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PDF TDA9171 Data sheet ( Hoja de datos )
| Número de pieza | TDA9171 | |
| Descripción | YUV picture improvement processor based on histogram modification and blue stretch | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TDA9171
YUV picture improvement
processor based on histogram
modification and blue stretch
Preliminary specification
Supersedes data of 1995 Aug 01
File under Integrated Circuits, IC02
1996 Jun 17
1 page  
Philips Semiconductors
YUV picture improvement processor based
on histogram modification and blue stretch
Preliminary specification
TDA9171
As the miscount detector shortens the effective
measurement period and, because of spreads of internal
and external components, the current source is controlled
in a closed-loop to provide a constant value of the sum of
the segment voltages. The dominant time constant of the
closed-loop is external and can be tuned with an
appropriate capacitor value at pin TAUHM (pin 8).
Processing of the measured histogram value
FIELD AVERAGING OF HISTOGRAM VALUES
With very rapid picture changes, also related to the field
interlace, flicker might result. The histogram values are
averaged at the field rate thus reducing the flicker effects.
The time constant of the averaging process is adapted to
the speed of the histogram changes.
ADAPTIVE WHITE-POINT STRETCHING
For dominant HM4 and HM5 voltages, or large white parts,
the histogram conversion procedure makes a transfer with
large gain in the white parts, however the amount of light
coming out of the scene is considerably reduced. The
white stretcher introduces additional overall gain for
increased light production and, as a result, violates the
principle of having a full scale reference.
STANDARD DEVIATION
For scenes, in which segments of the histogram
distribution are very dominant with respect to the others,
the non-linear amplification should be reduced in
comparison to scenes with a flat histogram distribution.
The standard deviation detector measures the spread of
the histogram distribution in the segments HM1 to HM5
and modulates the user setting of the non-linear amplifier.
Non-linear amplifier
The stored segment voltages relative to their average
value, averaged over two fields, determine the individual
gain of each segment in such a way that continuity is
guaranteed for the complete range. The maximum and
minimum gain of each segment is limited. Apart from the
adaptive white-point stretching the black and white
references are not affected by the non-linear processing.
The amount of linearity can be controlled externally by the
NLC pin (Non Linearity Control).
Colour compensation
Non-linear luminance processing influences the colour
reproduction, mainly the colour saturation. Therefore, the
U and V signals are also processed for saturation
compensation.
By convention −U and −V signals must be supplied to the
TDA9171. The −U and −V input signals are clamped
during the logic HIGH period of CLP, defined by the
sandcastle reference. In YC-applications just one colour
difference channel is required for processing the chroma
signal. However, external decoupling capacitors should be
applied to both inputs UIN and VIN. The external coupling
capacitor value should be such that the burst period of the
chroma signal is very softly clamped.
The processing is dependent on the amplitude and sign of
the colour difference signals whenever the blue stretch
circuitry is activated. Therefore, both the polarity and the
nominal amplitude of the colour difference signals are
relevant when using the blue stretch facility.
Blue stretch
The blue stretch circuit is intended to shift colours near
white, with sufficient contrast values, towards more blue
coloured white to give a brighter impression. The
chromaticity shift is proportional to the excess of the
contrast value of a white video signal with respect to a user
adjustable minimum level, defined by a voltage at
pin BLM. In this way blue shift in, for instance, human
faces can be prevented. The global amount of blue shift is
defined by the voltage level at pin BLG. The direction of
shift in the colour triangle is fixed by hardware.
It should be noted that the colour shift is different with a
wrong polarity of the colour difference signals. The
preferred BLG and BLM settings will be related to the
actual nominal amplitudes of the colour difference signals.
The blue stretch facility must be disabled in
YC-applications by setting both BLG and BLM to ground.
1996 Jun 17
5
5 Page 
Philips Semiconductors
YUV picture improvement processor based
on histogram modification and blue stretch
Preliminary specification
TDA9171
100
handbook, halfpage
QTHMS
(%)
80
MBE995
60
40
20
0
0 4 8 12 16 20
Weff = tnonblanking_of_SC x Rmiscount(ms)
Rmiscount = ratio of effective histogram measuring time and active video in one field
defined by the non-blanking periods of the sandcastle signal in one field.
Fig.4 Static error on average histogram amplitude (pin TAUHM) as a function of effective histogram
measuring time in a field (CHMx = 10 nF).
1
handbook, halfpage
GNLC
0.75
MBE996
0.5
0.25
0
1.25
2.25
3.25
4.25
5.25
ViNLC (V)
1996 Jun 17
Fig.5 Non-linear amplifier gain as a function of input voltage at pin NLC.
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet TDA9171.PDF ] | |
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