Daewoo DTR-14D3VG, Service Manual

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41
RGB processing and control
This paragraph can be divided into :
- YUV/RGB processing
- RGB-control
(1) YUV/RGB processing
• The main functions are :
- Y-signal processing/black stretcher
- (B-Y)/(R-Y) signal processing/matrixing
- Dynamic skin tone correction
- Second RGB insertion
• Y-signal processing/black stretcher
Internally the luminance signal is clamped and supplied to the RGB matrix circuit (via black stretcher).
The black stretcher circuit, which is only operational during line scan, extends the grey signal level towards the act 1
black level (i,e,actual black level is measured during burstkey). The amount of extension is dependent upon the
difference between actual black level and the darkest part of the incoming video signal; it is thus dependent upon
the IRE value of the video signal.
The darkest part of the video signal is registered on an internal-capacitor by means of an internal discharge current
of approximately 130mA.
For black stretcher input/output characteristics, refer to device specification.
The black stretcher can be switched on/off via the I 2 C bus (BKS). The black stretcher is fully integrated this means
that the black stretcher time constant is fixed.
• (B-Y)/(R-Y) Signal processing/matrixing
The (B-Y)/(R-Y) signals are clamped during the burstkey period. The saturation of the (B-Y)/(R-Y) signals is
controlled via the I
2 C bus(SAT). The control range is minimal 52dB with a 6dB (minimum) reserve above nominal;
refer also to device specification. The (B-Y)/(R-Y) signals are supplied to dynamic skin control function
The selected matrix is controlled via the I2C bus(MAT).
In the I 2 C bus description can be seen which matrix can be selected for the several TDA884X types. After the R-Y,
B-Y martixing, the output-signals are added with the luminance signal in order to generate the internal RGB signals
• Dynamic Skin Tone Correction
The Dynamic Skin Tone Correction (DSTC) circuit corrects the hue of those colours which are located in the UV-
plane area that matches to skin tones. Correction takes place by shifting those colours towards the preferred skin
tone axis. The amount of correction is dependent on the luminance, saturation and distance to preferred skin tone
axis. Therefore it’s hard to give an exact figure about the amount of correction. The DSTC can be switched on by the
I2C-bit DS(Dynamic Skin), also it is possible to switch between two skin tone correction angles by the DSA bit. If it
set to “0” the correction angle is 117 degrees;
If it is “1” the correction angle 123 degrees. There are two angles because depending on which part of the world
there is a preferred skin tone. For example the 117 degrees angel can be the preferred skin tone in Asia where as in
the USA 123 degrees may be preferred.