Surveillance Camera

Abstract

The present invention relates to a surveillance camera, comprising: an image sensor for capturing images; a dimming filter arranged in front of the imaging surface of the image sensor, for attenuating light incident on the imaging surface of the image sensor by controlling a liquid crystal layer in units of divided areas; and a processing unit for controlling the operation of the dimming filter.

Description

Technical Field

[0001] The present invention relates to a surveillance camera. Background Art

[0002] When strong light such as sunlight enters an observation device having an image sensor such as a surveillance camera, the output signal of the image sensor may exceed the dynamic range and overflow. The data of the pixel where such overflow occurs becomes substantially ineffective.

[0003] As a method for expanding the dynamic range of an image sensor, a method using HDR (High Dynamic Range) processing is known. This method is to capture a plurality of images with different exposures and synthesize the captured images to obtain an image with an expanded dynamic range.

[0004] In observation equipment such as surveillance cameras, it is important to ensure the evidentiary nature of the images captured. From the perspective of ensuring the evidentiary nature, in observation equipment such as surveillance cameras, it is desirable that the images captured are not processed as much as possible. Summary of the invention

[0005] The present invention provides a surveillance camera capable of capturing images that guarantee a certain degree of evidence while suppressing overflow of a dynamic range of an image sensor.

[0006] A surveillance camera of one embodiment includes: an image sensor for capturing images; a neutral density filter disposed in front of an imaging surface of the image sensor for attenuating light incident on the imaging surface of the image sensor by controlling a liquid crystal layer in units of divided areas; and a processing unit for controlling the operation of the neutral density filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a block diagram showing the structure of an example of a surveillance camera according to the embodiment.

[0008] Figure 2 is a plan view of a neutral density filter.

[0009] Figure 3 It is along Figure 2 Cross-sectional view of a III-III line dimming filter.

[0010] Figure 4A This is a conceptual diagram of the divided areas of the neutral density filter.

[0011] Figure 4B This is a diagram showing the concept of the operation of the neutral density filter.

[0012] Figure 5 This is a flowchart showing the operation of the surveillance camera.

[0013] Fig. 6A This is a conceptual diagram showing the operation of a surveillance camera.

[0014] Figure 6B This is a conceptual diagram showing the operation of a surveillance camera. DETAILED DESCRIPTION

[0015] Hereinafter, embodiments will be described with reference to the drawings. Figure 1 1 is a block diagram showing the configuration of an example of a surveillance camera according to an embodiment. The surveillance camera 1 includes a camera unit 2, a processor 3, a memory 4, a storage 5, and a communication device 6. The surveillance camera 1 is configured, for example, to include a surveillance object in an observation area. The surveillance camera 1 may be, for example, a fixed-point camera that regularly monitors the same observation area. The surveillance camera 1 may also include Figure 1 Elements other than those shown.

[0016] The camera unit 2 is a unit for acquiring an image of a surveillance object and includes an optical system 21 , an image sensor 22 , and a neutral density filter 23 .

[0017] The optical system 21 is an optical system for forming an image of light in an observation area on the image sensor 22. The optical system 21 includes a lens, etc. The lens may be composed of a single lens or a plurality of lenses.

[0018] The image sensor 22 is, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like, which is arranged at the focal position of the optical system 21. The image sensor 22 generates an image in the observation area based on the light in the observation area imaged by the optical system 21. The image sensor 22 has an imaging surface including pixels arranged two-dimensionally. Each pixel outputs an electrical signal corresponding to the amount of light received.

[0019] The light reduction filter 23 is arranged between the optical system 21 and the image sensor 22 in parallel with the imaging surface of the image sensor 22, and attenuates the light incident on the image sensor 22 via the optical system 21 under the control of the processor 3. The light reduction filter 23 of the embodiment is configured so that the attenuation of light can be controlled for each divided area. One divided area is an area corresponding to one or more pixels of the image sensor 22. The configuration of the light reduction filter 23 will be described later.

[0020] The processor 3 is a processing unit such as a CPU. The processor 3 controls the operation of the surveillance camera 1. For example, the processor 3 controls the exposure of the image sensor 22. In addition, the processor 3 detects the high-brightness portion in the image generated by the image sensor 22. In addition, the processor 3 controls the dimming filter according to the position of the high-brightness portion of the image. The processor 3 is not limited to the CPU, but may also be an MPU, etc. In addition, the processor 3 may also be an ASIC, an FPGA, etc. Furthermore, the processor 3 may not be a single CPU, etc. but may include a plurality of CPUs, etc.

[0021] The memory 4 includes a ROM and a RAM. The ROM stores various processing programs of the monitoring camera 1 executed by the processor 3. The RAM operates as a working memory for temporarily storing an image generated by the image sensor 22 or storing data processed by the processor 3.

[0022] The storage 5 includes a recording medium such as a flash memory. The storage 5 stores image data generated by the camera unit 2.

[0023] The communication device 6 is a communication device for the monitoring camera 1 to communicate with an external device. The external device may be, for example, a server that manages the monitoring camera 1. The communication device 6 may be a wireless communication device of any type or a wired communication device of any type.

[0024] Next, the dimming filter 23 will be further described. Figure 2 is a plan view of the light reduction filter 23. In addition, Figure 3 It is along Figure 2 2 is a cross-sectional view of the dimming filter 23 along line III-III. Figure 2 The X-axis shown in is, for example, a direction parallel to the horizontal direction of the imaging surface of the image sensor 22. Figure 2 The Y axis shown in , for example, is a direction parallel to the vertical direction of the imaging surface of the image sensor 22 .

[0025] The light reduction filter 23 is, for example, a transmissive and passive matrix liquid crystal shutter. The light reduction filter 23 includes substrates 101 and 102 disposed to face each other. The substrates 101 and 102 sandwich a liquid crystal layer 103 .

[0026] The substrates 101 and 102 are transparent substrates such as transparent glass substrates and transparent plastic substrates. The substrates 101 and 102 are arranged parallel to the imaging surface of the image sensor 22. The light passing through the optical system 21 enters the image sensor 22 via the substrate 101, the liquid crystal layer 103, and the substrate 102.

[0027] The liquid crystal layer 103 is a layer of liquid crystal filled between the substrate 101 and the substrate 102. Specifically, the liquid crystal material of the liquid crystal layer 103 is sealed in a region surrounded by the substrate 101, the substrate 102, and the sealing material 104. The sealing material 104 may be, for example, an ultraviolet curing resin, a heat curing resin, or an ultraviolet and heat curing resin.

[0028] The liquid crystal material constituting the liquid crystal layer 103 changes the orientation of the liquid crystal molecules according to the voltage applied between the substrate 101 and the substrate 102. The optical properties of the liquid crystal layer 103 change according to the orientation of the liquid crystal molecules. The mode of the liquid crystal layer 103 of the embodiment is, for example, the TN (Twisted Nematic) mode. Specifically, the liquid crystal layer 103 uses a positive (P-type) nematic liquid crystal having a positive dielectric constant anisotropy. In the TN mode, the directors of the liquid crystal molecules in the liquid crystal layer 103 are twisted, for example, by 90° along the thickness direction of the liquid crystal layer 103 when no voltage is applied. Then, when a voltage is applied, the directors of the liquid crystal molecules in the liquid crystal layer 103 face the thickness direction of the liquid crystal layer 103. The initial orientation of the liquid crystal molecules in the liquid crystal layer 103 is controlled by two unillustrated orientation films that are provided on each of the substrates 101 and 102 in a manner that sandwiches the liquid crystal layer 103.

[0029] Electrodes 105 extending along the Y direction are provided on the surface of the substrate 101 on the liquid crystal layer 103 side. The electrode 105 is composed of a transparent electrode such as ITO (indium tin oxide). One end of the electrode 105 is led outward from the sealing material 104 and electrically connected to the processor 3, for example. Here, the number of electrodes 105 can be appropriately set according to the number of divided regions described later. In addition, in order to suppress crosstalk, the intervals between the electrodes 105 are preferably separated to the extent of being electrically separated from each other.

[0030] Electrodes 106 extending along the X direction are provided on the surface of the substrate 102 on the liquid crystal layer 103 side. The electrode 106 is formed of a transparent electrode such as ITO (indium tin oxide) similarly to the electrode 105. One end of the electrode 106 is led outward from the sealing material 104 and electrically connected to the processor 3, for example. Here, the number of electrodes 106 can be appropriately set according to the number of divided regions described later. In addition, in order to suppress crosstalk, the intervals between the electrodes 106 are preferably separated to the extent of being electrically separated from each other.

[0031] In the dimming filter 23, the orientation of the liquid crystal molecules can be controlled in each intersection region where one electrode 105 and one electrode 106 intersect. For example, one intersection region between the electrode 105 and the electrode 106 is a square. One intersection region between the electrode 105 and the electrode 106 is not necessarily a square, but may be a rectangle.

[0032] The polarizing plate 107 and the polarizing plate 108 are arranged so as to sandwich the substrate 101 and the substrate 102. The polarizing plate 107 and the polarizing plate 108 have mutually orthogonal transmission axes and absorption axes in a plane orthogonal to the traveling direction of the light. The polarizing plate 107 and the polarizing plate 108 transmit linearly polarized light having a vibration plane parallel to the transmission axis among the light having a vibration plane in a random direction, and absorb linearly polarized light having a vibration plane parallel to the absorption axis. Here, in the embodiment, the polarizing plate 107 and the polarizing plate 108 are arranged so that their absorption axes are orthogonal to each other, that is, in a cross-Nicol state. At this time, the dimming filter 23 operates in a normally white mode. Therefore, when no voltage is applied to the liquid crystal layer 103, the light incident on the dimming filter 23 passes through the dimming filter 23. On the other hand, when a voltage is applied to the liquid crystal layer 103, the light incident on the dimming filter 23 is attenuated by the dimming filter 23.

[0033] In this way, the light reduction filter 23 is configured to attenuate incident light in units of the intersection area between the electrode 105 and the electrode 106 , for example. Figure 4A 2 is a conceptual diagram of the divided areas of the light reduction filter 23. For example, Figure 4A Each segmented area 201 corresponds to one intersection area. Figure 4A , the segmented regions 201 are 120 regions of 10 rows×12 columns. Such segmented regions can be formed by 12 electrodes 105 and 10 electrodes 106. Here, in the embodiment, the correspondence between the positions of the segmented regions and the positions of the pixels of the image sensor 22 is pre-stored in, for example, the ROM of the memory 4 in a manner that the processor 3 can recognize.

[0034] Figure 4B 2 is a diagram showing the concept of the operation of the light reduction filter 23. The light reduction filter 23 can attenuate the light incident on any segmented area 201. For example, Figure 4B As shown, when a high-brightness light source 202 such as the sun is detected at a position corresponding to the divided areas 201 of C3, C4, D2, D3, D4, D5, E2, E3, E4, E5, F3 and F4 in the image generated by the image sensor 22, a voltage is applied only to the liquid crystal layer 102 in these divided areas, thereby selectively attenuating the light incident on the image sensor 22 only from the high-brightness light source 202.

[0035] Here, the segmented area that is the control target of dimming of incident light does not necessarily have to coincide with the intersection area. For example, one segmented area may include a plurality of intersection areas.

[0036] In addition, the dimming filter 23 is preferably arranged outside the focal depth of the optical system 21, for example, at a distance of about 5 mm from the image sensor 22. The contrast of the boundary between the segmented area where dimming is implemented and the segmented area where dimming is not implemented in the dimming filter 23 is likely to be high. Therefore, the boundary may be visually recognized in the image generated by the image sensor 22. In contrast, by configuring the dimming filter 23 outside the focal depth of the optical system 21, the boundary of the segmented area is blurred in the image generated by the image sensor 22. Therefore, the possibility of the boundary of the segmented area being visually recognized in the image generated by the image sensor 22 is reduced.

[0037] Next, the operation of the surveillance camera 1 will be described. Figure 5 This is a flowchart showing the operation of the monitoring camera 1 . Figure 5 The operation of the dimming filter 23 is controlled by, for example, the processor 3. As described above, the liquid crystal layer 103 of the dimming filter 23 operates in the normally white mode. Therefore, when no voltage is applied to the liquid crystal layer 103, the dimming filter 23 transmits the incident light.

[0038] In step S1, the processor 3 performs exposure setting of the image sensor 22. For example, the processor 3 sets, for example, the exposure time of the image sensor based on, for example, the average value of the brightness of each divided area of ​​the image acquired by the image sensor 22. The exposure setting is not necessarily performed based on the average value of the brightness of each divided area.

[0039] In step S2, the processor 3 performs imaging by the image sensor 22. The data of the image generated by the image sensor 22 is stored in the memory 4, for example, in the RAM.

[0040] In step S3, the processor 3 obtains an image generated by the image sensor 22. Then, the processor 3 determines whether the brightness of the low brightness portion in the image is within the prescribed range, that is, whether it is a brightness higher than a prescribed value. Here, when the surveillance object of the surveillance camera 1 is determined, the brightness of the low brightness portion may also be the brightness of the surveillance object. In step S3, if it is determined that the brightness of the low brightness portion is within the prescribed range, the processing is transferred to step S6. In step S3, if it is determined that the brightness of the low brightness portion is outside the prescribed range, the processing is transferred to step S4.

[0041] In step S4, the processor 3 determines whether there is a high brightness portion in the image. The high brightness portion is a portion in the image having a brightness greater than a certain value, for example, a portion having a maximum brightness in the dynamic range of the image sensor 22. In step S4, if it is determined that there is a high brightness portion in the image, the process moves to step S5. In step S4, if it is determined that there is no high brightness portion in the image, the process moves to step S6.

[0042] In step S5, the processor 3 applies a voltage to the liquid crystal layer 103 of the divided area corresponding to the high brightness part in the image in the dimmer filter 23 to drive the liquid crystal layer 103. Then, the processing is transferred to step S6. That is, since the reason for the low brightness part in the image is the light from the high brightness part in the image, the light from the high brightness part is attenuated. Here, the magnitude of the voltage applied in step S5 can be a constant or variable. When the magnitude of the applied voltage is a constant, the dimmer filter 23 becomes two states: a state of transmitting light and a state of attenuating light. On the other hand, when the magnitude of the applied voltage is variable, the dimmer filter 23 changes the attenuation of light according to the magnitude of the applied voltage. When the magnitude of the applied voltage is variable, the processor 3 can determine the magnitude of the voltage applied to the liquid crystal layer 103 according to the brightness of the high brightness part, for example, it can also be determined in a manner that is slightly larger each time the image is taken.

[0043] In step S6, the processor 3 records the image stored in the memory 4, such as the RAM, as a dynamic image, for example, in the storage 5. Then, the process returns to step S1. The dynamic image recorded in step S6 can also be sent to an external device of the monitoring camera 1 using the communication device 6. Here, when the process returns to step S1 via step S5, the exposure setting of the image sensor 22 is performed in a state where the light from the high brightness portion is attenuated.

[0044] Fig. 6A as well as Figure 6B 2 is a conceptual diagram showing the operation of the surveillance camera 1. First, the surveillance camera 1 performs imaging with the neutral density filter 23 turned off. At this time, the image sensor 22 generates an image of the observation area of ​​the camera unit 2 as it is. Fig. 6A As shown in the figure, when there is a high-brightness light source such as the sun 302 in the observation area, when the exposure of the image sensor 22 is set based on the average value in the observation area, the image sensor 22 becomes overexposed due to the influence of the high-brightness light source. Therefore, the monitoring object of the monitoring camera 1, such as the house 301, may become backlit and appear dark in the image.

[0045] When the processor 3 determines that the house 301 to be monitored is a low-brightness portion outside the specification and that a high-brightness portion such as the sun 302 exists in the image, the processor 3 drives the liquid crystal layer 103 in the divided area corresponding to the high-brightness portion 302 in the dimming filter 23. Figure 6BAs shown, the light incident on the image sensor 22 from the high-brightness light source such as the sun 302 is attenuated. As a result, the influence of the incident light from the high-brightness light source when setting the exposure in the image sensor 22 is also suppressed. Therefore, the brightness of the house 301 and the like as the monitoring object is also appropriate. In addition, the clouds 303 and the like that are overexposed due to the influence of the high-brightness light source can also be visually recognized in the image.

[0046] As described above, according to the embodiment, the dimming filter 23 composed of a liquid crystal shutter of a passive matrix method is arranged in front of the camera surface of the image sensor 22. As a result, the light incident on the image sensor 22 can be attenuated in units of divided areas. Here, the position of the pixel of the image sensor 22 is corresponding to the position of the divided area. Therefore, in the embodiment, compared with the case where attenuation is implemented in units of all areas, it is possible to selectively attenuate only the light from the high-brightness light source without attenuating the light from the monitored object incident on the image sensor 22, so even if the light from the high-brightness light source is attenuated, the monitored object will not be completely dark, and the reduction in the quality of the recorded image is suppressed. In addition, since there is no image processing such as HDR processing, a certain degree of evidence can be guaranteed. In addition, by combining the attenuation of the incident light by the dimming filter 23 with the exposure control of the image sensor, the brightness of the monitored object can be made appropriate without image processing.

[0047] In addition, the dimming filter 23 adopts a liquid crystal gate of a passive matrix method. The attenuation of light is electrically controlled, so there is no need for a mechanical mechanism as when colored glass is inserted. In addition, in the passive matrix method, the transmittance can be improved compared to the active matrix method. And the liquid crystal layer is driven in a normally white mode. The dimming filter 23 is usually used in a light-transmitting state, so it is in a light-transmitting state when not driven, thereby reducing power consumption compared to when the liquid crystal layer is driven in a normally black mode. In addition, TN liquid crystal is used as liquid crystal. Therefore, the dimming filter can be manufactured at a low price. And, in the TN liquid crystal, unlike liquid crystals with a large temperature dependence such as guest-host effect liquid crystals, there is no need for a feedback circuit for temperature compensation.

[0048] [Modification 1]

[0049] The following describes a modified example of the embodiment. In the embodiment, the liquid crystal layer 103 uses a passive matrix method and a TN liquid crystal in a normally white mode. However, this is not limited to this. The liquid crystal layer 103 can also be driven in an active matrix method or in a normally black mode. In addition, the liquid crystal material can also use a liquid crystal material in a mode other than the TN liquid crystal.

[0050] [Modification 2]

[0051] By changing the polarizing plate material used in the liquid crystal panel to a material having a polarization effect in the near-infrared region, the same effect can be obtained in surveillance camera images at night and surveillance images based on near-infrared light. Specifically, at night, the brightest point in the near-infrared image is the lighting light of street lamps, etc.

[0052] In the embodiment, the processor 3 dims the divided areas corresponding to the detected high-brightness parts by the dimming filter 23. The divided areas to be dimmed by the dimming filter 23 may be designated by the administrator of the surveillance camera 1, for example.

[0053] Furthermore, the technology of the embodiment can be combined with various image processing. For example, by combining an image captured with the neutral density filter turned off and an image captured with the neutral density filter turned on, an HDR image with an expanded dynamic range can be generated.

[0054] The present invention is not limited to the above-mentioned embodiments, and various modifications can be made in the implementation stage without departing from the scope of the main purpose. In addition, each embodiment can also be implemented in combination as appropriate, and the effect of the combination can be obtained in this case. Moreover, the above-mentioned embodiments include various inventions, and various inventions can be extracted from the combination selected from the disclosed multiple constituent elements. For example, in the case where deleting several constituent elements from all the constituent elements shown in the embodiment can also solve the problem and obtain the effect, the structure from which the constituent elements are deleted can also be extracted as an invention.

Claims

1. A surveillance camera, comprising: An image sensor for capturing images; a neutral density filter disposed in front of the imaging surface of the image sensor, and configured to attenuate light incident on the imaging surface of the image sensor by controlling the liquid crystal layer in units of divided regions; and The processing unit controls the operation of the above-mentioned dimming filter. The dimming filter is arranged at a distance from the image sensor so as to be located outside the focal depth of an optical system that forms an image of light in the image sensor.

2. The surveillance camera according to claim 1, in, The processing unit controls the dimming filter so as to attenuate light in the divided area corresponding to the high-brightness portion detected in the image.

3. The surveillance camera according to claim 1 or 2, in, The liquid crystal layer is a TN mode liquid crystal layer.

4. The surveillance camera according to claim 1 or 2, in, The liquid crystal layer is a normally white mode liquid crystal layer.

Images