JPH0752959B2 - Video signal processing circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit for improving the image quality of a luminance signal when a video signal recorded by frequency division multiplexing is reproduced.

[Prior Art] A magnetic recording / reproducing apparatus will be described below as an example. FIG. 7 is a block circuit diagram showing a conventional video signal processing circuit shown in P176 to 177 of "VTR technology edited by Japan Broadcasting Corporation" (Japan Broadcast Publishing Association, 1982). In the figure, a signal recorded on a magnetic tape (1) is converted into an electric signal by a magnetic head (2) and then supplied to a preamplifier (3) to be amplified to a predetermined signal level. The frequency spectrum of the output signal of the preamplifier (3) is such that the chrominance signal is arranged on the low frequency side of the frequency-modulated luminance signal, as shown in FIG. The output signal of the preamplifier (3) is supplied to the high frequency filter (4), and the color signal unnecessary for the luminance signal processing is removed. The amplitude and group delay characteristics of the high frequency filter (4) are configured as shown in FIG.
The output signal of the high frequency filter (4) is supplied to the FM demodulator (5) and demodulated into a luminance signal.

Regarding the chrominance signal, the output signal of the preamplifier (3) is supplied to the low-pass filter (6) constituting the chrominance component extracting means to remove the unnecessary FM luminance signal, and then the chrominance signal processing circuit (7). ) And subjected to processing such as high frequency conversion and correction of time base fluctuation.

The output signal of the color signal processing circuit (7) and the output signal of the FM demodulator (5) are combined by the adder (8) and output as a composite video signal.

[Problems to be Solved by the Invention] As described above, in the conventional video signal processing circuit, the high frequency filter (4) having the fixed frequency characteristic is used as the color signal removal filter. When the color signal amplitude is large, the influence of the color signal on the FM luminance signal is large, so there is no problem even when the conventional high-pass filter (4) is used. However, when the amplitude of the chrominance signal is small, a high-pass filter that has a large amount of attenuation in the chrominance signal band is used even though there is little interference with the FM luminance signal even if the attenuation in the chrominance signal band is small. Therefore, the amplitude characteristic and the group delay characteristic of the high frequency filter influence the FM luminance signal, which causes the waveform characteristic deterioration after demodulation and the waveform distortion such as inversion reduction.

Since the conventional video signal processing circuit is configured as described above, problems such as deterioration of the resolution of the luminance signal and distortion of the waveform of the demodulated signal are caused by the influence of the amplitude characteristic and the group delay characteristic of the high frequency filter (4). Had a point.

The present invention has been made in order to solve the above problems, and an object thereof is to obtain a video signal processing circuit in which resolution deterioration of a luminance signal and waveform distortion are small while removing interference of a color signal.

[Means for Solving the Problems] In the video signal processing circuit according to the present invention, after extracting the color signal band from the output signal of the preamplifier by the color component extracting means, the color signal band is extracted by the large amplitude signal extracting means. It is characterized in that the amplitude signal is removed and the luminance signal is obtained by FM demodulating the signal obtained by subtracting the large-amplitude color component signal from the output signal of the preamplifier.

[Operation] Since the large-amplitude extracting means in the present invention removes the small-amplitude signal of the color component and passes only the large-amplitude signal, the output signal of the subtractor attenuates the low range when the color signal component is large. If the color signal is small, a signal having a substantially flat frequency characteristic can be obtained. Therefore, when the chrominance signal is a large amplitude signal, the chrominance signal band is sufficiently attenuated and the FM luminance signal is not affected.

Also, when the color signal is a small amplitude signal, the amount of attenuation in the color signal band is small, but since it is a small amplitude signal from the beginning, the color signal has a small effect on the FM luminance signal. The lower side wave is less attenuated, and the phase characteristics are good.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, the preamplifier (3) outputs a signal having a frequency spectrum as shown in FIG. 8 and the color signal is taken out from the low-pass filter (6) as in the conventional example shown in FIG. . The low-pass filter (6) has the second characteristic
It has the characteristics shown in the figure. The output signal of the low band filter (6) is supplied to a dead zone circuit (9) which constitutes a large amplitude signal extraction means having an input / output characteristic as shown in FIG.
The dead zone circuit (9) has a characteristic of removing low level signals and passing high level signals. An example of the dead zone circuit is shown in FIGS. 4 and 5. Next, low-pass filter (6),
A preamplifier (3) is added to a delay equalizer (10) having a delay amount and a phase amount equivalent to those including the dead zone circuit (9).
The output signal of the dead zone circuit (9) is subtracted from the output signal of the delay equalizer (10) by the subtractor (11).

The output signal of the subtractor (11) has the characteristic shown in FIG. 6 depending on the signal level of the color signal. That is, the color signal is FM
When a large-amplitude signal that interferes with the luminance signal is used, the low-frequency part is greatly suppressed, and when the signal has little effect, the frequency characteristics are almost flat, and the characteristics are changed depending on the magnitude of the color signal level. .

The output signal of the subtractor (11) is supplied to the FM demodulator (5) and demodulated into a baseband luminance signal.

On the other hand, as for the color signal, the output signal of the low-pass filter (6) is supplied to the color signal processing circuit (7), where it is subjected to processes such as high-pass conversion and time-axis fluctuation removal. The output signal of the FM demodulator (5) and the output signal of the color signal processing circuit (7) are added by the adder (8) and output as a composite video signal.

As described above, in this embodiment, in order to remove the color signal, a high band filter having a fixed characteristic as in the conventional case is not used, but a low band filter (6), a delay equalizer (10) and a dead band circuit are used. (9) By using a variable-frequency high-frequency filter composed of a subtractor (11), the characteristic of the high-frequency filter is changed according to the color signal level as shown in FIG.

Further, since the group delay characteristic can be improved by suppressing the attenuation of the color signal band to a small extent, the waveform distortion after demodulation can be suppressed and the image quality can be significantly improved.

In the above embodiment, the low band filter (6) is used for extracting the color signals, but a band filter may be used.

Further, the delay equalizer (10) may be omitted when the delay amount of the low-pass filter is short.

Further, although the low-pass filter (6) is also used for color signal processing, it is also possible to perform filtering independently.

Further, the dead band circuit is used as the large amplitude signal extraction means, but the invention is not limited to this configuration.

[Effects of the Invention] As described above, according to the present invention, the frequency characteristic of the low-frequency part of the FM luminance signal is changed according to the color signal level. The amplitude and delay characteristics of the part are improved, the resolution is improved, the waveform distortion is reduced, and the low frequency range is sufficiently suppressed even when the color signal level is high, so that the image does not affect the luminance signal. Has the effect of obtaining a signal processing circuit

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a characteristic diagram of a low-pass filter of this embodiment, FIG. 3 is a characteristic diagram of a dead zone circuit, and FIGS. 4 and 5 are dead zones. FIG. 6 is a diagram showing an example of a circuit, FIG. 6 is an output characteristic diagram of the subtractor of this embodiment, and FIG. 7 is a diagram showing a conventional video signal processing circuit.
The figure shows the frequency spectrum of the output signal of the preamplifier, No. 9.
The figure is a characteristic diagram of a high frequency filter. (5) ... FM demodulator, (6) ... low-pass filter (color component extraction means), (8) ... adder, (9) ... dead zone circuit (large amplitude signal extraction means), (10) ...... Delayed equalizer,
(11) ... It is a subtractor. In each drawing, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A video signal processing circuit for frequency-modulating a luminance signal, and for a color signal, frequency-multiplexed on the lower side of the frequency-modulated luminance signal to reproduce a recorded video signal. A color component extraction means for extracting a low-frequency color signal component from the signal, and a large-amplitude signal extraction for removing only a small-amplitude signal contained in the color-signal component extracted from the color-component extraction means and passing only a large-amplitude signal A video signal processing circuit comprising: means, a subtracter for subtracting the output signal of the large amplitude signal extraction means from the video signal, and means for frequency demodulating the output signal of the subtractor into a baseband luminance signal.