JPH0514769A - Frequency characteristic controller for video signal - Google Patents

Abstract

PURPOSE:To obtain a video signal with an improved/S/N by providing a frequency characteristic control circuit which controls the cut-off frequency of the low-pass filter of a video signal constituted of three colors whose cut-off frequency can be changed. CONSTITUTION:The video signal consisting of blue, green, and blue with a well-balanced white balance, is inputted through an LPF1 and an amplifier circuit 2 to a matrix 3, and a luminance signal Y, and color difference signals B-Y and R-Y are outputted. Then, the signal Y is inputted an automatic gain control circuit 4, a gain control signal is outputted to a frequency characteristic control circuit 5 and the circuit 2, and a frequency control signal is outputted from the circuit 5 to the LPF1. The circuit 4 increases the gain of the circuit 2 when the value of the signal Y is small, and decreases the gain when the value is large. And also, the circuit 5 decreases the cut-off frequency of the LPF1 when the gain of the circuit 2 is high, and increases the frequency when the gain is low. Thus, the video signal with the improved S/N can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency characteristic control device for a video signal of an amplifier circuit used in a video camera, an electronic still camera or the like.

[0002]

2. Description of the Related Art In recent years, with the spread of small color video cameras, there has been a strong demand for higher performance.

Video signal processing of a conventional three-plate video camera will be described below. As shown in FIG. 4, an amplifier circuit 2 for red (R), green (G), and blue (B) video signals,
The matrix 3 that outputs the color difference signals BY, RY, and the luminance signal Y from the red, green, and blue video signals, the automatic gain control circuit 4 that controls the gain of the amplifier circuit 2 from the luminance signal Y, and the cutoff frequency are It is composed of a fixed low-pass filter 14 for red, green, and blue video signals.

The operation of the video signal processing of the conventional three-plate type video camera configured as described above will be described.
White-balanced red, green, and blue video signals pass through the low-pass filter 14 and the amplification circuit 2 and the matrix 3
To enter. A luminance signal Y and color difference signals BY and RY are output from the matrix 3. The luminance signal Y output from the matrix 3 is input to the automatic gain control circuit 4. The automatic gain control circuit 4 operates to increase the gain of the amplifier circuit 2 when the value of the luminance signal Y is small, and to decrease the gain of the amplifier circuit 2 when the value of the luminance signal Y is large.

[0005]

However, in the above-mentioned conventional configuration, when the value of the luminance signal is small, the gain of the amplifier of the red, green and blue video signals is increased, so that the noise component as well as the signal component is amplified. Therefore, there is a problem that the S / N becomes worse.

The present invention solves the above-mentioned conventional problems. When the value of the luminance signal is small, the frequency characteristic of the video signal is configured so that the S / N does not deteriorate even if the gain is controlled to be increased. An object is to provide a control device.

[0007]

In order to achieve the above object, a frequency characteristic control device for a video signal according to the present invention comprises a low pass filter, an amplifying means having an automatic gain control means, and a low frequency range depending on a gain of the amplifying means. It is provided with a structure having a frequency characteristic control means for changing the frequency characteristic of the pass filter.

[0008]

According to the present invention, in the above structure, the cutoff frequency of the low pass filter is lowered when the gain of the video signal amplifier circuit is high, and the cutoff frequency is raised when the gain is low. The frequency characteristics of the signal will be changed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the same components as those shown in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. As shown in Fig. 1, a low-pass filter (hereinafter abbreviated as LPF) for red, green, and blue video signals whose cutoff frequencies can be changed 1
On the other hand, a frequency characteristic control circuit 5 for controlling the cutoff frequency of the LPF 1 is newly provided.

Next, FIG. 2 shows an LPF of a frequency characteristic control device for a video signal of a three-plate video camera according to an embodiment of the present invention.
1 shows a first example of 1, wherein 6 is a changeover switch 7, 8 and 9 are LPFs each having a different cutoff frequency.
One set is used for each red, green, and blue amplifier circuit.
The cutoff frequency can be changed by selecting the low-pass filters 7, 8 and 9 by the control signal.
FIG. 2 shows an example in which the cutoff frequency can be changed in three steps.

FIG. 3 is an LPF of a frequency characteristic control device for video signals of a digital three-plate type video camera according to an embodiment of the present invention.
1 shows a second example of the D-type flip-flop 10, a multiplier 11, an adder 12, and a ROM or R.
It is composed of AM13 and is used for each of the red, green and blue amplifier circuits. The cutoff frequency is changed by changing the coefficient of the filter by changing the value to be multiplied by the control signal.

A frequency control device for video signals of the three-plate video camera constructed as described above will be described with reference to FIG. White-balanced red, green, and blue video signals are input to the matrix 3 through the LPF 1 and the amplifier circuit 2. From the matrix 3, the luminance signal Y, the color difference signal BY,
RY outputs. The luminance signal Y, which is the output from the matrix 3, is input to the automatic gain control circuit 4. The gain control signal output from the automatic gain control circuit 4 is input to the frequency characteristic control circuit 5 and the amplification circuit 2. Then, the frequency characteristic control circuit 5 outputs a frequency control signal to the LPF 1. The automatic gain control circuit 4 works to increase the gain of the amplifier circuit 2 when the value of the luminance signal Y is small, and to decrease the gain of the amplifier circuit 2 when the value of the luminance signal Y is large. Further, when the gain of the amplifier circuit 2 is high, the frequency characteristic control circuit 5 uses the LPF 1
When the gain of the amplifier 2 is low, the cutoff frequency is increased.

As described above, according to this embodiment, when the gain of the amplifier circuit 2 is high, the cutoff frequency of the LPF 1 is lowered, and when the gain of the amplifier circuit 2 is low, the cutoff frequency is raised. By doing so, a video signal with good S / N can be obtained.

In the above-mentioned embodiment, each circuit may be constituted by either analog or digital except for FIG. Further, the LPF 1 may be provided in the subsequent stage of the amplifier circuit 2. A noise canceller is a special example of the LPF 1.

[0016]

As described above, the present invention works to lower the cut-off frequency of the low pass filter of the video signal even if the gain of the automatic gain control amplifier circuit increases.
It is possible to obtain a video signal whose S / N is not deteriorated.

[Brief description of drawings]

FIG. 1 is a block diagram of a frequency characteristic control device for video signals of a three-plate video camera according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a first configuration example of a low-pass filter used in the same embodiment.

FIG. 3 is a block diagram showing a second configuration example of a low-pass filter used in the digital three-panel video camera of the same embodiment.

FIG. 4 is a block diagram of a video signal amplifier circuit of a conventional three-panel video camera.

[Explanation of symbols]

1 low pass filter 5 Frequency characteristic control circuit

Claims (2)

[Claims] 1. A video signal comprising a low-pass filter, an amplifying means having an automatic gain control means, and a frequency characteristic control means for changing the frequency characteristic of the low-pass filter according to the gain of the amplifying means. Frequency characteristic control device. 2. The cutoff frequency of the low pass filter is lowered when the gain of the amplifying means is high, and the cutoff frequency of the low pass filter is raised when the gain of the amplifying means is low. Item 1. A frequency characteristic control device for video signals according to Item 1.