JPS62269477A - Noise eliminator - Google Patents

Abstract

PURPOSE:To prevent the omission of a signal in the signal of large level from generating, and to increase a noise eliminating effect at an edge part, by providing a non-linear circuit which compresses a signal level to a non-linear shape when the signal level outputted from a differential circuit is large, corresponding to the signal level. CONSTITUTION:The titled device is constituted so that a non-linear circuit 16 which outputs a signal almost in proportion to the signal level when it is small, but compresses the signal level to the nonlinear shape corresponding to the level when the signal is large, is provided between a differential circuit 13 which takes out a change part per prescribed time in an input signal, and a feedback loop consisting of a delay circuit 17, a multiplier 18, and an adder circuit 19. In this case, a factor P to compress the signal of the non-linear circuit 16 keeps a constant value B when the signal level in the high pass component of the signal inputted to the non-linear circuit 16, is small, and the signal in proportion to an input signal level is outputted. But at the time of inputting the signal of large level to the non-linear circuit 16, the signal is outputted after limiting the amplitude of the signal, therefore, no distortion is generated in the signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video signal noise removal device that is applied to VTRs, video disc devices, etc. and reduces minute noise components contained in video signals.

BACKGROUND OF THE INVENTION FIG. 4 shows a block diagram of a conventional noise removal device. 1 is the input terminal of the video signal digitized with the sampling period T, and 2 is the change per time of n times the sampling period T (n is a positive integer) of the video signal input from the input terminal 1. This difference circuit is composed of a delay circuit 3 having a delay time nT, and a subtraction circuit 4 that subtracts the output signal from the input signal of the delay circuit 3. 6 is a delay circuit having the same delay time nT as delay circuit 3; 6 is a multiplication circuit that multiplies the output of delay circuit 5 by a value A; An adder circuit, 8 is a multiplier circuit that multiplies the output of the adder circuit γ by a multiplier B, 9 is an amplitude limiter circuit that limits the amplitude of the output of the multiplier circuit 8, and 10 is a subtractor that subtracts the output of the amplitude limiter circuit 9 from the signal input from the input terminal 1. A circuit 11 is an output terminal which outputs the output of the subtraction circuit 10 as a video signal with reduced noise.

The noise removal characteristics of the conventional example configured as described below will be explained using a two-conversion equation representing a discrete system.

The delay time T (n=1) of the delay circuit 3 and the delay circuit 5 shown in FIG. 4 will be explained. "Amplitude limiting circuit 9 for the signal input to input terminal 1 when
The transfer function of the signals input to is expressed as H(z)d:゛. The above equation H(2) is a high-pass filter (HP
F), only high-frequency components are input to the amplitude limiting circuit 9. Therefore, when the amplitude of the high frequency component is small, the d amplitude limiting circuit 9 passes the signal, so the subtraction circuit 10 removes the minute high frequency component of the video signal. However, when the amplitude of the high frequency component inputted to the amplitude limiting circuit 9 is large, the amplitude limited signal is guided to the subtracting circuit 10, so that it is not removed from the input video signal. The characteristics described above reduce only the high-frequency noise of minute signal level superimposed on the video signal, and the amplitude of high-frequency components of large signal level that should be considered as signals is limited by the amplitude limiting circuit 9, so that the signal is Do not cause deletions.

The conventional noise removal apparatus configured as described above will be explained below using the operating waveform diagram of FIG. Here, for simplicity, as an input signal, 1=
It is assumed that a step confidence that changes from 0 to level U is used, and that minute level high frequency noise is superimposed on this. When this signal a is input to the input terminal 1, the output of the differential circuit 2 outputs a signal in which noise is superimposed on the J-like impulse signal shown in FIG. This signal passes through a feedback loop composed of a delay circuit 6, a multiplier circuit 6, and an adder circuit 7, and then is input to the amplitude limiting circuit 9 by a certain time constant (in this case, the multiplier circuit 70) as shown in FIG. (Determined by multiplier A)
A signal in which noise is superimposed on a signal that converges to a signal level of 0 is input. The amplitude control circuit 9 applies an amplitude limit to the portion of the signal C that exceeds a predetermined signal level (now assumed to be BV), so its output is 6. It becomes a flat signal at level BV between 1 and tlt. The time width of this flat portion is determined by the change level (U) of the input signal and the time constant (A) of the feed pack loop. The above output signal of the amplitude control circuit 9 is subtracted from the input signal a by the subtraction circuit 10, and the output signal from the output terminal 11 is output at time t1 as shown in FIG. 6d.
Thereafter, a signal from which minute high-frequency noise has been removed is output.

Problems to be Solved by the Invention 1-However, in the configuration as described in "-", the amplitude limiting circuit 9
During the period where the amplitude is limited by (1-=O-tl), the signal becomes flat, so the noise during that period is not removed as shown in d of FIG. Moreover, the amplitude limit level BV
By removing this signal from the input signal a, waveform distortion occurs in the edge portion, thereby worsening the S/N ratio in this portion. Also, if you want to shorten the flat part of the amplitude limiting circuit 9141 force, you can reduce the time constant A of the feedback loop as described above.
) The band through which the signal passes becomes narrower and distorted due to the HPF characteristics of the equation. On the contrary, it is better to increase the time constant A in order to widen the passband and reduce the noise component on the low frequency side even a little (~). This has the problem that the period of the flat portion of the output becomes long, which has a large effect on the edge portion of the signal, and the output signal becomes easily distorted, making the design extremely difficult.

In view of these points, the present invention does not cause signal deletion in high-level signals such as the step signal shown in FIG. Another object of the present invention is to provide a video signal noise removal device with extremely small waveform distortion.

Means for Solving the Problems The present invention includes a differential circuit that extracts a change in an input signal per predetermined time, and a differential circuit that outputs a signal that is approximately proportional to the signal level when the signal level is small, but is proportional to the signal level when the signal level is large. a delay circuit that delays the signal by the predetermined time; a multiplier circuit that multiplies the output of the delay circuit by a predetermined value; and a subtraction N that subtracts the adder circuit output from the signal input to the difference circuit.
This is a noise removal device equipped with a.

The present invention has the configuration shown in the foregoing.Since the amplitude of the signal input to the feedback loop consisting of the delay circuit, the first multiplier circuit, and the addition circuit is limited, To perform noise removal with no signal deletion even for high-level signals, by edge partial cutting, and with less waveform distortion even when noise removal is performed by low frequency area cutting.

Embodiment FIG. 1 is a block diagram of a noise removal device in an embodiment of the present invention. In the figure, 12 is an input terminal for a video signal digitized with a sampling period T, and 13 is an input terminal T.
-12 is a difference circuit that extracts the change per time n times the sampling period T of the input video signal, and has a delay time n
The delay circuit 14 includes a delay circuit 14 having T, and a subtraction circuit 16 that subtracts the output signal from the input signal of the delay circuit 14.

16 is a nonlinear circuit that compresses the output of the differential circuit 13 substantially in proportion when the signal level is small, but nonlinearly compresses the signal level when the signal level is large; 17 is a delay circuit having the same delay time nT as the delay circuit 14; 18 is a multiplier circuit that multiplies the output of the delay circuit 17 by a predetermined value; 19 is an adder circuit that adds the output of the multiplier circuit 18 to the output of the nonlinear circuit 16 and leads it to the delay circuit 17; and 20 is an adder that adds signals input from the input terminal 12. A subtraction circuit 21 subtracts the output of the circuit 19, and an output terminal 21 outputs the output of the subtraction circuit 20 as a video signal with reduced noise.

Further, for simplicity, the difference circuit 13 is assumed to take out the change per unit time T of the input signal, assuming that the delay time of the delay circuit 14 is T (n=1), and the delay circuit 1γ also outputs the signal which has been switched. It is assumed that there is a delay of unit time T. Let A be the multiplier by which the multiplier circuit 18 multiplies the signal, and P be the coefficient by which the nonlinear circuit 16 nonlinearly compresses the signal. An example of the input/output relationship of the nonlinear circuit 16 is shown in FIG. 2 by the solid line in the figure. If the human power of the nonlinear circuit 16 is V□ and the output is vo, use the coefficient p fr.■. -P・■. In digital signal processing, an arbitrary P can be obtained using FtOM. The characteristic shown by the broken line in FIG. 2 is another example of P, and is also a broken line approximation shown by the solid line.

The characteristic shown by this broken line can be easily obtained using a multiplication circuit, an addition/subtraction circuit, and a switch circuit. below,
This will be explained using the broken line characteristic shown by this broken line. The broken line characteristic is that when the input V is 1≦V, the coefficient P is B and its output V. is V. -B, Vi, and in the switched ■□〉■, ■. The amplitude is limited to a constant value BV like -B・■.

The operation of the noise removal apparatus of this embodiment configured as described above will be described below using a two-conversion equation representing a discrete time system and operation waveform diagrams of each part.

The transfer function "(Z) of this embodiment is 10°, where P is the coefficient for compressing the signal of the nonlinear circuit 16 without switching. Here, the signal input to the nonlinear circuit 16,
The transfer functions 1 to z-1 of the output of the differential circuit 13 to the input signal to the input terminal 12 themselves exhibit the characteristics of the HPF.

Therefore, only the high frequency components of the input signal are input to the nonlinear circuit 16. When the signal level of this high frequency component is small,
As shown in FIG. 2, the coefficient P has a constant value B and outputs a signal proportional to the input signal level. If the coefficient P in the above equation (2) is a constant value B, the second term on the right side of the equation (2) will be the same as the above (1).
Same as H(7,) in the equation (it shows the characteristics of HPF, so it has the characteristic of attenuating only the high frequency range of the input signal input to the input terminal 12. However, if the nonlinear circuit 16 is input, the amplitude of the signal is limited and output as shown in Fig. 2, so that it is not subtracted from the input signal.From the above, the noise removal effect of this embodiment is effective in reducing the minute level superimposed on the video signal. Although high-frequency noise is removed, the nonlinear circuit 16 limits the amplitude of high-level signals that should be considered signals, so that no distortion occurs in the signals.

Next, the operation when the signal shown in FIG. 2a is input to the noise removal apparatus of this embodiment will be explained using the waveform diagram of the same figure.

Figure 2a is the same as Figure 5a used for explanation in the prior art section.
Similarly, it is a signal in which minute level high frequency noise is superimposed on a step signal that changes to a sufficiently large level U at time 1=0. When this signal a is input to the input terminal 12, the differential circuit 13 outputs J: a signal in which noise is superimposed on an impulse signal as shown in FIG. 2 (same as shown in FIG. 6 described above). The signal non-linear circuit 16 compresses the impulse-like signal exceeding the signal Q level V at time j=Q to the level BV, and multiplies the other minute level signals by 8 times 1 to 1. The delay circuit 17 in the subsequent stage multiplies the signal. It leads to a feedback loop composed of a circuit 18 and an addition circuit 19. At this time, the output of the feedback loop from the one-by-one adder circuit 19 changes from the signal level BV to the time constant (
The result is a signal in which noise is superimposed on a signal that converges to a signal level of 0 (determined by the multiplier A of the multiplier circuit 18). 3rd lease f
is a signal obtained by subtracting the signal e from the signal a by the subtraction circuit 2o, and is the output signal of the noise removal device of this embodiment, which is output from the output terminal 21. As can be seen by comparing the output signal f of the present embodiment with the output signal of the conventional noise canceling device in FIG.
Edge-to-edge unloading with large level changes can remove minute level high frequency noise. This is the subtraction circuit 2 from the input signal.
The signal e subtracted by o is at the signal level BV at time t-○, and after that time (1=0) the signal e is at the signal level O.
It converges to. On the other hand, in the conventional example, the signal level is BU when the time is 10, as in the sixth period C, and the signal level is O after time 1 = 0, so the signal subtracted from the input signal is BU. This is because the amplitude is limited by the amplitude limiting circuit 9 in the figure, and the period at time t1t becomes flat. In addition, in this example, the above 1 = eel flanno]
Since there is no edge part, even if the multiplier A of the multiplier circuit 18 is increased in order to increase the removal effect even for lower frequency noise, the waveform distortion in the edge part is small, and the noise removal effect is improved by edge-to-edge weighting. can be lost.

As described in -1- above, according to this embodiment, when the signal level is small, the nonlinear circuit compresses the input signal substantially proportionally, but when the signal level is large, the nonlinear circuit compresses the signal nonlinearly according to the signal level. A noise removal device is constructed by providing a differential circuit for extracting the change in the noise component and a feedback loop composed of a delay circuit, a multiplier circuit, and an addition circuit to extract the noise component. Therefore, even for an input signal that changes at a large level, there is no signal deletion at the edge, that is, no S/N deterioration at the edge, and the S/N improvement effect is achieved even at the very edge 1, and the signal is low. Even if noise in the frequency band is removed, waveform distortion can be reduced.

Finally, an example of the input/output characteristics of the nonlinear circuit 16 is shown in the second section.
Although the solid line and the broken line are shown in the figure, the nonlinear characteristic shown by the solid line is not essential, and the broken line approximate characteristic may be used. However, the compression level changes rapidly in response to changes in the human power level, so characteristics like the one shown by the solid line in Figure 2 are desirable.

As described in detail, according to the present invention, even if a high-level signal is input, signal deletion at the edge portion, that is, S/
It is possible to provide a video signal noise removal device that does not cause N degradation, has a noise removal effect right up to the edge, and has extremely low waveform distortion even when removing noise in the low frequency band. The effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a noise removal device according to an embodiment of the present invention, FIG. 2 is an input/output relationship diagram of a nonlinear circuit constituting the embodiment, and FIG. 3 is an operation waveform diagram of the embodiment. Fig. 4 is a block diagram of a conventional noise removal device, and Fig. 5 is an operating waveform diagram of the conventional example shown in Fig. 4. ... Delay circuit, 16.20 ... Subtraction circuit, 16 ... Nonlinear circuit, 18 ... Multiplication circuit, 19 ... Addition circuit, 21 ... ...Output terminal.

Claims (1)

[Claims] A difference circuit extracts the change in the input signal per predetermined time, a nonlinear circuit compresses the signal approximately proportionally when the signal level of the difference circuit output is small, but nonlinearly according to the signal level when the signal level is large; a delay circuit that delays the above-described predetermined time; a multiplier circuit that multiplies the output of the delay circuit by a predetermined value; an adder circuit that adds the output of the multiplier circuit to the output of the nonlinear circuit and leads it to the delay circuit; A noise removal device comprising: a subtraction circuit that subtracts from a signal input to a difference circuit.