Patent Publication Number: US-2023156178-A1

Title: Detection device and image display module

Description:
TECHNICAL FIELD 
     The present disclosure relates to a detection device and an image display module. 
     BACKGROUND OF INVENTION 
     A known technique is described in, for example, Patent Literature 1. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2001-166259 
     SUMMARY 
     In one embodiment of the present disclosure, a detection device includes a camera and a detector. The camera captures an image of a human face. The detector detects a position of a human eye based on the captured image output from the camera by template matching. 
     In one embodiment of the present disclosure, an image display system includes a display, a barrier, a camera, a detector, and a controller. The display displays a parallax image to be projected to two human eyes through an optical system. The barrier defines a traveling direction of image light for the parallax image to generate parallax between the two human eyes. The camera captures an image of a human face. The detector detects positions of the two human eyes based on the captured image output from the camera by template matching. The controller controls the display based on the positions of the two human eyes detected by the detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, and advantages of the present disclosure will become more apparent from the following detailed description and the drawings. 
         FIG.  1    is a schematic diagram of an example movable body incorporating a detection device. 
         FIG.  2    is a schematic diagram describing template matching. 
         FIG.  3    is a schematic diagram of an example three-dimensional (3D) projection system. 
         FIG.  4    is a schematic diagram describing the relationship between the eyes of a driver, a display, and a barrier. 
         FIG.  5    is a flowchart of an example template image generation process performed by the detection device. 
         FIG.  6    is a flowchart of an example template matching process performed by the detection device. 
         FIG.  7    is a flowchart of another example template matching process performed by the detection device. 
         FIG.  8    is a schematic diagram of another example 3D projection system. 
         FIG.  9    is a flowchart of another example template matching process performed by the detection device. 
         FIG.  10    is a flowchart of another example template matching process performed by the detection device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The structure that forms the basis of the present disclosure obtains, when detecting the positions of the eyes of a user, positional data indicating the positions of the pupils using an image of the eyes of the user captured with a camera. For example, a three-dimensional (3D) display device displays an image on a display to allow the left and right eyes of the user to view the corresponding images based on the positions of the pupils indicated by the positional data (e.g., Patent Literature 1). 
     An embodiment of the present disclosure will now be described in detail with reference to the drawings. The drawings used herein are schematic and are not drawn to scale relative to the actual size of each component. 
     As illustrated in  FIG.  1   , a detection device  50  according to one embodiment of the present disclosure may be mounted on a movable body  10 . The detection device  50  includes a camera  11  and a detector  15 . The movable body  10  may include a 3D projection system  100 . The 3D projection system  100  includes the detection device  50  and a 3D projector  12 . 
     Examples of the movable body in one or more embodiments of the present disclosure may include a vehicle, a vessel, and an aircraft. Examples of the vehicle may include an automobile, an industrial vehicle, a railroad vehicle, a community vehicle, and a fixed-wing aircraft traveling on a runway. Examples of the automobile may include a passenger vehicle, a truck, a bus, a motorcycle, and a trolley bus. Examples of the industrial vehicle may include an industrial vehicle for agriculture and an industrial vehicle for construction. Examples of the industrial vehicle may include a forklift and a golf cart. Examples of the industrial vehicle for agriculture may include a tractor, a cultivator, a transplanter, a binder, a combine, and a lawn mower. Examples of the industrial vehicle for construction may include a bulldozer, a scraper, a power shovel, a crane vehicle, a dump truck, and a road roller. Examples of the vehicle may include man-powered vehicles. The classification of the vehicle is not limited to the above examples. Examples of the automobile may include an industrial vehicle travelling on a road. One type of vehicle may fall within multiple classes. Examples of the vessel may include a jet ski, a boat, and a tanker. Examples of the aircraft may include a fixed-wing aircraft and a rotary-wing aircraft. 
     In the example described below, the movable body  10  is a passenger vehicle. The movable body  10  is not limited to a passenger vehicle, but may be any of the above examples. The camera  11  may be attached to the movable body  10 . The camera  11  captures an image of a driver  13  of the movable body  10 . The image of the driver  13  includes a face (human face). The camera  11  may be attached at any position inside or outside the movable body  10 . For example, the camera  11  may be on a dashboard in the movable body  10 . 
     The camera  11  may be a visible light camera or an infrared camera. The camera  11  may function both as a visible light camera and an infrared camera The camera  11  may include, for example, a charge-coupled device (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor. 
     An image captured with the camera  11  is output to the detector  15 . The detector  15  uses template matching to detect the position of an eye  5  of the driver  13  based on the captured image output from the camera  11 . The camera  11  may output an image to the detector  15  for every frame. The detector  15  may detect the position of the eye  5  through template matching for every frame. The position of the eye  5  of the driver  13  may be the position of the pupil. Template matching is image processing of searching a target image for a position with the highest degree of matching with a template image. The detection device  50  according to an embodiment of the present disclosure uses a captured image  51  output from the camera  11  as a target image. A template image  52  includes the eye  5  of the driver  13  or a part of the face determined to have a relative positional relationship with the eye  5  of the driver  13 . The template image  52  may include, as the eye  5  of the driver  13 , the two eyes, the right eye alone, or the left eye alone. The facial part determined to have a relative positional relationship with the eye(s)  5  of the driver  13  may be, for example, the eyebrows or the nose. In the example of  FIG.  2   , the template image  52  includes the two eyes as the eye(s)  5  of the driver  13 . 
     The structure that forms the basis of the present disclosure performs pupil position detection based on a captured image using the captured image including the pupils of the user. With a captured image that does not include pupils, the pupil positions cannot be detected. For example, the pupil positions cannot be detected based on an image of the user captured when the user&#39;s eyes are closed, such as when the user is blinking. The structure in an embodiment of the present disclosure uses template matching of searching the captured image  51  for a position with the highest degree of matching with the template image  52 , and thus can search the captured image  51  for any position with the highest degree of matching using features other than the pupils in the template image  52  when the captured image  51  does not include pupils. The template image  52  is larger than the pupils. Thus, template matching involves less computation than pupil detection when each performed using the captured image  51  with the same size as the detection target. With such less computation, the detector  15  can output a detection result from template matching at a higher computation speed than a result from pupil detection. 
     The template image  52  may be shaped in correspondence with the shape of the captured image  51 . For the captured image  51  being rectangular, the template image  52  may be rectangular. The shape of the template image  52  may be or may not be similar to the shape of the captured image  51 . In the example described below, the captured image  51  and the template image  52  are rectangular as illustrated in  FIG.  2   . 
     A detection result obtained by the detection device  50  may be coordinate information indicating the pupil positions of the eyes  5  (two eyes) of the driver  13 . The coordinates of the position in the captured image  51  with the highest degree of matching with the template image  52  are determined through template matching. The coordinates of the matching position resulting from template matching may, for example, correspond to the coordinates of a representative position in the template image  52 . The representative position in the template image  52  may be, for example, any one of the vertexes or the center of the template image  52 . The relative coordinate positional relationship between the coordinates of the pupil positions in the template image  52  and the representative position in the template image  52  may be predefined. For the coordinates of the matching position in the captured image  51  determined by template matching, the coordinates and the predefined relative positional relationship can be used to determine coordinate information about the pupil positions in the captured image  51 . For the driver  13  with the eyes  5  being closed and the pupils not included in the captured image  51 , for example, coordinate information about the pupil positions of the eyes  5  being open can be obtained through estimation. The detection device  50  according to an embodiment of the present disclosure can determine coordinate information about the pupil positions although the driver  13  has the eyes  5  closed by, for example, blinking, allowing successive output of coordinate information without interruption. 
     The detection device  50  may include, for example, a sensor. The sensor may be, for example, an ultrasonic sensor or an optical sensor. The camera  11  may detect the position of the head of the driver  13  with the sensor, and detect the positions of the eyes  5  of the driver  13  based on the position of the head. The camera  11  may detect the positions of the eyes  5  of the driver  13  as the coordinates in a 3D space using two or more sensors. 
     The detection device  50  may output coordinate information about the detected pupil positions of the eyes  5  to the 3D projector  12 . The 3D projector  12  may control an image to be projected based on the received coordinate information. The detection device  50  may output information indicating the pupil positions of the eyes  5  to the 3D projector  12  through wired or wireless communication. Wired communication may include, for example, communication using a controller area network (CAN). 
     The detection device  50  may include the detector  15  that is an external device. The camera  11  may output the captured image  51  to the external detector  15 . The external detector  15  may detect the pupil positions of the eyes  5  of the driver  13  by template matching based on the image output from the camera  11 . The external detector  15  may output the coordinate information about the detected pupil positions of the eyes  5  to the 3D projector  12 . The 3D projector  12  may control an image to be projected based on the received coordinate information. The camera  11  may output the captured image to the external detector  15  through wired or wireless communication. The external detector  15  may output the coordinate information to the 3D projector  12  through wired or wireless communication. Wired communication may include, for example, communication using a CAN. 
     The 3D projector  12  may be at any position inside or outside the movable body  10 . For example, the 3D projector  12  may be on the dashboard in the movable body  10 . The 3D projector  12  emits image light toward a windshield  25 . 
     The windshield  25  reflects the image light emitted from the 3D projector  12 . The image light reflected from the windshield  25  reaches an eye box  16 . The eye box  16  is an area in a real space expected to include the eyes  5  of the driver  13  based on, for example, the body shape, posture, and changes in the posture of the driver  13 . The eye box  16  may have any shape. The eye box  16  may include a planar or 3D area. The solid arrow in  FIG.  1    indicates the traveling path of at least a part of the image light emitted from the 3D projector  12  to reach the eye box  16 . The traveling path of the image light is also referred to as an optical path. When the eyes  5  of the driver  13  are located within the eye box  16 , the driver  13  can view a virtual image  14  with the image light reaching the eye box  16 . The virtual image  14  is located on an extension of the path from the windshield  25  to the eyes  5  (on a straight line drawn with a dot-dash line in the figure). The extension is directed frontward from the movable body  10 . The 3D projector  12  can function as ahead-up display that allows the driver  13  to view the virtual image  14 . In  FIG.  1   , the direction in which the eyes  5  of the driver  13  are aligned corresponds to x- direction. The vertical direction corresponds to y-direction. The imaging range of the camera  11  includes the eye box  16 . 
     As illustrated in  FIG.  3   , the 3D projector  12  includes a 3D display device  17  and an optical element  18 . The 3D projector  12  may also be referred to as an image display module. The 3D display device  17  may include a backlight  19 , a display  20  including a display surface  20   a,  a barrier  21 , and a controller  24 . The 3D display device  17  may further include a communicator  22 . The 3D display device  17  may further include a storage  23 . 
     The optical element  18  may include a first mirror  18   a  and a second mirror  18   b.  At least one of the first mirror  18   a  or the second mirror  18   b  may have optical power. In the present embodiment, the first mirror  18   a  is a concave mirror having optical power. The second mirror  18   b  is a plane mirror. The optical element  18  may function as a magnifying optical system that magnifies an image displayed by the 3D display device  17 . The arrowed dot-dash line in  FIG.  3    indicates the traveling path of at least a part of image light emitted from the 3D display device  17  to be reflected from the first mirror  18   a  and the second mirror  18   b  and then exit the 3D projector  12 . The image light exiting from the 3D projector  12  reaches the windshield  25 , is reflected from the windshield  25 , and then reaches the eyes  5  of the driver  13 . Thus, the driver  13  can view the image displayed by the 3D display device  17 . 
     The optical element  18  and the windshield  25  are designed to cause image light emitted from the 3D display device  17  to reach the eyes  5  of the driver  13 . The optical element  18  and the windshield  25  may be included in an optical system. The optical system allows the image light emitted from the 3D display device  17  to travel along the optical path indicated by the dot-dash line and reach the eyes  5  of the driver  13 . The optical system may control the traveling direction of image light to enlarge or reduce an image viewable to the driver  13 . The optical system may control the traveling direction of image light to change the shape of the image viewable by the driver  13  based on a predetermined matrix. 
     The optical element  18  may have a structure different from the illustrated structure. The optical element  18  may include a concave mirror, a convex mirror, or a plane mirror. The concave mirror or the convex mirror may be at least partially spherical or aspherical. The optical element  18  may be one element or may include three or more elements, instead of two elements. The optical element  18  may include a lens instead of or in addition to a mirror. The lens may be a concave lens or a convex lens. The lens may be at least partially spherical or aspherical. 
     The backlight  19  is more away on the optical path of image light viewed from the driver  13  than the display  20  and the barrier  21 . The backlight  19  emits light toward the barrier  21  and the display  20 . At least a part of the light emitted from the backlight  19  travels along the optical path indicated by the dot-dash line and reaches the eyes  5  of the driver  13 . The backlight  19  may include a light-emitting diode (LED) or a light emitter such as an organic electroluminescence (EL) element and an inorganic EL element The backlight  19  may have any structure that allows control of the light intensity and the light intensity distribution. 
     The display  20  includes a display panel. The display  20  may be, for example, a liquid-crystal device such as a liquid-crystal display (LCD). In the present embodiment, the display  20  includes a transmissive liquid-crystal display panel. The display  20  is not limited to this example and may be any of various display panels. 
     The display  20  includes multiple pixels and controls the transmittance of light from the backlight  19  incident on each pixel to emit image light reaching the eyes  5  of the driver  13 . The driver  13  views an image formed with the image light emitted from each pixel in the display  20 . 
     The barrier  21  defines the traveling direction of incident light. In the example of  FIG.  3   , with the barrier  21  being nearer the backlight  19  than the display  20 , the light emitted from the backlight  19  enters the barrier  21 , and further enters the display  20 . In this case, the barrier  21  blocks or attenuates a part of light emitted from the backlight  19  and transmits another of the light to the display  20 . The display  20  emits incident light traveling in a direction defined by the barrier  21  as image light traveling in the same direction. With the display  20  being nearer the backlight  19  than the barrier  21 , the light emitted from the backlight  19  enters the display  20 , and further enters the barrier  21 . In this case, the barrier  21  blocks or attenuates a part of image light emitted from the display  20  and transmits another part of the image light toward the eyes  5  of the driver  13 . 
     Irrespective of whether the display  20  or the barrier  21  is nearer the driver  13 , the barrier  21  controls the traveling direction of image light. The barrier  21  allows a part of image light emitted from the display  20  to reach either the left eye  5 L or the right eye  5 R (refer to  FIG.  4   ) of the driver  13 , and to allow another part of the image light to reach the other of the left eye  5 L or the right eye  5 R of the driver  13 . In other words, the barrier  21  directs at least a part of image light toward the left eye  5 L of the driver  13  and toward the right eye  5 R of the driver  13 . The left eye  5 L is also referred to as a first eye, and the right eye  5 R as a second eye. In the present embodiment, the barrier  21  is located between the backlight  19  and the display  20 . In other words, light emitted from the backlight  19  first enters the barrier  21  and then enters the display  20 . 
     The barrier  21  defines the traveling direction of image light to allow each of the left eye  5 L and the right eye  5 R of the driver  13  to receive different image light. Each of the left eye  5 L and the right eye  5 R of the driver  13  can thus view a different image. 
     As illustrated in  FIG.  4   , the display  20  includes, on the display surface  20   a,  left-eye viewing areas  201 L viewable by the left eye  5 L of the driver  13  and right-eye viewing areas  201 R viewable by the right eye  5 R of the driver  13 . The display  20  displays a parallax image including left-eye images viewable by the left eye  5 L of the driver  13  and right-eye images viewable by the right eye  5 R of the driver  13 . A parallax image refers to an image projected to the left eye  5 L and the right eye  5 R of the driver  13  to generate parallax between the two eyes of the driver  13 . The display  20  displays left-eye images on the left-eye viewing areas  201 L and right-eye images on the right-eye viewing areas  201 R. In other words, the display  20  displays a parallax image on the left-eye viewing areas  201 L and the right-eye viewing areas  201 R. The left-eye viewing areas  201 L and the right-eye viewing areas  201 R are arranged in u-direction indicating a parallax direction. The left-eye viewing areas  201 L and the right-eye viewing areas  201 R may extend in v-direction orthogonal to the parallax direction, or in a direction inclined with respect to v-direction at a predetermined angle. In other words, the left-eye viewing areas  201 L and the right-eye viewing areas  201 R may be arranged alternately in a predetermined direction including a component in the parallax direction. The pitch between the alternately arranged left-eye viewing areas  201 L and right-eye viewing areas  201 R is also referred to as a parallax image pitch. The left-eye viewing areas  201 L and the right-eye viewing areas  201 R may be spaced from each other or adjacent to each other. The display  20  may further include a display area on the display surface  20   a  for displaying a planar image. A planar image is an image that generates no parallax between the eyes  5  of the driver  13  and is not viewed stereoscopically. 
     As illustrated in  FIG.  4   , the barrier  21  includes open areas  21   b  and light-blocking surfaces  21   a.  With the barrier  21  nearer the driver  13  than the display  20  on the optical path of image light, the barrier  21  controls the transmittance of image light emitted from the display  20 . The open areas  21   b  transmit light entering the barrier  21  from the display  20 . The open areas  21   b  may transmit light with a transmittance of a first predetermined value or greater. The first predetermined value may be, for example, 100% or a value close to 100%. The light-blocking surfaces  21   a  block light entering the barrier  21  from the display  20 . The light-blocking surfaces  21   a  may transmit light with a transmittance of a second predetermined value or less. The second predetermined value may be, for example, 0% or a value close to 0%. The first predetermined value is greater than the second predetermined value. 
     The open areas  21   b  and the light-blocking surfaces  21   a  are arranged alternately in u-direction indicating the parallax direction. The boundaries between the open areas  21   b  and the light-blocking surfaces  21   a  may extend in v-direction orthogonal to the parallax direction as illustrated in  FIG.  4   , or in a direction inclined with respect to v-direction at a predetermined angle. In other words, the open areas  21   b  and the light-blocking surfaces  21   a  may be arranged alternately in a predetermined direction including a component in the parallax direction. 
     In the present embodiment, the barrier  21  is more away from the driver  13  than the display  20  on the optical path of image light. The barrier  21  controls the transmittance of light directed from the backlight  19  to the display  20 . The open areas  21   b  transmit light directed from the backlight  19  to the display  20 . The light-blocking surfaces  21   a  block light directed from the backlight  19  to the display  20 . This structure allows light entering the display  20  to travel in a predetermined direction. Thus, the barrier  21  can control a part of image light to reach the left eye  5 L of the driver  13 , and another part of the image light to reach the right eye  5 R of the driver  13 . 
     The barrier  21  may include a liquid crystal shutter. The liquid crystal shutter can control the transmittance of light in accordance with a voltage applied. The liquid crystal shutter may include multiple pixels and control the transmittance of light for each pixel. The liquid crystal shutter can form an area with high light transmittance or an area with low light transmittance in an intended shape. The open areas  21   b  in the barrier  21  including the liquid crystal shutter may have a transmittance of the first predetermined value or greater. The light-blocking surfaces  21   a  in the barrier  21  including the liquid crystal shutter may have a transmittance of the second predetermined value or smaller. The first predetermined value may be greater than the second predetermined value. The ratio of the second predetermined value to the first predetermined value may be set to 1/100 in one example. The ratio of the second predetermined value to the first predetermined value may be set to 1/1000 in another example. The barrier  21  including the open areas  21   b  and the light-blocking surfaces  21   a  that can shift is also referred to as an active barrier. 
     The controller  24  controls the display  20 . When the barrier  21  is an active barrier, the controller  24  may control the barrier  21 . The controller  24  may control the backlight  19 . The controller  24  obtains coordinate information about the pupil positions of the eyes  5  of the driver  13  from the detection device  50 , and controls the display  20  based on the coordinate information. The controller  24  may control at least one of the barrier  21  or the backlight  19  based on the coordinate information. The controller  24  may receive an image output from the camera  11  and detect the eyes  5  of the driver  13  based on the received image. In other words, the controller  24  may have the same function as and may serve as the detector  15 . The controller  24  may control the display  20  based on the detected pupil positions of the eyes  5 . The controller  24  can control at least one of the barrier  21  or the backlight  19  based on the detected pupil positions of the eyes  5 . The controller  24  and the detector  15  may be, for example, processors. The controller  24  and the detector  15  may each include one or more processors. The processors may include a general-purpose processor that reads a specific program to perform a specific function, and a processor dedicated to specific processing. The dedicated processor may include an application-specific integrated circuit (ASIC). The processors may include a programmable logic device (PLD). The PLD may include a field-programmable gate array (FPGA). The controller  24  and the detector  15  may each be a system-on-a-chip (SoC) or a system in a package (SiP) in which one or more processors cooperate with other components. 
     The communicator  22  may include an interface that can communicate with an external device. The external device may include, for example, the detection device  50 . The external device may provide, for example, image information to be displayed on the display  20 . The communicator  22  may obtain various sets of information from the external device such as the detection device  50  and output the information to the controller  24 . The interface that can perform communication in one or more embodiments of the present disclosure may include, for example, a physical connector and a wireless communication device. The physical connector may include an electric connector for transmission with electric signals, an optical connector for transmission with optical signals, and an electromagnetic connector for transmission with electromagnetic waves. The electric connector may include a connector complying with IEC 60603, a connector complying with the universal serial bus (USB) standard, and a connector used for an RCA terminal. The electric connector may include a connector used for an S terminal specified by EIAJ CP-121 aA or a connector used for a D terminal specified by EIAJ RC-5237. The electric connector may include a connector complying with the High-Definition Multimedia Interface (HDMI, registered trademark) standard or a connector used for a coaxial cable including a British Naval Connector, also known as, for example, a Baby-series N Connector (BNC). The optical connector may include a connector complying with IEC 61754. The wireless communication device may include a wireless communication device complying with the Bluetooth (registered trademark) standard and a wireless communication device complying with other standards including IEEE 8021a. The wireless communication device includes at least one antenna. 
     The storage  23  may store various sets of information or programs for causing the components of the 3D display device  17  to operate. The storage  23  may include, for example, a semiconductor memory. The storage  23  may function as a work memory for the controller  24 . The controller  24  may include the storage  23 . 
     As illustrated in  FIG.  4   , light emitted from the backlight  19  passes through the barrier  21  and the display  20  to reach the eyes  5  of the driver  13 . The broken lines indicate the paths traveled by light from the backlight  19  to reach the eyes  5 . The light through the open areas  21   b  in the barrier  21  to reach the right eye  5 R passes through the right-eye viewing areas  201 R in the display  20 . In other words, light through the open areas  21   b  allows the right eye  5 R to view the right-eye viewing areas  201 R. The light through the open areas  21   b  in the barrier  21  to reach the left eye  5 L passes through the left-eye viewing areas  201 L in the display  20 . In other words, light through the open areas  21   b  allows the left eye  5 L to view the left-eye viewing areas  201 L. 
     The display  20  displays left-eye images on the left-eye viewing areas  201 L and right-eye images on the right-eye viewing areas  201 R. Thus, the barrier  21  allows image light for the left-eye images to reach the left eye  5 L and image light for the right-eye images to reach the right eye  5 R. More specifically, the open areas  21   b  allow image light for the left-eye images to reach the left eye  5 L of the driver  13  and image light for the right-eye images to reach the right eye  5 R of the driver  13 . The 3D display device  17  with this structure can project a parallax image to the two eyes of the driver  13 . The driver  13  views the parallax image with the left eye  5 L and the right eye  5 R to view the image stereoscopically. 
     Light through the open areas  21   b  in the barrier  21  is emitted through the display surface  20   a  of the display  20  as image light and reaches the windshield  25  through the optical element  18 . The image light is reflected from the windshield  25  and reaches the eyes  5  of the driver  13 . This allows the eyes  5  of the driver  13  to view a second virtual image  14   b  located more away in the negative z-direction than the windshield  25 . The second virtual image  14   b  corresponds to an image appearing on the display surface  20   a.  The open areas  21   b  and the light-blocking surfaces  21   a  in the barrier  21  form a first virtual image  14   a  in front of the windshield  25  and more away in the negative z-direction than the second virtual image  14   b.  As illustrated in  FIG.  1   , the driver  13  can view an image with the display  20  appearing to be at the position of the second virtual image  14   b  and the barrier  21  appearing to be at the position of the first virtual image  14   a.    
     The 3D display device  17  emits image light for the image appearing on the display surface  20   a  in a direction defined by the barrier  21 . The optical element  18  allows the image light to travel toward the windshield  25 . The optical element  18  can reflect or refract the image light. The windshield  25  reflects the image light and directs the light toward the eyes  5  of the driver  13 . The image light entering the eyes  5  of the driver  13  causes the driver  13  to view a parallax image as the virtual image  14 . The driver  13  views the virtual image  14  stereoscopically. An image of the virtual image  14  corresponding to the parallax image is also referred to as a parallax virtual image. A parallax virtual image is a parallax image projected through the optical system. An image of the virtual image  14  corresponding to the planar image is also referred to as a planar virtual image. A planar virtual image is a planar image projected through the optical system. 
     The detector  15  may use the entire range of the captured image  51  as a search range in template matching. The detector  15  may use a part of the captured image  51  as the search range in template matching. A part of the search range may include the face of the driver  13  in the captured image  51 . Before starting the search with the template image  52 , the detector  15  detects the face of the driver  13  in the captured image  51  captured with the camera  11  and defines a search range with a predetermined size (smaller than the entire range of the captured image  51 ) including the detected face. The detector  15  may perform template matching by searching the defined search range with the template image  52 . The search range with the template image  52  is smaller than the entire range of the captured image  51 . Thus, the template matching involves less computation. With such less computation, the detector  15  can output a detection result from template matching at a higher computation speed. 
     The detector  15  generates the template image  52  based on the captured image  51  captured with the camera before starting the search. The detector  15  may perform pupil detection in the captured image  51  and use the predetermined peripheral area including the detected pupils as the template image  52 . The predetermined peripheral area to be generated as the template image  52  may be, for example, an area corresponding to the eye box  16  in the 3D projector  12 . 
     The template image generation process will now be described with reference to a flowchart. The detection device  50  may perform, for example, the template image generation process in the flowchart of  FIG.  5   . The detection device  50  may start the template image generation process when, for example, the 3D projection system  100  is activated (powered on). In step A 1 , the camera  11  first captures an image to obtain a captured image  51  and outputs the image to the detector  15 . The captured image  51  captured with the camera  11  includes, for example, the face of the driver  13  seated in a seat in the movable body  10 . In subsequent step A 2 , the detector  15  extracts a first area including the eye box  16  from the captured image  51 . In step A 3 , the detector  15  performs face detection on the extracted first area to determine whether the face of the driver is detected. In response to the face being detected, the processing advances to step A 4 . In response to no face being detected, the processing returns to step A 1 , in which an image is captured again with the camera  11 . 
     In step A 4 , the detector  15  extracts a second area containing the detected face from the first area. In step A 5 , the detector  15  performs pupil detection on the second area to determine whether pupils are detected. In response to the pupils being detected, the processing advances to step A 6 . In response to no pupil being detected, the processing returns to step A 1 , in which an image is captured again with the camera  11 . In step A 6 , the detector  15  extracts a pupil peripheral area including the detected pupils as a template image  52 . The template image generation process ends. The detector  15  may store the extracted template image  52 , for example, into a storage area included in the detector  15  or into the storage  23 . The detector  15  may extract, for example, a pupil peripheral area with the same size as the eye box  16  as the template image  52 . The detector  15  may also store the relative coordinate positional relationship between each representative position and the corresponding pupil positions on the template image  52 , together with the template image  52 . 
     The template image  52  may be temporarily stored into the storage area in the detector  15  while the 3D projection system  100  is activated. The template image  52  may be, for example, associated with the imaged driver  13  and stored into the storage  23 . The template image  52  stored in the storage  23  can be subsequently read from the storage  23  by the detector  15  at, for example, subsequent activation of the 3D projection system  100 . This eliminates the template image generation process. The detector  15  can perform the template image generation process again to update (rewrite) the template image  52  stored in the storage  23 . 
     The template matching process will be described with reference to a flowchart. The detection device  50  may perform, for example, the template matching process in the flowchart of  FIG.  6   . The detection device  50  may perform, for example, the template image generation process in response to activation of the 3D projection system  100 , and start the template matching process after the template image generation process ends. Using the template image  52  prestored in the storage  23 , the detection device  50  may start the template matching process in response to activation of the 3D projection system  100 . 
     In step B 1 , the detector  15  first obtains the captured image  51  from the camera  11 . In step B 2 , the detector  15  extracts the area surrounding the position at which the template image  52  is extracted from the captured image  51  as a search range. The coordinates of the position at which the template image  52  is extracted may be associated with the template image  52  and be stored. In step B 3 , the detector  15  performs template matching for the search range using the template image  52 . The detector  15  determines a position with the highest degree of matching with the template image  52  within the search range and the degree of matching by template matching. In step B 4 , the detector  15  determines whether the determined degree of matching is greater than or equal to a threshold. When the value is greater than or equal to the threshold, the processing advances to step B 5 . When the value is less than the threshold, the processing returns to step B 1  and performs imaging with the camera  11  again. In step B 5 , the detector  15  determines the coordinates of the pupil positions in the captured image  51  based on the coordinates of the position with the highest degree of matching with the template image  52  within the search range and the predefined relative coordinate positional relationship, and ends the template matching process. The coordinate information about the determined pupil positions is output from the detection device  50  to the 3D projector  12 . In the 3D projector  12 , the controller  24  controls the parallax image displayed on the display  20  based on the coordinate information about the pupil positions obtained from the detection device  50 . 
     The driver&#39;s seat of the movable body  10  is, for example, movable in the front-rear direction. The posture of the driver  13  may also change during the operation of the movable body  10 . The front or rear position of the driver&#39;s seat or the posture of the driver  13  may change. The face of the driver  13  may then move in z-direction. When the face of the driver  13  moves in the positive z-direction, the face of the driver  13  is captured to be smaller in the captured image  51  than before the movement. When the face of the driver  13  moves in the negative z-direction, the face of the driver  13  is captured to be larger in the captured image  51  than before the movement. In this case, the template image  52  is to undergo a scaling process, and then template matching is to be performed using the resultant template image  52 . For example, multiple template images  52  with different enlargement factors may be used in template matching. For example, multiple template images  52  with different reduction factors may be used in template matching. 
     The template matching processes in another example will be described with reference to a flowchart. The detection device  50  may perform, for example, a template matching process in the flowchart of  FIG.  7   . The detection device  50  may perform, for example, the template image generation process in response to activation of the 3D projection system  100 , and start the template matching process after the template image generation process ends. Using the template image  52  prestored in the storage  23 , the detection device  50  may start the template matching process in response to activation of the 3D projection system  100 . 
     The processing in steps B 1  to B 4  in  FIG.  6    is the same as the processing in steps C 1  to C 4  in  FIG.  7    and will not be described repeatedly. In step C 5 , the detector  15  performs a scaling process on the template images using multiple scaling factors for the template images  52 . The detector  15  performs template matching using each template image  52  resulting from the scaling process. The detection device  50  does not detect directions of changes in the posture of the driver  13 , and performs both enlargement and reduction processes as the scaling process. With multiple template images  52  generated through the scaling process, the detector  15  performs template matching using the multiple template images  52  to determine the template image  52  with the highest degree of matching. In step C 6 , the detector  15  estimates the position of the driver in z-direction based on the scaling factor of the template image  52  with the highest degree of matching. In step C 7 , after determining the coordinates of the pupil positions in the captured image  51  in the same or similar manner to step B 5 , the pupil position coordinates are corrected based on the estimated position in z-direction, and the template matching process ends. The coordinate information about the determined pupil positions is output from the detection device  50  to the 3D projector  12 . 
     A 3D projection system  100 A in another example will be described. In the 3D projection system  100 A, as illustrated in  FIG.  8   , a detection device  50 A includes a camera  11 , a detector  15 A, and a predictor  30 . The components of the 3D projection system  100 A are the same as or similar to the components of the 3D projection system  100  described above except the detection device  50 A. The components of the 3D projection system  100 A are thus denoted with the same reference numerals as the corresponding components and will not be described in detail. The predictor  30  predicts the positions of the eyes  5  at a time later than the current time based on multiple positions of the eyes  5  detected by the detector  15 . The positions of the eyes  5  in the present embodiment may also be coordinate information indicating the pupil positions of the eyes  5  of the driver  13  as described above. The multiple positions of the eyes  5  include the positions of the eyes  5  at different detection times. The predictor  30  may predict future positions of the eyes  5  using multiple sets of data about detection time and coordinate information, and output the future positions as predicted positions. When detecting the positions of the eyes  5 , the detector  15 A may store coordinate information and detection time as data for prediction, for example, into the storage area in the detector  15 , the storage area in the predictor  30 , or the storage  23  sequentially. The future positions of the eyes  5  refer to the positions in the future with respect to the multiple sets of data stored for prediction. 
     The method of predicting the positions of the eyes  5  used by the predictor  30  may use, for example, a prediction function. The prediction function is derived from multiple sets of data stored for prediction. The prediction function uses a function formula with coefficients determined in advance by experiment or other means. The prediction function may be stored in the storage area in the detector  15 A, the storage area in the predictor  30 , or the storage  23 . The prediction function may be updated every time when the predictor  30  predicts the positions of the eyes  5 . 
     The predictor  30  inputs the future time to be predicted into the prediction function and outputs the coordinate information about the positions of the eyes  5  (predicted positions) at the time. The future time to be predicted is the time at which the next template matching is to be performed. This may be, for example, the time when the next frame is input from the camera  11 . As described above, the detector  15 A may search a part of the captured image  51  as a search range in template matching. The detector  15 A may search an area including the positions of the eyes  5  predicted by the predictor  30  defined as a search range in template matching. The detector  15 A defines an area including the predicted positions output by the predictor  30  as a prediction area in the captured image  51 , and defines the prediction range as a search range in template matching. The prediction range including the predicted positions may be smaller than the captured image  51  and larger than the template image  52 , and may contain the predicted positions within the area. For example, the prediction range may be an area in which the center coordinates of the prediction range match the coordinates of the predicted positions. The shape and size of the search range in template matching in the present embodiment may have, for example, similarity to the template image. 
     The detector  15 A performs template matching in such an area as the search range. The template matching in the present embodiment is the same as or similar to the template matching described above except the search range. In the template matching a position with the highest degree of matching with the template image  52  is searched in the prediction range as the search range. The detection result may be the coordinate information indicating the pupil positions of the eyes  5  of the driver  13 . The prediction area as the search range in the present embodiment includes the predicted positions output from the predictor  30 . The pupil positions of the eyes  5  are thus highly likely to be included in the search range after the search range is set smaller. With the smaller search range, the template matching involves less computation. With such less computation, the detector  15 A can output a detection result from template matching at a higher computation speed. 
     The predictor  30  may further calculate the change rate of the positions of the eyes  5  based on the multiple positions of the eyes  5  detected by the detector  15 A. As described above, sets of coordinate information and detection time are stored as prediction data. Multiple sets of prediction data are used to calculate the change rate of the positions of the eyes  5 . For example, the traveling distance from the positions of the eyes  5  can be calculated based on the difference between two sets of prediction data using the coordinate information. The time can be calculated from the detection time. The change rate of the positions of the eyes  5  can thus be calculated. The components in x- and y-directions can be calculated based on the traveling distance and the change rate of the positions of the eyes  5 . 
     The detector  15 A adjusts the size of the search range in template matching in accordance with the change rate calculated by the predictor  30 . When the change rate calculated by the predictor  30  is large, the moving distance of the positions of the eyes  5  can be predicted to be large. When, for example, the component of the calculated change rate in x-direction is compared with the component of the calculated change rate in y-direction, the traveling distance from the positions of the eyes  5  is estimated to be greater in the direction of the larger component of the change rate. In the present embodiment, the search range in template matching can be defined as a small area by predicting the positions of the eyes  5 . However, in the direction in which the component of the change rate is large, the positions of the eyes  5  may deviate from the predicted positions, and fall outside the search range. To prevent the positions of the eyes  5  from being outside the search range, for example, the detector  15 A may widen the area including the predicted positions in the direction of a larger component of the change rate. The detector  15 A performs template matching in this widened area as the search range. 
     The template matching process including pupil position prediction will be described with reference to a flowchart. The detection device  50 A may perform, for example, the template matching process in the flowchart of  FIG.  9   . The detection device  50 A may perform, for example, the template image generation process in response to activation of the 3D projection system  100 A, and start the template matching process after the template image generation process ends. Using the template image  52  prestored in the storage  23 , the detection device  50 A may start the template matching process in response to activation of the 3D projection system  100 A. 
     In step B 11 , the detector  15 A first obtains the captured image  51  from the camera  11 . In step B 12 , the detector  15 A extracts the search range from the captured image  51 . The search range extracted in step B 12  is the search range determined in step B 17  (described later). When the processing in step B 17  is yet to be performed and the search range is not predetermined, the area surrounding the position at which the template image  52  is extracted may be used as the search range. In step B 13 , the detector  15 A performs template matching in the search range using the template image  52 . The detector  15 A determines a position with the highest degree of matching with the template image  52  within the search range and its degree of matching by template matching. In step B 14 , the detector  15 A determines whether the determined degree of matching is greater than or equal to the threshold. When the value is greater than or equal to the threshold, the processing advances to step B 15 . When the value is less than the threshold, the processing returns to step B 1  and performs imaging with the camera  11  again. In step B 15 , the detector  15 A determines the coordinates of the pupil positions in the captured image  51  based on the coordinates of the position with the highest degree of matching with the template image  52  within the search range and the predefined relative coordinate positional relationship. The coordinate information about the determined pupil positions is output from the detection device  50  to the 3D projector  12 . In the 3D projector  12 , the controller  24  controls the parallax image displayed on the display  20  based on the coordinate information about the pupil positions obtained from the detection device  50 . 
     In step B 16 , the predictor  30  predicts future pupil positions and outputs the positions as predicted positions. The predictor  30  updates the prediction function based on, for example, the latest data for prediction, which is a set of coordinate information about the pupil positions determined in step B 15  and the detection time, and the past data stored for prediction. The predictor  30  predicts the pupil positions using the updated prediction function and outputs the predicted positions. In step B 17 , the detector  15 A determines the area including the predicted positions output from the predictor  30  as the search range. The processing returns to step B 11 . 
     As described above, the face of the driver  13  may move back and forth. When, for example, the driver  13  tilts the head, the face of the driver  13  may tilt. As the face of the driver  13  moves back and forth, the face of the driver  13  in the captured image  51  appears larger or smaller, similarly to when the image is processed for enlargement or reduction. When the face of the driver  13  is tilted, the face of the driver  13  in the captured image is similar to that in the rotation process. After the predictor  30  predicts the pupil positions, the detector  15 A compares the predicted positions with the latest pupil positions. When the comparison result indicates that, for example, the interocular distance has changed, the detector  15 A updates the template image  52  to a template image  52  with a scaling factor corresponding to the interocular distance. The detector  15 A may, for example, pre-generate multiple template images  52  with different enlargement factors and multiple template images  52  with different reduction factors through the scaling process, and select the template image  52  corresponding to the interocular distance. With the predictor  30  predicting the pupil position of the left eye and the pupil position of the right eye, the detector  15 A may detect the change in the interocular distance by comparing the latest pupil position of the left eye and the latest pupil position of the right eye. 
     When the pupil positions are tilted as a result of the detector  15 A comparing the predicted positions with the latest pupil positions, the detector  15 A updates the template image  52  to a template image  52  with a rotation angle corresponding to the tilt change. The detector  15 A may pre-generate, for example, multiple template images  52  with different rotation angles through the rotation process, and select the template image  52  corresponding to the tilt change. With the predictor  30  predicting the pupil position of the left eye and the pupil position of the right eye, the detector  15 A may detect the tilt change from the change in the position in y-direction by comparing the latest pupil position of the left eye and the latest pupil position of the right eye. When the face of the driver  13  is tilted, the respective pupil positions in y-direction (y-coordinates) of the left and right eyes change in different directions. For example, the pupil position in y-direction of the left eye changing upward and the pupil position in y-direction of the right eye changing downward correspond to a tilt change. The detector  15 A may calculate the rotation angle based on the magnitude of the position change of the left and right eyes in y-direction. 
     The template matching process including updating the template image will be described with reference to a flowchart. The detection device  50 A may perform, for example, the template matching process in the flowchart of  FIG.  10   . In step C 11 , the detector  15 A first obtains the captured image  51  from the camera  11 . In step C 12 , the detector  15 A extracts the search range from the captured image  51 . The search range extracted in step C 12  is the search range determined in step C 18  (described later). When the processing in step C 18  is yet to be performed and the search range is not predetermined, the area surrounding the position at which the template image  52  is extracted may be used as the search range. In step C 13 , the detector  15 A performs template matching in the search range using the updated template image  52 . The template image  52  is the template image  52  updated in step C 17  (described later). The detector  15 A determines a position with the highest degree of matching with the template image  52  within the search range and its degree of matching by template matching. In step C 14 , the detector  15 A determines whether the determined degree of matching is greater than or equal to the threshold. When the value is greater than or equal to the threshold, the processing advances to step C 15 . When the value is less than the threshold, the processing returns to step C 11  and performs imaging with the camera  11  again. In step C 15 , the detector  15 A determines the coordinates of the pupil positions in the captured image  51  based on the coordinates of the position with the highest degree of matching with the template image  52  within the search range and the predefined relative coordinate positional relationship. The coordinate information about the determined pupil positions is output from the detection device  50  to the 3D projector  12 . In the 3D projector  12 , the controller  24  controls the parallax image displayed on the display  20  based on the coordinate information about the pupil positions obtained from the detection device  50 . 
     In step C 16 , the predictor  30  predicts future pupil positions and outputs the position as predicted positions. In step C 17 , the detector  15 A updates the template image  52 . The detector  15 A compares the predicted positions with the latest pupil positions and updates the template image  52  to a template image  52  that has at least undergone the scaling process or the rotation process in accordance with the comparison result. In step C 18 , the detector  15 A determines the area including the predicted positions output from the predictor  30  as the search range. The processing returns to step C 11 . 
     In the present disclosure, the structure is not limited to the structure described in the above embodiments, but may be varied or altered. For example, the functions of the components are reconfigurable unless any contradiction arises. Multiple components may be combined into a single unit, or a single component may be divided into separate units. 
     The figures illustrating the configurations according to the present disclosure are schematic. The figures are not drawn to scale relative to the actual size of each component. 
     In the present disclosure, the first, the second, or others are identifiers for distinguishing the components. The identifiers of the components distinguished with the first, the second, and others in the present disclosure are interchangeable. For example, the first eye can be interchangeable with the second eye. The identifiers are to be interchanged together. The components for which the identifiers are interchanged are also to be distinguished from one another. The identifiers may be eliminated. The components without such identifiers can be distinguished with reference numerals. The identifiers such as the first and the second in the present disclosure alone should not be used to determine the order of components or to suggest the existence of smaller or larger number identifiers. 
     In the present disclosure, x-axis, y-axis, and z-axis are used for ease of explanation and may be interchangeable with one another. The orthogonal coordinate system including x-axis, y-axis, and z-axis is used to describe the structures according to the present disclosure. The positional relationship between the components in the present disclosure is not limited to being orthogonal. 
     The present disclosure may be implemented in the following forms. 
     In one embodiment of the present disclosure, a detection device includes a camera and a detector. The camera captures an image of a human face. The detector detects a position of a human eye based on the captured image output from the camera by template matching. 
     In one embodiment of the present disclosure, an image display system includes a display, a barrier, a camera, a detector, and a controller. The display displays a parallax image to be projected to two human eyes through an optical system. The barrier defines a traveling direction of image light for the parallax image to generate parallax between the two human eyes. The camera captures an image of a human face. The detector detects positions of the two human eyes based on the captured image output from the camera by template matching. The controller controls the display based on the positions of the two human eyes detected by the detector. 
     The detection device and the image display system according to one or more embodiments of the present disclosure allow processing involving less computation and successive detection. 
     The present disclosure may be embodied in various forms without departing from the spirit or the main features of the present disclosure. The embodiments described above are thus merely illustrative in all respects. The scope of the present disclosure is defined not by the description given above but by the claims. Any variations and alterations contained in the claims fall within the scope of the present disclosure. 
     Reference Signs 
     
         
           5  eye ( 5 L: left eye,  5 R: right eye) 
           10  movable body 
           11  camera 
           12  3D projector 
           13  driver 
           14  virtual image ( 14   a:  first virtual image,  14   b:  second virtual image) 
           15 ,  15 A detector 
           16  eye box 
           17  3D display device 
           18  optical element ( 18   a:  first mirror,  18   b:  second mirror) 
           19  backlight 
           20  display ( 20   a:  display surface) 
           201 L left-eye viewing area 
           201 R right-eye viewing area 
           21  barrier ( 21   a:  light-blocking surface,  21   b:  open area) 
           22  communicator 
           23  storage 
           24  controller 
           25  windshield 
           30  predictor 
           50 ,  50 A detection device 
           100 ,  100 A 3D projection system (image display system)