JPH06253179A - Contour correction circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] The sharpness of a video signal can be improved without causing deterioration of image quality. [Configuration] The maximum value circuit 12 or the minimum value circuit 13 always outputs the higher or lower level of the two signals h and i to obtain the maximum value output j or the minimum value output k. The subtraction circuits 4 and 5 and the addition circuit 6 extract and add the conventional delay line aperture control type preshoot and overshoot from the video signal to obtain the switching control signal f. The switching of the switching circuit 14 is controlled by the switching control signal f, and the maximum value output j and the minimum value output k
Is selectively output. The variable gain amplifier circuit 7 amplitude-adjusts the output signal of the switching circuit 14 to obtain the contour compensation signal 1. The adder circuit 8 adds the contour compensation signal 1 and the delayed video signal b to obtain a composite video signal m.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit for a television receiver or the like, and more particularly, to improving the sharpness of the video signal (that is, to make the contour portion of the image displayed by the video signal stand out). ), Which is suitable for the contour correction circuit.

[0002]

2. Description of the Related Art Conventionally, as a contour correction circuit, a delay line aperture control type is generally used. As a contour line correction circuit of a delay line aperture control type in the prior art, for example, "TV Technology October 1989" is used. Page 21 of the special edition Television Technical Book (Electronic Technology Publishing Co., Ltd.), "Principle of delay line aperture control", or page 82, "Double D
L-shaped contour correction method ".

FIG. 9 shows the circuit configuration of such a conventional contour correction circuit, and FIG. 10 shows the signal waveform of each part in the circuit of FIG.

In FIG. 9, 1 is an input terminal, 2 and 3 are delay lines having a delay time τ, 4 and 5 are subtraction circuits, 6 is an addition circuit, 7 is a variable gain amplification circuit, 8 is an addition circuit, and 9 is an addition circuit. Is an output terminal. The sign of each signal in FIG. 9 corresponds to the sign of the waveform in FIG.

The circuit operation of FIG. 9 will be described below with reference to FIG. Video signal a input from input terminal 1
Becomes a video signal b via the delay line 2 and further becomes a video signal c via the delay line 3.

Then, in the subtraction circuit 4, the video signals a, b
The preshoot signal d is obtained from the
An overshoot signal e is obtained from the video signals b and c. Further, the adder circuit 6 adds the preshoot signal d and the overshoot signal e and the amplitude is adjusted by the variable gain amplifier 7 to obtain the contour compensation signal f.

Next, in the adder circuit 8, the contour compensation signal f
Is added to the video signal b to obtain a composite video signal g, which is output from the output terminal 9. As described above, the preshoot signal and the overshoot signal are added before and after the changing portion of the video signal to improve the sharpness.

FIG. 11 shows the frequency characteristic of the contour compensation signal f, and the peak frequency f _{0 at} this time can be expressed by f ₀ = 1 / (2τ) [Hz].

[0009]

However, the above-mentioned conventional contour correction circuit has the following problems.

That is, as shown in FIG. 10, the temporal width β of the preshoot and overshoot portions of the contour compensation signal f
Is wider than the temporal width α of the contour portion of the video signal b,
When the contour compensation signal f is added to the video signal b in the adder circuit 8, a thick shoot signal is attached to the composite video signal g, and further, in order to improve the sharpness of the video signal,
If the addition amount of the contour compensation signal f is increased (that is, the amplitude of the contour compensation signal f is increased and then added), the shoot signal attached to the composite video signal g becomes noticeable and the image quality is significantly deteriorated. There was a problem.

Also, by shortening the delay time of the delay lines 2 and 3, the shoot signal attached to the composite video signal g can be made thin to some extent, but the signal band of the video signal is limited and its outline is limited. Since the frequency component of the part does not have a signal component above a certain value, no matter how short the delay time of the delay lines 2 and 3, the shoot signal attached to the composite video signal g does not become thinner than a certain value. Moreover, even if it becomes the thinnest, the composite video signal g
The temporal width γ of the changing portion (equal to the temporal width β of the preshoot and overshoot portion of the contour compensation signal f) does not become narrower than the temporal width α of the contour portion of the video signal b.

Moreover, in this way, the delay lines 2, 3
If the shoot signal attached to the composite video signal g is made thin by shortening the delay time of, the amplitude level of the shoot signal also generally becomes small. Therefore, it is necessary to increase the addition amount of the contour compensation signal f. In this case, the S / N deterioration becomes a problem rather than the improvement of the sharpness of the contour portion of the video signal, resulting in a significant deterioration of the image quality.

As described above, the conventional contour correction circuit has a problem that if the sharpness of the video signal is improved, the image quality is significantly deteriorated.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a contour correction circuit capable of improving the sharpness of a video signal without causing deterioration of image quality. .

[0015]

In order to achieve the above-mentioned object, in the present invention, a contour extraction circuit extracts a first high frequency component having two different polarities from an input video signal. Means, first selecting means for selecting a maximum amplitude value from the two extracted first high-frequency components, and second selection means for selecting a minimum amplitude value from the two extracted first high-frequency components Selection means, second extraction means for extracting two second high-frequency components having different polarities from the video signal, and the two extracted second high-frequency components are added and output as a control signal. A first adding means, a switching means for selectively switching the selected maximum amplitude value and minimum amplitude value according to the control signal and outputting as a contour compensation signal, the video signal or the video signal. The delayed signal is
A second adder circuit for adding the contour compensation signals to correct a portion where the signal amplitude of the video signal changes.

[0016]

According to the present invention, two first high frequency components having different polarities and two second high frequency components having different polarities are extracted from the input video signal. And the extracted 2
The maximum amplitude value and the minimum amplitude value selected from the two first high frequency components are selectively switched according to a control signal obtained by adding the two extracted second high frequency components. , As a contour compensation signal. In this way, an equivalently widened band edge compensation signal is obtained, and this edge compensation signal is added at an arbitrary ratio to the input video signal or the delay signal of the input video signal to improve the sharpness of the video signal. .

As a result, the switching point from the preshoot to the overshoot of the contour compensation signal, that is, the center of the change point of the input video signal becomes the point where the transient response of the contour compensation signal is the steepest. The combined video signal obtained by adding the signal and the contour compensation signal has improved contour response characteristics as compared with the conventional one.

Therefore, even if the addition amount of the contour compensation signal is reduced, the response characteristic of the video signal can be sufficiently improved, and the sharpness of the video signal can be obtained without adversely affecting the image quality such as S / N deterioration. The degree can be improved.

[0019]

Embodiments of the present invention will be described below with reference to FIGS. 1 is a block diagram showing a first embodiment of the present invention, and FIG. 2 is a waveform diagram showing signal waveforms of respective parts in the circuit of FIG.

In FIG. 1, the same components as those of the conventional example of FIG. 9 are designated by the same reference numerals, 1 is an input terminal, 2 and 3 are delay lines, 4 and 5 are subtraction circuits, and 6 is an addition circuit. , 7
Is a variable gain amplifier circuit, 8 is an adder circuit, 9 is an output terminal, 1
Reference numerals 0 and 11 are subtraction circuits, 12 is a maximum value circuit, 13 is a minimum value circuit, and 14 is a switching circuit.

The circuit operation of FIG. 1 will be described below with reference to FIG. The input video signal from the input terminal 1 of FIG.
The video signal b is passed through the delay line 2, and
Input to the delay line 3. The input video signal and the sequentially delayed video signal are respectively subtracted by the subtraction circuit 4,
5, 10 and 11 are input to the subtraction circuit 10 to obtain the signal h.
Then, the subtraction circuit 11 produces the signal i. Further, these signals h and i are input to the maximum value circuit 12 and the minimum value circuit 13, respectively, and the maximum value circuit 12 outputs two signals out of the two signals.
The one with the higher level is always output as the maximum value output j, and the minimum value circuit 13 always outputs the one with the lower level as the minimum value output k. Then, the maximum value output j and the minimum value output k are input to the switching circuit 14, respectively.

On the other hand, the video signals input to the subtraction circuits 4 and 5 are extracted and added with the conventional delay line aperture control type preshoot and overshoot, and become the switching control signal f. The switching of the switching circuit 14 is controlled by the switching control signal f. That is, when the switching control signal f is higher than a certain reference level, the maximum value output j is selected and outputted, and when it is smaller than a certain reference level, the minimum value output k is selected and outputted. After that, the output signal of the switching circuit 14 is amplitude-adjusted by the variable gain amplifier circuit 7 to become the contour compensation signal 1. Then, finally, the contour compensation signal 1 and the delayed video signal b are added by the adder circuit 8 to obtain the composite video signal m.

The composite video signal m thus obtained (FIG. 2)
Compared with the composite image g (FIG. 10) obtained by the conventional contour correction circuit, the thickness (temporal width) of the contour to which the shoot signal is added is the same, but The changing part is steep, and the transient response of the contour is significantly improved. That is, if the same improvement effect as in the conventional case is sufficient, the addition amount of the contour compensation signal may be small, which is advantageous in terms of S / N, and conversely, the addition amount of the contour compensation signal is the same as in the conventional case. If so, the effect of improving the transient response becomes large.

FIG. 3 is a block diagram showing a second embodiment of the present invention, and FIG. 4 is a waveform diagram showing signal waveforms of respective parts in the circuit of FIG.

In FIG. 3, the same components as those of the conventional example of FIG. 9 or the embodiment of FIG. 1 are designated by the same reference numerals, 1 is an input terminal, 2 and 3 are delay lines, and 4 and 5 are subtraction. Circuit, 6 adder circuit, 7 variable gain amplifier circuit, 8 adder circuit, 9 output terminals, 10 and 11 subtractor circuit, 12 maximum value circuit, 13 minimum value circuit, 14 switching circuit,
Reference numerals 15 and 16 are delay lines. The delay times of the delay lines 2, 3, 15, 16 are assumed to be the same.

In this embodiment, the number of signals to be used is increased as compared with the embodiment shown in FIG. 1 (in the embodiment shown in FIG. 1, a total of three signals are used as an input video signal and a delayed video signal. On the other hand, in this embodiment, a total of five are used as the input video signal and the delayed video signal.), And the contour compensation signal has a wide band.

The circuit operation of FIG. 3 will be described below with reference to FIG.

The video signal input from the input terminal 1 of FIG. 3 is sequentially input to the delay line and becomes a sequentially delayed video signal. Here, the delayed video signal c and two delayed video signals having a short time difference with respect to the delayed video signal c (the input signal of the delay line 3 and the delay line 15
Output signal of the subtraction circuit 10, 11, the maximum value circuit 1
2, the minimum value circuit 13 is input to the circuit for contour extraction, and the maximum value output n and the minimum value output o, respectively.
And is guided to the switching circuit 14.

On the other hand, the delayed video signal c and the input video signal and the delayed video signal (the input signal of the delay line 2 and the output signal of the delay line 15) having a long time difference with respect to the delayed video signal c are subtracted by the subtraction circuit 4. 5, and added by the adder circuit 6 to be the switching control signal p. Switching of the switching circuit 14 is controlled by the switching control signal p, and selects and outputs either the maximum value output n or the minimum value output o. After that, the output signal of the switching circuit 14 is amplitude-adjusted by the variable gain amplifier circuit 7 to become the contour compensation signal q. Then, finally, the contour compensation signal q and the delayed video signal c are added by the adder circuit 8 to obtain the composite video signal r.

The composite video signal r thus obtained (FIG. 4)
In the same manner as in the embodiment of FIG. 1, compared to the composite image g (FIG. 10) obtained by the conventional contour correction circuit, the thickness (temporal width) of the contour to which the shoot signal is added is the same. But,
The changing parts of the rising and falling edges of the contour are sharp,
The transient response of the contour is greatly improved. That is, if the same improvement effect as in the conventional case is sufficient, the addition amount of the contour compensation signal may be small, which is advantageous in terms of S / N, and conversely, the addition amount of the contour compensation signal is the same as in the conventional case. If so, the effect of improving the transient response becomes large.

FIG. 5 shows the frequency characteristics of the switching control signal p shown in FIG. 3, the maximum value output n, and the minimum value output o.
6 is a characteristic diagram showing the frequency characteristic of FIG. 6, and FIG. 6 is a characteristic diagram showing the frequency characteristic of the contour compensation signal q of FIG. In FIG. 5, A is the frequency characteristic of the switching control signal p, and B is the frequency characteristic of the maximum value output n and the minimum value output o.

That is, as shown in FIG. 5, in this embodiment,
Compared to the embodiment of FIG. 1, the peak frequency f ₁ of the switching control signal p is on the lower frequency side than the peak frequency f _{0 of} the maximum value output n or the minimum value output o.
Even if the delay time of each delay line is shortened, the amplitude of the contour compensation signal q can be secured, and thus the time width of the contour compensation signal q can be narrowed (for example, 1/2).
It is possible to synthesize a shoot signal that is thinner than that in the embodiment of FIG.

Further, by appropriately setting the switching gain, the correction frequency band can be widened as shown in FIG. 6 as compared with the conventional contour correction circuit, the horizontal frequency is the same, and the frequency of the video signal is the same. It can be understood that various video sources having different component distributions can be dealt with without changing the peak frequency of the contour compensation signal q (changing the delay time of the delay line).

FIG. 7 is a block diagram showing a third embodiment of the present invention. 7, the same components as those of the conventional example of FIG. 9 are designated by the same reference numerals, 1 is an input terminal, 2 and 3 are delay lines, 4 and 5 are subtraction circuits, 6 is an addition circuit, and 7
Is a variable gain amplifier circuit, 8 is an adder circuit, 9 is an output terminal, 1
0 and 11 are subtraction circuits, 12 is a maximum value circuit, 13 is a minimum value circuit, 14 is a switching circuit, 17 is a shoot balance control terminal (K control, 0 ≦ K ≦ 2), and 18 is a variable gain amplification circuit (K times). ) And 19 are variable gain amplifier circuits (2-K
Times).

This embodiment is different from the embodiment of FIG. 1 in that a shoot balance control terminal 17 and variable gain amplifier circuits 18 and 19 are added.

Therefore, the signal corresponding to the preshoot signal output from the subtraction circuit 10 is the variable gain amplification circuit (K
18) corresponds to the overshoot signal output from the subtraction circuit 11, but the variable gain amplification circuit (2-K times) 1
Through 9 respectively, it becomes as follows.

First, when K = 1, the amplitudes corresponding to the preshoot signal and the overshoot signal have the same amplitude, which is the same as the waveforms of the signal h and the signal i shown in FIG. The obtained contour compensation signal also has the same waveform as the contour compensation signal 1 shown in FIG. Next, when K = 0, the signal amplitude of the signal corresponding to the preshoot signal becomes zero, whereas the signal amplitude of the signal corresponding to the overshoot signal doubles, which is shown in FIG. The waveform is the same as the waveform obtained by doubling the signal amplitude of the signal i. Therefore, the contour compensation signal finally obtained is only the overshoot signal. On the contrary, when K = 2, the signal amplitude of the signal corresponding to the overshoot signal becomes zero, whereas the signal amplitude of the signal corresponding to the preshoot signal doubles, which is shown in FIG. The waveform is the same as the waveform obtained by doubling the signal amplitude of the signal h. Therefore, the contour compensation signal finally obtained is only the preshoot signal.

Therefore, it is possible to control the shoot balance by continuously controlling K.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

In FIG. 8, the same parts as those in the conventional example of FIG. 9 are designated by the same reference numerals, 1 is an input terminal, and 7 is
Variable gain amplifier circuit, 8 is an adder circuit, 9 is an output terminal,
12 is a maximum value circuit, 13 is a minimum value circuit, 14 is a switching circuit, 17 is a shoot balance control terminal (K control, 0 ≦ K ≦ 2), 18 is a variable gain amplifier circuit (K times), 20 is a primary differentiating circuit, 21 is a secondary differentiating circuit, 22 is a delay line, and 23 is an inverting variable gain amplifying circuit (2-K).

Compared with the embodiment of FIG. 7, this embodiment does not use a delay line and a subtraction circuit for extracting the contour signal component of the input video signal and synthesizing the switching signal. A differentiating circuit (high-pass filter or the like) is used, and the outline of each signal waveform in the pulse response is the same as that in FIG.

Therefore, the present embodiment is effective as a shoot balance variable type contour correction circuit using a differentiating circuit, which is difficult to realize by the conventional technique.

[0043]

According to the present invention, as compared with the conventional delay aperture compensation type contour correcting circuit, a contour correcting circuit which has a large effect of improving the transient response and does not cause deterioration of S / N is realized. can do. Also, the shoot balance variable function can be easily dealt with.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing signal waveforms of respective parts in the circuit of FIG.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a waveform diagram showing signal waveforms of respective parts in the circuit of FIG.

5 is a frequency characteristic of the switching control signal p of FIG.
FIG. 7 is a characteristic diagram showing frequency characteristics of the maximum value output n and the minimum value output o.

6 is a characteristic diagram showing frequency characteristics of the contour compensation signal q of FIG.

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

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a conventional contour correction circuit.

10 is a waveform diagram showing signal waveforms of various parts in the circuit of FIG.

11 is a characteristic diagram showing frequency characteristics of the contour compensation signal f of FIG.

[Explanation of symbols]

1 ... Input terminal, 2 ... Delay line, 3 ... Delay line, 4 ... Subtraction circuit, 5 ... Subtraction circuit, 6 ... Addition circuit, 7 ...
Variable gain amplifier circuit, 8 ... Adder circuit, 9 ... Output terminal, 10
... subtraction circuit, 11 ... subtraction circuit, 12 ... maximum value circuit, 13
... minimum value circuit, 14 ... switching circuit, 15 ... delay line, 16 ... delay line, 17 ... shoot balance control terminal, 18 ... variable gain amplifying circuit, 19 ... variable gain amplifying circuit, 20 ... primary differentiating circuit, 21 ... second Secondary differentiation circuit, 22 ... Delay line, 23 ... Inverting variable gain amplifier circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chiharu Ishino, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. Information & Video Media Division, Hitachi, Ltd.

Claims (5)

[Claims] 1. Two different polarities from an input video signal
First extraction means for extracting one first high-frequency component, first selection means for selecting a maximum amplitude value from the two extracted first high-frequency components, and two extracted first Second selecting means for selecting the minimum amplitude value from one high-frequency component, second extracting means for extracting two second high-frequency components having different polarities from the video signal, and the two extracted A first adding means for adding a second high frequency component and outputting it as a control signal, and the selected maximum amplitude value and minimum amplitude value are selectively switched according to the control signal to obtain a contour compensation signal. Switching means for outputting, and a second adding circuit for adding the contour compensation signal to the video signal or a signal obtained by delaying the video signal to correct a portion where the signal amplitude of the video signal changes. A contour correction circuit comprising: 2. The contour correction circuit according to claim 1, wherein the frequency characteristic of the selected maximum amplitude value and the selected minimum amplitude value is different from the frequency characteristic of the control signal. Contour correction circuit. 3. The contour correction circuit according to claim 1, wherein the first and second extraction means are differentiating circuits,
Alternatively, a contour correction circuit having a subtraction circuit for subtracting the video signal and a signal obtained by delaying the video signal. 4. The contour correction circuit according to claim 1, further comprising amplitude value varying means capable of changing the amplitude values of the two extracted first high frequency components. Contour correction circuit 5. The contour correction circuit according to claim 1, 2, 3 or 4, wherein each signal related to signal processing in each means is a digital signal.