Patent Publication Number: US-11656470-B2

Title: Head-mounted display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/161,072, filed on Oct. 16, 2018, which claims priority from and the benefit of Korean Patent Application No. 10-2018-0001449, filed on Jan. 5, 2018, each of which is hereby incorporated by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     Field 
     Exemplary embodiments relate to a head-mounted display device, and more particularly, to a head-mounted display device having an improved viewing angle. 
     Discussion of the Background 
     Head-mounted display devices are a head-worn device, which may include a display panel or be coupled to a display panel. The head-mounted display devices may be used to implement augmented reality or virtual reality. A head-mounted display device for realizing augmented reality may provide a virtual graphic image through a semitransparent display. In this case, a user may visually recognize a virtual graphic image and an actual object at the same time. The head-mounted display device for implementing virtual reality provides a virtual graphic image to the user&#39;s eyes. The user may experience the virtual reality through virtual contents. 
     The above information disclosed in this Background section is only for understanding of the background of the inventive concepts, and, therefore, it may contain information that does not constitute prior art. 
     SUMMARY 
     Devices constructed according to exemplary implementations of the invention are capable of providing an improved viewing angle. 
     Additional features of the inventive concepts will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the inventive concepts. 
     A head-mounted display device according to an exemplary embodiment includes a display panel including a planar portion and a curved portion extending from the planar portion, a controller to provide a data signal representing an image to be displayed on the planar portion and the curved portion to the display panel, and a case part on which the display panel is mounted, in which the controller is configured to provide a data signal representing an image that is reduced at a predetermined ratio to the curved portion, as compared with the planar portion. 
     The head-mounted display device may further include a cushion part disposed between the case part and a wearer, and a strap part coupled to the case part, in which the case part, the cushion part, and the strap part may define a viewing point of the wearer with respect to the display panel. 
     The head-mounted display device may further include a sensor to measure the viewing point of the wearer with respect to the display panel. 
     The curved portion may include first curved portions disposed on opposite sides of the planar portion in a first direction, and the controller may provide a data signal representing an image that is reduced in the first direction to the first curved portions. 
     The controller may provide a data signal representing an image that is reduced in a second direction substantially perpendicular to the first direction to the first curved portions. 
     The curved portion further may include second curved portions disposed on opposite sides of the planar portion in a second direction substantially perpendicular to the first direction, and the controller may provide a data signal representing an image that is reduced in the second direction to the second curved portions. 
     The controller may provide a data signal representing an image that is reduced in the first direction to the second curved portions. 
     The first curved portions and the second curved portions may be spaced apart from each other at a corner of the planar portion. 
     The corner of the planar portion may not be visually recognized by the wearer. 
     The first curved portions and the second curved portions may be connected to each other. 
     The controller may provide a data signal representing an image that is reduced at a greater extent to a portion of the curved portion that is disposed further away from the planar portion. 
     The ratio of the entire curved portion may be A/L, where “A” is a length of the curved portion in the first direction and “L” is a length of an equivalent area of the curved portion in the first direction, and the equivalent area may be on a virtual plane extending from the planar portion, and provides a viewing angle substantially the same as a viewing angle of the curved portion in the first direction when viewed from the wearer&#39;s viewing point. 
     The reduced image may be substantially the same as an image that is not reduced on a virtual plane extending from the planar portion, when viewed from the wearer&#39;s viewing point. 
     One side of the curved portion may contact the planar portion tangentially. 
     The ratio of the entire curved portion may be A/L, which is represented as the following Equation, 
                       A   L     =       θ   ⁡     [     1   -       (     R   /   D     )     ⁢     (     1   -     cos   ⁢           ⁢   θ       )         ]             (     B   /   D     )     ⁢     (     1   -     cos   ⁢           ⁢   θ       )       +     sin   ⁢           ⁢   θ           ,           [   Equation   ]               
where “R” is a radius of curvature of the curved portion, “θ” is a central angle of the curved portion, “D” is a distance between the viewing point of the wearer and the planar portion, and “B” is a distance in the first direction between a normal line of the planar portion that passes through the viewing point and a point where the planar portion and the curved portion meet.
 
     The ratio may be about 1 at a boundary between the planar portion and the curved portion and decreases at a greater ratio as is disposed further away from the planar portion. 
     Another side of the curved portion may be perpendicular to a line of sight of the wearer. 
     The ratio of the entire curved portion may be A/L, which is represented as the following Equation, 
                       A   L     =     θ     tan   ⁢           ⁢   θ         ,           [   Equation   ]               
where “θ” is a central angle of the curved portion.
 
     The head-mounted display device may further include an optical system spaced apart from the display panel by a predetermined distance. 
     The display panel may include a left eye display area and a right eye display area arranged in a left and right direction with respect to the wearer, and each of the left eye display area and the right eye display area may include a planar portion and a curved portion. 
     The display panel may include a left eye display panel and a right eye display panel arranged in the left and right direction with respect to the wearer, and each of the left eye display panel and the right eye display panel may include a planar portion and a curved portion. 
     The left eye display panel and the right eye display panel may be separated by a protrusion disposed therebetween. 
     Each of the curved portions of the left eye display panel and the right eye display panel may include a left curved portion disposed on a left side of the planar portion and a right curved portion disposed on a right side of the planar portion. 
     The left curved portion and the right curved portion may have substantially the same length in the left and right direction. 
     The left curved portion and the right curved portion may have different lengths in the left and right direction. 
     The left curved portion of the left eye display panel may be longer in the left and right direction than the right curved portion of the left eye display panel, and the right curved portion of the right eye display panel may be longer in the left and right direction than the left curved portion of the right eye display panel. 
     An equivalent area of the right curved portion of the left eye display panel and an equivalent area of the left curved portion of the right eye display panel may contact each other, and the equivalent area of the left or right curved portion may be on a virtual plane extending from the planar portion, and the curved portion and the equivalent area of the left or right curved portion may provide substantially the same viewing angle in the left and right direction, when viewed from the wearer&#39;s viewing point. 
     An equivalent area of the right curved portion of the left eye display panel and an equivalent area of the left curved portion of the right eye display panel may overlap each other, and the equivalent area of the left or right curved portion may be on a virtual plane extending from the planar portion, and the curved portion and the equivalent area of the left or right curved portion may provide substantially the same viewing angle in the left and right direction, when viewed from the wearer&#39;s viewing point. 
     Each of the curved portions of the left eye display panel and the right eye display panel may include upper and lower curved portions disposed on upper and lower sides of the planar portion. 
     A head-mounted display device according to another exemplary embodiment includes a display panel including a planar portion and a curved portion extending from the planar portion, and a case part on which the display panel is seated, in which the curved portion is configured to display an image that is reduced as compared with an image displayed on the planar portion. 
     The curved portion may have a resolution higher than that of the planar portion. 
     The display panel may include a plurality of gate lines, a plurality of data lines crossing the gate lines, and a plurality of pixels defined by the gate lines and the data lines, in which the number of pixels per unit area in the curved portion may be greater than the number of pixels per unit area in the planar portion. 
     An interval between the gate lines in the curved portion may decrease, as is disposed further away from the planar portion. 
     An interval between the data lines in the curved portion may decrease, as is disposed further away from the planar portion. 
     An area of each of the pixels disposed in the curved portion may become smaller, as a position thereof is further away from the planar portion. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the inventive concepts. 
         FIG.  1    is a block diagram of a head-mounted display device according to an exemplary embodiment. 
         FIG.  2 A  is a perspective view of a head-mounted display device according to an exemplary embodiment. 
         FIG.  2 B  is a view illustrating the use of a head-mounted display device according to an exemplary embodiment. 
         FIG.  3    is an exploded perspective view of a part of a head-mounted display device according to an exemplary embodiment. 
         FIG.  4    is a schematic cross-sectional view of a head-mounted display device according to an exemplary embodiment. 
         FIGS.  5 A and  5 B  are schematic cross-sectional views of a display panel according to exemplary embodiments. 
         FIGS.  6 A and  6 B  are a front view and a side view of a display panel, respectively, according to exemplary embodiments. 
         FIGS.  7 A and  7 B  are views illustrating a non-reduced image and a reduced image, respectively, according to exemplary embodiments. 
         FIG.  8    is an explanatory view illustrating conversion of an image displayed on a curved portion according to an exemplary embodiment. 
         FIG.  9    is a schematic cross-sectional view of an optical system according to an exemplary embodiment. 
         FIG.  10    is a schematic perspective view of a separated binocular head-mounted display device according to an exemplary embodiment. 
         FIG.  11    is a schematic cross-sectional view of a separated binocular head-mounted display device according to an exemplary embodiment. 
         FIG.  12    is a schematic cross-sectional view of a separated binocular head-mounted display device according to an exemplary embodiment. 
         FIG.  13 A  is a schematic perspective view of an integrated binocular display panel according to an exemplary embodiment. 
         FIGS.  13 B and  13 C  are cross-sectional views of the integrated binocular display panel of  FIG.  13 A . 
         FIG.  14    is a schematic perspective view of a separated binocular display panel according to an exemplary embodiment. 
         FIGS.  15 A and  15 B  are schematic development views illustrating an integrated binocular display panel according to an exemplary embodiment. 
         FIG.  16    is a schematic development view illustrating a separated binocular display panel according to an exemplary embodiment. 
         FIG.  17    is an enlarged view a part of a display panel according to an exemplary embodiment. 
         FIG.  18    is a cross-sectional view taken along line IV-IV′ of  FIG.  4   . 
         FIGS.  19 A and  19 B  are development views of a display panel according to exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments or implementations of implementations of the invention. As used herein “embodiments” and “implementations” are interchangeable words that are non-limiting examples of devices or methods employing one or more of the inventive concepts disclosed herein. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments. Further, various exemplary embodiments may be different, but do not have to be exclusive. For example, specific shapes, configurations, and characteristics of an exemplary embodiment may be used or implemented in another exemplary embodiment without departing from the inventive concepts. 
     Unless otherwise specified, the illustrated exemplary embodiments are to be understood as providing exemplary features of varying detail of some ways in which the inventive concepts may be implemented in practice. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions, and/or aspects, etc. (hereinafter individually or collectively referred to as “elements”), of the various embodiments may be otherwise combined, separated, interchanged, and/or rearranged without departing from the inventive concepts. 
     The use of cross-hatching and/or shading in the accompanying drawings is generally provided to clarify boundaries between adjacent elements. As such, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, dimensions, proportions, commonalities between illustrated elements, and/or any other characteristic, attribute, property, etc., of the elements, unless specified. Further, in the accompanying drawings, the size and relative sizes of elements may be exaggerated for clarity and/or descriptive purposes. When an exemplary embodiment may be implemented differently, a specific process order may be performed differently from the described order. For example, two consecutively described processes may be performed substantially at the same time or performed in an order opposite to the described order. Also, like reference numerals denote like elements. 
     When an element, such as a layer, is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. To this end, the term “connected” may refer to physical, electrical, and/or fluid connection, with or without intervening elements. Further, the D 1 -axis, the D 2 -axis, and the D 3 -axis are not limited to three axes of a rectangular coordinate system, such as the x, y, and z-axes, and may be interpreted in a broader sense. For example, the D 1 -axis, the D 2 -axis, and the D 3 -axis may be perpendicular to one another, or may represent different directions that are not perpendicular to one another. For the purposes of this disclosure, “at least one of X, Y, and Z” and “at least one selected from the group consisting of X, Y, and Z” may be construed as X only, Y only, Z only, or any combination of two or more of X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms “first,” “second,” etc. may be used herein to describe various types of elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the teachings of the disclosure. 
     Spatially relative terms, such as “beneath,” “below,” “under,” “lower,” “above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), and the like, may be used herein for descriptive purposes, and, thereby, to describe one elements relationship to another element(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and/or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms, “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It is also noted that, as used herein, the terms “substantially,” “about,” and other similar terms, are used as terms of approximation and not as terms of degree, and, as such, are utilized to account for inherent deviations in measured, calculated, and/or provided values that would be recognized by one of ordinary skill in the art. 
     Various exemplary embodiments are described herein with reference to sectional and/or exploded illustrations that are schematic illustrations of idealized exemplary embodiments and/or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not necessarily be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. In this manner, regions illustrated in the drawings may be schematic in nature and the shapes of these regions may not reflect actual shapes of regions of a device and, as such, are not necessarily intended to be limiting. 
     As customary in the field, some exemplary embodiments are described and illustrated in the accompanying drawings in terms of functional blocks, units, and/or modules. Those skilled in the art will appreciate that these blocks, units, and/or modules are physically implemented by electronic (or optical) circuits, such as logic circuits, discrete components, microprocessors, hard-wired circuits, memory elements, wiring connections, and the like, which may be formed using semiconductor-based fabrication techniques or other manufacturing technologies. In the case of the blocks, units, and/or modules being implemented by microprocessors or other similar hardware, they may be programmed and controlled using software (e.g., microcode) to perform various functions discussed herein and may optionally be driven by firmware and/or software. It is also contemplated that each block, unit, and/or module may be implemented by dedicated hardware, or as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Also, each block, unit, and/or module of some exemplary embodiments may be physically separated into two or more interacting and discrete blocks, units, and/or modules without departing from the scope of the inventive concepts. Further, the blocks, units, and/or modules of some exemplary embodiments may be physically combined into more complex blocks, units, and/or modules without departing from the scope of the inventive concepts. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
       FIG.  1    is a block diagram of a head-mounted display device according to an exemplary embodiment. The head-mounted display device according to an exemplary embodiment may include an image processor  10 , a display unit  20 , a controller  30 , a communication unit  40 , a storage unit  50 , and a user input unit  60 . 
     The image processor  10  may perform various image processing processes, and the type of the image processing processes performed by the image processor  10  is not particularly limited. For example, the image processor  10  may perform de-multiplexing for distributing a predetermined signal to each characteristic signal, decoding according to the image format of the image signal, de-interlacing for converting an interlaced image signal into a progressive mode, noise reduction for improving image quality, detail enhancement, conversion of a frame refresh rate, or the like. In addition, the image processor  10  may include a decoder, which may decode a source image corresponding to the image format of the encoded source image, and a frame buffer, which may store the decoded source image on a frame-by-frame basis. 
     The image processor  10  may be implemented as a system-on-chip (“SOC”), through which the aforementioned functions are integrated, or as an image processing board, through which individual components capable of independently performing each of the aforementioned processes are mounted on a printed circuit board. 
     The image processor  10  may perform various predetermined image processing processes for a broadcast signal including an image signal received from the communication unit  40 , and a source image including an image signal received from an image source. The image processor  10  may output the processed image signal to the display unit  20 , such that the processed source image may be displayed on the display unit  20 . The image processor  10  (or the controller  30  to be described below) may perform a process so that the image may be reduced to be displayed on a curved portion, which will be described in more detail below. 
     The display unit  20  may display images based on an image signal output from the image processor  10 . The display unit  20  may include a display panel  200 , on which images are displayed, and a panel driver for processing the input image signal to display the image on the display panel. However, the inventive concepts are not limited thereto, and various methods of implementing images may be applicable. The image signal received from an external input source through an interface may be displayed on the display unit  20  through image processing processes, such as decoding, deinterlacing, scaling, or the like. 
     The controller  30  may control the overall configuration inside the head-mounted display device. The controller  30  may be separated from or integrated with the image processor  10 . 
     The communication unit  40  may receive a signal of an external input and transmit the signal to the image processor  10  or the controller  30 . The communication unit  40  may be connected to various external input cables to receive a signal from a corresponding external input by wire or wirelessly according to a predetermined wireless communication standard. 
     The communication unit  40  may include a plurality of connectors, to which the respective cables are individually connected. The communication unit  40  may receive a signal from a connected external input, for example, a HDMI signal, a USB signal, a broadcast signal according to the specification of the component, an image signal, a data signal, or the like, or may receive a communication data through a communication network. 
     The communication unit  40  may include various additional configurations, such as a wireless communication module for wireless communication or a tuner for tuning a broadcast signal, in addition to the configurations that receive signals/data from an external input. The communication unit  40  may also transmit the information/data/signal of the head-mounted display device to an external device. That is, the communication unit  40  may not be limited to a configuration for receiving a signal from an external device, but may be implemented as an interface capable of bidirectional communication. The communication unit  40  may receive a control signal for selecting a user interface (UI) from a plurality of control devices. The communication unit  40  may include a communication module for publicly known short range wireless communication, such as Bluetooth, infrared (“IR”), ultra wideband (“UWB”), Zigbee®, or the like, or may include a publicly known communication port for wired communication. The communication unit  40  may be used for various purposes, such as receiving a command for operating the display, transmission/reception of data, and the like, in addition to the control signal for selecting a UI. 
     The storage unit  50  may be provided as a writeable nonvolatile memory (e.g., a writable ROM), so that data may remain on the head-mounted display device even when the power is turned off, and may reflect changes of the user. For example, the storage unit  140  may include one of a flash memory, an EPROM, or an EEPROM. 
     The user input unit  60  may transmit various preset control commands or information to the controller  30  according to a user&#39;s operation and input. The user input unit  60  may be implemented by a menu-key or an input panel provided outside the head-mounted display device, or a remote controller separated from the head-mounted display device. 
     The user input unit  60  may receive the user&#39;s motion and voice. The user&#39;s motion may include a touch input. The user input unit  60  may directly receive the user&#39;s motion and voice, or may receive information of the user&#39;s motion and voice from an external device. 
     In addition, the user input unit  60  may include a display panel  200  (see  FIG.  3   ), an optical system  400  (see  FIG.  3   ), and an adjustor capable of adjusting a distance of the user&#39;s viewing point. The adjustor may move the position of the display panel  200  and/or the optical system  400  in forward or backward direction (a Z-axis direction in  FIG.  3   ) from the user&#39;s point of view according to the user&#39;s operation. 
     In addition, the user input unit  60  may include a sensor capable of measuring the user&#39;s viewing point. A reduction ratio of an image displayed on a curved portion  220  of the display panel  200  (see  FIG.  4   ), to be described below, may be changed according to the measured user&#39;s viewing point and the distance of the display panel  200 . 
       FIG.  2 A  is a perspective view of a head-mounted display device according to an exemplary embodiment, and  FIG.  2 B  is a view illustrating the use of a head-mounted display device according to an exemplary embodiment. 
     Referring to  FIGS.  2 A and  2 B , the head-mounted display device HMD is a device worn on the head of a user  500 . The head-mounted display device HMD may provide an image while the actual peripheral vision of the user  500  may be blocked or substantially blocked. The user  500  wearing the head-mounted display device HMD may be more easily immersed into the virtual reality. 
     The head-mounted display device may include a case part  100 , a cushion part  300 , and a strap part  350 . 
     The case part  100  may be worn on the head of the user  500 . The display panel  200  (see  FIG.  3   ) for displaying images, an acceleration sensor, and the like may be accommodated in the case part  100 . The acceleration sensor senses the motion of the user  500  and may transmit a predetermined signal to the display panel  200 . Accordingly, the display panel  200  may provide an image that corresponds to the change of the eye sight of the user  500 . Accordingly, the user  500  may experience virtual reality similar to the actual reality. 
     In the case part  100 , components having various functions other than those described above may be accommodated. For example, the image processor  10 , the display unit  20 , the controller  30 , the communication unit  40 , the storage unit  50 , and the user input unit  60  described above may be accommodated therein. 
     The cushion part  300  may be disposed between the case part  100  and the head of the user  500 . The cushion part  300  may include a material that is deformable in its shape. For example, the cushion part  300  may include a polymer resin (e.g., polyurethane, polycarbonate, polypropylene, and polyethylene), a liquid rubber, a urethane-based material, or a sponge formed by foam-molding an acrylic-based material. However, the inventive concepts are not limited thereto, and the cushion part  300  may include various other materials. 
     The cushion part  300  may allow the case part  100  to be in close contact with the user  500  and improve the comfort of the user  500 . The cushion part  300  may be detachable from the case part  100 . In an exemplary embodiment, the cushion part  300  may be omitted. 
     The strap part  350  may be combined with the case part  100  so that the case part  100  may be easily worn by the user  500 . The strap part  350  may include a main strap  351  and an upper strap  352 . 
     The main strap  351  may be worn along the circumference of the head of the user  500 . The main strap  351  may secure the case part  100  to the user  500  so that the case part  100  may be brought into close contact with the head of the user  500 . The upper strap  352  may connect the case part  100  to the main strap  351  along an upper portion of the head of the user  500 . The upper strap  352  may substantially secure the case part  100  to the user  500 . In addition, the upper strap  352  may disperse the load of the case part  100  to improve the wearing comfort of the user  500 . 
     In  FIG.  2 A , the shapes of the main strap  351  and the upper strap  352  are shown as being adjustable in lengths, but the inventive concepts are not limited thereto. For example, in another exemplary embodiment, the main strap  351  and the upper strap  352  may have elasticity, and the length adjustable portions may be omitted. 
     The strap part  350  may be variously modified from those shown in  FIGS.  2 A and  2 B , as long as the case part  100  is securely fixed to the user  500 . For example, in another exemplary embodiment, the upper strap  352  may be omitted. In addition, in another exemplary embodiment, the strap part  350  may be transformed into various forms, such as a helmet combined with the case part  100 , or a pair of glasses coupled with the case part  100 . 
       FIG.  3    is an exploded perspective view of a part of a head-mounted display device according to an exemplary embodiment. In  FIG.  3   , the strap part  350  (see  FIGS.  2 A and  2 B ) is not illustrated for convenience of description. 
     Referring to  FIG.  3   , the case part  100  may be divided into a body  101  and a cover  102 . A display panel  200  is disposed between the body  101  and the cover  102 , and the cover  102  may cover a space where the display panel  200  is seated.  FIG.  3    shows that the body  101  and the cover  102  are separated from each other, but the inventive concepts are not limited thereto. For example, as illustrated in  FIG.  4   , the body  101  and the cover  102  may be provided unitarily and may not be separated from each other. 
     The display panel  200  may be disposed between the body  101  and the cover  102 . The display panel  200  may be unitarily embedded in the head-mounted display device to provide images, but the inventive concepts are not limited thereto. For example, a display device (e.g., a portable terminal) including the display panel  200  may be combined with the head-mounted display device to provide images. 
     In  FIG.  3   , a left eye image and a right eye image are displayed through a single display panel  200  (e.g., a binocular integration type) as an example. The display panel  200  may be divided into a left eye image display area  201 , in which the left eye image is displayed, and a right eye image display area  202 , in which the right eye image is displayed. The left eye image display area  201  and right eye image display area  202  may be driven by separate panel drivers, respectively. However, the inventive concepts are not limited thereto, and both the left eye image display area  201  and the right eye image display area  202  may be driven by a single panel driver. In addition, as illustrated in  FIG.  10   , according to another exemplary embodiment, the display panel  200  may include a left eye display panel  241  and a right eye display panel  242  that are separated from each other. The specific shape of the display panel  200  will be described below. 
     The display panel  200  generates an image corresponding to the input image data. The display panel  200  may include any one of various types of display panels, such as an organic light emitting diode (“OLED”) display panel, a liquid crystal display (“LCD”) panel, a plasma display panel, an electrophoretic display panel, and an electrowetting display panel. Hereinafter, the display panel  200  will be described as an OLED display panel, for example, but the inventive concepts are not limited thereto. The detailed structure of the OLED display panel will be described below with reference to  FIGS.  17  and  18   . 
     The optical system  400  may be disposed inside the body  101  of the case part  100 . The optical system  400  may be a convex aspherical lens. In addition, the optical system  400  may be a Fresnel lens, which is divided into several circular strap-shaped lenses to reduce the thickness of the lens. The optical system  400  may enlarge the image provided from the display panel  200 . The optical system  400  may be spaced apart from the display panel  200  in a first direction (Z-axis direction). The optical system  400  may be disposed between the display panel  200  and a user&#39;s eye  510  (see  FIG.  4   ). 
     The optical system  400  may include a left eye optical system  401  and a right eye optical system  402 . The left eye optical system  401  enlarges an image to provide the image to a left pupil  511  of the user  500  (see  FIG.  4   ), and the right eye optical system  402  enlarges the image to provide the image to a right pupil  512  of the user  500  (see  FIG.  4   ). The left eye optical system  401  and the right eye optical system  402  may be spaced apart from each other in left and right direction (X-axis direction). A distance between the left eye optical system  401  and the right eye optical system  402  may be adjusted corresponding to a distance between the two eyes of the user  500  (see  FIG.  2 B ). 
       FIG.  4    is a schematic cross-sectional view of a head-mounted display device according to an exemplary embodiment, which is taken along line I-I′ of  FIG.  3   . In  FIG.  4   , components other than the case part  100 , the display panel  200 , the user&#39;s eye  510 , and a user&#39;s face line  520  are not illustrated. Hereinafter, a left and right direction (X-axis direction), an up and down direction (Y-axis direction), and a front and back direction (Z-axis direction) are defined with respect to a line of sight of the user  500  (hereinafter, “a wearer”) in a state in which the display device is worn. 
     As illustrated in  FIG.  4   , left and right sides of the display panel  200  is concavely curved with respect to a line of sight of the wearer  500 . More specifically, the display panel  200  includes a central planar portion  210  and left and right curved portions  220 . The planar portion  210  is substantially flat. That is, the planar portion  210  has a curvature of about zero or substantially zero. The curved portion  220  extends in the left and right direction from the planar portion  210 . In a cross-sectional view, a left curved portion  221  and a right curved portion  222  are symmetrical with respect to a symmetry line  263  that passes through the center of the display panel  200 , which is perpendicular to the display panel  200 . 
     As used herein, unless otherwise stated, the planar portion  210  and the curved portion  220  may refer to an area where images are displayed. 
     The curved portion  220  has a predetermined width in the left and right direction (X-direction) and a predetermined length in the up and down direction (Y-direction). The width direction (Z-direction) has a predetermined curvature (which is defined as the inverse of the radius of curvature) other than zero. The longitudinal direction may have a curvature of zero. 
     The case part  100  supports the display panel  200 , so that the display panel  200  may maintain the curved state. The planar portion  210  is supported by the cover  102 , and the curved portion  220  may be supported by the body  101 , which extends in the front and back direction (Z-direction). 
       FIG.  5 A  is a cross-sectional view for explaining a reduction ratio of the image displayed on the curved portion  220  in the left and right direction according to an exemplary embodiment, and corresponds to the right side of  FIG.  4   . As illustrated in  FIG.  5 A , according to an exemplary embodiment, a wider viewing angle may be provided with a smaller display panel  200 . 
       FIG.  5 A  illustrates a part of the right side of the planar portion  210 , the right curved portion  222 , and the right eye (or pupil)  512  of the user. As used herein, a point or a line described with reference to a cross-sectional view may refer to a line or a plane that passes through the point or the line, respectively, and is perpendicular to the cross-sectional view. 
     Referring to  FIG.  5 A , a virtual plane  230  is a plane extending from the planar portion  210 . As used herein, “D” represents a distance between a viewing point  420  of the right eye  512  of the user  500  and the virtual plane  230  or the planar portion  210  (or “D” represents a line normal to the virtual plane  230 ). The distance D may have a predetermined value determined according to the arrangement of the display panel  200  in the case part  100 , the structure of the cushion part  300 , a refractive index of the optical system  400 , and the like. Alternatively, the distance D may be a value set by the user. Still alternatively, the distance D may be a value measured by the above-described sensor. 
     As used herein, “R” is a radius of curvature of the curved portion  222 . The center of the curved portion  222  is at a point where the planar portion  210  and the curved portion  222  meet, that is, at a starting point  422  of the curved portion  222  on a line normal to the display panel  200 . More particularly, the curved portion  222  contacts the virtual plane  230 . As used herein, “θ” represents a central angle of the curved portion  222 . As used herein, “A” represents a width of the curved portion  220  in the left and right direction, that is, a length of an arc of the curved portion  220  in the cross-sectional view of  FIG.  5 A . 
     As used herein, “B” represents a distance between the normal line D of the virtual plane  230  that passes through the viewing point  420  and the normal line of the virtual plane  230  that passes through the starting point  422  of the curved portion  222 . 
     Dotted lines  410  and  411  are straight lines that indicate the line of sight from the viewing point  420  of the user  500 . A dotted line  410  is a straight line that passes through the viewing point  420  and an end point  421  of the curved portion  222 , and a dotted line  411  is a straight line that passes through the viewing point  420  and the starting point  422  of the curved portion  222  (or the virtual plane  230 ). An end point  423  on the virtual plane  230  is a point where the virtual plane  230  intersects the dotted line  410 . 
     As used herein, “L” represents a distance between the normal lines that pass through the starting point  422  on the virtual plane  230  and the end point  423  on the virtual plane  230 . A plane between the starting point  422  on the virtual plane  230  and the end point  423  on the virtual plane  230  is defined as an equivalent area  231  of the curved portion  222 .
 
 y:D=x: R (1−cos θ)  [Equation 1]
 
 y−x=R  sin θ+ B   [Equation 2]
 
 L=x+R  sin θ  [Equation 3]
 
     The length L of the equivalent area  231  is derived from the above Equations 1, 2, and 3, as illustrated below in Equation 4. 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               B 
                               / 
                               D 
                             
                             ) 
                           
                           ⁢ 
                           
                             ( 
                             
                               1 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               cos 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               θ 
                             
                             ) 
                           
                         
                         + 
                         
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                         
                       
                       
                         1 
                         ⁢ 
                         
                           ( 
                           
                             R 
                             / 
                             D 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             1 
                             - 
                             
                               cos 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               θ 
                             
                           
                           ) 
                         
                       
                     
                     ⁢ 
                     R 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     In an exemplary embodiment, a length A of the curved portion is expressed by the following Equation 5.
 
 A=R θ (θ in radian)  [Equation 5]
 
     Accordingly, a left and right image reduction ratio A/L of the curved portion with respect to the planar portion is expressed by the following Equation 6. 
     
       
         
           
             
               
                 
                   
                     A 
                     L 
                   
                   = 
                   
                     
                       θ 
                       ⁡ 
                       
                         [ 
                         
                           1 
                           - 
                           
                             
                               ( 
                               
                                 R 
                                 / 
                                 D 
                               
                               ) 
                             
                             ⁢ 
                             
                               ( 
                               
                                 1 
                                 - 
                                 
                                   cos 
                                   ⁢ 
                                   θ 
                                 
                               
                               ) 
                             
                           
                         
                         ] 
                       
                     
                     
                       
                         
                           ( 
                           
                             B 
                             / 
                             D 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             1 
                             - 
                             
                               cos 
                               ⁢ 
                               θ 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         sin 
                         ⁢ 
                         θ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
             
           
         
       
     
       FIG.  5 B  is a cross-sectional view for explaining a reduction ratio of the image displayed on the curved portion  220  according to an exemplary embodiment, and illustrates a curved portion having R and  0 , which are different from those of  FIG.  5 A . 
     As illustrated in  FIG.  5 B , a central point of the curved portion  222  is located on the line of sight  410  that passes through the viewing point  420  of the user  500  and the end point  421  of the curved portion  222 . Accordingly, the line of sight  410  crosses the curved portion  222  at the end point  222  substantially perpendicularly. Other conditions are substantially the same as those described above with reference to  FIG.  5 A . According to the illustrated exemplary embodiment, since L=R tan θ, the left and right image reduction ratio A/L of the curved portion  222  with respect to the planar portion  210  is expressed by the following Equation 7. 
     
       
         
           
             
               
                 
                   
                     A 
                     L 
                   
                   = 
                   
                     θ 
                     
                       tan 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
             
           
         
       
     
     In an exemplary embodiment, the image reduction ratio A/L of the curved portion  222  with respect to the planar portion  210  is defined as a ratio of the size of a substantially same image displayed on the curved portion  222  to that displayed on the planar portion  210 . For example, when a size of an image displayed on the planar portion  210  is assumed as L 1 , and if the same image were displayed in the equivalent area  230 , the size thereof would also be L 1 . However, when the same image is displayed on the curved portion  222 , the size is reduced to L 2 . Accordingly, the image reduction ratio is L 2 /L 1 . 
     In an exemplary embodiment, the left and right image reduction ratios of the curved portion at each point of the curved portion  222  may all be the same as A/L, or may be different according to their respective positions on the curved portion  222 . For example, the left and right image reduction ratio at the starting point  422  of the curved portion  222  may be 1. That is, the image is reduced at a same proportion as the planar portion  210 , and as the point moves farther away from the starting point  422 , the image may be reduced at a greater ratio. In particular, the image displayed on the curved portion  222  may be reduced at a greater extent, as its distance from the planar portion  210  is increased. As used herein, the image being further reduced means that the ratio of the image of the curved portion  222  to the image of the planar portion  210  (e.g., the image reduction ratio) is smaller. Although the image reduction ratio differs depending on its position on the curved portion  222 , the reduction ratio of the entire image of the curved portion may be A/L. 
     For example, in the illustrated exemplary embodiment shown in  FIG.  5 B , the image reduction ratio dA/dL at an arbitrary point (a central angle θ) is represented by the following Equation. 
     
       
         
           
             
               
                 
                   
                     
                       d 
                       ⁢ 
                       A 
                     
                     
                       d 
                       ⁢ 
                       L 
                     
                   
                   = 
                   
                     
                       
                         
                           d 
                           ⁢ 
                           A 
                         
                         
                           d 
                           ⁢ 
                           θ 
                         
                       
                       
                         
                           d 
                           ⁢ 
                           L 
                         
                         
                           d 
                           ⁢ 
                           θ 
                         
                       
                     
                     = 
                     
                       
                         cos 
                         2 
                       
                       ⁢ 
                       θ 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
             
           
         
       
     
     Accordingly, when θ=0, that is, at the boundary line  422  between the planar portion  210  and the curved portion  222 , the image reduction ratio is about 1. As θ increases, that is, as the distance from the planar portion  210  increases, the image reduction ratio decreases at a greater ratio. 
       FIG.  6 A  is a front view and  FIG.  6 B  is a side view illustrating a part of a display panel according to an exemplary embodiment. An up and down reduction ratio will be described with reference to  FIGS.  6 A and  6 B . As described above with reference to  FIGS.  5 A and  5 B , the image displayed on the curved portion  220 , which is disposed on the right and left sides of the planar portion  210 , may be reduced in the left and right direction. In addition, according to an exemplary embodiment, the image displayed on the curved portion  220  may be reduced in the up and down direction, as shown in  FIGS.  6 A and  6 B . 
     For example, in the exemplary embodiments shown in  FIGS.  5 A and  5 B , an up and down image reduction ratio W 2 /W 1  at an arbitrary point (a central angle θ) may be obtained by the following Equation 9.
 
 D:D−R (1−cos θ)= W   1   :W   2   [Equation 9]
 
     In Equation 9, “W 2 ” is a length of the curved portion  222  in the up and down direction, “W 1 ” is a length in the up and down direction of the equivalent area  231  corresponding to the curved portion  222 , “R (1−cos θ)” is a distance between an arbitrary point (a central angle θ) and the equivalent area  231 , and “D” is a distance between the planar portion  210  and the viewing point  420 . 
     Accordingly, based on Equation 9, the up and down image reduction ratio W 2 /W 1  may be obtained by the following Equation 10. 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       2 
                     
                     
                       W 
                       1 
                     
                   
                   = 
                   
                     1 
                     - 
                     
                       
                         R 
                         ⁡ 
                         
                           ( 
                           
                             1 
                             - 
                             
                               cos 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               θ 
                             
                           
                           ) 
                         
                       
                       D 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
             
           
         
       
     
     Accordingly, when θ=0, that is, at the boundary line  422  between the planar portion  210  and the curved portion  222 , the up and down image reduction ratio is about 1. As θ increases, that is, as the distance from the planar portion  210  increases, the image reduction ratio decreases at a greater ratio. 
       FIG.  7 A  is a view illustrating a non-reduced image, and  FIG.  7 B  is a view illustrating a reduced image, according to an exemplary embodiment. 
     According to an exemplary embodiment, the communication unit  40  or the storage unit  50  provides a data of an image illustrated in  FIG.  7 A  to the controller  30  or the image processor  10  (hereinafter, may be collectively referred to as “a controller  30 ”). The controller  30  may convert the data of the image illustrated in  FIG.  7 A  into a data of a reduced image illustrated in  FIG.  7 B . However, the inventive concepts are not limited thereto, and the communication unit  40  or the storage unit  50  may provide a data of an image, which has been reduced in advance as in  FIG.  7 B , and the controller  30  may provide the data of the reduced image illustrated in  FIG.  7 B  to the display unit  20 . 
     As illustrated in  FIG.  7 A , in general, images are configured to be displayed on a flat display panel, and each portion of the display panel, for example, the central portion and the peripheral portion of the display panel may display images at the same ratio. Accordingly, if an image for a flat surface (hereinafter, “flat image”) illustrated in  FIG.  7 A  is displayed on the curved portion  220  of the display panel  200  as shown  FIG.  4   , the image may be distorted. Accordingly, the head-mounted display device according to an exemplary embodiment displays images that are reduced in the left and right direction and/or the up and down direction on the curved portion  220 , as described hereinabove with reference to  FIGS.  5 A to  6 B . 
     A flat image Im illustrated in  FIG.  7 A  includes partial images Im (i, j) each having substantially the same size. All of the partial images Im (1, 1) . . . Im (i, j) . . . Im (16, 8) may be displayed on the display panel at the same rate. The flat image Im may be an original image. Alternatively, the original image may be an image that is entirely scaled at the same rate for each partial image Im (i, j) by the controller  30 , according to the size of the planar portion  210  and the equivalent area  231 . 
     The controller  30  may determine the partial image Im (i, j) to be displayed on the planar portion  210  and the partial image Im (i, j) to be displayed on the equivalent area  231  (the curved portion  220 ). The controller  30  partially reduces the partial image Im (i, j) of the equivalent area  231  in the left and right direction and/or the up and down direction. 
     As illustrated in  FIG.  7 B , the partial image Im (i, j) of the equivalent area  231  are further reduced in the left and right direction and the up and down direction, as they are further spaced away from the planar portion  210 . The data for the partially reduced image Im′ is provided to the panel driver of the display unit  20 , and the panel driver displays the image Im′ illustrated in  FIG.  7 B  on the display panel  200 . 
     Accordingly to an exemplary embodiment, the image Im′, as shown in  FIG.  7 B , displayed on the curved portion  220  may be viewed to be substantially the same as the image Im, as shown in  FIG.  7 A , displayed on the virtual plane  230  or the equivalent area  231  extending from the planar portion  210 . In this manner, an exemplary embodiment of the present invention may provide a wider viewing angle to the user, while using a relatively small display panel. In addition, the distortion of the image of  FIG.  7 A  may be significantly suppressed, as the image is displayed on a general flat display panel. 
       FIG.  8    is an explanatory view illustrating a conversion of an image displayed on a curved portion according to an exemplary embodiment. 
     As described above, the curved surface image Im′ (hereinafter, “curved image”) displayed on the curved portion  220  according to an exemplary embodiment may be viewed to be substantially the same as the flat image Im displayed on the equivalent area  231  extending from the planar portion  210 . 
     Referring to  FIG.  8   , one point of the curved portion  220  and one point of the equivalent area  231 , through which one straight line passes from the viewing point  420 , correspond to each other, and substantially the same image may be displayed on the two points that correspond to each other. Accordingly, a partial image Im′ (i, j) that corresponds to a partial image Im (i, j) at the one point of the equivalent area  231  is displayed at the corresponding one point of the curved portion  220 . In addition, as described above, the curved partial image Im′ (i, j) may be reduced in the left and right direction and the up and down direction. 
     Although  FIG.  8    shows a curved portion has a partial cylinder shape, the inventive concepts are not limited thereto. The image conversion method described with reference to  FIG.  8    may be applied to a curved portion having an arbitrary shape. 
     In addition, although  FIGS.  4  to  8    show the curved portion  220  is disposed on the right and left sides of the planar portion  210 , the inventive concepts are not limited thereto. The exemplary embodiments described with reference to  FIGS.  4  to  8    may be equally applied to the curved portion disposed on the upper and lower sides of the planar portion  22 . 
       FIG.  9    is a schematic cross-sectional view of an optical system according to an exemplary embodiment, and shows refraction of the line of sight by the optical system  400 . Although  FIG.  9    is described with respect to the right eye optical system  402 , it may be similarly applied to the left eye optical system  401  (see  FIG.  3   ). 
     As illustrated in  FIG.  9   , lines of sight  412  and  413  from an actual viewing point  430  of the user are refracted while passing through the optical system  400 . Accordingly, in the descriptions with reference to  FIGS.  5 A and  5 B , the lines of sight  410  and  411  viewing the curved portion  222  and the equivalent area  230  may not form a straight line with the actual viewing point  430  of the user  500 . 
     In an exemplary embodiment, a refractive index n of the optical system  400  is expressed by the following Equation 11. 
     
       
         
           
             
               
                 
                   n 
                   = 
                   
                     
                       sin 
                       ⁢ 
                       
                         θ 
                         1 
                       
                     
                     
                       sin 
                       ⁢ 
                       
                         θ 
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   ] 
                 
               
             
           
         
       
     
     In  FIG.  9   , “OL” is a distance between the planar portion  210  and the right eye optical system  402 , “D′” a distance between the planar portion  210  and the actual viewing point  430  of the user  500 , “D” is a distance between the planar portion  210  and the virtual viewing point  420  of the lines of sight  410  and  411  that pass through the curved portion  222 . 
     Accordingly, when the head-mounted display device according to an exemplary embodiment includes the optical system  400 , the aforementioned viewing point  420  refers to the virtual viewing point  420 , rather than the actual viewing point  430  of the user, and “D” used in the Equations 1 to 7 refers to a distance D to the virtual viewing point  420 , rather than a distance D′ to the actual viewing point  430  of the user. 
     The distance D to the virtual viewing point  420  may be determined according to the distance D′ to the actual viewing point  430  of the user  500  and the refractive index of the right eye optical system  402 . 
       FIG.  10    is a schematic perspective view of a separated binocular head-mounted display panel  240  according to an exemplary embodiment.  FIG.  11    is a cross-sectional view of  FIG.  10   . Detailed descriptions of substantially the same elements described above will be omitted to avoid redundancy. 
     As illustrated in  FIG.  10   , the display panel  240  according to an exemplary embodiment includes a left eye display panel  241  and a right eye display panel  242 . 
     As illustrated in  FIGS.  10  and  11   , the display panels  241  and  242  are curved on the left and right sides with respect to the line of sight of the user  500 . More specifically, the left eye display panel  241  includes a planar portion  251 L at the central portion and curved portions  262 L and  261 L on the left and right sides of the planar portion  251 L. The planar portion  251 L is substantially flat. That is, the planar portion  251 L has a curvature of about zero or substantially zero. The curved portion  260 L extends in the left and right direction from the planar portion  251 L. The curved portion  260 L has a predetermined width in the left and right direction and a predetermined length in the up and down direction. The width direction has a predetermined curvature (which is defined as the inverse of the radius of curvature) other than zero. The longitudinal direction may have a curvature of zero. 
     In the cross-sectional view of the left eye display panel  241  according to an exemplary embodiment, the curved portion  262 L on the left side and the curved portion  261 L on the right side are symmetrical with respect to a symmetry line that passes through the center of the left eye display panel  241 , which is perpendicular to the left eye display panel  241 . The left eye display panel  241  and the right eye display panel  242  are symmetrical with respect to the symmetry plane  263  that passes through the center therebetween, which is perpendicular to the left eye display panel  241 . 
     The case part  100  supports the display panel  240  so that the display panel  240  may maintain the curved state. In addition, the case part  100  may further include a protrusion  103 , which separates the two display panels  241  and  242  and supports the right curved portion  261 L of the left eye display panel  241  and the left curved portion  262 L of the right eye display panel  242 . The protrusion  103  may block the view of each eye so that the left eye display panel  241  may not be viewed from the right eye  512 , and the right eye display panel  242  may not be viewed from the left eye  511 . In the following, the description will be focused on the left eye display panel  241 , but the same may be applied to the right eye display panel  242  as well. 
       FIG.  12    is a schematic cross-sectional view of a separated binocular head-mounted display device according to an exemplary embodiment. 
     The image reduction ratio of the curved portion with respect to the planar portion described hereinabove with reference to  FIGS.  5 A and  5 B  may be applied to the illustrated exemplary embodiment, and thus, repeated descriptions thereof will be omitted to avoid redundancy. 
     The left curved portion  262 L and the right curved portion  261 L of the left eye display panel  241  have the same radius of curvature R. However, the inventive concepts are not limited thereto, and the left curved portion  262 L and the right curved portion  261 L may have different radii of curvature. 
     In addition, the left curved portion  262 L and the right curved portion  261 L have central angles θ 3  and θ 1 , respectively. The central angles θ 3  and θ 1  may be substantially equal to each other, or may be different from each other. For example, the central angle θ 3  may be larger than the central angle θ 1  in order to secure the left viewing angle of the left eye  511  to be greater than the right viewing angle. 
     In an exemplary embodiment, an area of the right curved portion  261 L where the image is displayed may be changed. For example, the image may be displayed on the entire curved portion  261 L having the central angle θ 1 . Alternatively, according to exemplary embodiments, the image may be displayed only on a portion of the right curved portion  261 L, that is, only the curved portion that has a central angle θ less than the central angle θ 1 . 
     For example, the central angle θ of the area where the image is displayed may be determined according to the input of the user  500  and according to the type of the image to be displayed (e.g., 2D or 3D image). Accordingly, the length L 2  of the equivalent area corresponding to the image displayed on the curved portion may be varied. Although the present example is described with reference to the right curved portion  261 L, the inventive concepts are not limited thereto, and it may also be applicable to the left curved portion  262 L. 
     For example, a central angle θ 2  may be determined so that a sight of line that passes through an end point of the curved portion having the central angle θ 2  may meet the symmetry line  263  on the virtual plane  230 . Accordingly, the equivalent area L 2  of the right curved portion  261 L of the left eye display panel  241  and the equivalent area (the area symmetric to L 2 ) of the left curved portion  262 R of the right eye display panel  242  may contact each other. 
     In an exemplary embodiment, the image may be displayed up to the central angle θ 1  that is larger than the central angle θ 2 . Accordingly, the equivalent area L 1  of the right curved portion  261 L of the left eye display panel  241  and the equivalent area (the area symmetric to L 1 ) of the left curved portion  262 R of the right eye display panel  242  may overlap each other. Accordingly, the separated binocular display panel according to the illustrated exemplary embodiment may provide a viewing angle beyond the integrated binocular display panel  200  described above. 
       FIG.  13 A  is a schematic perspective view of an integrated binocular display panel according to an exemplary embodiment.  FIGS.  13 B and  13 C  are cross-sectional views of the integrated binocular display panel of  FIG.  13 A . 
     A display panel  270  illustrated in  FIGS.  13 A to  13 C  includes both left and right eye display areas. 
     In addition, the display panel  270  has a dome shape. More specifically, the display panel  270  includes a planar portion  271 , and curved portions  272  to  275  on the left and right sides and the upper and lower sides of the planar portion  271 . A radius of curvature and a central angle of the left and right curved portions  272  and  273  may be substantially the same or different from a radius of curvature and a central angle of the upper and lower curved portions  274  and  275 . The specific shape of the curved portion and the image reduction ratio of the curved portion to the planar portion have already been described above, and thus, repeated descriptions thereof will be omitted to avoid redundancy. 
     The left and right curved portions  272  and  273  display images that are reduced in the left and right direction, and the upper and lower curved portions  274  and  275  display images that are reduced in the up and down direction. However, the inventive concepts not limited thereto, and the left and right curved portions  272  and  273  may display images that are reduced further in the up and down direction, and the upper and lower curved portions  274  and  275  may display images that are reduced further in the left and right direction. 
     Although the display panel  270  in  FIG.  10 A  is illustrated as having the curved portions  272  to  275  connected to each other at corners of the display panel  270 , the inventive concepts are not limited thereto. For example, the curved portions  272  to  275  may not be connected to each other at corners of the display panel  270 , and may be opened. 
     In addition, in an exemplary embodiment, the planar portion  271  may have a substantially quadrangular shape. However, the inventive concepts are not limited thereto, and the planar portion  271  may have various shape of polygons, such as ellipses, circles, and hexagons. 
       FIG.  14    is a schematic perspective view of a separated binocular display panel according to an exemplary embodiment. Detailed descriptions of substantially the same elements as those described above with reference to  FIGS.  13 A to  13 C  will be omitted to avoid redundancy. 
     A display panel  280  illustrated in  FIG.  14    includes a left eye display panel  281  and a right eye display panel  282 , and each of the display panels  281  and  282  may be separated from each other. 
     In addition, each of the display panels  281  and  282  has a dome shape. That is, each of the display panels  281  and  282  includes a planar portion and a curved portion on the left and right sides and the upper and lower sides of the planar portion. Each of the display panels  281  and  282  may be substantially the same as the display panel  270  illustrated in  FIGS.  10 A to  10 B  except for the length in the left and right direction. In addition, the left and right curved portions of each of the display panels  281  and  282  have a structure substantially the same as or similar to the curved portion described above with reference to  FIGS.  7 A to  8   . 
     In addition, in an exemplary embodiment, the planar portion  281  has a substantially quadrangular shape. However, the inventive concepts are not limited thereto, and the planar portion  281  may have various shape of polygons, such as ellipses, circles, and hexagons. 
       FIGS.  15 A and  15 B  are schematic development views illustrating an integrated binocular display panel according to an exemplary embodiment. The display panel  270  illustrated in  FIGS.  15 A and  15 B  includes both the left eye and right eye display areas. 
     The display panel  270  may be formed by curving the flat display panel illustrated in  FIG.  15 A . More particularly, the curved portions  272  to  275  may be formed by curving areas extending in the up and down direction and the left and right direction from the planar portion  271  to have a predetermined curvature. A corner  276  between each curved portion may be notch-cut, so that the curved portions  272  to  275  may be curved separately. Accordingly, the display panel  270  having the developed view illustrated in  FIG.  15 A  has its corners opened. 
     On the other hand, each corner  276  of the developed view illustrated in  FIG.  15 B  may be cut in a curved line. Accordingly, the curved display panel  270  is not opened at the corners, and each curved portion  272  to  275  of the display panel  270  may be connected to each other. However, the inventive concepts are not limited thereto, and the shape of the display panel may be varied. For example, the display panel may have various types of dome shapes in various methods. 
     In an exemplary embodiment, viewing areas  277  and  278  of the left eye  511  and the right eye  512  may refer to the area visually recognized by the user while the user wears the head-mounted display device. Each viewing area  277  and  278  may have a substantially elliptical or circular shape. According to an exemplary embodiment, the viewing areas  277  and  278  overlap the planar portion  271  and a part of the curved portions  272  to  275 , and do not overlap the corner  276 . That is, the corner between the curved portions  272  to  275  may not be viewed by the user. In addition, the respective viewing areas  277  and  278  do not overlap each other. 
       FIG.  16    is a schematic development view of a separated binocular display panel according to an exemplary embodiment. The display panel  280  illustrated in  FIG.  16    includes a left eye display panel  281  and a right eye display panel  282 , and each of the display panels  281  and  282  may be separated from each other. 
     Each of the display panels  281  and  282  may be substantially the same as the display panel  270  illustrated in  FIG.  15 A  except for the length in the left and right direction. In addition, the left and right curved portions of each of the display panels  281  and  282  have a structure substantially the same or similar to that of the curved portion described with reference to  FIGS.  10  and  11   . 
     As described above with reference to  FIG.  15 A , corners between each curved portion are cut in the form of a quadrangle, and the corners of the display panel  270  having the developed view illustrated  FIG.  16    are opened. In addition, the open corner may not be included in a viewing area  283  of the left eye  511  and the right eye  512 . 
     According to an exemplary embodiment, the corners between each curved portion in each of the display panels  281  and  282  may be cut as similarly in  FIG.  15 B , and thus, the curved portions may be connected to each other. 
     In an exemplary embodiment, as illustrated in  FIG.  16   , each of the display panels  281  and  282  may include a display area  286 , in which images are displayed, and a non-display area  285  in the periphery, in which images are not displayed. In the non-display area  285 , various wirings for driving the display panels  281  and  282  may be disposed. The non-display area  285  may be included in all the display panels  200  described above. 
       FIG.  17    is an enlarged view of a part of a display panel according to an exemplary embodiment.  FIG.  18    is a cross-sectional view taken along line IV-IV′ of  FIG.  4   . 
     Referring to  FIGS.  17  and  18   , the display panel according to an exemplary embodiment includes a plurality of pixels, each including a switching thin film transistor, a driving thin film transistor, a capacitor, and an OLED  810 . The OLED  810  may be largely applied to flexible display devices as it may be deposited at a relatively low temperature and has low power consumption, high luminance, and the like. As used herein, the pixel may refer to a minimum unit for displaying images, and the display panel  200  may display images through the plurality of pixels. 
     Although  FIG.  17    shows that one pixel includes two thin film transistors and one capacitor, the inventive concepts are not limited thereto. For example, one pixel may include three or more thin film transistors and two or more capacitors, and may have various structures including additional wirings. 
     The display panel may include a substrate  710 , a gate line  751  disposed on the substrate  710 , and a data line  771  and a common power line  772  insulated from and crossing the gate line  751 . One pixel PX may be typically defined by the gate line  751 , the data line  771  and the common power line  772 , in which they become a boundary, but the inventive concepts are not limited thereto. The pixel may be defined by a pixel defining layer or a black matrix. 
     The substrate  710  may include a flexible plastic material. For example, the substrate  710  may include at least one of Kapton®, polyethersulphone (PES), polycarbonate (PC), polyimide (PI), polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyacrylate (PAR), fiber reinforced plastic (FRP), or the like. 
     The substrate  710  may a thickness in a range from about 5 μm to about 200 μm. When the substrate  710  has a thickness less than about 5 it is difficult for the substrate  710  to stably support the OLED  810 . On the other hand, when the substrate  710  has a thickness greater than about 200 flexible characteristics of the substrate  710  may be deteriorated. 
     A buffer layer  720  is disposed on the substrate  710 . The buffer layer  720  may prevent permeation of undesirable elements and to planarize a surface therebelow by including suitable materials for planarizing and/or preventing permeation. For example, the buffer layer  720  may include one of a silicon nitride (SiN x ) layer, a silicon oxide (SiO 2 ) layer, and a silicon oxynitride (SiO x N y ) layer. However, the buffer layer  720  may be omitted depending on the kinds of the substrate  710  and process conditions thereof. 
     A switching semiconductor layer  731  and a driving semiconductor layer  732  are disposed on the first buffer layer  720 . The switching semiconductor layer  731  and the driving semiconductor layer  732  may include at least one of a polycrystalline silicon layer, an amorphous silicon layer, and an oxide semiconductor, such as indium gallium zinc oxide (IGZO) and indium zinc tin oxide (IZTO). For example, when the driving semiconductor layer  732  includes a polycrystalline silicon layer, the driving semiconductor layer  732  includes a channel area, which is not doped with impurities, and p+ doped source and drain areas, which are formed on opposite sides of the channel area. In such an exemplary embodiment, p-type impurities, such as boron B, may be used as dopant ions, and B 2 H 6  is typically used. Such impurities may vary depending on the type of thin film transistors. The driving thin film transistor according to an exemplary embodiment may employ a p-channel metal oxide semiconductor (“PMOS”) thin film transistor including p-type impurities, but the inventive concepts are not limited thereto. For example, the driving thin film transistor may employ an n-channel metal oxide semiconductor (“NMOS”) thin film transistor or a complementary metal oxide semiconductor (“CMOS”) thin film transistor. 
     A gate insulating layer  740  is disposed on the switching semiconductor layer  731  and the driving semiconductor layer  732 . The gate insulating layer  740  may include at least one of tetraethylorthosilicate (TEOS), silicon nitride (SiN x ), and silicon oxide (SiO 2 ). For example, the gate insulating layer  740  may have a double-layer structure, in which a SiN x  layer having a thickness of about 40 nm and a TEOS layer having a thickness of about 80 nm are sequentially stacked. 
     A gate wiring, which includes gate electrodes  752  and  755  is disposed on the gate insulating layer  740 . The gate wiring further includes the gate line  751 , a first capacitor plate  758 , and other signal lines. In addition, the gate electrodes  752  and  755  are disposed to overlap at least a portion of the corresponding semiconductor layers  731  and  732 , for example, a channel area thereof. The gate electrodes  752  and  755  may substantially prevent impurities from being doped into the channel area of the corresponding semiconductor layers  731  and  732 , when the impurity is doped into a source area and a drain area of the semiconductor layer  731  and  732 , respectively. 
     The gate electrodes  752  and  755  and the first capacitor plate  758  are disposed on a substantially same layer and include a substantially same metal material. The gate electrodes  752  and  755  and the first capacitor plate  758  may include at least one of molybdenum (Mo), chromium (Cr), and tungsten (W). 
     An insulating interlayer  760  is disposed on the gate insulating layer  740  to cover the gate electrodes  752  and  755 . The insulating interlayer  760 , similar to the gate insulating layer  740 , may include or be formed of silicon nitride (SiN x ), silicon oxide (SiO x ), tetraethoxysilane (TEOS), or the like, but the inventive concepts are not limited thereto. 
     A data wiring, which includes source electrodes  773  and  776  and drain electrodes  874  and  777 , is disposed on the insulating interlayer  760 . The data wiring further includes the data line  771 , the common power line  772 , a second capacitor plate  778 , and other wirings. In addition, the source electrodes  773  and  776  and the drain electrodes  774  and  777  are connected to a source area and a drain area of the corresponding semiconductor layers  731  and  732 , respectively, through a contact hole defined at the gate insulating layer  740  and the insulating interlayer  760 . 
     As such, the switching thin film transistor includes the switching semiconductor layer  731 , the switching gate electrode  752 , the switching source electrode  773 , and the switching drain electrode  774 , and the driving thin film transistor includes the driving semiconductor layer  732 , the driving gate electrode  755 , the driving source electrode  776 , and the driving drain electrode  777 . However, the inventive concepts are not limited thereto, and configurations of the thin film transistors may be modified into various structures. 
     In addition, the capacitor includes the first capacitor plate  758  and the second capacitor plate  778  with the insulating interlayer  760  therebetween. 
     The switching thin film transistor may function as a switching element to select pixels to perform light emission. The switching gate electrode  752  is connected to the gate line  751 . The switching source electrode  773  is connected to the data line  771 . The switching drain electrode  774  is spaced apart from the switching source electrode  773  and is connected to the first capacitor plate  758 . 
     The driving thin film transistor applies, to a pixel electrode  811 , a driving power which allows a light emitting layer  812  of an OLED  810  in a selected pixel to emit light. The driving gate electrode  755  is connected to the first capacitor plate  758 . Each of the driving source electrode  776  and the second capacitor plate  778  is connected to the common power line  772 . The driving drain electrode  777  is connected to the pixel electrode  811  of the OLED  810  through a contact hole. 
     With the aforementioned structure, the switching thin film transistor is driven by a gate voltage applied to the gate line  751  and serves to transmit a data voltage, applied to the data line  771 , to the driving thin film transistor. A voltage equivalent to a difference between a common voltage applied to the driving thin film transistor from the common power line  772 , and the data voltage transmitted from the switching thin film transistor is stored in the capacitor, and a current corresponding to the voltage stored in the capacitor flows to the OLED  810  through the driving thin film transistor, and thus the OLED  810  may emit light. 
     A planarization layer  765  is disposed to cover the data wiring, e.g., the data line  771 , the common power line  772 , the source electrodes  773  and  776 , the drain electrodes  774  and  777 , and the second capacitor plate  778 , which are patterned into a substantially same layer on the insulating interlayer  760 . 
     The planarization layer  765  may substantially eliminate a step difference of a structure therebelow and planarize a surface therebelow, which may increase luminous efficiency of the OLED  810  to be formed thereon. The planarization layer  765  may include at least one of a polyacrylate resin, an epoxy resin, a phenolic resin, a polyamide resin, a polyimide resin, an unsaturated polyester resin, a polyphenylen ether resin, a polyphenylene sulfide resin and benzocyclobutene (BCB). 
     The pixel electrode  811  of the OLED  810  is disposed on the planarization layer  765 . The pixel electrode  811  is connected to the drain electrode  777  through a contact hole defined at the planarization layer  765 . 
     A pixel defining layer  790 , which exposes at least a portion of the pixel electrode  811  to define a pixel area, is disposed on the planarization layer  765 . The pixel electrode  811  is disposed to correspond to the pixel area defined by the pixel defining layer  790 . The pixel defining layer  790  may include a resin based on, for example, polyacrylate and polyimide. 
     The light emitting layer  812  is disposed on the pixel electrode  811  in the pixel area, and a common electrode  813  is disposed on the pixel defining layer  790  and the light emitting layer  812 . The light emitting layer  812  includes a low molecular organic material or a high molecular organic material. At least one of a hole injection layer HIL and a hole transport layer HTL may further be disposed between the pixel electrode  811  and the light emitting layer  812 , and at least one of an electron transport layer ETL and an electron injection layer EIL may further be disposed between the light emitting layer  812  and the common electrode  813 . 
     The pixel electrode  811  and the common electrode  813  may be formed as one of a transmissive electrode, a transflective electrode and a reflective electrode. 
     Transparent conductive oxide (“TCO”) may be used to form a transmissive electrode. TCO may include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In 2 O 3 ), of the like. 
     Metal, e.g., magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li), chromium (Cr), aluminum (Al), and copper (Cu), or an alloy thereof may be used to form a transflective electrode and a reflective electrode. In such an exemplary embodiment, whether an electrode is a transflective type or a reflective type depends on the thickness of the electrode. Typically, the transflective electrode has a thickness of about 200 nm or less, and the reflective electrode has a thickness of about 300 nm or more. As the thickness of the transflective electrode decreases, light transmittance and resistance may increase. On the contrary, as the thickness of the transflective electrode increases, light transmittance may decrease. 
     In addition, the transflective electrode and the reflective electrode may have a multilayer structure, which includes a metal layer including metal or an alloy thereof, and a TCO layer stacked on the metal layer. 
     An encapsulation layer  850  is disposed on the common electrode  813 . The encapsulation layer  850  includes one or more inorganic layers  851  and  853  and one or more organic layers  852 . In addition, the encapsulation layer  850  has a structure, in which the inorganic layers  851  and  853  and the organic layers  852  are laminated alternately with each other. In such an exemplary embodiment, the inorganic layer  851  is disposed at a lowermost portion. That is, the inorganic layer  851  is disposed most adjacent to the OLED  810 . 
     In  FIG.  18   , the encapsulation layer  850  according to an exemplary embodiment is illustrated as including two inorganic layers  851  and  853  and one organic layer  852 , but the inventive concepts are not limited thereto. 
     The inorganic layers  851  and  853  include one or more inorganic materials of Al 2 O 3 , TiO 2 , ZrO, SiO 2 , AlON, AlN, SiON, Si 3 N 4 , ZnO, and Ta 2 O 5 . The inorganic layers  851  and  853  may be formed through methods, such as a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method. However, the inventive concepts are not limited thereto, and the inorganic layers  851  and  853  may be formed through various methods generally known in the art. 
     The organic layer  852  may include or be formed of a polymer material. Examples of the polymer material may include, for example, an acrylic resin, an epoxy resin, polyimide and polyethylene. The organic layer  852  may be formed through a thermal deposition process. The thermal deposition process for forming the organic layer  852  may be performed in a range of temperature that may not damage the OLED  810 . However, the inventive concepts are not limited thereto, and the organic layer  852  may be formed through various methods generally known in the art. 
     The inorganic layers  851  and  853 , which have a high density of thin film, may substantially prevent or efficiently reduce permeation of, mostly, moisture or oxygen. Permeation of moisture and oxygen into the OLED  810  may be largely prevented by the inorganic layers  851  and  853 . 
     The encapsulation layer  850  may have a thickness of about 10 μm or less. Accordingly, an overall thickness of the display panel may become significantly small. By applying such an encapsulation layer  850 , the display panel may have optimized flexible characteristics. 
     A protective film  400  is disposed below the substrate  710 . The protective film  400  may be attached to a lower portion of the substrate  710  through an adhesive. The protective film  400  may improve the strength of the display panel and substantially prevent the display panel from being damaged. 
     The protective film  400  may include a flexible plastic material. In addition, the protective film  400  may have various thicknesses depending on Young&#39;s modulus. The protective film  400  according to an exemplary embodiment may have a substantially same shape as that of the substrate  710 . 
       FIGS.  19 A and  19 B  are development views illustrating a display panel according to exemplary embodiments. 
     Referring to  FIG.  19 A , the display panel  200  according to an exemplary embodiment may include a planar portion  210  and a curved portion  220  disposed at opposite sides of the planar portion  210 , for example, on the left or right sides or on the upper and lower sides. Referring to  FIG.  19 B , the display panel  200  according to an exemplary embodiment may include the planar portion  210  and the curved portion  220  disposed on the left and right sides and on the upper and lower sides. 
     As illustrated in  FIG.  19 A , in the display panel  200  according to an exemplary embodiment, the curved portion  220  has a resolution higher than that of the planar portion  210 . As used herein, the resolution may refer to the number of pixels PX per unit area or unit length. Accordingly, the pixels are disposed more densely in the curved portion  220 . 
     According to an exemplary embodiment, the resolution of the curved portion  220  in the left and right direction (the number of pixels PX per unit length in the left and right direction) is higher than the resolution of the planar portion  210 . In addition, according to an exemplary embodiment of the present invention, the resolution of the curved portion  220  in the up and down direction (the number of pixels PX per unit length in the up and down direction) is higher than the resolution of the planar portion  210 . 
     A ratio R 2 /R 1  of the resolution R 2  of the curved portion  220  to the resolution R 1  of the planar portion  210  corresponds to the reciprocal of the image reduction ratio described hereinabove with reference to  FIGS.  4  to  8   . That is, as the resolution becomes higher, the displayed image may be reduced to a greater extent. Accordingly, detailed descriptions of the resolution ratio R 2 /R 1  will be omitted. 
     In an exemplary embodiment, as described above with reference to  FIGS.  17  and  18   , the display panel  200  may include the gate line  751  extending, for example, in the left and right direction and the data line  771  extending, for example, in the up and down direction. One pixel may be defined by one of the gate lines  751  and one of the data lines  771 , and may be defined by these lines  751  and  771 . 
     In an exemplary embodiment, an interval between the data lines  771 , in the left and right curved portion  220  of the display panel  200  illustrated in  FIG.  19 A , which extend substantially in parallel in the up and down direction, may be decreased, as is disposed further away from the planar portion  210 . Accordingly, the image displayed on the curved portion  220  may be reduced more in the left and right direction, as it is positioned further away from the planar portion  210 . 
     In an exemplary embodiment, an interval between the gate lines  751 , in the left and right curved portion  220  of the display panel  200  illustrated in  FIG.  19 A , which extend substantially in parallel in the left and right direction, may be decreased, as is disposed further away from the planar portion  210 . Accordingly, the gate line  751  that passes through the center (a point most adjacent to the viewing point  420 ) of the planar portion  210  extends in a straight line even in the curved portion  220 , but the gate line  751  that passes through upper and lower sides of the planar portion  210  may be curved in the curved portion  220  more toward the gate line  751  that passes through the center, as is disposed further away from the planar portion  210 . Accordingly, the image displayed on the curved portion  220  may be reduced more in the up and down direction, as is positioned further away from the planar portion  210 . 
     In an exemplary embodiment, in  FIG.  19 B , the gate line  751  and the data line  771  disposed in the curved portion on the upper and lower sides of the planar portion are disposed similarly to the data line  771  and the gate line  751  disposed in the curved portion on the left and right sides of the planar portion  210 . 
     That is, an interval between the gate lines  751 , in the upper and lower curved portion  220 , which extend substantially in parallel in the left and right direction, may be decreased, as is disposed further away from the planar portion  210 . In addition, an interval between the data lines  771 , in the upper and lower curved portion  220 , which extend substantially in parallel in the up and down direction, may be decreased, as is disposed further away from the planar portion  210 . Accordingly, the data line  771  that passes through the center (a point most adjacent to the viewing point  420 ) of the planar portion  210  extends in a straight line even in the curved portion  220 , but the data line  771  that passes through left and right sides of the planar portion  210  may be curved in the curved portion  220  more toward the data line  771  that passes through the center, as is positioned further away from the planar portion  210 . 
     In addition, as described above, as the interval between the gate lines  751  and the interval between the data lines  771  decreases, a planar area of the pixel PX may be reduced. That is, a planar area of the pixel PX disposed at the curved portion  220  may decrease, as is disposed further away from the planar portion  210 . 
     Accordingly, in the illustrated exemplary embodiment, a reduced image may be displayed on the curved portion  220  without image conversion (partial reduction) by the controller  30 . 
     In  FIGS.  19 A and  19 B , although the head-mounted display device is described as a separated binocular display panel, the above-described exemplary embodiments may be applied to the left eye display area and the right eye display area of the integrated binocular display panel. 
     According to one or more exemplary embodiments, the head-mounted display device may provide an improved viewing angle. In addition, the head-mounted display device according to exemplary embodiments may reduce distortion of the image viewed by the user. 
     Although certain exemplary embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. Accordingly, the inventive concepts are not limited to such embodiments, but rather to the broader scope of the appended claims and various obvious modifications and equivalent arrangements as would be apparent to a person of ordinary skill in the art.