JPH01190183A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE:To minimizingly suppress the missing of a signal part caused in case of a signal with less noise by changing a limiter level of a noise rejection circuit automatically depending on the quantity of noise included in a video signal. CONSTITUTION:A video signal supplied from an input terminal 1 is inputted to a filter circuit 3 and a noise detection circuit 7 connected in parallel with a delay circuit 2. The circuit 7 detects a noise level and if much noise exists, the level of the variable limitter circuit 8 is increased to eliminate the noise of a larger level included in the signal by outputting the resulting signal from a terminal 6 through a subtractor 5, but the level of missing signal is also increased. If noise is less, the limiter level is decreased, some noise component remains but the missing signal is less. Thus, the signal missing is minimized by the optimum noise rejection level.

Description

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

[Prior Art] FIG. 5 shows an example of a conventional noise removal circuit. The video signal supplied from input terminal 1 is sent to delay circuit 2.
and is taken out from the output terminal 6 via the subtracter 5. Further, the video signal is branched and connected to a subtracter 5 via a filter circuit 3 and a limiter circuit 4.

The operation of this circuit is as follows. From the video signal supplied from the input terminal 1, a filter circuit 3 extracts a frequency band with many noise components, such as a high frequency range, and a limiter circuit 4 obtains a signal at a constant level. Subtractor 5
, the video signal that has passed through the delay circuit 2,
The inverted signal from the limiter circuit 4 is added.

The limiter circuit 4 extracts only noise components from a frequency band with many noise components, and the delay circuit 2 matches the phase of the video signal supplied to the subtracter 5 with the phase of the noise that has passed through the limiter circuit. It is for.

If the signal passing through the delay circuit 2 and the noise supplied from the limiter circuit 4 do not match in phase, the noise will not be removed. That is, this is a commonly used method in which noise is removed 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, as described above, when a limiter circuit is used to extract only noise components, depending on the level of the limiter, signal components may be missing or the noise removal effect may be small. do. Furthermore, since the optimum limiter level etc. differs depending on the content of the signal, even if it is optimum for a certain signal, it may be inappropriate for another signal. The conventional noise removal circuit as described above inevitably loses signal components when removing noise. Therefore, in order to prevent loss of signal components, a changeover switch or the like may be required to disable the noise removal circuit.

The present invention has been made 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 Problem] The video recording and reproducing device according to the present invention automatically changes the level of the limiter according to the amount of noise detected by the noise detection circuit, and adjusts the level of noise passing through the limiter. This noise is then subtracted from the video signal that has passed through the delay circuit in a subtracter.

[Operation] The noise removal circuit according to the present invention detects the amount of noise components contained in a video signal, and changes the gain of the signal passing through the limiter circuit depending on the detected amount. This changes the limiter level isometrically and changes the level of noise removed. Therefore, an optimal noise removal level can be obtained and signal loss can be minimized.

〔Example] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a video signal supplied from an input terminal 1 is taken out from an output terminal 6 through a delay circuit 2 and a subtracter 5. Further, the video signal is branched before being supplied to the delay circuit 2, and is supplied to the subtracter 5 via the filter circuit 3 and the variable limiter circuit 8. A noise detection circuit 7 is provided in parallel with the filter circuit 3. The noise level is detected by the noise detection circuit 7, and if the noise 9 is large, the limiter level of the variable limiter circuit 8 is increased to the level indicated by the solid line 10 shown in FIG. 2(a). As a result, the noise that is removed becomes the solid line 14 in FIG. 2(c), and even high-level noise contained in the video signal can be removed. In this case, even large signals are lost.

However, when the amount of noise is large, noise removal takes priority over signal loss.

On the other hand, when the noise is small, the limiter level is reduced to the level indicated by the dotted line 11 shown in FIG. 2(a). As a result, the noise removed becomes the solid line 12 in FIG. 2(b), and the number of signals missing during this period can be reduced.

A dotted line 13 shown in FIG. 2(b) is a noise component that remains without being removed at that time. In this way, by changing the limiter level depending on the amount of noise contained in the signal, the S/N ratio can be improved in the case of a noisy signal at the expense of some signal component loss, and in the case of a signal with little noise component. , since there is no need to improve the S/N so much, the noise removal level is reduced so that the loss of signal components is reduced.

An example of how to detect the amount of noise at this time is as follows:
Using a signal 15 that does not include video information before and after the vertical synchronization signal in the video signal as shown in FIG. 3(a), the portion of this signal excluding the horizontal synchronization signal is shown in FIG. 3(b). By extracting the alternating current component using the gate pulse 16 such as that shown in FIG.

Further, the limiter level is changed by a circuit as shown in FIG. The variable limiter circuit 8 has a variable gain amplifier circuit 17 , a limiter circuit 4 , and a variable attenuation ratio attenuation circuit 18 connected in series. The gain or attenuation ratio can be changed. Gain of variable gain amplifier circuit 17 and variable attenuation ratio attenuation circuit 18
The amount of attenuation is controlled to be constant, and the gain of the variable limiter circuit 8 does not change as a whole.

In addition, in the above embodiment, the case was described in which the extraction for noise removal was performed by the filter circuit 3.
Even with other linear correlation systems, vertical correlation systems, etc., as long as the noise detected by the limiter is canceled out by the noise in the video signal, the same method as in the above embodiment can be achieved by changing the level of the limiter. It can be effective.

[Effects of the Invention] As described above, according to the present invention, the limiter level of the noise removal circuit can be changed depending on the amount of noise contained in the video signal. It is possible to minimize the amount of signal loss and obtain higher quality images. Furthermore, in the case of a video signal with a lot of noise, by increasing the noise removal level, it is possible to obtain a video reproducing device with a good S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the noise removal circuit according to the present invention, FIGS. 2(a), (b), and (c) are diagrams showing the relationship between the limiter level and the amount of noise removed; FIGS. 3(a),
(b) is a diagram showing a waveform for obtaining a signal for noise detection, FIG. 4 is a block diagram of the variable limiter circuit 8,
FIG. 5 is a block diagram of a conventional noise removal circuit. In the figure, 2 is a delay circuit, 3 is a filter circuit, 5 is a subtracter, 7 is a noise detection circuit, and 8 is a variable limiter circuit.

Claims (1)

[Claims] A circuit that detects the amount of noise contained in a video signal, a limiter circuit whose operating range is changed by the output signal of this circuit, a circuit that delays the video signal, and a video signal that has passed through the circuit that delays the video signal. A video recording and reproducing device comprising a circuit that subtracts and mixes noise whose amplitude is limited by a limiter circuit.