JPH0416075A - Nonlinear filter circuit - Google Patents

Abstract

PURPOSE:To improve the S/N effectively without concentration of noise onto a picture edge by extracting a low frequency component through a variable coefficient circuit extracting a high frequency component and whose output is smaller as an input level is higher, multiplying the low frequency component with the above-mentioned high frequency component and subtracting the product from an input signal. CONSTITUTION:Only a high frequency component is extracted from an inputted video signal by using a high pass filter 2. A variable coefficient circuit 3 whose output is smaller as the input signal is higher is employed and a low pass filter 4 is provided to the output of the circuit 3. An output of the low pass filter 4 is multiplied with an output of the high pass filter 2 at a multiplier circuit 5, an output of the multiplier circuit 5 is subtracted from the input signal at a subtractor 6 to realize the nonlinear filter circuit which eliminates noise effectively without concentration of noise to the edge.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a nonlinear filter circuit such as a noise canceler circuit used for effectively removing noise from a video signal in a VTR or the like.

2. Description of the Related Art Conventionally, a maze canceller circuit has been used in playback devices such as VTRs to improve the S/N ratio of video signals.

FIG. 4 is a block diagram showing the configuration of a conventional noise canceler circuit. A high-pass filter (HPF) 21 extracts high frequency components from the video signal input from the input terminal 20. This signal is then input to the limiter circuit 22. Since the limiter circuit 22 has a characteristic of allowing the signal to pass only when the input signal is lower than a certain level, the output of the limiter circuit 22 shows only a signal with a small level among the high frequency components of the video signal input to the input terminal 20. .

Next, this signal is subtracted from the original input video signal by the subtraction circuit 28 and outputted to the output terminal 24. Therefore, low-level high-frequency components of the input video signal are removed from the signal appearing at the output terminal 24, resulting in a signal with an improved S/N ratio.

Such an example is shown in "Video Technology Handbook" (Denpa Shimbunsha), pp. 85-87.

Problems to be Solved by the Invention However, the above configuration has a drawback in that noise is noticeable at the edge portions of the input signal. Since the level of high-frequency components in the edge portion is high, the output of the IJ emitter circuit 22 is small, and the input video signal appears at the output terminal 24 as it is. In other words, noise at the edges is not removed. However, noise is removed before and after the edge,
Since the S/N is improved, the S/N of the edge part is displayed on the playback screen.
There was an issue where N suddenly changed and the noise appeared to be concentrated.

Means for Solving the Problems In order to solve the above problems, the nonlinear filter circuit of the present invention includes a high-pass filter for extracting high-frequency components of an input video signal, and an output of the high-pass filter is input, and the input level thereof is high. a variable coefficient circuit whose output becomes smaller as the frequency increases; a low-pass filter that extracts a low frequency band from the output of the variable coefficient circuit; a multiplier circuit that multiplies the output of the 0-has filter by the output of the high-pass filter; It is composed of a subtraction circuit that subtracts the output signal of the multiplication circuit from the signal.

Effect: With the above-described configuration, the present invention can provide a nonlinear filter circuit that effectively reduces noise without concentrating noise on the edge portions.

EXAMPLE Hereinafter, a nonlinear filter circuit of the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 3(b) is a characteristic diagram showing the input/output characteristics of the variable coefficient circuit 3 of the embodiment shown in FIG. In FIG. 1, an input video signal is passed through a high-pass filter 2 in which only high-frequency components are extracted.

In the conventional example, this high frequency component was passed through the limiter circuit 22 only when the level was low. The input/output characteristics of the limiter circuit 22, for example, as shown in FIG. 3(a), allow the signal to pass only when the input signal level is low.
This circuit can be thought of as a variable gain amplifier whose gain changes depending on the input level.

In this case, the gain decreases as the input signal becomes larger, so if a variable coefficient circuit 3 with input/output characteristics as shown in FIG. 3(b) is used, and the gain is controlled by its output, a limiter circuit Characteristics similar to those of No. 22 can be obtained. Therefore, in this embodiment, a variable coefficient circuit 3 having input/output characteristics shown in FIG. 3(b) is used. If the output of the variable coefficient circuit 3 is directly input to the multiplication circuit 5, characteristics similar to those of the conventional example can be obtained as described above. In this embodiment, a low-pass filter 4 is provided at the output of the variable coefficient circuit 3 in order to avoid concentration of noise on the edge portion, which is a drawback of the conventional example. The variable coefficient circuit 3 changes the coefficient according to the input and outputs it, but when noise is superimposed on the input, the output coefficient changes due to the input noise. This fluctuation is removed by a low-pass filter 4. Therefore, by multiplying the output of the low-pass filter 4 and the output of the high-pass filter 2 by the multiplication circuit 5, and by subtracting the output of the multiplication circuit 5 from the input signal by the subtraction circuit 6, it is possible to effectively prevent noise from concentrating on the edge portion. A nonlinear filter circuit that removes noise can be realized.

The above processing can be easily done using digital signal processing.
In that case, the variable coefficient circuit 3 is equipped with a ROM (Read Only Memo) in which input/output characteristic data is written in advance.
rY: read-only fist memory) can be used.

Next, a specific embodiment corresponding to the second invention will be described with reference to FIG. In this embodiment, an equalizer circuit 8 is provided between the high-pass filter 2 multiplier circuit 5 of the first embodiment, thereby making it possible to finely adjust the frequency characteristics of the nonlinear filter circuit. In the first embodiment, the input/output frequency characteristics may differ slightly due to the difference in configuration from the conventional example.

In particular, differences occur in frequency characteristics when the input signal is small. This difference does not pose any problem in terms of the function of removing noise, but if you want to obtain the same characteristics as the conventional example, by providing the equalizer circuit 8 as in this embodiment, you can achieve the same characteristics as in the first embodiment. In addition to the effects, it is possible to achieve the same frequency characteristics as the conventional example. If the gain of the equalizer circuit 8 in the first embodiment is lower in the high range than in the conventional example, the equalizer circuit 8 may have a characteristic that reduces the gain in the -1000 range.

Effects of the Invention As described above, the nonlinear filter circuit of the present invention effectively improves S/N without concentrating noise on the edge portions of an image.
can be improved.

Furthermore, the present invention can adjust the frequency characteristics by providing an equalizer circuit at the input of the multiplication circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a nonlinear filter circuit according to a first embodiment of the present invention, and FIG.
FIG. 3(a) is a characteristic diagram showing the input/output characteristics of the limiter circuit in the conventional example, and FIG. 3(b) is the variable gain circuit of the present invention. FIG. 4 is a block diagram showing the configuration of a conventional nonlinear filter circuit. 2...High pass filter, 3...Variable coefficient circuit, 4...Low pass filter, 5...Multiplication times o,
8... Equalizer circuit. Name of agent Patent attorney Awano m4 Haka 1 person 1 Figure 3 Figure input Figure 4

Claims (2)

[Claims] (1) a high-pass filter that extracts high-frequency components of an input video signal; a variable coefficient circuit to which the output of the high-pass filter is input and whose output decreases as the input level increases; and a variable coefficient circuit that reduces the output of the variable coefficient circuit. A nonlinear filter circuit comprising: a low-pass filter that extracts a frequency range; a multiplier circuit that multiplies the output of the low-pass filter and the output of the high-pass filter; and a subtraction circuit that subtracts the output signal of the multiplier circuit from the input signal. (2) a high-pass filter that extracts high-frequency components of an input video signal; a variable coefficient circuit to which the output of the high-pass filter is input and whose output decreases as the input level increases; and a variable coefficient circuit that reduces the output of the variable coefficient circuit; an equalizer circuit that adjusts the frequency characteristics of the output of the high-pass filter; a multiplier circuit that multiplies the output of the low-pass filter and the output of the equalizer circuit; and an output of the multiplier circuit from the input signal. A nonlinear filter circuit comprising a subtraction circuit that subtracts a signal.