JPS634754B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise reduction circuit, which separates the high-frequency component from the information signal by subtracting a signal obtained by delaying the information signal and removing the high-frequency component from the information signal. It is an object of the present invention to provide a noise reduction circuit that obtains an information signal from which the high-frequency component has been removed by subtracting the high-frequency component, and can reliably remove noise components, especially immediately after the rise of the information signal.

Small household magnetic recording and reproducing devices (hereinafter referred to as VTRs) are particularly equipped with a so-called noise reduction circuit that removes noise components superimposed on the FM demodulated reproduced brightness signal in the reproduction system.
Various circuits have been proposed in the past. FIG. 1 shows a block system diagram of an example of a conventional noise reduction circuit.

A part of the FM demodulated reproduced luminance signal containing noise components that has entered input terminal 1 is passed through high-pass filter 2.
The high frequency components are separated by the limiter 3, and the amplitude of the large amplitude components which are signal components is limited by the limiter 3. Only the small amplitude components considered to be noise components are taken out as they are and supplied to the adder 4 in reverse phase. On the other hand, the other part of this reproduced luminance signal is supplied as is to the adder 4 in the same phase. The adder 4 subtracts the noise component from the reproduced luminance signal on which the noise component has been superimposed, and the output terminal 5 takes out the reproduced luminance signal from which the noise component has been removed.

However, since this circuit uses a high-pass filter 2 and a limiter 3 as means for extracting noise components, as shown in Fig. When you do this, emphasis is being performed, so
This method has the drawback that it cannot remove the noise component n, which has a poor signal-to-noise ratio and requires high-precision noise removal in this area, making it impossible to obtain a high-quality image.

The present invention eliminates the above drawbacks, and the third
An example will be described below with reference to the drawings.

FIG. 3 shows a block system diagram of one embodiment of the noise reduction circuit according to the present invention. In the same figure, FM including noise components that entered input terminal 1
Demodulated reproduced luminance signal a (FIG. 4A is the rise time (0.5 μsec to 2 μsec) of the low-pass filter 6, which will be described later)
The signal is delayed by the delay circuit 8 having a delay amount of (1H - Δ) (H is one horizontal scanning period) where Δ is Δ. That is, the output of the delay circuit 8 is a signal b approximately 1H before the signal a as shown in FIG. C in FIG. 4, and is supplied to the adder 7 in reverse phase.However, since a low-pass filter generally has an integral action, the signal c rises with a certain time constant, and its waveform is somewhat rounded.

On the other hand, the reproduced luminance signal a is supplied to the adder 7 and the adder 4 in the same phase. In the adder 7, the signal a
The signal c is subtracted from the signal c to obtain only the high-frequency component, and the limiter 9 limits the amplitude of only the large amplitude signal component, which is the signal component, and outputs only the small amplitude component, which is considered to be a noise component, as it is, and the output of the limiter 9 is It is supplied to the adder 4 in reverse phase. At this time, since the adder 7 subtracts the fully risen H level signal of the signal c from the signal a, it is possible to reliably separate out the noise component of the signal a, especially immediately after the rise.

In the adder 4, the noise component of the output of the limiter 9 is subtracted from the signal a, and the noise component of the output of the limiter 9 is subtracted from the signal a.
A reproduced luminance signal d from which noise components have been removed is extracted as shown in Figure D. In addition, from signal a to signal c
When subtracting, signal c has a certain falling time constant, so the noise component of this falling part cannot be completely extracted. Although some noise remains immediately before the start, the falling noise of the VTR's reproduced brightness signal is generally smaller than the noise immediately after the rise, and the noise in this part is less noticeable than the noise immediately after the rise, so it is necessary to completely eliminate this noise. Even if it cannot be removed immediately, there is practically no problem.

Furthermore, the removal of the noise component immediately before the fall can be performed in combination with conventional methods.

FIG. 5 shows a block system diagram in which the circuit of the present invention is applied to an actual VTR, in which the same components as in FIG. 3 are given the same numbers. In the same figure, FM
A video signal is reproduced by a magnetic head 11 from a magnetic tape 10 on which a modulated luminance signal and a carrier color signal subjected to low frequency conversion are superimposed and recorded.
a′ is separated and extracted. Note that the carrier color signal system is omitted.

The luminance signal a' is amplitude limited by the limiter 14 and then FM demodulated by the FM demodulator 15 to form the signal a, which is supplied in phase to the adder 7 while being delayed by the delay circuit 8 and sent to the limiter 16. After the amplitude is limited at , the signal is FM demodulated into a signal b, which is converted into a signal c by a low-pass filter 6 and supplied to an adder 7 in reverse phase. Since the subsequent operations are similar to those described in FIG. 3, their explanation will be omitted.

According to this luminance signal reproduction system, the timing of the luminance signal taken out from the output terminal 5 remains the original luminance signal and is not delayed, so that the carrier color signal system can be processed with the same timing.

As described above, the noise reduction circuit of the present invention includes a filter circuit that removes high-frequency components after delaying an information signal by a predetermined amount, and a filter circuit that removes high-frequency components after delaying an information signal by a predetermined amount. For the arithmetic circuit and the output of this arithmetic circuit,
We installed a limiter that limits the amplitude of the large amplitude component that is the signal component, and outputs the small amplitude component that is considered to be a noise component as is, and a circuit that subtracts the output of the limiter from the information signal. In particular, it is possible to reliably separate the noise component immediately after the rise, thereby reliably removing the noise component. In particular, when applied to a noise reduction circuit for the brightness signal of a VTR, the noise component of the brightness signal can be removed using a high-pass filter. Compared to conventional circuits that separate the noise components using a chisel and subtract this noise component from the luminance signal, it is possible to reliably remove the noise component immediately after a sudden change from black to white, resulting in a high-quality image. Furthermore, since the luminance signal is taken out as is without being delayed, it has the advantage of not requiring a circuit for matching the timing with the carrier color signal system.

[Brief explanation of the drawing]

1 and 2 are block system diagrams and their output signal waveform diagrams, respectively, of an example of a conventional circuit, and FIGS. 3 and 4, A to D, are block system diagrams and their operations, respectively, of an embodiment of the circuit of the present invention. Explanatory signal waveform diagram, 5th
The figure is a block system diagram in which the circuit of the present invention is applied to a brightness signal reproducing system of a VTR. 1...Input terminal, 4, 7...Adder, 5...Output terminal, 6...Low pass filter, 8...Delay circuit,
9...Limitsuta.

Claims (1)

[Claims] 1. In a noise reduction circuit that separates and extracts a noise component from an information signal, calculates the information signal and the noise component, and removes the noise component from the information signal, after delaying the information signal by a predetermined amount. A filter circuit that removes high-frequency components; an arithmetic circuit that subtracts the output of the filter circuit from the information signal to separate and extract the high-frequency components; and a large amplitude signal component for the output of the arithmetic circuit. 1. A noise reduction circuit comprising: a limiter that limits the amplitude of components and outputs small amplitude components considered to be noise components as they are; and a circuit that subtracts the output of the limiter from the information signal.