Service manual

SERVICE MANUAL
TDA9178
YUV One Chip Picture Improvement Based on Luminance Vector-, Color Vector- and
Spectral Processor
1. Features
· Picture content dependent non-linear Y，U
and V processing by luminance histogram
analysis
· Variable gamma control
· Adaptive black and white stretch control
· Skin tone correction
· Green enhancement
· Blue stretch
· Luminance Transient Improvement (LTI)
· Smart peaking for detail enhancement
· Color Transient Improvement (CTI)
· Scan Velocity Modulation (SCAVEM) output
· Line Width Control (LWC)
· Video Dependent Coring (VDC)
· Color Dependent Sharpness (CDS)
· Noise measurement
· Feature Mode (FM) detector
· Cue Flash (CF) detector
· Three additional pins for access to 6-bit ADC
and I
2
C-bus
· Adjustable chrominance delay
· TV standard independent
· I
2
C-bus controlled
· 1f
H
and 2f
H
· Demonstration Mode (DEMO).
2. General Description
The TDA9178 is a transparent analog video
processor with YUV input and output
interfaces. It offers three main functions:
luminance vector processing， color vector
processing and spectral processing. Beside
these three main functions, there are some
additional functions.
In the luminance vector processor, the
luminance transfer function is controlled in a
non-linear way by the distribution, in 5 discrete
histogram sections, of the luminance values
measured in a picture. As a result, the contrast
ratio of the most important parts of the scene
will be improved. Black restoration is available
in the event of a set-up in the luminance
signal.
A variable gamma function, after the histogram
conversion, offers the possibilities of
alternative brightness control or factory
adjustment of the picture tube.
The adaptive black stretch function of the
TDA9178 offers the possibility of having a
larger ‘weight’ for the black parts of the video
signal, the white stretch function offers an
additional overall gain for increased light
production.
To maintain a proper color reproduction, the
saturation of the U- and V-colour difference
signals is also controlled as a function of the
actual non-linearity in the luminance channel.
In the color vector processor, the dynamic skin
tone correction locally changes the hue of
colors that match skin tones to the correct hue.
The green enhancement circuit activates
medium saturated green towards to more
saturated green. The blue stretch circuit can
be activated which shifts colors near white
towards blue.
The spectral processor provides 1D luminance
transient improvement, luminance detail
enhancement by smart peaking and a 1D color
transient improvement.
The TDA9178 can be used as a cost effective
alternative to (but also in combination with)
scan velocity modulation.
In the spectral processor line width control (or
aperture control) can be user defined. The
TDA9178 is capable of adjusting the amount
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