JP2003324748A - Television camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a television camera employing an imaging element with sensitivity from an infrared ray to a visible light, having an infrared ray cut filter switching function capable of preventing hunting of filter switching thereby properly selecting color or black/white. <P>SOLUTION: The television camera including: an imaging lens, an imaging element with sensitivity from an infrared ray to a visible light; an infrared ray cut filter for eliminating a wavelength components of a near infrared ray region; a video signal processing means for producing a black/white signal or a color signal in response to the video signal from the imaging element; and a filter exchange means that replaces the infrared ray cut filter with dummy glass (plain glass) and outputs a black/white video signal when an object is darker than prescribed lightness, and replaces the dummy glass with the infrared ray cut filter and outputs a color video signal, when bright. The television camera outputs a still picture before switching onto a monitor or the like while the television camera discriminates filter switching. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for switching between a color image and a near-infrared black and white image at low illuminance.

[0002]

2. Description of the Related Art The sensitivity characteristic of an image pickup device used for a color camera is usually in the wavelength region of about 400 nm to 900 nm, but an infrared cut filter is inserted in the light receiving surface of the image pickup device in order to make the color reproducibility closer to human eyes. Then, the wavelength component of about 700 nm or more in the near infrared region is removed. for that reason,
A good and easy-to-monitor color image is obtained when there are many wavelength components of 400 nm to 700 nm that are bright and in the visible light region, but become dark and the visible light component decreases, making it difficult to monitor.

Sensitivity improvement by automatic gain control (hereinafter referred to as AGC) and image storage using a frame memory (hereinafter referred to as AGC)
There is also a case where a storage operation is performed), but there is a disadvantage that the S / N ratio is lowered when the sensitivity is improved by AGC.
Further, in the accumulation operation, if the image accumulation period (hereinafter referred to as the accumulation magnification) is increased to improve the sensitivity, there is a disadvantage that blur occurs when a fast-moving subject is imaged, so that the image quality is maintained. Therefore, it is not possible to increase the AGC gain and the storage magnification unnecessarily.

As one of the methods for improving these, an image pickup element sensitive to near infrared light is used to emphasize color reproducibility when it is bright. Therefore, an infrared cut filter is attached to form a color image, and when it becomes dark, There is a television camera that automatically or manually removes the infrared cut filter to produce a black and white image that also uses wavelength components in the near infrared region. There are also cameras that emit near-infrared illumination to increase sensitivity. Further, even when the AGC and the storage operation are supplementarily combined, the AGC gain and the storage magnification can be suppressed low,
It is possible to compensate for the above-mentioned disadvantages such as a decrease in S / N ratio.

The problem here is the timing of switching the filters. In particular, when the infrared cut filter is removed and the near-infrared illumination is emitted, the brightness level may become higher than that in the case of color images.In the case of the method of detecting the brightness level and switching the filter, attach the infrared cut filter. It may return to a color image. When returning to a color image, the brightness level is low, so that the image is switched to a monochrome image again and this operation is repeated. That is, hunting in which color images and black-and-white images alternate with each other may occur. In order to prevent this hunting, in the conventional method, the following operations are performed so that once a black-and-white image is switched, it is not switched to a color image for a while. Prior art 1: When infrared illumination is applied, a signal is sent to a camera and fixed to a black and white image. Prior art 2: A large amount of hysteresis is provided to make it difficult to switch from a monochrome image to a color image.

[0006]

In the above-mentioned prior art 1,
Wiring is required to send a signal to the camera, and the camera alone may not be able to handle it. In addition, the conventional technique 2
Then, if the hysteresis is increased, the state of a color image may be maintained even if it becomes dark, or the state of a black and white image may be maintained even if it becomes bright. It is an object of the present invention to eliminate these drawbacks and prevent black and white images and color images from being output alternately.

[0007]

In order to achieve the above object, the present invention eliminates an imaging lens, an imaging device having sensitivity from near infrared light to visible light, and a wavelength component in the near infrared region. An infrared cut filter and a video signal processing means for generating a black-and-white signal and a color signal according to a video signal from the image pickup device are provided. When the subject is darker than a predetermined brightness, the infrared cut filter is replaced by a dummy glass ( (Glass) to output a black-and-white video signal, and when it is bright, the dummy glass is replaced with the infrared cut filter, and in a television camera having a filter exchanging means for outputting a color video signal, the switching of the filter is judged. During the operation, the still image before switching is output to a monitor or the like.

The brightness level and at least AGC gain data (AGC: automatic gain control) are used to determine whether to switch the infrared cut filter and the dummy glass.
Either one of the accumulation magnification data is used.

Further, the brightness level when the infrared cut filter is replaced with the dummy glass and at least one of the AGC gain data and the storage magnification data is recorded, the dummy glass is inserted, and a monochrome video signal is inserted. Is output, when it is determined that the brightness level is brighter than a predetermined threshold value, the display is switched to still image output, the dummy glass is replaced with the infrared cut filter, and the infrared cut filter is replaced. The brightness level and at least one of the AGC gain data and the storage magnification data is compared with the recording data, and if the difference between the brightness level after the replacement and the brightness level of the recording data is equal to or more than a predetermined value, the color It is judged that the video output is inappropriate, and it is replaced with the dummy glass again, and the black and white video output is maintained. The difference between the brightness levels of the recording data after the replacement is less than a predetermined value, and the AGC gain data and the storage ratio of the recording data are more than that of either the AGC gain data after the replacement or the storage ratio data. When either one of the data is large, it is determined that the color image output is appropriate, the color image output is switched to, and the moving image is output after the above determination is completed.

The brightness level of the entire screen or a predetermined area is detected, and when the brightness level becomes lower than a predetermined threshold value, it is judged to be dark, the infrared cut filter is removed to make a black and white image, and the brightness level after switching, AGC Record the gain and accumulated magnification data. When the subject becomes brighter, the brightness level becomes higher, and the AGC gain and storage magnification data change from the recorded values after switching, the current still image is output on the monitor screen, and the infrared cut is instantaneously made in a black and white image. Switch to the filter and determine if a sufficient brightness level can be secured even if the color image is restored. When the brightness level is higher than a predetermined threshold value, it is determined that the subject is bright and the color image is switched. If it is dark, put it back on the dummy glass. After that, the still image on the monitor screen is restored to the moving image. As a result, when monitoring in low light such as outdoors at night,
There is no hunting in which color images and black-and-white images are switched alternately even when irradiated with near-infrared illumination, which reduces the burden on the monitor and makes it easier to identify intruders and the like.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a long exposure type television camera of the present invention will be described below with reference to the circuit configuration of FIG.

In FIG. 1, 1 is an image pickup lens on which light from a subject is incident, and 2 is an image pickup device that photoelectrically converts light incident from the image pickup lens 1 and accumulates it in a pixel as an electric charge, and outputs it as a video signal after exposure. An element 3 is a correlated double sampling (CDS) circuit for removing noise of the video signal output from the image sensor 2, and an automatic gain control (AGC) 4 is for adjusting the video signal to a predetermined level designated by the microcomputer 9. ) Circuit, 5 is analog / digital (A /
D) conversion circuit, 6 is a digital signal processing circuit (DSP) that performs various processes of digital video signals, 7 is a digital / analog (D / A) conversion circuit, and 8 is an amplification circuit that amplifies the video signal to a required level and outputs it. , 9 are microcomputers for determining and controlling the gain of the automatic gain control circuit 4 and the video signal processed by the digital signal processing circuit 6 and having software for controlling the drive circuit 10 of the image pickup device 2, 9-1. Is a ROM that stores the control software built in the microcomputer 9, 9-2 is a RAM that is built in the microcomputer 9, and 10 is the charge reading of the image pickup device 2 so that the storage time designated by the microcomputer 9 is reached. Drive circuit that outputs pulses,
Reference numeral 11 outputs the digital video signal processed by the digital signal processing circuit 6 to the D / A conversion circuit 7 when a normal bright subject is present, and the frame when the sensitivity is improved by image storage at low illuminance (hereinafter referred to as storage operation). Reference numeral 12 denotes a signal switching circuit for outputting to the memory 12, and 12 denotes a frame memory for accumulating and adding the digital video signals processed by the digital signal processing circuit 6 during the accumulating operation and holding them.

In the television camera of the present invention, the light from the subject is incident on the image pickup device 2 after the wavelength component in the infrared region is removed by the infrared cut filter 14a via the image pickup lens 1. The incident light is photoelectrically converted by the image pickup device 2, accumulated in the pixel as an electric charge, and accumulated for a predetermined exposure time by an electric charge reading pulse output from the drive circuit 10 controlled by the microcomputer 9, and is accumulated for one screen. Image signal is correlated double sampling circuit 3
Is output to. The video signal is subjected to noise removal by the correlated double sampling circuit 3, sample-held, and then output to the automatic gain control circuit 4. The automatic gain control circuit 4 controls the gain of the video signal output from the correlated double sampling circuit 3 until it reaches a level designated by the microcomputer 9, and the video signal of a predetermined signal level is an A / D conversion circuit. It is output to 5. The video signal of the predetermined signal level output from the automatic gain control circuit 4 is converted into a digital video signal by the A / D conversion circuit 5 and output to the digital signal processing circuit 6. In the digital video signal processing circuit 6, under the control of the microcomputer 9, the digital video signal output from the A / D conversion circuit 5 is subjected to image quality control such as luminance processing, color processing, gamma correction, contour compensation, and white balance adjustment. Etc. signal processing is performed. The signal-processed digital video signal is directly output by the signal switching circuit 11 to the D / A conversion circuit 7 when a normal bright subject is present, and is output to the frame memory 12 during the accumulation operation. In the frame memory 12, during the accumulation operation, the digital video signal output from the digital video signal processing circuit 6 is added for a predetermined accumulation period (for example, 2 frames, hereinafter referred to as an accumulation magnification) and held. The D / A conversion circuit 7 converts the digital video signal output from the digital video signal processing circuit 6 into an analog video signal and outputs the analog video signal to the amplification circuit 8. During the accumulation operation, the video signal held in the frame memory 12 is converted into an analog video signal and output to the amplifier circuit 8. In the amplifier circuit 8, the analog video signal output from the D / A conversion circuit 7 is amplified to a predetermined signal level and output to another device such as a video monitor or a VTR. In addition,
The above-mentioned gain of the automatic gain control circuit 4 and the charge accumulation time are stopped increasing and decreasing when they reach predetermined limit values.

Further, when a predetermined area of the screen is designated as the target of the brightness level detection, it is selected from the areas divided by the screen dividing means in the digital signal processing circuit 6. (See (A) of FIG. 2) For example, when capturing a landscape including an object such as a neon advertisement that repeatedly blinks at night as shown in (B) of FIG. The blinking of the neon advertisement is detected as a change in the brightness level, and hunting in which color images and black-and-white images alternate with each other may occur. Therefore, by excluding the regions 3 and 4 shown in FIG. 2B from the target of the brightness level detection, it is possible to prevent the blinking of the neon advertisement from being detected and prevent hunting.

The operation of the above-mentioned television camera is similar to that of a normal long-exposure television camera. Hereafter, description will be given with reference to the flowchart of FIG. 3 and the filter switching operation diagram of FIG. FIG. 3 shows the operation of one embodiment of the present invention, and the reference numerals show the operation steps. FIG. 4 shows the filter switching operation, the brightness level, and the AG with the change in the brightness of the outside light as the horizontal axis.
9 shows changes in C gain data and storage magnification.

The microcomputer 9 detects the brightness level of the entire screen or a predetermined area of the screen, which has been signal-processed by the digital signal processing circuit 6, and is below the low brightness threshold (for example, 50% of the video level) shown in FIG. If there is, it is determined to be dark (step 213 in FIG. 3). Here, the image sensor 2
If the infrared cut filter 14a is inserted on the front surface of the device, a control signal is sent to the filter switching mechanism 13 to switch the infrared cut filter 14a to the dummy glass 14b (step 215 in FIG. 3), and the digital video signal. The processing circuit 6 removes the chroma signal component to produce a black and white image (step 216 in FIG. 3). In addition, the brightness level after switching, the AGC gain data, and the storage magnification data during long-time exposure operation are stored in a of the RAM 9-2 (timing (1) in FIG. 4).

Next, when the external light is further reduced and the sensitivity is lowered, the near-infrared illumination is emitted by the operation of a supervisor. As shown in FIG. 4, the irradiation of the near infrared light increases the brightness level of the entire screen or a predetermined area of the screen. When the brightness level is equal to or higher than the high brightness threshold value (for example, 120% of the video level) shown in FIG. 4, it is determined that the brightness has increased (FIG. 3, step 202). Further, when there is a change in the brightness level in the designated area, the infrared cut filter 14a
The filter is controlled so as not to switch unless a certain time has passed after switching to the dummy glass 14b (FIG. 3,
Step 203). If the conditions of steps 202 and 203 are satisfied, the currently captured image is recorded in the frame memory 1
2 and output this video to the D / A conversion circuit 7 to output a monochrome still image (FIG. 3, step 20).
5), replace the dummy glass 14b with the infrared cut filter 14a
(Step 206 in FIG. 3).

Then, the brightness level after switching and the AG
The C gain data and the storage magnification data are stored in b of the RAM 9-2 and compared with the values stored when switching to the dummy glass 14b (a of RAM 9-2) (FIG. 3, step 208).

In this case, since the infrared light is further removed from the light source having many near-infrared light components, the brightness level after switching is lowered as shown in the timing (2) of FIG. Therefore, when the brightness level stored in the RAM 9-2b is lower than the brightness level stored in the RAM 9-2a, it is determined that the color image cannot be switched, and the dummy glass 14b is switched again ( The luminance level, the AGC gain, and the storage magnification data are overwritten on a of the RAM 9-2 at the timing (3) in FIG. 3, step 209) and FIG. 4 (step 210 in FIG. 3). After that, the output of the frame memory 12 is switched to the currently picked up image and the image is returned to the monochrome moving image (step 212 in FIG. 3).

Next, when the external light increases due to dawn or the like, the AGC gain and the storage magnification data are decreased so that the brightness level is controlled to be constant, as shown in the timing (3) of FIG. . When the value further decreases to the minimum value, the brightness level increases. When the conditions of steps 202 and 203 are satisfied, the video image currently being captured is stored in the frame memory 12, and the video image is continuously output to the D / A conversion circuit 7 to output a monochrome still image (see FIG. 3, Step two
05), the dummy glass 14b is replaced with the infrared cut filter 14
Switch to a (step 206 in FIG. 3).

Then, the brightness level after switching and the AG
The C gain data and the storage magnification data are stored in b of the RAM 9-2 and compared with the values stored when switching to the dummy glass 14b (a of RAM 9-2) (FIG. 3, step 208).

In this case, since the brightness level is increased by the external light (light source having a small amount of near-infrared light component), the near-infrared light is removed by the infrared cut filter 14a as shown in the timing (4) of FIG. Even if the operation is performed, the brightness level is controlled by the RAM 9- by controlling the AGC gain data and the storage magnification data.
It is detected at almost the same level as 2a. In addition, the RA
In b of M9-2, the AGC gain data and the storage magnification data are almost the minimum values (timing (4) in FIG. 4).
In the RAM 9-2a, the AGC gain data and the storage magnification data have almost the maximum values. That is, A
RAM of the magnitude relationship between the GC gain data and the storage magnification data
If it is determined that the difference in luminance level is small with a of 9-2 <b of RAM 9-2, it is determined that the color image can be switched to, and the data of the chroma signal component of the digital image signal processing circuit 6 is restored to the original color image. It is output (FIG. 3, step 211).

After that, the output of the frame memory 12 is switched to the image that is currently being picked up, and a color moving image is output (step 212 in FIG. 3).

[0024]

As described above, according to the present invention, in the case of monitoring at low illuminance such as outdoors at night, hunting in which color images and black and white images are alternately switched does not occur even when irradiated with infrared light, and the burden on the observer is reduced. This makes it easier to identify intruders.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing an example of a screen division pattern.

FIG. 3 is a flowchart showing an embodiment of the present invention.

FIG. 4 is a diagram showing a switching operation of filters.

[Explanation of symbols]

1: Imaging lens, 2: Imaging element, 3: Correlated double sampling circuit, 4: Automatic gain control circuit, 5: A / D conversion circuit device, 6: Digital video signal processing circuit, 7: D / A conversion circuit, 8: Output amplifier circuit, 9: Microcomputer,
9-1: ROM, 9-2: RAM, 10: drive circuit, 1
1: signal switching circuit, 12: frame memory, 13:
Filter switching mechanism, 14a: infrared cut filter,
14b: Dummy glass

Claims (3)

[Claims] 1. An image pickup lens, an image pickup device having sensitivity from near infrared light to visible light, an infrared cut filter for removing wavelength components in the near infrared region, and an image signal from the image pickup device. Video signal processing means for generating a black and white signal and a color signal, and when the subject is darker than a predetermined brightness, the infrared cut filter is replaced with a dummy glass (blank glass) to output a black and white video signal, and when the subject is bright, In a television camera having a filter exchanging means for replacing the dummy glass with the infrared cut filter and outputting a color video signal, a still image before switching is output to a monitor or the like while determining whether to switch the filter. A television camera characterized by: 2. The television camera according to claim 1, wherein the brightness level, at least AGC gain data (AGC: automatic gain control), and storage magnification data are used to determine whether to switch the infrared cut filter and the dummy glass. A television camera characterized by using either one. 3. The television camera according to claim 1, wherein the brightness level when the infrared cut filter is replaced with the dummy glass, and at least one of AGC gain data and storage magnification data When it is determined that the brightness level is recorded, the dummy glass is inserted, and the monochrome video signal is output, and the brightness level is brighter than a predetermined threshold value, switching to still image output,
The dummy glass is replaced with the infrared cut filter, the brightness level after the replacement with the infrared cut filter is compared with at least one of AGC gain data and storage magnification data, and the recording data, and the replacement is performed. When the difference between the subsequent brightness level and the brightness level of the recorded data is equal to or more than a predetermined value, it is determined that the color image output is inappropriate, the color glass output is replaced again, and the black and white image output is held, and after the replacement. The difference between the brightness levels of the recording data is less than a predetermined value, and one of the AGC gain data and the storage magnification data of the recording data is more than the one of the AGC gain data and the storage magnification data after the replacement. When one is large, it is determined that the color video output is appropriate, switch to color video output,
A television camera, which outputs a moving image after the above determination is completed.