JPH01190184A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the S/N of a video signal and to attain high picture quality by giving a characteristic close to a noise frequency characteristic to a limiter circuit of a noise rejection circuit and adjusting the noise rejection level in response to the quantity of the noise of frequency hand. CONSTITUTION:A video signal supplied from an input terminal 1 is given to a filter circuit 3 and a noise detection circuit 14 connected in parallel with a delay circuit 2. The circuit 14 detects the noise frequency component, selects the closest frequency characteristic to switch a frequency band variable limiter circuit 13. Thus, the noise rejection level is increased at the frequency hand having much noise and the level is reduced in less band, the result is fed to a subtractor 5 and outputted from a output terminal 6. Thus, the noise rejection circuit approximates the frequency characteristic of the circuit 13 with the frequency characteristic of noise, minimizes the missing of signal component thereby eliminating noise effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for removing noise from video signals of video equipment such as video tape recorders and video disc players.

[Prior Art] FIG. 5 is an example of a conventional noise removal circuit. The video signal supplied from input terminal 1 is sent to delay circuit 2.
The signal is supplied to the subtracter 5 via the subtracter 5, and is subtracted from the signal branched from the input section of the delay circuit 2 and passed through the filter circuit 3 and limiter circuit 4. The subtracted video signal is taken out as an output from the output terminal 6. A video signal containing noise supplied from the input terminal 1 is filtered out from a frequency band, such as a high frequency band, containing many noise components by a filter circuit 3, and a noise signal of a certain level is obtained by a limiter circuit 4. This signal is sent to the subtracter 5 and mixed with the video signal that has passed through the delay circuit 2. In this case, the limiter circuit 4 is for removing the signal component extracted by the filter while leaving only the noise component, and the delay circuit 2 is used in the subtracter 5 to control the phase of the video signal from the delay circuit 2 and the limiter circuit. This is to keep the phase of the noise from the circuit 4 consistent. If the phase of the video signal from the delay circuit 2 and the phase of the noise from the transmitter circuit 4 do not match, the noise will not be removed. That is, this is a method of removing noise by extracting only the noise component from the original video signal, inverting it, and adding it to the original video signal.

[Problems to be Solved by the Invention] However, although the noise in the video signal is distributed over a wide frequency band, the above-mentioned noise removal circuit
Since noise at a certain limiter level is added to the video signal in reverse phase, many signal components are also lost at the same time as the noise. This state is shown in FIG. 6, in which the horizontal axis 9 is the frequency coordinate, and the vertical axis 10 is the amplitude coordinate. A dotted line 8 shows the limiter level, and a curve 7 shows the frequency characteristics of noise. In the diagonally shaded portion 11 between the dotted line 8 and the curve 7 in FIG. 6, the level of the limiter is higher than the noise level, so signal components are removed unnecessarily. On the other hand, in the diagonal line 12 above the dotted line 8 and surrounded by the curve 7, the noise level is higher than the limiter level, so a phenomenon occurs in which noise cannot be removed sufficiently.

Since the conventional noise removal circuit is configured as described above, it is inevitable that signal components will be dropped during noise removal. Therefore, in order to prevent loss of signal components, a changeover switch or the like is required to disable the noise removal circuit.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a circuit that suppresses loss of signal components to a minimum and removes noise.

[Means for Solving the Problems] In the present invention, a circuit for detecting frequency components of noise contained in a video signal is provided, and the output of this circuit changes the operating range of the limiter circuit to a plurality of frequency bands. , the video signal passing through the delay circuit and the noise supplied from the limiter circuit are subtracted.

[Function] The noise removal circuit according to the present invention can make the frequency characteristics of the limiter circuit the same as the frequency characteristics of noise, so that noise can be effectively removed.

[Example] FIG. 1 is a block diagram of one embodiment of the present invention.

A video signal supplied from an input terminal 1 is supplied to an output terminal 6 via a delay circuit 2 and a subtracter 5. On the other hand, the video signal is branched from the input section of the delay circuit 2 and is supplied to the subtracter 5 via the filter circuit 3 and variable frequency band limiter circuit 13.

Further, the video signal is connected to the noise detection circuit 14 so that the output signal thereof controls the frequency band variable limiter circuit 13.

A schematic diagram of the variable frequency band limiter circuit 13 is shown in FIG. This circuit includes, for example, amplifiers 15, 16, and 17 having three different frequency characteristics, a switch 23 that switches between them, and connects them to the limiter circuit 4, and an amplifier 15.
16.17 Amplifier 20.2 with opposite frequency characteristics
1.22 to the limiter circuit 4, and a switch 24 which switches the outputs of these amplifiers and connects them to the subtracter 5. It is being done. If the noise detection circuit 14 detects the frequency component of noise contained in the video signal and the result has the characteristic of curve 7 in FIG. Alternatively, select from 17 and switch. A curve 15-1 in FIG. 2 is the frequency characteristic of the amplifier 15, and a curve 16-1 in FIG.
The curve 17-1 in FIG. 2d is the frequency characteristic of the amplifier 17. The frequency characteristic closest to curve 7 in FIG. 2a is that of curve 17-1 in FIG. The amplitude is made constant by an amplifier 22 with opposite characteristics. At this time, the amplifier 17 and the amplifier 22 are controlled by the noise detection circuit 14.
The switches 23 and 24 are operated and selected simultaneously. Switching between the amplifier 15 and the amplifier 20 and between the amplifier 16 and the amplifier 21 is also performed in the same manner as described above.
Depending on the frequency characteristics of the noise detected by No. 4, the switching is made in accordance with the frequency characteristics of the noise detected by No. 4. Since the amplifiers 15 and 20, the amplifiers 16 and 21, and the amplifiers 17 and 22 each have frequency characteristics that compensate for each other, the gain of the frequency band variable limiter circuit 13 is approximately constant regardless of the characteristics. It can be made so that

An example of a noise detection method at this time is to use a signal 18 that does not include video information before and after a vertical synchronization signal in a video signal, as shown in FIG. 3a, and to detect this signal. By extracting the part excluding the horizontal synchronizing signal using one gate pulse as shown in Figure 3 and detecting the alternating current component of that part, it is possible to detect noise components that are not affected by changes in the amplitude of video information. can.

In the above embodiment, three types of switching of the limiter circuit depending on the frequency characteristics of noise are shown, but the number of types can be increased or decreased as desired. Furthermore, if an amplifier circuit with characteristics similar to the frequency characteristics of noise can be obtained using digital technology or other methods, the frequency band can be changed steplessly.

Furthermore, although the above embodiment describes a case in which a filter is used as the noise extraction circuit, a noise removal circuit that uses linear correlation or vertical correlation without using a filter can also remove the noise detected by the limiter from the original. As long as the method cancels out the noise of the video signal, the same effect can be achieved by the limiter that can change the frequency band according to the present invention. .

[Effects of the Invention] As described above, according to the present invention, the limiter circuit of the noise removal circuit can have a frequency characteristic that approximates the noise frequency characteristic. In addition, in frequency bands with less noise, the noise removal level can be lowered to reduce video signal dropout, which has the effect of obtaining a higher quality video signal with improved S/N ratio. .

[Brief explanation of the drawing]

Figure 1 is a block diagram of a noise removal circuit according to an embodiment of the present invention; Figures 2a, b, c, and d are diagrams showing a comparison between the frequency characteristics of noise and the frequency characteristics of the amplifier of the limiter circuit; Figures a and b are diagrams showing signals used for noise detection, and Figure 4 is the frequency band variable limiter circuit 1.
3, FIG. 5 is a block diagram of a conventional noise removal circuit, and FIG. 6 is a diagram showing the limiter operation according to the conventional method. In the figure, 2 is a delay circuit, 3 is a filter circuit, 5 is a subtracter, 13 is a variable frequency band limiter circuit, and 14 is a noise detection circuit.

Claims (1)

[Claims] A circuit that detects frequency components of noise contained in a video signal, a limiter circuit whose operating range can be changed to multiple frequency bands using the output signal of this circuit, a circuit that delays the video signal, and a circuit that delays the video signal. A video recording and reproducing device comprising a circuit that subtracts a video signal output from the circuit and noise supplied from a limiter circuit.