JPH0252576A - Picture quality adjustment circuit - Google Patents

Abstract

PURPOSE:To generate a picture with high definition without losing a contour correction function by providing a picture quality adjustment circuit controlling the rate of the amplitude of white and black shoot waveforms in the case of applying picture contour correction through the use of a second derivative waveform. CONSTITUTION:An adder 1 adds a video signal from an input terminal 11 and a signal via delay circuits 4, 5. The output is given to an adder 2 via an inverse amplifier 6 whose amplification factor is -1/2, added to the output of the circuit 4 to output a second derivative waveform correcting the leading and trailing of the video signal. This is given to the adder 3 via a multiplier circuit 9 and an amplifier 7 while suppressing the white level correction wave with the black level correction waveform by the square curved characteristic, the result is added to the signal of the circuit 4 to output a video signal subject to contour correction from an output terminal 12. Thus, the correction shoot waveform section added to the white level of the original video signal is suppressed and the video image with high definition without glitter is obtained.

Description

[Detailed Description of the Invention] [Statement of the Invention] (Industrial Application Field) The present invention relates to an image quality adjustment circuit that performs image contour correction using a quadratic differential waveform, and the amount of correction is adjusted depending on the level of a video signal. This circuit is designed to avoid unnecessary fluctuations.

(Prior Art) Generally, in television receivers, etc., preshoots are performed at the rising and falling edges of a video signal.

A known method is to add overshoot to clarify image outlines and clearly display pictures and characters. To do this, all you have to do is adjust the frequency characteristics of the video signal, and this kind of circuit can improve the image quality, 2! There is a circuit called a J rectifier circuit, as shown in FIG. 7, which adds a second-order differential waveform to an original signal.

In FIG. 7, the video signal Vi (L
) are series-connected delay circuits 4.5 (each delay period τ)
is supplied to the first input terminal of the adder 1 as a signal (c) with a delay time of 2τ, and the second input terminal of the adder 1
is supplied to the input end of

The output (d) of the adder is led to the first input terminal of the adder 2 via an inverting amplifier 6 with a predetermined amplification factor H. The second input terminal of the adder 2 receives the output (b
) is input to the adder 2, thereby obtaining a second-order differential waveform (e) for contour correction of the video signal.

Delay circuit 4.5, adder 1, 2 and inverting amplifier 6
constitutes the second-order differential waveform generation circuit 8.

The signal (e) from the second-order differential waveform generation circuit 8 is sent to the amplifier 7
is supplied to the adder 3 via. Adder 3 is amplifier 7
and the signal (b) are added, and a contour-corrected signal (f), that is, Vo(L), is derived at the output terminal -r-12.

FIG. 8 is an operation waveform diagram of each part signal of the circuit of FIG. 7,
(a) is the positive polarity human input video signal v Bt), (b) is the output of delay circuit 4, (C) is the output of delay circuit 5, (d) is the output of adder 1, (e) is the adder The output of adder 2, (f) is the output signal of adder 3.

The output of adder 1 is a step-like signal (d) that is a combination of signals (a) and (c), and the inverted amplification amplitude is halved.
is added to the signal (b), resulting in 2 as shown in (e).
It becomes the second derivative waveform.

Amplifier 7 amplifies the same signal (e) by a factor of 6.

This is to set the correction amount depending on the magnitude of G.

The output signal obtained by adding the signal (e) amplified by the amplifier 7 and the signal (b) by the adder 3 is obtained by adding the rising and falling edges of the original signal (b) as shown in FIG. 9(f). Preshoot and overshoot are added to the part, and the boundary (outline) of the negative polarity part (black screen) and IE polarity part (white side) of the video signal.
is made clear.

The following operation can be expressed mathematically as input signal Vt(t)-
sinω[, the output signal V o(L) is V o(
L) = sin ω(L-τ) +c [s1 mouth ω
([-τ)=fl+G(1-cos ωr) 1
slnω(tr)... (1) It becomes. Equation (1) shows that the frequency characteristic is the peak frequency f pn
(n-1, 2, 3, . . . ), where f pn is expressed by the following equation.

For example, if r-100 [n soe ], the frequency of n-1 is: From and l, the 5 [MHz] point becomes the most emphasized frequency characteristic.

Note that the outline of the tfi regular melon is 2 when using A and B in Figure 8.
01og (1+28/A) - (3). A indicates the amplitude of the video signal subjected to contour IF, and B indicates the size of the shoot waveform.

However, with the above-mentioned image quality adjustment circuit, when the amplitude change of the video signal is large, the contour correction signal also increases, and when the video signal is bright, the contours are corrected more than necessary, making the image glare and difficult to see. There were drawbacks.

Therefore, proposals have been made to control the contour correction signal according to the average brightness of the video signal (for example, Japanese Patent Publication No. 60-42668).

FIG. 9 is a block diagram showing an example of the control means. The control signal generation circuit 36 detects the average level (APL) of the video signal from the video signal of the video signal input terminal 34,
The detection output is supplied to the correction amount control circuit 37. The second-order differential waveform generation circuit 35 uses the video signal from the input terminal 34 to generate a second-order differential waveform signal, and the correction amount control circuit 37
supply to. The correction amount control circuit 37 controls the amplitude of the input second-order differential waveform signal according to the magnitude of APL, and supplies the amplitude to the adder 38. The adder 38 adds the video signal at the video signal input terminal 34 and the signal from the correction amount control circuit 37, and outputs hli to the output terminal 39 according to the APL of the video signal.
A contour correction signal having a positive amount is derived.

FIG. 10 shows an example of control characteristics in the correction amount control circuit of FIG. 9. The horizontal axis shows the APL, and the vertical axis shows the catch price. In this way, compared to a dark image (small APL), a bright image (
If the APL is large), the number of corrections is reduced to prevent glare in the image. However, with this method, the first
As shown in Figure 1 (a), the APL is small and the brightness of the video signal (
If the change (amplitude) is large, the image will be excessively edge-enhanced. On the other hand, when the APL is large as shown in FIG. 11(b), the contour correction aperture is limited, resulting in an image with unclear bright and dark parts, which also makes it difficult to see.

Therefore, instead of controlling the correction m using the APL, a method can be considered in which the peak level of the video signal is detected and the correction m is controlled. FIG. 12 shows the operating characteristics of the peak level control described above, and the horizontal axis represents the peak level.

The vertical axis indicates the amount of correction.

However, with this method, for example, if the signal in FIG. 8(a) is the peak level signal, it is difficult to generate the second-order differential waveform (e) with respect to the signal (a) at the same timing as the signal (b). This is difficult, and the correction aperture becomes large at the falling edge of the video signal, making it impossible to perform optimal lr control.

Furthermore, if the peak level detection timing is delayed, optimal control cannot be obtained at the peak of the video signal.

(Problem to be Solved by the Invention) In the conventional image quality adjustment circuit, it is difficult to obtain an optimal contour correction signal that corresponds to the brightness of the image. The drawback was that the screen glared and became difficult to see.

Therefore, the present invention proposes an image quality adjustment circuit that is effective in producing high-quality images without impairing the contour correction function.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for adding preshoot and overshoot waveforms to four rising and falling portions of an original video signal, respectively, using a second-order differential waveform signal generating means. A second-order differential waveform is generated, and the second-order differential waveform is simply calculated based on the average level of the video signal.
Rather than controlling the amplitude of the second-order differential waveform, the amplitude of the second-order differential waveform part for white side correction is adjusted to the black image hl.
A second-order differential waveform correction means having a region that is automatically controlled to be smaller than the amplitude of the second-order differential waveform portion for i-positive is newly provided, and the output of this second-order differential waveform correction means and the original video signal are combined. The configuration is such that a video signal whose contours have been corrected is obtained.

(Function) Contour correction is performed by the above means, but since the correction overshoot waveform added to the white side is automatically suppressed for the second-order differential waveform, iL, 1 etc. The glare in the image disappears.

(Example) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a video signal from 11 is passed through a delay circuit 4.5 connected in series to an adder 1.
and is added to the signal from the input terminal 11 that is supplied to the second input terminal of the adder. The output of the adder 1 is supplied to the first input terminal of the adder 2. The output from the delay circuit 4 is supplied to the second input terminal of the adder 2. The signals from the amplifier 6 are added.As a result, a second-order differential waveform is outputted from the adder S2 in order to correct the rising and falling parts of the video signal at the input terminal 11.

The output of adder 2 is given the human output characteristic as a square curve, and uses that characteristic to generate a second-order differential waveform part for correcting the white side of the video signal and a second-order differential waveform part for correcting the black image. The signal is supplied to the adder 3 via a multiplication circuit 9 which suppresses the signal and outputs the signal. The adder 3 adds the signal (secondary differential waveform) from the amplifier 7 and the signal (original signal) from the delay circuit 4,
The contour-corrected video signal is output to the output terminal 12.

The above-described image quality adjustment circuit can suppress the correction shoot waveform portion added to the white side of the original video signal, and can eliminate glare in the image.

FIG. 2 shows an example of the multiplication circuit 9 shown in FIG. 1 for obtaining the "bipod" effect.

In FIG. 2, a second-order differential waveform signal from an adder 2 is introduced to a terminal 13. Terminal 13 is connected via capacitor 16 to the base of transistor Q25, and via capacitor 17 to the base of transistor Q29.

Transistor Q25. Q2B, Q27. 02g constitutes a double balanced differential amplifier.

Transistor Q25. The emitter of 02G is connected to the collector of transistor Q29, and the emitter of transistors Q27 to Q28 is connected to the collector of transistor Q30. Transistor Q29. The emitters of Q30 are commonly connected to a constant current source 31 to form a differential amplifier.

The bases of transistors Q25 and 028 are
A voltage Vy' from a voltage source 18 is supplied via 19,
A voltage vy from a voltage source 19a is supplied to the bases of the transistors 02G and 027 via a resistor R2+.

Further, the voltage VX from the voltage source 19b is supplied to the base of the transistor Q29 via a resistor R23, and the voltage VX is supplied to the base of the transistor Q30 via a resistor R24. ! - The collectors of transistors Q25 and Q27 are connected to the power supply terminal vce via a resistor R32, and the collectors of transistors Q2G and Q28 are directly connected to the power supply terminal vec.

In the above circuit, among the signals supplied to terminal 13, transistor Q25. 02
The first input manually applied to the base of the transistor Q'29 and the second input manually applied to the base of the transistor Q'29 via the capacitor 17 are multiplied (squared) and output to the terminal 33.

This embodiment is structured like a "biped", and is shown in Figs. 3 and 4 below.
The operation will be explained with reference to the figure.

FIG. 3 is a diagram showing signal waveforms of each part of the circuit of FIG. 1,
(a) is the input video signal, (b) is the original signal, (c) is the output of the delay circuit 5, (d) is the output of the adder 1, (e) is the second-order differential waveform obtained by the adder 2, (f) is the output of the multiplication circuit 9 according to this embodiment, and (g) is the output signal waveform. Furthermore, FIG. 4 is an operating characteristic diagram of the multiplication circuit 9, in which the horizontal axis shows the input terminal inputted to the terminal 13, and the vertical axis shows the output voltage appearing at the terminal 33.

Now, as shown in Fig. 3(a), a signal (a
) is led to terminal 11, the third
As shown in FIGS. (b) and (C), signals (b) and (C) delayed by τ are obtained, respectively. Adder 1 adds signals (a) and (c) and outputs a staircase wave signal (d) as shown in FIG. 3(d). The inverting amplifier 6 inverts the signal (d
) and attenuates the amplitude by half, so the output waveform (e) of adder 2 that adds the output and the original signal (b) is white, as shown in Figure 3 (e). The two-blow differential waveform portion P1 for side correction and the second-order differential waveform portion P2 for black image correction are second-order differential waveforms having approximately the same amplitude.

The second-order differential waveform (e) in 1- is the l111 shown in FIG.
It is supplied to the end of the road F13. This results in transistor Q
25. The base of Q2g is centered around the voltage y' from the voltage source 18, and the base of the transistor Q29 is centered around the voltage Vx from the voltage source 19b, iF.

It acts as a signal with a two-stroke differential waveform section P1 for white side correction on the side and a second-order differential waveform section P2 for black image correction on the negative side.

Here, if vy-vy', the output signal voltage ■0 appearing at the terminal 33 is expressed as VO=-k ・Vl 2 (kl; is a constant), where the input signal voltage at the terminal 13 is Vi, and the multiplier circuit The input/output characteristics of No. 9 are given by a square curve as shown in FIG. 5(A). Next, if the relationship between voltages vy and vy' is Vy>Vy', the output signal voltage vO is VO--
-V+ -[V[+(Vy'-V'/'')+(k
is a constant), and the human output characteristic of the multiplier circuit 9 is 2, where the output voltage is maximum when the input terminal is on the positive side, as shown in Figure 5 (B).
It is given by the power curve.

In this embodiment, the relationship between voltages vy and Vy' is Vy > Vy
” By using the characteristics shown in FIG. 5(B), as shown in the figure, the white side correction waveform part P1' of the output waveform ■0 is changed to the black image correction waveform part P2. 'More oppressive,
This prevents the phenomenon in which the outline is excessively emphasized.

Note that the multiplication circuit 9 is just one example, and other embodiments are possible.
It is Noh. Furthermore, in the multiplication circuit shown in FIG. 2, by making the voltage source 18 adjustable, the suppression level of PI = can be arbitrarily varied.

In this embodiment, the quadratic differential waveform is automatically controlled in the multiplication circuit 9 so that the amplitude of the white side hIi Ichikawa Ichikawa 2 bone microform part is smaller than the amplitude of the quadratic differential waveform part of the black image capture 1:. hand[
Achieved target 1. However, as shown in FIG. 5, the average level (APL) of the video signal may be used as control information to control the amplitude of preshoot and overshoot.

This embodiment does not simply control the amplitudes of preshoot and open neat in the same way by APL, but rather controls the rate of change in the amplitudes of both.

The embodiment shown in FIG. 5 is different from the conventional example shown in FIG.
The difference is that a contour 1111 compensation control circuit 20 is added between the contour 1111 and the adder 3, which controls the ratio of the overshoot amount and the contour 1111 of the video signal to be compensated. Since the other parts are the same, the same parts are given the same reference numerals and the explanation will be omitted.

In the contour F+li compensation control circuit 20, the second-order differential waveform signal shown in FIG. 6(b) outputted by the amplifier 7 is inverted by the amplifier 21 (FIG. 6(c)), and the second-order differential waveform signal shown in FIG. It is also supplied to the multiplier 22.

On the other hand, the video signal input to the terminal 11 is also manually input to the control signal generation circuit 24, and the average brightness level of the video signal is detected. This detection output is inputted to one side of the amplifier 23,
The amplitude of the output of the multiplier 22 (FIG. 2(d)) input to the other input is controlled so that it increases when the brightness level is high and decreases when the brightness level is low. The amplitude-controlled signal is added to the original second-order differential waveform signal in addition 2 at 25, resulting in a second-order differential waveform signal having a different amplitude under -1 and x as shown in FIG. 6Ce). The dotted line in the figure represents the range controlled by the output of the control signal generation circuit 24.

The output signal of the adder 25 is added to the video signal delayed by the adder 3 (FIG. 6(a)), and the output signal is added to the video signal (FIG. 6(a)), which is a signal to which preshoots and overshoots with different amplitudes are added to the edge portions (Fig. 6(a)). 6 (f)) is output to the terminal 12. Therefore, depending on the brightness level of the human video signal, the higher the brightness level is, the higher the preshoot (overshoot at the falling edge of the signal) can be increased.

As a result, in a bright single image, the black level side of the contour can be emphasized more than the self level side (the white level side can be suppressed), so even if the contour compensation signal is large, it is possible to solve the problem that the image is difficult to see due to glare even if the contour compensation signal is large.

[Effects of the Invention] As described below, the present invention provides a method for controlling the ratio of the amplitude of the shoot waveforms on the white side and the black side, especially when suppressing excessive contour bli compensation when the brightness level is large. Therefore, it is possible to provide an image quality adjustment circuit that is effective in obtaining high-quality images without impairing the contour correction function.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the multiplication circuit of FIG. 1, FIG. 3 is a waveform diagram of each part of the circuit of FIG. 1, and FIG. 2 is a characteristic diagram shown to explain the operation of the circuit, FIG. 5 is a circuit diagram showing another embodiment of the present invention, and FIG. 6 is a characteristic diagram shown to explain the operation of the circuit shown in FIG. 7 is a circuit diagram showing an example of a conventional image quality adjustment circuit. FIG. 8 is an operation waveform diagram shown to explain the operation of the circuit in FIG. 9. FIG. 9 is a circuit diagram showing an example of a conventional image quality adjustment circuit. The circuit diagrams illustrating examples, FIG. 10, FIG. 11, and FIG. 12 are explanatory diagrams shown to explain the operation of the circuit of FIG. 9. 2.3...Adder, 4.5...Delay circuit, 6...
Inverting amplifier, 7... Amplifier, 9... Multiplier circuit, 19
a. 19b... Voltage source, Q25-Q30... Transistor, 20... Contour compensation control circuit, 22... Multiplier,
24...Control signal generation circuit.

Claims (3)

[Claims] (1) Second-order differential waveform generating means for generating second-order differential waveforms for adding preshoot and overshoot waveforms to the rising and falling parts of the original video signal, respectively, and a signal from the second-order differential waveform generating means Among them, a second-order differential waveform correction means having an area for automatically controlling so that the amplitude of the second-order differential waveform portion for white side correction is smaller than the amplitude of the second-order differential waveform portion for black side correction; An image quality adjustment circuit comprising means for synthesizing the output of the waveform correction means and the original video signal to obtain a video signal whose contour has been corrected. (2) The second-order differential waveform correction means uses a multiplier to
The means is characterized in that the signal from the same second-order differential waveform generating means is inputted to the two inputs to generate a square curve, and the white side correction waveform part is suppressed from the black side correction waveform part by the characteristics of the square curve. An image quality adjustment circuit according to claim 1. (3) In the rising portion of the video signal, the second-order differential waveform correction means makes the ratio of the preshoot amount when the brightness level is high larger than the ratio of the preshoot amount when the brightness level is low. In the falling part of the signal, the brightness level of the video signal is detected and the detection output is 2. The image quality adjustment circuit according to claim 1, further comprising means for controlling the second-order differential waveform signal from the second-order differential waveform generating means.