Patent Publication Number: US-2022217324-A1

Title: Information processing apparatus, information processing method, and program

Description:
TECHNICAL FIELD 
     The present disclosure relates to an information processing apparatus, an information processing method, and a program. 
     BACKGROUND ART 
     Some conventional display devices achieve a stereoscopic image display. Patent Document 1 discloses an image display system that includes an image display device that displays a stereoscopic image by using a ray-of-light regeneration method. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2008-146221 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the conventional technology described above, a motion parallax is achieved in all of the three-dimensional directions by using the ray-of-light regeneration method, and therefore it is difficult to simplify a configuration of a device that regenerates rays of light in all of the three-dimensional directions. Furthermore, a device that regenerates rays of light regenerates rays of light in all of the three-dimensional directions, and therefore there is a possibility of causing an unnatural image to be visually recognized according to processing performance of the device. 
     Accordingly, the present disclosure proposes an information processing apparatus, an information processing method, and a program that are capable of causing a stereoscopic image to be visually recognized by using rays of light, even if a processing load relating to emission of rays of light is reduced. 
     Solutions to Problems 
     In order to solve the problems described above, an information processing apparatus according to an embodiment of the present disclosure includes: a specification unit that specifies a viewpoint position of an observer of a display device that reproduces rays of light that have been sent out by a three-dimensional object; a setting unit that sets a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified by the specification unit; and a display control unit that performs control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set by the setting unit, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     Furthermore, an information processing method according to an embodiment of the present disclosure is an information processing method performed by an information processing apparatus that controls a display device that reproduces rays of light that have been sent out by a three-dimensional object. The information processing method includes: a step of specifying a viewpoint position of an observer of the display device; a step of setting a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and a step of performing control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     Furthermore, a program according to an embodiment of the present disclosure causes an information processing apparatus that controls a display device that reproduces rays of light that have been sent out by a three-dimensional object to perform: a step of specifying a viewpoint position of an observer of the display device; a step of setting a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and a step of performing control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a display system that includes an information processing apparatus according to an embodiment. 
         FIG. 2  is a diagram illustrating an example of a configuration of the information processing apparatus according to the embodiment. 
         FIG. 3  is a diagram for explaining a viewpoint position in the information processing apparatus according to the embodiment. 
         FIG. 4  is a diagram illustrating a relationship between a region that the information processing apparatus according to the embodiment has set by using a viewpoint position as a reference and a ray of light. 
         FIG. 5  is a diagram for explaining a ray-of-light group that the information processing apparatus according to the embodiment causes to be reproduced. 
         FIG. 6  is a diagram for explaining an example of a relationship among a ray of light, an image, and a viewpoint position in the information processing apparatus according to the embodiment. 
         FIG. 7  is a flowchart illustrating an example of a processing procedure performed by the information processing apparatus according to the embodiment. 
         FIG. 8  is a diagram for explaining a relationship among a ray of light, an image, and a viewpoint position in the information processing apparatus according to the embodiment. 
         FIG. 9  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus in Variation (1) of the embodiment. 
         FIG. 10  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus in Variation (2) of the embodiment. 
         FIG. 11  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus in Variation (3) of the embodiment. 
         FIG. 12  is a diagram for explaining a relationship among a ray of light, an image, and a viewpoint position in an information processing apparatus in Variation (4) of the embodiment. 
         FIG. 13  is a hardware configuration diagram illustrating an example of a computer that achieves functions of an information processing apparatus. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present disclosure is described in detail below with reference to the drawings. Note that in each of the embodiments described below, the same portion is denoted by the same reference sign, and therefore a duplicate description is omitted. 
     Embodiment 
     [Outline of Display System According to Embodiment] 
       FIG. 1  is a diagram illustrating a schematic configuration of a display system that includes an information processing apparatus according to an embodiment. A display system  100  illustrated in  FIG. 1  causes an observer  200  to visually recognize a three-dimensional object in a stereoscopic manner by using a ray-of-light group emitted from a display device  10 . The display system  100  includes the display device  10 , a measurement device  20 , and an information processing apparatus  30 . The information processing apparatus  30  can perform communication with the display device  10  and the measurement device  20 . 
     The display device  10  is a light field display that reproduces rays of light that have been sent out by a three-dimensional object. The display device  10  of a light field scheme is a device that causes the observer  200  to visually recognize a stereoscopic video or the like with naked eyes without using dedicated glasses. For example, a three-dimensional object to be visually recognized sends out rays of light in various directions. The rays of light mean light obtained by reflecting sunlight, illumination, or the like. A human or the like stereoscopically recognizes a three-dimensional object, by grasping rays of light that have been sent out by the object. The display device  10  makes it possible to stereoscopically view a three-dimensional object, by reproducing, in a pseudo manner, rays of light that have been sent out by the three-dimensional object. The display device  10  reproduces rays of light that have been sent out by a three-dimensional object according to a scheme of reproducing rays of light that have been sent out by a three-dimensional object under the control of the information processing apparatus  30 . As the display device  10 , for example, a will-known device that regenerates rays of light according to a panel laminated scheme, a projector array scheme, a parallax barrier/lens array scheme, or the like can be used. 
     For example, the display device  10  can use a ray-of-light regeneration scheme that can change a region in which rays of light will be reproduced, by performing signal processing. In the present embodiment, a case where a display of the panel laminated scheme is used, for example, as the display device  10  is described. The display device  10  can change a ray of light to be emitted from a pixel, for example, by changing a plurality of pixel values of a liquid crystal panel  11 . 
     The measurement device  20  is provided in an upper portion of the display device  10  in such a way that a position or the like of an eye  201  of the observer  200  who observes the display device  10  can be measured. As the measurement device  20 , for example, a single device of an RGB camera, an IR camera, a depth camera, an ultrasonic sensor, or the like, or a combination thereof can be used. The measurement device  20  may perform measurement at all times, or may perform measurement periodically. The measurement device  20  transmits measurement information indicating a result of measurement to the information processing apparatus  30  in wireless communication or wired communication. A measurement result includes, for example, information that can identify a position, a distance, or the like of the head, a left or right eye  201 , or the like of the observer  200  in a space where the liquid crystal panel  11  can be visually recognized. The measurement result includes, for example, an image of the left or right eye  201  or the like of the observer  200 . 
     [Configuration of Information Processing Apparatus According to Embodiment] 
       FIG. 2  is a diagram illustrating an example of a configuration of the information processing apparatus  30  according to the embodiment. The information processing apparatus  30  illustrated in  FIG. 2  is, for example, a dedicated or general-purpose computer. The information processing apparatus  30  includes a communication unit  31 , a storage  32 , and a control unit  33 . The information processing apparatus  30  is provided, for example, outside the display device  10 , but this is not restrictive. For example, the information processing apparatus  30  may be incorporated into the display device  10 . The control unit  33  of the information processing apparatus  30  is electrically connected to the communication unit  31  and the storage  32 . 
     The communication unit  31  has a function of performing communication with the display device  10  and the measurement device  20  directly or via a network. The communication unit  31  is, for example, a communication device that can perform wired communication or wireless communication. The communication unit  31  outputs, to the control unit  33 , information that has been received from the display device  10  and the measurement device  20 . The communication unit  31  transmits information, a signal, or the like that has been input from the control unit  33  to the display device  10 , the measurement device  20 , or the like. Note that the communication unit  31  may include, for example, a connector that is connected to a cable or the like. 
     The storage  32  stores each type of data and program. The storage  32  is implemented, for example, by a semiconductor memory element such as a RAM or a flash memory, or a storage device such as a hard disk or an optical disk. The storage  32  stores a measurement result of the measurement device  20  in a time-series manner. The storage  32  stores image data  32 A to be regenerated by the display device  10 , setting data  32 B, or the like. The image data  32 A includes, for example, information indicating an image group at a time when an observer has observed a three-dimensional object from all angles. The setting data  32 B includes, for example, information relating to a region, coordinates, or the like that have been set for the eye  201  of the observer  200 . The setting data  32 B includes, for example, information for setting a region by using a viewpoint position as a reference. 
     The control unit  33  controls the information processing apparatus  30 . The control unit  33  includes respective processing units, a specification unit  331 , a setting unit  332 , a display control unit  333 , and a detection unit  334 . In the present embodiment, the respective processing units of the control unit  33 , including the specification unit  331 , the setting unit  332 , the display control unit  333 , and the detection unit  334 , are implemented, for example, by a central processing unit (CPU), a micro control unit (MCU), or the like executing a program stored in the information processing apparatus  30  by using a random access memory (RAM) or the like as a working area. Furthermore, the respective processing units may be implemented, for example, by an integrated circuit such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). 
     The specification unit  331  specifies a viewpoint position of the observer  200  of the display device  10  that displays a three-dimensional object. The specification unit  331  specifies the viewpoint position, for example, on the basis of a measurement result of the measurement device  20  that has been acquired via the communication unit  31 . The specification unit  331  may specify the viewpoint position by using various known techniques. For example, the specification unit  331  specifies information relating to a position, a distance from the measurement device  20 , and the like of the eye  201  of the observer  200  from the measurement result of the measurement device  20 , and specifies viewpoint positions of the left eye and the right eye of the observer  200  on the basis of the specified information. The viewpoint position indicates a position in a viewpoint coordinate system that has been set for the observer  200 . Furthermore, the specification unit  331  may specify a direction that a line-of-sight of the right eye faces, for example, on the basis of a captured image of an eyeball of the right eye of the observer  200  and a positional relationship with the right eye. Similarly, the specification unit  331  may specify a direction that a line-of-sight of the left eye faces on the basis of a captured image of an eyeball of the left eye of a user and a positional relationship with the left eye. 
     The specification unit  331  may specify which position of the liquid crystal panel  11  is visually recognized, on the basis of a position of the eye  201  of the observer  200 . The specification unit  331  may cause a specification result to include specification precision of the viewpoint position of the observer  200 . For example, in a case where a position of the eye  201  of the observer  200  has failed to be grasped on the basis of an image or the like and the viewpoint position has been estimated on the basis of a position, a shape, or the like of the head of the observer  200 , the specification unit  331  may cause a specification result to include information indicating low specification precision. For example, in a case where the precision of the measurement device  20  includes uncertainty and has a certain distribution of probability, the specification unit  331  may specify a position, a range, or the like in which a viewpoint is likely to be located, by using the probability as a weight. Then, the specification unit  331  stores the specified viewpoint position of the observer  200  in the storage  32 , and also outputs the viewpoint position to the setting unit  332 . 
     The setting unit  332  sets a region that makes it possible for the observer  200  to stereoscopically view a three-dimensional object, by using, as a reference, the viewpoint position specified by the specification unit  331 . The setting unit  332  sets a region around the viewpoint position that makes it possible to stereoscopically view a three-dimensional object even if the viewpoint position of the observer  200  slightly deviates. For example, the setting unit  332  may set a region having a size that has been set in advance, by using the viewpoint position of the observer  200  as a reference. For example, the setting unit  332  may set a region that changes according to an observer  200 , by using the viewpoint position of the observer  200  as a reference. For example, the setting unit  332  may set a region having a range that surrounds the eye  201  of the observer  200  with the viewpoint position as a center. The region includes, for example, a plane, a stereoscopic space, or the like. For example, the setting unit  332  may set a region having a size that changes according to the expression capability of the display device  10 , the specifications of the information processing apparatus  30 , or the like. For example, the setting unit  332  may set a first region having a wider range in the case of an observer  200  who has a tendency for a viewpoint to move more frequently, and may set a second region having a size that is smaller than a size of the first region in the case of an observer  200  who has a tendency for a viewpoint to move less frequently. Then, the setting unit  332  stores, in the storage  32 , region information indicating the set region, and also outputs the region information to the display control unit  333 . 
     In the present embodiment, a case where the setting unit  332  sets two regions that correspond to the left eye and the right eye of the observer  200  is described, but this is not restrictive. For example, the setting unit  332  may set a single region that includes both the left eye and the right eye of the observer  200 . For example, in a case where it is sufficient if rays of light of either the left eye or the right eye of the observer  200  are reproduced, the setting unit  332  may set a region that uses a viewpoint position of one eye  201  as a reference. Furthermore, the setting unit  332  can reduce the number of rays of light to be reproduced by imposing restrictions on dimensions, a size, or the like per region. 
     The display control unit  333  performs control to cause the display device  10  to emit a ray-of-light group that makes it possible to stereoscopically view a three-dimensional object from an inside of the region that has been set by the setting unit  332 , and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. Stated another way, the display control unit  333  causes the observer  200  to visually recognize a three-dimensional object by using rays of light that pass through the inside of the region from among the ray-of-light group emitted by the display device  10 . For example, the display control unit  333  may control the display device  10  to continuously emit different rays of light to the inside of the region. The display control unit  333  can employ a scheme of changing a region in which rays of light will be reproduced by performing signal processing. For example, the display control unit  333  calculates what value each pixel of the display device  10  is to output, and controls the display device  10  according to a result of calculation. As a result, the display device  10  regenerates a pixel value from the display control unit  333  to emit rays of light that correspond to the pixel value. Note that an example of calculating a pixel value will be described later. 
     Furthermore, the display control unit  333  compares a ray-of-light group that passes through the region from the display device  10  with a virtual ray-of-light group that is desired to reproduce a three-dimensional object, and reflects a result of comparison in a ray-of-light group to be emitted by the display device. The display control unit  333  simulates rays of light that pass through the region from among a ray-of-light group emitted by the display device  10 , compares the rays of light that have been simulated and pass through the region with the virtual ray-of-light group, and causes the display device  10  to emit a ray-of-light group based on a pixel value that reduces an error. For example, the display control unit  333  performs simulation to obtain a ray-of-light group that passes through the region in a current state and a virtual ray-of-light group to be reproduced, and contrasts them. In a case where there is a difference as a result of contrast, the display control unit  333  determines a pixel value that eliminates the difference. 
     The detection unit  334  detects a movement of a viewpoint of the observer  200 . For example, the detection unit  334  compares the viewpoint position specified by the specification unit  331  with a previous viewpoint position. In a case where the viewpoint positions are different from each other or an amount of movement of the viewpoint is greater than or equal to a threshold, the detection unit  334  detects that the viewpoint has moved. For example, the detection unit  334  compares the viewpoint position specified by the specification unit  331  with the region set by the setting unit  332 . In a case where the viewpoint position is located outside the region or is located close to the outside of the region, the detection unit  334  detects that the viewpoint has moved. 
     A configuration example of the information processing apparatus  30  according to the embodiment has been described above. Note that the configuration that has been described above with reference to  FIG. 2  is merely an example, and a configuration of the information processing apparatus  30  according to the present embodiment is not limited to this example. A functional configuration of the information processing apparatus  30  according to the present embodiment can be flexibly changed according to specifications or operation. 
     [Method for Reproducing Rays of Light by Performing Signal Processing according to Embodiment] 
       FIG. 3  is a diagram for explaining a viewpoint position in the information processing apparatus  30  according to the embodiment. An xy coordinate system illustrated in  FIG. 3  defines plane coordinates on a surface of the liquid crystal panel  11  of the display device  10 . The xy coordinate system is an example of a display coordinate system. The xy coordinate system has an x-axis in a horizontal direction along a longer side of the liquid crystal panel  11  of the display device  10 , and a y-axis in a vertical direction along a shorter side of the liquid crystal panel  11 . An st coordinate system is a coordinate system that passes through the left and right eyes  201  of the observer  200  who is apart from the display device  10  by a distance d, and is parallel to the xy coordinate system. The st coordinate system is an example of a viewpoint coordinate system. The st coordinate system is plane coordinates that are defined in a depth of the viewpoint of the observer  200  who is apart from the display device  10  by the distance d. The st coordinate system has an s-axis along the horizontal direction, and a t-axis along the vertical direction. 
     In a three-dimensional space, two plane coordinates (the xy coordinate system and the st coordinate system) have been defined, and therefore all of the rays of light that are transmitted around in a space can be expressed. For example, a ray of light that passes through the point (x′, y′) in the xy coordinate system and the point (s, t) in the st coordinate system is expressed as R(x′, y′, s, t). In the description below, in a description in which coordinate positions of the left and right eyes  201  are distinguished from each other, the point (s l , t l ) and the point (s r , t r ) are used. 
     Next, a correspondence relationship between a ray of light that is transmitted around in a space and a pixel of the display device  10  is defined. The display device  10  can employ, for example, a panel laminated scheme, a projector array scheme, a parallax barrier/lens array scheme, or the like. A correspondence relationship between a ray of light and a pixel of the display device  10  changes according to schemes, and therefore in the present embodiment, details of the correspondence relationship are not described for the sake of versatility. Then, it is assumed that a set of pixels of the display device  10  is P, a transform function from P described above into rays of light is defined as f(P), and it is assumed that a correspondence relationship between each of the rays of light and a pixel of the display device  10  is expressed as Formula (1). Formula (1) indicates that f(P) is obtained if R(x′, y′, s, t) is obtained, and R(x′, y′, s, t) is obtained if f(P) is obtained. 
         R ( x,y,s,t )&lt;=&gt; f ( P )  Formula (1)
 
     Next, faithful reproduction of only a specified ray of light is formalized as an optimization problem. It is assumed that in a viewpoint position measured by the measurement device  20 , position coordinates of the left eye are the point (s l , t l ), and position coordinates of the right eye are the point (s r , t r ). If it is assumed that a range in which contribution will be reproduced is a range of ±r from a position of each of the left and right eyes  201 , the optimization problem is expressed as Formula (2). 
     
       
         
           
             
               
                 
                   
                       
                   
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     In Formula (2), R(x, y, s, t) is a luminance value of a ray of light to be reproduced that is given as an input. X and Y respectively correspond to a horizontal width and a vertical width of the liquid crystal panel  11  in the xy coordinate system. Stated another way, Formula (2) is an optimization problem that minimizes an error between a ray of light to be regenerated and a ray of light reproduced by the display device  10  in a ray-of-light group that passes through (x:[0, X], y:[0, Y]) on the liquid crystal panel  11 , and passes through a peripheral region (s: [s l −r, s l +r], t: [t l −r, t l +r]) of the left eye or a peripheral region (s: [s r −r, s r +r], t: [t r −r, t r +r]) of the right eye, from among all of the rays of light that are transmitted around in a space. 
     A resolution of the optimization problem is obtained according to a technique based on a gradient effect. Specifically, the information processing apparatus  30  simulates a ray of light that will be reproduced in a current state (step S 1 ). Then, the information processing apparatus  30  makes a comparison with a ray-of-light group to be reproduced that will be given as an input, and calculates an error (step S 2 ). Then, if the error is less than or equal to a certain value, the information processing apparatus  30  terminates calculation. If the error exceeds the certain value, the information processing apparatus  30  updates a pixel value in such a way that the error becomes smaller, and the processing returns to step S 1 . Then, the information processing apparatus  30  can faithfully reproduce a ray of light only in regions E l  and E r  that are peripheral regions of the viewpoint of the observer  200 , by reflecting a finally obtained pixel value P′ of the display device  10  in the display device  10 . Stated another way, the regions E l  and E r  serve as regions that make it possible for the observer  200  to stereoscopically view a three-dimensional object, by using a viewpoint position of the observer  200  as a reference. 
       FIG. 4  is a diagram illustrating a relationship between a region that the information processing apparatus  30  according to the embodiment has set by using a viewpoint position as a reference and a ray of light. In  FIG. 4 , an stu coordinate system has an s-axis that indicates the horizontal direction, a t-axis that indicates the vertical direction, and a u-axis that indicates a depth. The depth means a direction toward the display device  10 . 
     In the example illustrated in  FIG. 4 , the information processing apparatus  30  has set the region E l  by using, as a reference, a viewpoint position EP l  of the left eye of the observer  200 . In this case, the information processing apparatus  30  causes a ray-of-light group L to be emitted toward the region E l  from the point (x′, y′) in the xy coordinate system of the liquid crystal panel  11 . The ray-of-light group L is a ray-of-light group that makes it possible to stereoscopically view a three-dimensional object from an inside of the region E l . The ray-of-light group L includes a ray of light that passes through the inside of the region E l . 
     Furthermore, the information processing apparatus  30  may or may not cause a ray of light to be emitted toward an outside of the region E l  from the point (x′, y′) of the liquid crystal panel  11 . For example, the information processing apparatus  30  may cause emission of a ray-of-light group that makes it impossible to stereoscopically view a three-dimensional object and indicates the same image. Note that in the example illustrated in  FIG. 4 , for simplification of description, the region E. and rays of light that correspond to the right eye of the observer  200  are omitted. However, the information processing apparatus  30  causes the display device  10  to emit a ray-of-light group toward the region E r , similarly to the left eye. 
     In the example illustrated in  FIG. 4 , a case where the information processing apparatus  30  sets a cubic space as the region E l  has been described, but this is not restrictive. For example, the information processing apparatus  30  may set, as a region, a roughly spherical space or a plane. 
       FIG. 5  is a diagram for explaining a ray-of-light group that the information processing apparatus  30  according to the embodiment causes to be reproduced. For example, in contrast to a parallax scheme for causing an object to be visually recognized as if the object popped up or were located in the back, the display device  10  of the light field scheme causes an object to be visually recognized as if the object existed inside the display device  10 . In Reference Example Ex of  FIG. 5 , a light field regeneration device  300  emits a plurality of rays of light that has been sent out by a three-dimensional image indicating an apple. In order to widen a viewing angle in the horizontal direction of stereoscopic vision, it is requested that the light field regeneration device  300  cause a plurality of rays of light to be reproduced to be emitted to a wide range. For example, in order to emit 100 rays of light, it is requested that the display device  10  simultaneously display 100 images. Therefore, in order to regenerate rays of light in all of the three-dimensional directions, the light field regeneration device  300  needs a high resolution that enables videos in several hundred to several thousand viewpoints to be simultaneously displayed, or becomes a large-scale device. 
     The information processing apparatus  30  according to the embodiment limits a ray-of-light group L to be reproduced by the display device  10  to a peripheral region of a viewpoint position EP of the observer  200 , as illustrated as Mode M 1  of  FIG. 5 . By doing this, the information processing apparatus  30  can prevent a reduction in visibility due to a movement of the observer  200 , and can also reduce the number of rays of light of the ray-of-light group L to be reproduced. Then, as illustrated as Mode M 2  of  FIG. 5 , the display device  10  can be caused to only emit a ray-of-light group L for stereoscopic vision to the peripheral region of the viewpoint position EP of the observer  200 , and emit rays of light that make it impossible to perform stereoscopic vision to a region that is different from the peripheral region. 
     [Relationship Between Ray of Light and Observer in Display Device According to Embodiment] 
       FIG. 6  is a diagram for explaining an example of a relationship among a ray of light, an image, and a viewpoint position in the information processing apparatus  30  according to the embodiment. In the example illustrated in  FIG. 6 , the display device  10  displays an image G. The image G includes, for example, a moving image, a still image, or the like. The image G is an image that includes a vehicle that is located in the back, and a human that is located in front of the vehicle. The image G is an image for reproducing rays of light that have been sent out by the vehicle and the human. Then, in the observer  200  who observes the display device  10 , a viewpoint position EP l  of the left eye is located at the point (2, t) on the s-axis of the st coordinate system, and a viewpoint position EP r  of the right eye is located at the point (6, t) on the s-axis of the st coordinate system. Note that in the example illustrated in  FIG. 6 , coordinates on the t-axis of the st coordinate system are fixed, for simplification of description. 
     The information processing apparatus  30  causes the specification unit  331  to specify the viewpoint positions EP l  and EP r  of the observer  200  on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the setting unit  332  to set the regions E l  and E r  by using the respective viewpoint positions EP l  and EP r  as a reference. Specifically, the information processing apparatus  30  sets, as the region E l , a range from the point (1, t) to the point (3, t) with the point (2, t) of the viewpoint position EP l  of the left eye as a center (a reference). Then, the information processing apparatus  30  sets, as the region E r , a range from the point (5, t) to the point (7, t) with the point (6, t) of the viewpoint position EP r  of the right eye as a center. In this case, the information processing apparatus  30  performs control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the image G from an inside of the regions E l  and E r , and makes it impossible to stereoscopically view the image G from an outside of the regions E l  and E r . 
     For example, the display device  10  causes emission of a ray-of-light group L including rays of light L 1 , L 2 , and L 3 , and a ray-of-light group L including rays of light L 5 , L 6 , and L 7 . The ray of light L 1  is a ray of light that indicates an image G 1  in a case where the observer  200  performs visual recognition from the point (1, t). The ray of light L 2  is a ray of light that indicates an image G 2  in a case where the observer  200  performs visual recognition from the point (2, t). The ray of light L 3  is a ray of light that indicates an image G 3  in a case where the observer  200  performs visual recognition from the point (3, t). The ray of light L 5  is a ray of light that indicates an image G 5  in a case where the observer  200  performs visual recognition from the point (5, t). The ray of light L 6  is a ray of light that indicates an image G 6  in a case where the observer  200  performs visual recognition from the point (6, t). The ray of light L 7  is a ray of light that indicates an image G 7  in a case where the observer  200  performs visual recognition from the point (7, t). Note that the images G 1 , G 2 , G 3 , G 5 , G 6 , and G 7  are respectively images different from each other in the cases of observation from viewpoints different from each other, and are respectively images indicated by different rays of light that have been sent out by the vehicle and the human. 
     In the example illustrated in  FIG. 6 , the observer  200  can stereoscopically view the vehicle and the human, by visually recognizing the image G 2  by using the left eye and visually recognizing the image G 6  by using the right eye. Then, in the observer  200 , it is assumed, for example, that the viewpoint position EP l  of the left eye has moved to the point (1, t), and the viewpoint position EP r  of the right eye has moved to the point (5, t) on the s-axis of the st coordinate system. In this case, the observer  200  can stereoscopically view the vehicle and the human, by visually recognizing the image G 1  by using the left eye and visually recognizing the image G 5  by using the right eye. Then, in the observer  200 , it is assumed, for example, that the viewpoint position EP l  of the left eye has moved to the point (0, t), and the viewpoint position EP r  of the right eye has moved to the point (4, t) on the s-axis of the st coordinate system. In this case, the viewpoint position EP l  of the left eye has moved to an outside of the region E l , and therefore the observer  200  fails to visually recognize a ray-of-light group in which rays of light indicating the image G have been reproduced. Furthermore, the viewpoint position EP r  of the right eye has moved to an outside of the region E r , and therefore the observer  200  fails to visually recognize a ray-of-light group in which rays of light indicating the image G have been reproduced. As a result, it becomes difficult for the observer  200  to stereoscopically view the image G of the display device  10 . 
     Next, an example of a processing procedure of the information processing apparatus  30  according to the embodiment is described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating an example of the processing procedure performed by the information processing apparatus  30  according to the embodiment. The processing procedure illustrated in  FIG. 7  is implemented by the control unit  33  of the information processing apparatus  30  executing a program. 
     As illustrated in  FIG. 7 , the control unit  33  of the information processing apparatus  30  specifies viewpoint positions EP l  and EP r  of the observer  200  on the basis of measurement information of the measurement device  20  (step S 101 ). For example, the control unit  33  acquires measurement information from the measurement device  20  via the communication unit  31 , and specifies the viewpoint positions EP l  and EP r  of the observer  200  from the measurement information. The control unit  33  functions as the specification unit  331  by performing the process of step S 101 . When the process of step S 101  has terminated, the processing of the control unit  33  moves on to step S 102 . 
     The control unit  33  sets regions E l  and E r  that correspond to the left and right eyes  201  of the observer  200 , by using the viewpoint positions EP l  and EP r  as a reference (step S 102 ). For example, the control unit  33  specifies the regions E l  and E r  that correspond to the left and right eyes  201 , by using various known techniques, and stores region information indicating the regions E l  and E r  in the storage  32 . The control unit  33  functions as the setting unit  332  by performing the process of step S 102 . When the process of step S 102  has terminated, the processing of the control unit  33  moves on to step S 103 . 
     The control unit  33  performs control to cause the display device  10  to emit a ray-of-light group that passes through the set regions (step S 103 ). For example, the control unit  33  determines a pixel value of the display device  10  for causing a ray-of-light group to be reproduced to be emitted, on the basis of image data  32 A of the storage  32 , and issues, to the display device  10 , an instruction to conduct a display based on the pixel value. As a result, the display device  10  causes a ray-of-light group to be emitted on the basis of the pixel value indicated by the instruction. When the process of step S 103  has terminated, the processing of the control unit  33  moves on to step S 104 . 
     The control unit  33  specifies viewpoint positions EP l  and EP r  of the observer  200  on the basis of measurement information of the measurement device  20  (step S 104 ). Then, the control unit  33  detects a movement of viewpoint positions on the basis of the specified viewpoint positions EP l  and EP r  and previous viewpoint positions EP l  and EP r  (step S 105 ). For example, in a case where it has been detected that a difference between the specified viewpoint positions EP l  and EP r  and the previous viewpoint positions EP l  and EP r  is an amount of movement of viewpoints that is greater than or equal to a threshold, the control unit  33  detects a movement of the viewpoint positions EP l  and EP r . For example, in a case where the specified viewpoint positions EP l  and EP, are different from the previous viewpoint positions EP l  and EP r , and the specified viewpoint positions EP l  and EP r  are located close to an outside of the regions E l  and E r , the control unit  33  detects a movement of the viewpoint positions EP l  and EP r . The control unit  33  functions as the detection unit  334  by performing the process of step S 105 . The control unit  33  stores, in the storage  32 , a detection result that includes whether or not a movement of viewpoint positions has been detected, viewpoint positions EP l  and EP r  for which a movement has been detected, or the like, and the processing moves on to step S 106 . 
     The control unit  33  determines whether or not a movement of the viewpoint positions EP l  and EP r  has been detected, on the basis of the detection result of step S 105  (step S 106 ). In a case where the control unit  33  has determined that a movement of the viewpoint positions EP l  and EP r  has not been detected (No in step S 106 ), viewpoints of the observer  200  have not moved, and therefore the processing moves on to step S 113  described later. Furthermore, in a case where the control unit  33  has determined that a movement of the viewpoint positions EP l  and EP r  has been detected (Yes in step S 106 ), the processing moves on to step S 107 . 
     The control unit  33  sets regions E l  and E r  that correspond to the left and right eyes  201  of the observer  200 , by using the viewpoint positions EP l  and EP r  after movement as a reference (step S 107 ). The control unit  33  functions as the setting unit  332  by performing the process of step S 107 . When the process of step S 107  has terminated, the processing of the control unit  33  moves on to step S 108 . 
     The control unit  33  simulates a current ray-of-light group that passes through the set regions (step S 108 ). For example, the control unit  33  performs simulation in which transform is performed from a set P of pixel values at which the display device  10  has been caused to conduct a display or updated pixel values to a ray-of-light group, and a correspondence relationship between each ray of light and a pixel of the display device  10  is calculated. In the simulation, a correspondence relationship between each of the rays of light and a pixel of the display device  10  is calculated, for example, according to the method described above for reproducing a ray of light. When the control unit  33  has stored a result of simulation in the storage  32 , the processing moves on to step S 109 . 
     The control unit  33  compares a current ray-of-light group with a virtual ray-of-light group to be reproduced, and calculates an error (step S 109 ). For example, the control unit  33  calculates a virtual ray-of-light group to be reproduced that passes through the regions E l  and E r , on the basis of image data  32 A of the storage  32 . Then, the control unit  33  compares the current ray-of-light group that has been calculated in step S 108  with the virtual ray-of-light group, and calculates an error. For example, the control unit  33  calculates a smaller error as a degree of matching between the current ray-of-light group and the virtual ray-of-light group increases, and the control unit  33  calculates a larger error as one latitude decreases. When the process of step S 109  has terminated, the processing of the control unit  33  moves on to step S 110 . 
     The control unit  33  determines whether or not the error satisfies change conditions (step S 110 ). The change conditions include, for example, conditions, such as a threshold or a range, for determining a change in a ray-of-light group. In a case where the control unit  33  has determined that the error satisfies the change conditions (Yes in step S 110 ), the processing moves on to step S 111 . The control unit  33  updates a pixel value of the display device  10  in such a way that the error becomes smaller (step S 111 ). For example, the control unit  33  determines a pixel value of the display device  10  for causing a ray-of-light group to be reproduced to be emitted, on the basis of the image data  32 A of the storage  32 , and performs updating. When the process of step S 111  has terminated, the processing of the control unit  33  returns to step S 108  that has already been described, and a processing procedure of step S 108  and processes that follow is continued. 
     Furthermore, in a case where the control unit  33  has determined that the error does not satisfy the change conditions (No in step S 110 ), the processing moves on to step S 112 . The control unit  33  reflects pixel values that correspond to the regions E l  and E r  in the display device  10  (step S 112 ). For example, the control unit  33  issues, to the display device  10 , an instruction to conduct a display based on the pixel value updated in step S 111 . As a result, the display device  10  causes a ray-of-light group based on the pixel value indicated by the instruction to be emitted toward the regions E l  and E r  after movement. Then, when the process of step S 112  has terminated, the processing of the control unit  33  moves on to step S 113 . 
     The control unit  33  determines whether or not the processing will be terminated (step S 113 ). For example, in a case where a power source of the display device  10  that has received a request of termination from the observer  200  or the like has been turned off, the control unit  33  determines that the processing will be terminated. In a case where the control unit  33  has terminated that the processing will not be terminated (No in step S 113 ), the processing returns to step S 104  that has already been described, and a processing procedure of step S 104  and processes that follow is continued. Furthermore, in a case where the control unit  33  has determined that the processing will be terminated (Yes in step S 113 ), the processing procedure illustrated in  FIG. 7  is terminated. 
     In the processing procedure illustrated in  FIG. 7 , the control unit  33  functions as the display control unit  333  by performing the processes of step  3103  and step S 108  to step S 112 . 
     [Operation of Display System According to Embodiment] 
     Next, an example of an operation of the display system  100  according to the embodiment is described with reference to  FIG. 8 .  FIG. 8  is a diagram for explaining a relationship among a ray of light, an image, and a viewpoint position in the information processing apparatus  30  according to the embodiment. In the example illustrated in  FIG. 8 , the display device  10  displays the image G illustrated in  FIG. 6 , in Situation SN 1  illustrated in  FIG. 8 , in the observer  200  who observes the display device  10 , a viewpoint position EP l  of the left eye is located at the point (2, t) on the s-axis of the st coordinate system, and a viewpoint position EP r  of the right eye is located at the point (6, t) on the s-axis of the st coordinate system. Note that in the example illustrated in  FIG. 8 , coordinates on the t-axis of the st coordinate system are fixed, for simplification of description. 
     In Situation SN 1 , the information processing apparatus  30  causes the specification unit  331  to specify the viewpoint positions EP l  and EP r  of the observer  200  on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the setting unit  332  to set the regions E l  and E r  by using the respective viewpoint positions EP l  and EP r  as a reference. Specifically, the information processing apparatus  30  sets, as the region E l , a range from the point (1, t) to the point (3, t) with the point (2, t) of the viewpoint position EP l  of the left eye as a center (a reference). Then, the information processing apparatus  30  sets, as the region E r , a range from the point (5, t) to the point (7, t) with the point (6, t) of the viewpoint position EP r  of the right eye as a center. In this case, the information processing apparatus  30  performs control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the image G from an inside of the regions E l  and E r , and makes it impossible to stereoscopically view the image G from an outside of the regions E l  and E r . 
     In Situation SN 1 , the observer  200  is stereoscopically viewing the vehicle and the human, by visually recognizing the image G 2  by using the left eye and visually recognizing the image G 6  by using the right eye. In this state, the observer  200  has moved the viewpoint position EP l  of the left eye from the point (2, t) to the point (3, t), and has moved the viewpoint position EP r  of the right eye from the point (6, t) to the point (7, t). 
     In Situation SN 2 , the observer  200  has moved the viewpoint position EP l  of the left eye and the viewpoint position EP r  of the right eye to the point (3, t) inside the region E l  and the point (7, t) inside the region E r , respectively. In this case, the observer  200  is stereoscopically viewing the vehicle and the human, by visually recognizing the image G 3  that deviates from the point (2, t) by using the left eye and visually recognizing the image G 7  that deviates from the point (6, t) by using the right eye. 
     In Situation SN 2 , the information processing apparatus  30  causes the specification unit  331  to specify that the viewpoint position EP l  of the observer  200  is the point (3, t), and the viewpoint position EP r  is the point (7, t), on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the detection unit  334  to detect that the viewpoint position EP l  of the left eye has moved from the point (2, t) to the point (3, t), and the viewpoint position EP r  of the right eye has moved from the point (6, t) to the point (7, t). The information processing apparatus  30  causes the setting unit  332  to set regions E l ′ and E r ′ by using the respective viewpoint positions EP l  and EP r  as a reference. Specifically, the information processing apparatus  30  sets, as the region E l ′, a range from the point (2, t) to the point (4, t) with the point (3, t) of the viewpoint position EP l  of the left eye as a center (a reference). Then, the information processing apparatus  30  sets, as the region E r ′, a range from the point (6, t) to the point (8, t) with the point (7, t) of the viewpoint position EP r  of the right eye as a center. The information processing apparatus  30  compares a current ray-of-light group L with a virtual ray-of-light group to be reproduced, and calculates an error. The information processing apparatus  30  updates a pixel value of the display device  10  in such a way that the error becomes smaller. 
     In Situation SN 3 , the information processing apparatus  30  reflects the updated pixel value in the display device  10 . Stated another way, the information processing apparatus  30  performs control to cause the display device  10  to emit a ray-of-light group L′ that makes it possible to stereoscopically view the image G from an inside of the regions E l ′ and E r ′, and makes it impossible to stereoscopically view the image G from an outside of the regions E l ′ and E r ′. As a result, the display device  10  emits a ray-of-light group L′ including rays of light L 2 , L 3 , and L 4  of the images G 2 , G 3 , and G 4 , and a ray-of-light group L′ including rays of light L 6 , L 7 , and L 8  of the images G 6 , G 7 , and G 8  toward the regions E l ′ and E r ′ that deviate from the regions E l  and E r . 
     In Situation SN 3 , the observer  200  is stereoscopically viewing the vehicle and the human, by visually recognizing the image G 3  by using the left eye and visually recognizing the image G 7  by using the right eye. As a result, the observer  200  can stereoscopically view the image G by using the ray-of-light groups L and L′ of the display device  10 , even if the viewpoint positions EP l  and EP r  have moved. 
     As described above, the information processing apparatus  30  according to the embodiment causes the specification unit  331  to specify a viewpoint position EP of the observer  200 , and then causes the setting unit  332  to set a region E that makes it possible for the observer  200  to stereoscopically view a three-dimensional object, by using the viewpoint position EP as a reference. The information processing apparatus  30  causes the display control unit  333  to perform control to cause a display device to emit a ray-of-light group that makes it possible to stereoscopically view a three-dimensional object from an inside of the region E set by the setting unit  332 , and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region E. By doing this, it is sufficient if the information processing apparatus  30  causes the display device  10  to emit a ray-of-light group that makes it possible to stereoscopically view a three-dimensional object to the inside of the region E that has been set to correspond to the viewpoint position EP of the observer  200 . As a result, a range in which rays of light of the three-dimensional object will be reproduced can be limited. Therefore, the information processing apparatus  30  can cause the observer  200  to visually recognize a stereoscopic image by using rays of light that have been emitted by the display device  10 , even if a processing load relating to emission of rays of light is reduced. Furthermore, a region E that uses a viewpoint position of the observer  200  as a reference can be set. Even if the viewpoint position slightly deviates, the information processing apparatus  30  can cause the observer  200  to visually recognize a stereoscopic image, by setting the region E according to a movement of the head of the observer  200 . Stated another way, the information processing apparatus  30  can provide the observer  200  with depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally, by using a ray-of-light group that the display device  10  has emitted to a limited region E. Furthermore, the information processing apparatus  30  can achieve a reproduction range having a wide viewing area and a wide depth, even if a display device that can omnidirectionally emit rays of light is not used. 
     Furthermore, the information processing apparatus  30  calculates a pixel value for the display device  10  to emit a ray-of-light group L that passes through an inside of a region E toward the observer  200 , and causes the display control unit  333  to control the display device  10  on the basis of the pixel value. By doing this, a pixel value of the display device  10  only for the region E is calculated, and therefore, the information processing apparatus  30  can control the display device  10  on the basis of the pixel value. As a result, in the information processing apparatus  30 , a processing load of controlling the display device  10  is reduced, and this enables a reduction in a cost of a display system. 
     Furthermore, when the detection unit  334  has detected a movement of a viewpoint position EP of the observer  200 , the information processing apparatus  30  causes the setting unit  332  to set a region E that uses, as a reference, a viewpoint position EP after movement. When the setting unit  332  has set the region E according to a movement of a viewpoint, the information processing apparatus  30  causes the display control unit  333  to perform control to cause a display device to emit a ray-of-light group L that makes it possible to stereoscopically view a three-dimensional object from an inside of the region E. By doing this, the information processing apparatus  30  resets the region E according to detection of a movement of the viewpoint position EP of the observer  200 , and can cause the display device  10  to emit a ray-of-light group L to the region E after movement. As a result, the information processing apparatus  30  can adjust the region E according to a movement of the viewpoint position EP of the observer  200  to adjust a focus of the observer  200 , and can maintain stereoscopic vision. Therefore, a reduction in visibility can be prevented. 
     Furthermore, when the detection unit  334  has detected a movement of the viewpoint position EP from an inside to an outside of the region E, the information processing apparatus  30  causes the setting unit  332  to set the region E by using the viewpoint position EP after movement as a reference. By doing this, when the viewpoint position EP of the observer  200  that is located inside the region E has moved toward an outside of the region E, the information processing apparatus  30  can reset the region E by using the viewpoint position EP after movement as a reference. As a result, even if the viewpoint position EP has moved to the outside of the region E, the information processing apparatus  30  can reset the region E, and can maintain stereoscopic vision performed by the observer  200 . Therefore, a reduction in visibility can be prevented. 
     Furthermore, when the setting unit  332  has set the region E according to a movement of the viewpoint position EP, the information processing apparatus  30  compares a current ray-of-light group L that passes through the region E with a virtual ray-of-light group desired to reproduce a three-dimensional object, and reflects a result of comparison in a ray-of-light group L to be emitted from the display device  10 . By doing this, when the region E has been reset, the information processing apparatus  30  can reflect a result of comparing the current ray-of-light group L with the virtual ray-of-light group in the ray-of-light group L to be emitted from the display device  10 . As a result, it is sufficient if the information processing apparatus  30  controls the display device  10  on the basis of a result of comparing the current ray-of-light group L with the virtual ray-of-light group. This enables a reduction in a processing load relating to control of the ray-of-light group L to be emitted from the display device  10 . 
     Furthermore, the information processing apparatus  30  calculates a current ray-of-light group L that passes through the region E from the display device  10 . In a case where an error between the calculated current ray-of-light group L and a virtual ray-of-light group satisfies change conditions, a ray-of-light group L to be emitted from the display device  10  is changed in such a way that the error becomes smaller. By doing this, the information processing apparatus  30  can change the ray-of-light group L to be emitted from the display device  10  in accordance with the error between the current ray-of-light group L and the virtual ray-of-light group. As a result, it is sufficient if the information processing apparatus  30  controls the display device  10  in accordance with the error between the current ray-of-light group L and the virtual ray-of-light group. This enables a reduction in a processing load relating to control of the ray-of-light group L to be emitted from the display device  10 . 
     The embodiment described above has described an example, and a variety of changes and applications can be made. For example, the information processing apparatus  30  according to the embodiment can set a variety of regions on the basis of a state of a movement of the viewpoint positions EP l  and EP r  of the observer  200 , the number of observers  200 , or the like. 
     [Variation (1) of Embodiment] 
       FIG. 9  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus  30  in Variation (1) of the embodiment. In the example illustrated in  FIG. 9 , the display device  10  displays the image G illustrated in  FIG. 6 , in the example illustrated in  FIG. 9 , in the observer  200  who observes the display device  10 , a viewpoint position EP l  of the left eye is located at the point (2, t) on the s-axis of the st coordinate system, and a viewpoint position EP r  of the right eye is located at the point (6, t) on the s-axis of the st coordinate system. Note that in the example illustrated in  FIG. 9 , coordinates on the t-axis of the st coordinate system are fixed, for simplification of description. 
     The information processing apparatus  30  causes the specification unit  331  to specify the viewpoint positions EP l  and EP r  of the observer  200  on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the setting unit  332  to set, as a region E, a range from the point (1, t) to the point (7, t) by using a center of the viewpoint positions EP l  and EP r  on the s-axis as a reference. Then, the information processing apparatus  30  causes the display control unit  333  to perform control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the image G from an inside of the region E, and makes it impossible to stereoscopically view the image G from an outside of the region E. By doing this, the display device  10  causes emission of a ray-of-light group L including rays of light L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7  toward the region E. 
     In the example illustrated in  FIG. 9 , the observer  200  can stereoscopically view the vehicle and the human, by visually recognizing the image G 2  by using the left eye and visually recognizing the image G 6  by using the right eye. Then, in the observer  200 , it is assumed, for example, that the viewpoint position EP l  of the left eye has moved to the point (1, t), and the viewpoint position EP r  of the right eye has moved to the point (5, t) on the s-axis of the st coordinate system. In this case, the observer  200  can stereoscopically view the vehicle and the human, by visually recognizing the image G 1  by using the left eye and visually recognizing the image G 5  by using the right eye. Then, in the observer  200 , it is assumed, for example, that the viewpoint position EP l  of the left eye has moved to the point (0, t), and the viewpoint position EP r  of the right eye has moved to the point (4, t) on the s-axis of the st coordinate system. In this case, the viewpoint position EP l  of the left eye has moved to an outside of the region E l , and therefore the observer  200  fails to visually recognize a ray-of-light group in which rays of light indicating the image G have been reproduced. Furthermore, the viewpoint position EP r  of the right eye has moved to an outside of the region E r , and therefore the observer  200  fails to visually recognize a ray-of-light group in which rays of light indicating the image G have been reproduced. As a result, it becomes difficult for the observer  200  to stereoscopically view the image G of the display device  10 . 
     As described above, the information processing apparatus  30  according to the embodiment causes the setting unit  332  to set a single region E that includes viewpoint positions EP l  and EP r  of both eyes of the observer  200  that have been specified by the specification unit  331 . By doing this, the information processing apparatus  30  can set a single region E by using the viewpoint positions EP l  and EP r  as a reference. As a result, a ray-of-light group L is reproduced in a single region, and therefore the information processing apparatus  30  can further reduce a processing load. 
     [Variation (2) of Embodiment] 
       FIG. 10  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus  30  in Variation (2) of the embodiment. In the example illustrated in  FIG. 10 , the display device  10  displays the image G illustrated in  FIG. 6 , in the example illustrated in  FIG. 10 , in the observer  200  who observes the display device  10 , a viewpoint position EP l  of the left eye is located at the point (2, t) on the s-axis of the st coordinate system, and a viewpoint position EP r  of the right eye is located at the point (6, t) on the s-axis of the st coordinate system. Note that in the example illustrated in  FIG. 10 , coordinates on the t-axis of the st coordinate system are fixed, for simplification of description. 
     In the example illustrated in  FIG. 10 , the observer  200  is directing the head toward a right-hand side in front of the display device  10 . In this case, the measurement device  20  has output, to the information processing apparatus  30 , measurement information indicating that the left eye of the observer  200  can be measured, but the right eye fails to be measured. 
     The specification unit  331  of the information processing apparatus  30  specifies that the viewpoint position EP l  of the left eye of the observer  200  is the point (2, t), and estimates the viewpoint position EP r  of the right eye on the basis of the point (2, t), and therefore the specification unit  331  specifies that the viewpoint position EP r  is the point (6, t). In this case, the specification unit  331  associates a low precision of specification of the right eye with the viewpoint position EP r , and outputs the viewpoint positions EP l  and EP r  of the observer  200  to the setting unit  332 . 
     The setting unit  332  of the information processing apparatus  30  sets regions E l  and E r  that have sizes different from each other on the basis of the precisions of the viewpoint positions EP l  and EP r  that have been specified by the specification unit  331 . For example, the setting unit  332  sets, as the region E l , a range from the point (1, t) to the point (3, t) with the point (2, t) of the viewpoint position EP l  of the left eye as a center (a reference). Then, the precision of specification of the viewpoint position EP r  of the right eye is low, and therefore the setting unit  332  sets the region E r  of the right eye to be wider than the region E l  of the left eye. Specifically, the setting unit  332  sets, as the region E r , a range from the point (4, t) to the point (8, t) with the point (6, t) of the viewpoint position EP r  of the right eye as a center. 
     The display control unit  333  performs control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the image G from an inside of the regions E l  and E r , and makes it impossible to stereoscopically view the image G from an outside of the regions E l  and E r . Specifically, the display control unit  333  causes the display device  10  to emit a ray-of-light group L including rays of light L 1 , L 2 , and L 3  to the region E l , and emit a ray-of-light group L′ including rays of light L 4 , L 5 , L 6 , L 7 , and L 8  to the regions E l  and E r . As a result, the observer  200  can stereoscopically view the vehicle and the human, by visually recognizing any of the image G 0  to the image G 3  by using the left eye and visually recognizing any of the image G 4  to the image G 8  by using the right eye. 
     As described above, the information processing apparatus  30  according to the embodiment sets regions E l  and E r  that have sizes different from each other on the basis of the precisions of viewpoint positions EP l  and EP r  that have been specified by the specification unit  331 . By doing this, the regions E l  and E r  that have sizes different from each other are set, and therefore the information processing apparatus  30  can cause the display device  10  to emit ray-of-light groups L and L′ that are suitable for the regions E l  and E r . As a result, even if an orientation of the head of the observer  200  changes or moves, the information processing apparatus  30  can adjust a focus of the observer  200 , and can maintain stereoscopic vision. Therefore, a reduction in visibility can be prevented. 
     Note that in a case where the specification precisions of both the viewpoint positions EP l  and EP r  of both eyes of the observer  200  are low, the information processing apparatus  30  in Variation (2) of the embodiment may set both the regions E l  and E r  to be wider than the regions E l  and E r  in a case where the specification institutions are high. Alternatively, the information processing apparatus  30  may set a single region that includes both the viewpoint positions EP l  and EP r . 
     [Variation (3) of Embodiment] 
       FIG. 11  is a diagram for explaining a relationship among a ray of light, a region, and a viewpoint position in an information processing apparatus  30  in Variation (3) of the embodiment. In the example illustrated in  FIG. 11 , the display device  10  displays the image G illustrated in  FIG. 6 , in Situation SN 11  illustrated in  FIG. 11 , the observer  200  is observing the display device  10  in a stationary state. Stated another way, viewpoint positions EP l  and EP r  of the observer  200  are in a stationary state where a range of movement is small. In the observer  200 , the viewpoint position EP l  of the left eye is located at the point (2, t) on the s-axis of the st coordinate system, and the viewpoint position EP r  of the right eye is located at the point (6, t) on the s-axis of the st coordinate system. Note that in the example illustrated in  FIG. 11 , coordinates on the t-axis of the st coordinate system are fixed, for simplification of description. 
     In Situation SN 11 , the information processing apparatus  30  causes the specification unit  331  to specify the viewpoint positions EP l  and EP, of the observer  200  on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the setting unit  332  to set the regions E l  and E, in a state where the observer  200  is in the stationary state, by using the respective viewpoint positions EP l  and EP r  as a reference. Specifically, the information processing apparatus  30  sets, as the region E l , a range from the point (1, t) to the point (3, t) with the point (2, t) of the viewpoint position EP l  of the left eye as a center (a reference). Then, the information processing apparatus  30  sets, as the region E r , a range from the point (5, t) to the point (7, t) with the point (6, t) of the viewpoint position EP r  of the right eye as a center. In this case, the information processing apparatus  30  performs control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the image G from an inside of the regions E l  and E r , and makes it impossible to stereoscopically view the image G from an outside of the regions E l  and E r . 
     In Situation SN 12 , the observer  200  is observing the display device  10  in a moving state. Stated another way, the viewpoint positions EP l  and EP r  of the observer  200  are in a moving state where a range of movement is large. In the observer  200 , the viewpoint position EP l  of the left eye is moving in a rightward direction from the point (2, t) on the s-axis of the st coordinate system, and the viewpoint position EP r  of the right eye is moving in the rightward direction from the point (6, t) on the s-axis of the st coordinate system. 
     In Situation SN 12 , the information processing apparatus  30  causes the specification unit  331  to specify the viewpoint positions EP l  and EP r  in the moving state of the observer  200  on the basis of measurement information of the measurement device  20 . The information processing apparatus  30  causes the setting unit  332  to set regions E l ′ and E r ′ that extend in the rightward direction, by using the respective viewpoint positions EP l  and EP r  at the point in time of specification as a reference. Specifically, a direction of movement of the viewpoint positions EP l  and EP r  is the rightward direction, and therefore the information processing apparatus  30  sets, as the region E l ′, a range from the point (1, t) to the point (4, t) by using the point (2, t) of the viewpoint position EP l  of the left eye a reference. Then, the information processing apparatus  30  sets, as the region E r ′, a range from the point (5, t) to the point (8, t) by using the point (6, t) of the viewpoint position EP r  of the right eye as a reference. Stated another way, the information processing apparatus  30  sets regions E l ′ and E r ′ that have ranges that are wider than the regions E l  and E r  in the stationary state, and have shapes that correspond to a direction of movement. In a case where the viewpoint positions EP l  and EP r  are moving, the information processing apparatus  30  sets regions E l ′ and E r ′ that are wide in the direction of movement and are narrow in a direction opposite to the direction of movement. In this case, the information processing apparatus  30  performs control to cause the display device  10  to emit a ray-of-light group L′ that makes it possible to stereoscopically view the image G from an inside of the regions E l ′ and E r ′, and makes it impossible to stereoscopically view the image G from an outside of the regions E l ′ and E r ′. 
     Thereafter, when the viewpoint positions EP l  and EP r  of the observer  200  has become stationary, the information processing apparatus  30  causes the setting unit  332  to set regions E l  and E r  in a state where the observer  200  is in a stationary state, by using the respective viewpoint positions EP l  and EP r  in the stationary state as a reference, similarly to Situation SN 11 . 
     As described above, in a case where the detection unit  334  has detected a movement of the viewpoint positions EP l  and EP r , the information processing apparatus  30  according to the embodiment causes the setting unit  332  to set regions E l ′ and E r ′ that are larger than regions E l ′ and E r ′ in a case where the viewpoint positions EP l  and EP r  are stationary. By doing this, the information processing apparatus  30  sets regions E l ′ and E r ′ that correspond to a state of movement of the viewpoint positions EP l  and EP r , and can cause the display device  10  to emit a ray-of-light group L′ that is suitable for the regions E l ′ and E r ′. As a result, the information processing apparatus  30  can avoid a situation where stereoscopic vision fails to be performed due to deviation of the viewpoint positions EP l  and EP r  from the regions E l ′ and E r ′ during movement. Therefore, a reduction in visibility can be prevented. 
     The information processing apparatus  30  in Variation (3) of the embodiment may change sizes, shapes, or the like of regions E l  and E r  to be set in accordance with the speed of movement of the viewpoint positions EP l  and EP r . Furthermore, the information processing apparatus  30  may estimate the speed of movement of the viewpoint positions EP l  and EP r . In a case where the speed of movement is high, the information processing apparatus  30  may optimize the region E by lightly weighting a wide range, and may set the region E. In a case where the speed of movement of the viewpoint positions EP l  and EP r  is low, the information processing apparatus  30  may optimize the region E by weighting, at a medium level, a range that is narrower than a range in the case of a high speed of movement. In a case where the viewpoint positions EP l  and EP r  are stationary, the information processing apparatus  30  may optimize the region E by heavily weighting a narrower range. 
     [Variation (4) of Embodiment] 
     A case where an information processing apparatus  30  in Variation (4) of the embodiment reproduces a ray-of-light group for a plurality of observers  200  is described. 
       FIG. 12  is a diagram for explaining a relationship among a ray of light, an image, and a viewpoint position in the information processing apparatus  30  in Variation (4) of the embodiment. In the example illustrated in  FIG. 12 , the display device  10  displays the image G illustrated in  FIG. 6 , in the example illustrated in  FIG. 12 , two observers  200  who line up in an s-axis direction of the st coordinate system are observing the display device  10 . 
     The detection unit  334  of the information processing apparatus  30  detects viewpoint positions EP l  and EP r  of each of the two observers  200 A and  200 B on the basis of measurement information of the measurement device  20 . The setting unit  332  of the information processing apparatus  30  sets four regions ES 1 , ES 2 , ET 1 , and ET 2  that respectively correspond to a plurality of observers  200 . The regions ES 1  and ES 2  respectively correspond to the viewpoint positions EP l  and EP r  of the observer  200 A. The regions ET 1  and ET 2  respectively correspond the viewpoint positions EP l  and EP r  of the observer  200 A. The display control unit  333  of the information processing apparatus  30  performs control to cause the display device  10  to emit ray-of-light groups LS 1 , LS 2 , LT 1 , and LT 2  that make it possible to stereoscopically view a three-dimensional object from an inside of the four regions ES 1 , ES 2 , ET 1 , and ET 2  set by the setting unit  332 , and make it impossible to stereoscopically view the three-dimensional object from an outside of the four regions ES 1 , ES 2 , ET 1 , and ET 2 . As a result, the observer  200 A can stereoscopically view the vehicle and the human by visually recognizing the ray-of-light groups LS 1  and LS 2 . The observer  200 B can stereoscopically view the vehicle and the human by visually recognizing the ray-of-light groups LT 1  and LT 2 . 
     As described above, when the detection unit  334  has detected viewpoint positions EP l  and EP r  of a plurality of observers  200 A and  200 B, the information processing apparatus  30  in Variation (4) of the embodiment causes the setting unit  332  to set four regions ES 1 , ES 2 , ET 1 , and ET 2  that respectively correspond to a plurality of observers  200 . The information processing apparatus  30  performs control to cause the display device  10  to emit ray-of-light groups LS 1 , LS 2 , LT 1 , and LT 2  that correspond to the four regions ES 1 , ES 2 , ET 1 , and ET 2 . By doing this, when the plurality of observers  200 A and  200 B is observing the display device  10 , the information processing apparatus  30  can cause emission of the ray-of-light groups LS 1 , LS 2 , LT 1 , and LT 2  that are suitable for the four regions ES 1 , ES 2 , ET 1 , and ET 2  of the observers  200 A and  200 B. As a result, the information processing apparatus  30  can limit a range in which rays of light of a three-dimensional object will be reproduced. This enables a reduction in a processing load relating to emission of rays of light in comparison with the case of omnidirectionally emitting rays of light. Furthermore, the information processing apparatus  30  can provide the plurality of observers  200 A and  200 B with depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally. 
     Note that a case where the information processing apparatus  30  in Variation (4) of the embodiment sets four regions ES 1 , ES 2 , ET 1 , and ET 2  for a plurality of observers  200 A and  200 B has been described, but this is not restrictive. For example, the information processing apparatus  30  may set a single region for each of the plurality of observers  200 A and  200 B, or may set a single region that corresponds to both the plurality of observers  200 A and  200 B. 
     Note that Variation (1) to Variation (4) of the embodiment may be applied to an information processing apparatus  30  in another variation, or may be combined. 
     [Hardware Configuration] 
     The information processing apparatuses  30  according to the first to fourth embodiments described above may be implemented, for example, by a computer  1000  having a configuration illustrated in  FIG. 13 . Description is provided below by using the information processing apparatus  30  according to the embodiment as an example.  FIG. 13  is a hardware configuration diagram illustrating an example of a computer  1000  that achieves functions of the information processing apparatus  30 . The computer  1000  includes, a CPU  1100 , a RAM  1200 , a read only memory (ROM)  1300 , a hard disk drive (HDD)  1400 , a communication interface  1500 , and an input/output interface  1600 . Respective units of the computer  1000  are connected by a bus  1050 . 
     The CPU  1100  operates on the basis of a program stored in the ROM  1300  or the HDD  1400 , and controls respective units. For example, the CPU  1100  develops the program stored in the ROM  1300  or the HDD  1400  in the RAM  1200 , and performs processing that corresponds to each type of program. 
     The ROM  1300  stores a boot program, such as a basic input output system (BIOS), that is executed by the CPU  1100  at the time of activating the computer  1000 , a program that depends on hardware of the computer  1000 , or the like. 
     The HDD  1400  is a computer-readable recording medium that non-transitorily records a program executed by the CPU  1100 , data that is used by the program, and the like. Specifically, the HDD  1400  is a recording medium that records an information processing program according to the present disclosure that serves as an example of a program data  1450 . 
     The communication interface  1500  is an interface for the computer  1000  to be connected to an external network  1550  (for example, the Internet). For example, the CPU  1100  receives data from another device or transmits data generated by the CPU  1100  to another device via the communication interface  1500 . 
     The input/output interface  1600  is an interface for connecting an input/output device  1650  and the computer  1000 . For example, the CPU  1100  receives data from an input device such as a keyboard or a mouse via the input/output interface  1600 . Furthermore, the CPU  1100  transmits data to an output device such as a display, a speaker, or a printer via the input/output interface  1600 . Furthermore, the input/output interface  1600  may function as a medium interface that reads a program or the like that has been recorded in a predetermined recording medium (a medium). The medium is, for example, an optical recording medium such as a digital versatile disc (DVD), a magneto-optical recording medium such as a magneto-optical disk (MO), a tape medium, a magnetic recording medium, a semiconductor memory, or the like. 
     For example, in a case where the computer  1000  functions as the information processing apparatus  30  according to the embodiment, the CPU  1100  of the computer  1000  achieves functions of the specification unit  331 , the setting unit  332 , the display control unit  333 , the detection unit  334 , and the like by executing a program loaded into the RAM  1200 . Furthermore, a program according to the present disclosure or data in the storage  32  is stored in the HDD  1400 . Note that the CPU  1100  reads the program data  1450  from the HDD  1400 , and executes the program data  1450 . However, in another example, these programs may be acquired from another device via the external network  1550 . 
     A preferred embodiment of the present disclosure has been described in detail above with reference to the attached drawings, but the technical scope of the present disclosure is not limited to the examples described above. It is obvious that a person with ordinary skill in the art to which the present disclosure pertains could conceive a variety of variations or modifications without departing from a technical idea described in the claims, and it should be understood that the variations or modifications fall under the technical scope of the present disclosure. 
     Furthermore, effects described herein are only exemplary or illustrative, and are not restrictive. Stated another way, a technology according to the present disclosure can exhibit other effects that would be obvious to those skilled in the art from the description provided herein in addition to the effects described above or instead of the effects described above. 
     Furthermore, a program for causing hardware, such as a CPU, a ROM, or a RAM, that is incorporated into a computer to achieve functions that are similar to a configuration that the information processing apparatus  30  has can also be generated, and a computer-readable recording medium that records the program can also be provided. 
     Furthermore, respective steps in processing performed by the information processing apparatus  30  herein do not always need to be performed in time series in the order described in a flowchart. For example, the respective steps in the processing performed by the information processing apparatus  30  may be performed in an order that is different from the order described in the flowchart, or may be performed in parallel. 
     Furthermore, the information processing apparatus  30  of the present embodiment can cause an observer  200  to perceive depth feeling of the display device  10 , but this is not restrictive. For example, the information processing apparatus  30  can reproduce a light field around a viewpoint of an observer  200 , and therefore the information processing apparatus  30  can also be used to correct eyesight of the observer  200 . In this case, the information processing apparatus  30  has stored eyesight information relating to eyesight of the observer  200  in the storage  32  or the like, and the display control unit  333  controls the display device  10  to emit a ray-of-light group corrected on the basis of the eyesight information to the regions described above. A target for eyesight correction includes, for example, short-sightedness, far-sightedness, astigmatism, or the like. 
     Furthermore, in the present embodiment, a case where the information processing apparatus  30  is provided outside the display device  10  has been described, but this is not restrictive. For example, the information processing apparatus  30  may be incorporated into the display device  10  or the measurement device  20 . For example, the information processing apparatus  30  may be implemented by an information processing server or the like that is communicable with the display device  10 . 
     Furthermore, the information processing apparatus  30  according to the present embodiment can be used, for example, in a head-mounted display (HMD). For example, the information processing apparatus  30  can achieve an HMD that can adjust a focus, by using the display device  10  in a display panel of the HMD and being combined with line-of-sight tracking (eye tracking). 
     (Effects) 
     An information processing apparatus  30  includes: a specification unit  331  that specifies a viewpoint position of an observer of a display device that reproduces rays of light that have been sent out by a three-dimensional object; a setting unit  332  that sets a region E that makes it possible for an observer  200  to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified by the specification unit  331 ; and a display control unit  333  that performs control to cause a display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the three-dimensional object from an inside of the region E that has been set by the setting unit  332 , and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     By doing this, it is sufficient if the information processing apparatus  30  causes the display device  10  to emit a ray-of-light group that makes it possible to stereoscopically view a three-dimensional object to the inside of the region E that has been set to correspond to a viewpoint position EP of the observer  200 . As a result, a range in which rays of light of the three-dimensional object will be reproduced can be limited. Therefore, the information processing apparatus  30  can cause the observer  200  to visually recognize a stereoscopic image by using rays of light that have been emitted by the display device  10 , even if a processing load relating to emission of rays of light is reduced. Furthermore, a region E that uses a viewpoint position of the observer  200  as a reference can be set. Even if the viewpoint position slightly deviates, the information processing apparatus  30  can cause the observer  200  to visually recognize a stereoscopic image, by setting the region E according to a movement of the head of the observer  200 . Stated another way, the information processing apparatus  30  can provide the observer  200  with depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally, by using a ray-of-light group that the display device  10  has emitted to a limited region E. Furthermore, the information processing apparatus  30  can achieve a reproduction range having a wide viewing area and a wide depth, even if a display device that can omnidirectionally emit rays of light is not used. 
     In the information processing apparatus  30 , the display control unit  333  calculates a pixel value for the display device  10  to emit a ray-of-light group L that passes through the inside of the region E toward the observer  200 , and controls the display device  10  on the basis of the pixel value. 
     By doing this, a pixel value of the display device  10  only for the region E is calculated, and therefore, the information processing apparatus  30  can control the display device  10  on the basis of the pixel value. As a result, in the information processing apparatus  30 , a processing load of controlling the display device  10  is reduced, and this enables a reduction in a cost of a display system  100 . 
     The information processing apparatus  30  further includes a detection unit  334  that detects a movement of the viewpoint position of the observer  200 . When the detection unit  334  has detected the movement of the viewpoint position, the setting unit  332  sets the region E by using the viewpoint position after movement as a reference. When the region E according to a movement of a viewpoint has been set by the setting unit  332 , the display control unit  333  performs control to cause the display device  10  to emit the ray-of-light group L that makes it possible to stereoscopically view the three-dimensional object from the inside of the region E. 
     By doing this, the information processing apparatus  30  resets the region E according to detection of the movement of the viewpoint position of the observer  200 , and can cause the display device  10  to emit the ray-of-light group L to the region E after movement. As a result, the information processing apparatus  30  can adjust the region E according to a movement of the viewpoint position of the observer  200  to adjust a focus of the observer  200 , and can maintain stereoscopic vision. Therefore, a reduction in visibility can be prevented. 
     In the information processing apparatus  30 , when the detection unit  334  has detected a movement of the viewpoint position from the inside to the outside of the region E, the setting unit  332  sets the region E by using a viewpoint position after movement as a reference. 
     By doing this, when the viewpoint position of the observer  200  that is located inside the region E has moved toward the outside of the region E, the information processing apparatus  30  can reset the region E by using the viewpoint position EP after movement as a reference. As a result, even if the viewpoint position has moved to the outside of the region E, the information processing apparatus  30  can reset the region E, and can maintain stereoscopic vision performed by the observer  200 . Therefore, a reduction in visibility can be prevented. 
     In the information processing apparatus  30 , when the region E according to a movement of the viewpoint position has been set by the setting unit  332 , the display control unit  333  compares a current ray-of-light group L that passes through the region E with a virtual ray-of-light group desired to reproduce the three-dimensional object, and reflects a result of comparison in a ray-of-light group L to be emitted from the display device  10 . 
     By doing this, when the region E has been reset, the information processing apparatus  30  can reflect a result of comparing the current ray-of-light group L with the virtual ray-of-light group in the ray-of-light group L to be emitted from the display device  10 . As a result, it is sufficient if the information processing apparatus  30  controls the display device  10  on the basis of a result of comparing the current ray-of-light group L with the virtual ray-of-light group. This enables a reduction in a processing load relating to control of the ray-of-light group L to be emitted from the display device  10 . 
     In the information processing apparatus  30 , the display control unit  333  calculates a current ray-of-light group L that passes through the region E from the display device  10 . In a case where an error between the calculated current ray-of-light group L and the virtual ray-of-light group satisfies change conditions, a ray-of-light group L to be emitted from the display device  10  is changed in such a way that the error becomes smaller. 
     By doing this, the information processing apparatus  30  can change the ray-of-light group L to be emitted from the display device  10  in accordance with the error between the current ray-of-light group L and the virtual ray-of-light group. As a result, it is sufficient if the information processing apparatus  30  controls the display device  10  in accordance with the error between the current ray-of-light group L and the virtual ray-of-light group. This enables a reduction in a processing load relating to control of the ray-of-light group L to be emitted from the display device  10 . 
     In the information processing apparatus  30 , the setting unit  332  sets a single region E that includes viewpoint positions of both eyes of the observer  200  that have been specified by the specification unit  331 . 
     By doing this, the information processing apparatus  30  can set a single region E by using the viewpoint positions of both observers  200  as a reference. As a result, a ray-of-light group L is reproduced in a single region, and therefore the information processing apparatus  30  can further reduce a processing load. 
     In the information processing apparatus  30 , the setting unit  332  sets regions E that have sizes different from each other on the basis of precisions of the viewpoint positions that have been specified by the specification unit  331 . 
     By doing this, the information processing apparatus  30  enables the display device  10  to emit ray-of-light groups L that are suitable for the regions E, by setting the regions E that have sizes different from each other. As a result, even if an orientation of the head of the observer  200  changes or moves, the information processing apparatus  30  can adjust a focus of the observer  200 , and can maintain stereoscopic vision. Therefore, a reduction in visibility can be prevented. 
     In the information processing apparatus  30 , in a case where a movement of the viewpoint positions has been detected by the detection unit  334 , the setting unit  332  sets a region E that is larger than a region E in a case where the viewpoint positions are stationary. 
     By doing this, the information processing apparatus  30  sets a region E according to a state of movement of the viewpoint positions of the observer  200 , and can cause the display device  10  to emit a ray-of-light group L that is suitable for the region E. As a result, the information processing apparatus  30  can avoid a situation where stereoscopic vision fails to be performed due to deviation of the viewpoint positions from the region E during movement, and a reduction in visibility can be prevented. 
     In the information processing apparatus  30 , the detection unit  334  detects viewpoint positions of a plurality of observers  200 , the setting unit  332  sets a plurality of regions E that respectively correspond to the plurality of observers  200 , and the display control unit  333  performs control to cause a display device to emit a ray-of-light group L that makes it possible to stereoscopically view a three-dimensional object from an inside of the plurality of regions E that has been set by the setting unit  332 , and makes it impossible to stereoscopically view the three-dimensional object from an outside of the plurality of regions E. 
     By doing this, when the plurality of observers  200  is observing the display device  10 , the information processing apparatus  30  can cause emission of a ray-of-light group L that is suitable for the plurality of regions E of the plurality of observers  200 . As a result, the information processing apparatus  30  can limit a range in which rays of light of a three-dimensional object will be reproduced. This enables a reduction in a processing load relating to emission of rays of light in comparison with the case of omnidirectionally emitting rays of light. Furthermore, the information processing apparatus  30  can provide the plurality of observers  200  with depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally. 
     An information processing method of an information processing apparatus  30  is an information processing method performed by an information processing apparatus  30  that controls a display device  10  that reproduces rays of light that have been sent out by a three-dimensional object, and the information processing method includes: a step of specifying a viewpoint position of an observer  200  of the display device  10 ; a step of setting a region E that makes it possible for the observer  200  to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and a step of performing control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the three-dimensional object from an inside of the region E that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region E. 
     By doing this, in the information processing method, it is sufficient if the information processing apparatus  30  causes the display device  10  to emit a crossing-line group that makes it possible to stereoscopically view the three-dimensional object to the inside of the region E that has been set to correspond to a viewpoint position EP of the observer  200 . As a result, in the information processing method, a range in which rays of light of a three-dimensional object will be reproduced can be limited. Therefore, even if a processing load relating to emission of rays of light is reduced, the observer  200  is enabled to visually recognize a stereoscopic image by using rays of light that have been emitted by the display device  10 . Furthermore, in the information processing method, a region E that uses a viewpoint position of the observer  200  as a reference can be set. Even if the viewpoint position slightly deviates, the observer  200  is enabled to visually recognize a stereoscopic image, by setting a region E according to a movement of the head of the observer  200 . Stated another way, in the information processing method, depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally can be provided to the observer  200 , by using a ray-of-light group that the display device  10  has emitted to the limited region E. Furthermore, in the information processing method, a reproduction range having a wide viewing area and a wide depth can be achieved, even if a display device that can omnidirectionally emit rays of light is not used. 
     A program causes an information processing apparatus  30  that controls a display device  10  that reproduces rays of light that have been sent out by a three-dimensional object to perform: a step of specifying a viewpoint position of an observer  200  of the display device  10 ; a step of setting a region E that makes it possible for the observer  200  to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and a step of performing control to cause the display device  10  to emit a ray-of-light group L that makes it possible to stereoscopically view the three-dimensional object from an inside of the region E that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region E. 
     By doing this, the program enables the information processing apparatus  30  to limit a range in which rays of light of a three-dimensional object will be reproduced. Therefore, even if a processing load relating to emission of rays of light of the information processing apparatus  30  is reduced, the observer  200  is enabled to visually recognize a stereoscopic image by using rays of light that have been emitted by the display device  10 . Furthermore, the program enables the information processing apparatus  30  to set a region E that uses a viewpoint position of the observer  200  as a reference. Even if the viewpoint position slightly deviates, the observer  200  is enabled to visually recognize a stereoscopic image, by setting a region E according to a movement of the head of the observer  200 . Stated another way, the program can provide the observer  200  with depth perception that is similar to depth perception in a case where rays of light are emitted omnidirectionally, by using a ray-of-light group that the display device  10  has emitted to a limited region E. Furthermore, the program enables a reproduction range having a wide viewing area and a wide depth to be achieved, even if a display device that can omnidirectionally emit rays of light is not used. 
     Note that the configuration described below also falls under the technical scope of the present disclosure. 
     (1) 
     An information processing apparatus including: 
     a specification unit that specifies a viewpoint position of an observer of a display device that reproduces rays of light that have been sent out by a three-dimensional object; 
     a setting unit that sets a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified by the specification unit; and 
     a display control unit that performs control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set by the setting unit, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     (2) 
     The information processing apparatus according to (1) described above, 
     in which the display control unit calculates a pixel value for the display device to emit the ray-of-light group that passes through the inside of the region toward the observer, and controls the display device on the basis of the pixel value. 
     (3) 
     The information processing apparatus according to (1) or (2) described above, further including: 
     a detection unit that detects a movement of the viewpoint position of the observer, 
     wherein, when the detection unit has detected the movement of the viewpoint position, the setting unit sets the region by using the viewpoint position after the movement as a reference, and 
     when the region according to the viewpoint position after the movement has been set by the setting unit, the display control unit performs control to cause the display device to emit the ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from the inside of the region. 
     (4) 
     The information processing apparatus according to (3) described above, 
     in which, when the detection unit has detected a movement of the viewpoint position from the inside to the outside of the region, the setting unit sets the region by using, as a reference, the viewpoint position after the movement. 
     (5) 
     The information processing apparatus according to (3) or (4) described above, 
     in which, when the region according to the movement of the viewpoint position has been set by the setting unit, the display control unit compares a current ray-of-light group that passes through the region with a virtual ray-of-light group desired to reproduce the three-dimensional object, and reflects a result of comparison in the ray-of-light group to be emitted from the display device. 
     (6) 
     The information processing apparatus according to (5) described above, 
     in which the display control unit calculates the current ray-of-light group that passes through the region from the display device, and in a case where an error between the current ray-of-light group that has been calculated and the virtual ray-of-light group satisfies change conditions, the ray-of-light group to be emitted from the display device is changed in such a way that the error becomes smaller. 
     (7) 
     The information processing apparatus according to any of (1) to (6) described above, 
     in which the setting unit sets a single region that includes a plurality of the viewpoint positions of both eyes of the observer, the plurality of the viewpoint positions having been specified by the specification unit. 
     (8) 
     The information processing apparatus according to any of (1) to (7) described above, 
     in which the setting unit sets a plurality of the regions having sizes different from each other on the basis of a precision of the viewpoint position that has been specified by the specification unit. 
     (9) 
     The information processing apparatus according to (3) described above, 
     in which, in a case where the movement of the viewpoint position has been detected by the detection unit, the setting unit sets the region that is larger than the region in a case where the viewpoint position is stationary. 
     (10) 
     The information processing apparatus according to (3) described above, 
     in which the detection unit detects the viewpoint positions of a plurality of the observers, 
     the setting unit sets a plurality of the regions each of which corresponds to each of the plurality of the observers, and 
     the display control unit performs control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the plurality of the regions that has been set by the setting unit, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the plurality of the regions. 
     (11) 
     An information processing method performed by an information processing apparatus that controls a display device that reproduces rays of light that have been sent out by a three-dimensional object, the information processing method including: 
     a step of specifying a viewpoint position of an observer of the display device; 
     a step of setting a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and 
     a step of performing control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     (12) 
     A program that causes an information processing apparatus that controls a display device that reproduces rays of light that have been sent out by a three-dimensional object to perform: 
     a step of specifying a viewpoint position of an observer of the display device; 
     a step of setting a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified; and 
     a step of performing control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     (13) 
     A display system including: 
     a display device that reproduces rays of light that have been sent out by a three-dimensional object; and 
     an information processing apparatus that controls the display device, 
     in which the information processing apparatus includes: 
     a specification unit that specifies a viewpoint position of an observer of the display device; 
     a setting unit that sets a region that makes it possible for the observer to stereoscopically view the three-dimensional object, by using, as a reference, the viewpoint position that has been specified by the specification unit; and 
     a display control unit that performs control to cause the display device to emit a ray-of-light group that makes it possible to stereoscopically view the three-dimensional object from an inside of the region that has been set by the setting unit, and makes it impossible to stereoscopically view the three-dimensional object from an outside of the region. 
     REFERENCE SIGNS LIST 
     
         
           10  Display device 
           11  Liquid crystal panel 
           20  Measurement device 
           30  Information processing apparatus 
           31  Communication unit 
           32  Storage 
           33  Control unit 
           200  Observer 
           331  Specification unit 
           332  Setting unit 
           333  Display control unit 
           334  Detection unit 
         E Region 
         EP Viewpoint position 
         L Ray-of-light group