JPH0472881A - Magnetic reproducing device provided with line noise camceller - Google Patents

Abstract

PURPOSE:To prefer the reproducibility of details in the case of the use of a video tape of less noise like a high-grade tape by suppressing the operation of a line noise canceller at the time when the level of a reproduced video signal is higher than a prescribed level. CONSTITUTION:A means 11 to detect the level of a reproduced video signal is provided, and a line noise canceller 19 is not operated when the reproducing level detected by the means 11 is higher than the prescribed level. Consequently, the reproducing level detected by this means 11 is higher than the prescribed level and the operation of the line noise canceller 19 is not operated when a high-grade tape is used. Thus, the reproducibility of the like of details is preferred when a video tape of less noise such as the high-grade tape is used.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic playback device such as a video tape recorder (hereinafter abbreviated as "VTR") and a videotape player (playback-only machine) equipped with a line noise canceller. It is something.

[Prior Art] A line noise canceler is generally known as a noise canceling means used in a reproduction circuit of a VTR. FIG. 2 shows an example of this line noise canceller, which is composed of an IH delay element 1 made of a CCD or the like, a first adder 2, a limiter 3, an attenuator 4, a second adder 5, etc. There is. Reference numeral 6 denotes an input terminal, to which a luminance signal reproduced by a video head (not shown) and FM demodulated is input, and the luminance signal is supplied to the IH delay element 1, adders 2 and 5. Ru. I
The H delay element 1 delays the luminance signal by one horizontal scanning period (hereinafter abbreviated as r I HJ), inverts the phase, and inputs the signal to the adder 2 . This adder 2 is I
The luminance signal before iH (with its phase inverted) delayed by the H delay element 1 is added to the undelayed original luminance signal, but since it is added to the luminance signal with its phase inverted, this Adder 2 acts as a subtracter.

Since the luminance signal can be considered to have a correlation with the luminance signal before IH, the output of the adder 2 provides a noise component that has no correlation. This minute level signal that can be regarded as a noise component is extracted by the limiter 3, and the level is attenuated to 1/2 by the attenuator 4, and the phase is inverted. This attenuated minute level signal is input to the adder 5, where it is substantially subtracted from the original luminance signal, and the minute level signal that can be considered as a noise component is removed from the original luminance signal, and the signal is sent from the output terminal 7 to the next stage. Output.

[Problems to be Solved by the Invention] By the way, the above-mentioned line noise canceler does not cancel only the noise component, but also subtracts a small level signal component (detail signal) to a certain extent, and its level becomes small.

Further, in the case of a luminance signal that is exactly the same as the luminance signal before lH and has a correlation with the luminance signal, there is no attenuation of the luminance signal, but when the correlation is lost, the level becomes smaller by the amount of the correlation.

A case where the correlation is exactly the same and a case where the correlation is different will be explained with reference to FIGS. 3 and 4. Figure 3 a-e
are cases of exactly the same correlation, a is the original signal, and b is I
This is the signal before H. These have the same phase relationship. C
shows the output of adder 2, which is 0 level. d is the output of the attenuator 4, which is also at 0 level. e is the output of the adder 5, and the same signal as the original signal shown in a above is obtained. C1 to C1 in Figure 3
is a case where the phase of the signal before IH is ahead of the original signal by 90 degrees, and this signal and the signal before IH are passed through limiter 3.
It is assumed that the signal is at a very small level and has no limitations. al is the original signal, expressed as sinθ, and bl is the signal before IH, 5in(θ+π/2), that is, 5i
It is expressed as n(θ+n/2)=cosθ. cl indicates the output of adder 2, and a 1 - b 1 =
sin θ−cos θ, and according to the composition formula, sin
θ-cos θ=-v'T 5in (θ-π/4).

dl is the output of attenuator 4, which is 1/1 of the level shown in C1.
2, that is, twin 5 inches (θ-π/4). eλ 1 is the output of the adder 5, and is expressed as sin θ−H (sin θ + 5 in (θ+π/4)).

As described above, the level of the original signal a1 is decreased by 30% in the output signal e1, and the phase is advanced by 45 degrees.

In general, small signals have less line-by-line correlation than large amplitude signals. A large amplitude signal cannot be recognized as a screen unless there is a correlation for each line, but a small signal can be recognized as a screen even if there is no correlation. As a small signal,
For example, there is no correlation in the case of unevenness of human skin. C2 to C2 in Figure 4 are cases where there is no correlation between the original signal and the signal before IH, C2 is a convex original signal, and b2 is a flat IH signal.
This is the signal before H. These original signals and the pre-IH signals have such small amplitudes that the amplitudes are not limited by the limiter 3. C2 shows the output of the adder 2, which is a convex signal that is the same as the original signal. d
2 is the output of the attenuator 4, which is a signal with an amplitude of 172 times that of the original signal. C2 is the output of the adder 5, and the a
The signal has an amplitude 1/2 of the original signal shown in 2.

In this way, although the line noise canceler reduces noise, it also has the disadvantage that the level of the detail signal decreases to a certain extent, and if the correlation with the brightness signal before IH is lost, the level decreases by the amount of the difference. .

On the other hand, recently, high-rate tapes, which have better performance than normal tapes, have been used as video tapes. This high-rate tape provides a higher level reproduction signal and has less noise than a normal tape.

The present invention aims to provide a magnetic playback device in which a line noise canceler is automatically disabled when using a video tape with low noise such as a high rate tape, giving priority to detail reproducibility. This is the purpose.

[Means for Solving the Problems] In order to solve the problems 1 and 2, the present invention is provided with means for detecting noise in a reproduced video signal, and when the reproduction level detected by the means is lower than a predetermined level. The line noise canceller is configured to stop operating when the noise level increases.

[Function] In the magnetic playback device equipped with the line noise canceler of the present invention configured as described above, when a high rate tape is used, the playback level detected by the means for detecting the bottom of the playback video signal is When the noise level becomes higher than a predetermined level, the line noise canceler stops operating.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram schematically showing the main parts of a VTR playback system. In FIG. 1, reference numeral 8 denotes a video tape, and a video signal reproduced from the tape by a video head 9 is amplified by a reproduction preamplifier 10, reproduced, and sent to a detector 11, an HP FI 2, and an LPF 13. Supplied. In the reproduction level detector, the level of the video signal, for example, the horizontal synchronizing signal, is sampled and held, and the level of the video signal is detected as a DC level. This detected DC level is input to a comparator 14 and compared with a reference voltage from a DC voltage source 15. This reference voltage is set to a value higher than the recording/reproduction level when a standard tape is used as the videotape 8. When the DC level is higher than the reference voltage, a switch 16, which will be described later, is opened, and when it is lower, the switch is closed.

In the HP F 12, a luminance signal is extracted from the video signal, and this luminance signal is sent to the FM by a luminance signal processing circuit 17.
The signal is demodulated, and further de-emphasized by a main day emphasis 18 and supplied to a line noise canceller 19. This line noise canceller 19 is composed of an IH delay element 1, an adder 2, a limiter 3, an attenuator 4, an adder 5, etc., as described in the conventional example, and further includes an attenuator 4, an adder 5, etc. It has the aforementioned switch 16 interposed between the two. When this switch 16 is closed, the signal from the attenuator 4 is supplied to the adder 5, and the line noise canceller 19 is activated, but when the switch 16 is opened, the signal from the attenuator 4 is supplied to the adder 5. 5 is cut off, and the line noise canceller 19 becomes inactive.

The luminance signal from the main day emphasis 18 is supplied to the noise canceller 20 after passing through the line noise canceller 19 (without passing through the line noise canceller when the line noise canceler 19 is inactive). As is well known, this noise canceler uses a filter to separate the high-frequency components in the reproduced luminance signal where noise tends to concentrate, and then extracts the low-level signal components using a slice circuit, and converts these high-frequency and low-level signals into noise. It is configured to subtract it from the original luminance signal. The luminance signal that has passed through the noise canceller 20 is supplied to an adder 21 .

The L P F 13 extracts only the color signal that has undergone low frequency conversion from the video signal from the reproduction preamplifier 10 and supplies it to the color signal processing circuit 22 . This color signal processing circuit 22 converts the color signal that has undergone low frequency conversion into a color signal of a subcarrier band.

The color signal from the color signal processing circuit 22 and the luminance signal from the noise canceller 20 are added by the adder 21, and supplied to a CRT or the like (not shown) via the output terminal 23 to reproduce a color image.

In the VTR, when a normal tape is used as the videotape 8, the DC level from the playback level detector 11 is lower than the reference voltage from the DC voltage source 15, so the switch 16 is closed. Therefore, the line noise canceller 19 is in an operating state. On the other hand, when a high rate tape is used, the above-mentioned DC level from the reproduction level detector 11 is higher than the above-mentioned reference voltage from the DC voltage source 15, and therefore the switch 16 is opened, so that the line noise canceller 19 becomes inactive.

[Effects of the Invention] As described above, the present invention delays the luminance signal of the reproduced video signal by one horizontal scanning period, subtracts the delayed luminance signal and the undelayed original luminance signal using a subtracter, and calculates the luminance signal of the reproduced video signal by one horizontal scanning period. A magnetic reproducing device equipped with a line noise canceller that extracts only a minute level signal that can be considered as a noise component from the subtracted signal using a limiter, and subtracts this minute level signal from the luminance signal to substantially cancel out the noise component. The line noise canceler is configured to include means for detecting a noise in the reproduced video signal, and to cause the line noise canceler to stop operating when the reproduction level detected by the means becomes higher than a predetermined level. When using a video tape with low noise such as a high-rate tape, priority is given to detail reproducibility, and the line noise canceller can be automatically set to a non-operating state.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention,
This figure schematically shows the main parts of a VTR playback system. FIG. 2 is a block diagram showing the configuration of a conventional line noise canceller, and FIGS. 3 and 4 are waveform diagrams for explaining the operation of the one shown in FIG. 1: IH delay element, 2: Adder, 3: Limiter, 4
- Attenuator, 5: Adder, 8: Videotape, 9: Video head, 10: Playback preamplifier, 11: Playback level detector, 14: Comparator, 15: DC voltage source, 16: Switch, 19 Ni-line noise Canceler.

Claims (1)

[Claims] The luminance signal of the reproduced video signal is delayed by one horizontal scanning period,
This delayed luminance signal and the undelayed original luminance signal are subtracted by a subtracter, and from the subtracted difference signal, only a minute level signal that can be considered as a noise component is extracted by a limiter. A magnetic reproducing device equipped with a line noise canceler that substantially cancels noise components by subtracting it from a luminance signal of the video signal, the magnetic reproducing device comprising means for detecting the level of a reproduced video signal, and the reproduction level detected by the means is set to a predetermined level. 1. A magnetic reproducing device equipped with a line noise canceler, characterized in that the line noise canceler is configured to stop operating when the noise level becomes higher than .