JPS63242089A - Vertical contour correction circuit - Google Patents

Abstract

PURPOSE:To prevent glittering on the screen by integrating a vertical contour signal so as to obtain a vertical profile component output picture in the screen and controlling the gain in a variable gain amplifier circuit in response to the value, suppressing the correction as the vertical contour component output picture is more in the pattern. CONSTITUTION:When a switching diode 183 is reset, the correction quantity voltage (that is, a DC voltage) outputted to a variable amplifier circuit 13 is divided an output of a variable DC power supply 14 and outputted to an emitter follower by a transistor 184. In varying the output voltage of the variable DC power supply 14 by using an external adjustment knob, the gain in the variable gain amplifier circuit 13 is changed and the amplitude of the vertical profile signal (j) is changed to control the correction of the vertical contour correction. Moreover, the correction control circuit 18 suppresses the correction as the vertical contour component output picture is more in the pattern. Thus, the flittered pattern is prevented and natural vertical contour correction is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a contour correction circuit for improving image quality in color television receivers, color display devices, etc. This invention relates to a vertical contour correction circuit that can perform vertical contour correction and change the amount of correction.

[Conventional technology]

In general, vertical contour correction means that when looking at changes in the luminance signal in the vertical direction of the screen, overshoots or undershoots occur in the rising or falling portions (i.e., the contours of the image) where the changes are abrupt. This is to emphasize the change and make corrections to make the edges look sharper. In particular, the method that adds both overshoot and undershoot is called second-order differential vertical contour correction.

In addition, addition of overshoot and undershoot,
This is usually done by adding a vertical contour signal extracted from the video signal to a luminance signal also obtained from the video signal.

Now, in the conventional vertical contour correction circuit, for example,
As described in Japanese Patent No. 6-85986, an IH delay line having a delay time of one horizontal period (hereinafter referred to as IH) is
A second-order differential type vertical contour correction was performed by using the two.

The amount of correction can be changed by changing the amplitude of the vertical contour signal using a variable gain amplifier circuit.

However, with this vertical contour correction circuit, expensive IH
Since two delay lines are used as described above, there is a problem in that the cost is high.

Therefore, as a quadratic differential vertical contour correction circuit that uses only one such expensive IH delay line, a cyclic vertical contour correction circuit such as the one discussed in Toshiba Review Vol. 40, No. 2 has been proposed. has been done.

However, in this cyclic vertical contour correction circuit, the amplitude of the extracted vertical contour signal is different between the amplitude of the part added as an overshoot and the amplitude of the part added as an undershoot. Even if vertical contour correction is performed by adding the signal to the luminance signal, the result will be an unbalanced vertical contour correction (i.e., as a result of the correction, the addition of the signal to the rising or falling portion of the luminance signal will result in an unbalanced vertical contour correction). (This results in an unbalanced state of overshoot and undershoot.) When viewed, the problem is that the image looks unnatural. Also, such a rising part,
Changing the correction amount in a well-balanced manner for both the falling portion was not difficult due to the circuit configuration.

Furthermore, it has not been considered to automatically control the amount of correction depending on the image content.

[Problem that the invention seeks to solve]

As mentioned above, conventional cyclic vertical contour correction circuits cannot perform well-balanced vertical contour correction, resulting in images that look unnatural or unbalanced (the amount of correction cannot be changed). there were.

The purpose of the present invention is to solve the problems of the prior art described above,
Even if correction is performed using cyclic vertical contour correction, there may be a good balance between overshoot and undershoot added to the rising or falling portions of the luminance signal, while maintaining that balance. An object of the present invention is to provide a vertical contour correction circuit that can change the amount of correction.

[Means for solving problems]

In order to achieve the above object, the present invention inputs an unbalanced vertical contour signal obtained in a cyclic vertical contour correction circuit, and the level widths from the average level in the signal are approximately equal to each other. A first level that is higher than the average level and a second level that is lower than the average level are respectively set, and a portion of the signal that is higher than the average level is set to the first level, and a portion that is lower than the average level is set to the second level. A waveform shaping circuit that shapes the waveform so that it becomes a well-balanced vertical contour signal and outputs it, and a variable gain amplification circuit whose gain can be changed that amplifies the vertical contour signal from the waveform shaping circuit are provided. did.

[Effect]

In the present invention, by inputting the unbalanced vertical contour signal obtained in the cyclic vertical contour correction circuit to the waveform shaping circuit, the amplitude of the portion added as an undershoot and the amplitude of the portion added as an overshoot are adjusted. The amplitudes are approximately the same, and a well-balanced vertical contour signal can be obtained. Note that the waveform shaping method in the waveform shaping circuit includes, for example, a method of slicing the input signal at a predetermined level and shaping the waveform, or a method of compressing the amplitude of the input signal and shaping the waveform. etc. are possible.

Further, by inputting the well-balanced vertical contour signal obtained from the waveform shaping circuit to the variable gain amplifier circuit, it can be amplified while maintaining its balance, and its gain can be varied.

Therefore, by performing vertical contour correction by adding this amplified vertical contour signal to the luminance signal delayed by the IH period, undershoot is added to the rising or falling portion of the luminance signal. The balance between overshoot and overshoot is good, and the amount of correction can be changed while maintaining that balance.

(Example〕 An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing one embodiment of the present invention. That is, the circuit shown in FIG. 1 is a vertical contour correction circuit that performs cyclic vertical contour correction and also performs yc (luminance signal/chrominance signal) separation.

In Figure 1, 1 is an input terminal, 2.8.10 is an inverting buffer 1.3.6.9.17 is an adder, and 4 is an input terminal for input signals.
IH consisting of a CCD (charge-coupled device) that delays the H period
Delay line, 5 is a low-pass filter (LPF) for adjusting the delay time of the CCD constituting the IH delay line 4 and removing clock noise, 7 is a band-pass filter (BPF) for color signal extraction, 11 12 is a waveform shaping circuit; 13 is a variable gain amplifier circuit whose gain can be controlled by input DC voltage; 14 is a variable DC voltage source; 18 is a correction amount control It is a circuit.

Next, the operation of this circuit will be explained using FIG. 2.

FIG. 2 is a waveform diagram showing the waveforms of the main signals in FIG. 1.

In FIG. 2, signals a to k in FIG.
(However, i is not shown in FIG. 1). Note that the horizontal axis represents time, and represents approximately one vertical period. That is, the horizontal axis may be considered as the distance in the vertical direction of the screen.

Consider a case where a composite video signal as shown in FIG. 2a is input to the input terminal 1 shown in FIG. 1. This composite video signal a
is inverted by an inverting buffer 2 and input to an adder 3. At this time, the feedback signal C obtained from the latter stage of the circuit is also input to the adder 3, and therefore, these two signals are added together. Then, this added signal passes through an IH delay line 4 and a low-pass filter 5, and becomes an IH-delayed signal like signal d.

Next, this signal d is inverted by an inverting buffer 8 and added to the previous signal a by an adder 9. The output g of this adder 9 corresponds to the Y separation ratio in YC separation.

On the other hand, when the signal d and the previous signal a are added together by the adder 6, a vertical contour signal such as the signal e is obtained. This vertical contour signal e corresponds to a C separation output in yc separation, and becomes a C signal (color signal) through a bandpass filter 7. Also, this vertical contour signal e is transmitted to the inversion buffer 1.
o is inverted and fed back as a feedback signal C to the adder 3 mentioned earlier.

Further, the output C from the inversion buffer 10 is converted into a vertical contour signal after high-frequency components are removed by a low-pass filter 11. Here, the level of this vertical contour signal has the same amplitude as the amplitude A in the previous signal g. Therefore, when this signal 1 and the signal g are added in the adder 17, a luminance signal, such as the signal i, which has almost the same waveform as the IH-delayed original signal a is obtained.

Now, when performing vertical contour correction, the vertical contour signal is again added to this luminance signal i, but as is clear from Fig. 2, the vertical contour signal is
The part corresponding to the rise and the part corresponding to the fall are not symmetrical, and furthermore, the part that should be an undershoot and the part that should be an overshoot are not balanced ( That is, the amplitude A
and amplitude B do not match. , ), so there is a problem in adding them as is.

Therefore, in this embodiment, this unbalanced vertical contour signal is first input to the waveform shaping circuit 12.

3 is a circuit diagram showing a specific circuit example of the waveform shaping circuit in FIG. 1, and FIG. 4 is a waveform diagram showing waveforms of input signals and output signals of the waveform shaping circuit in FIG. 3.

In FIG. 3, 121 is a buffer transistor;
2 is a clamp capacitor, 123 is a clamp transistor, 124 is a clamp voltage source, 125 is a buffer transistor, and 126 and 127 are slicing diodes.

First, an unbalanced vertical contour signal as shown in FIG. 4 is input to the buffer transistor 121 as shown in FIG. 3, and clamped in synchronization with the voltage of the clamp voltage source 124 by the clamp transistor 123. The clamped waveform passes through the buffer transistor 125 and is sliced up and down by the next slicing diodes 126 and 127. Here, by slicing along the dotted line shown in FIG. 4, a well-balanced vertical contour signal such as signal j° can be obtained.

In this way, the waveform shaping circuit 12 inputs an unbalanced vertical contour signal such as the signal j, performs waveform shaping by slicing it at a predetermined level, and generates a luminance signal such as the signal j''. A waveform is output in which the portion corresponding to the rising edge of i and the portion corresponding to the falling edge of i are symmetrical, and the portions that should cause overshoot and undershoot are well-balanced.

In this embodiment, a slicer circuit is used as the waveform shaping circuit 12 to slice the unbalanced vertical contour signal at a predetermined level, thereby obtaining a well-balanced vertical contour signal j''. Alternatively, a well-balanced vertical contour signal j' may be obtained by compressing the amplitude of an unbalanced vertical contour signal to a predetermined level using an amplitude compression circuit or the like.

Next, this well-balanced vertical contour signal j° is input to the variable gain amplification circuit 13. In this variable gain amplifier circuit 13, this input balanced vertical contour signal j°
is amplified while maintaining its balance, and is output as a vertical contour signal j. At this time,
The gain of this variable gain amplifier circuit 13 is determined by the correction amount control circuit 1
It is controlled by DC voltage from 8.

Next, this amplified vertical contour signal j is input to an adder 17. In the adder 17, as mentioned above, the luminance signal i is obtained by adding the signal ri and the signal g, and the input vertical contour signal j is added to this luminance signal i, and the vertical contour signal j is added to the signal as shown in FIG. A contour-corrected luminance signal is obtained. That is, it is possible to obtain a contour correction waveform in which the rising portion and the falling portion are substantially symmetrical, and the undershoot and overshoot are well balanced.

Next, the correction amount control circuit 18 shown in FIG. 1 will be explained.

FIG. 5 is a circuit diagram showing a specific circuit example of the correction amount control circuit in FIG. 1, and FIG. 6 is a graph showing the relationship between the vertical contour component output amount and the correction amount in the correction amount control circuit in FIG. 5. It is.

In FIG. 5, 180 is an integrating circuit, 181 and 182 are transistors, 183 is a switching diode, and 18
4 is a transistor.

First, the vertical contour signal from the low-pass filter 11 is input to the correction amount control circuit 18 .

This vertical contour signal is transmitted to the integrator circuit 1 as shown in FIG.
80, and is inverted and amplified by transistor 181, the output of which is passed through transistor 182''.
It passes through the emitter follower circuit of and reaches the switching diode 183. As a result, the emitter voltage of the transistor 182 changes depending on the amount of the vertical contour signal, that is, the amount of the vertical contour component in the screen.

Here, when the switching diode 183 is in the OFF state, the correction amount voltage (i.e., DC voltage) output to the variable gain amplifier circuit 13 is obtained by dividing the output voltage of the variable DC voltage source 14 and dividing the output voltage from the emitter by the transistor 184. This is the value output by the follower. Therefore, by changing the output voltage of the variable DC power supply 14 using an external adjustment knob or the like, the gain in the -1° variable gain amplifier circuit 13 changes, the amplitude of the vertical contour signal j changes, and the vertical contour correction The amount of correction can be controlled.

On the other hand, if the emitter voltage of transistor 182 is lower than the emitter voltage of transistor 184, that is,
When the output amount of the vertical contour component is large, the switching diode 183 is turned on, and the variable gain amplifier circuit 1
It works so that the value of the DC voltage to 3 decreases. As a result, the gain in the variable gain amplifier circuit 13 decreases, and the amplitude of the vertical contour signal j that is its output decreases, so that the amount of correction to the contour-corrected luminance signal decreases. That is,
In this correction amount control circuit 18, as shown in FIG.
．． The correction amount for the vertical contour component image output amount is controlled.

As described above, according to this embodiment, as shown in FIG. 2k, the rising and falling portions of the luminance signal are almost symmetrical, which improves the balance between undershoot and overshading. Vertical contour correction can be performed. Moreover, it is also possible to continuously change the correction amount while maintaining such a balanced state.

Furthermore, the correction amount control circuit 18 suppresses the correction amount as the amount of vertical contour components in the screen increases, so that the screen can be prevented from becoming glaring, and more natural vertical contour correction can always be performed.

Note that when actually using the circuit shown in Figure 1, a delay circuit is required to adjust the time of the waveform.
It is omitted in the circuit shown in the figure.

Next, other embodiments of the present invention will be described.

FIG. 7 is a block diagram showing another embodiment of the present invention.

In the embodiment shown in FIG. 1, only vertical contour correction was performed alone, but in this embodiment, vertical contour correction is performed together with horizontal contour correction.

That is, in this embodiment, with regard to correction amount control, not only vertical contour correction but also horizontal contour correction are combined and collectively controlled.

In FIG. 7, 100 is a horizontal contour extraction circuit, 200 is a variable gain amplification circuit, 300 is a vertical contour extraction circuit, and 400 is a vertical contour extraction circuit.
is an output terminal, 17° is an adder, and 18° is a correction amount control circuit.

First, a composite video signal is input from the input terminal 1 to the horizontal contour extraction circuit 100 and the vertical contour extraction circuit 300.

The horizontal contour extraction circuit 100 extracts a horizontal contour signal, and the signal is input to the horizontal variable gain amplification circuit 200, amplified, and output to the adder 17°.

Further, the signal that has passed through the IH delay line 4 in the vertical contour extraction circuit 300 is outputted to the adder 17' as a source signal.

Further, the well-balanced vertical contour signal extracted by the vertical contour extraction circuit 300 is input to the vertical variable gain amplification circuit 13, amplified, and output to the adder 17''.

The adder 17' adds the original signal, the vertical contour signal, and the horizontal contour signal and outputs the resultant signal to the output terminal 400 as an output signal.

On the other hand, the horizontal contour signal from the horizontal contour extraction circuit 100,
The well-balanced vertical contour signals from the vertical contour extraction circuit 300 are respectively input to the correction amount control circuit 18'.

This correction amount control circuit 18' controls the horizontal and vertical contour correction amounts so that they can be changed simultaneously and to the same extent using one external adjustment knob of the variable DC voltage source 14.

In addition, this correction amount control circuit 18'' controls to change each correction amount as shown in FIG. 8, depending on the horizontal and vertical contour components of the input composite video signal. .

FIG. 8 is an explanatory diagram for explaining the control operation of the correction amount control circuit in FIG. 7.

Now, FIG. 8 will be explained.

When both the horizontal and vertical contour component output amounts are small, the correction amount remains unchanged as determined by the external adjustment knob of the variable DC voltage source 14. Then, when the horizontal contour component image output amount is large, the horizontal contour correction amount is decreased, and when the vertical contour component image output amount is large, the correction amount is controlled so that the vertical contour correction amount is decreased. .

Therefore, horizontal for any video signal.

Contour enhancement (contour correction) to the same degree both vertically and vertically can be automatically controlled, and more natural contour enhancement can always be performed.

〔Effect of the invention〕

According to the present invention, by simply adding a waveform shaping circuit and a variable gain amplification circuit to a conventional cyclic vertical contour correction circuit, undershoot and overshoot added to the rising or falling portion of the luminance signal change portion can be improved. In addition, the amount of correction can be changed while maintaining the balance.

Furthermore, if the vertical contour component output amount in the screen is determined by integrating the vertical contour signal and the gain in the variable gain amplifier circuit is controlled according to the value, the vertical contour component output amount in the screen is The larger the number, the more the correction amount is suppressed, which has the effect of preventing screen glare and always performing more natural contour correction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the waveforms of the main signals in FIG. 1, and FIG. 4 is a waveform diagram showing the waveforms of the input signal and output signal in FIG. 3, FIG. 5 is a circuit diagram showing a specific circuit example of the correction amount control circuit in FIG. 1, and FIG. A graph showing the relationship between the vertical contour component output amount and the correction amount in FIG.
FIG. 7 is a block diagram showing another embodiment of the present invention, and FIG. 8 is an explanatory diagram for explaining the control operation of the correction amount control circuit in FIG. Explanation of symbols 4... IH delay line, 12... Waveform shaping circuit, 13... Variable gain amplifier circuit, 18...
...Correction amount control circuit agent Patent attorney Akio Namiki @ 2 Figure 113 Figure 4 Figure 15 Figure 6 Figure @ 7 Figure 1Ea Figure

Claims (1)

[Claims] 1. A first inversion buffer that inverts an input composite video signal, a first addition circuit that adds and outputs the output from the first inversion buffer and a feedback signal, and 1st
a delay line that delays the output from the adder circuit by one horizontal period in the composite video signal; a second inversion buffer that inverts the output from the delay line; and an output from the second inversion buffer. a second addition circuit that adds and outputs the composite video signal; a third addition circuit that adds and outputs the output from the delay line and the composite video signal; and an output from the third addition circuit. a bandpass filter that inputs, limits the band and outputs a color signal, and a third inverter that inverts and outputs the output from the third adder circuit and inputs it as the feedback signal to the first adder circuit. buffer and
a low-pass filter that inputs the output from the third inverting buffer and removes its high-frequency components; and a low-pass filter that adds the output from the low-pass filter and the output from the second adder circuit to output a luminance signal. a first level higher than the average level and a first level lower than the average level, which input the output from the low-pass filter and whose level widths from the average level in the output are substantially equal to each other; a second level, and a portion of the output higher than the average level is set to the first level;
a waveform shaping circuit that performs waveform shaping so that the lower portion is at the second level and outputs it as a vertical contour signal; a variable gain amplifier circuit that can change the gain that amplifies the vertical contour signal from the waveform shaping circuit; and adding the amplified vertical contour signal to the luminance signal in the fourth addition circuit to perform vertical contour correction, and correcting the vertical contour correction by changing the gain of the variable gain amplifier circuit. A vertical contour correction circuit characterized in that the amount can be changed. 2. In the vertical contour correction circuit according to claim 1, the output from the low-pass filter is input, the output amount of the vertical contour component in the screen is determined, and the variable gain amplification is performed according to the value. A vertical contour correction circuit comprising a correction amount control circuit that controls the gain of the circuit.