Patent Publication Number: US-11656534-B2

Title: Imaging apparatus and monitoring system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/519,265, filed on Jul. 23, 2019, which claims the benefit of and priority to Japanese Patent Application No. 2018-142871, filed on Jul. 30, 2018, each of which is hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an imaging apparatus having an illuminator. 
     Description of the Related Art 
     For example, Japanese Patent Laid-Open No. (“JP”) 11-281879 discloses an imaging apparatus that can provide so-called tilt imaging that inclines an optical axis of a camera lens to an image sensor, when an object plane inclines to a principal plane of the lens o as to maintain deep a depth of field even if the camera lens uses a telephoto lens with a bright F-number. For example, JP 2013-41282 discloses a network camera including an illuminator, such as an infrared LED, in order to obtain a clear object image even at a low illuminance at night or the like. 
     However, the following problem occurs when the illuminator disclosed in JP 2013-41282 is applied to the imaging apparatus that provides the tilt imaging as disclosed in JP 11-281879 in order to improve the visibility at the low illuminance. In general, in the tilt imaging, the object plane inclines to the principal plane of the camera lens. In other words, the distance from the imaging apparatus to the object differs within an angle of view of the image sensor. Thus, as in the network camera disclosed in JP 2013-41282, when the optical axis of the lens and the optical axis of the illuminator coincide with each other, the object has an uneven luminance distribution within an angle of view and the captured image quality is degraded. In particular, a large uneven luminance distribution is likely to cause clipped whites and crashed shadows in the captured image. 
     SUMMARY OF THE INVENTION 
     The present invention provides an imaging apparatus and a monitoring system, each of which can improve the captured image quality by reducing an uneven luminance distribution of an object in tilt imaging using an illuminator. 
     An imaging apparatus according to one aspect of the present invention includes an image sensor, an angle controller configured to change an angle between a plane orthogonal to an optical axis of an imaging optical system and an imaging plane of the image sensor, an illuminator; and an illumination controller configured to change an optical axis direction of the illuminator based on the angle. A monitoring system including the above imaging apparatus also constitutes another aspect of the present invention. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an imaging apparatus according to a first embodiment. 
         FIG.  2    is an explanatory view of a focus plane in tilt imaging according to the first embodiment. 
         FIGS.  3 A and  3 B  are illumination distribution views of an object plane. 
         FIG.  4    illuminates a relationship between an image sensor and an illumination element in tilt imaging according to the first embodiment. 
         FIG.  5    is an illuminance distribution diagram of the object plane according to the first embodiment. 
         FIG.  6    is an illuminance distribution diagram of the object plane when a second angle in the first embodiment is changed. 
         FIGS.  7 A and  7 B  are explanatory diagrams of the object plane according to the first embodiment. 
         FIG.  8    is a block diagram of an imaging apparatus according to a second embodiment. 
         FIGS.  9 A and  9 B  are illumination distribution diagrams of the object plane according to the second embodiment. 
         FIGS.  10 A and  10 B  are a block diagram of an imaging apparatus according to a third embodiment and illustrate a relationship between an image sensor and an illumination element in tilt imaging. 
         FIGS.  11 A and  11 B  are a light intensity distribution and an illuminance distribution diagram for each ratio of the current flowing in the plurality of illumination elements according to the third embodiment. 
         FIG.  12    is a variation of the imaging apparatus according to the third embodiment. 
         FIG.  13    is a block diagram of a monitoring system according to a fourth embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the accompanying drawings, a description will be given of embodiments according to the present invention. In respective figures, corresponding elements will be designated by the same reference numerals, and a duplicate description thereof will be omitted. 
     First Embodiment 
     Referring now to  FIG.  1   , a description will be given of an imaging apparatus according to a first embodiment of the present invention.  FIG.  1    is a block diagram of an imaging apparatus  100  according to this embodiment. The imaging apparatus  100  includes an imaging optical system (image capturing optical system)  101 , an illumination element (illuminator)  102 , an illumination direction control mechanism (illumination controller)  103 , an image sensor (solid-state image pickup element)  104 , and a tilt mechanism (angle controller)  105 , and a controller  106 . The controller  106  controls each component in the image apparatus  100 . The imaging optical system  101  may be of a removable interchangeable lens type. 
     The image sensor  104  is a CMOS sensor or a CCD sensor, and photoelectrically converts an object image (optical image) formed through the imaging optical system  101 . The illumination element  102  emits light having a wavelength to which the image sensor  104  is sensitive. For example, when the image sensor  104  is made of silicon (Si), the illumination element  102  may use an LED made of a compound semiconductor, such as AlGaAs and InGaN. The controller  106  controls turning on and off of the illumination element  102  and the light intensity emitted from the illumination element  102 . The illumination direction control mechanism  103  controls the orientation of the illumination element  102  by rotating the illumination element  102 . The illumination direction control mechanism  103  includes a motor and a gear. The controller  106  can rotate the illumination element  102  on the XZ plane by controlling the current flowing through the motor of the illumination direction control mechanism  103 . The tilt mechanism  105  can rotate the orientation of the image sensor  104  in the XZ plane. 
     Referring now to  FIG.  2   , a focus plane  107  in the tilt imaging will be described.  FIG.  2    is an explanatory view of the focus plane  107  in the tilt imaging. According to the shine proofing principle, the light incident surface (imaging plane) of the image sensor  104 , the principal plane  108  (surface orthogonal to the optical axis  109 ) of the imaging optical system  101 , and the focus plane  107  intersects with a straight line L that extends in the Y axis direction. Thus, the focus plane  107  inclines to the principal plane  108  of the imaging optical system  101  in the XZ plane. In  FIG.  2   , reference numeral  109  denotes an optical axis of the imaging optical system  101 . 
     Next, assume that the optical axis  110  of the illumination element  102  accords with the optical axis  109  of the imaging optical system  101  in the imaging apparatus  100  in which the focus plane  107  inclines to the principal plane  108  of the imaging optical system  101 , as disclosed in the prior art, such as JP 2013-41282.  FIG.  3 A  is an illuminance distribution diagram of the focus plane  107  (object plane) when the optical axis  110  of the illumination element  102  coincides with the optical axis  109  of the imaging optical system  101  in tilt imaging. In  FIG.  3 A , the abscissa axis denotes the image height, and the ordinate axis denotes the illuminance (illuminance relative value). As illustrated in  FIG.  3 A , the illuminance largely differs according to the image heights, and a large uneven illuminance occurs at the angle of view. This is because the distance between the illumination element  102  and the focus plane  107  is largely different within the angle of view of the imaging apparatus  100  in tilt imaging. Since the illuminance is high at a position where the distance between the illumination element  102  and the focus plane  107  is close (in an area  107 A in  FIG.  2   ), and low at the position where the distance between the illumination element  102  and the focus plane  107  is long ( FIG.  2   ) (in an area  107 B), an uneven illuminance occurs. As a result, the uneven illuminance of the image occurs and the visibility reduces. 
       FIG.  3 B  is, as a comparative example, an illuminance distribution diagram where the tilt imaging is not performed. As illustrated in  FIG.  3 B , the same uneven illuminance occurs even when the tilt imaging is not performed. However, where the tilt imaging is not performed, an in-focus range R is narrow in which the object is in focus. Thus, the uneven illuminance is small within the in-focus range. In other words, where the tilt imaging is not performed, the visibility reduces due to the uneven illuminance only in the area where the object image is blurred because the object is not in focus. 
     In general, for an imaging apparatus for an observation, it is a big issue whether the blur degree is beautiful or not even in the area where the object image is blurred. Thus, the visibility decrease caused by the uneven illuminance becomes an issue. However, in the imaging apparatus for a recognition such as monitoring purposes, the result that the object is too blurred to be recognized does not change in an area where the object image is blurred, regardless of the uneven illuminance. Thus, in the area where the object image is blurred, the problematically reduced visibility caused by the uneven illuminance does not frequently occur. Hence, the problematically reduced visibility of the object image caused by the uneven illuminance does not frequently occur when the imaging apparatus for the recognition does not perform the tilt imaging. The present invention suppresses the problematically reduced visibility of the object image in the imaging apparatus for the recognition due to the uneven illuminance in the tilt imaging. Hereinafter, this embodiment will be specifically described. 
     Referring now to  FIG.  4   , a description will be given of a relationship between the image sensor  104  and the illumination element  102  in the tilt imaging using the imaging apparatus  100 .  FIG.  4    illustrates a relationship between the image sensor  104  and the illumination element  102  in the tilt imaging, or a relationship among the light incident surface (imaging plane) of the image sensor  104 , the principal plane  108  of the imaging optical system  101 , the focus plane  107 , and the optical axis  110  of the illumination element  102 . The direction of the optical axis  110  of the illumination element  102  is the center of gravity direction of the light intensity distribution emitted from the illumination element  102 . 
     As illustrated in  FIG.  4   , the light incident surface of the image sensor  104  rotates counterclockwise with the Y axis as the rotation center and based on the principal plane  108  of the imaging optical system  101 . The imaging apparatus  100  according to this embodiment sets the optical axis  110  of the illumination element  102  to the rotation center which is the Y axis and rotates it counterclockwise based on the optical axis  109  of the imaging optical system  101  as the light incident surface of the image sensor  104  rotates. Now assume that an angle (tilt angle)  01  formed between the principal plane  108  of the imaging optical system  101  and the light incident surface of the image sensor  104  is a first angle  111 . In addition, assume that an angle θ 2  formed between the optical axis  110  of the illumination element  102  and the optical axis  109  of the imaging optical system  101  is a second angle  112 . At this time, a code of the first angle  111  (the rotation direction of the light incident surface of the image sensor  104  based on the principal plane  108  of the imaging optical system  101 ) and a code of the second angle  112  (the rotation direction of the optical axis  110  of the illumination element  102  based on the optical axis  109  of the imaging optical system  101 ) coincide with each other. In other words, the rotation direction of the first angle  111  (counterclockwise direction in  FIG.  4   ) and the rotation direction of the second angle  112  (counterclockwise direction) coincide with each other. Hence, the uneven illuminance can be reduced by changing (rotating) the direction of the optical axis  110  of the illumination element  102  in accordance with the tilt direction of the image sensor  104 . 
     Referring now to  FIG.  5   , a description will be given of the illuminance distribution of each of the focus plane  107  (object plane) when the optical axis  110  of the illumination element  102  is rotated relative to the optical axis  109  of the imaging optical system  101  and when the optical axis  110  of the illumination element  102  is not rotated.  FIG.  5    is an illuminance distribution diagram of the focus plane  107  (object plane) when the optical axis  110  of the illumination element  102  is rotated relative to the optical axis  109  of the imaging optical system  101  and when the optical axis  110  is not rotated. In  FIG.  5   , the abscissa axis represents the image height, and the ordinate axis represents the illuminance (logarithm). In  FIG.  5   , a solid line represents the illuminance distribution when the optical axis  110  of the illumination element  102  is rotated as in this embodiment, and a broken line represents the illuminance distribution when the light axis  110  of the illumination element  102  is not rotated as in a comparative example. As illustrated in  FIG.  5   , the solid line changes more gently than the broken line. Hence, the uneven illuminance can be reduced by rotating the optical axis  110  of the illumination element  102  relative to the optical axis  109  of the imaging optical system  101 . The reason will be described below. 
     As described above, the uneven illuminance in the tilt imaging is caused by the distance between the illumination element  102  and the focus plane  107  that is largely different within the angle of view of the imaging apparatus  100 . Thus, the uneven illuminance when the strong light is irradiated onto the position (area  107 B in  FIG.  4   ) in which the distance between the illumination element  102  and the focus plane  107  is long is lower than that when the strong light is irradiated onto the position (area  107 A in  FIG.  4   ) in which the distance between the illumination element  102  and the focus plane  107  is short. In general, the illumination element  102  reflects the structure of the LED and has an orientation distribution having a strong directivity in the direction (optical axis direction) perpendicular to the surface of the LED. Hence, the uneven illuminance can be reduced by inclining the optical axis  110  of the illumination element  102  in the direction in which the distance between the illumination element  102  and the focus plane  107  is long. As a result, the captured image quality can be improved, and the recognition accuracy of the object can be improved. 
     The second angle  112  formed between the optical axis  109  of the imaging optical system  101  and the optical axis  110  of the illumination element  102  may be determined according to the first angle  111  formed between the principal plane  108  of the imaging optical system  101  and the light incident surface (imaging plane) of the image sensor  104  so as to sufficiently reduce the uneven illuminance. The second angle  112  is determined according to the first angle  111  so as to most reduce the uneven illuminance. 
     Referring now to  FIG.  6   , a description will be given of the illuminance distribution of the focus plane  107  when the second angle  112  is changed.  FIG.  6    is an illuminance distribution diagram of the focus plane  107  when the second angle  112  is changed. In  FIG.  6   , the abscissa axis represents the image height, and the ordinate axis represents the illuminance (logarithm). In  FIG.  6   , a broken line represents that the absolute value of the second angle  112  is small, a dotted line represents that an absolute value of the second angle  112  is large, and a solid line represents that an absolute value of the second angle  112  is intermediate between them. As illustrated in  FIG.  6   , as the absolute value of the second angle  112  is made larger, the uneven illuminance becomes lower. In particular, when the absolute value of the second angle  112  is made equal to or more than a half of the angle of view of the imaging apparatus  100 , the uneven illuminance can be sufficiently reduced. 
     On the other hand, as illustrated by the dotted line in  FIG.  6   , as the absolute value of the second angle  112  is made excessively large, the uneven illuminance decreases, but the average illuminance within the angle of view of the imaging apparatus  100  decreases. This is because if the absolute value of the second angle  112  is made excessively large, a light amount emitted from the illumination element  102  to the outside of the angle of view of the imaging apparatus  100  increases. In particular, when the absolute value of the second angle  112  is made equal to or less than the angle of view of the imaging apparatus  100 , a light amount emitted to the outside the angle of view of the imaging apparatus  100  is reduced. 
     The tilt imaging needs to control the first angle  111  in accordance with the angle between the object plane (focus plane  107 ) and the principal plane  108  of the imaging optical system  101 .  FIGS.  7 A and  7 B  are explanatory diagrams of the object plane (focus plane  107 ).  FIGS.  7 A and  7 B  illustrate the relationship among the focus plane  107 , the principal plane  108 , and the light incident surface (imaging plane) of the image sensor  104  for the small absolute value of the first angle  111  and for the large absolute value of the first angle  111 , respectively. 
     As illustrated in  FIGS.  7 A and  7 B , as the absolute value of the first angle  111  is larger, the distance between the illumination element  102  and the focal plane  107  is largely different within the angle of view of the imaging apparatus  100 . When the absolute value of the first angle  111  is small, the uneven illuminance within the angle of view does not become a big issue. When the absolute value of the first angle  111  is small (when the first angle  111  is smaller than a predetermined angle), the optical axis  110  of the illumination element  102  may not be tilted as illustrated in  FIG.  7 A . For example, if the absolute value of the first angle  111  is less than one degree, then the absolute value of the second angle  112  may be set to zero. In other words, when the first angle  111  is one degree or more, the orientation of the illumination element  102  may be changed so that the optical axis  110  of the illumination element  102  is different from the optical axis  109  of the imaging optical system  101  as in this embodiment. 
     This embodiment may continuously change the second angle  112  in accordance with the first angle  111 . More specifically, the absolute value of the second angle  112  is made larger as the absolute value of the first angle  111  is larger. This can effectively reduce the uneven illuminance. 
     Second Embodiment 
     Referring now to  FIG.  8   , a description will be given of an imaging apparatus according to a second embodiment of the present invention.  FIG.  8    is a block diagram of an imaging apparatus  200  according to this embodiment. The image sensor  200  according to this embodiment is different from the imaging apparatus  100  of the first embodiment described with reference to  FIG.  1    in that it includes an illumination range control mechanism  213  that changes the illumination range (irradiation angle range) of the illumination element  102 . The illumination range control mechanism  213  changes the illumination range of the illumination element  102  according to the first angle  111 . This configuration can more effectively reduce the uneven illuminance on the focus plane  107  (object plane). 
     Referring now to  FIGS.  9 A and  9 B , a description will be given of the illuminance distribution on the focus plane  107  (object plane) when the illumination range of the illumination element  102  is changed and when the illumination range is not changed.  FIGS.  9 A and  9 B  are illuminance distribution diagrams of the focus plane  107  when the illumination range of the illumination element  102  is changed and when the illumination range is not changed. In  FIGS.  9 A and  9 B , the abscissa axis represents the image height, and the ordinate axis represents the illuminance (logarithm).  FIG.  9 A  illuminates the small absolute value of the first angle  111  because the angle between the object plane and the principal plane  108  of the imaging optical system  101  is made small. On the other hand,  FIG.  9 B  illustrates the large absolute value of the first angle  111  because the angle between the object plane and the principal plane  108  of the imaging optical system  101  is made large. 
     In  FIGS.  9 A and  9 B , a solid line represents the illumination range of the illumination element  102  is changed according to the first angle  111 . In  FIGS.  9 A and  9 B , a broken line and a dotted line show use of the illumination element  102  used to illuminate in a constant illumination range regardless of the first angle  111  as in the imaging apparatus  100  of the first embodiment. A broken line represents the illumination range of the illumination element  102  as a first illumination range, and a dotted line indicates the illumination range of the illumination element  102  as a second illumination range. In  FIG.  9 A , the solid line and the broken line overlap each other, and in  FIG.  9 B , the solid line and the dotted line overlap each other. 
     As illustrated in  FIGS.  9 A and  9 B , where the illumination range is not changed (fixed) according to the first angle  111 , an attempt to reduce the uneven illuminance when the absolute value of the first angle  111  is small may increase the uneven illumination when the absolute value of the first angle  111  is large (broken line). On the other hand, an attempt to reduce the uneven illuminance when the absolute value of the first angle  111  is large increase the uneven illuminance when the absolute value of the first angle  111  is small (dotted line). 
     On the other hand, when the illumination range is changed according to the first angle  111 , the uneven illuminance can be reduced regardless of the absolute value of the first angle  111  (solid line). More specifically, as the absolute value of the first angle  111  is larger, the illumination range of the illumination element  102  may be narrowed. In this embodiment, the illumination range means the full width at half maximum of the light intensity distribution emitted from the illumination element  102 . 
     In order to control the illumination range of the illumination element  102 , an illumination optical system may be provided on the light emission side of the illumination element  102 , and part of the lenses of the illumination optical system may be driven in the optical axis direction of the illumination optical system. Thereby, the focal length of the illumination optical system changes, and the illumination range can be controlled. In order to drive the lens, a motor and a gear may be used to control the current flowing through the motor. 
     Third Embodiment 
     Referring now to  FIGS.  10 A and  10 B , a description will be given of an imaging apparatus according to a third embodiment of the present invention.  FIG.  10 A  is a block diagram of an imaging apparatus  300  according to this embodiment, and  FIG.  10 B  illustrates a relationship between the image sensor  104  and the illumination element  102  in tilt imaging. 
     Each of the imaging apparatuses  100  and  200  according to the above embodiments includes a single illumination element  102 , and rotates the illumination element  102  itself to control the illumination direction, or drives a lens as part of the illumination optical system to control the illumination range. On the other hand, the imaging apparatus  300  according to this embodiment includes a plurality of illumination elements  321  and  322  (first and second illumination elements) both having different illumination directions and illumination ranges. This configuration enables the imaging apparatus  300  to control the effective illumination direction and the illumination range of the plurality of illumination elements as a whole by controlling the current supplied to each of the plurality of illumination elements  321  and  322 . This configuration eliminates a rotation mechanism of the illumination element  102  and a lens drive mechanism of the illumination optical system. 
     As illustrated in  FIGS.  10 A and  10 B , the imaging apparatus  300  includes a plurality of illumination elements  321  and  322  both having different illumination directions. The controller  106  can control the current supplied to each of the plurality of illumination elements  321  and  322 . The direction of the optical axis  331  of the illumination element  321  coincides with the direction of the optical axis  109  of the imaging optical system  101 . On the other hand, the optical axis  332  of the illumination element  322  inclines counterclockwise to the optical axis  109  of the imaging optical system  101 . 
     Referring to  FIGS.  11 A and  11 B , a description will be given of a relationship between a ratio of the current flowing through the illumination element  321  and the current flowing through the illumination element  322  of the imaging apparatus  300  and a total distribution of the light intensities irradiated from the illumination elements  321  and  322 .  FIG.  11 A  is a distribution diagram (light intensity distribution diagram) of the total light intensities emitted from the illumination elements  321  and  322  for each ratio of the currents flowing through the plurality of illumination elements  321  and  322  of the imaging apparatus  300 . In  FIG.  11 A , the abscissa axis represents the image height, and the ordinate axis represents the light intensity distribution (logarithm).  FIG.  11 B  is an illuminance distribution diagram of the focus plane  107  (object plane) for each current ratio illustrated in  FIG.  11 A . In  FIG.  11 B , the abscissa axis represents the image height, and the ordinate axis represents the illuminance distribution (logarithm). 
     A dotted line, a broken line, an alternate long and short dash line, and a solid line in  FIGS.  11 A and  11 B  represent the ratios of the currents supplied to the illumination elements  321  and  322  are 0:1 (322/321=0), 5:1 (322/321=0.2), 2:1 (322/321=0.5), and 1:1 (322/321=1). In other words, the ratio of the current flowing through the illumination element  322  to the current flowing through the illumination element  321  is increased in order of the dotted line, the broken line, the alternate long and short dash line, and the solid line. 
     As illustrated in  FIG.  11 B , when the ratio of the current supplied to the illumination element  322  to the current supplied to the illumination element  321  is made larger, the uneven illuminance on the focus plane  107  is reduced. Thus, controlling the currents flowing through the plurality of illumination elements  321  and  322  having different directions can reduce the uneven illuminance on the focus plane  107 . As a result, the captured image quality can be improved. 
     As illustrated in  FIG.  11 A , when the ratio of the current flowing through the illumination element  322  to the current flowing through the illumination element  321  is made larger, the center of gravity (direction of the illuminator) of the light intensity distribution of the illumination elements  321  and  322  tilts counterclockwise. Thus, in even the configuration of the imaging apparatus  300  illustrated in  FIGS.  9 A and  9 B , the code of the first angle  111  (rotation direction of the light incident surface of the image sensor  104 ) and the code of the second angle  112  (the rotation direction  110  of the optical axis  110  of the illumination element  102 ) coincide with each other. 
     Referring now to  FIG.  12   , a description will be given of a variation of this embodiment.  FIG.  12    is an explanatory diagram of an imaging apparatus including a plurality of illumination elements  323  and  324  having different illumination ranges in addition to the illumination elements  321  and  322  having different orientations. The orientations of the illumination elements  323  and  321  coincide with each other and the orientations of the illumination elements  324  and  322  coincide with each other. In addition, the illumination ranges of the illumination elements  323  and  324  are narrower than the illumination ranges of the illumination elements  321  and  322 . 
     The configuration illustrated in  FIG.  12    can control the effective illumination range of the illumination element in addition to the effective orientation of the illumination element. More specifically, when the tilt imaging is not performed, the current flowing through the illumination element  321  is increased to widen the illumination range while the absolute value of the second angle  112  is reduced. On the other hand, when the absolute value of the first angle  111  is large, the current flowing through the illumination element  324  is increased to narrow the illumination range while the absolute value of the second angle  112  is maintained large. This configuration can reduce the uneven illuminance on the focus plane  107  regardless of the first angle  111 . 
     As described above, this embodiment may narrow the illumination range of the illumination element, as the absolute value of the second angle  112  is larger. Thus, as the angle between the optical axis of the illumination element and the optical axis  109  of the imaging optical system  101  is larger, the number of required illumination elements decreases by arranging the plurality of illumination elements whose illumination range is narrow. More specifically, in  FIG.  12   , the illumination elements  322  and  323  may be removed, and only the illumination elements  321  and  324  may be left. 
     Fourth Embodiment 
     Referring now to  FIG.  13   , a description will be given of a monitoring system according to a fourth embodiment of the present invention.  FIG.  13    is a block diagram of a monitoring system  400  according to this embodiment. The monitoring system  400  includes a client device  401  and an imaging apparatus  403 . The imaging apparatus  403  corresponds to any one of the imaging apparatuses  100  to  300  according to the first to third embodiments described above. 
     The client device  401  and the imaging apparatus  403  are connected in a mutually communicable state via a network  402 . The client device  401  transmits a variety of commands to the imaging apparatus  403  so as to control the imaging apparatus  403 . The imaging apparatus  403  receives a command from the client device  401 , and transmits a response according to the command and captured image data to the client device  401 . The user can select, via the client device  401 , whether to drive the imaging apparatus  403  in a desired mode such as a depth of field priority mode. The client device  401  is an external apparatus such as a PC. The network  402  includes a wired LAN or a wireless LAN. This embodiment may supply the power to the imaging apparatus  403  via the network  402 . 
     Hence, in each embodiment, the imaging apparatus includes the angle controller (tilt mechanism  105 ) and the illumination controller (illumination direction control mechanism  103 ). The angle controller changes an angle (tilt angle) formed between the principal plane  108  of the imaging optical system (imaging optical system  101 ) and the imaging plane (light incident surface) of the image sensor  104 . The illumination controller changes the optical axis direction (direction of the optical axis  110 ) of the illuminator based on the angle changed by the angle controller. 
     The illumination controller changes the optical axis direction (direction of the optical axis  110 ) of the illuminator so that it is different from the optical axis direction (direction of the optical axis  109 ) of the imaging optical system. The illumination controller changes the optical axis direction of the illuminator so that it is closer to the normal direction of the imaging plane of the image sensor. The illumination controller changes the light axis direction of the illuminator so that the illumination intensity for the second area (area  107 B) is higher than the illumination intensity for the first area (area  107 A) on the focal plane  107  determined based on the angle changed by the angle controller. Herein, the first area is an area in which the distance from the illuminator is a first distance, and the second area is an area in which the distance from the illuminator is a second distance longer than the first distance. The angle controller may change the angle by rotating the imaging plane of the image sensor relative to the principal plane of the imaging optical system. 
     The illumination controller may change the optical axis direction of the illuminator so that a code of the first angle  111  formed between the principal plane of the imaging optical system and the imaging plane of the image sensor and a code of the second angle  112  formed between the optical axis of the imaging optical system and the optical axis of the illuminator coincide with each other. The absolute value of the second angle may be half or more of the angle of view of the image sensor. The absolute value of the second angle may be equal to or less than the angle of view of the imaging apparatus. The absolute value of the first angle may be one degree or more. 
     When the absolute value of the first angle may be a first value, the illumination controller sets the absolute value of the second angle to a third value, and when the absolute value of the first angle is a second value larger than the first value, the illumination controller sets the absolute value of the second angle to a fourth value larger than the third value. In other words, the illumination controller makes larger the absolute value of the second angle as the absolute value of the first angle is larger. 
     The imaging apparatus may include an illumination range controller (illumination range control mechanism  213 ) that changes the illumination range of the illuminator. When the absolute value of the first angle is a first value, the illumination range controller sets the illumination range to the first illumination range, and when the absolute value of the first angle is a second value larger than the first value, the illumination range controller sets the illumination range to a second illumination range narrower than the first illumination range. In other words, the illumination range controller makes narrower the illumination range as the absolute value of the first angle is larger. The illuminator may include a first illumination element (illumination element  321 ) and a second illumination element (illumination element  322 ) both having different illumination ranges. The illumination controller controls the illumination range (effective illumination range) of the illuminator based on the ratio between the current flowing through the first illumination element and the current flowing through the second illumination element. The angle formed between the optical axis of the first illumination element and the optical axis of the imaging optical system is larger than the angle formed between the optical axis of the second illumination element and the optical axis of the imaging optical system. The illumination range of the first illumination element is narrower than the illumination range of the second illumination element. In other words, the illumination range of the illumination element is made narrower as the angle is larger between the optical axis of the illumination element and the optical axis of the imaging optical system. 
     The illumination controller changes the optical axis direction of the illuminator by controlling the orientation of the illuminator. The angle formed between the optical axis of the first illumination element and the optical axis of the imaging optical system may be different from the angle formed between the optical axis of the second illumination element and the optical axis of the imaging optical system. The illumination controller changes the optical axis direction (effective optical axis direction) of the illuminator by controlling the ratio between the current flowing through the first illumination element and the current flowing through the second illumination element. 
     Each embodiment can provide an imaging apparatus and a monitoring system, each of which can improve the captured image quality by reducing the uneven luminance distribution of the object in the tilt imaging using the illuminator. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2018-142871, filed on Jul. 30, 2018, which is hereby incorporated by reference herein in its entirety.