JPH0467272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a noise canceling circuit suitable for application to VTRs and the like.

BACKGROUND TECHNOLOGY AND PROBLEMS There is a noise cancel circuit configured as shown in FIG. 1, which is used, for example, in a reproduction system of a VTR and cancels noise contained in a luminance signal.

In Fig. 1, the current signal _IN consisting of the noise component S _N and the luminance signal S _Y supplied to terminal 1 (Fig. 2 A)
is the noise component in the frequency band of 1 to 2 MHz that is supplied to high-pass filter 2 and included in the current signal S _IN
Output S _H including S _N ′ and high frequency component Y _H of luminance signal S _Y
(B in the same figure) is output, and the output S _H is the limiter 3
The high-frequency component _YH above a predetermined level is milled, and its limiter output S _L (C in the same figure) is added to the current signal S _IN in reverse phase in the adder circuit 4, and is sent to terminal 5. A luminance signal S _Y from which the noise component S _N has been removed is obtained (D in the same figure).

In this case, the high frequency component Y _H added to the current signal S _O
has a relatively wide pulse width as shown in Figure 2C, so
As a result of the addition, the rising portion (video transient portion) of the luminance signal S _Y deteriorates, and the noise component S _N of this rising portion remains without being removed. In this example, about 400 nsec remains.

In order to eliminate this drawback, for example, the luminance signal is
It is possible to pre-emphasize the high-frequency component _YH of S _Y , but even if this is done, the noise component _S The noise component S _N included in the part cannot be removed.

OBJECTS OF THE INVENTION Therefore, in the present invention, it is possible to prevent signal deterioration in a video transient portion and to reliably remove noise components contained in this video transient portion.

Summary of the Invention Therefore, in the present invention, a first filter having a high cutoff frequency outside the video signal band;
A first limiter that limits the output, a second filter that has a low cutoff frequency that boosts the low range of the output, a second limiter that limits the output, and subtracts the output from the current video signal. A noise canceling circuit is configured with the subtracting circuit.

Embodiment Next, a case in which an example of the noise cancel circuit according to the present invention is applied to a reproduction system of a VTR will be described with reference to FIG. 3 and subsequent figures.

In FIG. 3, a current signal S _IN containing a noise component S _N and a luminance signal S _Y supplied to a terminal 1 is supplied to a high pass filter (first filter) 11. As shown in FIG. 4A, the cutoff frequency of this filter 11 is a frequency outside the video signal band (for example, 8
~10MHz, in this example 10MHz), and therefore, as shown in FIG. 5B, high-frequency noise components _NHH above the cutoff frequency are
A high-frequency luminance component _YHH having a steep differential characteristic is output.

Since the frequency characteristics below the cutoff frequency are selected as shown in the figure, the low frequency noise component _NLL and the low frequency luminance component _YLL below the cutoff frequency are also output with levels corresponding to the frequency characteristics.

This filter output S _F1 is supplied to the first limiter 12, and as shown in FIG. 5C, the high frequency luminance component _YHH above a predetermined level is milled out. In this case, the differential characteristic of the high-frequency luminance component Y _HH is steep, so even if the high-frequency luminance component Y _HH is limited, the noise component S _N contained in the high-frequency luminance component Y _HH is reduced by this limiter processing. Very few are erased.

The first limiter output S _L1 is supplied to a low pass filter (second filter), in this example a filter 13 having low frequency boost characteristics. The low cutoff frequency of this filter 13 is selected as a predetermined frequency within the video signal band, in this example 1.5MHz, as shown in FIG. be done. Therefore, this filter 13 is a double time constant type filter, and the combined frequency characteristic with the high-pass filter 11 becomes flat as shown in FIG. 4C.

As a result, from the filter _{13 ,} as shown in _FIG. High-band luminance signals Y _HH are output, respectively.

The second filter output S _F2 is further supplied to the second limiter 14 to reduce the low-frequency luminance component above a predetermined level.
Y _LL is limited (Figure 5E). The second limiter output S _L2 is supplied in an opposite phase to the adder 16 via a variable resistor 15 for fine level adjustment provided as required, and added to the current signal S _IN .

As a result, the current luminance signal S _Y from which the noise component S _N has been removed is obtained at the output terminal 17 (FIG. 5F).
In this case, the low-range luminance signal Y _LL included in the output S _F2 of the low-pass filter 13 is an extremely weak pulse signal, so even if it is added to the current luminance signal S _Y , the degradation of the video transient portion is extremely small. Moreover, since the waveform of this video transient portion is extremely slightly rounded, it is possible to reliably remove noise components included in this video transient portion.

In this invention, the first and second filters 11 and 13 are used to transmit the entire noise component band from low to high frequencies and add it to the current video signal S _Y. components can be removed.

In addition, in FIG. 3, a filter having an amplification function is used as the second filter 13, but as shown in FIG.
1 can achieve similar behavior.

Effects of the Invention As explained above, according to the present invention, it is possible to almost certainly remove noise components over the entire band included in a video signal, and also remove noise components included in video transient parts. can do. Furthermore, this noise removal operation can also minimize the deterioration of the video transient portion, thereby preventing deterioration of the resolution.

Therefore, the present invention is extremely suitable for application to a VTR playback system.

[Brief explanation of the drawing]

Figure 1 is a system diagram of an example of a noise canceling circuit, Figure 2 is a waveform diagram to explain its operation, and Figure 3
6 and 6 are system diagrams showing an example of the noise cancel circuit according to the present invention, and FIGS. 4 and 5 are waveform diagrams for explaining the respective operations. 11 is a first filter, 13 is a second filter, 12 is a first limiter, 14 is a second limiter, and 16 is an adder.

Claims (1)

[Claims] 1. A first filter that has a high cutoff frequency outside the video signal band, a first limiter that limits its output, a second filter that has a low cutoff frequency that boosts its output in the low range, and its output. a second limiter that limits the
and a subtraction circuit that subtracts the output from the current video signal.