JP4289629B2 - Surveillance camera system - Google Patents

Description

  The present invention relates to a surveillance camera system using a plurality of cameras, and more specifically, while continuing to shoot under automatic exposure control, shooting is performed with extreme overexposure and underexposure in a local area within the photographic area. The present invention relates to a surveillance camera system that prevents information from being lost.

  Cameras used for surveillance purposes are required to shoot at a magnification that can easily identify a subject while covering a wide surveillance area on the one hand. Against this background, surveillance camera systems have been devised that combine a wide-angle camera that covers the entire shooting area and a telephoto camera that has a higher shooting magnification than the wide-angle camera. As these cameras, digital cameras having an automatic exposure control function are used, and each camera normally performs photographing by automatic exposure control based on average photometry.

  In automatic exposure control using average photometry, one photometric value is calculated from the image signal output from the image sensor, and the aperture built into the photographic lens is adjusted based on this photometric value and the charge of the image sensor. The accumulation time is adjusted. Such an exposure control system is less burdensome on the hardware and software side, and the operation is stable. On the other hand, if there is a large brightness fluctuation in a part of the shooting area, the effect is likely to affect the entire screen. There is a problem that it is difficult to obtain appropriate image information because the object to be monitored is overexposed or underexposed.

  This problem is alleviated if the dynamic range of the image sensor is sufficiently wide. However, the dynamic range of a CCD type or CMOS type image sensor used in a general digital camera is about 50 to 60 db, which is a normal photograph. Since the dynamic range of the film is about 70 db, it is not so wide. In order to widen the dynamic range, it is possible to improve by increasing the size of the photoelectric conversion unit consisting of the photodiode and the signal charge storage unit, but with this, the number of pixels decreases and the resolution is unavoidable. .

For these reasons, when the brightness level change in the shooting area can be predicted temporally and seasonally, the brightness level of the subject to be monitored should not be changed excessively using the known information. A method of controlling exposure is known (Patent Document 1). In addition, the maximum luminance and the minimum luminance in the shooting screen are detected, and a high luminance region included from a predetermined high luminance level to the maximum luminance, and a low luminance region included from a predetermined low luminance level to the minimum luminance, There is known a method in which a photometric value is calculated in accordance with the area ratio of the entire photographing screen and exposure control is performed based on this photometric value (Patent Document 2).
JP 2001-211133 A JP 2003-319248 A

  However, the method known in Patent Document 1 is effective for a presumed environmental change such as a change in the position of the sun or a change in the weather, but it can cope with an artificial or sudden change. Can not. In addition, in the method known in Patent Document 2, in order to evaluate the luminance distribution pattern of the entire screen, it is necessary to acquire luminance information by dividing the photographing screen into pixel units or a plurality of regions, which complicates image processing. The processing time also becomes longer. For this reason, in the case where a part of the luminance in the photographing screen changes in a short time, followability also becomes a problem. In addition, when creating a gradation signal corresponding to the brightness based on the imaging signal obtained from the image sensor, various gradation conversion processes are performed to reproduce the image of the main subject within a sufficient dynamic range. However, in order to identify the main subject, it is necessary to analyze the motion vector in the shooting screen, complicating signal processing, and when changing the camera type and shooting magnification according to the monitoring application The photometry or exposure control program must also be changed, which is problematic in terms of versatility.

  Furthermore, among general-purpose image sensors, for example, “Super CCD Honeycomb SR” (trade name), an image sensor having a dynamic range increased to about 70 db while maintaining resolution is also known. Compared with a general dynamic range image sensor, the cost burden is large, and the signal processing for the imaging signal obtained from the image sensor is complicated. Therefore, the use of such an image sensor for each of a plurality of cameras constituting the surveillance camera system as described above is not only disadvantageous in terms of cost but also requires surveillance that requires continuous shooting in time. Not suitable for camera systems.

  The present invention has been made in consideration of the above-mentioned background, and when a local area that needs to be monitored in detail is assumed in a monitoring area that needs to be monitored over time, the brightness in the imaging area is assumed. It is an object of the present invention to provide a surveillance camera system in which extreme overexposure / underexposure does not occur in a local area at low cost.

  In order to achieve the above object, the present invention includes an image sensor that photoelectrically converts a formed subject image, and uses a plurality of types of cameras having different focal lengths. When configuring a surveillance camera system that sets the longer camera to the far side and shoots almost common shooting areas under individual automatic exposure control, select the camera with the longest focal length among the multiple types of cameras. Consists of a plurality of camera modules with the same focal length, and each of the divided areas divided by dividing the shooting area into a plurality of divided areas according to the number of the camera modules is individually shot with the camera module, Only one of the camera modules has an image with a wider dynamic range of photoelectric conversion characteristics than other camera modules. It is characterized by the use of Jisensa.

  In general, since the shooting area is usually long in the horizontal direction, it is practical to divide the shooting area into three equal parts in the horizontal direction and shoot each with a separate camera module. is there. In this case, since it is probable that the central section area contains important monitoring information, it is preferable to use an image sensor having a wide dynamic range as a camera module for photographing the section area.

  In addition, in an in-vehicle surveillance camera system, etc., the subject image in the shooting area changes dynamically, so in order to make it easier to grasp the state of the change, a single camera with the optimum shooting distance set to a short distance is used. Using a wide-angle camera, a standard camera with an optimal shooting distance set to a medium distance, and a telephoto camera with an optimal shooting distance set to a long distance, the standard camera is a section that bisects the shooting area horizontally. It is effective to be composed of two standard camera modules that shoot the area separately, and the telephoto camera is composed of three telephoto camera modules that individually shoot the section area that is divided into three equal parts in the horizontal direction. In this case, it is effective to use an image sensor having a wide dynamic range for the telephoto camera module that captures the central divided area among the divided divided areas. That. The automatic exposure control performed by each camera or camera module can be easily performed based on average photometry using the image pickup signal from each image sensor.

  According to the present invention, in a shooting area to be monitored, a local area requiring particularly detailed monitoring is shot with a camera module using an image sensor having a wide dynamic range of photoelectric conversion characteristics. Therefore, even if some luminance fluctuation occurs in the local area, it is possible to prevent a part of the image included in the area from disappearing due to so-called white stripes and black blurring.

  As an embodiment of the present invention, FIG. 1 shows the appearance of a surveillance camera system used for the purpose of monitoring the running of a vehicle on the road. This camera system includes a photographing unit 2, a control unit 3 that controls the driving of a plurality of types of cameras or camera modules incorporated in the photographing unit 2, and incorporates a recording device that records each obtained image data, The portable personal computer 4 is connected to the control unit 3. An image is displayed on the monitor 4 a of the personal computer 4 based on the edited image signal output from the control unit 3. An image display may be performed by connecting a dedicated monitor instead of the personal computer 4.

  The photographing unit 2 is attached to the inside of the vehicle by a support device having a vibration absorbing action together with the control unit 3, and various cameras incorporated in the photographing unit 2 photograph a vehicle traveling forward through the windshield of the vehicle. The portable personal computer 4 is operated by, for example, an operator at the passenger seat, and is capable of appropriately switching the display mode of the image and the operation of the camera by performing an input operation from a keyboard in addition to observing the image. When observing an image on a dedicated monitor instead of the personal computer 4, the operation of the camera and the display mode of the image can be switched via an operation panel provided in the control unit 3.

  The photographing unit 2 incorporates a first camera 5, a second camera 6 comprising two camera modules 6a and 6b, and a third camera 7 comprising three camera modules 7a, 7b and 7c. These cameras 5 to 7 shoot at substantially the same angle of view, but the focal length of each photographic lens is set so that the focal length becomes longer in this order, and the optimum shooting distance is also longer in this order. The focus of the photographic lens is set so that The first camera 5, the second camera 6, and the third camera 7 are relatively equivalent to a wide-angle camera, a standard camera, and a telephoto camera, respectively.

  The camera modules 6a and 6b are structurally identical, including the photographic lens, but their photographic optical axes are tilted so that the photographic area of the second camera 6 can be bisected and photographed. Similarly, the camera modules 7 a, 7 b, and 7 c are completely the same in structure including the photographic lens, and the photographic optical axes of the camera modules 7 a, 7 b, and 7 c are tilted so that the photographic area of the third camera 7 can be divided into three. ing. The camera modules 6a and 6b and the camera modules 7a, 7b, and 7c are arranged horizontally to eliminate parallax in the vertical direction. You don't have to be particular.

  FIG. 2 schematically shows an aspect of the shooting area of each camera. The first camera 5 with an angle of view θ1 is set in focus so that the optimum shooting distance is L1, the shooting area S1 at the shooting distance L1 is the shooting range, and has a depth of field d1 across the shooting distance L1. . The camera modules 6a and 6b having the angle of view θ2 are focused so that the optimum shooting distance is L2, and as shown by the broken line, the shooting optical axes of the first camera 5 are divided so that the shooting area S1 can be divided into two. Is tilted. The second camera 6 including these camera modules 6a and 6b as a whole has a shooting area S2 as a shooting range at a shooting distance L2, and the second camera 6 also spans the shooting distance L2 before and after the shooting distance L2. have.

  The camera modules 7a, 7b, and 7c with the angle of view θ3 are set so that the optimum shooting distance is L3, and the shooting area S2 of the second camera 6 can be divided into three equal parts as shown by a one-dot chain line. The optical axes of each other are tilted. The third camera 7 as a whole has a shooting area S3 as a shooting range at the shooting distance L3, and has a depth of field d3 so as to extend before and after the shooting distance L3. Note that each of the angle of view θ1 to θ3 described above represents the angle of view in the horizontal direction, and the angle of view in the vertical direction is considered as a monitoring target in consideration of the case of shooting at the respective optimum shooting distances L1 to L3. This is appropriately set according to the image size of the subject.

  The shooting distances L1 to L3 of the first to third cameras 5 to 7 correspond to the focal lengths f1 to f3 of the shooting lenses of the respective cameras, and are set to satisfy f1 / L1 = f2 / L2 = f3 / L3. Yes. For example, if the focal lengths f1, f2, and f3 of the respective photographing lenses are 50 mm, 100 mm, and 200 mm, the respective photographing distances L1, L2, and L3 are 50 m, 100 m, and 200 m. As a result, the image magnification when the subject located at the photographing distance L 1 is photographed by the first camera 5, the image magnification when the subject located at the photographing distance L 2 is photographed by the second camera 6, and the third camera 7. The image magnifications when the subject located at the shooting distance L3 is shot are equal.

  The width of the depth of field d1 to d3 of each camera varies depending on the focal length of each photographing lens and the set optimum photographing distance, and also depends on the diameter of the diaphragm provided in the photographing lens system. Change. As is well known, when the aperture diameter of the stop is reduced, the depth of field is greatly improved, and the range that can be regarded as being in focus can be expanded. For example, in the first camera 5 having a focal length of 50 mm and the second camera 6 having a focal length of 100 mm, a wide range of depth of field can be obtained by reducing the aperture to about F4 or F5.6. It is possible to cover up to infinity with depth of field. Further, since the depth of field of the first camera 5 and the second camera 6 and the second camera 6 and the third camera 7 partially overlap each other, the subject to be monitored is the depth of field d1 to d1. If it is within the shooting distance included in d3, it is possible to take a picture in focus with at least one of the cameras.

  FIG. 4 shows an outline of the electrical configuration of the first camera 5. The camera modules 6a and 6b constituting the second camera 6 and the camera modules 7a, 7b and 7c constituting the third camera 7 have the same basic electrical configuration. For example, the image signal is obtained by photoelectrically converting a subject image. As the image sensor for outputting the signal, a CCD type is used, and the processing of the image pickup signal is performed in the same manner. The camera module 7b of the third camera 7 is different in that an image sensor 10a having a wider dynamic range than other cameras and camera modules is used, and the AE control circuit 21a is also partially different. Although only the portion is illustrated, other configurations are omitted in order to avoid duplication and complication of the drawing.

  The first camera 5 includes the photographing lens 5c having a focal length of 50 mm as described above, and forms a subject image on the CCD type image sensor 10 through the diaphragm 12. An imaging signal from the image sensor 10 is amplified to an appropriate level by the AGC amplifier 13 and input to the system bus 15 as image data for each pixel digitized by the A / D converter 14. The image data thus input is subjected to well-known image processing by the image signal processing circuit 18 under the control of the system controller 17 and is written in the flash memory 20 as image data in frame units of a predetermined format.

  The AE control circuit 21 performs average photometry for each frame based on the image data input from the A / D converter 14, and determines whether the average luminance for one screen is within an appropriate range. Then, the system controller 17 drives the iris motor 22a via the iris driver 22 according to the determination result to control the aperture diameter of the diaphragm 12. At this time, the maximum aperture diameter is limited by the aperture value data written in the EEPROM 24 so that the aperture 12 does not open too much. If the exposure amount is insufficient even when the aperture 12 reaches the maximum aperture diameter limited by the aperture value data, the gain of the AGC amplifier 13 is adjusted via the system controller 17.

  As is well known, the AF control circuit 25 evaluates the degree of focus based on the contrast component of the image signal, and inputs the evaluation signal to the system controller 17. The system controller 17 drives the focus motor 26a via the focus driver 26 so that the evaluation signal becomes the highest. As a result, the photographing lens 5c is feedback-controlled to a position where the contrast component of the image signal is maximized, and the photographing lens 5c is moved to the in-focus position in an automatic tracking manner.

  However, such focusing operation by the AF control circuit 25 is normally omitted in the camera system of the present invention. Then, the system controller 17 moves the photographing lens 5c to the focus set position by the focus driver 26 and the focus motor 26a so that the photographing distance L1 written in the EEPROM 24 is in focus. The image is taken with a fixed focus. Regarding the camera modules 6a and 6b constituting the second camera 6 and the camera modules 7a, 7b and 7c constituting the third camera 7, the focal length of each photographing lens is different from that of the photographing lens 5c of the first camera. The basic electrical configuration is the same except that the optimum shooting distances L2 and L3 and aperture value data written in the EEPROM 24 are different.

  Thus, the image data obtained for each camera is input to the control unit 3 via the interface circuit 28. The control unit 3 is provided with an input / output control circuit 30, an image composition device 31, a recording control device 32, a recording device 33, and an operation panel 34, and a personal computer 4 with a monitor 4 a is connected to the control unit 3. The input / output control circuit 30 controls input / output of image data and control data with the interface circuit 28 provided for each camera. The image composition device 31 individually processes the image data from the first camera 5, the second camera 6, and the third camera 7, and the second camera 6 and the third camera 7 have two or three images. Is combined into a single image.

  The recording control device 32 controls the operation of the recording device 33 such as a DVD recorder in response to an operation input from the operation panel 34 or the personal computer 4. The recording device 33 records the image data obtained from each camera and synthesized for one screen as necessary as a moving image. Note that it is also possible to record still images in parallel in response to a release operation signal input from the operation panel 34 or the personal computer 4 or a release signal output at regular intervals set by a timer.

  The camera module 7b used in the third camera 7 uses a CCD-type image sensor 10a that has a wider dynamic range of photoelectric conversion characteristics than image sensors incorporated in other cameras and camera modules. . In this image sensor 10a, for example, as conceptually shown in FIG. 4A, the pixel arrangement structure on the light receiving surface is devised, and one pixel 40 has a main pixel 40a having a large light receiving area and a sub pixel having a small light receiving area. 40b. The main pixel 40a and the sub-pixel 40b are each configured by a photodiode that photoelectrically converts subject light, and stores signal charges obtained by photoelectric conversion in individual charge storage units. The signal charges stored in each charge storage unit are individually read out from each charge transfer path and output as an imaging signal. FIG. 4B shows an example in which the main pixel 41a and the sub-pixel 41b are separately arranged. With such a pixel arrangement, the same function as that of the image sensor of FIG.

  An imaging signal output for each pixel from the image sensor is digitally converted by the A / D converter 14 and converted into image data for each pixel, but a general image sensor has a narrow dynamic range. For example, as shown in FIG. 5, when it is assumed that the exposure amount from the dark part (exposure amount 0) to the clear sky (exposure amount B2) is quantized with a digital amount from signal level 0 to Smax. The image sensor outputs an image pickup signal having an output level corresponding to the exposure amount from the exposure amount 0 to the exposure amount B1, but the output level of the image pickup signal is saturated for the exposure amount greater than the exposure amount B1. Can be obtained only with the same signal level Smax with respect to the exposure amount greater than the exposure amount B1.

  Such a signal conversion characteristic K1 is caused by a photoelectric conversion characteristic of the image sensor, and a region where the signal level changes according to a change in exposure amount corresponds to a dynamic range. The dynamic range can be relatively shifted to the high exposure amount side in FIG. 5 by restricting the exposure amount by narrowing the aperture of the taking lens, but conversely it is narrowed on the low exposure amount side, so-called black. As a result, the range of blur is widened. Therefore, no matter how the dynamic range is shifted by adjusting the aperture or charge accumulation time according to the average luminance of the entire screen, there are low-luminance subjects and high-luminance subjects that cannot be covered by the dynamic range. If there is, it is inevitable that the subject information will be lost due to black spots and white stripes.

  On the other hand, if one pixel is composed of a high-sensitivity main pixel 40a and a low-sensitivity sub-pixel 40b as shown in FIG. 4A, the main pixel 40a as shown in FIG. 6A. In addition to the image data obtained by quantizing the image pickup signal from, image data obtained by quantizing the image pickup signal from the sub-pixel 40b can be obtained, and these image data have different signal levels. Image data with the signal conversion characteristic K1 is obtained from the main pixel 40a as in FIG. 5, whereas image data with the signal conversion characteristic K2 with the photoelectric conversion characteristic of the subpixel 40b is obtained from the subpixel 40b. A wide dynamic range can be obtained by combining these image data.

  As indicated by a broken line in FIG. 6B, the signal level corresponding to the exposure amount B2 becomes twice the original signal level Smax by simply adding the two types of image data based on the signal conversion characteristics K1 and K2. End up. Therefore, as shown by the solid line, a signal conversion characteristic K3 in which compression is performed on the high exposure amount side so that the signal level Smax is obtained at the exposure amount B2 with respect to the characteristic obtained by adding the signal conversion characteristics K1 and K2 is prepared in advance. The conversion characteristic data is stored in the AE control circuit 21a used in the camera module 7b of the third camera 7. By using this signal conversion characteristic K3 together with the image sensor 10a that constitutes one pixel by the main pixel and the sub-pixel as shown in FIG. 4, the camera module 7b becomes a digital camera with a wide dynamic range. Note that even if it is attempted to obtain image data only from the imaging signal from the sub-pixel 40b having a wide dynamic range, a sufficient signal level cannot be obtained in the normal charge accumulation time, so that a significant amplification process is required for the imaging signal. . However, in a region where the subject brightness is low, a lot of noise components typified by dark current are included, so that it is difficult to obtain appropriate image data only by such amplification processing.

  In addition, as shown in FIG. 6B, it is practical to perform a process of connecting the inflection points of the signal conversion characteristics K3 with a smooth curve. Furthermore, various known methods can be used as the synthesis method of the signal conversion characteristics K1 and K2 or the compression method on the high exposure amount side, and the profile of the signal conversion characteristics K3 is not necessarily limited to that shown in the drawing. It suffices that the entire range of the amount 0 to B2 is included in the dynamic range. Methods for expanding the dynamic range using such main pixels and sub-pixels are known in Japanese Patent Application Laid-Open Nos. 2004-220438 and 2004-297407.

  Hereinafter, the operation of the camera system will be described. Prior to photographing, initial setting is performed by an operation input from the operation panel 34 of the control unit 3 or the personal computer 4. Initially set items include shooting distances L1, L2, and L3 of the first camera 5, the second camera 6, and the third camera 7, and these data are written in the EEPROM 24 of each camera. The system controller 17 reads these setting data, and positions the respective photographing lenses so as to focus on the optimum photographing distances L1, L2, and L3 by the focus driver 26 and the focus motor 26a.

  After setting the shooting distance of each camera, the inclination of the shooting optical axis in the horizontal direction of each camera is adjusted. The base of the photographing unit 2 that holds each camera is provided with an adjustment mechanism that tilts the photographing optical axis of the camera in the horizontal direction. For convenience, the adjustment mechanism can be operated while observing an image displayed on the monitor 4a. Operate manually. Of course, if this adjustment mechanism is electrically operated, it is possible to automatically adjust the direction of the photographing optical axis at the time when the initial setting of the optimum photographing distance is performed. Note that the tilt of the photographic optical axis in the vertical direction may be basically horizontal for each camera, but it is also possible to tilt the photographic optical axis in the vertical direction in order to absorb errors during assembly of each camera. Good.

  After the focus setting of each camera is initialized, aperture value data for limiting the maximum aperture diameter of the aperture 12 of each camera is written in the EEPROM 24. In consideration of the depth of field determined by the focal length of the photographing lens and the optimum photographing distance, the maximum aperture diameter of the diaphragm 12 is such that the depths of field d1, d2, and d3 shown in FIG. 2 partially overlap each other. Decided. The depth of field value can be calculated from the focal length of the photographic lens, the shooting distance, and the aperture value, so if you use a calculation algorithm that requires overlapping the depth of field, the aperture value data can be entered manually. It is also possible to set automatically without depending on.

  If the aperture value for determining the maximum aperture diameter of the aperture 12 is set to about F4 for the first camera 5 and about F5.6 for the second camera 6 and the third camera 7, for example, it is extremely high, such as at night. Except for the situation where the brightness is insufficient, as shown in FIG. 2, it is possible to capture images with substantially appropriate exposure while ensuring the depths of field d1, d2, and d3 that overlap each other. Further, since the iris 12 is stopped by the iris motor 22a during shooting in bright daylight, the first camera 5 and the second camera 6 can be within the depth of field up to infinity. If the maximum aperture diameter of the diaphragm 12 is limited by the diaphragm value data written in the EEPROM 24 and the brightness is insufficient even in this state, the AGC amplifier 13 works effectively to prevent underexposure.

  Images from the first camera 5, camera modules 6a and 6b, and camera modules 7a, 7b, and 7c can be arranged and displayed as they are on the monitor 4a, but preferably the monitor screen 4b shown in FIG. As described above, the image 45 from the first camera 5, the images 46a and 46b from the camera modules 6a and 6b are combined into one sheet, and the images 47a and 47b from the camera modules 7a, 7b and 7c. A composite image 47 obtained by combining 47c into one sheet is arranged and displayed on the monitor screen 4b. The monitor screen 4b displays date information 49 representing the shooting date and time, and position information 50 representing latitude and longitude obtained from a GPS device incorporated in the control unit 3, and moving image data. At the same time, the data is recorded on the recording medium by the recording device 33.

  In the image synthesis process, the boundary between the images to be synthesized is identified by pattern recognition, trimmed with an appropriate boundary line, and then combined. Since the images to be synthesized are individually controlled for exposure by separate cameras, a difference in density tends to occur at the boundary portion, but they may be simply combined as they are. It is also possible to adjust the gradation so that the density difference at the boundary portion is not noticeable by performing the smoothing process, or to adjust the density of the combined images by averaging the densities of the individual images.

  An example of the monitor screen 4b during the continuous shooting of a specific vehicle T traveling on the road as a monitoring target using the monitoring camera system is as shown in FIG. FIG. 7 shows the situation when the vehicle number is checked while photographing the vehicle T from a distance. Under such circumstances, the inter-vehicle distance close to the photographing distance L3 of the third camera 7 having the longest focal length is maintained. Shooting is performed. Since the shooting distance L3 is considerably longer than the shooting distances L1 and L2, the image size of the vehicle T obtained from the first camera 5 and the second camera 6 is considerably smaller as shown in FIG. Even if it is within the depth of field of the first and second cameras, it is difficult to confirm the vehicle number.

  The image 47 of the third camera 7 has a sufficient vehicle number confirmation as the image size, and the image of the vehicle T is taken by the camera module 7b. The AE control circuit 21 of the camera module 7b performs exposure control with a so-called average photometric method so that the average brightness of the entire screen shot individually is at an appropriate level regardless of other cameras and camera modules. Is going. For this reason, when the dark part inside the tunnel spreads in the image 47b, the aperture diameter of the diaphragm 12 is controlled to be increased so as to increase the exposure amount of the entire image 47b. Then, after the aperture diameter of the diaphragm 12 is limited by the aperture value data of the EEPROM 24, the AGC amplifier 13 amplifies the imaging signal, and the image 47b is controlled to become bright as a whole.

  However, since the vehicle T itself is still sufficiently bright before entering the tunnel, when the exposure adjustment is performed so that the image 47b becomes entirely bright as described above, the vehicle T is photographed with an overexposure tendency. Is called. If the image sensor used in the camera module 7b has a narrow dynamic range, the license plate portion is overexposed and the vehicle number is buried in the overtone. There is concern about disappearing. Such a problem is different from a general digital camera that can perform framing arbitrarily, and is in-vehicle type or fixed installation type that is used indefinitely in which position in a predetermined shooting area the vehicle T to be monitored comes. It is difficult to avoid with the surveillance camera. This situation is not necessarily limited to exposure control based on full-screen average metering, but center spot metering for metering only the center area of the screen, or metering by weighting from the periphery to the center of the screen. This is likely to occur even with multi-pattern center-weighted metering.

  However, since the camera module 7b uses an image sensor 10a having a photoelectric conversion characteristic with a wide dynamic range as shown in FIG. 6B, exposure control is performed so that the entire image 47b is brightened by average photometry. Even if it is broken, it is possible to take a picture in a state in which the license plate is not overexposed and the vehicle number is sufficiently visible. Further, when the vehicle T enters the tunnel, the entire image 47b is photographed by the exposure control of the camera module 7b, so that the vehicle number is photographed with a brightness that is easier to observe. Conversely, when the vehicle exits from the tunnel, exposure control is performed so that the image 47b becomes dark as a whole due to the influence of a bright background outside the tunnel, and the license plate is photographed darkly. Since the image is taken by the wide image sensor 10b, the vehicle number is not taken together with the picker plate in a black blurred state.

  Even when the image 47b itself captured by the camera module 7b is captured with a wide dynamic range, the license plate is in a state where the license plate is white or black when the display dynamic range of the monitor 4b is narrow. May also be displayed. However, since the image 47b itself is taken with a wide dynamic range, the image data is not partially lost. For example, the vehicle number can be easily confirmed by adjusting the brightness of the monitor 4b. . In addition, when shooting at dusk or at night, there is a concern that the headlights of oncoming cars, street lights, lighting from shopping streets, etc. may greatly change the brightness around the car being monitored. According to the method, the influence can be reduced. The surveillance camera system of the present invention is equally applicable not only to a vehicle-mounted type but also to a fixed installation type surveillance camera.

  As described above, the present invention has been described based on the illustrated embodiment, but specific values such as the focal length, the angle of view, the optimum shooting distance, and the aperture value of the shooting lens used in the area monitoring camera are merely examples. However, these may be appropriately changed according to the use and usage of the surveillance camera system.

1 is an external view of a surveillance camera system using the present invention. It is explanatory drawing which shows the angle of view and imaging | photography area of each camera. It is a block diagram which shows the outline of an electrical structure of the surveillance camera system. It is a conceptual diagram which shows the image sensor of a wide dynamic range. It is a graph which shows the signal conversion characteristic at the time of using the image sensor of a narrow dynamic range. It is a graph which shows the signal conversion characteristic at the time of using the image sensor of a wide dynamic range. It is explanatory drawing which shows an example of the picked-up image when a vehicle is made into the monitoring object.

Explanation of symbols

2 photographing unit 3 control unit 4 personal computer 4a monitor 4b monitor screen 5 first camera 6a, 6b camera module (second camera)
7a, 7b, 7c Camera module (third camera)

Claims (5)

It is equipped with an image sensor that photoelectrically converts the formed subject image, using multiple types of cameras with different focal lengths, and setting the optimum shooting distance of each of the cameras to a longer distance side as the camera has a longer focal length. In a surveillance camera system that shoots a common shooting area under individual automatic exposure control,
The camera having the longest focal length among the plurality of types of cameras is constituted by a plurality of camera modules having the same focal length, and the shooting area is divided into a plurality of divided areas according to the number of the camera modules. A surveillance camera system characterized in that an image sensor having a wider dynamic range of photoelectric conversion characteristics than any of the other camera modules is used for any one of the camera modules.   The plurality of divided areas are set by horizontally dividing a long shooting area into three equal parts in the horizontal direction, and the image sensor having a wide dynamic range is used for a camera module for shooting the central divided area. The surveillance camera system according to claim 1.   Multiple types of cameras with a long shooting area in the horizontal direction and different focal lengths, one wide-angle camera with the optimal shooting distance set to a short distance, and a standard with the optimal shooting distance set to a medium distance The standard camera is composed of two standard camera modules that individually shoot a section area that is divided into two equal parts in the horizontal direction. The telephoto camera is composed of three telephoto camera modules that individually shoot the divided areas obtained by dividing the shooting area into three equal parts in the horizontal direction, and also shoots the central divided area among the three divided divided areas. 2. The surveillance camera system according to claim 1, wherein an image sensor having a wide dynamic range is used for the telephoto camera module.   The surveillance camera system according to claim 1, wherein the automatic exposure control is performed based on average photometry using an imaging signal from each image sensor. The surveillance camera system according to any one of claims 1 to 4, wherein the surveillance camera system is used in a vehicle as a traffic monitoring device for an automobile traveling on a road.

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