JPH0418122Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention demodulates the reproduced FM signal of a tape to obtain a demodulated luminance signal, and performs de-emphasis processing and noise reduction processing on the demodulated luminance signal for reproduction. The present invention relates to a video tape recorder that obtains a luminance signal.

[Prior art]

Conventionally, in order to improve the recording and playback characteristics of video tape recorders, the recording circuit section performs FM modulation of the luminance signal and low frequency conversion of the color signal.
The FM signal formed by FM modulation and the low-frequency color signal formed by the low-frequency conversion are mixed and recorded on a tape.

By the way, when performing FM modulation on a luminance signal, the higher the modulation frequency component of the FM modulation wave, the more susceptible to the influence of noise, so before the luminance signal is FM modulated,
Emphasis processing is performed by a pre-emphasis circuit in the recording circuit section to emphasize high frequencies.

On the other hand, the reproduced FM signal of the tape reproduction signal is input to the luminance signal reproduction circuit of the reproduction circuit section, and the reproduced low-frequency color signal of the reproduction signal is input to the color signal reproduction circuit of the reproduction circuit section.

The luminance signal reproducing circuit is configured as shown in FIG. Ru.

Note that a low-pass filter is provided on the output side of the demodulation circuit 2, and only the demodulated luminance signal is output to the de-emphasis circuit 3.

Further, the de-emphasis circuit 3 performs de-emphasis processing on the demodulated luminance signal, and the output signal of the de-emphasis circuit 3 is input to the noise reduction circuit 4.
The noise of the output signal is reduced, and a reproduced luminance signal is output from the reduction circuit 4 to the luminance/color mixing section via the output terminal 5.

Further, the frequency of the reproduction reduced color signal is restored by the reproduction circuit section to form a reproduction color signal, and the reproduction color signal is output to the luminance and color mixing section.

Then, the reproduced luminance signal and the reproduced color signal are mixed by the luminance and color mixing section to form a reproduced video signal.

By the way, the pre-emphasis characteristic by the pre-emphasis circuit is a non-linear characteristic with respect to frequency, and the noise superimposed on the demodulated luminance signal is not uniform with respect to frequency.

The de-emphasis circuit 3 is provided to cancel out the pre-emphasis, and is formed using a large number of trap circuits so that a peak occurs in the high range of the demodulated luminance signal.

Further, the noise reduction circuit 4 is provided to reduce noise superimposed on the demodulated luminance signal and remove noise from the reproduced luminance signal, but since the level of high-frequency noise is lower than the level of low-frequency noise, , for example, is formed by a CR type high-pass filter.

On the other hand, the image quality of the reproduced image based on the aforementioned reproduced video signal is determined by the frequency characteristics of the reproduced video signal and the S/S/
De-emphasis circuit 3
If the emphasis characteristic of is the optimum emphasis characteristic that completely cancels out the pre-emphasis, and the filter characteristic of the noise reduction circuit 4 is the optimum filter characteristic that completely reduces noise in all bands of the demodulated luminance signal, then the reproduction video signal Frequency characteristics and S/N characteristics are ideal frequency characteristics and S/N
It is possible to provide reproduced images with natural image quality and no noise.

However, since the optimal de-emphasis characteristic of the demodulated luminance signal is non-linear with respect to frequency,
No matter how many trap circuits are used, it is impossible to make the de-emphasis characteristics of one de-emphasis circuit 3 optimal for all band components of the demodulated luminance signal.

Since the de-emphasis circuit 3 cannot completely cancel out the emphasis and correctly restore the frequency characteristics of the demodulated luminance signal, the frequency characteristics of the reproduced luminance signal become different from the frequency characteristics of the luminance signal recorded on the tape, and the reproduced image The brightness level becomes unnatural.

In addition, since the noise in the front band component of the demodulated luminance signal that has undergone de-emphasis processing is not uniform with respect to frequency, no matter how complex the filter is, the filter characteristics of one noise reduction circuit 4 will be
It is impossible to obtain optimal filter characteristics for all band components of the demodulated luminance signal that has been subjected to de-emphasis processing, and the reproduced luminance signal output from the noise reduction circuit 4 has a poor S/N ratio and can only be used as a reproduced image with a lot of noise. can't get it.

Note that if the de-emphasis amount of the de-emphasis circuit 3 and the noise reduction amount of the noise reduction circuit 4 are increased too much, waveform distortion will occur at the boundary between changes in the brightness level of the reproduced image. It is impossible to increase the noise reduction amount of the noise reduction circuit 4 too much. For example, if the noise reduction amount of the noise reduction circuit 4 is set to be optimal for the high frequency range, even the necessary components of the low frequency range can be reduced. is also reduced.

By the way, if the brightness level of the reproduced image becomes unnatural due to the de-emphasis process of the de-emphasis circuit 3 and the noise reduction process of the noise reduction circuit 4, the level of the reproduced brightness signal is adjusted using more trap circuits to eliminate the above-mentioned unnaturalness. Although attempts are made to reduce the naturalness, it is actually not very effective and it is difficult to reduce the unnaturalness.

[Purpose of invention]

This idea was made with the above points in mind, and the demodulated luminance signal is divided into multiple bands and de-emphasized, noise reduction processed, and the demodulated luminance signal is subjected to de-emphasis processing with optimal de-emphasis characteristics. The purpose of the present invention is to perform noise reduction processing with optimal filter characteristics.

[Structure of the idea]

This idea applies emphasis processing to the luminance signal.
A tape on which an FM signal formed by performing FM modulation is recorded, a demodulator that demodulates the reproduced FM signal of the tape and outputs a demodulated luminance signal, and a demodulator that divides the demodulated luminance signal into a plurality of bands and a filter section that outputs a band signal of the band signal, a plurality of de-emphasis circuits that perform de-emphasis processing on each of the band signals according to the optimum de-emphasis characteristics of each of the band signals, and output a plurality of de-emphasis signals respectively; a plurality of noise reduction circuits that perform noise reduction processing on a composite signal of each de-emphasis signal using optimum filter characteristics of each of the de-emphasis signals; The present invention is a video tape recorder in which a reproduced luminance signal is formed by the composite signal passed through a reduction circuit.

[Effect of idea]

Therefore, according to the video tape recorder of this invention, the demodulated luminance signal is divided into a plurality of band signals by a filter section, and each band signal is de-emphasized by a plurality of de-emphasis circuits according to the optimum de-emphasis characteristics of each band signal. In addition, each de-emphasis signal of each de-emphasis circuit or a composite signal of each de-emphasis signal is subjected to noise reduction processing by a plurality of noise reduction circuits having optimal filter characteristics for each de-emphasis signal to form a reproduced luminance signal. It is possible to de-emphasize the demodulated luminance signal with an optimal de-emphasis characteristic that is significantly better than when de-emphasis processing is performed on all bands at once using a de-emphasis circuit, and at the same time, a single noise reduction circuit can de-emphasize noise on all bands at once. It is possible to perform noise reduction processing on the demodulated luminance signal that has undergone de-emphasis processing using an optimal filter characteristic that is significantly better than that in the case of reduction processing, and it is possible to return the luminance level of the reproduced image based on the reproduced luminance signal to its natural level. This makes it possible to reduce noise and improve image quality.

〔Example〕

Next, this invention will be explained in detail with reference to the drawings from FIG. 2 showing one embodiment thereof.

First, as in the case of conventional video tape recorders, the tape contains an FM signal formed by FM modulating the luminance signal that has been subjected to emphasis processing, and a color signal formed by converting the color signal to the low frequency of the FM signal. The low frequency color signal is mixed and recorded.

On the other hand, the luminance signal reproducing circuit in the reproducing circuit section is configured as shown in Fig. 2, and reproduces the tape reproduced signal.
An FM signal is input to an FM demodulator 2 via an input terminal 1.

Note that in FIG. 2, the same symbols as in FIG. 1 indicate the same or equivalent items.

The demodulator 2 demodulates the reproduced FM signal, removes the multiplied component using a built-in low-pass filter, and outputs a demodulated luminance signal in which noises of various frequencies are non-uniformly superimposed, as shown in FIG. 3a.

Further, the demodulated luminance signal is input to a low-pass filter 6a and a high-pass filter 6b provided in the filter section 6, respectively.

The low-pass filter 6a is configured to extract components of 1 MHz or less, and the high-pass filter 6b is configured to extract components of 1 MHz or more.
As a result, a low band signal consisting of low frequency components of 1 MHz or less of the demodulated luminance signal is extracted, and a high band signal consisting of high frequency components of 1 MHz or more of the demodulated luminance signal is extracted by the filter 6b. .

That is, both filters 6a, 6 of the filter section 6
b, the demodulated luminance signal is divided into a low-band component and a high-band component, and the demodulated luminance signal and noise are divided into 1MHz from the filter 6a to the low-band side nonlinear de-emphasis circuit 7a as shown in FIG. 3b. A low band signal consisting of the following low band components is output, and at the same time, the demodulated luminance signal and the noise of 1 MHz or more are sent from the filter 6b to the high band non-linear de-emphasis circuit 7b as shown in c. A high band signal consisting of band components is output.

Furthermore, as is clear from Figure 3 b and c, 1MHz
The level of high frequency noise above 1MHz is higher than the level of low frequency noise below 1MHz.

Both band signals are then subjected to de-emphasis processing by both de-emphasis circuits 7a and 7b, respectively.
In this case, the de-emphasis circuit 7a only needs to de-emphasize the components of the demodulated luminance signal of 1 MHz or less, and the de-emphasis circuit 7b only needs to de-emphasize the components of the demodulated luminance signal of 1 MHz or more.

Therefore, both de-emphasis circuits 7a and 7b
The de-emphasis characteristic should be optimal for each of the components below 1 MHz and above 1 MHz of the demodulated luminance signal by using a large number of trap circuits. Since it is not necessary to consider the entire band of the luminance signal, both de-emphasis circuits 7a,
7b de-emphasis characteristic of the demodulated luminance signal
The optimal de-emphasis characteristic is significantly better than that of the de-emphasis circuit 3 shown in FIG. 1 for each of the components below 1 MHz and the components above 1 MHz.

Then, from the de-emphasis circuit 7a to the low-frequency noise reduction circuit 8a, the low-frequency band signal is de-emphasized using the optimal de-emphasis characteristic of the signal, as shown in FIG. As the de-emphasis signal is output, the de-emphasis circuit 7b sends the high-frequency side noise reduction circuit 8b to the high-frequency side noise reduction circuit 8b, as shown in FIG. A good high frequency side de-emphasis signal is output.

Furthermore, the noise of both de-emphasis signals is reduced by the noise reduction processing of both noise reduction circuits 8a and 8b, and in this case, the noise reduction circuit 8a
should have filter characteristics that reduce only noise below 1 MHz, and noise reduction circuit 8b may have filter characteristics that reduce only noise above 1 MHz, and the noise reduction circuit 8b may have filter characteristics that reduce only noise above 1 MHz. Since it is not necessary to set the filter characteristics in consideration of noise, both noise reduction circuits 8a and 8
b is formed by, for example, a CR type filter or the like so as to have optimum filter characteristics for both de-emphasis signals.

Therefore, the filter characteristics of both noise reduction circuits 8a and 8b are significantly better optimum filter characteristics than the noise reduction circuit 4 of FIG. 1 with respect to noise of 1 MHz or less and noise of 1 MHz or more, respectively.

Then, from the noise reduction circuit 8a to the mixing circuit 9,
S/N with reduced noise as shown in Figure 3f
A low-frequency side de-emphasis signal with high characteristics is output, and the noise reduction circuit 8b to the mixing circuit 9
Then, as shown in g in the same figure, the noise is reduced.
A high-frequency side de-emphasis signal with a high N characteristic is output, and both de-emphasis signals are mixed and added by the mixing circuit 9, and a signal with good frequency characteristics and a low S/N ratio is sent from the mixing circuit 9 to the output terminal 5, as shown in h of the figure. A high sum signal is output as a demodulated luminance signal.

Therefore, according to the embodiment, the demodulated luminance signal is obtained by both filters 6a and 6b of the filter section 6.
In order to divide into a low band component of 1 MHz or less and a high band component of 1 MHz or more, and to perform de-emphasis processing on the low band side signal and high band side signal formed by the division by both de-emphasis circuits 7a and 7b, respectively. In this case, by simply setting the de-emphasis characteristics of both de-emphasis circuits 7a and 7b to the optimal de-emphasis characteristics for both band signals, the entire band of the demodulated luminance signal can be de-emphasized using the optimal de-emphasis characteristics.

Further, both de-emphasis signals of both de-emphasis circuits 7a and 7b are transferred to both noise reduction circuits 8a and 8b.
In order to perform noise reduction processing on each of the two de-emphasis signals, the amount of noise reduction for the high-frequency side de-emphasis signal with a high noise level is made larger than the noise reduction amount on the low-frequency side de-emphasis signal with a low noise level, and noise reduction processing is performed on both de-emphasis signals respectively. In this case, by subjecting both de-emphasis signals to noise reduction processing using the optimum filter characteristics, the entire band of the demodulated luminance signal can be subjected to noise reduction processing using the optimum filter characteristics.

After the demodulated luminance signal is de-emphasized using the optimum de-emphasis characteristic, it is subjected to noise reduction processing using the optimum filter characteristic, so that a reproduced luminance signal with good frequency characteristics and high S/N can be obtained at the output terminal 5, and the reproduced luminance signal is The reproduced image of the reproduced video signal obtained by mixing the signal and the reproduced color signal has a natural brightness level and less noise, and can provide a reproduced image of extremely good image quality.

In the above embodiment, two filters 6a and 6b are provided in the filter section 6, and the demodulated luminance signal is converted to 1MHz.
Although the demodulated luminance signal is divided into components of two bands, the following components and the component of 1 MHz or more, three or more filters may be provided in the filter section 6 to divide the demodulated luminance signal into components of three or more bands. In this case, The number of de-emphasis circuits and noise reduction circuits may be increased depending on the number of divisions.

Further, in the above embodiment, both de-emphasis circuits 7
After inputting both de-emphasis signals a and 7b to both noise reduction circuits 8a and 8b, respectively, a mixing circuit 9
For example, a mixing circuit is provided at the next stage of both de-emphasis circuits 7a, 7b, and the mixing circuit forms a composite signal of both de-emphasis signals of both de-emphasis circuits 7a, 7b. Noise reduction circuits 8a and 8b may be provided in series after the mixing circuit, and the composite signal may be sequentially subjected to noise reduction processing by the noise reduction circuits 8a and 8b.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a part of a conventional video tape recorder, Fig. 2 is a block diagram of a main part of an embodiment of the video tape recorder of this invention, and Fig. 3a.
~h are signal waveform diagrams of various parts in FIG. 2. 1... Input terminal, 2... FM demodulator, 5... Output terminal, 6... Filter section, 6a, 6b... Filter, 7a, 7b... De-emphasis circuit, 8
a, 8b... noise reduction circuit, 9... mixing circuit.

Claims (1)

[Claims for Utility Model Registration] A tape on which an FM signal formed by applying emphasis processing and FM modulation to a luminance signal is recorded, and a demodulator that demodulates the reproduced FM signal of the tape and outputs a demodulated luminance signal. , a filter unit that divides the demodulated luminance signal into a plurality of bands and outputs a plurality of band signals; and a filter unit that performs de-emphasis processing on each of the band signals according to an optimum de-emphasis characteristic of each band signal, and outputs a plurality of de-emphasis signals, respectively. a plurality of de-emphasis circuits that perform noise reduction processing on each of the de-emphasis signals or a composite signal of the de-emphasis signals using optimum filter characteristics of each of the de-emphasis signals; A video tape recorder in which a reproduced luminance signal is formed by a sum signal of the de-emphasis signals passed through the de-emphasis signal or a composite signal passed through the noise reduction circuits.