Patent Publication Number: US-2019170583-A1

Title: Display device, and method for correcting display state of display device

Description:
TECHNICAL FIELD 
     The present invention relates to a display device and a method for calibrating a display state of a display device. 
     BACKGROUND ART 
     Display devices such as liquid crystal displays and organic EL (electro luminescence) displays have advanced in high definition, high color gamut, and high luminance, and high-value added monitors using these are widely used in industries including photography and printing. Since the state of the light source, the liquid crystal, and the like of the display device deteriorates over time, it is required to maintain and control the display quality. In order to maintain the display state, a so-called monitor calibration operation is performed by using a measuring instrument or by having a built-in optical sensor in the device to re-adjust to a desired brightness or chromaticity (for example, refer to Patent Document 1, Patent Document 2, and Patent Document 3). 
     To perform a calibration operation, it is necessary to measure the light emitted from the monitor at the center of the screen of the monitor so as to not include external light. For this reason, when a non-contact type measuring instrument is used, it is necessary to prepare a dark room in order to shield external light. However, it is often difficult to prepare a large measurement environment such as a dark room. Therefore, in general, a measurement probe equipped with a light shielding object is arranged in the center of the screen, and light emitted from the monitor is measured. In this case, there is a method for holding the probe that is at the center of the screen with a person&#39;s hand or fixating it with a tripod. However, the operation of holding the probe with a human hand or a tripod is cumbersome. Moreover, there is a problem in that that use of the monitor, which is the primary purpose of the monitor, is hindered by arranging the measuring instrument (sensor) or the probe in the center of the screen. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         [Patent Document 1] U.S. Pat. No. 7,391,514 
         [Patent Document 2] PCT International Publication No. WO 13/179370 pamphlet 
         [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2011-22226 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     As described above, when performing the monitor calibration operation, it is necessary to arrange the measuring probe provided with a light shielding object in the center of the screen, and the method in which the probe is held by a person&#39;s hand or is fixated with a tripod, is used. In order to solve such complication, there has been proposed a method of suspending an optical sensor as in Patent Document 1. 
     However with this method it is necessary to interrupt the use of the monitor, and then install the sensor and perform a calibration operation. Also, since the sensor and the display surface are distanced from each other, it is affected by external light, and since the sensor is not fixated, it is difficult to set the angles of the display surface and the sensor so that they face each other squarely when tilted downward. 
     On the other hand, as disclosed in Patent Document 2, there has been proposed a method in which a sensor (front sensor) including a light shielding object is arranged in the screen. According to this method, measurement can be performed regardless of changes in the attitude of the monitor. 
     However, in this method, the sensor part hides the screen display. Therefore in order to reduce the area, the optical sensor and the light shielding object need to be brought close to each other, and the width of the light shielding object needs to be narrowed. The entering external light includes not only direct light and surface reflected light but also external light that enters from the panel surface and that enters by internal reflection. If the width of the light shielding object is narrowed, it becomes more likely to be influenced by external light that enters from the panel surface and that enters by internal reflection. 
     As with Patent Document 2, Patent Document 3 can follow the changes in the attitude of the monitor. However, if the light shielding hood is narrowed, it becomes more likely to be influenced by external light that enters from the panel surface and that enters by internal reflection. In Patent Document 3, for light shielding it is stated that it is better to take a large light shielding hood arranged around the sensor. However, the dimension of the shielding hood is not clearly specified. 
     As described above, in Patent Document 2 and Patent Document 3, there is a mode of partially shielding the surroundings of the sensor, and it is not possible to sufficiently shield external light. Disclosed in Patent Document 2 and Patent Document 3 are methods in which the position close to the edge of the screen is measured, the correlation value with respect to the center of the screen is preliminarily stored, and the brightness and the color of the central portion of the screen are predicted by aged deterioration. Therefore, it is necessary on a regular basis to re-correlate with the center due to changes in unevenness in the panel. 
     In view of the above problems, an object of the present invention is to provide a display device capable of calibrating a monitor screen regardless of changes in the attitude of the monitor and without being influenced by external light, and a method for calibrating a display state of a display device. 
     Means for Solving the Problem 
     In order to solve the above-mentioned problems, a display device according to one exemplary aspect of the present invention includes: a display device main body including a display panel; and a cover that covers the display panel, the cover includes an optical sensor in a surface facing the display panel, the display device main body includes a screen calibration function unit that calibrates a display state of the display panel, the optical sensor measures a screen state of the display panel in a state where the display panel is covered with the cover, and sends a measured value of the optical sensor to the display device main body, and the screen calibration function unit calibrates the display state of the display panel. 
     A method for calibrating a display state of a display device including a display panel, according to one exemplary aspect of the present invention includes: covering the display panel with a cover; measuring a screen state of the display panel by an optical sensor provided in a surface of the cover, the surface facing the display panel; sending a value measured by the optical sensor to the display device; and calibrating a display state of the display panel. 
     Effect of the Invention 
     According to the present invention, an optical sensor is provided inside a cover, and the cover having the optical sensor is brought into close contact with a display panel. The screen of a monitor is calibrated by using a detection signal of the optical sensor. As a result, the screen of the monitor can be calibrated regardless of the attitude change of the monitor and without being influenced by external light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view showing an appearance configuration of a display device according to a first exemplary embodiment of the present invention. 
         FIG. 1B  is a perspective view showing an appearance configuration of the display device according to the first exemplary embodiment of the present invention. 
         FIG. 2  is a plan view showing a configuration inside a cover in the display device according to the first exemplary embodiment of the present invention. 
         FIG. 3A  is a plan view used for describing an example of a cover piece in the display device according to the first exemplary embodiment of the present invention. 
         FIG. 3B  is a cross-sectional view used for describing an example of the cover piece in the display device according to the first exemplary embodiment of the present invention. 
         FIG. 4A  is a plan view used for describing another example of the cover piece in the display device according to the first exemplary embodiment of the present invention. 
         FIG. 4B  is a cross-sectional view used for describing the another example of the cover piece in the display device according to the first exemplary embodiment of the present invention. 
         FIG. 5  is a block diagram showing an internal configuration of the display device main body according to the first exemplary embodiment of the present invention. 
         FIG. 6  is a plan view showing a configuration inside a cover in a display device according to a second exemplary embodiment of the present invention. 
         FIG. 7  is a block diagram showing an internal configuration of the display device according to the second exemplary embodiment of the present invention. 
         FIG. 8  is a plan view showing a configuration inside a cover in a display device according to a third exemplary embodiment of the present invention. 
         FIG. 9  is a perspective view showing a back-side configuration of the display device according to the third exemplary embodiment of the present invention. 
         FIG. 10  is a plan view showing a configuration inside a cover in a display device according to a fourth exemplary embodiment of the present invention. 
         FIG. 11  is a perspective view showing a front-side configuration of the display device main body according to the fourth exemplary embodiment of the present invention. 
         FIG. 12  is a block diagram showing an internal configuration of the display device main body according to the fourth exemplary embodiment of the present invention. 
         FIG. 13  is a plan view showing a configuration inside a cover in a display device according to a fifth exemplary embodiment of the present invention. 
         FIG. 14A  is a perspective view of the display device main body according to the fifth exemplary embodiment of the present invention. 
         FIG. 14B  is a perspective view of the display device main body according to the fifth exemplary embodiment of the present invention. 
         FIG. 15A  is a plan view used for describing an example of a cover piece in the display device according to the fifth exemplary embodiment of the present invention. 
         FIG. 15B  is a cross-sectional view used for describing the example of the cover piece in the display device according to the fifth exemplary embodiment of the present invention. 
         FIG. 16A  is an explanatory diagram of another example of attachment between the display device main body and the cover in the display device according to the fifth exemplary embodiment of the present invention. 
         FIG. 16A  is an explanatory diagram of another example of attachment between the display device main body and the cover in the display device according to the fifth exemplary embodiment of the present invention. 
         FIG. 16C  is an explanatory diagram of another example of attachment between the display device main body and the cover in the display device according to the fifth exemplary embodiment of the present invention. 
         FIG. 17A  is a perspective view showing an appearance configuration of a display device according to a sixth exemplary embodiment of the present invention. 
         FIG. 17B  is a perspective view showing an appearance configuration of the display device according to the sixth exemplary embodiment of the present invention. 
         FIG. 18  is a schematic block diagram showing a basic configuration of the display device according to the present invention. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. 
     First Exemplary Embodiment 
       FIG. 1  A and  FIG. 1B  are perspective views each showing an appearance configuration of a display device according to a first exemplary embodiment of the present invention.  FIG. 1A  shows a state of a monitor when in use, and  FIG. 1B  shows a state of the monitor when not in use. 
     As shown in  FIG. 1A , the display device according to the first exemplary embodiment of the present invention includes a display device main body  10  and a light shielding cover  20  attached to the display device main body  10 . 
     The display device main body  10  has a display panel  11 . Moreover, the display device main body  10  has a screen calibration function for calibrating the display state of the display panel  11 . The display panel  11  is, for example, an LCD (liquid crystal display) panel. On the display device main body  10  there is arranged a display operation and input unit  16 . By operating the display operation and input unit  16 , as described later, it is possible to set the time and the like for performing brightness calibration of the monitor. This operation may be performed by a remote controller (not shown in the figure). In a bezel  12  of the display device main body  10 , there is arranged a magnet attraction material  13  so as to surround the left and right sides and the lower side of the display panel  11 . To the upper edge of the display device main body  10  there is attached a cover  20 . The magnet attraction material  13  may be any material as long as it is a material that is attracted to a magnet. 
     The cover  20  is freely foldable, and as shown in  FIG. 1A , when the monitor is in use, it is folded and arranged on an upper portion of the back face of the display device main body  10 . As shown in  FIG. 1B , when the monitor is not in use, the cover  20  is arranged spread out so as to cover the display surface of the display panel  11 . 
       FIG. 2  is a plan view showing a configuration inside the cover  20 . As shown in  FIG. 2 , the cover  20  is of a structure such that three cover pieces  21   a ,  21   b , and  21   c  are connected via fold portions  22   a  and  22   b . As light shielding members used as the cover pieces  21   a ,  21   b , and  21   c , it is preferable to use a material that shields external light (with a light shielding rate of 99.99% or higher in the light shielding property test of a JIS L 1055 black-out curtain). Moreover, magnets (permanent magnets)  26  are arranged inside the three cover pieces  21   a ,  21   b , and  21   c . The mounting position of the magnets  26  corresponds to the position of the magnet attraction material  13  ( FIG. 1A ) of the bezel  12  of the display device main body  10 . Further, attachment pieces  25   a  and  25   b  are provided on the upper portion of the cover  20  via fold portions  22   c  and  22   d . The attachment piece  25   a  is a portion to be fixed to the upper edge of the display device main body  10  and the attachment piece  25   b  is a portion to be fixed to the back face of the display device main body  10 . In addition, among the three cover pieces  21   a ,  21   b , and  21   c , at the center on the inner side of the center cover piece  21   b , there is provided an optical sensor  30 . 
       FIG. 3A  shows a configuration of the inside of the cover piece  21   b  (the surface facing the display surface of the display panel  11 ), and  FIG. 3B  is a cross-sectional view on A-A′ thereof. As shown in  FIG. 3A  and  FIG. 3B , the optical sensor  30  is arranged on a substrate  31 . On the substrate  31  there is mounted a circuit for driving the optical sensor  30 . Further, a wiring  32  is led out from the substrate  31 . To a distal end of the wiring  32  there is attached a connector  40  ( FIG. 1B ). In each cover piece  21   b  there is provided a rigidity maintaining material  23  such as a resin or a steel plate. As described above, in the present exemplary embodiment, the cover  20  includes the rigidity maintaining material  23  such as a steel plate. Therefore, the position of the optical sensor  30  and the position of the display panel  11  are stably maintained. 
     As shown in  FIG. 3A  and  FIG. 3B , instead of providing the rigidity maintaining material  23  inside the cover piece  21   b , a spacer  35  composed of high hardness urethane may be arranged as shown in  FIG. 4A  and  FIG. 4B . With such a spacer  35 , it is possible to stably maintain the distance between the position of the optical sensor  30  and the position of the display panel  11 . 
     The cover  20  is folded at the fold portions  22   c  and  22   d  and is fixed to the display device main body  10  in a state where the positions of the attachment pieces  25   a  and  25   b  are in contact with the upper edge and the back face of the display device main body  10 . For fixing the attachment pieces  25   a  and  25   b  of the cover  20  to the display device main body  10 , a double-sided tape or a hook and loop fastener may be used, or a magnet may be used. Further, the connector  40  is connected to a terminal  50  of the display device main body  10  (refer to  FIG. 5 ). 
     As described above, the cover  20  is of a structure such that the three cover pieces  21   a ,  21   b , and  21   c  are connected via fold portions  22   a  and  22   b , and is freely foldable at the portions of the fold portions  22   a  and  22   b . As shown in  FIG. 1A , the cover  20  is held on the back face of the display device main body  10  and is folded at the portions of the fold portions  22   a  and  22   b  when the monitor is in use. In this state, since the display surface of the display panel  11  is exposed to the outside, the user can visually recognize the display screen by displaying an image on the display panel  11 . Further, since the cover  20  is held on the back face of the display device main body  10 , it does not hinder the user&#39;s use. 
     When the monitor is not in use, as shown in  FIG. 1B , the three cover pieces  21   a ,  21   b , and  21   c  are spread out, and the entire surface of the display surface of the display panel  11  is covered with the cover  20 . At this time, the magnets  26  of the cover pieces  21   a ,  21   b , and  21   c  are attracted to the magnet attraction material  13  of the bezel  12 . As a result, the cover  20  is brought into close contact with and fixed on the display surface of the display panel  11 . Therefore, the display surface of the display panel  11  is shielded from light by the cover  20 , and almost no light from the outside enters onto the display panel  11 . That is to say, by shielding the front face of the display surface of the display panel  11  from light by means of the cover  20 , not only direct light and surface reflected light but also external light entering from the panel surface and entering by internal reflection are shielded. In this example, a magnet is used to fix the cover  20  to the display panel  11 , but the cover  20  may be fixed to the display panel  11  using a hook and loop fastener or the like. 
     In this manner, in a state where the entire surface of the display surface of the display panel  11  is covered with the cover  20 , the screen state of the display device main body  10  is measured using the optical sensor  30 , and the calibration operation is performed. This calibration operation can be executed according to a set time schedule. 
     Next, an internal configuration of the display device main body  10  will be described.  FIG. 5  is a block diagram showing an internal configuration of the display device main body  10  according to the first exemplary embodiment of the present invention. Here within the internal configuration of the display device main body  10 , only the portions related to a screen calibration function  19  will be described. 
     As shown in  FIG. 5 , the display device main body  10  includes the display panel  11 , the display operation and input unit  16 , a time management and instruction unit  51 , a backlight unit  52 , a backlight (BL) control unit  53 , a gradation control unit  54 , a video signal generation unit  55 , an image control unit  56 , a storage unit  57 , and a signal control unit  58 . 
     The time management and instruction unit  51  sets a time schedule for performing the calibration process on the basis of an input from the display operation and input unit  16 . 
     The backlight unit  52  irradiates backlight to the display panel  11  from the back face of the display panel  11 . The backlight control unit  53  drives the backlight unit  52  and controls the brightness of the backlight irradiated from the backlight unit  52  to the display panel  11 . 
     The gradation control unit  54  controls the gradation of an image to be displayed on the display panel  11 . The video signal generation unit  55  generates a video for performing brightness calibration of the monitor. The image control unit  56  supplies control signals to the backlight control unit  53 , the gradation control unit  54 , and the video signal generation unit  55 , and controls the brightness and gradation of the screen. 
     The storage unit  57  stores correction adjustment values related to the light quantity and the gradation of the backlight. The signal control unit  58  performs control processing of backlight and gradation by using the correction adjustment values from the storage unit  57  and the detection value of the optical sensor  30  sent via the connector  40  and the terminal  50 . 
     Prior to starting the calibration operation, the user sets a calibration start time. When setting the calibration start time, the user removes the cover  20  from the display surface of the display panel  11 , and places the display device main body  10  in a monitor use state as shown in  FIG. 1A . Then, the user operates the display operation and input unit  16  to set the calibration start time in the time management and instruction unit  59 . Thereafter, as shown in  FIG. 1B , the user covers the display panel  11  with the cover  20 , and places the display device main body  10  in a monitor unused state. 
     The time management and instruction unit  51  determines whether or not it is the specified calibration start time. When it is determined that it is the calibration start time, the time management and instruction unit  51  sends a calibration start signal to the signal control unit  58 . 
     Upon receiving the calibration start signal from the time management and instruction unit  51 , the signal control unit  58  reads out current correction adjustment values (for example, backlight setting, gradation characteristics, and brightness for each gradation) from the storage unit  57 , and sends the adjustment values to the image control unit  56 . 
     Upon receiving the correction adjustment values from the signal control unit  58 , the image control unit  56  sets a brightness of the backlight on the basis of the correction adjustment values, and transmits a backlight control signal on the basis of the brightness to the backlight control unit  53 . The backlight control unit  53  turns on the backlight unit  52  with the brightness that corresponds to the backlight control signal. 
     On the other hand, the image control unit  56  instructs the video signal generation unit  55  to generate a video image of the highest gradation at the center of the image, that is, the position that can be detected by the optical sensor  30 . The gradation control unit  54  performs gradation control according to the gradation characteristics. The video image from the video signal generation unit  55  has the gradation characteristic thereof adjusted via the gradation control unit  54 , and is then sent to the display panel  11  and displayed on the display panel  11 . 
     When the image is displayed on the display panel  11 , a detection value is output from the optical sensor  30  according to the brightness of the image on the display panel  11 . The detection value of the optical sensor  30  is sent to the signal control unit  58  via the connector  40  and the terminal  50 . The detection value of the brightness from the optical sensor  30  is acquired by the signal control unit  58 . 
     The signal control unit  58  sets a target value of the brightness on the basis of the correction adjustment values read out from the storage unit  57  and the gradation adjustment value, and compares the brightness detection value of the optical sensor  30  and the determined target brightness value. Then, the signal control unit  58  determines whether or not the error between the brightness detection value of the optical sensor  30  and the target brightness value exceeds a preliminarily set range. 
     If the error between the brightness detection value of the optical sensor  30  and the target brightness value exceeds the preliminarily set range, the signal control unit  58  changes the backlight setting value so that the error between the brightness detection value of the optical sensor  30  and the target brightness value becomes smaller. Then, the image control unit  56  sets the brightness of the backlight on the basis of the changed value, and the backlight control unit  53  turns on the backlight unit  52  on the basis of this brightness and repeats the same processing. 
     By repeating such processing, the brightness value corresponding to the detection value of the optical sensor  30  approaches the target brightness. When the error between the brightness detection value of the optical sensor  30  and the target brightness value falls within the preliminarily set range, the signal control unit  58  stores the correction adjustment values at this time into the storage unit  57 , and the processing is finished. With the above processing, the backlight is turned on with the same brightness as the brightness attained when the previously set backlight is turned on, and the brightness of the display device main body is calibrated. 
     In the above description, the example of calibrating the brightness of the backlight of the display panel  11  has been described. However, by having a constant backlight and replacing the brightness change with a gradation change, it is possible to calibrate the gradation characteristics. Furthermore, if the brightness and gradation are separated into RGB, it can be replaced with color calibration. 
     As described above, in the display device according to the first exemplary embodiment of the present invention, the cover  20  that widely covers the display surface of the display panel  11  is provided in order to shield external light during measurement. The optical sensor  30  is arranged at the center of the rear surface of the cover  20  (at the center of the surface facing the display surface of the display panel  11  when the cover  20  is covering it) so as to directly face the display surface of the display panel  11 . When the monitor of the display device main body  10  is not in use, the display surface of the display panel  11  is covered with the cover  20 , and during this time, the screen state of the display device main body  10  is measured using the optical sensor  30  and the calibration operation is performed. As a result, even when no user is present, the brightness calibration of the display device main body can be performed. 
     Moreover, in the present exemplary embodiment, the cover  20  includes the rigidity maintaining material  23  such as a steel plate, and the cover  20  is fixed in a state of surface contact by means of the magnet  26  or the like. Therefore, it is possible to eliminate intrusion of external light, and maintain the distance between the optical sensor  30  and the display surface of the display panel  11 , even when there is an attitude change of the monitor, that is, a vertical and horizontal rotation and/or a tilt angle change, and it is possible to open and close the cover  20  easily. Also, when using the spacer  35  instead of providing the rigidity maintaining material  23 , it is possible to stably maintain the distance between the position of the optical sensor  30  and the position of the display panel  11 . As a result, stable calibration becomes possible without being influenced by external light and regardless of the orientation or angle of the monitor. 
     Second Exemplary Embodiment 
     Next, a second exemplary embodiment of the present invention will be described.  FIG. 6  shows a configuration inside a cover  220  (a surface facing a display surface of a display panel  11 ) in a display device according to the second exemplary embodiment of the present invention. In the first exemplary embodiment described above, one optical sensor  30  is arranged at the center of the cover  20 . In contrast, in this exemplary embodiment, a plurality of, five in this example, optical sensors  230   a  to  230   e  are uniformly arranged. By arranging the plurality of optical sensors  230   a  to  230   e  in this manner, uniformity measurement and correction can be performed. 
     As shown in  FIG. 6 , the cover  220  is of a structure such that three cover pieces  221   a ,  221   b , and  221   c  are connected via fold portions  222   a  and  222   b . The optical sensors  230   b ,  230   c  are arranged at both of substantially end parts in the longitudinal direction of the cover piece  221   a . The optical sensor  230   a  is arranged at a substantially center portion in the longitudinal direction of the cover piece  221   b . The optical sensors  230   d ,  230   e  are arranged at both of substantially end parts in the longitudinal direction of the cover piece  221   c . In this manner, the optical sensors  230   a  to  230   e  are arranged substantially uniformly inside the cover  220 . Further, attachment pieces  225   a  and  225   b  are provided on the upper portion of the cover  220  via fold portions  222   c  and  222   d . Moreover, inside the cover  220  there is arranged magnets  226  so as to surround the periphery. 
       FIG. 7  is a block diagram showing an internal configuration of a display device main body  210  according to the second exemplary embodiment of the present invention. As shown in  FIG. 7 , the display device main body  210  includes a display panel  211 , a display operation and input unit  216 , a time management and instruction unit  251 , a backlight unit  252 , a backlight (BL) control unit  253 , a gradation control unit  254 , a video signal generation unit  255 , an image control unit  256 , a storage unit  257 , and a signal control unit  258 . The display panel  211 , the display operation and input unit  216 , the time management and instruction unit  251 , the backlight unit  252 , the backlight control unit  253 , the gradation control unit  254 , the video signal generation unit  255 , the image control unit  256 , the storage unit  257 , and the signal control unit  258  are similar to the display panel  11 , the display operation and input unit  16 , the time management and instruction unit  51 , the backlight unit  52 , the backlight control unit  53 , the gradation control unit  54 , the video signal generation unit  55 , the image control unit  56 , the storage unit  57 , and the signal control unit  58  in the first exemplary embodiment. 
     In the present exemplary embodiment, the calibration operation is performed in the state where the entire display panel  211  is covered with the cover  220 . At this time, in the present exemplary embodiment, by using the plurality of optical sensors  230   a  to  230   e , uniformity measurement and correction can be performed. 
     That is to say, when an image is displayed on the display panel  211 , detection values are output from the optical sensors  230   a  to  230   e  according to the brightness of the image on the display panel  211 . The detection values of the optical sensors  230   a  to  230   e  are sent to the signal control unit  258  via a connector  240  and a terminal  250 . 
     The signal control unit  258  sets a target value of the brightness on the basis of the correction adjustment values read out from the storage unit  257  and the gradation adjustment value, and compares the brightness detection values of the optical sensors  230   a  to  230   e  and the determined target brightness value. Then, the signal control unit  258  determines whether or not the error between the brightness detection values of the optical sensors  230   a  to  230   e  and the target brightness value exceeds a preliminarily set range. If the error between the brightness detection values of the optical sensors  230   a  to  230   e  and the target brightness value exceeds the preliminarily set range, the signal control unit  258  changes the backlight setting value so that the error between the brightness detection values of the optical sensors  230   a  to  230   e  and the target brightness value becomes smaller. Then, the image control unit  256  sets the brightness of the backlight on the basis of the changed value, and the backlight control unit  253  turns on the backlight unit  252  on the basis of this brightness and repeats the same processing. As a result of these operations, the gradation setting for each portion is changed with respect to the previous correction adjustment values. Therefore, brightness uniformity of the display device main body is corrected. 
     As described above, in the present exemplary embodiment, the plurality of optical sensors  230   a  to  230   e  are arranged inside the cover  220 . By using the plurality of optical sensors  230   a  to  230   e , uniformity measurement and correction can be performed. 
     Third Exemplary Embodiment 
     Next, a third exemplary embodiment of the present invention will be described.  FIG. 8  shows a configuration inside a cover  320  (a surface facing a display surface of a display panel  11 ) in a display device according to the third exemplary embodiment of the present invention. In the first exemplary embodiment described above, the connector  40  is led out from the cover  20 , and the connector  40  and the terminal  50  are connected to electrically connect the optical sensor  30  and the display device main body  10 . In contrast, in this exemplary embodiment, an optical sensor  330  of the cover  320  communicates with the display device main body  310  in a non-contact manner. 
     As shown in  FIG. 8 , the cover  320  is of a structure such that three cover pieces  321   a ,  321   b , and  321   c  are connected via fold portions  322   a  and  322   b . In addition, among the three cover pieces  321   a ,  321   b , and  321   c , at the center on the inner side of the center cover piece  321   b , there is provided the optical sensor  330 . Further, attachment pieces  325   a  and  325   b  are provided on the upper portion of the cover  20  via fold portions  322   c  and  322   d . Moreover, inside the cover  320 , there is arranged magnets  326  so as to surround the periphery. Furthermore, in the present exemplary embodiment, the attachment piece  325   b  is provided with a power receiving part  371  for non-contact power feeding. The power receiving part  371  is electrically connected to the optical sensor  330 . 
       FIG. 9  shows a back face configuration of the display device main body  310 . As shown in  FIG. 9 , a power transmission part  372  for non-contact power feeding is provided on the upper portion of the back face of the display device main body  310 . The position of the power receiving part  371  of the cover  320  and the position of the power transmission part  372  of the display device main body  310  correspond to each other. The cover  320  is fixed while the positions of the attachment pieces  325   a  and  325   b  are in contact with the upper edge and the back face of the display device main body  310 . At this time, the power receiving part  371  of the cover  320  faces the power transmission part  372 . 
     In the first exemplary embodiment described above, the connector  40  is connected to perform communication between the optical sensor  30  and the display device main body  10 . On the other hand, in the third exemplary embodiment of the present invention, the power transmission part  372  for non-contact power feeding is provided on the back face of the display device main body  310 , and the power transmission part  371  is arranged in the back face of the cover  320  at a position opposite thereto. Thereby, the optical sensor  330  of the cover  320  can communicate with the display device main body  310  in a non-contact manner. 
     Various types of non-contact power feeding systems are commercially available, and any of them may be used. Here, taking the electromagnetic induction method as an example, the non-contact power transmission part  372  is a coil and an alternating current is passed through the coil to generate an alternating magnetic field. The power receiving power  371  facing the power transmission part  372  is also a coil, and an induced current flows through the power receiving part  371  by the alternating magnetic field of the power transmission part  372  to transmit power. By rectifying this, a direct current power supply is obtained and used as a power supply for the optical sensor  330 . 
     There are various methods for non-contact communication, and any of these methods may be used. As an example of this, there is RFID (radio frequency identification), and there is a communication method standardized by IEC10536. Among them, there are a plurality of methods, and electromagnetic induction is capable of signal transmission by an operation similar to that of the non-contact power feeding, and optical sensor values can be read according to instructions from the main body side. Some non-contact communication methods have a power transmission function, and when this is adopted, the power transmission part  372  and the power receiving part  371  for non-contact power feeding also become unnecessary. 
     As described above, in the present exemplary embodiment, no connector is required, eliminating the need for the wiring work when attaching the cover. For non-contact power feeding and non-contact communication, a relatively large area is required for antenna wiring patterns for power transmitting/receiving or for signal transmitting/receiving. In the present exemplary embodiment, by using non-contact communication, the space of the back face of the cover can be effectively utilized. 
     Fourth Exemplary Embodiment 
     Next, a fourth exemplary embodiment of the present invention will be described.  FIG. 10  shows a configuration inside a cover  420  (a surface facing a display surface of a display panel  11 ) in a display device according to the fourth exemplary embodiment of the present invention. In the first exemplary embodiment described above, the connector  40  is led out from the cover  20 , and the connector  40  and the terminal  50  are connected to thereby electrically connect the optical sensor  30  and the display device main body  10 . In contrast, in this exemplary embodiment, an optical sensor  430  of the cover  420  communicates with the display device main body  410  by means of optical communication in a non-contact manner. 
     As shown in  FIG. 10 , the cover  420  is of a structure such that three cover pieces  421   a ,  421   b , and  421   c  are connected via fold portions  422   a  and  422   b . In addition, among the three cover pieces  421   a ,  421   b , and  421   c , at the center on the inner side of the center cover piece  421   b , there is provided the optical sensor  430 . Further, on the inner side of the cover  420  there are provided solar cell panels  471 . Each solar cell panel  471  is provided with a light shielding object  472  therearound so as not to affect dark portion measurement, and the solar cell panels  471  are arranged at positions away from the optical sensor  430 . In this example, four solar cell panels  471  are arranged, but the number of solar cell panels  471  is arbitrary. Further, attachment pieces  425   a  and  425   b  are provided on the upper portion of the cover  420  via fold portions  422   c  and  422   d . Inside the cover  420  there is arranged magnets  426  so as to surround the periphery. Furthermore, in the present exemplary embodiment, an optical sensor  481  and an LED (light emitting diode)  482  for communication are provided on the lower edge of the cover  420 . 
       FIG. 11  shows a front-side configuration of the display device main body  410  according to the fourth exemplary embodiment of the present invention. As shown in  FIG. 11 , the display device main body  410  has a display panel  411 . On the display device main body  410  there is arranged a display operation and input unit  416 . Moreover, in a bezel  412  of the display device main body  410 , there is arranged magnet attraction material  413  so as to surround the display panel  411 . On the upper edge of the display device main body  410  there is attached a cover  420 . Furthermore, in the present exemplary embodiment, an optical sensor  491  and an LED  492  for communication are provided on the lower edge of the display panel  411 . 
     When the monitor of the display device main body  410  is not in use, the entire surface of the display panel  411  is covered with the cover  420 . At this time, the optical sensor  481  and the LED  482  on the lower edge of the cover  420  face the LED  492  and the optical sensor  491  on the lower edge of the display device main body  410 . Thereby, the optical sensor  430  can communicate with the display device main body  410  in a non-contact manner. Further, by driving the display panel  411 , the solar cell panels  471  generate electricity by light emitted from the display panel  411 . This power supply is used to drive the optical sensor  430 . 
       FIG. 12  is a block diagram showing an internal configuration of the display device main body  410 . As shown in  FIG. 12 , the display device main body  410  includes the display panel  411 , a display operation and input unit  416 , a time management and instruction unit  451 , a backlight unit  452 , a backlight (BL) control unit  453 , a gradation control unit  454 , a video signal generation unit  455 , an image control unit  456 , a storage unit  457 , and a signal control unit  458 . The display panel  411 , the display operation and input unit  416 , the time management and instruction unit  451 , the backlight unit  452 , the backlight control unit  453 , the gradation control unit  454 , the video signal generation unit  455 , the image control unit  456 , the storage unit  457 , and the signal control unit  458  are similar to the display panel  11 , the display operation and input unit  16 , the time management and instruction unit  51 , the backlight unit  52 , the backlight control unit  53 , the gradation control unit  54 , the video signal generation unit  55 , the image control unit  56 , the storage unit  57 , and the signal control unit  58  in the first exemplary embodiment. Furthermore, in the present exemplary embodiment, the optical sensor  491  and the LED  492  for communication, and a transmission and reception control unit  493  are provided in the display device main body  410 . 
     On the other hand, the cover  420  is provided with the optical sensor  430 , the solar cell panels  471 , the optical sensor  481  and the LED  482  for communication, and a transmission and reception control unit  483 . In a state where the entire surface of the display panel  411  is covered with the cover  420 , the optical sensor  491  and the LED  492  of the display device main body  410  face the LED  482  and the optical sensor  481  of the cover  420 . 
     At a calibration start time, a calibration start signal is transmitted from the signal control unit  458 . This calibration start signal is sent from the signal control unit  458  to the transmission and reception control unit  493 . The calibration start signal is optically modulated by the transmission and reception control unit  493  and output from the LED  492 . The output light of the LED  492  is received by the optical sensor  481  on the cover  420  side and demodulated by the transmission and reception control unit  483 . As a result, a detection signal is output from the optical sensor  430 . 
     When the detection signal of the optical sensor  430  is transmitted from the cover  420  to the display device main body  410 , the detection signal of the optical sensor  430  is supplied to the transmission and reception control unit  483 . The detection signal of the optical sensor  430  is optically modulated by the transmission and reception control unit  483  and output from the LED  482 . The output light of the LED  482  is received by the optical sensor  491  on the display device main body  410  side, demodulated by the transmission and reception control unit  493 , and sent to the signal control unit  458 . 
     Further, in the present exemplary embodiment, solar cell panels  471  are provided on the cover  420 . When the display panel  411  is driven in a state where the entire display panel  411  is covered with the cover  420 , the solar cell panels  471  generate electricity by light emitted from the display panel  411 . The solar cell panels  471  are used as a power supply for the optical sensor  430 , the transmission and reception control unit  483 , the LED  482 , and the optical sensor  481 . 
     As described above, in the present exemplary embodiment, no connector is required, eliminating the need for the wiring work when attaching the cover. Further, by arranging the solar cell panels  471 , there is no need to provide a battery or the like. 
     Fifth Exemplary Embodiment 
     Next, a fifth exemplary embodiment of the present invention will be described.  FIG. 13  shows a configuration inside a cover  520  (a surface facing a display surface of a display panel  11 ) in a display device according to the fifth exemplary embodiment of the present invention.  FIG. 14A  and  FIG. 14B  show a state when the cover  520  is attached to the display device main body  510 . 
     As shown in  FIG. 13 , the cover  520  according to the fifth exemplary embodiment of the present invention is of a structure such that three cover pieces  521   a ,  521   b , and  521   c  are connected via fold portions  522   a  and  522   b . In addition, among the three cover pieces  521   a ,  521   b , and  521   c , at the center on the inner side of the center cover piece  521   b , there is provided an optical sensor  530 . Further, attachment pieces  525   a  and  525   b  are provided on the upper portion of the cover  520  via fold portions  522   c  and  522   d . A magnet  526  is arranged on the attachment piece  525   b . Further, the attachment pieces  527   a  and  527   b  are provided on the left side of the cover  520  via fold portions  522   e  and  522   f . Attachment pieces  527   c  and  527   d  are provided on the right side of the cover  520  via fold portions  522   g  and  522   h . Magnets  526  are arranged on the attachment pieces  527   d  and  527   d  on both of the left and right ends. 
     In the above-described first exemplary embodiment, the magnet attraction material  13  is arranged on the bezel  12 . On the other hand, in the present fifth exemplary embodiment, as shown in  FIG. 14B , magnet attraction material  513  is provided on the back side of the display device main body  510 . 
     When attaching the cover  520  to the display device main body  510 , as shown in  FIG. 14A , the cover  520  is attached in a manner such that the display device main body  510  is sandwiched by the attachment pieces  527   a  and  527   b  and the attachment pieces  527   c  and  527   d  on the left side and the right side of the cover  520 . The magnets  526  on both sides of the cover  520  and the magnet attraction material  513  on the back side of the display device main body  510  are attracted to each other to fix the cover  520  to the display device main body  510 . 
     As described above, in the fifth exemplary embodiment of the present invention, the cover  520  is attached in a manner such that the display device main body  510  is sandwiched by the attachment pieces  527   a  and  527   b  and the attachment pieces  527   c  and  527   d  on the left side and the right side of the cover  520 , and the magnets  526  on both sides of the cover  520  and the magnet attraction material  513  on the back side of the display device main body  510  are attracted to each other to fix the cover  520 . Therefore, even with a display device main body with a narrow bezel width or a display device main body with no bezel, the screen can be shielded from light and the center of the screen can be measured. 
     In the fifth exemplary embodiment of the present invention, a tensile force is applied to the cover  520  from the both sides to the rear side. For this reason, as shown in  FIG. 15A  and  FIG. 15B , the area of the spacer  535  is made large. As shown in  FIG. 15A  and  FIG. 15B , the optical sensor  530  is arranged on a substrate  531  and is provided on the cover piece  521   b . The spacer  535  is provided in order to stably maintain the distance between the position of the optical sensor  530  and the position of the display panel. In this exemplary embodiment, a spacer having a large area is used as the spacer  535  so that the positional relationship between the position of the optical sensor  530  and the display panel does not change even when a force is applied from both sides. 
     In the above example, as shown in  FIG. 14B , the magnet attraction material  513  is provided on the back side of the display device main body  510 , the magnets  526  are provided on the attachment pieces  527   b  and  527   d  at the left and right ends of the cover  520 , and the cover  520  and the display device main body  510  are fixed with the magnets. The means for fixing the cover  520  and the display device main body  510  is not limited to magnets. 
       FIG. 16A  and  FIG. 16B  illustrate a manner in which hook and loop fasteners are used to fix the cover  520  and the display device main body  510 . Also,  FIG. 16B  is an enlarged view of the region P 1 . In  FIG. 16A  and  FIG. 16B , convex side surface fasteners  571  are provided on the attachment pieces  527   b ,  527   d  at the left and right ends of the cover  520 . On the back side of the display device main body  510 , concave side surface fasteners  572  are provided. When attaching the cover  520  to the display device main body  510 , the cover  520  is attached in a manner such that the display device main body  510  is sandwiched by the attachment pieces  527   a  and  527   b  and the attachment pieces  527   c  and  527   d  on the left side and the right side of the cover  520 , so that the convex side surface fastener  571  on both sides of the cover  520  and the concave side surface fastener  572  on the back side of the display device main body  510  are coupled to fix the cover  520  to the display device main body  510 . 
     Moreover, as shown in  FIG. 16C , the cover  520  may be fixed to the display device main body  510  in a manner such that: hooking hooks  581  are provided on the attaching pieces  527   b  and  527   d  at both the left and right ends of the cover  520 ; protrusions  582  are provided on the back side of the display device main body  510 ; and the hooking hooks  581  on both sides of the cover  520  and the protrusions  582  on the back side of the display device body  510  are engaged with each other. 
     In those cases where there is a concern that the magnet&#39;s magnetism may affect other devices, or where the monitor main body cannot use magnetism, adopting these attachment methods enables shielding of the screen from light without using magnetism, and enables measurement of the center of the screen. 
     Sixth Exemplary Embodiment 
     Next, a sixth exemplary embodiment of the present invention will be described.  FIG. 17A  and  FIG. 17B  are perspective views each showing an appearance configuration of a display device according to the sixth exemplary embodiment of the present invention.  FIG. 17A  shows a state of a monitor when not in use, and  FIG. 17B  shows a state of the monitor when in use. 
     A cover  620  is of a structure such that three cover pieces  621   a ,  621   b , and  621   c  are connected via fold portions  622   a  and  622   b . At the center of the inner side of the cover piece  621   a  there is arranged a light sensor (not shown in the figure). In the present exemplary embodiment, side hoods  671   a  and  671   b  are further provided on the left and right sides. Moreover, there are provided skirt portions  672   a  and  672   b  that extend in the longitudinal direction of the cover pieces  621   a  and  621   b . The cover  620  is attached to the display device main body  610 . 
     The side hoods  671   a  and  671   b  include reinforcing portions  673   a  and  673   b . The reinforcing portions  673   a  and  673   b  are provided in order to prevent the side hoods  671   a  and  671   b  from shifting backward due to the weights of the cover pieces  621   a ,  621   b , and  621   c  and the side hoods  671   a  and  671   b  when they are opened at the time of using the monitor. In addition, as shown by the arrow A 1 , the distal end cover piece  621   c  is folded inward so that the optical sensor arranged on the rear surface of the cover piece  621   b  is hidden. 
     In the present exemplary embodiment, a place for housing the cover  620  at the time of using the monitor is not necessary. The cover  620  is intended to shield external light and can be used as a main body hood when using the monitor. Since the cover piece  621   c  is folded inward when the monitor is in use so that the optical sensor arranged on the rear surface of the cover piece  621   b  does not receive light, deterioration of the materials caused by ultraviolet rays or visible light can be suppressed. As a result, the optical sensor measurement values are reliable for a longer period of time. 
       FIG. 18  is a schematic block diagram showing a basic configuration of the display device according to the present invention. 
     The basic configuration of the display device according to the present invention is as shown in  FIG. 18 . That is to say, the display device according to the present invention comprises a display device main body  900  having a display panel  901 , and a cover  902  that covers the display panel  901 . The cover  902  has an optical sensor  903  on the back surface thereof. The display device main body  900  has a screen calibration function  904  for calibrating the display state of the display panel  901 . In a state where the cover  902  covers the display panel  901  and shields the display panel  901  from light, the screen state of the display panel  901  is measured by the optical sensor  903 , the measured value of the optical sensor  903  is sent to the display device main body  900 , and the display state of the display panel  901  is calibrated by the screen calibration function  904 . 
     The present invention is not limited to the above-described exemplary embodiments, and various modifications and applications may be made within a range that does not depart from the gist of the present invention. 
     REFERENCE SYMBOLS 
     
         
           10  Display device main body 
           11  Display panel 
           12  Bezel 
           13  Magnet attraction material 
           19  Screen calibration function 
           20  Cover 
           23  Rigidity maintaining material 
           26  Magnet 
           30  Optical sensor 
           35  Spacer