JP2020048133A - Imaging apparatus and control method of the same - Google Patents

Abstract

To solve the problem in which, if a mask is created by image processing, a load of image processing increases if the mask is created for each frame, heat generated by a video engine increases, thus, it is necessary to create a mask without using image processing.SOLUTION: A monitoring system including an imaging apparatus including an optical system including a polarizing filter and a rotation mechanism of the polarizing filter, creates a privacy mask using reflected light by changing a polarization angle of the polarizing filter of the imaging apparatus.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging device, and more particularly, to an imaging device having a polarizing filter.

  In a surveillance camera that constantly monitors the entrance of a roadway or parking lot, it is possible to shoot the inside of the car through the glass, so personal information such as "when" "who" "where" "with whom" remains as data I will. Therefore, privacy infringement is regarded as a problem.

  There is a technique called a privacy mask as a technique for protecting privacy in photographing data. A privacy mask is a mask that superimposes mask data on an unnecessary area in a captured video so as to make the unnecessary area invisible or difficult for a user to see.

  As a conventional technique for creating a privacy mask (hereinafter, referred to as a mask), there is a technique using image processing. In this method, a masking process is performed on a portion to be hidden on an image by using image processing.

  Patent Literature 1 describes a technique for creating a privacy mask using image processing. In this method, the image correction unit masks a predetermined area of the image data with the mask data stored in the mask data storage unit based on the position information data of the image data.

JP-A-2006-122892

  However, when the technique disclosed in Patent Document 1 is applied to a mask, it is necessary to acquire data for each frame and create a mask in that area. Therefore, when the frame rate increases, the processing load on the video engine increases, and there is a concern that the video engine generates heat. Therefore, in order to create a mask while suppressing heat generation of the video engine, it is necessary to perform mask processing independent of image processing.

In order to solve the above-described problems, an imaging device according to the present invention includes:
Imaging means having an optical system with a polarizing filter;
A rotation mechanism for the polarizing filter,
Analysis means for analyzing the image acquired by the imaging means,
Control means for changing a polarization angle of the polarizing filter so that a predetermined subject is hard to be confirmed by reflected light according to an analysis result by the analysis means;
It is characterized by having.

  ADVANTAGE OF THE INVENTION According to the imaging device which concerns on this invention, in an imaging device which monitors an object which has a transmission surface, such as glass, it becomes possible to create a mask without increasing the load of image processing.

Imaging device according to the first embodiment Characteristics of the polarizing filter shown in the first embodiment Polarization characteristics shown in Embodiment 1 A method for releasing a mask using polarized light according to the second embodiment Control sequence shown in Embodiment 2 Embodiment 3 Method for Switching Polarizing Element Image of switching of polarization element shown in Embodiment 3. Polarization direction switching timing according to the fourth embodiment Control sequence shown in Embodiment 4

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an imaging device according to an embodiment of the present invention.

(First embodiment)
<Imaging device>
Hereinafter, an imaging device and a control method of the imaging device according to the first embodiment of the present invention will be described with reference to FIG. The imaging apparatus 100 includes an optical system including a polarizing filter 101 and a lens 102, and a main body 103 having a video engine for performing image processing. The incident light 300 from the outside is reflected by the windshield 201 of the vehicle (moving body) 200, and the reflected light 301 of the windshield is generated. First, the polarization filter and the polarization of the imaging device will be described.

<About the polarizing filter>
The polarization filter 101 of the imaging device 100 has a role of filtering light entering the imaging device 100. The polarization filter 101 has a property of transmitting only “light having a specific polarization direction”. The characteristics of the polarizing filter will be described with reference to FIGS.

  In FIG. 2A, since the vibration direction of the incident polarized light 302 matches the opening direction of the polarizing filter 101, the light passes through the polarizing filter 101. FIG. 2B shows a case where the polarization filter is rotated by 90 degrees with respect to FIG. In FIG. 2B, since the vibration direction of the incident polarized light 302 and the opening direction of the polarizing filter 101 are orthogonal to each other, the polarized light 302 does not pass through the polarizing filter 101. Therefore, the polarized light 302 does not enter the lens 102.

  FIG. 2C shows the case where the incident light is the natural light 303. Since natural light is unpolarized, there are countless vibration directions. Therefore, although the light in the same vibration direction as the polarization filter is transmitted by the polarization filter 101, the light in the other vibration directions is not transmitted.

  As described above, in an optical imaging system including a polarizing filter, the light taken into the main body is determined by the angle of the polarizing filter and the direction of oscillation of polarized light entering the imaging device.

<About polarized light>
With reference to FIG. 3, a description will be given of a mechanism in which polarized light is generated by being reflected on a windshield of a car, with reference to FIG. FIG. 3 illustrates a case where the incident light (natural light) 304 is incident on an interface 403 between two substances (substances A401 and B402) having different refractive indexes. At this time, the incident light 304 is separated into reflected light 305 and refracted light 306. Further, the light vibration is separated into a polarized light component (p-polarized light) parallel to the incident surface and a polarized light component (s-polarized light) perpendicular to the incident surface. This is because the reflectance differs depending on the angle between the vibration axis of the light wave and the interface. Further, since the reflectance of p-polarized light becomes 0 at a specific angle, there is an angle at which reflected light is only s-polarized light (polarization angle (θB)).

  Formula 1 shows the calculation formula of the polarization angle (θB). For example, when natural light enters the glass (transmittance n2: 1.5) from the air (transmittance n1: 1), the polarization angle is about 56 degrees. When the incident angle of the natural light becomes the polarization angle, the polarization property becomes the strongest.

θB = Arctan (n2 / n1) (Equation 1)
Next, a method of forming a mask using a polarizing filter and reflected light will be described with reference to FIG. FIG. 1 shows a case where incident light 300 from the outside hits a windshield 301 of a car. At this time, the angle of the opening of the polarizing filter 101 matches the vibration direction of the reflected light (s-polarized light) on the windshield. Therefore, the reflected light 301 polarized by the windshield 201 is transmitted by the polarization filter 101 without being attenuated. On the other hand, only natural light that directly enters the imaging device passes through the light that matches the aperture of the polarizing filter. As a result, the amount of natural light decreases, and the reflection of the windshield becomes noticeable. As a result, the amount of light from the inside of the vehicle taken into the imaging device is relatively reduced with respect to the amount of light reflected from the windshield. Therefore, since the reflected light is dominant in the windshield, a mask can be formed on the windshield.

  Although the case of linearly polarized light has been described for the polarizing filter, circularly polarized light or elliptically polarized light may be used. The configuration of the imaging apparatus is not limited to the configuration in which the polarizing filter 101 is provided in the stage preceding the lens 102 as shown in FIG. Further, the type of the polarizing element is not limited to the polarizing filter, and does not depend on the kind of the imaging element including a polarizing mechanism in its structure.

  In addition, although the description has been given by taking the windshield of a car as an example, any transparent material having a refractive index different from that of air may be used. Natural light is not limited to sunlight but may be artificial light such as a streetlight. Further, the incident light 300 from the outside shown in FIG. 1 is not necessarily natural light, but may be light having the same polarization direction as the s-polarized light of the reflected light.

(Second embodiment)
Example 1 shows a method of forming a mask on the windshield of all vehicles. Second Embodiment In a second embodiment, a method of removing a mask when an abnormal vehicle is photographed to make it easier to see inside the vehicle will be described with reference to FIG.

  In the first embodiment, since the angle of the opening of the polarizing filter 101 is fixed, only light having the same vibration axis as the opening of the polarizing filter is transmitted. Therefore, the reflected light polarized by the windshield transmits through the polarizing filter 101 and is taken into the main body of the imaging device. On the other hand, in the second embodiment, by providing the rotation mechanism 104 to the polarization filter 101, the vibration direction of light that can be taken into the main body of the imaging device is changed. As described above, the second embodiment is characterized in that the vibration direction of the light taken into the imaging device is variable.

  FIG. 4 illustrates a state in which the polarization filter 101 is rotated by 90 degrees with respect to FIG. 1 of the first embodiment. In FIG. 1, the oscillation direction of the reflected light 301 of the windshield and the opening of the polarizing filter 101 are parallel. Therefore, the reflected light 301 is transmitted through the polarizing filter 101. On the other hand, in FIG. 4, the vibration direction of the reflected light 301 on the windshield and the opening of the polarizing filter 101 are perpendicular. Therefore, the reflected light cannot pass through the polarizing filter. At this time, the image acquired by the imaging device does not show the reflected light of the windshield, but shows the inside of the vehicle. However, the removal rate of reflected light from the windshield also depends on the polarization. Therefore, when removing the reflected light, a state of the polarization angle at which the polarization property becomes strong is preferable.

  A control sequence according to the second embodiment will be described with reference to FIG. The use case of the second embodiment is an imaging apparatus that constantly monitors a car. When the vehicle captured by the imaging device is not an abnormal vehicle, the mask is maintained, and when the vehicle is abnormal, the mask is removed.

  It is preferable to create a mask from the viewpoint of privacy protection until it is determined whether the vehicle is abnormal. For this reason, the rotation angle of the polarizing filter is controlled to adjust the angle so that a large amount of reflected light from the windshield can be taken in (S01). Then, the vehicle (moving object) is recognized by image processing of the main body 103 including the video engine (S02), and a license plate is identified from the image (S03). It is determined from the license plate whether the vehicle is an abnormal vehicle such as a stolen vehicle, an unregistered vehicle, a fake vehicle, or a wanted vehicle (S04, S05).

  As a result of querying the data in S04, if the vehicle is not an abnormal vehicle, the mask can be maintained by maintaining the angle of the polarizing filter in which the reflected light component increases from the viewpoint of privacy protection. On the other hand, in the case of an abnormal vehicle, the mask can be released by rotating the polarizing filter and changing the angle of the polarizing filter to reduce the reflected light component (S06). By changing the angle of the polarizing filter in this way, the presence or absence of the mask can be made variable.

  Here, the license plate is used to determine the abnormal vehicle, but the determination may be made based on the type of the vehicle or the characteristics of the vehicle body. The abnormal car refers to a stolen car, a wanted car, or a violating car.

  Although a rotation mechanism has been described as a mechanism for changing the opening angle of the polarizing filter, the present invention is not limited to this. For example, a polarizing filter having another opening direction may be replaced.

(Third embodiment)
In the second embodiment, the angle of the polarization filter is changed by providing the rotation mechanism to the polarization filter. However, if a dedicated rotation mechanism is provided only for rotating the polarizing filter, the cost and size will increase accordingly. Therefore, in a third embodiment, a method of changing the polarization angle without providing a dedicated rotation mechanism will be described with reference to FIG.

  6, an explanation will be given using an image sensor 105 instead of the polarization filter 101 in FIG. Unlike the polarizing filter 101, the polarizing element 105 is disposed after the lens 102. The polarizing element 105 has different aperture axes in the same polarizing element. The imaging device 100 has a drive mechanism 106 for changing and adjusting the imaging direction of the imaging device 100. Therefore, as shown in FIG. 6, the opening angle of the polarizing filter differs depending on the position of the screen of the imaging device. In FIG. 6, the upper side of the screen is the opening in the vertical axis direction, and the lower side of the screen is the opening in the horizontal axis direction. Therefore, the images of FIG. 6A in which the vehicle is captured on the upper side of the screen and FIG. 6B in which the vehicle is captured on the lower side of the screen are as shown in FIGS. 7A and 7B, respectively.

  In FIG. 7A, since the vibration direction of the reflected light is parallel to the axis of the opening of the polarizing element, the reflected light component increases. Conversely, in FIG. 7B, the direction of oscillation of the reflected light is perpendicular to the axis of the opening of the polarizing element, and therefore the reflected light component is reduced. Therefore, a mask can be created when captured on the upper side of the screen (FIGS. 7A and 107), and can be released when captured on the lower side of the screen (FIGS. 7B and 108). By using the driving mechanism of the surveillance camera in this way, the mask can be switched by changing the angle at which polarized light is transmitted without having a driving mechanism dedicated to the polarizing filter.

(Fourth embodiment)
In the second embodiment, when the vehicle captured by the imaging device is an abnormal vehicle, the angle of the aperture axis of the polarizing filter is changed to remove the reflected light from the windshield. At this time, the effect of removing the reflected light is highest when the light incident on the windshield has a polarization angle.

  Therefore, if the angle of the polarizing filter is changed without considering the reflection removal rate, the reflection removal rate of the car that wants to maintain the surrounding masks despite the low reflection removal rate of the car whose mask is to be released is low. The rate will be high. Therefore, as a picture, even when the mask is switched, the mask of the target abnormal vehicle is not released, and the mask of the surrounding vehicle is released. Thus, in a fourth embodiment, a description will be given of control for switching masks at appropriate timing.

  First, an outline of FIG. 8 will be described. FIG. 8 shows an example in which the imaging device 100 is installed beside a road 202. The car moves from point A to point B in the figure. Further, the image pickup apparatus stores the points A and B within the same angle of view. The incident angle of the car 203 at the point A with respect to the windshield is 30 degrees, and the incident angle of the car 204 at the point B with respect to the windshield is 56 degrees (polarization angle).

  Next, with reference to FIG. 8 and FIG. 9, a description will be given of control for switching masks at an appropriate timing according to the fourth embodiment. However, a part overlapping with the description of the control sequence in FIG. 5 is omitted.

  The moving object is recognized at point A in FIG. 8 (S02 in FIG. 9). At this time, when the car 203 at the point A is an abnormal car, the control of the polarizing filter is performed to remove the reflected light. However, when the target vehicle is at point A, the polarization angle is not the same and the polarization elimination rate is low, and the mask is not sufficiently released. However, since the wheel 204 at the point B has a polarization angle, the polarization removal rate is high and the mask is released.

  Therefore, the switching of the mask in S09 in FIG. 9 is switched at the timing when the abnormal vehicle is located immediately before the point B, and it is necessary to take an image with the mask released at the point B. By controlling the switching timing in this manner, the mask of the abnormal vehicle can be removed most effectively, and the release of the mask of the vehicles other than the abnormal vehicle can be suppressed.

  It is preferable to determine the position of point B from the actual image at the time of installation, from which the angle of polarization is determined. Further, it is preferable that the switching control of the polarizing filter is completed before the target reaches the point B, but the same effect can be expected even if the switching is performed before and after the point B.

  The timing of re-creating the mask may be arbitrarily determined. For example, it may be calculated from the image as if it were shifted by 10 degrees from the polarization angle, or may be determined by a time such as 2 seconds after the release.

  The above is the description of the preferred embodiment of the present invention. However, the present invention is not limited to the above-described embodiment within the scope of the technical idea of the present invention. It is something to do. For example, the camera described as the imaging device in the above-described embodiment can be applied to a digital still camera or a digital video camera.

  Further, the present invention can be embodied as, for example, a system, an apparatus, a method, a computer program, a recording medium, or the like. More specifically, the present invention is applicable to a system including a plurality of apparatuses even if realized by one apparatus. May be. Each unit of the imaging apparatus according to the present embodiment and each step of the control method of the imaging apparatus can be realized by operation of a program stored in a memory of a computer or the like. The computer program and a computer-readable recording medium on which the program is recorded are included in the present invention.

  The present invention supplies a program for realizing one or more functions of the above-described embodiments to a system or an apparatus via a network or a storage medium, and one or more processors in a computer of the system or the apparatus read and execute the program. This processing can be realized. Further, it can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

100 imaging device, 101 polarizing filter, 102 lens, 103 body,
104 rotating mechanism, 105 polarizing element, 106 driving mechanism,
107 Image when creating mask, 108 Image when unmasking, 200 car,
201 windshield, 202 road, 203 A point car, 204 B point car,
300 incident light from outside, 301 reflected light from windshield, 302 polarized light,
303 natural light, 304 incident light, 305 reflected light, 306 refracted light,
401 substance A, 402 substance B, 403 interface

Claims (5)

Imaging means having an optical system with a polarizing filter;
A rotation mechanism for the polarizing filter,
Analysis means for analyzing the image acquired by the imaging means,
Control means for changing a polarization angle of the polarizing filter so that a predetermined subject is hard to be confirmed by reflected light according to an analysis result by the analysis means;
An imaging device comprising:   The imaging apparatus according to claim 1, wherein the control unit changes a polarization angle of the polarization filter so as to reduce the reflected light according to an analysis result by the analysis unit.   The imaging device according to claim 1, wherein the polarization filter includes a plurality of polarization elements having different polarizations.   The imaging apparatus according to claim 3, wherein the control unit corrects the polarization angle according to a polarization direction of the polarization element when changing a polarization angle of the polarization filter.   5. The imaging device according to claim 1, wherein the control unit switches the polarization direction at a location where the reflection elimination ratio of the polarization filter is high. 6.