JPS63142983A - Noise eliminating circuit for vtr - Google Patents

Abstract

PURPOSE:To eliminate noise at the edge part of a reproducing luminance signal, by slicing the peak part of an input signal at a peak slicing circuit, extracting a high-pass frequency component by passing a slice peak signal through a high- pass filter, and setting a signal obtained by subtracting the high-pass frequency component from an original input signal by a subtractor as an output signal. CONSTITUTION:An FM demodulated luminance signal (b) outputted from an FM demodulator 3 is sliced by the peak slicing circuit 9, and only the signal component of a white peak and that of a dark peak are extracted. Since peak signal component (e) includes the noise of the edge of the reproducing luminance signal, only the noise component of the edge is extracted by passing the peak signal (e) through the high-pass filter 10. And the noise of the edge is eliminated by subtracting the noise component (f) of the edge from the FM demodulated luminance signal (b) which includes the noise component by the subtractor 11.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is for efficiently removing noise generated at the horizontal edges of a VTR (video tape recorder) playback signal when displayed on a monitor screen. The present invention relates to a noise removal circuit.

In the conventional technology '/TR, which records and reproduces the luminance signal by iFM modulation, when the reproduced signal is displayed on a monitor, an abnormally large amount of noise is generated in the horizontal edge parts of the image compared to other flat parts. There was a problem with that. This noise caused the outline of the image to fluctuate, making it very unsightly.

The factors that cause this edge noise will be briefly explained using drawings.

FIG. 3 is a block diagram of a reproduction signal processing system of a conventional VTR. Moreover, FIG. 4 shows all the waveforms of each part of the circuit of FIG. 3. The reproduced FM luminance signal reproduced by the video head 1 is amplified by the hesodon amplifier 2 and then sent to the FM demodulator 3.
The signal is FM demodulated by Here, since the signal a input to the 7M demodulator 3 is a signal obtained by emphasizing the luminance signal and then FM modulating it, the signal at the edge part of the image has a higher carrier frequency than the signal at the flat part, and has sideband waves. This is an FM signal with a wide spread. This is because the brightness signal of the flat portion has many DC component signals and no high frequency signal components, whereas the brightness signal of the edge portion has many high frequency signal components. Further, the carrier frequency of the FM signal in the flat portion is within the FM deviation range at most, whereas the FM carrier frequency of the FM signal in the edge portion increases to the range limited by clipping. For example, in 8mm video, the deviation is 4.2 to 6. a MHz, whereas white
Since the J knob is 220%, the maximum frequency of the FM carrier in the flat portion is 5.2 MHz, while the maximum frequency of the FM carrier in the edge portion is 6.84 MHz. The carrier frequency of the FM signal in the edge portion is higher than that in the flat portion, so the C/N of the carrier is lower.
Furthermore, the C/N of the sideband is also poor because the sideband has spread and extends to low frequency components and is affected by adjacent crosstalk. Therefore, 7 in Figure 3
On the FM modulated luminance signal input to the M demodulator 3, the portion corresponding to the edge portion of the luminance signal as shown in FIG. 4B becomes an FM modulated signal with extremely poor S/H. Of course, the edge part of the FM demodulated luminance signal output from the 7M demodulator 3 has a higher S/N than the flat part, as shown in Figure 4.
is played back as a bad signal. This FM demodulated luminance signal is restored to a normal reproduced luminance signal C through linear de-emphasis 4 and non-linear de-emphasis 6.

In this case, the non-linear de-emf 7 system has the characteristic of greatly de-emphasizing low-level high-frequency components and hardly de-emphasizing (suppressing) high-level high-frequency components. Although noise is suppressed, relatively large level high-frequency and low-frequency noises are hardly suppressed. Therefore, in the reproduced luminance signal C output from the non-linear de-emphasis 6, the noise in the edge portion is more υ emphasized than the noise in the flat portion, as shown in FIG. 4C. Further, this reproduced luminance signal C is passed through a noise canceller circuit 6 to become a reproduced luminance signal d from which noise has been removed. Here, since the noise canceler circuit 6 is a noise canceling circuit as shown in, for example, Japanese Patent Laid-Open No. 61-53878, the noise in the flat part of the reproduced waveform is sufficiently removed, but the noise in the edge part is removed. It had the characteristic that it was not removed at all. (Refer to the signal S4 shown in Figure 1, page 3 of the same publication, and the signal S6 shown in Figure 3, page 4 of the same publication) Therefore, the noise canceller circuit 6
The reproduced luminance signal d outputted from the above is a good signal of 37H with most of the noise removed in the flat part, as shown in Figure 3d, but the edge part has a very large S/N noise component.
This is a bad signal. The reproduced luminance signal d of this edge portion having a very poor S/N ratio is mixed with the reproduced chroma signal obtained from the chroma signal processing circuit 9, passed through the entire output amplifier 7, and outputted from the video output terminal 8.

As explained above, in VTRs that record and reproduce luminance signals by FM modulating them, the problem of large edge noises cannot be avoided.

The problem of edge noise like this was solved in the 1980s.
It is also described in detail in Publication No. 866.

Regarding this edge noise problem, the publication proposes that an amplitude limiting circuit be inserted between the FM demodulator and the de-emphasis circuit as a method to completely reduce this noise. The idea is to limit the amplitude level and sufficiently suppress this noise component in a de-emphasis circuit, thereby reducing noise even more than in the past.

However, since the method of inserting an amplitude limiting circuit is to control the level of U noise and suppress it by de-emphasis, the noise is basically suppressed as shown in SN in Figure 2, D and E of the same publication. It's not something that can be removed.

Therefore, the noise reduction effect was not so great. Moreover, when the amplitude limiting circuit limits the noise level of the edge portion, it also limits the amplitude of the edge component of the original signal at the same time, so in the output reproduced luminance signal, the noise of the edge portion is reduced to a certain degree. However, it had the disadvantage that the edge signal components were largely lost, the edge waveform became dull, and details were lost.

As described above, the current situation is that there is no particularly good solution to the noise generated at the edge portions of the reproduced luminance signal of a VTR.

Problems to be Solved by the Invention In view of the above-mentioned problems, the present invention can effectively remove the noise at the edge portions of the reproduced brightness signal of a VTR, but the original signal waveform at the edge portions is almost degraded. The object of this invention is to provide a noise removal circuit that does not cause noise.

Means for Solving the Problems The noise removal circuit of the present invention is inserted between an FM demodulator and a de-emphasis circuit, and slices the peak portion of an FM demodulated signal and processes the sliced peak signal. It is configured to extract a high frequency component through a high-pass filter and subtract this component from the original FM demodulated signal to obtain an output signal.

Since the luminance signal demodulated by the active FM demodulator is still in an emphasized state, the noise generated at the edge portions exists in the waveform peak portion of the luminance signal. Therefore, only the edge noise components are extracted by extracting that part by peak slicing and passing it through a high-pass filter. Then, by subtracting the noise component from the original demodulated luminance signal, the noise in the edge portion can be removed.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. Further, FIG. 2 shows waveforms at various parts of the circuit shown in FIG. 1. Circuits having the same functions as those of the conventional example shown in FIG. 3 are given the same numbers. In FIG. 1, 9 is a peak slice circuit. The FM demodulated luminance signal output from the FM demodulator 3 is peak-sliced by the peak slicing circuit 9 at the level indicated by B in FIG. 2, resulting in a white peak signal as shown in FIG. Only the dark peak signal components are completely extracted. This peak signal component e contains edge noise components of the reproduced luminance signal, but
This peak signal component 5 (y7) is passed through the pass filter 10 to extract only the edge noise component as shown in FIG. By subtracting the edge noise component i from the edge noise component, it is possible to obtain an FM demodulated luminance signal sound from which edge noise has been removed, as shown in FIG. 2g. Further, by passing this FM demodulated luminance signal sound linear de-emphasis 6 and non-IJ=adi-emphasis 6, it is possible to obtain a reproduced luminance signal hl in which almost no edge noise occurs.

The peak slice circuit 9 slices the waveform peak portion of the input FM demodulated luminance signal, but at this time, the input signal is lightly clamped so that the slice level does not change due to changes in the APL of the input signal.I) It is desirable to input via direct connection to C. Also, the slice level person shown in Figure 2.

As for the setting of B, for example, in an 8 mm video, the white clip is 220% and the dark clip is 200 inches, so slice levels A and B may be set to about 160 inches. Furthermore, since edge noise generally occurs at a rising edge from black to white in a reproduced image, slice B of the dark peak in FIG. 2 may be omitted.

, and the high-pass filter 10 has a cutoff frequency i1
It is best to set the frequency to about MHz to 1.6 MH2.0 The signal f output from the high-pass filter 10 is shown in Fig. 2 f.
As shown in Figure 2, most of the noise components are edge noise components, but it also contains a small amount of edge components of the original FM demodulated signal. Therefore, since this is subtracted from the original FM demodulated signal, most of the edge noise components are removed from the reproduced luminance signal output from the nonlinear de-emphasis 7, but the rising waveform of the signal is also slightly degraded. However, this waveform deterioration is hardly noticeable on the playback screen, and moreover, the edge noise removal effect is very poor.

Furthermore, the present invention can be implemented with a relatively simple circuit.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention uses a relatively simple circuit to efficiently remove edge noise components that occur in the reproduced luminance signal of a VTR that performs recording and reproduction by subjecting the luminance signal to iFM modulation. This has the effect that the edges are hardly degraded and details are not lost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of output signals of each part in the block diagram of Fig. 1, and Fig. 3 is a block diagram of a conventional VTR playback signal processing system. , FIG. 4 is a waveform diagram of the output signal of each part in the block diagram of FIG. 3. 1...Video head, 2...Head amplifier, 3...FM repeater, a...Linear de-emphasis, 6... Non-linear de-emphasis, 6...Noise canceller, complete
... Output amplifier, 8 ... Video signal output terminal, 9 ... Peak slice circuit, 1Q ...
...High-pass filter, 11...Subtractor. Name of agent: Patent attorney Toshio Nakao and one other name
2 figure

Claims (1)

[Claims] In a VTR playback circuit system that performs non-linear emphasis on a brightness signal, performs FM modulation and records it, demodulates the reproduced FM signal, and then applies non-linear de-emphasis to obtain a reproduced brightness signal. , a circuit that takes the signal demodulated by the FM demodulator as an input signal and sends the output signal to a nonlinear de-emphasis circuit, which slices the peak portion of the input signal with a peak slice circuit and sends the sliced peak signal to a high-pass filter. A noise removal circuit for a VTR, characterized in that a high frequency component is extracted through a subtracter, and the high frequency component is subtracted from an original input signal by a subtracter to obtain an output signal.