JP2017073622A - Imaging apparatus - Google Patents

Abstract

An image pickup apparatus capable of acquiring a picked-up image that enables smooth confirmation of the inside of a vehicle even during the daytime. An image pickup apparatus includes an image pickup element, a lens that forms an image of light from a target area on the image pickup element, and a liquid crystal shutter disposed on the target area side with respect to the image pickup element. Prepare. The liquid crystal shutter 30 includes an incident side polarizing plate 301 and an outgoing side polarizing plate. The polarization axis 301a of the incident side polarizing plate 301 is set so that the light component in the polarization direction perpendicular to the vertical direction of the apparatus main body 101 is blocked by the incident side polarizing plate 301 after passing through the lens 10. Selection diagram] Fig. 7

Description

  The present invention relates to an imaging device that images a target area, and is particularly suitable for imaging outdoor scenery such as an intersection.

  2. Description of the Related Art An imaging device that captures images of streets and intersections with a monitoring camera is known. In this type of imaging apparatus, the captured image is used, for example, for verification of a traffic accident. In the verification, the status of the vehicle and the pedestrian and the lighting status of the traffic light are confirmed. That is, it is confirmed with reference to the captured image what kind of situation the street or intersection was in the event of an accident.

  Patent Document 1 below describes an imaging device that captures images of streets and intersections with a monitoring camera. In this imaging apparatus, an image captured by the monitoring camera is processed to extract a person image, and when the extracted person image matches or approximates the suspicious person list, the image captured by the monitoring camera is transmitted to the terminal. .

JP 2013-153304 A

  When using images obtained by capturing streets and intersections for verification of traffic accidents or the like, it is desirable to be able to smoothly check the driver and passengers of the vehicle that caused the accident. However, in the streets and intersections, sunlight is reflected by the windshield of the vehicle during the daytime, so the visibility inside the vehicle is significantly reduced. For this reason, it is difficult to check the driver and passengers of the vehicle from the image captured by the imaging device.

  In view of such a problem, an object of the present invention is to provide an imaging device capable of acquiring a captured image that can smoothly check the inside of a vehicle even during the daytime.

  An imaging apparatus according to a main aspect of the present invention includes an imaging element, a lens that forms an image of light from a target area on the imaging element, and a liquid crystal shutter disposed on the target area side with respect to the imaging element. Prepare. Here, the liquid crystal shutter includes an incident-side polarizing plate and an outgoing-side polarizing plate, and a light component having a polarization direction perpendicular to the vertical direction of the apparatus main body is transmitted by the lens and then blocked by the incident-side polarizing plate. As described above, the polarization axis of the incident side polarizing plate is set.

  According to the imaging apparatus according to this aspect, the S-polarized light component reflected by the vehicle windshield is shielded by the incident-side polarizing plate. For this reason, it can suppress that the visibility in a vehicle falls because sunlight reflects with the windshield of a vehicle. Therefore, it is possible to acquire a captured image that allows smooth confirmation of the interior of the vehicle even during the daytime.

Here, after the S-polarized light component reflected by the windshield is taken in by the lens, the polarization direction does not rotate and reaches the liquid crystal shutter as it is.
When the optical system of the imaging apparatus is configured, the incident-side polarizing plate may be arranged so that the vertical direction of the apparatus main body is substantially parallel to the polarization axis of the incident-side polarizing plate. Thereby, the S-polarized light component reflected by the windshield of the vehicle can be shielded by the incident side polarizing plate.

  The imaging apparatus according to this aspect includes a control unit that controls the imaging element and the liquid crystal shutter. In addition, the image sensor may be configured to accumulate and output charges corresponding to the amount of received light for each line. In this case, the control unit controls the image sensor so that a part of the charge accumulation period in each line on the image sensor overlaps each other, and the charge accumulation period for all the lines overlaps with each other in the overlap accumulation period. The liquid crystal shutter can be opened. In this case, since the image sensor is exposed during the overlapping accumulation period, the light of the target area is irradiated to all lines at the same timing and exposure period. For this reason, even when a subject moving at high speed is included in the target area, the captured image of the subject is not distorted.

  In the imaging apparatus according to this aspect, the imaging element has a function of a high-speed reading mode that outputs a signal at high speed, and the control unit sets the control mode for the imaging element to the high-speed reading mode, It may be configured to cause the overlapping accumulation period. In this configuration, since the distortion of the captured image is suppressed using the high-speed reading mode, it is possible to suppress the distortion of the subject while maintaining the frame transfer rate of the captured image.

  As described above, according to the present invention, it is possible to provide an imaging device capable of acquiring a captured image that can be confirmed smoothly inside the vehicle even during the daytime.

  The effects and significance of the present invention will become more apparent from the following description of embodiments. However, the embodiment described below is merely an example when the present invention is implemented, and the present invention is not limited to what is described in the following embodiment.

FIG. 1A is a diagram illustrating an external configuration of an image management system according to the embodiment. FIG. 1B is a diagram illustrating an example of a captured image according to the embodiment. FIG. 2 is a diagram illustrating a configuration of the imaging apparatus according to the embodiment. FIG. 3 is a diagram illustrating a configuration of the CMOS image sensor according to the embodiment. FIGS. 4A and 4B are diagrams for explaining read control of the CMOS image sensor according to the embodiment. FIG. 5A is a graph showing reflection characteristics of P-polarized light and S-polarized light. FIG.5 (b) is a figure which shows the incident and reflection condition of the light ray with respect to reflective surfaces, such as a windshield. 6A and 6B are diagrams schematically illustrating the configuration and operation of the liquid crystal shutter according to the embodiment. FIG. 7 is a front view schematically showing the positional relationship among the apparatus main body, the incident-side polarizing plate, and the imaging element of the imaging apparatus according to the embodiment. FIG. 8A is a diagram illustrating a captured image obtained by actually capturing the windshield of the vehicle with the imaging device having the configuration of the embodiment. FIG. 8B is a diagram illustrating a captured image obtained by actually capturing the windshield of the vehicle using a general camera (comparative example). FIGS. 9A and 9B are diagrams for explaining a control method of the CMOS image sensor according to the modified example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A is a diagram illustrating an external configuration of an image management system according to the embodiment.

  As illustrated in FIG. 1A, the image management system includes an imaging device 1 and an external device 2. The imaging device 1 is a surveillance camera, and is installed on the installation object 3 so as to be able to capture images of streets and intersections including traffic lights. The imaging device 1 is installed on the installation object 3 so that the top and bottom are along the vertical direction. The installation object 3 is, for example, an outer wall such as a building, a roof structure, a utility pole, or the like. The imaging device 1 records the captured image on an internal recording medium as needed. The external device 2 is a portable personal computer. In addition, the external device 2 may be another mobile information terminal such as a mobile phone or a tablet.

  The image recorded in the imaging device 1 is collected by the external device 2 as appropriate. The imaging device 1 and the external device 2 can communicate by wireless LAN. The external device 2 establishes a wireless LAN communication path and downloads an image from the imaging device 1. Communication between the imaging device 1 and the external device 2 is not limited to a wireless LAN, and may be another communication method such as Bluetooth.

  FIG. 1B is a diagram illustrating an example of a captured image captured by the imaging apparatus 1. Here, the intersection 5 including the traffic signal 4 is set as the target area. For convenience, FIG. 1B shows a traffic light 4 and a vehicle 6 (passenger car) that face the direction of the imaging apparatus 1. The image picked up by the image pickup device 1 is collected by the external device 2 and then used, for example, for verification of a traffic accident. In this verification, the situation of the vehicle and the pedestrian traveling through the intersection 5 and the lighting condition of the traffic light 4 are confirmed.

  FIG. 2 is a diagram illustrating a configuration of the imaging apparatus 1.

  The imaging device 1 includes a lens 10, an iris 20, a liquid crystal shutter 30, an imaging element 40, a control unit 50, a storage unit 60, and a communication unit 70.

  The lens 10 takes in light from the target area and forms an image of the target area on the light receiving surface of the image sensor 40. The iris 20 limits light from the outside so that an appropriate amount of light enters the image sensor 40 according to the intensity of light from the target area. The iris amount of the iris 20 is adjusted by an iris driving circuit 21.

  For example, the liquid crystal shutter 30 has a so-called normally white characteristic in which the transmittance is maximum when no voltage is applied and the transmittance is decreased when a voltage is applied. In this case, the liquid crystal shutter 30 transmits light when no voltage is applied, and blocks light when a voltage is applied. In addition, the liquid crystal shutter 30 is a liquid crystal shutter having a so-called normally black characteristic in which the transmittance is maximized when a voltage is applied and the transmittance is lowered when the voltage application is interrupted. Also good. The liquid crystal shutter 30 is switched between open and closed states by a drive signal from the shutter drive circuit 31.

  The image sensor 40 is a CMOS image sensor. The image sensor 40 has a photodiode at a position corresponding to each pixel on the light receiving surface. The image pickup device 40 is controlled by the image pickup signal processing circuit 41 so as to accumulate and output charges to the photodiode for each line.

  The control unit 50 includes an arithmetic processing circuit such as a CPU (Central Processing Unit) and controls each unit according to a program held in the storage unit 60. The storage unit 60 includes a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The storage unit 60 holds a control program and is also used as a work area for control by the control unit 50. The control unit 50 controls the iris driving circuit 21, the shutter driving circuit 31, and the imaging signal processing circuit 41 by the program held in the storage unit 60. The communication unit 70 communicates with the external device 2 shown in FIG.

  FIG. 3 is a diagram schematically illustrating the configuration of the image sensor 40. For convenience, FIG. 3 shows the configuration of portions corresponding to nine pixels, but in reality, similar configurations are arranged corresponding to a predetermined number of pixels in the vertical and horizontal directions.

  The image sensor 40 has a photodiode 40a at a position corresponding to each pixel. When the photodiode 40a receives light, the photodiode 40a accumulates charges according to the amount of received light. The accumulated electric charge is converted into a voltage by the amplifier 40b and amplified. The amplified voltage is transmitted to the vertical signal line 40d for each line L when the switch 40c is turned on. The transmitted voltage is temporarily stored by the column circuit 40e arranged for each vertical signal line 40d. The stored voltage is sent to the horizontal signal line 40g when the column selection switch 40f is turned on. Then, the voltage sent to the horizontal signal line 40g is sent to the imaging signal processing circuit 41. As described above, the image sensor 40 transmits a voltage signal for each line L.

  Further, the image pickup device 40 is controlled so that charge is stored in the photodiode 40a for each line L. That is, the photodiode 40a on one line L is set in a state in which charge can be accumulated for a predetermined period, and after this period, the charge generated in each photodiode 40a on the line L is output. The This control is sequentially performed from the uppermost line L to the lowermost line L. When light is irradiated to the photodiode 40a on the line L when the line L is in a state where charge can be accumulated, the charge corresponding to the amount of the irradiated light is changed to each photodiode 40a on the line. Accumulated in. The charges accumulated in this way are read for each line L as described above, converted into a voltage signal, and output to the imaging signal processing circuit 41.

  Hereinafter, a period in which each line is set in a state where charge can be accumulated is referred to as a “charge accumulation period”.

  Returning to FIG. 2, the imaging signal processing circuit 41 sequentially sets each line on the imaging element 40 to the charge accumulation period, and reads out the charge for each line. The imaging signal processing circuit 41 includes an A / D conversion circuit, converts a voltage signal for each line supplied from the imaging element 40 via the horizontal signal line 40g (see FIG. 3) into a digital signal, and controls the control unit 50. Output to. The control unit 50 stores the digital signal (luminance signal) supplied from the imaging signal processing circuit 41 in the storage unit 60. In this way, one captured image is formed from the luminance signals for all lines (for one frame) output from the imaging signal processing circuit 41.

  FIGS. 4A and 4B are diagrams illustrating the reading control of the image sensor 40. FIG. 4A is a diagram schematically showing control (hereinafter referred to as “normal read mode”) in the case where charges are read from each line at a normal speed, and FIG. It is a figure which shows typically the control (henceforth "high-speed read mode") in the case of reading an electric charge from each line.

  On the left side of FIGS. 4A and 4B, the light receiving surface of the image sensor 40 and each line L are schematically shown. Here, the uppermost line L is L0, and the lowermost line is Ln. Also, the control timing for each line is schematically shown on the right side of FIGS. 4 (a) and 4 (b).

  Referring to FIG. 4A, in the normal read mode, control for the uppermost line L0 starts at timing t1 and ends at timing t2. The control for the line L2 that is one step below starts after a predetermined time from the timing t1. In this way, each time the line L changes to the lower stage, the control for each line is sequentially performed while the start timing is delayed by a predetermined time. The start timing of the lowermost line Ln is a timing t2 delayed by Δt from the timing t1.

  In the uppermost line L0, charges are accumulated between the timing t1 and the timing t2. For example, the entire period Δt between the timing t1 and the timing t2 is the charge accumulation period. The charge accumulation period is similarly set for the other lines L. At the timing t2 when the period Δt has elapsed from the timing t1, the charge is read from the uppermost line L0.

  For the second-stage line L1, charge accumulation is started at a timing delayed by a predetermined time from the timing t1, and charge reading is executed at a timing delayed by a predetermined time from the timing t2. Thus, every time the line L changes, the charge accumulation start timing is delayed by a predetermined time, and the charge read execution timing is also delayed by a predetermined time. The charge accumulation start timing for the lowermost line Ln is a timing t2 delayed by Δt from the timing t1, and the charge read execution timing is a timing t3 delayed by Δt from the timing t2.

  Thus, in the normal read mode, the charge accumulation end timing for the uppermost line L0 is the charge accumulation start timing for the lowermost line Ln. For this reason, in the normal read mode, a period in which the charge accumulation periods of all lines overlap does not occur.

  Referring to FIG. 4B, in the high-speed read mode, the amount of deviation of the control start timing between the lines L is shortened compared to the normal read mode by increasing the charge read speed for each line L. In the example of FIG. 4B, the shift amount of the control start timing between the lines L is reduced by half compared to the normal read mode. Therefore, the control start timing for the lowermost line Ln is delayed by Δt / 2 from the control start timing t1 for the uppermost line L0.

  The charge reading speed for each line L is increased by reducing the number of bits when sampling (A / D conversion) the charge signal of each line, compared to the number of bits in the normal reading mode. This process is performed by the imaging signal processing circuit 41 under the control of the control unit 50 in FIG. In the high-speed readout mode, the number of sampling bits is reduced in this way, so that the image quality of the captured image is slightly degraded as compared with the normal readout mode. However, this deterioration is such that there is no particular problem in visibility in applications such as surveillance cameras. Alternatively, the number of sampling bits can be reduced to the same number by improving and speeding up the imaging device 40 and the imaging signal processing circuit 41.

  As described above, by setting the control mode for the image sensor 40 to the high-speed reading mode, as shown in FIG. 4B, an overlapping accumulation period in which the charge accumulation periods of all the lines overlap with each other occurs. Then, by performing exposure during this overlapping accumulation period, each line L is irradiated with light from the target region at the same timing, and charges are applied to the photodiodes 40a on all the lines L at the same timing and exposure amount. It will be accumulated. For this reason, it can suppress that distortion arises in the picked-up image of the to-be-photographed subject. That is, the rolling shutter phenomenon is suppressed, and a global shutter function using the image sensor 40 is realized.

  In the present embodiment, the control mode of the image sensor 40 is set to the high-speed reading mode. In the overlapping accumulation period, the liquid crystal shutter 30 is opened, and light from the target area is guided to the image sensor 40. Specifically, the control unit 50 in FIG. 2 opens and closes the liquid crystal shutter 30 so that the light collected by the lens 10 is irradiated onto the light receiving surface of the image sensor 40 at a predetermined timing during the overlapping accumulation period. Let The control unit 50 causes the shutter drive circuit 31 to stop applying the voltage to the liquid crystal shutter 30 to open the liquid crystal shutter 30, and then again, the voltage of the voltage to the liquid crystal shutter 30 is applied to the liquid crystal shutter drive circuit 31 again with a predetermined time width. Application is started and the liquid crystal shutter 30 is closed. Thus, for example, as shown in FIG. 4B, an exposure period for guiding light to the image sensor 40 is set within the overlapping accumulation period.

  By the way, as shown in FIGS. 1A and 1B, when the imaging device 1 is installed so as to capture an intersection, the captured image captured by the imaging device 1 is a traffic accident or the like that occurs at the intersection. Used for verification. In this case, it is desirable that the driver or passenger of the vehicle that has caused the accident can be confirmed smoothly. However, since the intersection is exposed to sunlight during the day, sunlight is reflected by the windshield of the vehicle 6, and the visibility inside the vehicle is significantly reduced due to this reflection. If it becomes like this, it will become difficult to confirm the driver | operator and passenger of a vehicle with the image imaged by the imaging device 1. FIG.

  Therefore, in the present embodiment, the imaging apparatus 1 is provided with a configuration for acquiring a good captured image even during the daytime. Hereinafter, this configuration will be described.

  First, with reference to FIG. 5 (a), (b), the sunlight reflecting effect by a windshield is demonstrated.

  FIG. 5A is a graph showing reflection characteristics of P-polarized light and S-polarized light. FIG. 5B is a diagram schematically showing the incidence and reflection of light rays on a reflecting surface such as a windshield.

  Here, P-polarized light means that when a light ray is incident on the reflection surface and reflected as shown in FIG. 5B, the polarization direction is parallel to a surface (incident surface) including both the incident light beam and the reflected light beam. It is a certain polarization state. S-polarized light is a polarization state in which the polarization direction is perpendicular to the plane (incident plane).

  In general, the relationship between the angle of incident light (incident angle) θ with respect to the normal line standing on the reflecting surface and the reflectance of P-polarized light and S-polarized light is as shown in FIG. In the graph of FIG. 5, the horizontal axis is the incident angle θ, and the vertical axis is the reflectance. The vertical axis is standardized with a maximum value of 1.

  As shown in FIG. 5A, the S-polarized light component is dominant in the reflected light on the reflecting surface. Accordingly, the S-polarized component is dominant in the reflected light of the windshield. Therefore, when the S-polarized light component reflected by the windshield is removed during imaging, the influence of the windshield reflection on the captured image can be suppressed, and the visibility inside the vehicle can be improved.

  Here, the windshield is inclined in a horizontal direction by a predetermined angle from a substantially vertical direction, and sunlight enters the windshield from above. Therefore, the polarization direction of the S-polarized light component of the reflected light on the windshield is substantially parallel to the substantially horizontal direction. In the present embodiment, the liquid crystal shutter 30 is configured to remove this S-polarized component.

  6A and 6B are diagrams schematically showing the configuration and operation of the liquid crystal shutter 30. FIG.

  As shown in FIG. 6A, the liquid crystal shutter 30 includes an incident side polarizing plate 301, two electrodes 302 and 303, and an output side polarizing plate 304. Liquid crystal is filled between the two electrodes 302 and 303. Reference numeral 305 denotes liquid crystal molecules. The polarization axis 301a of the incident side polarizing plate 301 and the polarization axis 304a of the output side polarizing plate 304 are orthogonal to each other. The incident side polarizing plate 301 transmits only light whose polarization direction is parallel to the polarization axis 301a, and the output side polarizing plate 304 transmits only light whose polarization direction is parallel to the polarization axis 304a.

  As shown in FIG. 6A, when no voltage is applied to the electrodes 302 and 303, the light taken in through the lens 10 (see FIG. 2) has only a light component whose polarization direction is parallel to the polarization axis 301a. Is transmitted through the incident-side polarizing plate 301. While the light component passes through the liquid crystal, the polarization direction is rotated by 90 degrees by the liquid crystal molecules 305. That is, the liquid crystal molecules 305 are aligned so as to give the light the action of rotating the polarization direction by 90 degrees in a state where no voltage is applied to the electrodes 302 and 303. Thus, the polarization direction of the light component transmitted through the incident side polarizing plate 301 becomes parallel to the polarization axis 304 a of the outgoing side polarizing plate 304 by the action of the liquid crystal molecules 305. As a result, this light component is transmitted through the exit-side polarizing plate 304 and guided to the image sensor 40 (see FIG. 2).

  As shown in FIG. 6B, when a voltage is applied to the electrodes 302 and 303, the liquid crystal molecules 305 are aligned in one direction. For this reason, the light component which permeate | transmitted the incident side polarizing plate 301 reaches | attains the output side polarizing plate 304, without rotating a polarization direction. Therefore, the polarization direction of this light component is orthogonal to the polarization axis 304 a of the exit side polarizing plate 304. For this reason, this light component is blocked by the output-side polarizing plate 304 and is not guided to the image sensor 40 (see FIG. 2).

  As described above, the liquid crystal shutter 30 transmits light when no voltage is applied to the electrodes 302 and 303, and blocks light when a voltage is applied to the electrodes 302 and 303. The control unit 50 in FIG. 2 cancels the application of the voltage to the electrodes 302 and 303 in the exposure period of FIG. 4B, and applies the voltage to the electrodes 302 and 303 in the other periods. Thereby, light from the target area is guided to the image sensor 40 during the exposure period within the overlapping accumulation period.

  In the present embodiment, by adjusting the direction of the polarization axis 301 a of the incident side polarizing plate 301, the light of the S polarization component reflected by the windshield is blocked by the incident side polarizing plate 301.

  FIG. 7 is a front view schematically showing the positional relationship between the apparatus main body 101 of the imaging apparatus 1, the incident-side polarizing plate 301, and the imaging element 40.

  As shown in FIG. 7, the liquid crystal shutter 30 is arranged so that the vertical direction of the apparatus main body 101 is parallel or substantially parallel to the polarization axis 301 a of the incident side polarizing plate 301. Here, as shown in FIG. 1, the imaging apparatus 1 is installed such that the vertical direction of the apparatus main body 101 is along the vertical direction. Therefore, when the liquid crystal shutter 30 is arranged so that the vertical direction of the apparatus main body 101 is parallel or substantially parallel to the polarization axis 301a of the incident side polarizing plate 301, the polarizing axis 301a of the incident side polarizing plate 301 is perpendicular to the horizontal plane. It is almost parallel to a flat surface.

  On the other hand, as described above, of the light reflected by the vehicle windshield, the polarization direction Rs of the S polarization component is horizontal, and the polarization direction Rp of the P polarization component is perpendicular to the polarization direction Rs. It has become. Therefore, when the incident-side polarizing plate 301 is arranged so that the polarization axis 301a is parallel or substantially parallel to the vertical direction of the apparatus main body 101 as described above, the polarization direction of the S-polarized light component reflected by the windshield. Rs is substantially perpendicular to the polarization axis 301 a of the incident-side polarizing plate 301. For this reason, the S-polarized light component reflected by the windshield is blocked by the incident-side polarizing plate 301, and only the P-polarized light component is transmitted through the incident-side polarizing plate 301. As a result, the S-polarized component that is dominant in the light reflected by the windshield is excluded by the incident-side polarizing plate 301.

  As described above, in this embodiment, the S-polarized component that is dominant in the light reflected by the windshield is excluded by the incident-side polarizing plate 301, so that the influence of the windshield reflection in the captured image is suppressed. Thereby, the visibility in a vehicle can be improved.

  FIG. 8A is a diagram illustrating a captured image obtained by actually capturing the windshield of the vehicle by the imaging apparatus 1 having the configuration of the above embodiment. FIG. 8B is a diagram illustrating a captured image obtained by actually capturing the windshield of the vehicle using a general camera (comparative example).

  As shown in FIG. 8B, in the captured image obtained by capturing the windshield of the vehicle with a general camera (comparative example), the interior of the vehicle cannot be visually recognized due to the reflection of sunlight on the windshield.

  On the other hand, in the captured image obtained by imaging the windshield of the vehicle by the imaging device 1 having the configuration of the above embodiment, the reflection of sunlight on the windshield is effectively suppressed as shown in FIG. The visibility of the captured image is improved to such an extent that the inside of the vehicle can be satisfactorily confirmed. From this verification result, the improvement effect of the visibility by the structure of the said embodiment was confirmed.

<Effect of embodiment>
According to this embodiment, the following effects are produced.

  The light component of S-polarized light reflected by the vehicle windshield is shielded by the incident-side polarizing plate 301. For this reason, it is suppressed that the visibility in a vehicle falls because sunlight reflects with the windshield of a vehicle. Therefore, it is possible to acquire a captured image that allows smooth confirmation of the interior of the vehicle even during the daytime.

  The image sensor 40 is configured to store and output charges corresponding to the amount of received light for each line, and the control unit 50 captures images so that a part of the charge accumulation period in each line on the image sensor 40 overlaps each other. The element 40 is controlled. In addition, the control unit 50 opens the liquid crystal shutter 30 in the overlapping accumulation period in which the charge accumulation periods overlap each other for all lines. Thereby, since the image sensor 40 is exposed during the overlapping accumulation period, the light of the target region is irradiated to the image sensor 40 at the same timing and exposure period for all lines. For this reason, even when a subject moving at high speed is included in the target area, the captured image of the subject is not distorted.

  In the imaging device according to this aspect, the image sensor has a function of a high-speed reading mode that outputs a signal at high speed, and the image sensor control unit sets a control mode for the image sensor to the high-speed reading mode. Causes the overlap accumulation period. According to this configuration, since the distortion of the captured image is suppressed using the high-speed reading mode, it is possible to suppress the distortion of the subject while maintaining the frame transfer rate of the captured image.

<Example of change>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications other than the above can be made in the embodiments of the present invention.

  For example, in the above embodiment, as shown in FIG. 4B, the overlapping accumulation period is generated by setting the control mode of the image sensor 40 to the high-speed readout mode, but as shown in FIG. 9B. In addition, the overlapping accumulation period may be generated by setting the control mode of the image sensor 40 to the low speed mode. In the low speed mode, the imaging period of each line is set to twice the normal readout mode shown in FIG. 9A, that is, 2Δt. Also in this case, the liquid crystal shutter 30 is controlled so as to be opened during the overlapping accumulation period, for example. That is, an exposure period for guiding light to the image sensor 40 is set within the overlapping accumulation period. By setting the exposure period in this way, even when a subject moving at high speed is included in the target area, the captured image of the subject is not distorted.

  In the above embodiment, a liquid crystal shutter having normally white characteristics is used as the liquid crystal shutter 30, but a liquid crystal shutter having normally black characteristics may be used as the liquid crystal shutter 30.

  When the liquid crystal shutter 30 having a normally black characteristic is used, the liquid crystal molecules 305 are aligned as shown in FIG. 6B in a state where no voltage is applied to the electrodes 302 and 303, and light from the target region is emitted. It is blocked by the output side polarizing plate 304. In a state where a voltage is applied to the electrodes 302 and 303, the liquid crystal molecules 305 are aligned as shown in FIG. 6A, and light from the target region is transmitted through the emission side polarizing plate 304.

  Thus, when the liquid crystal shutter 30 having normally black characteristics is used, the vertical direction of the apparatus main body 101 is parallel or substantially parallel to the polarization axis 301a of the incident-side polarizing plate 301, as in the above embodiment. By arranging the incident-side polarizing plate 301 so that the S-polarized light reflected by the vehicle windshield is blocked by the incident-side polarizing plate 301. For this reason, it is suppressed that the visibility in a vehicle falls because sunlight reflects with the windshield of a vehicle. Therefore, it is possible to acquire a captured image that allows smooth confirmation of the interior of the vehicle even during the daytime.

  However, for the following reasons, it is preferable to use a liquid crystal shutter having normally white characteristics as a liquid crystal shutter 30 rather than a liquid crystal shutter having normally black characteristics.

  The liquid crystal shutter 30 has different transmittance changing speeds at the start of voltage application and the stop of voltage application depending on the characteristics of the liquid crystal. In general, the change rate of transmittance when a voltage is applied to a liquid crystal is fast, but the change rate of the transmittance when a voltage application is stopped is slow. This is because the rate of change of transmittance when voltage application is stopped depends on the viscosity of the liquid crystal, and it takes time for the alignment of the liquid crystal to return to the original direction.

  Due to the characteristics of the liquid crystal, for example, in a so-called normally black liquid crystal shutter, the transmittance is low when no voltage is applied, and the transmittance is high when a voltage is applied. The transmittance is maximized immediately after starting, but the transmittance does not easily return to the minimum value even when the voltage application is stopped. For this reason, when a normally black liquid crystal shutter is used as the liquid crystal shutter 30, the exposure time for the image sensor 40 becomes longer than the expected length, and this tends to cause blur in the captured image of the subject.

  On the other hand, in the so-called normally white type liquid crystal shutter, the transmittance is maximum when no voltage is applied and the transmittance is lowered when the voltage is applied. However, when the voltage application is started, the transmittance quickly returns to the minimum value. For this reason, when a normally white liquid crystal shutter is used as the liquid crystal shutter 30, the exposure time for the image sensor 40 does not become longer than the expected time, and it is effective that the captured image of the subject is blurred. Can be suppressed.

  For the above reasons, it is preferable to use a normally white liquid crystal shutter as the liquid crystal shutter 30 as in the above embodiment. Thereby, it is possible to effectively suppress the occurrence of blurring in the captured image of the subject.

  Further, in the above-described embodiment, the S-polarized light component reflected by the windshield is incident on the assumption that the polarized light direction reaches the liquid crystal shutter 30 without being rotated after being captured by the lens 10. The direction of the polarization axis 301a of the side polarizing plate 301 was set. In contrast, the optical system from the lens 10 to the liquid crystal shutter 30 is designed so that the polarization direction of the S-polarized light component reflected by the windshield is rotated by a predetermined angle after being captured by the lens 10. In this case, the direction of the polarization axis 301a of the incident side polarizing plate 301 is adjusted so that the polarization direction of the S-polarized light component reflected by the windshield is substantially orthogonal to the polarization axis 301a at the position of the incident side polarizing plate 301. It only has to be done. That is, the light component in the polarization direction perpendicular to the vertical direction of the apparatus main body 101 (polarization direction parallel to the horizontal direction) passes through the lens 10 and is then blocked by the incident-side polarizing plate 301 of the liquid crystal shutter 30. The polarization axis 301a of the incident side polarizing plate 301 may be set. As a result, the S-polarized light component reflected by the windshield can be removed by the incident side polarizing plate 301 as in the above embodiment.

  In the above-described embodiment, an example in which an intersection is imaged by the imaging device 1 is shown, but the imaging area is not necessarily an intersection, and may be another area through which a vehicle passes.

  Moreover, in the said embodiment, although the imaging device 1 was installed in the outer wall, such as a building, a rooftop structure, an electric pole, etc., the structure of the imaging device 1 may be included in a streetlight etc. integrally, for example. The imaging device 1 is not limited to the monitoring camera, and may be another imaging device.

  In addition, the embodiment of the present invention can be variously modified as appropriate within the scope of the technical idea shown in the claims.

DESCRIPTION OF SYMBOLS 1 ... Imaging device 10 ... Lens 30 ... Liquid crystal shutter 40 ... Image pick-up element 50 ... Control part 301 ... Incident side polarizing plate 301a ... Polarization axis 304 ... Outgoing side polarizing plate

Claims (4)

An image sensor;
A lens that focuses light from a target area on the image sensor;
A liquid crystal shutter disposed on the target area side with respect to the image sensor, and
The liquid crystal shutter includes an incident-side polarizing plate and an outgoing-side polarizing plate so that a light component in a polarization direction perpendicular to the vertical direction of the apparatus main body is transmitted by the lens and then blocked by the incident-side polarizing plate. The polarization axis of the incident-side polarizing plate is set,
An imaging apparatus characterized by that. The imaging device according to claim 1,
The imaging apparatus, wherein the incident-side polarizing plate is arranged so that a vertical direction of the apparatus main body is substantially parallel to the polarization axis of the incident-side polarizing plate. The imaging device according to claim 1 or 2,
A controller for controlling the image sensor and the liquid crystal shutter;
The imaging device accumulates and outputs charges corresponding to the amount of received light for each line,
The controller is
Controlling the image sensor so that a part of the charge accumulation period in each line on the image sensor overlaps each other;
An imaging apparatus, wherein the liquid crystal shutter is opened in an overlapping accumulation period in which charge accumulation periods of all the lines overlap each other. The imaging device according to claim 3.
The image sensor has a function of a high-speed readout mode for outputting a signal at high speed,
The control unit causes the overlap accumulation period by setting a control mode for the image sensor to the high-speed readout mode.
An imaging apparatus characterized by that.