JPH0763188B2 - Video adjustment circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video adjustment circuit, and more particularly to a circuit for adjusting the level of a color signal (chroma signal) of a video signal.

[0002]

2. Description of the Related Art Generally, when changing the level of a chroma signal, gain control is performed after separating an input video signal into a luminance signal component (Y signal) and a chroma signal component (C signal) using a filter. ing. The conventional circuit will be described with reference to FIG.

In the conventional image adjusting circuit shown in FIG. 3, the image signal applied to the input terminal 21 is filtered by the filter 25.
The signal is separated into a Y signal and a C signal by the gain control circuit, the gain control circuits 23 and 26 control the gains of the two signals, and the addition circuit 24 adds them again and sends them to the output terminal 22. In this case, the gain control terminals 27 and 28 are used to adjust the gain.

[0004]

Since the above-mentioned conventional circuit uses the two gain control circuits 23 and 26, the video signal level is adjusted unless the characteristics of the two circuits 23 and 26 are exactly the same. However, there is a drawback in that the frequency amplitude characteristic changes when this is performed.

Therefore, a circuit using the balanced modulator shown in FIG. 4 has been proposed. In this circuit, only the C signal to be adjusted is separated by a bandpass filter (BPF) 15 and the gain is adjusted by the balanced modulator 16 according to the control signal input 17. However, the BPF 15 and the modulator 1
Since 6 causes a signal delay, there is a drawback in that the phase of the chroma signal changes when the chroma signal level is changed.

There is a technique disclosed in Japanese Patent Laid-Open No. 62-264789 for controlling the level of a video signal in the PinP (picture-in-picture) function. In such technique, Y / C separation is performed. Because there is no
It is not possible to adjust only the chroma signal.

On the other hand, as a technique for separating and recording the chroma signal, there is one disclosed in Japanese Patent Application Laid-Open No. 2-290397, which adjusts the chroma signal to a constant level, and the gain thereof can be freely adjusted. Cannot be changed to

Further, as a technique for adjusting the gain of the luminance signal, there is one disclosed in Japanese Patent Application Laid-Open No. 61-295793, but this is not related to the gain adjustment of the chroma signal, and it can be adjusted freely from the outside. Not something you can do.

Therefore, the present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is to provide an image adjusting circuit capable of adjusting the level of a chroma signal without accompanying phase fluctuation. Is.

[0010]

In order to solve the above problems, a video adjusting circuit according to the present invention provides a filter for extracting a predetermined signal component from an input video signal, and a gain of the extracted signal component to an external device. Gain changing means for changing according to a control signal, delay means for delaying the video signal by the same time as the delay time in the filter and the gain changing means, a delay output by the delay means and an output of the gain changing means And adding means for mixing and.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a video adjusting circuit according to the present invention. In the figure, a video adjusting circuit according to an embodiment of the present invention includes a BPF 5 for separating a C signal from a video signal applied to an input terminal 1, and a balanced modulator 6 having the separated C signal as an input. , These BPF
5 and the delay circuit 3 having a delay time equivalent to that of the balanced modulator 6, and an adder circuit 4 for adding the delay output and the output of the balanced modulator 6.
In the figure, 7 is a control signal input terminal and 2 is an output terminal.

According to this structure, since the delay circuit 3 is provided, the phases of the input signal and the C signal may coincide with each other during the addition processing of the addition circuit 4.

Here, the balanced modulator 6 has a well-known multiplier configuration as shown in FIG. 2, for example, and changes not only the gain of an input signal but also the polarity of its output signal. Have a function. That is, a signed operation is performed on the input gain control signal. Therefore, if the output polarity of the balanced modulator 6 is in phase with the signal applied to the input terminal, the chroma signal level of the output of the adder circuit 4 will increase, and if it is of the opposite polarity, the chroma signal level will decrease. Returning to FIG. 1, in such a configuration, the video signal applied to the input terminal 1 is supplied to the BPF 5 and the delay circuit 3, respectively. The gain of the balanced modulator 6 changes according to the voltage of the control signal input terminal 7. When the control signal is on the + side, the input phase is the same and the level changes depending on the magnitude of the + potential. When the control signal is negative, the output signal is inverted. Therefore, the gain becomes zero when the control voltage is zero.

The output whose gain and phase are controlled by the balanced modulator 6 is added by the adder circuit 4 to the signal passed through the delay circuit 3. Therefore, when the output of the balanced modulator 6 is zero, the input signal is sent to the output terminal 2 as it is. When the output of the balanced modulator 6 is an inverted signal, the signals are added, so that the chroma signal level is lowered.

As described above, by using the balanced modulator, the chroma signal level can be freely changed. As a result, there is an advantage that the control can be performed from a distant place as compared with the case where the level conversion is performed using the volume (variable resistance element). If a well-known video mixing amplifier (fader amplifier) is used, the gain is set to 1
Generally, it can be changed from double to 0 times, but if a balanced modulator is used as in this embodiment, it is +1 to 0.
It can be changed from double to -1.

This balanced modulator has already been integrated into an IC, but MC1496 of Motorola Co., Ltd., MC1495, etc. may be used.

Regarding the delay time in the delay circuit 3,
The delay time in the BPF 5 and the balanced modulator 6 may be measured in advance and an appropriate element may be selected. For example, the number 10 [n
S].

It is obvious that the present invention can be applied not only to the level adjustment of the chroma signal but also to the adjustment of various video signals.

[0020]

As described above, according to the present invention, by providing the delay circuit having the delay time corresponding to the delay time of the sum of the BPF and the balanced modulator, only the chroma signal level is changed while matching the phases. The effect is that it can be done.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a video adjustment circuit according to the present invention.

FIG. 2 is a circuit diagram showing an internal configuration example of a balanced modulator shown in FIG.

FIG. 3 is a block diagram showing an example of a conventional image adjustment circuit.

FIG. 4 is a block diagram showing another example of a conventional image adjustment circuit.

[Explanation of symbols]

 3 Delay circuit 4 Adder circuit 5 Bandpass filter 6 Balanced modulator

Claims (3)

[Claims] 1. A filter for extracting a predetermined signal component from an input video signal, a gain changing means for changing the gain of the extracted signal component according to an external control signal, the filter for the video signal, and A video adjustment circuit comprising: a delay unit for delaying the same time as the delay time in the gain changing unit, and an adding unit for mixing a delay output of the delay unit and an output of the gain changing unit. 2. The image adjustment circuit according to claim 1, wherein the signal component is a chroma signal. 3. The image adjusting circuit according to claim 1, wherein the gain changing means is a balanced modulator.