JP2002271688A - Television camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a television camera that is used for monitoring an outdoor place at nights and can more clearly identify an object, depending on the motion of the object. SOLUTION: The television camera selects provision of an output of a color image for the object without motion and an output of a black/white image, including a wavelength component in the near-infrared ray region with image blurs in the case of intrusion of the object with a motion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for switching between a color long-time exposure image at low illuminance and a black-and-white image containing a wavelength component of near-infrared light.

[0002]

2. Description of the Related Art Sensitivity characteristics of an image pickup device used in a color camera are from 400 nm to 9 nm in a wavelength range from visible light to near infrared light.
In most cases, it has sensitivity characteristics to light of about 00 nm. In order to make the color reproducibility of the image sensor having this sensitivity characteristic close to the color reproducibility when viewed by human eyes, an infrared cut filter is provided in front of the light receiving surface of the image sensor, that is, in the optical axis of the imaging light. Insertion removes light of a wavelength component exceeding about 700 nm in the near-infrared light region. Therefore, a good and easy-to-monitor color image can be obtained when the image to be imaged is bright and there are many wavelength components in the visible light range of about 400 nm to 700 nm. However, when the image becomes darker and the visible light component decreases, monitoring is performed. It becomes difficult.

Conventionally, there are the following two methods for capturing an image of a subject having low illuminance such as outdoor monitoring at night. First method: An image sensor having sensitivity up to the near-infrared light region is used. In order to emphasize the color reproducibility when the image is bright, an infrared cut filter is attached to make a color image, and when the image becomes dark, the infrared cut filter is removed. There is a television camera that produces a black-and-white image including a wavelength component in the near infrared region. There are also cameras that emit illumination for near-infrared light to further increase sensitivity. Second method: There is a long-time exposure type television camera that increases the sensitivity by increasing the exposure time while the infrared cut filter is attached even when it is dark.

In each of the first and second systems, switching is not performed by the movement of the subject only by controlling the brightness of the subject.

[0005]

In the above-mentioned prior art, when imaging a low-illuminance subject, the first method can cope with a fast-moving subject. However, since the image is a black-and-white image, the color of the subject cannot be recognized. In addition, the second method is a color image when it is dark, but has a problem that the image is blurred when a fast-moving subject is imaged due to a long exposure time. The first method is suitable for capturing an image of a moving subject. The second method is more suitable for capturing an image of a motionless subject.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate these problems, and to make it easier to monitor a video by making it possible to automatically select the first system or the second system depending on the situation of a subject at low illuminance. It is to do.

[0007]

In order to achieve the above object, the present invention provides an image pickup lens on which light from a subject is incident, and an image pickup lens including visible light to near-infrared light incident from the image pickup lens. An image sensor that photoelectrically converts light to output a video signal; an infrared cut filter that removes a wavelength component in a near-infrared light region; a video signal processing unit that generates a black and white video signal and a color video signal; A filter exchange means for replacing the infrared cut filter with glass having the same optical path length as the infrared cut filter on the light receiving surface of the element, and a luminance level of the entire screen or a predetermined area for each readout field of the image sensor. Means for detecting the amount of change in color, and if the amount of change is greater than or equal to a predetermined value, the exposure time is set to the predetermined exposure time if the amount of change is greater than or equal to a predetermined value. Insert the glass from the optical axis by removing the infrared cut filter outputs a black-and-white video signal,
If the change amount is smaller than the predetermined value, the exposure time is made longer than the predetermined exposure time, the glass is removed from the optical axis of the imaging light, the infrared cut filter is inserted, and a color video signal is output. The operation is switched so as to perform the operation.

[0008] The above operation may be switched when the brightness of a captured image is lower than a predetermined brightness.

As a result, for example, in monitoring at low illuminance such as outdoors at night, a color image can be obtained for an object that does not move, and when a fast-moving object enters, there is little blur according to the detection result. Switching to black and white video makes it easier to identify intruders.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the television camera according to the present invention will be described below with reference to the flowchart of FIG. 1 and the block diagram of FIG. In FIG. 2, reference numeral 1 denotes an imaging lens on which light from a subject enters, and 2 denotes a photoelectric conversion of the light incident from the imaging lens 1 and accumulates each pixel as an electric charge. An image sensor 3 that outputs a video signal is a correlated double sampling (CD) that removes noise of a video signal output from the image sensor 2.
S) The circuit 4 controls automatic gain control (A) for adjusting the video signal to a required level specified by the microcomputer 9.
GC) circuit, 5 is an analog / digital (A / D) conversion circuit, 6 is a digital signal processing circuit (DSP) for performing various processing of digital video signals, 7 is a digital / analog (D / A) conversion circuit, 8 is An amplification circuit (amplifier) 9 amplifies the video signal to a required level and outputs the signal. The amplifier 9 controls the amount of gain of the automatic gain control circuit 4 and the video signal processing performed by the digital signal processing circuit 6. The microcomputer 10 controls the drive circuit 10. The drive circuit 10 outputs a charge readout pulse of the image sensor 2 so that the exposure time specified by the microcomputer 9 is reached.
Reference numeral 1 denotes a signal switching circuit that outputs the digital video signal processed by the digital signal processing circuit 6 to the D / A conversion circuit 7 when the subject is a normal bright subject, and outputs the digital video signal to the frame memory 12 when the exposure time is increased. 2 shows a frame memory for holding digital video signals processed by the digital signal processing circuit 6 when increasing the number.

In the television camera according to the present invention, light from a subject passes through the imaging lens 1 to remove wavelength components in the near-infrared light region by the infrared cut filter 14a, and is incident on the imaging device 2. The incident light is subjected to photoelectric conversion, accumulated as a charge for each pixel, accumulated until a required exposure time by a charge readout pulse output from a drive circuit 10 controlled by a microcomputer 9, and a video signal for one screen is correlated. Output to the double sampling circuit 3.

The correlated double sampling circuit 3 includes an 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 the 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.

Under control of the microcomputer 9, the digital video signal processing circuit 6 converts the digital video signal input from the A / D conversion circuit 5 into image quality adjustments such as luminance processing, color processing, gamma correction, contour compensation and white balance. And performs signal processing such as adjustment.

The digital video signal subjected to the signal processing is directly output to the D / A conversion circuit 7 for a normal bright subject by the signal switching circuit 11, and is output to the frame memory 12 for a long exposure operation.

When the exposure time is increased, the frame memory 12 interpolates the required digital signal processed from the digital video signal processing circuit 6, and
Hold until the next reading.

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

During a long-time exposure 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
As shown in FIG. 1, each time a microcomputer 9 reads out a digital video signal processed by a digital signal processing circuit 6 from an image sensor, the microcomputer 9 determines the amount of change in luminance level and the amount of change in color for the entire screen or a predetermined area thereof. If the change is greater than a predetermined value, it is determined that the subject has moved (step 102 in FIG. 1), a control signal is sent to the filter switching mechanism 13, and the infrared cut filter 14a is inserted into the optical axis of the imaging light. The dummy glass 1
4b is inserted (step 104).
In addition, the exposure time of the image sensor 2 is reduced (step 10).
5).

Further, it is determined whether or not the luminance level and the amount of color change of the entire screen or a predetermined area of the screen are smaller than predetermined values (step 102). If so, it is determined that the subject has not moved. Then, it is determined whether the state has not changed for a predetermined time or more (step 106). If the state has not changed, the infrared glass is cut from the state where the dummy glass has been inserted into the optical axis of the imaging light. Switch to the state where the filter is inserted (Step 10
8) Control is performed so as to increase the exposure time of the image sensor 2 (step 109).

When the gain and the exposure time of the automatic gain control circuit 4 reach a predetermined limit value, the increase and decrease are stopped.

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 increase / decrease of the exposure time and the presence / absence of the infrared cut filter differs depending on the sensitivity characteristics of the imaging device used.
For example, if the infrared cut filter is replaced with dummy glass and the exposure time is reduced to 1/4, the screen is divided as shown in FIG. 27 seconds (16 fields) and
If an appropriate image level is obtained when there is an infrared cut filter, when an intruder appears in the area 6, the exposure time is switched to about 0.06 seconds (four fields) and the dummy glass is switched. What should I do?

[0026]

According to the present invention, a color image can be obtained for an object that does not move when monitoring an outdoor object at night or the like, and when a moving object enters, a wavelength component in the near-infrared light region with less blur is obtained. The image is switched to a black-and-white image, which makes it easier to identify the intruder.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an operation example of a television camera according to the present invention.

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

FIG. 3 is a diagram showing an example of a screen division pattern according to the present invention.

[Explanation of symbols]

1: imaging lens, 2: imaging device, 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 amplification circuit, 9: microcomputer, 10: drive circuit, 11: signal switching circuit, 12: frame memory, 13: filter switching mechanism, 14a: infrared cut filter, 14b: dummy glass .

Claims (2)

[Claims] An imaging lens on which light from a subject is incident;
An imaging element that photoelectrically converts imaging light including visible light to near-infrared light incident from the imaging lens and outputs a video signal; an infrared cut filter that removes wavelength components in the near-infrared light region; Video signal processing means for generating a video signal and a color video signal, and a filter replacement means for replacing the infrared cut filter and glass having the same optical path length as the infrared cut filter on the light receiving surface of the image sensor,
Means for detecting the amount of change in the brightness level or color of the entire screen or a predetermined area for each readout field of the image sensor, according to the detection result of the change amount detection means,
If the change amount is equal to or more than a predetermined value, the exposure time is set to the predetermined exposure time, the infrared cut filter is removed from the optical axis of the imaging light, the glass is inserted, and a black-and-white video signal is output. If the change amount is smaller than that, the operation is performed such that the exposure time is longer than the predetermined exposure time, the glass is removed from the optical axis of the imaging light, the infrared cut filter is inserted, and a color video signal is output. A television camera characterized by switching. 2. The television camera according to claim 1, wherein said operation is switched when the brightness of a captured image is lower than a predetermined brightness.