Patent Publication Number: US-7710387-B2

Title: Image display device

Description:
This is a divisional of application Ser. No. 10/462,674 filed Jun. 17, 2003 now U.S. Pat. No. 7,609,360. The entire disclosure(s) of the prior application(s), application Ser. No. 10/462,674 is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention belongs to a technical field of an image display device and in particular a medical image display device for displaying an image photographed by a medical diagnostic apparatus or the like. More particularly, the present invention relates to a medical image display device capable of displaying a plurality of medical images arranged in a row as visible images. 
     2. Description of the Related Art 
     A medical image photographed (measured) by a medical diagnostic apparatus such as an ultrasonic diagnostic apparatus, a CT diagnostic apparatus, an MRI diagnostic apparatus, an X-ray diagnostic apparatus, or a CR apparatus including an FCR (Fuji computed radiography) is subjected to various image processing operations as required. After that, generally, the medical image is reproduced as a visible image on a film-shaped recording material by a printer such as a laser printer or a thermal printer and outputted as a hard copy. 
     On a medical site, the film on which the medical image is reproduced is observed using a light box called Schaukasten, and is used for various diagnoses. 
     Also, in recent years, the diagnosis has been conducted by reproducing as a soft copy the medical image photographed by the medical diagnostic apparatus on a display device such as a CRT (cathode ray tube) or a liquid crystal display. In addition, such a diagnosis has come to be conducted, in which a work station for diagnosis provided with a CRT is connected to the medical diagnostic apparatus through a network, and the diagnosis is conducted through observing the photographed medical image in a consulting room or the like which is located apart from the medical diagnostic apparatus. 
     Also, more recently, a thin type liquid crystal display can attain high quality image display. As a result, the liquid crystal display has been increasingly used instead of the CRT in various display fields. In the liquid crystal display, light emitted from a backlight is made incident on a liquid crystal, and a voltage applied to the liquid crystal is changed for each corresponding pixel in accordance with image data. Thus, the transmittance of light passing through the liquid crystal is changed to display an image on a surface side thereof. 
     In particular, in a liquid crystal display for medical use including medical diagnosis, a cold cathode fluorescent lamp (CCFL) is used as a backlight. The CCFL functions on the principle that the luminance can be controlled based on the adjustment of a ramp current value. In addition, for the CCFL, there are a direct type structure and an edge light structure. 
     A plurality of shapes are used for the direct type CCFL, which may be a straight tube, a U-shaped tube, a W-shaped tube, or the like. The direct type CCFL is located immediately under a display region surface of an array substrate in which a liquid crystal is sealed and has a structure in which a liquid crystal in the display region is directly irradiated with light. Note that a light curtain and a diffusing plate are attached onto the upper surface of the direct type CCFL to reduce luminance unevenness. 
     According to the direct type CCFL, because the liquid crystal in the display region is directly irradiated with light, the amount of light can be efficiently utilized, so that high luminance can be achieved easily. Therefore, such a structure is the mainstream particularly in image display on a film viewer (so-called electronic film viewer) used in the medical field that requires high luminance. In other words, a liquid crystal display on which the direct type CCFL is mounted is more appropriate for obtaining high luminance than a liquid crystal display on which an edge light type CCFL to be described later is mounted. Therefore, the former is very often used for the film viewer in the medical field. 
     On the other hand, for the edge light type CCFL, a straight tube, a U-shaped tube, an L-shaped tube, or the like is used. The edge light type CCFL is located in the edge of a light guide plate opposed to the liquid crystal in the display region and has a structure in which the liquid crystal in the display region is indirectly irradiated with light through the light guide plate. Note that a reflector for condensing reflected light to the light guide plate is disposed near the CCFL. In addition, a reflecting sheet for reflecting incident light from the edge to the liquid crystal in the display region is provided in the light guide plate. 
     A liquid crystal display on which the edge light type CCFL is mounted can also be used for the film viewer (electronic film viewer) in the medical field by increasing the luminance of light emitted from the CCFL itself. 
     Here, in order to conduct further accurate diagnosis in medical examination and treatment using the medical diagnostic apparatus, it is general that a large number of images are photographed for each diagnosis while changing a photographing condition, a photographing angle, and a photographing region. In general diagnosis using the film viewer, a plurality of films on which the thus photographed medical images are reproduced, are arranged on the film viewer and the diagnosis is conducted through observing and comparing the respective images. 
     However, when a plurality of medical images photographed by the medical diagnostic apparatus are displayed on a plurality of CRTs or liquid crystal displays to conduct the diagnosis, it is general that one image is displayed on the screen of a CRT or the screen of a liquid crystal display. Accordingly, the luminance must be adjusted for each CRT or each liquid crystal display. 
     In particular, in a liquid crystal display on which the direct type CCFL is mounted, a plurality of light emitting tubes are disposed for the liquid crystal in the display region. Therefore, if the amounts of light of the respective light emitting tubes are not uniform, luminance unevenness is caused. The thus caused luminance unevenness is a serious problem leading to a false diagnosis particularly in the medical field, so that the luminance unevenness should be rapidly compensated for. In addition, in any of the direct type CCFL and the edge light type CCFL, the reduction in luminance causes a problem in that an image is hard to view and so on, which leads to a false diagnosis. Accordingly, it is necessary to keep adequately high luminance. 
     The luminance unevenness has been conventionally adjusted by measurement using a luminance meter for each case. This is inconvenient because a luminance meter is necessary for each case. Therefore, a hole is formed on the rear side of the liquid crystal display to locate an optical sensor so that the luminance of a backlight may be measured. Alternatively, an optical sensor is located in the front side of the liquid crystal display, with which the luminance may be measured. 
     However, when the hole is formed on the rear side of the liquid crystal display, the hole causes the luminance unevenness. In addition, when the optical sensor is located on the front side of the liquid crystal display, a space for the optical sensor is necessary, which causes a problem in that a screen view is blocked. 
     In the case of a diagnosis using an image reproduced on a film, the image is fixed on the film and hence the diagnosis can be basically conducted by observing the single image, although certain differences may occur due to the luminance of a film viewer used or observation environment. 
     On the other hand, when conducting the diagnosis using an image displayed on a display device such as a CRT or a liquid crystal display, the displayed image, that is, the diagnostic image is changed by the type, state and aging of a display device used, because it is image data that is fixed thereon. Such a difference in the image causes a serious problem which may lead to a false diagnosis. Therefore, the quality control (QC) for appropriately retaining the state of a display device used is important when conducting diagnosis using the display device. 
     Various test items including observation condition, (luminance) gradation properties, spatial resolution and geometry are set for the quality control of display devices. The important measurement for conducting these tests is the measurement of luminance such as maximum luminance and minimum luminance of a display device, and surface reflection luminance of a display device in association with peripheral light. 
     An exterior luminance meter must be used to measure the luminance, which is laborious. In particular, the high-accuracy luminance measurement requires the use of a telescopic luminance meter, which is however expensive and is not easy to handle. A contact type luminance meter is known as the meter capable of simple luminance measurement but luminance cannot be appropriately measured in the contact type luminance meter because a displayed image is changed when a force is applied to the image display screen of a liquid crystal display, which is well known in the art. 
     Further, it is necessary to measure the surface reflection luminance under observation conditions using a telescopic luminance meter when quality control is performed according to DICOM (Digital Imaging and Communications in Medicine; transmission standard of medical image data, waveform data and the like), which makes the quality control work of a display device complicated. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is, therefore, to solve the above-mentioned problems inherent in the related art, and to provide an image display device in which a screen view is not obstructed by an optical sensor for measuring luminance unevenness of a liquid crystal panel which is caused by a service life of a backlight, and which is capable of down sizing and easy measurement of environmental light (exterior light) and light from the backlight. 
     A second object of the present invention is to provide an image display device which meets the first object described above and is also capable of simple measurement of surface reflection luminance, maximum luminance and minimum luminance without using any exterior luminance meter, thus enabling significant improvement of the workability for the quality control of display devices, and in particular a device and a system for medical image display which are capable of easy display quality control of medical images. 
     In order to achieve the above-mentioned objects, according to the present invention, there is provided an image display device which includes a liquid crystal panel, the liquid crystal panel comprising: at least one optical sensor for outputting an electric signal resulting from light irradiation; pixel electrodes for driving a liquid crystal; switching elements for switching the pixel electrodes; and a single transparent substrate on which the at least one optical sensor, the pixel electrodes and the switching elements are formed by laminating thin films. 
     The at least one optical sensor and the switching elements are preferably formed by using an identical material. 
     The term “identical material” used herein means that a semiconductor serving as a substrate which includes no dopant for producing a p-type or n-type semiconductor is the same so that pn-junction portions in the optical sensor and the switching elements (TFTs) can be formed by laminating thin films without greatly increasing the number of steps. It is preferable that amorphous silicon or polycrystalline silicon is used as the identical material. 
     In a preferred embodiment, the image display device of the present invention further includes a control section for monitoring an output from the at least one optical sensor. 
     Besides, the image display device may further include display means for displaying on a monitor a measurement result obtained by the optical sensor or voice output means for outputting a voice indicating the measurement result. In addition, the control section, the display means, and the voice output means may be provided in the image display device or on the side of an image display system (e.g., electronic film viewer system in medical image display) on which the image display device is mounted. 
     It is preferable that the at least one optical sensor can detect at least one of light emitted from a backlight located on a rear side of an image display screen and environmental light incident from a front side of the image display screen. 
     It is preferable that a hole is provided in a black matrix located above the image display side of the optical sensor to facilitate incidence of environmental light. In particular, a light transmitting member is preferably formed in the hole by thin film lamination. SiO 2  may be used as a material for an insulating film, because SiO 2  is a transparent material and enables electrical insulation between the upper and lower layers. Alternatively, a material used in one of the upper and lower layers may be filled into the hole. 
     The at least one optical sensor is preferably located in a non-display region. 
     If the optical sensor is thus located in the non-display region outside a display region of the image display screen, there is no influence on image display in the display region. In addition, the optical sensor is preferably a diode made of amorphous silicon or polycrystalline silicon. In particular, when the optical sensor is formed by laminating the thin film by polycrystalline silicon, a circuit density is increased. Accordingly, an area in which the optical sensor is formed can be decreased, so that there is no increase in the size as compared with a conventional liquid crystal panel. 
     Preferably, the image display device of the present invention further includes a backlight for the liquid crystal panel and control means for controlling the backlight and the control means turns off the backlight when environmental light (exterior light) is measured using the at least one optical sensor and turns on the backlight when light from the backlight is measured using the at least one optical sensor. 
     It is preferable to acquire in advance the relation between the maximum luminance of the liquid crystal panel (image display device, that is, image display therein) and the results of the measurement of light from the backlight in a darkroom, and the relation between the minimum luminance of the liquid crystal panel and the results of the measurement of light from the backlight in a darkroom, and detect the maximum luminance and the minimum luminance of the liquid crystal panel from the results of the measurement of light from the backlight using the optical sensor. It is further preferable to acquire in advance the relation between the surface reflection luminance of the liquid crystal panel and the results of the measurement of exterior light and detect the surface reflection luminance of the liquid crystal panel from the results of the measurement of environmental light (exterior light) using the optical sensor. 
     The image display device of the present invention is preferably a medical image display device for displaying a medical image on the liquid crystal panel. 
     According to the structure of the present invention, the optical sensor is formed by laminating thin film, that is to say, laminated on the same transparent substrate made of glass, a transparent resin, or the like together with the pixel electrodes and the switching elements. In particular, the optical sensor can be thin-film-laminated on the transparent substrate together with the pixel electrodes and the switching elements by the same steps. In other words, if a pattern for the optical sensor is incorporated in a pattern for the pixel electrodes and the switching elements, the optical sensor can be easily thin-film-laminated on the transparent substrate together with the pixel electrodes and the switching elements by repeating the steps such as resist formation, development, etching, and resist peeling. 
     Thus, according to the structure of the present invention, the amount of environmental light or the amount of light from a backlight can be measured without locating a separate optical sensor in the liquid crystal panel or using a separate luminance meter. 
     Also, because the optical sensor is incorporated in the transparent substrate, it is unnecessary to prepare for each measurement a specific measurement device such as a luminance meter. Therefore, the measurement is conducted in a real time, so that luminance unevenness can be compensated for. In addition, there can be provided a structure useful to reduce the size of the image display device on which the optical sensor for detecting the amount of environmental light (exterior light) and the amount of light from the backlight is mounted. 
     In particular, the image display device of the present invention is capable of easy measurement of environmental light and light from the backlight, which enables significant improvement of the workability for display quality control and particularly easy display quality control of medical images. Therefore, the image display device of the present invention is useful as the medical image display device. 
     Also, in particular, in the case of a direct type backlight in which a plurality of CCFLs are arranged, the optical sensor is located for each of the CCFLs, the measurement is conducted, and a current flowing into a CCFL whose luminance is reduced is controlled. Thus, a change with time with respect to the uniformity of luminance can be compensated for. 
     Note that the thin-film-laminated optical sensor detects the environmental light incident from the front side or the rear side of the liquid crystal panel and outputs a signal corresponding to the amount of light (for example, a current value, a voltage value, or a power value). The quantitative determination can preferably be conducted by a control section (CPU) provided separately from the liquid crystal panel. Alternatively, the control section may be formed by thin film lamination in the liquid crystal panel itself. 
     Further, according to the present invention, there is provided an image display system comprising image display devices each having display means for displaying on a monitor a measurement result obtained by the optical sensor or voice output means for outputting a voice indicating the measurement result. 
     Note that the image display system of the present invention is particularly useful as the medical image display system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a plan view showing a main part structure of an example of a liquid crystal panel used for a medical image display device of the present invention; 
         FIG. 2  is a block diagram showing an example of a main part structure for explaining optical measurement processing and display processing of a medical image display system of the present invention; 
         FIG. 3A  is a sectional view for explaining a main part structure of an exemplary array substrate of the medical image display device of the present invention; 
         FIG. 3B  is a sectional view for explaining a main part structure of another example; 
         FIGS. 4A to 4D  are explanatory step views for steps of manufacturing the array substrate shown in  FIG. 3A , which are sectional views in the respective steps of manufacturing the array substrate; 
         FIGS. 5E to 5H  are explanatory step views for steps of manufacturing the array substrate shown in  FIG. 3A , which are sectional views in the respective steps of manufacturing the array substrate; 
         FIG. 6  is a schematic view showing a main part structure of the liquid crystal panel of the medical image display device according to the present invention; 
         FIGS. 7A to 7C  are explanatory views of another example in which the pn-junction is not used in the optical sensor mounted on the medical image display device of the present invention, in which  FIG. 7A  is a sectional view of the optical sensor,  FIG. 7B  is a plan view of a gate electrode, and  FIG. 7C  is a plan view of a gate electrode as another example; 
         FIG. 8A  is a graph for explaining detection of surface reflection luminance in the present invention; 
         FIG. 8B  is a graph for explaining detection of maximum luminance and minimum luminance in the present invention; 
         FIG. 9  is a plan view showing a main part structure of a liquid crystal panel as another example used for the medical image display device of the present invention; 
         FIG. 10  is a block diagram showing a main part structure for explaining optical measurement processing of the medical image display system of the present invention; 
         FIG. 11  is an explanatory view of an example of an electronic film viewer using the medical image display device of the present invention; and 
         FIG. 12  is an explanatory view of another example of the electronic film viewer using the medical image display device of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, the image display device and the image display system using this device according to the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings. A medical image display device and a medical image display system using this device will be described below as a typical case but it is to be understood that this is not the sole case of the present invention. 
       FIG. 1  is a plan view showing a main part structure of an exemplary liquid crystal panel used for the medical image display device of the present invention. Reference numeral  10  denotes a liquid crystal panel. In the liquid crystal panel  10  shown in  FIG. 1 , an array substrate in which driver circuits for pixel electrodes and switching elements are formed is mainly indicated, and a counter substrate which is located opposite to the array substrate and in which a color filter and the like are formed is omitted. 
     The liquid crystal panel  10  includes: a display region  20  in which thin film transistors (TFTs), transparent pixel electrodes made of indium tin oxide (ITO), and a wiring pattern, which are not shown, are formed by thin film lamination on the array substrate made of flat glass; and a non-display region  30  provided outside the display region  20 . 
     An optical sensor  40  is formed by the thin film lamination in the non-display region  30 . The optical sensor  40  has a structure of a pn-junction using the same amorphous silicon (a-Si) as in the TFTs. The optical sensor  40  is an optical sensor utilizing a photovoltaic effect. According to the optical sensor  40 , when the interface of the pn-junction is irradiated with light, a photoproduction carrier is produced. Then, an electron and hole which are generated are drifted in opposite directions to each other by an electric field to cause the separation of charges. Therefore, an electromotive force resulting from light reception is generated. Thus, the optical sensor  40  outputs the electromotive force as an electric signal. 
     Also, the liquid crystal panel  10  is electrically connected with a gate driver  50  for controlling the gates of the TFTs and a source driver  51  for controlling the signal level of a voltage applied to the liquid crystal panel  10  in accordance with image data of an image to be displayed through TABs  60 . Similarly, the optical sensor  40  is electrically connected with a higher level unit through the TAB  60 . 
     A backlight  70  for emitting light transmitting through pixel electrodes is located on the rear side of the liquid crystal panel  10 . The optical sensor  40  is located near the backlight  70 . In addition, a light guide plate for guiding light emitted from the backlight  70 , which is not shown, is located on the rear surface of the display region  20 . 
       FIG. 2  is a block diagram showing a main part structure for explaining optical measurement processing and display processing of the medical image display system including the medical image display device of the present invention. Reference numeral  80  denotes a medical image display system. The medical image display system  80  includes the optical sensor  40 , an amplifier  81  for amplifying a voltage value sent from the optical sensor  40 , an A/D converter  82  for converting the voltage value sent from the amplifier  81  as an analog value into light amount data as a digital value, a light amount monitor  83  for monitoring the light amount data, a control section  84  for receiving a signal from the light amount monitor  83  to conduct the optical measurement processing and display processing, the backlight  70  controlled by the control section  84 , and a backlight driver  73  located between the control section  84  and the backlight  70 . Note that the control section  84  has a gradation correcting portion which receives an image data signal R from an exterior image data supply source (not shown) and corrects the luminance gradation of the liquid crystal panel  10 , that is, a gradation correcting LUT (look-up table)  87 . The gradation correction using the LUT  87  and the calibration thereof will be described later. 
     In other words, according to the medical image display system  80 , when the optical sensor  40  receives environmental light or light from the backlight to generate an electromotive force, a voltage value (an electric signal) corresponding to the electromotive force is amplified by the amplifier  81  and the voltage value as the analog value is converted into the light amount data as the digital value by the A/D converter  82 . 
     Then, when an abnormal state is caused while the light amount monitor  83  monitors the light amount data sent in real time, the light amount monitor  83  sends an abnormality signal to the control section  84  as a higher level unit. When receiving the abnormality signal, the control section  84  controls the gate driver  50  or the source driver  51  to display light amount abnormality of the environmental light (exterior light) or that of the backlight  70  on the liquid crystal panel  10 , or to issue an alarm on the light amount abnormality from a speaker (not shown), or to perform both of the display and the issuance of an alarm on the light amount abnormality. 
     Note that, when the backlight  70  is a CCFL capable of adjusting luminance depending on current, the control section  84  may control the value of the current to be supplied to adjust the CCFL. 
       FIG. 3A  is a sectional view for explaining a main part structure of an example of the array substrate of the medical image display device of the present invention. The array substrate has a structure in which the optical sensor  40  which is composed of an insulating film  92 , a p-type a-Si film  94 , an n-type a-Si film  98 , and optical sensor electrodes  102 ,  102 ; pixel electrodes  99 ; and TFTs  22  each of which is composed of a gate electrode  91 , the insulating film  92 , a non-doped a-Si film  93 , n-type a-Si films  96  and  97 , a source electrode  100 , and a drain electrode  101  are thin-film-laminated on a single transparent substrate  90 . In particular, the optical sensor  40  and the TFTs  22  are made of the same material, a-Si. Note that, as the same material which composes the optical sensor  40  and the TFTs  22 , polycrystalline silicon may be used instead of a-Si. 
     Although not shown, the optical sensor  40  and the TFTs  22  have a protective layer made of silicon nitride (SiN x ) formed thereon. 
     Also, it is possible that the insulating film  92  of the optical sensor  40  is omitted and the p-type a-Si film  94  is directly formed on the transparent substrate  90 . In general, because SiO 2  is used for the insulating film  92  and the reflection is caused on its interface at incidence and exit of light, the amount of light entered into the optical sensor  40  is reduced. Therefore, when the p-type a-Si film is directly formed on the transparent substrate  90 , it can be expected that the transmittance of light be increased as compared with the case where the insulating film  92  is interposed therebetween. 
     According to the optical sensor  40 , the movement of carriers is produced at the bonded interface between the p-type a-Si film  94  and the n-type a-Si film  98 , which results from both light from a direction indicated by an arrow α (environmental light) and light from a direction indicated by an arrow β (light from the backlight), thereby generating the electromotive force due to light irradiation. The generated electromotive force is led as an electric signal from the optical sensor electrodes  102 ,  102  to the outside. 
     When it is desired to block out the light from the direction β (light from the backlight  70 ), in other words, when it is desired to measure only the environmental light (exterior light), a dummy electrode  91   a  for shielding need only be provided beneath the p-type a-Si film  94  between the transparent substrate  90  and the insulating film  92  as shown in  FIG. 3B . The dummy electrode  91   a  for shielding can be formed on the transparent substrate  90  at the same time as the gate electrode  91 . 
       FIGS. 4A to 4D  and  5 E to  5 H are explanatory step views for steps of manufacturing the array substrate shown in  FIG. 3A . For the array substrate, a series of steps such as metallic film formation, resist formation, masking, exposure, development, etching, and resist peeling are repeated, so that the optical sensor  40  is formed by thin film lamination together with the pixel electrodes  99  and the TFTs  22 . First, the gate electrode  91  is formed on the transparent substrate (glass substrate)  90  (see  FIG. 4A ) and then the insulating film  92  is formed (see  FIG. 4B ). 
     After that, the non-doped a-Si film  93  is formed (see  FIG. 4C ), the p-type a-Si film  94  doped with boron is formed (see  FIG. 4D ), an insulating film  95  is formed (see  FIG. 5E ), the n-type a-Si films  96 ,  97 , and  98  doped with phosphorus are formed (see  FIG. 5F ), the pixel electrode  99  is formed (see  FIG. 5G ), and the source electrode  100 , the drain electrode  101 , and the optical sensor electrodes  102 ,  102  are then formed (see  FIG. 5H ). In this way, the optical sensor  40 , the pixel electrodes  99 , and the TFTs  22  are formed by the thin film lamination on the same transparent substrate  90 . 
       FIG. 6  is a schematic view showing a main part structure of an example of the liquid crystal panel of the medical image display device according to the present invention. The liquid crystal panel has a structure in which the transparent substrate  90  in which the optical sensor  40 , the TFTs  22 , and the pixel electrodes  99  are formed by the thin film lamination and a transparent substrate  1  are bonded to each other by a sealing member  4 . A liquid crystal and spacers, which are not shown, are sealed between the transparent substrate  90  and the transparent substrate  1 . Note that, in  FIG. 6 , the backlight  70  for emitting light, a light guide plate  71  for guiding the light emitted from the backlight  70  onto substantially the entire surface of the transparent substrate  90 , and a diffusion plate  5  for diffusing the light guided by the light guide plate  71  to reduce the luminance unevenness, thereby making the light enter into the transparent substrate  90  side are disposed under the transparent substrate  90 . 
     A black matrix  2  for shielding the upper portion of the TFT  22  from light and a color filter  3  located above the pixel electrode  99  are mainly laminated on the transparent substrate  1 . A window hole  2   a  for the admission of external environmental light is formed in the black matrix  2  above the optical sensor  40 . Note that a single layer film made of metallic chromium, a composite film made of metallic chromium and chromium oxide, or a resin film into which carbon is incorporated is very often used for the black matrix  2 . In addition, it is preferable that the window hole  2   a  formed in the black matrix  2  is filled with a transparent insulating material such as SiO 2 . 
     Note that a region of the optical sensor  40  may be located outside the sealing member  4 . In the case of such a structure, the window hole  2   a  for the admission of environmental light (exterior light) is not necessarily formed. In addition, it is preferable that the window hole  2   a  is not formed in the structure in which light from the backlight  70  is measured. When environmental light and light from the backlight  70  are measured separately, the optical sensor  40  in which the window hole  2   a  for the admission of environmental light is formed and the optical sensor  40  in which the window hole  2   a  is not formed for measuring light from the backlight  70  are provided in separate portions. 
     The case where the number of optical sensors is one has been described above, but it is preferable that a plurality of optical sensors are arranged to further improve the sensitivity. In addition, it is preferable that a plurality of optical sensors for measuring environmental light and a plurality of optical sensors for measuring the amount of light from the backlight are separately arranged. 
       FIGS. 7A to 7C  are explanatory views of another example in which the pn-junction is not used in an optical sensor mounted on the medical image display device of the present invention.  FIG. 7A  is a sectional view of the optical sensor,  FIG. 7B  is a plan view of a gate electrode, and  FIG. 7C  is a plan view of a gate electrode as another example. In  FIG. 7A , reference numeral  140  denotes an optical sensor. The optical sensor  140  has a structure in which the gate electrode  91 , the insulating film  92 , the non-doped a-Si film  93 , the n-type a-Si films  96  and  97 , the source electrode  100 , the drain electrode  101 , and a transparent member  141  with which a hole formed in the gate electrode  91  is filled are thin-film-laminated on the transparent substrate  90 . 
     As is apparent from the same reference numerals given to the elements having the same structure as in the TFT  22 , whether or not the transparent member  141  is provided in the gate electrode  91  is the difference between the TFT  22  and the optical sensor  140 . The transparent member  141  has a function of transmitting light of the backlight  70  (not shown here) from the transparent substrate  90  side to the a-Si film  93 . Accordingly, an electromotive force resulting from a leak current due to light irradiation is generated and output as an electric signal in the a-Si film  93  without making the pn-junction, so that the characteristic of the optical sensor  140  can be utilized while the structure of the TFT  22  is kept. 
     Also, the transparent member  141  may be formed, for example, concentrically with respect to the circular gate electrode  91  as shown in  FIG. 7B . Note that, as shown in  FIG. 7C , an H-shaped transparent member  142  may be formed in the gate electrode  91 . Exemplary shapes of the transparent members  141  and  142  were mentioned above, but the present invention is not limited to these shapes. As shown by chain double-dashed lines in  FIGS. 7B and 7C , the gate electrode  91  may be of a rectangular shape or other shapes. 
     Note that, in consideration of the transparent member  141  which is a thin film, lamination is preferably made using for example SiO 2 . 
     The optical measurement processing and display processing in the medical image display system  80  of the present invention shown in  FIG. 2  which includes the medical image display device using the liquid crystal panel  10  shown in  FIG. 1 , in particular the gradation correction using the. gradation correcting LUT (gradation correcting portion)  87  for correcting the luminance gradation of the liquid crystal panel  10  and the calibration of the LUT  87  will be described below. 
     In the illustrated medical image display system  80 , image data R of an image displayed on the liquid crystal panel  10  is supplied from an exterior image data supply source (not shown) to the control section  84  and then to the LUT (gradation correcting portion)  87 . 
     The LUT (gradation correcting portion)  87  is a block in which the supplied image data R is corrected using the gradation correcting LUT prepared (updated) by the calibration (of the luminance gradation) to produce image data corresponding to an image having specified (luminance) gradation properties. 
     In the illustrated case, the LUT  87  corrects the supplied image data R so that the displayed image can be an image having gradation properties corresponding to the DICOM GSDF (Grayscale Standard Display Function). 
     The image data corrected by the LUT  87  is then supplied to an LCD driver of the liquid crystal panel  10 . 
     The LCD driver includes the gate driver  50  and the source driver  51  and converts the image data supplied from the LUT  87  into a drive signal corresponding to the liquid crystal panel  10  and sends the drive signal to the gate driver  50  and the source driver  51  to drive a corresponding TFT  22  of the liquid crystal panel  10 . 
     In the illustrated medical image display system  80 , environmental light (hereinafter referred to as exterior light) is measured to detect the surface reflection luminance of the liquid crystal panel  10  (image view surface) or light from the backlight  70  is measured to detect the maximum luminance and the minimum luminance of the liquid crystal panel  10 , both according to the optical measurement processing as described above. 
     The image display device and system, and the method for the optical measurement processing according to the present invention will described below in greater detail by explaining the detection of the surface reflection luminance based on the measurement of exterior light, the detection of the maximum luminance and minimum luminance based on the measurement of light from the backlight  70 , and the operations of the control section  84  and the LUT  87  during the luminance detection. 
     A telescopic luminance meter and an illuminometer are used to determine in advance the relation between the illuminance E [lx] of exterior light incident on the liquid crystal panel  10  and the surface reflection luminance L amb  [cd/m 2 ], and the relation between the illuminance E and the output signal x (digital data) from the optical sensor  40  (see  FIG. 6 ) thereby detecting the surface reflection luminance based on the measurement of exterior light. 
     When the relation between the illuminance E and the surface reflection luminance L amb  is determined, the control section  84  activates the LCD driver (gate driver  50  and source driver  51 ) and the backlight driver  73  (hereinafter the operation of the control section  84  will be omitted) to render the liquid crystal panel  10  in black display state (in which the whole area of the display region (effective pixel region)  20  in the liquid crystal panel  10  has the minimum luminance or a minimum amount of light passes through liquid crystal). The backlight is turned off. The illuminometer is placed on the surface of the liquid crystal panel  10  to measure the illuminance E of exterior light on the surface of the liquid crystal panel  10 , and the surface reflection luminance L amb  of the liquid crystal panel  10  at the time of the illuminance measurement is also measured with the telescopic luminance meter. The measurement is repeatedly performed in illumination with various amounts of light to thereby determine the relation between the illuminance E and the surface reflection luminance L amb . 
     A diffuse reflection coefficient p is used to represent the above relation by “L amb =ρE”. In other words, the surface reflection luminance L amb  is increased proportionately with the illuminance E. 
     On the other hand, when the relation between the illuminance E and the output signal x from the optical sensor  40  is determined, the backlight is turned off, the illuminance E on the surface of the liquid crystal panel  10  is measured in the same manner and the amount of exterior light at the time of the illuminance measurement is also measured with the optical sensor  40 . The measurement is repeatedly performed in illumination with various amounts of light to determine the relation between the illuminance E and the output signal x from the optical sensor  40 . 
     As described above, when the backlight is turned off, the output signal x from the optical sensor  40  is increased proportionately with the amount of exterior light incident on the liquid crystal panel  10 , that is, the illuminance E. The relation between the illuminance E of exterior light and the output signal x is represented by “x=k 1 E” wherein k 1  is a constant of proportionality. 
     The surface reflection luminance L amb  is represented by “L amb =ρE” and is increased proportionately with the illuminance E of exterior light. The output signal x from the optical sensor is also increased proportionately with the illuminance E of exterior light based on the equation “x=k 1  E”. Therefore, the surface reflection luminance L amb  has a proportional relation with the output signal x from the optical sensor  40 . 
     To be more specific, the following equation is derived:
 
 E=x/k   1   =L   amb /ρ
 
Then,
 
 x=L   amb   k   1 /ρ
 
Therefore,
 
 L   amb =(ρ/  k   1 ) x  
 
Assuming that (ρ/k 1 ) is k 2 , the equation of the graph as shown in  FIG. 8A :
 
L amb =k 2 x
 
is obtained.
 
     Therefore, by determining the relation shown in  FIG. 8A  and the constant of proportionality k 2  (hereinafter referred to as reflection luminance coefficient k 2 ) in advance and measuring exterior light using the optical sensor  40  while the backlight is turned off, the surface reflection luminance L amb  can be detected from the measurement results, that is, the output signal x from the optical sensor  40 . 
     On the other hand, in order to detect the maximum luminance and the minimum luminance of the liquid crystal panel  10  based on the measurement of light from the backlight  70  with the optical sensor  40  covered with the black matrix  2  having no window hole  2   a  as described above, the telescopic luminance meter is used to determine in advance the relation between the maximum luminance and minimum luminance, and the results of the measurement of light from the backlight  70  with the optical sensor  40 . 
     When this relation is determined, the output signal y from the optical sensor  40  is measured in a darkroom while the backlight  70  is turned on and the display luminance of the liquid crystal panel  10  under the action of the luminance of the backlight is measured with the telescopic luminance meter in black display state (minimum luminance L min ) and in white display state (maximum luminance L max ). The white display state refers to the state in which the whole area of the display region (effective pixel region)  20  in the liquid crystal panel  10  has the maximum luminance or a maximum amount of light passes through liquid crystal. The measurement is repeatedly performed with various backlight luminance values (various outputs from the backlight  70 ) to thereby determine the relation between the output signal y from the optical sensor  40 , and the maximum luminance L max  and minimum luminance L min . 
     If there is no aging in the medical image display device (liquid crystal panel  10 ), the maximum luminance L max  and the minimum luminance L min  of the liquid crystal panel  10  are proportional to the luminance of the backlight  70 , that is, the output signal y of the optical sensor  40 . In other words, the equations “L max =ay” and “L min =by” are obtained where a is a constant of proportionality between the maximum luminance L max  and the output signal y, and b is a constant of proportionality between the minimum luminance L min  and the output signal y. 
     Therefore, by determining in advance the relation shown in  FIG. 8B , the constant of proportionality a (hereinafter referred to as maximum luminance coefficient a) and the constant of proportionality b (hereinafter referred to as minimum luminance coefficient b), and measuring light from the backlight  70  with the optical sensor  40  while the liquid crystal panel  10  is in black display state and the backlight  70  is turned on, the maximum luminance L max  and the minimum luminance L min  of the liquid crystal panel  10  can be detected from the measurement results, that is, the output signal y from the optical sensor  40 . 
     The control section  84  in the medical image display device (liquid crystal panel  10 ) stores the reflection luminance coefficient k 2 , the maximum luminance coefficient a and the minimum luminance coefficient b calculated as described above. 
     In accordance with an instruction entered from the exterior, the control section  84  turns off the backlight  70  to measure exterior light with the optical sensor  40  and detect the surface reflection luminance L amb  of the liquid crystal panel  10  (medical image display device) using the output signal x and the reflection luminance coefficient k 2 , or renders the liquid crystal panel  10  in black display state and turns on the backlight  70  to measure light from the backlight  70  with the optical sensor  40 , and detect the maximum luminance L max  and the minimum luminance L min  of the liquid crystal panel  10  using the output signal y, and the maximum luminance coefficient a and the minimum luminance coefficient b. 
     In other words, according to the present invention, the surface reflection luminance of the liquid crystal panel  10 , and the maximum luminance and the minimum luminance of the liquid crystal panel  10  can be detected without using a telescopic luminance meter or the like by measuring environmental light (exterior light) and light from the backlight  70 . Therefore, the quality control of the liquid crystal panel  10  (medical image display device) can be readily performed by a simple operation. 
     When performing the calibration (for the luminance gradation) in the medical image display system  80 , the control section  84  detects the surface reflection luminance L amb  of the liquid crystal panel  10 , and the maximum luminance L max  and the minimum luminance L min  of the liquid crystal panel  10  as described above to thereby update the gradation correcting LUT  87  in the gradation correcting portion. Since the medical image display device displays an image conforming to the DICOM GDSF gradation as described above, the control section  84  calculates the luminance range of from L min ′ to L max ′ in the liquid crystal panel  10  (medical image display device) by the following equations:
 
 L   max   ′=L   max   +L   amb  
 
 L   min   ′=L   min   +L   amb .
 
The gradation assignment is performed so as to provide the GSDF gradation in this luminance range and the gradation correcting LUT  87  in the gradation correcting portion is updated, thereby performing the calibration. The gradation assignment or the like can be performed by any known method.
 
     In other words, according to the present invention, the medical image display device can be calibrated by a simple operation without using a telescopic luminance meter or the like. 
     In the examples described above, the coefficients (functions) were used to detect the surface reflection luminance of the liquid crystal panel  10 , and the maximum luminance and the minimum luminance of the liquid crystal panel  10 . However, this is not the sole case of the present invention. An LUT prepared by performing the similar measurement may be used to detect the surface reflection luminance or the like. 
       FIG. 9  is a plan view showing a main part structure of a liquid crystal panel as another example used for the medical image display device of the present invention. Reference numeral  110  denotes a liquid crystal panel. In the liquid crystal panel  110  shown in  FIG. 9 , an array substrate in which driver circuits for pixel electrodes and switching elements are formed is mainly indicated, and a counter substrate which is located opposite to the array substrate and in which a color filter and the like are formed is omitted. 
     The liquid crystal panel  110  includes: a display region  20  in which thin film transistors (TFTs), transparent pixel electrodes made of ITO, and a wiring pattern, which are not shown, thin-film-laminated on the array substrate made of flat glass; and a non-display region  30  provided outside the display region  20 . 
     Optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e  similar to the optical sensor  40  described above are thin-film-laminated in the non-display region  30 . In addition, the liquid crystal panel  110  is electrically connected with a gate driver  50  and a source driver  51  through TABs  60 . Similarly, the optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e  are electrically connected with a higher level unit through the TABs  60 . 
     Backlights  70   a ,  70   b ,  70   c ,  70   d , and  70   e  for emitting light to be transmitted through pixel electrodes are located in the rear side of the liquid crystal panel  110 . The backlights  70   a ,  70   b ,  70   c ,  70   d , and  70   e  are located near the optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e , respectively. 
       FIG. 10  is a block diagram showing an example of a main part structure for explaining optical measurement processing and display processing of the medical image display system (device) of the present invention. Reference numeral  180  denotes a medical image display system. The medical image display system  180  includes: the optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e ; amplifiers  81   a ,  81   b ,  81   c ,  81   d , and  81   e  for amplifying respective voltage values sent from the optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e ; a switch  85  for selectively outputting the voltage values inputted from the amplifiers  81   a ,  81   b ,  81   c ,  81   d , and  81   e ; an A/D converter  82  for converting a voltage value as an analog value which is sent from the switch  85  into light amount data as a digital value; a light amount monitor  83  for monitoring the light amount data; a control section  86  which receives a signal from the light amount monitor  83  and conducts the optical measurement processing and display processing; the five backlights  70   a  to  70   e controlled by the control section  86 ; and backlight drivers  73   a  to  73   e  provided between the control section  86  and the backlights  70   a  to  70   e.    
     Note that the control section  86  also controls switching operation of the switch  85 . Further, the control section  86  has a gradation correcting LUT (gradation correcting portion)  88  which receives an image data signal R from an exterior image data supply source (not shown) and corrects the luminance gradation of the liquid crystal panel  110 . The gradation correction using the LUT  88  of the control section  86  and the calibration of the LUT  88  can be performed in the same manner as the gradation correction using the LUT  87  of the control section  84  and the calibration of the LUT  87 . 
     According to the medical image display system  180 , the switch  85  switches the outputs from the optical sensors  40   a ,  40   b ,  40   c ,  40   d , and  40   e , and the control section  86  checks the signal from the light amount monitor  83 . Note that the description related to the same measurement operation as in the above description by reference to  FIG. 2  is omitted. When receiving the abnormality signal, the control section  86  controls the gate driver  50  or the source driver  51  to display the light amount abnormality of the environmental light (exterior light) or that of the backlights  70   a ,  70   b ,  70   c ,  70   d , and  70   e  on the liquid crystal panel  10 , or to issue an alarm on the light amount abnormality from a speaker (not shown), or to perform both of the display and the issuance of an alarm on the light amount abnormality. Further, the control section  86  determines which of the backlights  70   a ,  70   b ,  70   c ,  70   d , and  70   e  is abnormal. In the case of the CCFL, the value for a current supplied to the abnormal backlight  70   a ,  70   b ,  70   c ,  70   d  or  70   e  may be controlled to conduct luminance adjustment. 
     Thus, the image display apparatus of the present invention and in particular the medical image display apparatus and system, and the method for the optical measurement processing have been described in detail. However, the present invention is not limited to the above embodiments. As a matter of course, various improvements and modifications may be made without departing from the spirit and scope of the present invention. 
     For example, according to the above embodiments, the medical image display system includes one optical sensor or five optical sensors. However, the present invention is not limited to such embodiments. The medical image display system may include two optical sensors, three optical sensors, or four optical sensors. Alternatively, the medical image display system may include six or more optical sensors. 
     The embodiments described above referred to the case where the number of the liquid crystal panels  10  is one. However, it is preferable that an optical sensor is provided for each of a plurality of liquid crystal panels, the luminance of backlight in each liquid crystal panel is measured, and adjustment is conducted such that the luminance of each liquid crystal panel is uniform. The liquid crystal panels can be used for the electronic film viewers as shown in  FIGS. 11 and 12 , for example. 
       FIG. 11  shows an example of an electronic film viewer using the medical image display device according to the present invention. In an electronic film viewer  200 , a control device  205  controls liquid crystal displays  201 ,  202 ,  203 , and  204  in which the above-mentioned liquid crystal panel according to the present invention is incorporated. 
       FIG. 12  shows another example of an electronic film viewer using the medical image display device according to the present invention. An electronic film viewer  300  has a structure in which liquid crystal displays  301 ,  302 ,  303 , and  304  in which the above-mentioned liquid crystal panel according to the present invention is incorporated are incorporated in a case in which a control device  305  is integrally formed. 
     In the embodiments shown in  FIGS. 2 and 10 , the gradation correcting LUTs (gradation correcting portions)  87  and  88  for correcting the luminance gradation of the liquid crystal panels  10  and  110  are located in the control sections  84  and  86 , respectively. However, this is not the sole case of the present invention. The gradation correcting LUT (gradation correcting portion) may be provided in the control device  205  or  305  shown in  FIG. 11  or  12  so that the gradation correction using the LUT and the calibration of the LUT can be performed. 
     The embodiments described above referred to an active matrix liquid crystal panel of TFT system. However, a structure called MIM (metal insulator metal) system which is suitable to increase a circuit density may be used. This is a structure in which a thin-film-laminated switching element made from metal-insulator-metal (MIM) is formed instead of the switching element of TFT system. In this case, an optical sensor made of a-Si or the like is thin-film-laminated outside the non-display region of the panel. Therefore, the optical sensor may be formed before or after the formation of MIM. If one is being thin-film-laminated, the other is preferably masked. 
     Note that, in the above embodiments, the amounts of light from the respective light emitting tubes may be quantitatively measured by the optical sensor  40  and the control section  84  or  86  may inform of their states. 
     Furthermore, in the above embodiments, light amount adjusting means for adjusting the amount of light from the backlight (CCFL)  70  may be provided in the control section  84  or  86 , and the amount of light may be adjusted to compensate for the luminance unevenness. The light amount adjusting means can be realized by using a program having a plurality of steps for adjusting the amount of light, a recording medium such as a ROM or a RAM into which the program is written, and a CPU for reading the program from the recording medium and executing the read program. 
     The programs considered are, for example, a program having a step of comparing the outputs of a plurality of optical sensors and a step of controlling ramp currents of the respective optical sensors based on the comparison result such that the outputs of the respective optical sensors coincide with one other, and a program having a step of setting a threshold value for the outputs of optical sensors in advance and comparing the threshold value with the outputs of the respective optical sensors and a step of controlling ramp currents based on the comparison result such that the output from the optical sensor which is lower than the threshold value becomes a value exceeding the threshold value (value equal to the threshold value or an arbitrary value exceeding the threshold value). However, the present invention is not limited to such programs. 
     Thus, as described above, according to the present invention, the optical sensor(s) for sensing the amount of environmental light and the amount of light from the backlight, the pixel electrodes, and the switching elements are provided on the same transparent substrate. Accordingly, the medical image display device which can achieve down sizing without preventing the optical sensor from obstructing screen view can be provided. 
     Therefore, it is not necessary to prepare a specific measurement device such as a luminance meter for each measurement as in a conventional case. Accordingly, the measurement is conducted in real time, so that luminance unevenness can be compensated for. In addition, particularly, if the optical sensor is formed on the transparent substrate together with the pixel electrodes and the switching elements using the same material, thin film lamination can be easily made without greatly increasing the number of steps. Thus, the medical image display device on which the optical sensor is mounted can be provided at low costs. 
     According to the present invention, the surface reflection luminance, maximum luminance, and minimum luminance can be measured simply without using any exterior luminance meter such as a telescopic luminance meter, which enables significant improvement of the workability for the display quality control.