JPH11215431A - Television camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with good S/N with respect to a motionless object and an image with less shake for a moving object by detecting the motion of the object from a change in a luminance level and a color change amount of a video signal image picked by an image-pickup element and controlling a drive circuit and an AGC circuit, depending on a degree of a motion. SOLUTION: A microcomputer 9 detects a change in a luminance level and a color level each time an image-pickup element reads a digital video signal. Whether or not an object is moving is discriminated by comparing each change with a threshold which has been decided in advance. When a motion is detected, the microcomputer 9 drives a drive circuit 10 to increase the read time of the image-pickup element and controls an AGC circuit 4 to increase is gain. When no motion is detected, the microcomputer 9 controls the drive circuit 10 and the AGC circuit 4 to decrease the gain and to increase the charge storage time of the image-pickup element 2, thereby enhancing the S/N ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television camera, and more particularly, to a television camera that obtains the best image according to a subject.

[0002]

2. Description of the Related Art The following method has conventionally been considered for capturing an image of a subject having low illuminance such as outdoor monitoring at night. That is, in the first method, an image is taken by a television camera having sensitivity to infrared light. Second, when the image becomes darker, the exposure time is lengthened, and when the image is darker, an image is taken with a long-exposure television camera that prioritizes the S / N ratio to increase the gain.
Third, when it gets darker, increase the gain, and when it gets darker,
2. Description of the Related Art There is a long-exposure-type television camera that gives priority to a movement that lengthens the exposure time.

[0003]

In the case of the above-mentioned prior art, the first method has a problem as a surveillance camera since the color of a subject is not known because the image is a monochrome image. Second
The method has a problem that the S / N ratio is relatively good, but the exposure time is long, so that when a fast-moving subject is imaged, blurring becomes large and it becomes difficult to confirm the subject.

The third method can cope with a fast-moving subject, but the noise is increased due to a high gain, and the second method is more suitable for imaging a subject that does not move.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate these problems, and to monitor a moving object outdoors by automatically or manually switching the gain and exposure time so as to be appropriate depending on the state of the object. And

[0006]

In order to achieve the object of the present invention, the movement of a subject is detected, that is, the brightness level and the color change of the entire screen or a predetermined area of the screen every time the image sensor is read. The amount is detected, and when there is a change equal to or more than a certain fixed value, it is determined that the subject is moving, the exposure time is shortened, and the AGC gain is increased. When the amount of change is smaller than a certain value, it is determined that the subject is not moving, and the exposure time is lengthened and the AGC gain is lowered.

As a result, in monitoring outdoors or the like at night,
When the subject does not move, an image with a good S / N ratio can be obtained. When a moving subject enters, the image is switched to a less blurred image, and the intruding object can be identified. Ideal for

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the television camera of the present invention will be described below with reference to the flowchart of FIG. 1 and a block diagram of the present invention of FIG.

In FIG. 2, reference numeral 1 denotes an image pickup lens on which light from a subject enters, and 2 denotes an image pickup for photoelectrically converting light incident from the image pickup lens 1, accumulates the electric charge in a pixel, and outputs a video signal after completion of exposure. The element 3 is a correlated double sampling (CDS) circuit for removing noise of the video signal output from the imaging element 2, and the automatic gain control (AGC) 4 is for adjusting the video signal to a required level specified by the microcomputer 9. ) Circuit, 5 is analog / digital (A /
D) a conversion circuit, 6 is a digital signal processing circuit (DSP) for performing various processing of a digital video signal, 7 is a digital / analog (A / D) conversion circuit, and 8 is an amplification circuit for amplifying and outputting a video signal to a required level. , 9 determine and control the gain of the automatic gain control circuit 4 and the video signal to be processed by the digital signal processing circuit 6. A driving circuit that outputs a charge reading pulse of the image sensor 2 so that the accumulated time is reached.
A signal switching circuit 11 outputs the digital video signal processed by the digital signal processing circuit 6 to the D / A conversion circuit 7 when the object is a normal bright object, and outputs it to the frame memory 12 during the accumulation operation. 4 shows a frame memory for holding a digital video signal processed by the signal processing circuit 6.

In the television camera of the present invention, light from a subject enters the image pickup device 2 via the image pickup lens 1, is photoelectrically converted, accumulates as electric charges in the pixels, and is controlled by the microcomputer 9. The charges are accumulated until a required exposure time by the charge readout pulse output from 10, and a video signal for one screen is output to the correlated double sampling circuit 3.

The correlated double sampling circuit 3 includes the image pickup device 2
, Removes noise from the video signal output from, performs sample hold, and outputs the result to the automatic gain control circuit 4.

The automatic gain control circuit 4 controls the gain of the video signal input from the correlated double sampling circuit 3 until it reaches a level specified by the microcomputer 9, and A / D converts the video signal of a required signal level. Output to the circuit 5.

The A / D conversion circuit 5 converts a video signal of a required signal level input from the automatic gain control circuit 4 into a digital signal in order to adapt it to digital processing, and outputs the digital signal to a digital signal processing circuit 6.

The digital video signal processing circuit 6 controls image quality control such as luminance processing, color processing, gamma correction, contour compensation, and white balance on the digital video signal input from the A / D conversion circuit 5 under the control of the microcomputer 9. And performs signal processing such as adjustment. The signal-switching circuit 11 directly outputs the processed digital video signal to the D / A conversion circuit 7 for a normal bright subject, and outputs it to the frame memory 12 for an accumulation operation.

During the accumulation operation, the frame memory 12 stores the digital video signal subjected to the required signal processing inputted from the digital video signal processing circuit 6 and holds the digital video signal until the next reading from the image sensor 2.

The D / A conversion circuit 7 converts the required digital video signal input from the digital video signal processing circuit 6 into an analog signal, and outputs the analog video signal to the amplifier circuit 8.

During the accumulation operation, the video signal held in the frame memory 12 is converted into an analog signal, and the analog video signal is output to the amplifier circuit 8.

The amplification circuit 8 amplifies the analog video signal input from the D / A conversion circuit 7 to a required signal level.
Output to other devices, for example, devices such as video monitors and VTRs.

The operation of the above-described television camera is the same as that of a normal long-exposure television camera, and the digital signal processing circuit 6 performs various signal processing. In
The microcomputer 9 detects the change in the luminance level and the change in the color level for each reading of the image pickup device of the digital video signal that has been subjected to the signal processing by the digital signal processing circuit 6,
These respective amounts of change are compared with predetermined values experimentally determined in advance, and respective control signals are output from the microcomputer 9 to the automatic gain circuit 4 and the drive circuit 10 depending on whether they are larger or smaller than the predetermined values. .

The operation of the present invention will be described below with reference to the flowchart of FIG. First, in the television camera of the present invention, the microcomputer 9 detects, from the digital video signal processing circuit 6, the amount of change in the luminance level and the color level in the entire screen shown in FIG. The microcomputer 9 compares each amount of change with a threshold experimentally determined in advance to determine whether or not the subject is moving. As a result, if there is a motion, the microcomputer 9 is operated in accordance with the "motion priority" flowchart of the flowchart of FIG.
Controls the drive circuit 10 to increase the readout time of the image sensor 2 and to increase the gain of the AGC circuit 4, for example. On the other hand, if there is no movement, "S /
The microcomputer 9 controls the drive circuit 10 and the AGC circuit 4 according to the flowchart of “N ratio priority”.

As described above, the television camera of the present invention detects a change in luminance level and a change in color of the entire screen or a predetermined area of the screen. It is determined that there is movement, and the charge accumulation time of the image sensor 2 is shortened and the gain of the automatic gain control circuit 4 is increased while keeping the level of the video signal constant.

On the other hand, when the change amount of the luminance level and the change amount of the color of the entire screen or a predetermined area of the screen are smaller than the predetermined values, it is determined that the subject is not moving and the current state is held. , When it has not changed for a predetermined time or more, the gain of the automatic gain control circuit 4 is gradually reduced,
The charge storage time of the image sensor 2 is increased.

The gain and the charge storage time of the automatic gain control circuit 4 are stopped from increasing or decreasing when they reach predetermined limit values.

When designating a predetermined area of the screen,
Selection is made from the areas divided by the screen dividing means in the digital signal processing circuit 6.

The relationship between the accumulation time and the increase or decrease of the AGC gain is as follows.
When the accumulation time is reduced to half, the AGC gain is increased by 6 dB.

For example, the screen is divided as shown in FIG.
When the area 6 is designated and the AGC gain is 0 dB in about 0.25 seconds (16 fields) and an appropriate video level is obtained, when an intruder appears in the area 6, the accumulation time is reduced to about 0. At the same time as switching to .03 seconds (2 fields), the AGC gain is switched to 18 dB.

[0027]

According to the present invention, in monitoring outdoors or the like at night, an image having a good S / N ratio can be obtained when there is no moving subject, and when a moving subject enters, the image is switched to a less blurred image. You will be able to identify intruders.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an embodiment of the present invention.

FIG. 2 is a block diagram showing one embodiment of the present invention.

FIG. 3 is a screen division pattern used in the present invention.

[Explanation of symbols]

1: imaging lens, 2: imaging element, 3: correlated double sampling circuit, 4: automatic gain control circuit, 5: A / D conversion circuit, 6: digital video signal processing circuit, 7: D / A conversion circuit, 8: output amplifier circuit, 9: microcomputer,
10: drive circuit, 11: signal switching circuit, 12: frame memory

Claims (3)

[Claims] An image pickup lens on which light from a subject enters, an image pickup element for photoelectrically converting the light incident from the image pickup lens to output a video signal, a driving circuit for driving the image pickup element, and the image pickup element AG to adjust the gain of video signal from
C circuit, and a digital signal processing circuit for digitally processing the video signal, and detects the movement of the subject from the amount of change in the luminance level and the amount of change in the color of the video signal captured by the image sensor,
A television camera, wherein the driving circuit and the AGC circuit are controlled according to the degree of the movement. 2. The television camera according to claim 1, wherein the means for detecting a moving subject detects the change based on a change in luminance level and color of the entire screen or a partial area of the screen. John camera. 3. A television camera according to claim 2, wherein said means for detecting a change in luminance level and color uses control data obtained from a digital signal processing circuit for processing a video signal. camera.