Philips 7629, Service Manual

Page: 68 / 374

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Black stretch This function corrects the black level of incoming signals, which
have a difference between the black level and the blanking level. The amount of
extension depends upon the difference between actual black level and the
darkest part of the incoming video signal level. It is detected by means of an
internal capacitor.
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White stretch This function adapts the transfer characteristic of the luminance
amplifier in a non-linear way depending on the average picture content of the
luminance signal. It operates in such a way that maximum stretching is obtained
when signals with a low video level are received. For bright pictures, stretching is
not active.
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Dynamic skin tone correction This circuit corrects (instantaneously and locally)
the hue of those colors which are located in the area in the UV plane that
matches the skin tone. The correction is dependent on the luminance, saturation
and distance to the preferred axis.
The YUV signal is then fed to the color matrix circuit, which converts it to R, G and B
signals.
The OSD/TXT signal from the microprocessor is mixed with the main signal at this point,
before being output to the CRT board (pins 56, 57 and 58).
Picture in picture (if present)
The PIP controller M65669FP is an NTSC video processor for TV applications. It
contains all of the analog signal processing, control logic and memory, necessary to
provide sub-picture insertion from a second, non-synchronized, video source into the
main picture of the TV. This can be an external source (via the rear I/O inputs) or the
video signal of the tuner.
Sync signals are derived from the sandcastle signal and separated by circuit 7171-7174
on the PIP-interface, and then fed to pins32 and 33 of the PIP processor 7803.