JP4219201B2 - Imaging system - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an imaging system used for surveillance cameras and the like.
[0002]
[Prior art]
When the illuminance of the subject is sufficient, such as in the daytime, it can function as a color camera with excellent color reproducibility by mounting an infrared cut filter on the front side of the imaging unit. There is known a so-called day / night switching type surveillance camera that illuminates with illumination and functions as a highly sensitive black-and-white camera by removing the infrared cut filter (see Patent Document 1). The infrared cut filter is automatically attached and detached by an actuator such as a motor in accordance with the brightness of the subject and the illumination state. Near-infrared light is a wavelength region that cannot be detected by human eyes at all. However, an image sensor such as a CCD used in a surveillance camera has high sensitivity to the near-infrared light, and can sufficiently capture an image. As a light source for such near infrared illumination, a near infrared LED or a near infrared bulb is used.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-45512
[Problems to be solved by the invention]
However, the near-infrared LEDs and near-infrared light bulbs described above are generally directional in the direction of illumination, and subjects such as persons directly exposed to near-infrared illumination are very bright, while other backgrounds are used. Since illumination light is not uniformly irradiated, the whole image tends to be very dark. Here, when average value metering, which is a photometric method widely used in surveillance cameras, is used, the average value of the video signal of the entire screen is determined to be dark as a whole screen because the influence of the background is large. For this reason, the lens aperture is opened, and as shown in FIG. 3B, the video signal level of the subject that needs to be truly photographed becomes too high and becomes saturated and becomes white and cannot be monitored. FIG. 3A shows a state in which the same aperture value as that in FIG. 3B is set when the entire screen is dark.
[0005]
Therefore, for example, a method of switching the photometry method of the camera to peak-priority photometry only at night can be considered. With this method, photometry is performed with emphasis on the peak component of the video signal, so the lens aperture is narrowed compared to average value metering, and the video signal level of the subject that needs to be truly photographed is appropriate. Become. However, as shown in FIGS. 4A and 4B, when a high-luminance area such as an emergency light is always photographed on a part of the screen, the high-luminance area such as the emergency light is not displayed. Since control is performed so as to capture images properly, there is a drawback that the lens aperture is always in a narrowed state and monitoring becomes difficult.
[0006]
In view of the above circumstances, the present invention provides an imaging system capable of avoiding a situation in which a subject that truly needs to be captured is not properly captured in night shooting using near-infrared illumination or the like. With the goal.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, an imaging system according to the present invention includes an imaging unit having sensitivity to light of a predetermined wavelength band, an illumination device that irradiates light of a predetermined wavelength band toward an imaging direction, Illumination control means for controlling the amount of light emitted from the illumination device in accordance with the luminance value in the captured video imaged by the imaging means, and the brightness level of each part in the captured video imaged by the imaging means When V, the luminance level threshold value is Va, the total amount of the portion where V ≧ Va in the captured image or the ratio of the portion in the captured image is S, and the threshold value is N, the illumination control means satisfies S> N In some cases, the amount of light emitted from the illumination device is decreased, and when N> S, the amount of light emitted from the illumination device is increased.
[0008]
In the above configuration, for example, if the luminance level threshold value Va is set to a luminance value that causes halation, the light amount control is performed so that the total amount or the ratio of the portions that cause halation in the captured image is S. In this case, the S may be a total amount or a ratio that is small, for example, in the captured video. That is, while avoiding a dark screen by increasing the amount of emitted light from the illumination device as much as possible, by reducing the amount of emitted light when S> N, the amount of emitted light is too much and halation is increased. This situation can be avoided.
[0009]
The imaging system of the present invention is imaged by the imaging means having sensitivity to light of a predetermined wavelength band, an illumination device that irradiates light of the predetermined wavelength band toward the imaging direction, and the imaging means. Illumination control means for controlling the amount of light emitted from the illuminating device in accordance with the luminance value in the captured image, and the brightness level of each part in the captured image captured by the imaging means is V, and the brightness level threshold is Va. , When the total amount of the portion where V ≧ Va in the captured image or the ratio of the portion in the captured image is S, and the first threshold and the second threshold are N1, N2 (N1> N2), The illumination control means controls to decrease the emitted light amount of the illumination device when S ≧ N1, and to increase the emitted light amount of the illumination device when N2 ≧ S.
[0010]
In the above configuration, the amount of emitted light is controlled so that halation occurs, for example, in a range of N1>S> N2, that is, a range of a predetermined width. While avoiding a dark screen by increasing, by reducing the amount of emitted light when S ≧ N1, it is possible to avoid a situation in which the amount of emitted light is too much and halation is increased.
[0011]
When the state of S> N or S ≧ N1 continues even after the amount of light emitted from the illuminating device is reduced to the minimum, it is preferable to control the diaphragm of the imaging unit to be closed by a predetermined amount. Further, when the state of N> S or N2 ≧ S continues even after the aperture of the image pickup unit is fully opened, it is preferable to control the amount of light emitted from the illumination device to be increased by a predetermined amount.
[0012]
Each part in the captured image may be each pixel, or each region obtained by dividing the captured image into a plurality of regions.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an imaging system according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
[0014]
FIG. 1 is a block diagram showing the configuration of the imaging system. The lens 1 receives the light reflected by the subject, collects it, and guides it to the imaging unit 3. The diaphragm unit 2 adjusts the amount of light guided to the imaging unit 3. The imaging unit 3 is composed of a CCD, for example, and outputs a signal corresponding to the amount of received light for each pixel. The signal processing unit 4 is composed of an ASIC (Large Scale Integrated circuit) or a microcomputer, inputs the signal output from the imaging unit 3, generates an NTSC signal, for example, and supplies it to a monitor or a recording device (not shown). Further, the signal processing unit 4 outputs a command signal to the aperture control unit 5 and the illumination control unit 6 based on the signal output from the imaging unit 3.
[0015]
The diaphragm unit 2 is provided with an actuator (not shown). This actuator is operated by a drive control signal given from the diaphragm control unit 5 and drives the diaphragm blades to adjust the opening amount of the diaphragm.
[0016]
The illuminating device 7 includes a near infrared LED, a near infrared light bulb, and the like. When the voltage supplied to the near infrared LED or the near infrared light bulb changes, the amount of emitted light in the near infrared is changed. The illumination control unit 6 controls the drive voltage in the illumination device 7 based on a command from the signal processing unit 4. For example, if the command is performed with an 8-bit signal, the emitted light quantity control in 256 steps can be performed.
[0017]
For example, the signal processing unit 4 divides the captured image into 16 × 16 256 regions (see FIG. 3 of the conventional section), and performs a process of calculating an average luminance value V in each region. A memory (not shown) (not shown) stores a luminance level threshold Va. The brightness level threshold value Va is set to a brightness value that causes halation (in other words, the saturation value of the CCD in the imaging unit 3). The brightness level threshold Va may be fixedly set, but may be changed by the user. Further, the signal processing unit 4 performs a process of comparing the brightness value V of each area with the brightness level threshold Va, and performs a process of calculating the number S of areas where V ≧ Va. A threshold value N1 and a threshold value N2 (N1> N2) for the number S are also stored in the memory. For example, if there are about 20 areas where halation occurs, if it is sufficient to recognize the photographed subject, “20” may be set as the threshold value N1. For the threshold N2, for example, “5” may be set. Of course, the threshold value may be changed by the user. Here, when there is an emergency light within the imaging range, the video area corresponding to the emergency light can be saturated even in the absence of illumination by the illumination device 7, and V ≧ Va in several areas. It becomes. If this number is “3”, for example, “8” (5 + 3) may be set as the threshold value N2. When setting for night photography, for example, the illumination device 7 is not illuminated, the aperture is set to full open, and the number V ≧ Va is displayed on, for example, a monitor. The setter can also set the threshold value N2 and the threshold value N1 corresponding to the number displayed on the monitor.
[0018]
Next, illumination control and aperture control during night shooting will be described based on the flowchart of FIG.
[0019]
When executing the night photographing mode, the signal processing unit 4 first gives a command to the illumination control unit 6 and the aperture control unit 5 to maximize the amount of light emitted from the illumination device 7 and fully open the lens aperture of the camera (step S1). ). Then, the signal processing unit 4 performs a process of comparing the luminance value V of each region with the luminance level threshold Va, and calculates the number S of regions where V ≧ Va (step S2). Next, the signal processing unit 4 determines whether or not N1>S> N2 (step S3), and if YES, the process returns to step S2. On the other hand, when NO is determined in step S3, it is determined whether S ≧ N1 (step S4). When S ≧ N1, it is determined whether or not the amount of light emitted from the illumination device 7 is minimum (step S5). If it is not minimum, the light amount is decreased by one level (step S6). If the amount of light is minimum, the diaphragm is closed by one step (step S7). Thereby, when the intruder enters the imaging range of the camera and the amount of near-infrared rays reflected by the intruder and entering the camera is large, the intruder video portion causes halation and the S becomes N1 or more. First, the amount of emitted light is reduced, and further, the diaphragm is closed, so that the amount of near-infrared rays reflected by the intruder and entering the camera is reduced, and halation in the intruder image portion is avoided.
[0020]
When YES is determined in step S4 (when N2 ≧ S), it is determined whether or not the aperture is fully opened (step S8). If the aperture is not fully open, the aperture is opened by one level (step S9). If the aperture is fully open, the emitted light quantity of the illumination device 7 is improved by one step (step S10). That is, when the number S of regions where halation occurs is N2 or less, the diaphragm is first opened, and the amount of emitted light is increased after the diaphragm is fully opened.
[0021]
Differences between the control described above and the conventional control shown in FIGS. 3 and 4 will be summarized. In the above-described control, attention is paid to the area of the region that causes halation in the entire screen, not the average value photometry of the entire imaging screen. Therefore, the system itself can recognize the difference between the state of FIG. 3A and the state of FIG. Further, in the average value metering of the entire imaging screen, even if it is attempted to control the illumination light quantity based on the photometric value, the above-mentioned two states cannot be distinguished, and thus the illumination light quantity cannot be appropriately controlled. On the other hand, if it is control of this embodiment, both said states can be distinguished, and if the state of FIG.3 (b) is S> = N1, first, the emitted light quantity will be decreased, and also a diaphragm will be reduced. It will be closed. Further, in the control of this embodiment, when an emergency light is present in the imaging range, the high-intensity area such as an emergency light is merely some of the number S, and the high-intensity area of the emergency light is reduced. There is no inconvenience that the lens aperture is narrowed more than necessary as in the conventional control for appropriately photographing.
[0022]
In the process shown in the flowchart of FIG. 2, the brightness level of each region in the captured video is V, the brightness level threshold is Va, the number of regions in the captured video where V ≧ Va is S, the first threshold and the first threshold The threshold values of 2 are set to N1 and N2 (N1> N2), respectively, and control is performed to decrease the emitted light amount when S ≧ N1 and increase the emitted light amount when N2 ≧ S. However, the present invention is not limited to this. For example, the brightness level of each region in the captured image is V, the brightness level threshold value is Va, the number of regions in the captured image where V ≧ Va is S, the threshold value is N, and when S> N, the emitted light amount is reduced, and N When> S, control for increasing the amount of emitted light may be performed. Even in such a configuration, the amount of light emitted from the illumination device is increased as much as possible to avoid a dark screen, and when S> N, the amount of light emitted is too large to cause halation by reducing the amount of emitted light. It will be possible to avoid the situation.
[0023]
The luminance level threshold value Va is set to a value that causes halation, but a value lower than this may be set. However, the lower the value is, the more insufficient the amount of light emitted from the illumination device is as much as possible, and the greater the possibility that a dark image will be captured.
[0024]
In the above example, the number of regions satisfying V ≧ Va is detected in the captured video, but it may be a ratio to the entire captured video instead of the number. In addition, although the area division is illustrated, the number of pixels satisfying V ≧ Va may be detected, or the pixel ratio with respect to the entire captured image may be generated.
[0025]
【The invention's effect】
As described above, according to the present invention, by increasing the emitted light amount of the illumination device as much as possible and avoiding a dark screen, for example, by reducing the emitted light amount when the number of areas causing halation exceeds a threshold value, It is possible to avoid a situation in which the amount of emitted light is too large and the number of portions that cause halation increases, and there is an effect that monitoring and the like can be performed satisfactorily with a clear captured image.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an imaging system of the present invention.
FIG. 2 is a flowchart showing control contents.
FIGS. 3A and 3B are explanatory diagrams for explaining a problem caused by average value photometry. FIG.
FIGS. 4A and 4B are explanatory diagrams for explaining a problem caused by peak-oriented photometry. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lens 2 Aperture 3 Imaging part 4 Signal processing part 5 Aperture control part 6 Illumination control part 7 Illumination device

Claims (6)

An imaging unit having sensitivity to light of a predetermined wavelength band, an illumination device that irradiates light of a predetermined wavelength band toward the imaging direction, and the luminance value in the captured image captured by the imaging unit Illumination control means for controlling the total amount of light emitted from the illumination device, wherein the brightness level of each part in the captured image captured by the imaging means is V, the brightness level threshold is Va, and V ≧ Va in the captured image When the total amount of the part or the ratio of the part in the captured image is S and the threshold value is N, the illumination control means lowers the total emitted light quantity of the illumination device when S> N, and N> S An imaging system characterized in that control is performed to increase the total amount of light emitted from the illumination device. An imaging unit having sensitivity to light of a predetermined wavelength band, an illumination device that irradiates light of a predetermined wavelength band toward the imaging direction, and the luminance value in the captured image captured by the imaging unit Illumination control means for controlling the total amount of light emitted from the illumination device, wherein the brightness level of each part in the captured image captured by the imaging means is V, the brightness level threshold is Va, and V ≧ Va in the captured image When the total amount of the part or the ratio of the part in the captured video is S, and the first threshold value and the second threshold value are N1 and N2 (N1> N2), the illumination control means is S ≧ N1 imaging system characterized by lowering the overall amount of emitted light of the lighting device, when the N2 ≧ S performs control for increasing the overall amount of emitted light of the lighting device when the. 3. The imaging system according to claim 1, wherein the diaphragm of the imaging unit is closed by a predetermined amount when the state of S> N or S ≧ N <b> 1 continues even after the total amount of light emitted from the illuminating device is minimized. An imaging system characterized by being controlled. 4. The imaging system according to claim 1, wherein when the state of N> S or N2 ≧ S continues even after the aperture of the imaging unit is fully opened, the total emitted light amount of the illumination device is determined. An imaging system that is controlled to increase the quantity.   5. The imaging system according to claim 1, wherein each part in the captured image is a pixel. 6.   5. The imaging system according to claim 1, wherein each part in the captured video is a region obtained by dividing the captured video into a plurality of regions.

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