Patent Publication Number: US-2015070477-A1

Title: Image processing device, image processing method, and program

Description:
TECHNICAL FIELD 
     The present disclosure relates to an image processing device, an image processing method, and a program. 
     BACKGROUND ART 
     Recently, a 3D display device which can cause a user to perceive a stereoscopic image by displaying a left-eye image (L image) and a right-eye image (R image) has been distributed. By using the 3D display device, while the user can obtain an effect that realistic sensation of the user is enhanced, the user easily gets eyestrain. Although there are diverse factors of the eyestrain, the factors include crosstalk occurring from a mixture of L images and R images, and flicker occurring from lack of a refresh rate of a liquid crystal shutter, as examples. Accordingly, a frame rate of a liquid crystal has been improved, and shutter grasses have been improved. However, a matter of the eyestrain has not solved enough. 
     Moreover, it has been considered that occurrence of the eyestrain depends not only on display types and equipment, but also individual characteristics of a user who views video and a way the user views the video. According to such situation, a guideline for viewing ways and equipment has been issued. For example, 3D Consortium promoting progress of 3D industry by public and private cooperation made a guideline for viewing stereoscopic video and aims to achieve comfortable stereoscopic-image viewing. 
     In addition, in a case where display is extruded excessively or in a case where change of disparity difference is wide, fatigue of the user becomes severe. From such a standpoint, a technology of comfortable 3D display has been investigated. For example, Patent Literature 1 discloses a disparity conversion device configured to adjust disparity between an L image and an R image by shifting the L image and/or the R image in a horizontal direction. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2011-55022A 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, it has been possible to adjust a position in a depth direction in an image having a large extrusion amount by shifting the L image and/or the R image in a horizontal direction. However, when the position in the depth direction in the image having a large extrusion amount is adjusted, a relative relation with another image at a position in the depth direction is changed. 
     Accordingly, the present disclosure proposes a novel and improved image processing device, image processing method, and program capable of decreasing fatigue of a user without damaging a relation of a sense of depth of a plurality of stereoscopically-displayed frames. 
     Solution to Problem 
     According to the present disclosure, there is provided an image processing device including a determination unit configured to determine whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition, and an adjustment unit configured to adjust the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where the determination unit determines that the difference satisfies the threshold condition. The adjustment unit adjusts the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     According to the present disclosure, there is provided an image processing method including determining whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition, adjusting the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where it is determined that the difference satisfies the threshold condition, and adjusting the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     According to the present disclosure, there is provided a program causing a computer to function as a determination unit configured to determine whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition, and an adjustment unit configured to adjust the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where the determination unit determines that the difference satisfies the threshold condition. The adjustment unit adjusts the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     Advantageous Effects of Invention 
     As described above, according to the present disclosure, fatigue of a user can be decreased without damaging a relation of a sense of depth of a plurality of stereoscopically-displayed frames. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram showing a configuration of a display system according to an embodiment of the present disclosure. 
         FIG. 2  is an explanatory diagram showing a configuration of a display device according to a first embodiment. 
         FIG. 3  is an explanatory diagram showing a way of calculating extrusion amount of an image. 
         FIG. 4  is an explanatory diagram showing a relation between a threshold th and viewing time. 
         FIG. 5  is an explanatory diagram showing an example of adjusting perceived display positions of 3D video. 
         FIG. 6  is an explanatory diagram showing that movement amount of a plurality of objects in a depth direction are a same, the plurality of objects being included in a single frame. 
         FIG. 7  is an explanatory diagram showing that movement amount of respective objects in a depth direction are a same, the respective objects corresponding to a plurality of frames. 
         FIG. 8  is a flowchart showing operation of a display device according to the first embodiment. 
         FIG. 9  is an explanatory diagram showing a specific example of a notification window. 
         FIG. 10  is an explanatory diagram showing another notification example of presence or absence of adjustment. 
         FIG. 11  is an explanatory diagram showing a configuration of a display device according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the appended drawings. Note that, in this specification and the drawings, elements that have substantially the same function and structure are denoted with the same reference signs, and repeated explanation is omitted. 
     Also, in the present specification and the drawings, different letters are sometimes suffixed to the same reference signs to distinguish a plurality of constituent elements having substantially the same functional configuration from each other. However, when it is not necessary to distinguish the plurality of constituent elements having substantially the same functional configuration, only the same reference signs are given. 
     Note that the present disclosure will be explained in the following order. 
     1. Fundamental Configuration of Display System 
     2. First Embodiment 
     2-1. Configuration of Display Device according to First Embodiment
 
2-2. Operation of Display Device according to First Embodiment
 
     2-3. Supplemental Remarks 
     3. Second Embodiment 
     4. Conclusion 
     1. Fundamental Configuration of Display System 
     A technology according to the present disclosure may be performed in various forms as described in detail in “2. First Embodiment” to “3. Second Embodiment” as examples. A display device  100  which is according to each embodiment and which has functions as a display control device includes: 
     A. a determination unit (adjustment-necessity determination unit  124 ) configured to determine whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition; and 
     B. an adjustment unit (display control unit  132 ) configured to adjust the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where the determination unit determines that the difference satisfies the threshold condition. 
     The adjustment unit (display control unit  132 ) adjusts the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     First, with reference to  FIG. 1  and  FIG. 2 , a fundamental configuration of a display system which is common to each embodiment will be described as follows. 
       FIG. 1  is an explanatory diagram showing a configuration of a display system according to an embodiment of the present disclosure. As shown in  FIG. 1 , the display system according to the embodiment of the present disclosure includes a display device  100  and shutter glasses  200 . 
     As shown in  FIG. 1 , the display device  100  includes a display unit  110  on which an image is displayed. The display device  100  can cause a user to perceive a stereoscopic image (3D image) by displaying a left-eye image (L image) and a right-eye image (R image) on the display unit  110 . In addition, the display device  100  includes an imaging unit  114  for imaging a range from which the display device  100  can be viewed. By analyzing a captured image obtained by the imaging unit  114 , it is possible to recognize a user who views the display device  100 . 
     The shutter glasses  200  include a right-eye image transparent unit  212  and a left-eye image transparent unit  214  which are composed of a liquid crystal shutter, for example. The shutter glasses  200  performs open/close operation on the right-eye image transparent unit  212  and the left-eye image transparent unit  214  in response to a signal transmitted from the display device  100 . The user can perceive, as a 3D image, the left-eye image and the right-eye image that are displayed on the display unit  110  by seeing light radiated from the display unit  110  through the right-eye image transparent unit  212  and the left-eye image transparent unit  214  of the shutter glasses  200 . 
       FIG. 1  shows the display device  100  as an example of the image processing device. However, the image processing device is not limited thereto. For example, the image processing device may be an information processing apparatus such as a personal computer (PC), a household video processing apparatus (a DVD recorder, a video cassette recorder, and the like), a personal digital assistant (PDA), a household game device, a cellular phone, a portable video processing apparatus, or a portable game device. Alternatively, the display control device may be a display installed at a theater or in a public space. 
     In addition, the present specification explains a control method using shutter operation so as to a left-eye image is perceived by a left eye and a right-eye image is perceived by a right eye. However, the control method is not limited thereto. For example, similar effect can be obtained by using a polarization filter for the left eye and a polarization filter for the right eye. 
     (Background) 
     However, in a general display device having a 3D display function, fatigue of a user becomes severe in a case where display is extruded excessively or in a case where change of disparity is wide. From such a standpoint, a technology of comfortable 3D display has been investigated. For example, the technology of adjusting disparity between an L image and an R image by shifting the L image and/or the R image in a horizontal direction has been known. Moreover, it has been considered that occurrence of the eyestrain depends not only on display types and equipment, but also individual characteristics of a user who views video and a way the user views the video. According to such situation, a guideline for viewing ways and equipment has been issued. For example, 3D Consortium promoting progress of 3D industry by public and private cooperation made a guideline for viewing stereoscopic video and aims to achieve comfortable stereoscopic-image viewing. 
     As described above, by adjusting disparity or by devising viewing ways, it is possible to improve a certain amount of fatigue of the user. However, even if the disparity has been adjusted and the viewing ways have been devised, the fatigue of the user increases as time for viewing 3D-displayed video becomes longer. In addition, when the position in the depth direction in the image having a large extrusion amount is adjusted, a relative relation with another image at a position in the depth direction is changed. 
     Accordingly, with the above circumstance taken into point of view, the display device  100  according to respective embodiments of the present disclosure has been achieved. The display device  100  according to the respective embodiments of the present disclosure can decrease fatigue of a user without damaging a relation of a sense of depth of a plurality of stereoscopically-displayed frames. Hereinafter, there is subsequently and specifically described the display device  100  according to the respective embodiments of the present disclosure. 
     2. First Embodiment 
     2-1. Configuration of Display Device According to First Embodiment 
       FIG. 2  is an explanatory diagram showing a configuration of the display device  100  according to a first embodiment. As shown in  FIG. 2 , the display device  100  according to the first embodiment includes a display unit  110 , an imaging unit  114 , an extrusion-amount calculation unit  120 , an adjustment-necessity determination unit  124 , a setting unit  128 , a display control unit  132 , a shutter control unit  136 , and an infrared communication unit  140 . Since the description is made in “1. Fundamental Configuration of Display System,” the repeated descriptions of the display unit  110  and the imaging unit  114  will be omitted hereafter. 
     (Extrusion-Amount Calculation Unit) 
     To the extrusion-amount calculation unit  120 , a 3D video signal including image data composed of L image data and R image data is input. The 3D video signal may be a received video signal or a video signal read out from a storage medium. The extrusion-amount calculation unit  120  evaluates difference between the L image data and the R image data that are included in the 3D video signal. For example, the extrusion-amount calculation unit  120  calculates extrusion amount from the display unit  110  to a position at which the user perceives that an image exists when 3D display is performed on the basis of the L image data and the R image data. With reference to  FIG. 3 , a specific example of a way of calculating the extrusion amount will be explained hereinafter. 
       FIG. 3  is an explanatory diagram showing a way of calculating extrusion amount of an image. As shown in  FIG. 3 , when an R image and an L image are displayed at different positions on the display unit  110 , the user perceives that an image exists at an intersection (hereinafter, perception position P) between a line connecting the right eye and the R image and a line connecting the left eye and the L image. 
     By using an interval E between the left eye and the right eye of the user, a distance D between the user and the display unit  110 , and difference X between the L image and the R image that are shown in  FIG. 3 , a distance between the perception position P and the display unit  110 , that is, extrusion amount S of the perception position P from the display unit  110  is calculated in accordance with the following numerical formula, for example. 
       Extrusion Amount  S=D×X /( X+E ) 
     Note that, the interval E between the left eye and the right eye of the user and the distance D between the user and the display unit  110  can be estimated from a captured image acquired by the imaging unit  114 . Alternatively, the interval E between the left eye and the right eye of the user and the distance D between the user and the display unit  110  may be values set in advance. 
     Note that, the difference X between the L image and the R image can be identified using diverse ways. For example, the extrusion-amount calculation unit  120  can identify the difference X by using a stereo matching method of extracting feature points in the L image and the R image and measuring gaps between the feature points. More specifically, the stereo matching method includes a feature-based method and an area-based method. The feature-based method extracts edges in an image on the basis of brightness values, extracts edge strengths and edge directions as feature points, and measures gaps between similar edge points. The area-based method analyses a degree of matching of patterns for every certain image area, and measures gaps between similar image areas. 
     Note that, the example in which the extrusion amount is the distance between the perception point P and the display unit  110  has been explained in the above description. However, the present embodiment is not limited thereto. For example, an angle of convergence θ shown in  FIG. 3  may be used as the extrusion amount. Note that, the extrusion-amount calculation unit  120  may divide a 3D video signal for unit time and may calculate an average of the extrusion amount in a section. 
     (Adjustment-Necessity Determination Unit) 
     When 3D display is performed on the basis of a 3D video signal, the adjustment-necessity determination unit  124  determines whether or not convergence movement which is uncomfortable for the user occurs. In a case where it is determined that the uncomfortable convergence movement occurs, the adjustment-necessity determination unit  124  instructs the display control unit  132  to adjust extrusion amount. 
     More specifically, when the 3D display is performed, the adjustment-necessity determination unit  124  determines whether or not the uncomfortable convergence movement occurs on the basis of extrusion amount S calculated by the extrusion-amount calculation unit  120 . Here, it is considered that stereoscopic effect increases as the extrusion amount S calculated by the extrusion-amount calculation unit  120  becomes bigger. 
     Moreover, when viewing stereoscopic video, the convergence movement (cross-eyed state) occurs on the eyes. Accordingly, the user can obtain a sense of depth. However, in a case where the stereoscopic video is extremely extruded, uncomfortable convergence movement which does not occur in a usual life circumstance occurs. It has been considered that such uncomfortable convergence movement is one of causes of eyestrain. 
     Accordingly, in a case where the extrusion amount S calculated by the extrusion-amount calculation unit  120  is greater than or equals to a threshold th set by the setting unit  128  described later, the adjustment-necessity determination unit  124  instructs the display control unit  132  to adjust the extrusion amount. 
     (Setting Unit) 
     The setting unit  128  sets the threshold th used by the adjustment-necessity determination unit  124  for determining a display type. For example, in a case where viewing time of the user becomes longer, it is considered that the user accumulates fatigue. Accordingly, the setting unit  128  may lower the threshold th as the viewing time of the user becomes longer. In such a configuration, it is possible to increase frequency of extrusion-amount adjustment in a case where the viewing time of the user becomes longer. With reference to  FIG. 4 , specific examples will be given as follows. 
       FIG. 4  is an explanatory diagram showing a relation between a threshold th and viewing time. As shown in  FIG. 4 , the setting unit  128  may continuously decrease the threshold th as the viewing time becomes longer. In an example in  FIG. 4 , since extrusion amount S in t1 to t2 falls below the threshold th, extrusion-amount adjustment is not performed in t1 to t2. However, near t3 where extrusion amount S is relatively low and where the extrusion-amount adjustment is not performed if the threshold th remains the initial value, since extrusion amount S exceeds the decreased threshold th, the extrusion-amount adjustment is performed. As described above, by continuously decreasing the threshold th as the viewing time becomes longer, it becomes easy to perform extrusion-amount adjustment. Accordingly, it is possible to decrease eyestrain of the user. 
     Note that, the threshold th which decreases in accordance with the viewing time may be a value obtained by multiplying an initial value by a rate inversely proportional to the viewing time. 
     Note that, the way of setting a threshold th is not limited to the above-described way using viewing time. For example, since it has been worried about effect of 3D video having an extremely-large extrusion amount to visual function development of a child user, the setting unit  128  may determine whether a user is an adult or a child, and in a case where the user is a child, the setting unit  128  may set the threshold th at a lower value than a case where the user is an adult. Note that, it is possible to estimate whether the user is an adult or a child on the basis of a captured image acquired by the imaging unit  114 . 
     Alternatively, the setting unit  128  may set the threshold value by considering video additional information (for example, a genre of the video and duration) included in a 3D video signal, input from a sensor capable of acquiring a viewing environment, information (eyesight, wearing contacts or glasses, age, distance between eyes) about a living body of the user, a type (a portable device, s stationary device, a screen) of the display device  100  or the like. In addition, the setting unit  128  may set the threshold th at a value designated by the user in accordance with user operation. 
     (Display Control Unit) 
     The display control unit  132  functions as an adjustment unit configured to adjust image data (L image and/or R image) displayed on the display unit  110  in accordance with necessity or unnecessity for adjustment instructed by the adjustment-necessity determination unit  124 . Specifically, in a case where the adjustment-necessity determination unit  124  issues an instruction that the adjustment is necessary, the display control unit  132  (adjustment unit) adjusts the image data in a manner that an angle of convergence become smaller (extrusion amount becomes smaller) when the 3D video is viewed. That is, the display control unit  132  (adjustment unit) adjusts the image data in a manner that a display position of an image (object) of the 3D video moves in a depth direction. For example, the display control unit  132  (adjustment unit) moves the display position of the image (object) of the 3D video in the depth direction by performing control in a manner that difference between an L image and an R image becomes smaller. 
     In addition, the display control unit  132  (adjustment unit) calculates movement amount in a manner that extrusion amount of an image having a largest angle of convergence, that is, having a largest extrusion amount among the respective pieces of the image data becomes less than or equals to the reference value (threshold th). 
     Here, with reference to  FIG. 5 , the adjustment performed by the display control unit  132  will be specifically explained.  FIG. 5  is an explanatory diagram of adjustment performed by the display control unit  132 . As shown in the left side of  FIG. 5 , the adjustment-necessity determination unit  124  determines that the adjustment is necessary, in a case where extrusion amount S from the display unit  110  at a position P1 where the user perceives that an image exists when 3D display is performed on the basis of L image data and R image data exceeds the threshold th. In this case, as shown in the right side of  FIG. 5 , the display control unit  132  adjust the image data (L image and/or R image) in a manner that the position P1 perceived by the user moves in a depth direction G. 
     Alternatively, the display control unit  132  may adjust the image data in a manner that the position P1 perceived by the user moves to, for example, a position P2 where the extrusion amount S become smaller than the threshold th to be a criterion for determination of the adjustment necessity. In the example shown in the right side of  FIG. 5 , the display control unit  132  performs adjustment in a manner that the position P1 perceived by the user moves through movement amount F in the depth direction G. 
     As described above, by causing the position P1 perceived by the user to move in the depth direction G, an angle of convergence θ becomes smaller, and cross-eyed state of the user is eased. Accordingly, fatigue is decreased. 
     The example shown in  FIG. 5  shows movement of the single position P in the depth direction G However, it is also possible that a plurality of images (objects) are included in 3D video and each of the objects has different extrusion amount S. In this case, the adjustment-necessity determination unit  124  may determine adjustment necessity on the basis of extrusion amount S at a most-extruded position, for example. 
     Subsequently, as shown in  FIG. 6 , the display control unit  132  adjusts an image data in a manner that extrusion amount S of an object having a largest extrusion amount among a plurality of objects included in a single frame falls below the threshold th, and in a manner that movement amount of the plurality of objects become a same. In this way, parallel movement is performed in a manner that the movement amount of the plurality of object in the depth direction G becomes the same. Accordingly, eyestrain of a user can be decreased without damaging a relation of a sense of depth of a plurality of objects included in a single frame of 3D image. 
     In addition, the display control unit  132  according to the present embodiment adjust image data (L image and/or R image) in a manner that movement amount of respective images (objects) corresponding to a plurality of frames at display positions in the depth direction G become a same. 
     For example, as shown in  FIG. 7 , the adjustment-necessity determination unit  124  determines that adjustment is necessary in a case where extrusion amount S of at least an object (object in frame  2  in  FIG. 7 ) among a plurality of perceived objects respectively according to frames  1  to  3  exceeds the threshold th. 
     Next, as shown in  FIG. 7 , the display control unit  132  adjusts an L image and an R image which constitute each frame in a manner that movement amount of a plurality of perceived objects respectively according to frames  1  to  3  at display positions in a depth direction become a same. Note that, as described above, the movement amount here means difference between a display position of an object (object in frame  2  in the example in  FIG. 7 ) having a largest extrusion amount and a goal display position where the extrusion amount S of the object falls below the threshold th. 
     In this way, by conforming movement amount of each object corresponding to each of a plurality of frames at a 3D display position in a depth direction G, the display control unit  132  can reduce fatigue of the user without damaging a relation of a sense of depth of a plurality of 3D-displayed frames. 
     Note that, the display control unit  132  may change movement amount in a depth direction for every object in a frame, in a range where a relation of a sense of depth of 3D display is not damaged. 
     (Shutter Control Unit and Infrared Communication Unit) 
     The shutter control unit  136  generates a shutter control signal for controlling shutter operation of the shutter glasses  200 . In the shutter glasses  200 , open/close operation of the right-eye image transparent unit  212  and the left-eye image transparent unit  214  is performed on the basis of the shutter control signal generated by the shutter control unit  136  and emitted from the infrared communication unit  140 . Specifically, the shutter operation is performed in a manner that the left-eye image transparent unit  214  opens while the left-eye image is displayed on the display unit  110  and the right-eye image transparent unit  212  opens while the right-eye image is displayed on the display unit  110 . 
     2-2. Operation of Display Device According to First Embodiment 
     The configuration of the display device  100  according to the first embodiment has been explained. Next, with reference to  FIG. 6 , operation of the display device  100  according to the first embodiment will be described. 
       FIG. 8  is a flowchart showing operation of the display device  100  according to the first embodiment. As shown in  FIG. 8 , a 3D video signal is first input to the extrusion-amount calculation unit  120  (S 204 ). Subsequently, on the basis of L image data and R image data included in the 3D video signal, the extrusion-amount calculation unit  120  calculates extrusion amount S of an image in a case where 3D display is performed (S 208 ). Note that, the extrusion-amount calculation unit  120  in the present embodiment calculates extrusion amount S of each image data in an arbitrary unit time or in an arbitrary number of frames. 
     Next, the adjustment-necessity determination unit  124  determines whether or not the extrusion amount S calculated by the extrusion-amount calculation unit  120  is greater than or equals to a threshold th set by the setting unit  128  (S 212 ). Subsequently, in a case where the extrusion amount S is less than the threshold th set by the setting unit  128  (NO in step S 212 ), the adjustment-necessity determination unit  124  determines that adjustment of a 3D display position (position perceived by the user) is not necessary (S 228 ). 
     On the other hand, in a case where the extrusion amount S is greater than or equals to the threshold th (YES in step S 212 ), the adjustment-necessity determination unit  124  determines that adjustment of the 3D display position is necessary and instructs the display control unit  132  to perform adjustment (S 216 ). 
     In this way, the display control unit  132  calculates movement amount at a 3D display position in a depth direction (S 220 ). As described above, the movement amount means difference between a display position of an object having a largest extrusion amount among a plurality of frames and a goal display position where the extrusion amount S of the object falls below the threshold th. 
     Subsequently, the display control unit  132  adjusts the image data in a manner that movement amount of respective images (objects) in a plurality of frames at display positions in a depth direction become a same (S 224 ). 
     Subsequently, the display device  100  repeats the processing of S 204  to S 228  until display based on the 3D video signal ends (S 232 ). 
     2-3. Supplemental Remarks 
     The configuration and the operation of the display device  100  according to the first embodiment of the present disclosure have been explained. Hereinafter, supplemental remarks about the first embodiment will be described. 
     (Notification of Presence or Absence of Adjustment) 
     The display control unit  132  may overlay a notification window for notifying the user of presence or absence of 3D-video-signal adjustment. With reference to  FIG. 9 , specific examples will be given as follows. 
       FIG. 9  is an explanatory diagram showing a specific example of a notification window. As shown in  FIG. 9 , in a case where the 3D-video-signal adjustment has been performed, a notification window  30  includes text showing “FATIGUE REDUCING MODE” and a character image which gives a user a gentle impression. The display control unit  132  may perform control in a manner that the notification window  30  is displayed for a certain time when the 3D-video-signal adjustment starts. 
     On the basis of such a notification window  30 , the user can easily recognize that 3D video which is currently displayed has been adjusted for reducing the fatigue. 
     Note that, the notification way of presence or absence of adjustment is not limited thereto. For example, as shown in  FIG. 10 , it may be possible that a light-emitting unit  112  is provided on a front surface of the display device  100  and the light-emitting unit  112  emits light in a case of performing the 3D-video-signal adjustment. In such a configuration, the user can be notified of presence or absence of adjustment without disturbing viewing of a content image displayed on the display unit  110 . 
     (Control Based on Gaze of User) 
     While 3D display is performed on the display device  100 , attention of the user may be shifted to another device such as a mobile device. In this period, flicker occurs when the user sees the another device if the shutter operation of the shutter glasses  200  continues. In addition, there is little significance of performing the 3D display on the display device  100  while the user does not see the display device  100 . 
     Accordingly, the shutter control unit  136  may stop the shutter operation of the shutter glasses  200  in a case where the attention of the user wanders from the display device  100 . Note that, it is possible to determine whether the attention of the user wanders from the display device  100  by recognizing gaze of the user from the captured image acquired by the imaging unit  114 . In such a configuration, the user can use the another device comfortably without taking off the shutter glasses  200 . 
     In addition, the display control unit  132  may stop 3D display on the display unit  110  in a case where the attention of the user wanders from the display device  100 . Moreover, the display device  100  may turn off a power supply of the display device  100  in the case where the attention of the user wanders from the display device  100 . In such a configuration, it is possible to reduce power consumption of the display device  100 . 
     3. Second Embodiment 
     The first embodiment of the present disclosure has been explained. Next, a second embodiment of the present disclosure will be explained. 
       FIG. 11  is an explanatory diagram showing a configuration of a display device  100 ′ according to a second embodiment. As shown in  FIG. 11 , the display device  100 ′ according to the second embodiment includes a display unit  110 , an imaging unit  114 , an extrusion-amount calculation unit  120 , an adjustment-necessity determination unit  126 , a setting unit  128 , a display control unit  132 , a shutter control unit  136 , an infrared communication unit  140 , an analysis unit  144 , and a variation-pattern storage unit  148 . Since the description is made in “2. First Embodiment,” the repeated descriptions of the display unit  110 , the imaging unit  114 , the extrusion-amount calculation unit  120 , the setting unit  128 , the display control unit  132 , and the shutter control unit  136  will be omitted hereinafter. 
     The display device  100 ′ according to the second embodiment acquires biological information of a user such as pulses and movement of mimic muscles from a user using device. For example, the shutter glasses  200  worn by the user acquires biological information of the user, and the infrared communication unit  140  receives the biological information of the user from the shutter glasses  200 . 
     On the basis of changes in the biological information of the user, the analysis unit  144  analyses an image pattern which causes the user to get fatigue. For example, in a case where the biological information of the user indicates that the user gets fatigue, the analysis unit  144  analyses a variation pattern of difference (that is, variation pattern of extrusion amount) between an L image and an R image that are displayed when the biological information is acquired. Subsequently, the variation-pattern storage unit  148  stores the variation pattern acquired from the analysis performed by the analysis unit  144 . For example, the variation pattern includes a pattern in which an increase and decrease of the extrusion amount is repeated three times in a unit period. 
     The adjustment-necessity determination unit  126  determines whether a variation pattern of extrusion amount calculated by the extrusion-amount calculation unit  120  matches with a variation pattern stored in the variation-pattern storage unit  148 . Here, in a case where the variation pattern of the extrusion amount calculated by the extrusion-amount calculation unit  120  matches with the variation pattern stored in the variation-pattern storage unit  148 , it is considered that the 3D display causes the user to get fatigue. Accordingly, in the case where the variation pattern of the extrusion amount calculated by the extrusion-amount calculation unit  120  matches with the variation pattern stored in the variation-pattern storage unit  148 , the adjustment-necessity determination unit  126  instructs the display control unit  132  to adjust image data. 
     According to the above-described second embodiment, it is possible to automatically generate an adjustment-necessity determination condition tailored to an individual user on the basis of biological information of the user acquired while the user views a 3D image, and it is also possible to determine the necessity of adjustment according to the adjustment-necessity determination condition. 
     4. Conclusion 
     As described above, according to the embodiments of the present disclosure, a display position (position perceived by the user) of 3D video can be moved in a depth direction. Accordingly, uncomfortable convergence movement can be suppressed and eyestrain of the user can be reduced. In addition, according to the embodiments of the present disclosure, respective objects corresponding to a plurality of frames are moved in a parallel manner. Accordingly, fatigue of the user can be reduced without damaging a relation of a sense of depth of respective 3D-displayed objects corresponding to a plurality of frames. 
     Moreover, according to the embodiments of the present disclosure, power consumption can be reduced since unnecessary 3D display or driving of shutter glasses can be suppressed by estimating a gaze direction of the user. Further, according to the embodiments of the present disclosure, it is possible to automatically generate a determination condition of presence or absence of adjustment tailored to an individual user on the basis of biological information of the user acquired while the user views 3D video, and it is also possible to determine the presence or absence of adjustment in accordance with the determination condition. 
     In addition, the eyestrain of the user from the excessively-extruded 3D display can be decreased. Accordingly, it is possible to impress a user who concerns about bad effect of the 3D display with attractions of the 3D display. In this way, the embodiments of the present disclosure can contribute the progress of 3D industry. 
     The preferred embodiments of the present disclosure have been described above with reference to the accompanying drawings, whilst the present disclosure is not limited to the above examples, of course. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention. 
     For example, it may not be necessary to chronologically execute respective steps in the processing, which is executed by the display device  100  according to this specification, in the order described in the flowchart. For example, the respective steps in the processing which is executed by display device  100  may be processed in the order different from the order described in the flow charts, and may also be processed in parallel. 
     Further, a computer program for causing hardware, such as a CPU, ROM and RAM built into the display device  100  to exhibit functions the same as each of the elements of the above described display device  100  can be created. Further, a storage medium on which this computer program is recorded can also be provided. 
     Additionally, the present technology may also be configured as below. 
     (1) 
     An image processing device including: 
     a determination unit configured to determine whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition; and 
     an adjustment unit configured to adjust the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where the determination unit determines that the difference satisfies the threshold condition, 
     wherein the adjustment unit adjusts the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     (2) 
     The image processing device according to (1), 
     wherein the adjustment unit calculates the movement amount in a manner that extrusion amount of image data having a largest angle of convergence among the respective pieces of image data falls below a reference value. 
     (3) 
     The image processing device according to (2), 
     wherein, as the threshold condition, the determination unit determines whether or not to satisfy a condition that extrusion amount according to the difference between the left-eye image data and the right-eye image data is greater than or equals to the reference value. 
     (4) 
     The image processing device according to any one of (1) to (3), further including: 
     a setting unit configured to set the threshold condition. 
     (5) 
     The image processing device according to (4), 
     wherein the setting unit sets the threshold condition on the basis of continuous use time of a display device by a user of the display device, the display device performing display using the image data. 
     (6) 
     The image processing device according to (5), 
     wherein the setting unit widens a range of the difference satisfying the threshold condition as the continuous use time becomes longer. 
     (7) 
     The image processing device according to any one of (4) to (6), 
     wherein the setting unit sets the threshold condition on the basis of an attribute of a user of a display device performing display using the image data. 
     (8) 
     The image processing device according to (7), 
     wherein, in a case where the user is a child, the setting unit widens a range of the difference satisfying the threshold condition more than the range of the difference satisfying the threshold condition in a case where the user is an adult. 
     (9) 
     The image processing device according to (4), 
     wherein the setting unit sets the threshold condition in accordance with user operation. 
     (10) 
     The image processing device according to (1), further including: 
     a storage unit configured to store a specific variation pattern of the difference, 
     wherein the determination unit further determines whether or not a variation pattern of difference between left-eye image data and right-eye image data of target image data matches with the specific variation pattern stored in the storage unit, and 
     wherein the adjustment unit adjusts the image data in a case where the determination unit determines that the difference satisfies the threshold condition and determines that the variation pattern of the target image data matches with the specific variation pattern. 
     (11) 
     The image processing device according to (10), further including: 
     an analysis unit configured to analyze left-eye image data and right-eye image data of image data to which biological information of a user shows a specific reaction when stereoscopic display is performed, and then extract the specific variation pattern. 
     (12) 
     An image processing method including: 
     determining whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition; 
     adjusting the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where it is determined that the difference satisfies the threshold condition; and 
     adjusting the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     (13) 
     A program causing a computer to function as: 
     a determination unit configured to determine whether or not difference between left-eye image data and right-eye image data which constitute image data satisfies a threshold condition; and 
     an adjustment unit configured to adjust the image data in a manner that an angle of convergence become smaller in a case of stereoscopically displaying the image data, in a case where the determination unit determines that the difference satisfies the threshold condition, 
     wherein the adjustment unit adjusts the image data in a manner that respective pieces of image data become a same in movement amount of display positions in a depth direction perceived at a target point, the pieces of image data corresponding to a plurality of frames. 
     (14) 
     The program according to (13), 
     wherein the adjustment unit calculates the movement amount in a manner that extrusion amount of image data having a largest angle of convergence among the respective pieces of image data falls below a reference value. 
     (15) 
     The program according to (14), 
     wherein, as the threshold condition, the determination unit determines whether or not to satisfy a condition that extrusion amount according to the difference between the left-eye image data and the right-eye image data is greater than or equals to the reference value. 
     (16) 
     The program according to any one of (13) to (15), further causing the computer to function as: 
     a setting unit configured to set the threshold condition. 
     (17) 
     The program according to (16), 
     wherein the setting unit sets the threshold condition on the basis of continuous use time of a display device by a user of the display device, the display device performing display using the image data. 
     (18) 
     The program according to (16) or (17), 
     wherein the setting unit sets the threshold condition on the basis of an attribute of a user of a display device performing display using the image data. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  100 ′ display device 
           110  display unit 
           112  light-emitting unit 
           114  imaging unit 
           120  amount calculation unit 
           124 ,  126  adjustment-necessity determination unit 
           128  setting unit 
           132  display control unit 
           136  shutter control unit 
           140  infrared communication unit 
           144  analysis unit 
           148  variation-pattern storage unit 
           200  shutter glasses 
           212  right-eye image transparent unit 
           214  left-eye image transparent unit