JPH05176202A - Video signal equalizer circuit - Google Patents

Abstract

PURPOSE:To offer a video signal equalizer circuit to sharpen a contour unsharpened due to a band limit when a video signal subject to the band limit processing is reproduced. CONSTITUTION:A video signal 1 is separated into a high frequency component signal EH and a low frequency component signal EL by a branching device 2 and the signal EH is fed to an amplitude detector 3 and a zero cross generator 4. A zero cross signal from the zero cross generator 4 is fed to a gain control circuit 5, the signal is amplitude-modulated by a detection signal from the amplitude detector 3 and the amplitude modulated signal subject to gain control is inputted to a blanking gate circuit 7. The amplitude modulated signal is gated in the circuit 7 by a blanking signal 6 and the gated amplitude modulated signal is added to the low frequency component signal EL by an adder circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal equalizer circuit, and more particularly to a structure for sharpening a reproduced image by emphasizing a zero cross of a high frequency component of a band limited video signal.

[0002]

2. Description of the Related Art In a conventional TV transmitting / receiving system, a video signal is often transmitted with its band limited.
For example, in the NTSC system used for broadcasting, the band of the luminance signal E _Y is 4.2 MHz, and the color difference signal E _I is 1.
5MHz, E _Q has become a 0.5MHz.

Looking at the example of the luminance signal, 0 to 0 in FIG.
In the 4.2 MHz transmission band, a square wave signal near f = 1 MHz and 2 MHz (the original scene corresponds to white and black stripes), same figure (b)
(C) in the figure due to the band limitation in (a).
Particularly, at f = 2 MHz, only the sine wave of the fundamental wave is displayed as the luminance signal of the reproduction pattern.

[0004]

As described above, in the prior art,
Square wave (stripe pattern) of the fundamental wave of the luminance signal of f = 2 MHz
As shown in FIG. 4C, the sine wave of the fundamental wave is displayed, and the sharpness of the pattern is lost. For E _Q , the frequency is 0.5 MHz, which is 0.2
Since the square wave of MHZ is also only the fundamental wave, the image quality is deteriorated.

An object of the present invention is to propose a video signal equalizer circuit for sharpening a contour which is unclear due to band limitation when reproducing a video signal of a band-limited transmission system.

[0006]

In order to achieve the above object, the first invention of the present application provides a video signal, a low frequency component signal having a predetermined cutoff frequency or less, and a high frequency component signal having the cutoff frequency or more. Frequency component separation means for separating into a frequency component, an amplitude detection means for amplitude-detecting the high frequency component signal to obtain a detection signal, a zero cross point detecting the zero cross point of the high frequency component signal, and a zero cross detection means for outputting a zero cross signal, the zero cross signal Amplitude modulation means for amplitude-modulating the above-mentioned detection signal to obtain an amplitude modulation signal whose gain is controlled; and a blanking gate for switching the amplitude modulation signal by a predetermined blanking signal to output a gated amplitude modulation signal. Means for synthesizing the gated amplitude-modulated signal and the low-frequency component signal of the video signal to obtain a synthesized signal Have, characterized in that to sharpen the contour of the zero crossing of the high-frequency component is emphasized reproduced video of the video signal.

According to a second invention of the present application, in the first invention, the frequency component separating means divides the video signal into the low frequency component signal and a plurality of different frequency bands above the cutoff frequency. A high-frequency component signal, and outputs each high-frequency component signal to the amplitude detection means, the high-frequency component extraction means and the cross detection means, and supports a plurality of high-frequency component signals from the amplitude modulation means. It is characterized by further comprising adding means for adding the respective amplitude modulated signals and outputting the added amplitude modulated signal to the blanking gate means.

[0008]

In the circuit of the first aspect of the invention, the video signal is separated into a low frequency component signal below a predetermined cutoff frequency and a high frequency component signal above it. A zero cross point is detected from the high frequency component signal. The zero-cross signal is amplitude-modulated by a detection signal obtained by amplitude-detecting the high-frequency component signal to obtain an amplitude-modulated signal whose gain is controlled, and the signal is switched by the blanking signal. As a result, the gated amplitude modulation signal and the low frequency component signal of the video signal are combined.

In the circuit of the second invention, the high frequency component signal is divided into a plurality of different frequency bands, the amplitude modulation signals corresponding to the respective divided high frequency component signals are added, and switching is performed by the blanking signal. To be done.

[0010]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 2 shows the appearance of a visual spatial sine wave pattern. A pattern in which the luminance changes with cosx as shown in FIG. 2A becomes a square wave shape as shown in FIG. 2B when the spatial frequency becomes high. It is known to be visible. That is, if the spatial frequency is high, the visual appearance is that there is no discomfort even if the sine wave pattern approaches the square wave pattern. From the viewpoint of visual characteristics, in order to make an image clear in a high frequency region where the resolution is lowered, a sine wave is displayed as it is at f _x <f _L with a spatial frequency f _L as a boundary, as shown in FIG. However, when f _x > f _L , it is better to make the sine wave a square wave (zero cross waveform of the sine wave). Then, it becomes a form that emphasizes the characteristics of vision. For example, to _{f x = f L (cosω L} x) the emphasized waveform zero crossing of the sine wave as shown in FIG.

FIG. 1 shows an embodiment of a video signal equalizer circuit according to the present invention based on the above-mentioned principle. In the figure, 1 is a video signal and 2 is a demultiplexer, which corresponds to the frequency component separating means. An amplitude detector 3 corresponds to the amplitude detecting means. Reference numeral 4 is a zero-cross generator, which corresponds to the zero-cross detecting means. A gain control circuit 5 corresponds to the amplitude modulation means. 6 is a blanking (BLK) signal,
A blanking gate circuit 7 corresponds to the blanking gate means. Reference numeral 8 is an adding circuit, which corresponds to the signal synthesizing means, and 9 is an output signal.

The video signal 1 has its band f _c (f _{c in} broadcasting _).
= 4.2 MHz), and the demultiplexer 2 separates the low frequency component signal E _L and the high frequency component signal E _H.

An example of the characteristics of the duplexer 2 is shown in FIG. Figure 6
In the characteristic, and a f _L = 1.5 MHz and so the hem of the low frequency range L _P and the high frequency band H _P changes smoothly as a boundary, also f = the 1-2 MHz E _H and E _L Coexist. These 1MHz and 2MHz are not exact. f _c =
Because it is 4.2 MHz, the frequency that the gain is lowered in the low frequency region L _P of the duplexer 2 shown in FIG. 6, as described in FIG. 4 f _c
It is preferably / 3 (= 1.4 MHz) or less.

The high frequency component signal E output from the demultiplexer 2
_H is applied to the amplitude detector 3 and the zero-cross generator 4 (eg amplitude limiter). The zero-cross signal output from the zero-cross generator 4 is input to the gain control circuit 5 (or amplitude modulator), and the amplitude modulation is performed by the circuit so that the amplitude becomes equal to E _H according to the detection signal from the amplitude detector 3. The gain-controlled amplitude modulation signal is output. This amplitude modulation signal is added to the blanking gate circuit 7, and the amplitude modulation signal gated by switching by the blanking signal 6 is sent to the adding circuit 8 to send the low frequency component signal E.
_L is added and the output signal 9 is obtained.

Although the demultiplexer 2 is configured to obtain the high frequency component signal from one channel E _H in the above-described embodiment, it may be configured to have a plurality of channels if necessary.

[0016] Figure 7 is a demultiplexer 10, two channels (f _H1, f _H2) f _H1, in order to obtain a high frequency component signal f
A bandpass filter whose center frequency is _H2 is used. 3-1 and 3-2 are 2-channel amplitude detectors, 4-
1, 4-2 are 2-channel zero-cross generators, 5-
Reference numerals 1 and 5-2 are 2-channel gain control circuits, and 11 is an adder. Two output signals E _H1 and E _H2 from the duplexer 10 are added to the respective channels and processed as described above.

In the embodiment of FIG. 1, the input signal is as shown in FIG.
Assuming that a signal of 3 MHz is multiplexed with a signal of 1.5 MHz as shown in (a), an output signal having a waveform as shown in (b) of the figure is obtained.

On the other hand, in the embodiment of FIG. 7, the E _H1 ,
E _H2 is shown in FIGS. 9A and 9C, respectively, and the gain control circuit 5
The output signal obtained by adding the E _L to the output of the -1 FIG. 9 (b), the
Since the output signal of the gain control circuit 5-2 is as shown in FIG. 9 (d), the output signal of the adder circuit 8 is as shown in FIG. 9 (e).

Therefore, the embodiment of FIG. 6 is preferable in terms of simplicity of construction, but the method of FIG. 7 or the number of channels n> 2 is preferable in order to make the contour clear even for high frequency component signals.

[0020]

As described above, according to the video signal equalizer circuit of the present invention, a band-limited video signal is separated into a low frequency component signal and a high frequency component signal, and a zero cross obtained from the high frequency component signal. By adding a signal to the low-frequency component signal, the rising and falling edges of the video signal waveform are made clear, so that it is possible to obtain an easy-to-see image that matches the visual characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing how a visual spatial sine wave looks.

FIG. 3 is a characteristic diagram showing a relationship between expected spatial frequency and brightness contrast.

FIG. 4 is an explanatory diagram of a reproduction capability of a television system.

FIG. 5 is a waveform diagram in which the zero cross of a sine wave is emphasized.

FIG. 6 is a characteristic diagram showing an example of the characteristics of the duplexer.

FIG. 7 is a block diagram showing another embodiment of the present invention.

FIG. 8 is a waveform chart showing an example of input / output signals of the embodiment of FIG.

9 is a waveform chart showing an example of input / output signals of the embodiment of FIG.

[Explanation of symbols]

 1 Video signal 2 Demultiplexer 3 Amplitude detector 4 Zero cross generator 5 Gain control circuit 6 Blanking signal 7 Blanking gate circuit 8 Adder circuit

Claims (2)

[Claims] 1. A frequency component separating means for separating a video signal into a low frequency component signal having a predetermined cutoff frequency or lower and a high frequency component signal having a cutoff frequency or higher, and an amplitude detection signal for detecting the high frequency component signal. And a zero-crossing detecting means for detecting the zero-crossing point of the high-frequency component signal and outputting a zero-crossing signal, and an amplitude-modulating the zero-crossing signal with the detection signal to obtain a gain-controlled amplitude-modulated signal. Modulation means, blanking gate means for switching the amplitude modulation signal by a predetermined blanking signal to output a gated amplitude modulation signal, low-frequency component signal of the gated amplitude modulation signal and the video signal And a signal synthesizing means for synthesizing and obtaining a synthesized signal, and Video signal equalizer circuit, characterized in that to sharpen the contours of the reproduced video Te. 2. The frequency component separating means separates the video signal into the low frequency component signal and a high frequency component signal divided into a plurality of different frequency bands at the cutoff frequency or higher, and the respective high frequency components. The component signal is output to the amplitude detection means, the high frequency component extraction means, and the cross detection means, and each amplitude modulation signal corresponding to the plurality of high frequency component signals from the amplitude modulation means is added and the sum is added. 2. The video signal equalizer circuit according to claim 1, further comprising adding means for outputting the amplitude modulated signal to the blanking gate means.