JPH0328875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a video signal peaking method that emphasizes the horizontal detail display effect of a reproduced image, and more particularly, the present invention relates to a video signal peaking method that emphasizes the horizontal detail display effect of a reproduced image, and in particular, a peaking signal formed to be added to a signal to induce a desired detail emphasis effect. The present invention relates to a peaking method suitable for a television receiver capable of coring such that the coring level can be changed without substantially impairing the peaking effect of the television receiver.

Coring a signal (i.e., removing the average near-axis "core" of that signal by processing the signal with a translator that exhibits a transfer characteristic with a null region for near-axis signal swings)
For example, an article by J.P.Rossi published on pages 134-140 of SMPTE magazine published in March 1978, ``Digital technology to reduce television noise.''
Techniques for Reducing Television Noise)
is a well-known signal processing function often used for noise reduction purposes as described in . Depending on the use of the coring circuit, it may be desirable to be able to easily adjust the level of coring to be performed.
If this adjustment is easy (for example, McMann (RH
Mcmann et al.'s paper "Improved Signal Processing for Color Television Broadcasting"
Techniques for Color Television
It allows for manual adjustment of the coring level (as shown in ``Broadcasting''), and it also allows for manual adjustment of the coring level (as shown in ``Broadcasting''), and allows for manual adjustment of the coring level (as shown in U.S. Pat. No. 4,167,749). Dynamic adjustment of the coring level can also be performed (e.g., by varying it as a function of the coring level).

In television receivers, a horizontal peaking signal component can be formed and added to the received luminance signal to enhance details.
It is desirable to core the peaking signal components to reduce the possibility that desired image detail enhancement is accompanied by unwanted background noise enhancement.

U.S. Patent Application No. 373,750 (corresponding to U.S. Pat. No. 4,437,124) describes the depth of coring according to changes in the level of the low frequency content of the luminance signal to be peaked within the limits of white and black. A method for controlling the coring of the horizontal peaking component has been proposed to adjust for changes in the horizontal peaking component. The dynamic control orientation proposed in this U.S. application is driven by the observed phenomenon that low-level background noise is more distracting to the viewer in dark areas than in bright areas of the display screen. It is chosen such that the maximum and minimum coring takes place at the white end. Therefore, using this method to control the coring depth of peaking signal components provides the most protection from enhanced noise in areas of the screen where the noise enhancement is most obtrusive, and less protection in areas where higher noise levels are acceptable. Become.

An undesirable consequence of changing the level of coring of the horizontal peaking signal is that the magnitude of the cored signal, ie, the residual signal that remains after the core is removed, also changes. Therefore, for example, as the coring level increases, the peaking effect obtained by adding a reduced peaking component to the luminance signal may be unnecessarily reduced.

In an exemplary scheme for variable coring of a horizontal peaking signal, it is desirable for the coring level to range from 0 to 6% of the maximum peak-to-peak amplitude of the peaking signal. Adjusting the coring between the minimum and maximum levels introduces a small change in the residual amplitude of the highest amplitude peaking signal component, but always introduces a much larger change in the residual amplitude of other peaking signal components of low or medium amplitude. be introduced. Since these other peaking signal components significantly contribute to the overall image clarity effect provided by the peaking method, the coring level adjustment as described above may significantly impair the peaking effect obtained with the residual signal.

The present invention relates to a horizontal peaking scheme that uses coring of horizontal peaking signal components and allows the level of the coring to be varied without substantially impairing the realization of the desired peaking effect. In accordance with the principles of the invention, a variable cored peaking signal shaper is used to automatically adjust the amplitude changes in the residual signal associated with coring level changes without substantially impairing the realization of the desired peaking effect. Provides input to a responsive automatic peaking control scheme.

In an exemplary embodiment of the invention, a variable level of coring is applied to a horizontal peaking signal formed in response to a video signal representative of the brightness of an image before being applied to a gain controlled peaking signal translator. The output of the translator is combined with the luminance signal to form a peaked luminance signal. A peak detector generates a control voltage to control the gain of the peaking signal translator when a component of the peaked luminance signal falls within a selected frequency range. The orientation of this gain control is such that it is effected by changes in the amplitude of the component fed to the peak detector, and when there is a variation in the coring level, this causes the residual signal fed to the input of the peaking signal translator to be Amplitude changes that occur in the signal are substantially canceled by compensating for changes in the gain of the translator.

FIG. 1 shows part of a brightness channel of a color television receiver. At the input terminal I, a video signal representative of the brightness of the reproduced image is derived from the received composite color video signal by means of a suitable comb filter (see, for example, US Pat. No. 4,096,516).

The luminance signal at terminal I is applied to the input terminal of delay line 16 via a series circuit of blocking capacitor 14 and resistor 15. The value of resistor 15 is chosen so that the input end of delay line 16 is terminated with an impedance that substantially matches the characteristic impedance of the delay line. Luminance signal amplifier 17 corresponds to the delayed luminance signal produced at output terminal L' of delay line 16.

To form a horizontal peaking signal, delay line 1
Preferably, the output end of No. 6 is terminated to provide a reflective effect. Therefore, the signals generated at both ends of the delay line 16 are (1) the once-delayed luminance signal at terminal L', and (2) the sum of the undelayed luminance signal at terminal L and the twice-delayed luminance signal. For example, delay line 16 is a broadband device that exhibits a linear phase characteristic over the frequency band occupied by the luminance signal (eg, up to 4.0 MHz) and provides a signal delay of 140 ns.

The difference in the signals at terminals L and L' corresponds to a suitable horizontal peaking signal that is added to the luminance signal to enhance the details of the luminance signal by boosting the high frequency luminance component with a maximum boost occurring at about 3.5 MHz. This peaking signal subjected to variable coring is formed by a variable coring horizontal peaking signal generator 18 in response to inputs from terminals L and L'. The coring depth of the peaking signal generated by this signal shaper varies according to the coring level control voltage applied to the shaper 18 from the output terminal CC of the variable coring level control voltage source 25.

The variable cored horizontal peaking signal output of the signal former 18 is applied, for example, in a push-pull manner to a gain-controlled horizontal peaking signal translator 19. The magnitude of the horizontal peaking signal of the translator 19 changes depending on the gain control input to the terminal PC of the translator 19, which will be described below.

In response to the push-pull output of the luminance signal amplifier 17 and the push-pull output of the horizontal peaking signal translator 19, the signal combiner 20 forms a peaked luminance signal. The peaked luminance signal amplifier 21 generates a single-ended output at the peaked signal output terminal PL in response to the push-pull type peaked luminance signal generated by the signal combiner 20.

The peaked luminance signal produced at this terminal PL is applied to a bandpass amplifier 22 for automatic peaking control. This amplifier 22 exhibits a pass band of about 1 MHz centered around a frequency of about 2 MHz, for example, and supplies peaked luminance signal components within the pass band to a peak detector 23 . Detector 23 generates a control voltage proportional to the peak amplitude of the supplied component. This control voltage is applied to the gain control input terminal PC of translator 19 to control the magnitude of the horizontal peaking signal supplied to combiner 20 in a direction that counteracts changes in the magnitude of the component produced by amplifier 22. A more detailed explanation of the operation of such an automatic peaking control scheme and elements 17, 19, 20, 21,
An example of a convenient circuit that performs the functions of 22 and 23 (as well as manual peaking control) is shown on October 9, 1981.
Dated U.S. Patent Application No. 310139 (U.S. Patent No. 4399460)
(corresponding to the number) stated in the specification.

If only manual control of the coring level of the peaking signal input of the translator 19 is required, the variable coring level control voltage source 25 is simply connected between both fixed terminals with a suitable DC voltage source and the variable tap connected to the control terminal CC. may include a potentiometer connected to the Adjusting this tap changes the magnitude of the DC voltage applied to the control terminal CC, thereby changing the magnitude of the "core" of the signal that is removed by the signal shaper 18. Although a change occurs in the magnitude of the residual signal applied to the input of the translator 19, the peak detector 23, responsive to the applied peaked signal component, changes the gain control voltage applied to the terminal PC appropriately, A compensating gain change is introduced in the translator 19 so that the resulting peaking effect is not significantly affected.

If it is desired to dynamically control the coring level of the peaking signal in the manner proposed in U.S. Patent Application No. 373,750, the variable coring level control voltage source 25 may be
4437123) and is preferably in the form shown in FIG. 2 as described below.

In FIG. 2, the signal produced at terminal I (the luminance signal input terminal of the method of FIG. 1) includes a luminance signal whose polarity (blacker than black) deflection synchronization pulse component extends in the negative direction. The signal at terminal I is applied via a series circuit of a blocking capacitor 81 and a resistor 82 to an NPN transistor 83 for amplification. Capacitor 81 and resistor 82 are coupled in this order between terminal I and the base electrode of transistor 83. The emitter electrode of transistor 83 is directly grounded, and the collector electrode is connected to operating potential supply terminal +V _CC via load resistor 84 . Resistor 89 directly shunts the base-emitter path of transistor 83.

Feedback between the collector and base of the transistor 83 is provided by a pair of resistors 85 and 8 connected in series between them.
6, a capacitor 88 connected in shunt to this, and a capacitor 8 that grounds the connection point of series resistors 85 and 86.
This is done by a bridge T-type filter network formed by 7.

PNP transistor 9 that acts as a feedback clamp
0 directly connects the emitter electrode to the amplifying transistor 8
3, and the collector electrode is connected to a connection point between a connecting capacitor 81 and a resistor 82. A pair of resistors 91 and 93 are connected between the ground point and the +V _CC terminal to form a voltage divider, generate a reference DC potential at the connection point, and apply this directly to the base electrode of the transistor 90. .

The circuit described above forms an inverted signal translator for the input luminance signal that exhibits a low-pass frequency response characteristic and provides a signal delay suitable to substantially match the delay due to delay line 16. As an example of a circuit constant, the high frequency roll-off of the frequency response characteristic is gradual, and the cutoff frequency (3 dB on the characteristic curve)
It is desirable that the frequency (point) decreases at approximately 1.05MHz.

During operation of the circuit described above with respect to the voltage source 25, the capacitor 81 isolates the signal translator from any changes in the DC level occurring at the terminal I and thus from any fluctuations in the adjustment of the swing of the input signal, for example. DC restoration is provided by a clamp transistor 90 which is normally turned on periodically during the synchronization pulse. The changes on capacitor 81 are readjusted during this conduction period, thereby clamping the synchronized pulse peak of the translator output to a potential determined by (slightly off) the reference potential generated by voltage dividers 93,91. This reference potential is chosen such that the output potential of the translator (terminal CC) generated in response to the black level input leads to the required coring depth (for example 6%). Value of resistor 82 and resistor 8
The gain of the signal translator, determined by the ratio of the sum of the values 5 and 86, is chosen such that the required range of coring depth changes is obtained by the swing of the signal from black to white with respect to the translator output potential at terminal CC. . As an example, the gain is white level is 70-80IRE
Choose to reach the zero coring level when exceeding the unit.

In the circuit described above, a "soft" clamping effect is obtained by keying the clamp transistor 90 by the signal itself (i.e., without external keying). Although conduction of transistor 90 may be interrupted for a few lines due to some scene changes, such transients have been found to be tolerable, thus eliminating the need for complex and costly external keying. There is the convenience of avoiding adding more.

When using the circuit shown in FIG. 2, when the low frequency component of the luminance signal at terminal I changes, the level of coring performed by the peaking signal generator 18 shown in FIG. adjusted to. This adjustment of the coring level causes an unnecessary amplitude change in the residual signal applied to the input of the signal translator 19 of the type shown in FIG. Compensatory changes in gain substantially prevent the negative effects of this amplitude change.

The above-mentioned U.S. Patent Application No. 373,531 also includes
Details of circuitry useful in carrying out the functions of the variable cored horizontal peaking signal former 18 of the illustrated scheme are shown. In this circuit, the peaking signal former 18 includes a linear signal conversion channel and a nonlinear signal conversion channel, both of which, depending on the difference between the signals at both ends of the delay line 16, the linear signal conversion channel then forms a horizontal peaking signal. , a nonlinear signal conversion channel produces a twice-clipped version of that peaking signal. This coring of the peaking signal is performed by appropriately combining the outputs of both channels to erase the core portion of the horizontal peaking signal. The nonlinear signal conversion channel is in the form of a multistage limiting amplifier in which the gain distribution between the cascaded stages changes as the coring control amplifier changes. Each cascade of limiting amplifier stages includes a differential amplifier that draws its operating current from the collector electrode of each current source transistor, the base-emitter path of each current source transistor being connected in series to a common bias power supply. . The desired coring level control is achieved by varying a variable DC impedance shunt connected to the base-emitter path of one of the current source transistors, which adjusts the bias of the base-emitter junction. It consists of a collector-emitter circuit of a control transistor.
A second control transistor of opposite conductivity type to the first control transistor is shunt connected to a common bias power supply, the base of which is applied to the base of the first control transistor, to bring the lowest coring level to a zero value. It is designed to respond to the same coring level control inputs as the

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a part of the brightness channel of a color television receiver using the peaking method according to an embodiment of the present invention, and FIG. 2 shows the generation of coring level control voltage using the peaking method shown in FIG. FIG. 2 is a circuit diagram of a circuit that can be used for. 18... Variable cored horizontal peaking signal output forming means, 19... Gain control type peaking signal translator, 20... Signal combining means, 22
...Frequency selective amplifier, 23...gain control means,
25...Variable coring level control potential generation means.

Claims (1)

[Scope of Claims] 1. An image reproduction method including a signal source of a video signal representing the brightness of an image to be reproduced, which has a coring level control terminal and has a horizontal core that is variably cored according to the video signal. means for forming a peaking signal output such that the coring depth of the horizontal peaking signal output is dependent on a potential level developed at said control terminal; and generating a variable coring level control potential applied to said control terminal. a gain-controlled peaking signal translator responsive to the variably cored horizontal peaking signal output of the means for forming a horizontal peaking signal output; a frequency selective amplifier having an input responsive to the peaked luminance signal and exhibiting a passband encompassing a portion of the frequency band occupied by the video signal; The gain of the peaking signal translator is controlled in response to the amplitude of the output of the frequency selective amplifier to counteract changes in the amplitude so that variations in the coring level do not substantially disturb the peaking. A video signal peaking method including a feedback means for