Philips tda9171 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

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

Philips Semiconductors Preliminary speciﬁcation

YUV picture improvement processor based

TDA9171

on histogram modiﬁcation and blue stretch

FEATURES

• Picture content dependent non-linear Y and U,V processing by luminance histogram analysis

• TV standard independent

• Incredible blue stretch

• Optional YC-processing.

GENERAL DESCRIPTION

The TDA9171 is a transparent analog video processor with YUV input and output interfaces.

The luminance transfer 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

QUICK REFERENCE DATA

SYMBOL PARAMETER MIN. TYP. MAX. UNIT

supply voltage 7.2 − 8.8 V

contrast ratio of the most important parts of the scene will be improved.

So as to maintain a proper colour reproduction the saturation of the −U and −V colour difference signals are also controlled as a function of the actual non-linearity in the luminance channel.

Optionally, the YUV blue stretch circuitry can be activated which offsets colours near white towards blue.

The supply voltage is 8 V. The device is contained in a 20 lead dual in-line package.

ORDERING INFORMATION

TYPE

NUMBER

TDA9171 DIP20 plastic dual in-line package; 20 leads; (300 mil); no heat spreader SOT146-1

NAME DESCRIPTION VERSION

PACKAGE

1996 Jun 17 2

Philips Semiconductors Preliminary speciﬁcation

YUV picture improvement processor based on histogram modiﬁcation and blue stretch

BLOCK DIAGRAM

book, full pagewidth

UIN

VIN

YIN

AMPLIFIER

TIMING

CONTROL

INPUT

AND

AMPSEL

TAUHM BLM BLG

TDA9171

HISTOGRAM

MEASUREMENT

9 10 11 12 13

SATURATION

COMPENSATION

NON-LINEAR

AMPLIFIER

HISTOGRAM

PROCESSOR

AMPLIFIER

20 1

BLUE

STRETCH

OUTPUT

AMPSEL

SUPPLY

AND

BIASING

16 15 17

TDA9171

UOUT

VOUT

YOUT

MBE990

HM1 to HM5

Fig.1 Block diagram.

NLC

ref

1996 Jun 17 3

Philips Semiconductors Preliminary speciﬁcation

YUV picture improvement processor based on histogram modiﬁcation and blue stretch

PINNING

SYMBOL PIN DESCRIPTION

BLG 1 blue stretch gain input UIN 2 U colour difference input −UIN VIN 3 V colour difference input −VIN NLC 4 non-linear gain control input SC 5 sandcastle input AMPSEL 6 amplitude select input YIN 7 luminance input TAUHM 8 time constant histogram input HM1 9 histogram segment memory 1 input HM2 10 histogram segment memory 2 input HM3 11 histogram segment memory 3 input HM4 12 histogram segment memory 4 input HM5 13 histogram segment memory 5 input YOUT 14 luminance output V

ref

VOUT 18 colour difference output −VOUT UOUT 19 colour difference output −UOUT BLM 20 activation level blue stretch input

15 ground 16 supply voltage 17 reference voltage output

handbook, halfpage

AMPSEL

BLG

UIN

VIN

NLC

YIN

TAUHM

HM1 HM2

6 7 8 9

TDA9171

MBE989

Fig.2 Pin configuration.

TDA9171

BLM

UOUT

VOUT V

ref

YOUT

HM5

HM4

HM3

FUNCTIONAL DESCRIPTION Input selection and ampliﬁcation

The dynamic range of the luminance input amplifier is

0.3 or 1 V (excluding sync) typically, depending on the

logic level at pin AMPSEL (pin 6). Amplitudes which extend the corresponding specified range will be clipped smoothly, however, the sync is processed to the output transparently. The non-linear gain setting will have minimum effect.

Optionally, in the 1 V input mode, the Y output can be attenuated by a factor of 0.7 by means of an intermediate level at pin AMPSEL. This option is meant for correctly interfacing the combed CVBS signal to the video processor in a YC-application.

The input is clamped during the logic HIGH period of the CLP, defined by the sandcastle reference, and should be DC-decoupled with an external capacitor.

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Histogram measurement

For the luminance signal the histogram distribution is measured in real-time over five segments (HM1 to HM5) in each field. During the period that the luminance is in one segment, a corresponding external capacitor HMx is loaded via a current source. At the end of the field five segment voltages are stored from the external capacitors into on-board memories. The external capacitors are discharged and the measurements are repeated.

Parts in the scene that do not contribute to the information in that scene should be omitted from the histogram measurement. No measurements are performed during the blanking period defined by the sandcastle.

The miscount detector disables measurements until it detects changing parts. Additionally, luminance values close to full scale (or white) do not contribute as well in order to maintain the absolute light output. This procedure is allowed because the eye is less sensitive to detail in white.

Philips Semiconductors Preliminary speciﬁcation

YUV picture improvement processor based on histogram modiﬁcation and blue stretch

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.

DAPTIVE WHITE-POINT STRETCHING

A 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.

TANDARD DEVIATION

S 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).

TDA9171

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.

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