JPH05328301A - Video signal processor for video reproduction - Google Patents

Abstract

PURPOSE:To obtain an image of high quality having modulation as an image to be used for video reproduction. CONSTITUTION:A video-reproducing video signal circuit is provided with a noise extracting circuit 5 and a comparator 7 for switching the band of an LPF 4 in accordance with the quantity of a noise component included in an output signal outputted from the circuit 5. The LPF 4 receives an output signal from a deemphasis circuit 3 and a band control signal from the comparator 7, switches cut-off frequency to a proper value and sends the noise-reduced signal to the succeeding reproducing system circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing apparatus for video reproduction, which can automatically switch the band of an LPF (low-pass filter) depending on the magnitude of noise contained in a reproduced video.

[0002]

2. Description of the Related Art Conventionally, when a noise contained in a video signal for video reproduction, for example, a tape recorded in a state where the reception condition of an antenna is not good, or a tape demagnetized repeatedly is reproduced, As a measure for improving the S / N ratio of the playback screen, which is difficult to see, a user-controlled image quality adjustment volume was provided and the image quality was improved by operating it.

[0003]

However, when the image quality adjusting volume is used as a measure for improving the playback screen, the boost amount is varied centering on the frequency in the middle and low frequencies, so that the S / N ratio is visually improved. However, there is a problem that the image quality is deteriorated by deteriorating the frequency characteristics in the middle and low frequencies that affect the sharpness of the image quality. Therefore, the object of the present invention is to provide an S / N ratio without deteriorating the frequency characteristics in the low / middle range which affects the sharpness of the image quality even when the S / N ratio is poor.
An object of the present invention is to provide a video signal processing device for video playback capable of improving the above.

[0004]

The present invention has been made to solve the above problems, and is an LPF for removing an unnecessary component such as a carrier leak in a demodulation output when a video signal of a video is reproduced. And a noise extracting circuit for extracting a noise component contained in the reproduced video signal, and a comparator for outputting a control signal for switching the band of the LPF according to the magnitude of the noise component contained in the reproduced video signal based on the output of the noise extracting circuit. The gist of the present invention is a video signal processing device for video reproduction provided with and.

[0005]

When the video image signal is reproduced, the output signal from the FM demodulation circuit that is input to the LPF is input to the noise extraction circuit, and the output level of the noise extraction circuit differs depending on the amount of noise components included in the input signal. However, the comparator receiving the output from the noise extraction circuit outputs the output control signal to the LPF, and the LPF automatically switches and adjusts the cutoff frequency according to the output level of the control signal output from the comparator. The S / N ratio can be improved without reducing the high-frequency noise component and deteriorating the frequency characteristics in the low and middle frequencies.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram showing an embodiment of the device of the present invention. The structure will be described with reference to the drawing. The reproduction FM signal processing circuit 1 is a block including a head amplifier, an FM equalizer, a limiter, etc. It is connected and outputs the reproduced FM signal to the FM demodulation circuit 2.

The FM demodulation circuit 2 is a de-emphasis circuit 3
FM output from the reproduction FM signal processing circuit 1 connected to the
The signal is demodulated into a video signal (luminance signal system) and output to the de-emphasis circuit.
4 and the noise extraction circuit 5 to receive the video signal from the FM demodulation circuit, attenuate the high frequency component emphasized by the emphasis during recording, and output the video signal to the LPF 4 and the noise extraction circuit 5. To do.

The noise extraction circuit 5 is connected to the peak hold circuit 6 and outputs the peak voltage of the noise component extracted in synchronization with the input pulse from the noise extraction timing pulse generation circuit 8 to the peak hold circuit 6.

The peak hold circuit 6 is connected to the + side input terminal of the comparator 7, holds the peak voltage and outputs it as a DC voltage to the comparator 7, and the comparator 7 is connected to the-side input terminal with a reference voltage. When the output voltage from the peak hold circuit 6 exceeds the reference voltage, the band control signal for switching the cutoff frequency of the LPF 4 to the lower one is output to the LPF 4.

Next, the operation of the embodiment of the present invention having the above structure will be described with reference to FIG. Figure 1
In the reproduction FM signal processing circuit 1, the head amplifier, FM
Subsequent FM with a block composed of equalizer, limiter, etc.
The reproduced FM signal is output to the demodulation circuit 2. The FM signal output from the reproduction FM signal processing circuit 1 is demodulated into a video signal (luminance signal system) by the FM demodulation circuit 2 and output to the de-emphasis circuit 3.

The de-emphasis circuit 3 receives the FM-demodulated video signal, attenuates the high frequency components emphasized by the emphasis during recording, and outputs the video signal at L level.
It is output to the PF 4 and the noise extraction circuit 5. The noise sampling circuit 5 receives the output signal from the de-emphasis circuit 3 and obtains noise from the sampling timing pulse creating circuit 8 for a period corresponding to the blanking period of the vertical synchronizing signal, thereby synchronizing with the input of the noise sampling timing pulse. The high frequency noise component contained in the reproduced video signal is extracted.

The peak hold circuit 6 holds the peak voltage of the noise component extracted by the noise extraction circuit 5, and outputs it as a DC voltage to the comparator 7.
Further, in the comparator 7, the reference voltage set in advance on the negative terminal side is compared with the output voltage of the peak hold circuit 6, and when the output voltage from the peak hold circuit 6 exceeds the reference voltage (that is, there is much noise). In the case), a band control signal for switching the cutoff frequency of the LPF 4 to the lower one is output to the LPF 4.

The LPF 4 receives the output signal from the de-emphasis circuit to remove unnecessary noise components such as leakage of the FM carrier signal, and when there are many noise components, receives the band control signal from the comparator 7 to cut off. By switching the frequency to a lower frequency to attenuate noise components in the high frequency range, improving the S / N ratio, and sending the result to the reproduction system circuit in the next stage, it is possible to reproduce a clear and high-quality image. 2 shows an example of the LPF characteristic.

In FIG. 1, one LPF is provided and its cutoff frequency is switched. However, two kinds of LPFs having different cutoff frequencies are connected in parallel, and each output is subjected to band control of the comparator 7. You may make it switch according to a signal.

[0015]

With the circuit configuration as described above, in the video signal processing apparatus for video reproduction, the LPF
The cutoff frequency of can be automatically switched to an appropriate value, and even if the S / N ratio of the video signal for reproduction is poor, the LPF can be adjusted without degrading the low-mid frequency characteristics that affect the sharpness of the image quality. It is possible to improve the S / N ratio of the video signal output from the device and reproduce a high quality image with sharpness.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment of a video signal processing device for video reproduction according to the present invention.

FIG. 2 is a diagram showing characteristics of the LPF of FIG.

[Explanation of symbols]

 4 LPF 5 Noise extraction circuit 7 Comparator

Claims (1)

[Claims] 1. An L for removing an unnecessary component such as a carrier leak in a demodulation output when a video signal of a video is reproduced.
PF, a noise extraction circuit for extracting a noise component included in the reproduced video signal, and the size of the noise component included in the reproduced video signal based on the output of the extraction circuit,
A video signal processing device for video reproduction, comprising: a comparator that outputs a control signal for switching the band of the LPF.