .Y with the sync
signal added.
- 4-1 6 -
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of
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