JPS5953602B2 - Noise removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal device, and in particular, it is an object of the present invention to provide a noise removal device that removes noise in a low frequency band from a reproduced video signal.

Conventional home video tape recorders have ample frequency range, and even if the reproduced video signal contains noise over the entire frequency band, the noise in the high frequency band is visually noticeable. For this reason, the main purpose of this method was to remove noise in this high frequency band, but as home video tape recorders have become more compact in recent years, the use of shorter wavelength bands and the addition of more metal to reproduced video signals, etc. The noise components are different from those of conventional noise, and it is now necessary to remove noise in a lower frequency band than before. First, a conventional noise removal device will be explained with reference to FIGS. 1 to 3. In FIG. 1, 1 is a buffer circuit;
2 is a high-pass filter, 3 is a beam transmitter circuit, 4 is a phase inversion circuit, and 5 is a mixer.

Now, the buffer circuit 1 and the high-pass filter 2 have a second
When the reproduced video signal shown in FIG. 3A having the frequency characteristics shown in FIG. 3B is input, the reproduced video signal shown in FIG. 3 having the frequency characteristics shown in FIG. That is, this reproduced video signal has a differentiated waveform because the high-pass filter 2 constitutes a differentiating circuit. The reproduced video signal is suppressed to within a certain amplitude by the transmitter circuit 3, and then phase inverted by the phase inversion circuit 4 and input to the mixer 5. In this mixer 5, the reproduced video signal that has passed through the buffer circuit 1,
The signal passed through the phase inversion circuit 4 is added to output the reproduced video signal shown in FIG. 3C having the frequency characteristics shown in FIG. 2C. However, noise appears in the reproduced video signal shown in FIG. That is, in the limiter circuit 3, since the noise in the period A having an amplitude greater than a certain amplitude has been removed, the reproduced video signal that has passed through the buffer circuit 1 and the limiter circuit 3
Naturally, noise as shown in B in FIG. 3 appears in the difference signal between the signal and the signal that has passed through. As described above, noise that cannot be removed by conventional noise removal devices has caused deterioration in image quality in small video tape recorders.

The present invention eliminates the drawbacks of the conventional noise removal device described above, and in particular completely removes noise in the video band. An embodiment of the present invention will be described below with reference to FIGS. 4 to 6.

FIG. 4 is a block diagram of a noise removal device showing one embodiment of the present invention.

In this FIG. 4, reference numeral 11 is an input terminal, and the reproduced video signal of FIG. 6a having the frequency characteristics shown in FIG.
high-pass filter 13, second high-pass filter 14
is input. Note that the cutoff frequency FCl of the first high-pass filter 13 is set lower than the cutoff frequency FC2 of the second high-pass filter 14. The output of the first high-pass filter 13 has the reproduced video signal NA? of FIG. 6b having the frequency characteristics shown in FIG. 5b. 5ζ appears.
On the other hand, the output of the second high-pass filter 14 is as shown in FIG.
The reproduced video signal N of FIG. 6c has the high frequency characteristics shown in FIG.
B appears, and the phase of this reproduced video signal is inverted by the phase inverting circuit 15 and inputted to the mixer 16. In this mixer, the reproduced video signal NA that has passed through the first high-pass filter 13 and the reproduced video signal that has passed through the phase inversion circuit 15 are combined after matching their respective maximum amplitudes E8l and e82. The signal Nc shown in FIG. 6d having the frequency characteristic shown in FIG. 5d is output. However, this signal Nc in FIG.
contains a large amplitude signal (not shown) for an extremely short period of time, so the limiter circuit 17 at the subsequent stage suppresses this large amplitude signal to within a certain amplitude. The signal that has passed through the limiter circuit 17 mainly contains only noise components. 2.The phase of the signal that has passed through the limiter circuit 17 is inverted by a phase inversion circuit 18. input to mixer 19; In this mixer 19, the reproduced video signal that has passed through the buffer arrow circuit 12 and the signal that has passed through the phase inverter circuit 18 are combined, and a sixth signal having the frequency characteristics shown in FIG. The reproduced video signal shown in Figure e is output. Although this output playback video signal contains high-frequency noise, it has almost no visual impact on a small home video table recorder, and there is no waveform deletion at the rising edge of the signal. 6. You can get a sharp and tight screen. As described above, according to the present invention, it is possible to uniformly remove noise components in a specific frequency band and to obtain a playback video without waveform deletion, which is particularly suitable for small home video tape recorders. With this, the screen becomes tight and tight, and certain noises no longer stand out.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional noise removal device, Figure 2 A, C, and C are frequency characteristic diagrams of the main parts of the same device, and Figure 3 A, C, and C are frequency characteristic diagrams of the main parts of the same device.
C is a waveform diagram of the main part of the same device; FIG. 4 is a block diagram of a noise removal device showing an embodiment of the present invention; FIGS. 5A, b, c,
d, e are frequency characteristic diagrams of the main parts of the same device, Figure 6 A, b, c
, d, and e are waveform diagrams of the main parts of the same device. 13, 14... High pass filter, 15, 18
... Phase inversion circuit, 16, 19 ... Mixer, 17 ... Limiter circuit.

Claims (1)

[Claims] 1. A first means for extracting a reproduced video signal in a high frequency band from a reproduced video signal, a second means for extracting a reproduced video signal only in a high frequency band higher than the high frequency band, and a reproduced video obtained by the first means. a third means for obtaining a first difference signal which is the difference between the signal and the reproduced video signal obtained by the second means; and a fourth means for suppressing the first difference signal to a signal having a predetermined amplitude or less. and means for extracting a second difference signal that is the difference between the reproduced video signal and the signal obtained by the fourth means.