JPH0244973A - Noise reduction device - Google Patents

Abstract

PURPOSE:To prevent deterioration in the transient characteristic from being called for even if the noise component is reduced by extracting a signal component without any line correlation of each input signal with a correlation device comprising a nonlinear circuit and subtracting the extracted signal from the input signal. CONSTITUTION:A signal retarding an input signal by a 2-horizontal scanning period (2H) with 1H delay devices 5, 6 to eliminate a low frequency component, a signal whose low frequency component with 1H delay by a 1H delay device 5, a signal whose low frequency component is eliminated without any delay are generated and they are inputted to a correlation device 7 comprising a nonlinear circuit. Then an output of the correlation device 7 is subject to amplitude limit by a limiter 8 and the result is subtracted from the signal whose low frequency component is eliminated with 1H delay. The correlation device 7 consisting of the nonlinear circuit does not output the correlation signal of the transient part of the input signal. Thus, even if the noise component is reduced, the vertical transient characteristic is not deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for reducing noise in a noisy video signal such as a home VTR.

[Prior Art] Unlike broadcast VTRs, home VTRs do not need to faithfully record and reproduce television signals, and because they cannot obtain a sufficient S/N ratio, they are equipped with an electric circuit called a noise canceller. A method is used to reduce noise. 11th
The figure shows the H-correlation noise reduction circuit described in "NHK Home Video Technology" edited by Japan Broadcasting Corporation, written by Katsuya Yokoyama, pages 102 to 104. In the figure, (1) is an amplifier, (
21) is an IH delayer that delays by one horizontal scanning period (hereinafter referred to as "IH"), (22) and (24) are subtracters, and (23) is a limiter that limits the amplitude.

Next, the operation will be explained. The video signal has a strong vertical correlation, and the difference between the reproduced luminance signal and the IH delay signal of the reproduced luminance signal delayed by the IH delay device (21) by the subtracter (22) yields a noise component with no line correlation. . However, even in signal components, there are portions without line correlation, and those signal components without line correlation are also obtained as differential outputs.

However, since the noise component is generally smaller than the signal component,
In order to pass only the noise component of the output of the subtracter (22), it is sufficient to pass it through a limiter (23) that does not allow large amplitude signals to pass. That is, signal components without line correlation cannot pass through the limiter (23). Therefore, the output of the limiter (23) is a small amplitude noise component with no line correlation. This component is subtracted from the original signal (24)
By subtracting , the noise component included in the original signal can be reduced.

[Problems to be Solved by the Invention] Since the conventional noise reduction device is configured as described above, for example, when a signal A with a luminance change as shown in FIG. The output of the device (22) is the 12th
The signal waveform shown in figure (b) becomes zero, and the limiter (23)
The amplitude is limited by this, resulting in a signal having the waveform shown in FIG. 12(C). Therefore, the output signal of the subtracter (24) has the waveform shown in FIG. 12(d). That is, the conventional H-correlated noise reduction device has a problem in that the transient characteristics in the vertical direction deteriorate.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a noise reduction device that does not deteriorate vertical transient characteristics.

[Means for Solving the Problems] A noise reduction device according to the present invention has a signal obtained by delaying an input signal by 2H to remove a low frequency component, a signal obtained by delaying an input signal by IH and removing a low frequency component, and a signal obtained by removing a low frequency component by delaying an input signal by IH. A signal with low frequency components removed is created and input to a correlator configured with a nonlinear circuit, the output of the correlator is amplitude limited, and subtracted from the above IH-delayed signal with low frequency components removed. It is structured like this.

[Operation] Since the correlator configured with the nonlinear circuit of the present invention does not output any correlation signal of the transient portion of the input signal, even if the output signal of the correlator is subtracted from the input signal, the characteristics of the transient portion will deteriorate. Never.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
In the figure, (1) is an amplifier, and (2), (3), and (4) are low frequency component removal circuits, which are bypass filters HPF in this embodiment, but may also be bandpass filters. (5
), (8) is an IH delay device, (7) is a correlator composed of a nonlinear circuit, (8) is a limiter that limits the amplitude, (9)
is an adder, (18) is an inverter, and (18) is a delay correction circuit.

Figure 2 is a block circuit diagram showing an embodiment of the correlation detector (7), in which (10), (11), (+5) are maximum value selection circuits, (12), (13), (14) are minimum value selection circuits, and (12), (13), (14) are minimum value selection circuits. In the value selection circuit, (1B) is an adder, and (17) is an amplifier with a local gain.

Figure 3 shows the maximum value selection circuits (10), (11),
A diagram showing an example of (15), FIG. 4 is a minimum value selection circuit (
12).

It is a figure showing an example of (13) and (14).

Next, the operation of this embodiment will be explained. 5th as input signal
Considering the case of a video signal as shown in FIG. 5(a), the waveform that has passed through the low frequency component removal circuits (2), (3), and (4) becomes the waveform shown in FIG. 5(b).

Considering only the part indicated by the dotted line A in Fig. 5(b), the second input signal 2 of the correlator (7) is as shown in Fig. 5(C).
The waveform is shown in . The output signal T of the correlator (7) has a waveform shown in FIG. 5(d) for reasons described later. Therefore, the output signal of the subtracter (9) has the waveform shown in FIG. 5(e), and the vertical transient characteristics are not deteriorated.

Note that the delay correction circuit (18) is for making the phase of the signal input to the subtracter (8) match the phase of the signal Q.

Moreover, the second input signal 2 of the correlator (7) is shown in FIG. 6(a).
If the waveform is as shown in Figure 6(b), the second output signal of the correlator (7) will have a waveform as shown in Figure 6(b) for reasons to be described later, and the output signal of the limiter (8) will have an amplitude Due to the limitations, the waveform becomes as shown in FIG. 6(c). Therefore, the output signal of the subtracter (9) has the waveform shown in FIG. 6(e).

If there is no limiter (8) for limiting the amplitude, the output signal of the subtracter (8) will have the waveform shown in FIG. 6(d).

That is, the limiter (8) is an essential circuit and performs important operations in order to prevent a certain specific pattern from being erased.

Next, the reason why the relationship between the input signal of the correlator (7) and the output signal is as described above will be explained.

In FIG. 2, the signal level of input 1 is S1, and the signal level of input 2 is S2. If the signal level of input 3 is 53,
From the configuration in Figure 2, if 51=S2=S3, the correlator output is S2 (or Sl or 53).Sl) If S2=S3, the correlator output is S2 (or 53).Sl)S2)In the case of S3, The correlator output is 52S2)S
If 1=83, the correlator output is S2+53 S2)S3)St, the correlator output is (□)S3)S
When 2=S1, the correlator output is S2 (or 5l). When S3>S2>Sl, the correlator output is 10 patterns of S2. This output pattern is shown in Figure 5 (C).
When applied to , the input waveforms of inputs 1, 2, and 3 are the waveforms shown in FIGS. 7(a), (b), and (c), respectively. When the above-mentioned output pattern is applied to this input, the output waveform of the correlator (7) becomes the waveform shown in FIG. 7(d). That is, a step-like signal is not output from the correlator (7).

On the other hand, if the input signal of the correlator (7) has the waveform shown in FIG. 6(a), the three input waveforms of the correlator (7) will be as shown in FIG. 8(a), (b), ( The waveform shown in C) will be obtained. When the above-mentioned output pattern is applied to this input, the output signal of the correlator (7) has the waveform shown in FIG. This is equivalent to the waveform in FIG. 6(b).

Furthermore, in the waveform pattern shown in FIG. 6(a), those with small amplitudes are noise components with no vertical correlation. Therefore,
The noise component passes through the limiter (8) for amplitude limitation, and the signal component generally has a large signal amplitude, so it passes through the limiter (8).
8), the output signal of the subtracter (8) has a signal component as shown in FIG. 6(e).

Note that the connection of the H P F (3) and the inverter (18) in the embodiment of FIG. 1 may be reversed.

In addition, in the embodiment of FIG. 1, if the adder (8) is to be used as a subtracter, the input of the correlator (7) is compared with the input of the correlator (7) of FIG. An example of the configuration is shown in FIG. 9. In the figure, (25
), (2El) is an inverter, and (27) is a subtractor.

Further, although the low frequency component removing means in FIG. 1 is placed after the IH delay, it may be placed before the IHH delay device, and an example of this configuration is shown in FIG. 10. In the figure, (28) is an IHH wire extension.

Furthermore, the maximum value selection circuit and minimum value selection circuit shown in FIGS. 3 and 4 are not limited to the configurations shown in FIGS. 3 and 4, and in the case of digital signals, an AND element, an OR element It can be easily configured using .

Further, in the above embodiment, the case where the delay time τ of the delay device is IH is explained, but it may be 2H or nH (where n is a real number), or it may be l field or n
A similar effect can be obtained by using fields, l frames, or n frames.

Furthermore, in the above embodiment, the correlation detector (7) inputs signals with three delay time differences and has a correlation detection characteristic expressed by the following formula %)))]; The number of input signals is not limited to three, and the same effect can be obtained by using a signal having the correlation detection characteristic shown in the equation below, in which an odd number of 3 or more signals are input, shifted by the unit delay time τ. can get.

So, for example, f(i-3) indicates a signal delayed by S from signal fi, and f(i-90τ) indicates a signal delayed from signal fi by S.
It shows a signal that is advanced by τ from S).

[Effects of the Invention] As described in -1- below, according to the present invention, an input signal from which low-frequency components have been removed is processed into a correlation constructed by a nonlinear circuit from at least three signals delayed by nH, n fields, or n frames. The correlator is configured to extract signal components with no line correlation of each human input signal and subtract this extracted signal from the input signal, so the above correlator outputs a signal in the transient part for a step signal input. In order not to
This provides an advantageous effect of providing a noise reduction device that has an excellent effect of not causing deterioration of transient characteristics even when noise components are reduced by subtracting the output of the correlator from the input signal.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a block circuit diagram showing an example of the structure of a correlator of this embodiment, and FIG. 3 is a maximum value selection circuit diagram of this correlator. Fig. 4 is a minimum value selection circuit diagram of this correlator, Figs. 5 and 6 are signal waveform diagrams of various parts to explain the operation of this embodiment, and Figs. 7 and 8 are as shown in Fig. 2. FIGS. 9 and 10 are block circuit diagrams of other different embodiments of the present invention, FIG. 11 is a block circuit diagram of a conventional H-correlation noise reduction circuit, and FIG. The figure is a signal waveform diagram of each part of this conventional example. (2), (3), (4)...Low frequency component removal circuit, (
5). (8), (28)... IH delay device, (7)... Correlator, (8)... Limiter, (9), (1B)... Adder, (18), (25 ), (2B)...Inverter, (27)...Subtractor, (10), (11), (
+5)...Maximum value selection circuit, (12), (13)
, (14)... Minimum value selection circuit, (28)... Delay correction circuit. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A low-frequency component removing means for removing the low-frequency components of the input video signal, and a signal from which the low-frequency components have been removed is delayed by a unit time τ of n horizontal scanning periods, n field periods, or n frame periods. A means of creating k signals and the following characteristic formula for detecting line correlation, field correlation, or frame correlation of these k signals ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [However, MAX: Function for selecting the maximum value MIN: Function for selecting the minimum value f(i): Input signal to the correlation detection means at time i S = τ(k-1)/2 τ: n horizontal scanning period , unit delay time k of n field periods or n frame periods (n is an integer of 1 or more): number of odd input signals of 3 or more shifted by τ used for correlation detection]; A noise reduction device comprising: amplitude limiting means for limiting the amplitude of a signal; and means for subtracting the amplitude limiting signal from the input signal whose phase has been adjusted to be in the same phase as the amplitude limiting signal.