JPS62262583A - Method for varying high frequency gain - Google Patents

Abstract

PURPOSE:To improve a phase characteristic and to correct the aperture distortion without changing a low frequecy gain by permitting a varying means to modify and control a gain in the prescribed way and varying the high frequency gain of a video signal. CONSTITUTION:A signal delay circuit 2 and a low-pass filter 3 delay input signal Vi(t) by a time tau and output them as signal V1 and V2 denoted by Vi(t-tau) and Vi(t-tau)gL(omega). Here the gL(omega) is a function to express the amplitude frequency characteristic of the low-pass filter 3. The signals V1 and V2 are applied to the positive and negative input terminals of a differential amplifier 4, and a gain varying knob can give a k-folded gain. A signal V3 expressed by Rui(t-tau)gH(omega) [gH(omega)=1-gL(omega)] is outputted from the differential amplifier 4, and an adder 5 adds the signals V3 and V2 and outputs the added signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for varying a high frequency portion of a video signal in video equipment such as a television receiver, a VTR, and an image processing device. More specifically, the present invention relates to a method of correcting aperture distortion by changing the amplitude of a predetermined high frequency component of a video signal without causing phase distortion.

(Prior Art) In recent years, demand for higher image quality has been increasing year by year in video equipment such as television receivers and VTR9 image processing devices.

Most of these video devices use a pre-defined pre-vision signal, and in order to improve the image quality, the reliability band is extended to high frequencies so that details can be seen. A widely used method is to correct the distortion caused by the beam having a finite size and emphasize the contour.

Correction of aperture distortion usually requires emphasizing the amplitude of a predetermined i01 frequency component of the signal without producing phase distortion. This is because if there is phase distortion, ringing or overshoot will occur in the image.

Conventionally, the two-time differential method and the delay line method are widely known as such correction methods.

The circuit of the two-time differentiation method is cheap and simple, but the normally used differentiation circuit itself has the property that the higher the frequency, the more the differential characteristics deteriorate, and a certain amount of phase distortion is unavoidable. ? This shows the characteristic that the positive amount of io increases. This characteristic is only in terms of contour enhancement,
In other words, it has good characteristics; however, the higher the frequency, the worse the signal-to-noise ratio of the signal itself, so the drawback is that noise is emphasized.

On the other hand, the delay line method has good phase characteristics, and the center frequency for high-frequency emphasis can be set by changing the delay time due to the U line extension. By setting it lower than the highest frequency, S/
It is also possible to make the deterioration of the N ratio smaller than in the double differentiation method. Therefore, many high-end machines use this method.

However, with this method, when the high frequency gain j [) is changed, the difference in the low frequency side? What to do about the disadvantage that the contrast changes as well. Therefore, although this method is good for fixed correction, it is not a very suitable method for continuous correction.

Also, there is a problem common to both the differential method and the delay line method.
In general, it is easy to design υj so that the high frequency part of the original signal is emphasized more than the original signal, but it is difficult to design it so that it is both attenuated and emphasized more than the original Δ. It is. What about the original signal? Good up to level 3<r
For images with S/N ratio, only enhancement t′j NowJ
, only 1 is enough, but on the other hand, if the original signal is extremely noisy (
For example, ``Derebijin 1 received in an area with poor radio wave conditions.
(high-frequency signals), emphasizing the high frequencies will have the opposite effect. In this case, it is desirable to attenuate the higher frequencies of the original signal to improve the S/N ratio.

(Object of the invention) The present invention has been made in view of the above circumstances, and has good Q compatibility and does not change the low frequency gain.
It is possible to change the area gain 1r7, and it is also easy to emphasize that this high frequency range is attenuated from the original signal, and the gain 7 can be changed continuously between this attenuation and emphasis. In addition, it is an object of the present invention to provide a method for easily setting the center frequency of high-frequency emphasis and varying the frequency in the 10-range frequency range 4!1.

(Structure of the Invention) The method of varying IU1 for each high frequency of the present invention is to input an image signal in parallel to a signal delay circuit that allows all frequencies to pass and a low-pass filter that allows only low frequency components to pass. Then, the output signals 4i: from this Riken circuit and the low-pass filter are respectively input to a predetermined X1pH input section of a differential amplifier, and only the high frequency component is differentially amplified. The signal is input to the signal synthesis means and accumulated, and at that time, the amplification factor variable means installed in the F-notation amplifier is operated to change only the high-frequency gain with respect to the input signal. The present invention is characterized in that a video signal in which only the high-frequency gain is changed is extracted as an output signal of the signal synthesizing means.

Here, the signal delay circuit has a pass frequency band equal to or higher than six bands of the input signal, and has a substantially constant delay time characteristic within the input signal band.

Furthermore, a low-pass filter has a pass frequency band narrower than the band of the input signal, is approximately constant within the pass band, and has delay time characteristics that are approximately the same as the signal delay circuit described above.
For example, a vessel type is used.

Furthermore, the differential amplifier is equipped with amplification factor variable means as described above, and this variable means can vary the amplification factor for the difference between two input signals. This means that only the high frequency region (high frequency region) can be emphasized or attenuated relative to the original signal.

Here, the high frequency range refers to the high frequency range, for example, 4 M
NTSC video signal with Hz frequency band ¥3
'C- usually refers to a region of 2 to 4 M l-I Z.

In addition, the signal synthesis means refers to a device that performs input or subtraction of two input signals, as well as a device that adds a constant to the result of (a), such as a difference amplifier, a signal adder, etc. etc.

Note that inputting each to a predetermined differential input section means inputting either the output signal B from the delay circuit or the output signal B from the filter to either the positive or negative input section of the differential amplifier, and outputting This means inputting the other side of the signal to the other side of this input section.

(Effects of the Invention) According to the first variable high frequency gain method of the present invention as described above, the following effects can be obtained. For example, input No. 13 is v; (t), (delay time of delay circuit and reduction filter is τ, amplitude frequency characteristic of reduction filter (one stroke width with respect to DC normalized to base special) is (
If IL(ω) and the final output signal are vo(t), and the output a of each part is expressed by a model formula, the output signal of the No. 18 delay circuit VL(t) =V; (-τ)... ...
・・・・・・・・・・・・・・・1) Reduction filter output No. a V2 (t) = v; (t r ) OL
(ω) ...2) Output signal of the difference fII amplifier V3 (t) = kvr (t - r) (1
−(l L (ω) )−kvH(t−τ)LJ? +
(ω)...3)(g8(ω)-1-gL (ω
)) Most # winter horn signal f Vo (t) = AVi (t-4) ((J L <
(t)) 10kgH(ω))−△v;(t−τ)G(ω
)・Old・・・4)(G(ω)=(lL(ω)10k
gH(ω)). Note that here ω is the angular frequency (-2
π'), [ is the frequency, 8 is the fixed column 1!' of the signal synthesis means
7, k (is the variable gain of the differential amplifier. Therefore,
As shown in equation 4, the phase characteristics of this system have no frequency dependence and no distortion (delayed by a constant time τ), whereas the amplitude characteristics are frequency dependent as shown by G(ω). It can be set to have gender.

Furthermore, the characteristics of the low range side! Characteristics on the high frequency side without changing IL(ω)9. Only l<ω) can be changed by k. Therefore, for example, if the input signal is a signal having amplitude-frequency characteristics as shown in FIG.
By changing the value of from O to 1 or more -F, it is possible to smoothly change the high-frequency gain from an attenuated state to an emphasized state according to the value of C, as shown in Figure 6. . Furthermore, by changing the set value of the high cutoff frequency of the low-pass filter, the center frequency for emphasizing the t'& region can be freely selected.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows the implementation of the method for varying the frequency range of the present invention.
There is a block diagram showing the circuit configuration of the Shin@Renobu section.

This signal processing section 1Ict's delay circuit 2, (l' is passed through the pass filter 3, differential amplifier 4 and signal adder 5. ;(t
) are input to the signal delay circuit 2 and the low-pass filter 3 in parallel. The input signal v; (t) is delayed by the time τ by the signal delay circuit 2 and the fII band filter 3, and becomes vi(t-τ) and Vi(-τ)9L, respectively.
(ω) is the signal V1. It is output as V2.

Here, gL (ω) is a function that expresses the amplitude frequency characteristic of the low-pass filter, and ω is the angular frequency. (No. 2 Vl
, V2 is input to the positive and negative input terminals of the differential amplifier 4, and the gain is given twice by the variable knob (15). From this difference first amplification ding 4, kv; (j-τ) (1-OL(ω)
A signal J expressed as l(=kv; (tr)gH(ω)) is output. Here, gH(ω) is 1(IL
It is a functional expression equivalent to (ω). Signals v2 and ■3 are modified by a signal adder 5. The final output from this No. 18 σ adder 5 is Av+ (t Z: ) (OL (ω
) +kgH(ω)): (A is signal addition] 'J5 fixed edition 1r7.

) is output 1: i gv□ (t ).

Note that it is also possible to use a differential amplification S instead of the adder C7 5.

FIG. 2 is a block diagram showing an example of the case where the signal delay section 1 of FIG. 1 is used in an NTS C color television receiver.

The video carrier wave applied to the antenna terminal 11 of the receiver is transmitted to the tuner section 12. Medium frequency amplifier 13. Image detection section 14
is extracted as a color television signal. This color television signal is input to the signal delay section 1 and color signal band amplification section 15 shown in FIG.
While the image is amplified by G, the carrier color signal from the band amplification section 15 is color demodulated by the color demodulation section 17 and inputted to the matrix circuit 18 as EY, ER-Y and Eu-y signals, respectively. After this, R from the matrix circuit 18
,G.

An 833 signal is applied to the picture tube 19.

FIG. 3 shows a specific example of the signal delay section 1. Color TV signal synthesis equipment and demodulation equipment! The F11 degree signal system includes a delay line (hereinafter referred to as I11) for time adjustment with the color signal.
The signal delay section 1 shown in FIG. 3 also uses all or part of this luminance signal delay line 20 as the signal delay circuit 2 shown in FIG. 1. It is configured as follows. Normally, the luminance signal delay line 20 is 0
．． 3μs~1.2μSPi! It is extremely convenient to match the delay time of the low-pass filter 3, which normally requires a delay time of 0.2 to 0.3 μs. When a part of the luminance signal delay line 20 is used as the signal d extension circuit 2, an intermediate tap section 20a is provided in this ff if rA 20, and a subsequent stage section is used.

In addition, the luminance signal delay line 20 with the center gate tap is a distributed constant type or a pseudo distributed constant type using a 1-1C lattice circuit.
It can be easily formed by drawing wire. Since the signal delay line 2 is quite expensive, by making it also serve as the luminance signal delay line 20, the cost can be reduced significantly. a3, resistor 21a,
21b is a resistor inserted for the characteristic impedance of the luminance IfLiA line 20, and if necessary, a buffer for impedance matching is inserted between the intermediate tap section 20a of the luminance signal delay line and the low-pass filter 3. 1 may be inserted.

4M is a block diagram showing an example of the case where the signal delay unit 1 of FIG. 1 is used in an NTSC color camera.

The h° subject image photoelectrically converted into three color (R, G, B) color signals by the color camera 31 is sent to the wrestling amplifier 3.
2 and input to the matrix circuit 33 as signals ER, EGr, and Ev. 71-EY of the three signals EY, EI, [Eα, outputted from the RX circuit 33]
The signal g (P degree signal j3) is shown in Figure 1 and is the jingo'! i extension part 1
719! and video amplifier 3
4 and input to the mouthpiece 35. On the other hand, E
The Ei Δ signal is delayed by a predetermined time ff by a delay l51136, passes through a 1.5M, NZ low-pass filter 37, and is sent to the modulator 3.
8 and Eαfz舅 is input to 0 without delay.
．． ! iM HZ low pass filter 39 to modulator 38
The balanced modulated signals are then input to the adder 35.
It is combined with the 'CE Y signal and transmitted as a video carrier wave from the i-machine 4o. In this case, a circuit as shown in FIG. 3 can be used as the signal delay section 1. Note that the layered portion from the matrix circuit 33 to the adder 35 is normally included in a color coder.

<K: In the above explanation, the case where the method of the present invention is applied to a color blurri image receiving RJ3 and a color camera is detailed, but the method of the present invention is not limited to these application examples. It can also be applied to various other image processing devices such as VTR image processing devices and video disc image processing devices.

Furthermore, the method of the present invention is not limited to image processing apparatuses of the NTSC system, but can also be applied to image processing apparatuses of the PAL system, SECAM system, or the like.

Furthermore, when the method of the present invention is applied to an image processing IIP device, if it is used together with a comb-shaped filter, it will provide better IIP.
ζ image can be (q).

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the circuit configuration of a signal delay section for implementing the 1q variable method for each high frequency of the present invention, and Fig. 2 shows an application of the signal delay section of Fig. 1 to a color television receiver. FIG. 3 is a block diagram showing an example of the signal delay section shown in FIG. 1.
Figure 4 is a block diagram for explaining the situation when the signal delay unit shown in Figure 1 is applied to a color camera, and Figure 5 and Figure 6 are block diagrams for explaining the prior art. It is a schematic diagram. 1...Signal delay section 2...No. 18 distribution circuit 3
...Low-pass filter 4...Difference V] Amplifier 5...
・Signal adder Q unit 20... Luminance signal delay line 20a
...middle tap

Claims (1)

[Claims] 1) A signal delay circuit that has a delay characteristic that delays an input signal for a predetermined time and has a pass frequency band that is equal to or higher than the frequency band of this input signal, and A video signal is input in parallel to a low-pass filter that has a delay characteristic and limits the passage of high-frequency components of the input signal, and the video signal is inputted in parallel to a low-pass filter that has a delay characteristic and limits the passage of high-frequency components of the input signal, and a full-frequency delayed signal from the delay circuit and a high-frequency component from the filter are input. The delayed signals whose components are limited are respectively input to predetermined differential input sections of a differential amplifier equipped with variable gain means, and the difference between the two is amplified to produce a high frequency component output signal having a gain by operating the variable means. The high frequency component output signal from the differential amplifier and the output signal not containing the high frequency component from the filter are input to a signal synthesizing means, and by a predetermined gain changing operation of the variable means, the image A high frequency gain variable method characterized by obtaining a final output signal in which the high frequency gain is changed with respect to a signal. 2) A patent characterized in that the signal delay circuit is formed by all or part of a luminance signal delay line inserted for time adjustment with a color signal in a color television signal synthesis system or demodulation system. A high frequency gain variable method according to claim 1.