JPH0468692A - Noise canceller for magnetic reproducing device - Google Patents

Abstract

PURPOSE:To eliminate mesh noises in a reproduced screen by providing a chroma level detector detecting the level of a regenerated chroma signal and controlling the slice level of a slice circuit so as to be increased as the detected chroma level is increased. CONSTITUTION:The slice level of a slice circuit 12 is controlled to be decreased as the reproduction level of an FM luminance signal is increased, and to be increased as the level of the chroma signal is increased. Therefore, even when the reproduction level of the FM luminance signal is increased and the noise cancel amount is decreased, the noise cancel amount is increased when the level of the chroma signal is high, and unnecessary components are cancelled. Thus, the luminance signal, in which the noises are cancelled, reaches an adder 15 from a subtracter 13, is added with the chroma signal from a chroma signal processing circuit 7 by the adder, outputted from an output terminal 16, and the reproduced screen can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a noise canceler in a magnetic playback device such as a video tape recorder (hereinafter abbreviated as "VTRJ") or a videotape player (playback only machine). be.

[Prior Art] Generally, a noise canceller used in a VTR reproduction circuit uses a filter to separate high-frequency components in reproduced luminance signals where noise tends to concentrate, and then uses a slice circuit to extract low-level signal components. , and is configured to treat low-level signals as noise and subtract them from the original signal.

Since the above noise canceler uniformly cancels high-frequency and low-level signal components, it also cancels original signal components other than noise. In this sense, the smaller the amount of cancellation, the better.

Therefore, the characteristics of a noise canceller are the S/N of the video,
It is decided based on the consideration of resolution.

Incidentally, the resolution and resolution of the reproduced brightness signal of a VTR are greatly influenced by the level of the signal extracted from the tape.

In addition, in recent years, the performance of tapes has rapidly improved, and so-called high-grade tapes have become more popular, but when comparing high-grade tapes and ordinary tapes (normal tapes), there is a difference of more than 3 dB in playback level. Sign.

When such a high-grade tape is used, the amount of cancellation by the noise canceller can be kept low; on the other hand, the larger the amount of cancellation, the more the resolution deteriorates. Since there are various tape performances as described above, there is also known a noise canceler in which the amount of cancellation of the noise canceller is varied depending on the playback level (see Japanese Patent Application Laid-Open No. 14178/1999).

The outline of the noise canceler disclosed in this publication is as follows.

That is, an FM reproduction level detector for detecting a reproduction level of a reproduction preamplifier that amplifies an FM luminance signal reproduced from a videotape, means for extracting a noise component from a luminance signal demodulated from the FM luminance signal, and the noise component. a slicing circuit having a slicing level for removing components larger than a predetermined level from the slicing circuit, and this slicing level is controlled to become smaller as the reproduction level becomes larger;
The noise canceller includes a subtracter that subtracts the output of the slice circuit from the luminance signal.

By the way, when a color video signal is reproduced by a VTR and the luminance signal is demodulated, the demodulated luminance signal has approximately 1
, 2M1 (Z) is known to exist.The level of this unnecessary component increases as the level of the reproduced chroma signal increases, that is, the color saturation increases.

The reason why this unnecessary component is generated will be explained.

In the case of magnetic recording in a VTR, the recording current is subjected to third-order distortion due to hysteresis characteristics and is magnetized on the tape.

Assuming that the luminance FM signal is As1nα and the low-frequency conversion color signal is B sinβ, then on the tape it becomes the same as the following equation.

y = (Asina + Bs1nβ)3= A 3
sin3a + B 3sin3a+3A2Bsin2
aφSInβ+3AB2sinαesin2β brightness FM
Signal component = A 3 sin 3 a low frequency conversion color signal component =
B 3sin3a then 3A 2B 5in2α-si
nβ; Expand 3A B 2sina・5in2β.

5in2a ・sinβ= −((os(α−β)−c
os(α+β))”sin α=−(coscα−β)@SInα−CO8(α; ÷β)aSInα) =1(CO5(α−β)−sinβ−(os(α+βdoorsinβ)−sin(α+β -β))] = -(2sina -5In(a-2β)-5in(
α+2β)) −sin(α+β−α))] = ? (sin(2α-β)-sin(2a+β)-
sin(-β)+sinβ) Similarly, 5ina ・5in2β=yu(cos(a-β)-CO
8((!+β)) space conflict sinβ becomes 0 as the slice level increases as described above.
The above-mentioned unnecessary components s and d are also canceled.

However, when canceling noise in a luminance signal reproduced from a high-grade tape, and when playing back an animation-like image with high color saturation, even though the slice level is small, Since the levels of the unnecessary components s and d are relatively large, the unnecessary components are not canceled.

If the above-mentioned unnecessary components s and d are present in the luminance signal, mesh-like noise will appear all over the reproduced screen, making it extremely difficult to see.

Note that in the case of a screen with low color saturation, the levels of unnecessary components b and d are low even if the signal is reproduced from a high-grade tape, and therefore the mesh noise described above does not occur.

It is an object of the present invention to provide a noise canceler that also prevents the occurrence of the mesh noise described above.

[Means for Solving the Problems] In order to solve the above ':jB, the present invention includes an FM reproduction level detector that detects the reproduction level of the reproduced FM luminance signal, and an FM reproduction level detector that detects the reproduction level of the reproduced FM luminance signal. A slicing circuit having means for extracting a noise component from a luminance signal, and a slicing level for removing a component larger than a predetermined level from the noise component, and the slicing level is controlled to become smaller as the reproduction level becomes larger. ,
A noise canceler in a magnetic reproducing device that includes a subtracter that subtracts the output of the slice circuit from the luminance signal includes a chroma level detector that detects the level of the reproduced chroma signal. A noise canceler in a magnetic reproducing device characterized in that the slice level of the slice circuit is controlled to be increased.

[Function] In the noise canceller in the magnetic reproducing device of the present invention configured as described above, the higher the reproduction level of the reproduced FM luminance signal, the smaller the amount of cancellation becomes, improving the resolution, and the chroma level of the reproduced chroma signal increases. In this case, the amount of cancellation becomes large, the unnecessary components included in the luminance signal are removed, and mesh noise does not occur on the reproduced screen.

[Example 1] An example 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 1 denotes a video tape, and a color video signal recorded on the tape is reproduced by a video head 2.

The color video signal reproduced by the head is amplified by a reproduction preamplifier 3 and supplied to an LPF 4, an HPF 5, and a noise canceller 6. In LPF4, only the chroma signal is extracted from the color video signal, and chroma signal processing step #1
7. In this chroma signal processing circuit 7, the chroma signal that has undergone low frequency conversion is converted into a chroma signal in the subcarrier band.

The HPF 4 extracts the FM luminance signal from the color video signal, and the FM luminance signal is demodulated by the luminance signal demodulation circuit 8.

The noise canceller 6 includes a reproduction level detector 9, a chroma level detector 10. HPF 11, slice circuit 12,
It is composed of a subtracter 13, a slice level control circuit 14, and the like. The high frequency component of the luminance signal from the luminance signal demodulation circuit 8 is extracted by the HPFII, and this high frequency component is supplied to the slice circuit 12. The slicing circuit 12 has a slicing level for removing components higher than a predetermined level from inputted high-frequency components, and components exceeding the slicing level are removed. The high frequency low level component (regarded as a noise component) that has passed through the slice circuit 12 is supplied to a subtracter 13 and subtracted from the luminance signal from the luminance signal demodulation circuit 8. The slice level of the slice circuit 12 is controlled by a signal from a slice level control circuit 14. This slice level control circuit 14 controls the level of the FM luminance signal from the reproduction preamplifier 3 detected by the reproduction level detector 9 and the level of the chroma signal from the chroma signal processing circuit 7 detected by the chroma signal detector 10. The output signal is controlled by

That is, the slice level of the slice circuit 12 is controlled so that it becomes smaller as the reproduction level of the FM luminance signal becomes larger, and becomes larger as the level of the chroma signal becomes larger.

Therefore, even if the reproduction bell of the FM luminance signal is large and the amount of noise cancellation is small,
When the level of the chroma signal is high, the amount of noise cancellation becomes large, and the unnecessary components t and d are canceled.

The luminance signal whose noise has been canceled in this way reaches the adder 15 from the subtracter 13, where it is added to the chroma signal from the chroma signal processing circuit 7, and from the output terminal 16 to the CRT (not shown). etc., and a reproduced image is obtained.

[Effects of the Invention] As described above, the present invention includes an FM reproduction level detector for detecting the reproduction level of a reproduced FM luminance signal;
It has a means for extracting a noise component from a luminance signal demodulated from an M luminance signal, and a slice level for removing a component larger than a predetermined level from the noise component, and the slice level becomes smaller as the reproduction level increases. A noise canceler in a magnetic reproducing device comprising a controlled slice circuit and a subtracter for subtracting the output of the slice circuit from the luminance signal, the noise canceler comprising a chroma level detector for detecting the level of the reproduced chroma signal; Since the slice level of the slice circuit is controlled so that the higher the chroma level is, the slice level of the slice circuit becomes higher.
The larger the reproduction level of the luminance signal is, the smaller the signal becomes, and the higher the level of the chroma signal is, the larger the signal becomes. When the level of the chroma signal is high, the amount of noise cancellation becomes large, the above-mentioned unnecessary components are canceled, and mesh noise on the playback screen can be removed.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention.
This figure shows an outline of the main parts of the R regeneration system. Figure 2 shows V
This is a spectrum obtained by reproducing a signal magnetized on a magnetic tape by a TR using a video head. 1: Video tape, 2: Video head, 3: Playback preamplifier, 4: LPF, 5: HPF, 6: Noise canceller, 7: Chroma signal processing circuit, 8: Luminance signal demodulation circuit, 9
: Playback level detector, 10: Chroma level detector, 11
: HPF, 12 slice circuit, 13: Subtractor, 14
Nislice level control circuit, 15: adder, 1
6: Output terminal.

Claims (1)

[Scope of Claims] An FM reproduction level detector for detecting a reproduction level of a reproduced FM luminance signal, means for extracting a noise component from a luminance signal demodulated from the FM luminance signal, and a means for extracting a noise component from a predetermined level from the noise component. It has a slice level for removing large components, and includes a slice circuit that is controlled such that the slice level becomes smaller as the reproduction level increases, and a subtracter that subtracts the output of the slice circuit from the luminance signal. A noise canceler for a magnetic reproducing device, comprising a chroma level detector that detects the level of a reproduced chroma signal, and controlling the slice level of the slice circuit so that the higher the detected chroma level, the higher the slice level of the slice circuit. Noise canceller in magnetic playback equipment.