Patent Publication Number: US-2011057965-A1

Title: Liquid crystal display device including edge-type backlight unit and method of controlling the liquid crystal display

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority from U.S. Provisional Application No. 61/239,835, filed Sep. 4, 2009, and Korean Patent Application No. 10-2009-0104424, filed Oct. 30, 2009, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     Apparatuses and methods consistent with exemplary embodiments relate to a liquid crystal display (LCD) devices. 
     2. Description of the Related Art 
     Three-dimensional (3D) image display devices which display stereoscopic images have been recently developed. A stereoscopic image is generated by the stereoscopic viewing principle of human&#39;s eyes, and binocular parallax, which is the apparent difference in position of an object as seen separately by the human eyes separated by a distance of approximately 65 mm. By showing images which are the same as actually seen by the eyes, stereoscopic depth can be produced. Images are captured by using two cameras of the same type that are separated from each other by the distance of the human eyes. An image captured using the left-side camera is shown to a left eye, and an image captured using the right-side camera is shown to a right eye. 
     The 3D image display devices are classified as glasses type and glasses-free type. Examples of a stereoscopic display method of the glasses type includes a polarizing glasses method and a shutter glasses method. Examples of glasses-free stereoscopic display method include a parallax barrier method, a lenticular method, an integral imaging method, a holography method, etc. 
     In the shutter glasses method, glasses including a liquid crystal shutter, that is, liquid crystal shutter glasses, are used to create a stereoscopic image. In the liquid crystal shutter glass method, different images are respectively shown to a left eye and a right eye during a frequency period of 60 Hz. A 3D display device using the liquid crystal shutter glasses method alternately and rapidly displays a left image and right image, and opens or closes liquid crystal shutters for the left eye image and the right eye image alternately. 
     However, when the data holding is generated in an LCD device, the cross-talk or X-talk between a left image and a right image which exist mixedly within one frame output by the LCD device is generated due to the data holding phenomenon. 
     In detail, when a left image or a right image is output on an upper portion of the screen, an area for a right image or a left image is reversely output on a lower portion of the screen, and accordingly, there is a time when the left image and the right image are output on the screen at the same time. When the backlight unit is turned on, a left image and a right image of one frame, which are adjacent to each other, are mixedly seen to one eye of the viewer, and a cross-talk is generated. Thus, the left eye and the right eye of the viewer see a distorted image due to the cross-talk, and the viewer may become fatigued watching a 3D image. 
     SUMMARY 
     Exemplary embodiments address at least the above problems and/or disadvantages and other disadvantages not described above. Also, an exemplary embodiment is not required to overcome the disadvantages described above, and an exemplary embodiment may not overcome any of the problems described above. 
     Exemplary embodiments provide an LCD device and a method of controlling the LCD device. 
     According to an aspect of an exemplary embodiment, there is provided a method of controlling an LCD device including an LCD panel and an edge-type backlight unit, the method including: controlling turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit so as to be synchronized with a period during which a 3D image is output on the LCD panel, wherein the upper light source includes a light source disposed at an upper edge of the edge-type backlight unit, and the lower light source includes a light source disposed at a lower edge of the edge-type backlight unit. 
     The controlling of the turned-on and turned-off periods of an upper light source and an lower light source of the edge-type backlight unit may include turning-on the upper light source and turning-off the lower light source when a current image is output on an upper portion of a screen and a previous image remains on a lower portion of the screen. 
     The controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit may include turning-off the upper light source and turning-on the lower light source when a next image starts to be output on an upper portion of a screen and a current image is output on a lower portion of the screen. 
     The controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit may include turning-off both the upper light source and the lower light source when a ratio of a current image to a previous image that mixedly exists on the whole screen is a predetermined threshold or greater. 
     The controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit may include turning-on both the upper light source and the lower light source when a ratio that a current image and a previous image mixedly exist over the whole screen is smaller than a predetermined threshold. 
     When the edge-type backlight unit further includes light sources disposed on left and right edges of the edge-type backlight unit, the light sources may be classified into upper light sources and lower light sources, and the upper light sources of the edge-type backlight unit may include a light source at an upper edge and light sources at upper left and right edges of the edge-type backlight unit, and the lower light sources of the edge-type backlight unit may include a light source at a lower edge and light sources at lower left and right edges of the edge-type backlight unit of the edge-type backlight unit. 
     In the controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit, the turn-on and turn-off periods may be synchronized with a period in which a 3D image is output on the LCD panel by using a vertical synchronization (V-sync) signal. 
     The method may further include controlling the LCD panel such that a left image and a right image of the 3D image are alternately output on the LCD panel. 
     In the controlling of the LCD panel, during a period in which a pair of a left image and a right image corresponding to each other are alternately output, the left image, a black image, the right image, and the black image may be sequentially output. 
     In the controlling of the LCD panel, during a period in which a pair of a left image and a right image corresponding to each other are alternately output, the left image, the left image, the right image, and the right image may be sequentially output. 
     In the controlling of the LCD panel, the images may be sequentially output from an upper portion to a lower portion of the LCD panel. 
     In the controlling of the LCD panel, the 3D image may be controlled to be output on the LCD panel at a frequency of 240 Hz. 
     In the controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit, a period T, during which one of a left image and a right image of the 3D image is output and a next image is output on the LCD panel, may be divided into six sections, and the upper light source may be turned on in a second section and a third section, and turned off in a first section, a fourth section, a fifth section, and a sixth section, and the lower light source may be turned on in the fourth section and the fifth section, and turned off in the first section, the second section, the third section, and the sixth section, wherein the controlling during the period T is repeated. 
     In the controlling of the turn-on and turn-off periods of an upper light source and a lower light source of the edge-type backlight unit, a period T, during which one of a left image and a right image of the 3D image is output and a next image is output on the LCD panel, may be divided into eight sections, and the upper light source may be turned on in a second section, a third section, a fourth section, and an fifth section, and turned off in a first section, a sixth section, a seventh section, and a eighth section, and the lower light source may be turned on in the fourth section, the fifth section, the sixth section, and the seventh section, and turned off in the first section, the second section, the third section, and the eighth section, wherein the controlling during the period T is repeated. 
     When the LCD panel further includes a shutter glass for a left image of the 3D image and a shutter glass for a right image of the 3D image, the method may further include, during a period T in which one of the left image and the right image of the 3D image is output and a next image is output on the LCD panel, controlling the shutter glasses such that the shutter glass for the left image is opened while the left image is being output if the left image is first output, and the shutter glass for the right image is opened while the right image is being output if the right image is first output. 
     According to an aspect of another exemplary embodiment, there is provided an LCD device including: an LCD panel; an edge-type backlight unit in which light sources are disposed at upper and lower edges of the edge-type backlight unit; an LCD panel control unit controlling the LCD panel such that a left image and a right image of a 3D image are alternately output on the LCD panel; and a backlight control unit classifying the light sources of the edge-type backlight unit into upper light sources including light sources disposed at the upper edge of the edge-type backlight unit and lower light sources including light sources disposed at the lower edge of the edge-type backlight unit and controlling turn-on and turn-off periods of the upper light sources and the lower light sources of the edge-type backlight unit to be synchronized with a period during which a 3D image is output on the LCD panel. 
     The LCD device may further include: shutter glasses respectively for the left image and the right image; and a shutter glass control unit controlling opening and closing of the shutter glasses so as to be synchronized with a period during which the 3D image is output on the LCD panel. 
     According to an aspect of another exemplary embodiment, there is provided a computer-readable recording medium having embodied thereon a program for executing the method of controlling the LCD device described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects will become more apparent by describing certain exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a block diagram of an LCD device including an edge-type backlight unit, according to an exemplary embodiment; 
         FIGS. 2A and 2B  illustrate synchronization between an output period of a 3D image to an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses; 
         FIGS. 3A and 3B  illustrate an edge-type backlight unit in which light sources are disposed at an upper edge or a lower edge of the edge-type backlight unit, according to an exemplary embodiment; 
         FIGS. 4A and 4B  illustrate an edge-type backlight unit in which light sources are disposed at upper and lower edges and at left and right edges of the edge-type backlight unit, according to an exemplary embodiment; 
         FIG. 5  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to an exemplary embodiment; 
         FIG. 6  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment; 
         FIG. 7  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment; 
         FIG. 8  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment; and 
         FIG. 9  illustrates a flowchart illustrating a method of controlling an LCD device including an edge-type backlight unit, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Certain exemplary embodiments are described in greater detail below with reference to the accompanying drawings. 
     In the following description, like drawing reference numerals are used for the like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of exemplary embodiments. However, exemplary embodiments can be practiced without those specifically defined matters. 
       FIG. 1  illustrates a block diagram of an LCD device  100  including an edge-type backlight unit  120 , according to an exemplary embodiment. 
     The LCD device  100  includes an LCD panel  110 , an edge-type backlight unit  120 , an LCD panel control unit  130 , and a backlight control unit  140  for controlling light sources of the edge-type backlight unit  120 . 
     The LCD panel  110  receives an image signal and outputs the image signal on a screen. The LCD device  100  outputs a 3D image signal to the LCD panel  110  to display a 3D image. The 3D image signal includes a left image signal and a right image signal by which a left image and a right image are alternately output on the LCD panel  110 , thereby generating a 3D image. 
     In a 3D display method using a liquid crystal shutter glass method, a left image and a right image are displayed to a left eye and a right eye at a predetermined frequency, respectively. In the LCD device  100  using the liquid crystal shutter glass method, a left image and a right image are alternately and rapidly output on the LCD panel  110 . A shutter glass for a left image and a shutter glass for a right eye are alternately open or closed. 
     The edge-type backlight unit  120  includes an upper light source unit and a lower light source unit. For example, the upper light unit includes at least one light source disposed at an upper edge and the lower light source unit includes at least one light source disposed a lower edge of the edge-type backlight unit  120 . As light is irradiated by a light source of the edge-type backlight unit  120  to the LCD panel  110 , an image output on the LCD panel  110  may be visualized. 
     Additionally, the edge-type backlight unit  120  may include light sources disposed on left and right edges of the edge-type backlight unit  120 . In this case, the upper light source unit of the edge-type backlight unit  120  may include at least one upper left light source disposed at an upper portion of the left edge and/or at least one upper right light source disposed at an upper portion of the right edge, in addition to or instead of the light source disposed at the upper edge. The lower light source unit of the edge-type backlight unit  120  may include at least one lower left light source disposed at a lower portion of the left edge and/or at least one lower right light source disposed at a lower portion of the right edge, in addition to or instead of the lower light source disposed at the lower edge. 
     The LCD panel control unit  130  controls the output periods of image signals output to the LCD panel  110 . The LCD panel control unit  130  may control left and right images among 3D images to be alternately output on the LCD panel  110  in order to generate a 3D image. As driving voltages corresponding to a left image signal and a right image signal among 3D image signals input to the LCD panel  110  are alternately applied to the LCD panel  110 , a left image and a right image may be alternately output on the LCD panel  110 . 
     Also, the LCD panel control unit  130  may control the output periods of a left image and a right image output to the LCD panel  110  to generate a 3D image. For example, the LCD panel control unit  130  may control the output periods of the images such that a left image, a black image, a right image, and a black image are sequentially output during one period in which a pair of a left image and a right image corresponding to each other are alternately output. Also, the LCD panel control unit  130  may control the output periods of the images such that a left image, a left image, a right image, and a right image are sequentially output during one period in which a pair of a left image and a right image corresponding to each other are alternately output. 
     The LCD panel control unit  130  may control a left image and a right image of one frame to be converted to four frames including a left image, a black image, a right image, and a black image or to four frames including a left image, a left image, a right image, and a right image and may control to output one set including four frames at a frequency period of 240 Hz. 
     As a left image and a right image are rapidly and alternately output, a 3D image is displayed. However, due to the data holding characteristics of the LCD panel  110 , if a new frame is output before an afterimage of a previous frame disappears, a cross-talk may be generated. Accordingly, by inserting a black image between a left image and a right image, or increasing a frequency period by repeating one identical frame, the cross-talk may be further reduced. 
     The LCD panel control unit  130  controls the images to be sequentially output from an upper portion to a lower portion of the LCD panel  110 . Accordingly, a previous frame is output on a lower portion of a screen of the LCD panel  110 , and a section of a new frame is output on an upper portion of the screen of the LCD panel  110 . 
     The backlight control unit  140  for the light sources of the edge-type backlight unit  120  controls turning the light sources on and off in synchronization with an output period of a 3D image output to the LCD panel  110 . The backlight control unit  140  may obtain information about an output period of a 3D image of the LCD panel  110  from the LCD panel control unit  130 . Also, the backlight control unit  140  may obtain information about an output period of a 3D image by using a V-sync signal. 
     The backlight control unit  140  controls turning on and off of the upper light source unit and the lower light source unit of the edge-type backlight unit  120 . For example, if a current main frame is output on an upper portion of the screen of the LCD panel  110 , the backlight control unit  140  may turn on the upper light source unit of the edge-type backlight unit  120 , and if a current main frame is output on a lower portion of the screen of the LCD panel  110 , the backlight control unit  140  may turn on the lower light source unit of the edge-type backlight unit  120 . 
     Also, the backlight control unit  140  may turn on the upper light source unit and turn off the lower light source unit while a current image is output on the upper portion of the screen and a previous image is left on the lower portion of the screen. In a similar manner, the backlight control unit  140  may turn off the upper light source unit and turn on the lower light source unit when a next image starts to be output on the upper portion of the screen and a current image is output on the lower portion of the screen. 
     The backlight control unit  140  may turn on or off the upper light source unit and the lower light source unit of the edge-type backlight unit  120  based on a ratio of a left image and a right image that mixedly exist on the screen, which may cause the cross-talk. For example, if the ratio of a current image and a previous image that mixedly exist over the entire screen of the LCD panel  110  is a predetermined threshold or greater, the upper light source unit and the lower light source unit may be turned off. Further, the backlight control unit  140  may turn on the upper light source unit and the lower light source unit when a ratio of a left image and a right image that mixedly exist on the screen is smaller than a predetermined threshold. 
     The LCD device  100  may control an opening/closing period of a shutter glass in synchronization with an output period of a 3D image. For example, one of a left image and a right image is output on the LCD panel  110  and a next image (e.g., a remaining image of one of a left image and a right image, or a black image) is output during a period T. The LCD device  100  may control such that if a left image is output first, a shutter glass for the left image is open while the left image is being output, and if a right image is output first, a shutter glass for the right eye may be open while the right image is being output. 
     Accordingly, the LCD device  110  controls turning on or off the light sources in the upper and lower portions of the edge-type backlight unit  120  individually according to a V-sync signal, thereby preventing the cross-talk that is generated due to the data holding characteristics of the LCD device  100 . 
       FIGS. 2A and 2B  illustrate synchronizations between a 3D image output period of an LCD panel, a turn-on/off period of a light source of a backlight unit, and an opening/closing period of a shutter glass. 
     In  FIGS. 2A and 2B , a horizontal axis of timing diagrams  210 ,  220 ,  230 ,  240 ,  250 , and  260  is a time axis. The timing diagram  220  or  230  of an output period of a 3D image, the timing diagram  240  of a turn-on/off period of the backlight unit, and the timing diagrams  250  and  260  of an opening/closing period of shutter glasses are illustrated in synchronization with the timing diagram  210  of a V-sync start signal STV. 
     A vertical axis of the timing diagram  220  or  230  of the output period of a 3D image denotes a vertical axis viewed on the screen of the LCD panel. Accordingly, referring to the timing diagram  220  or  230  of the output period of the 3D image, one sheet of frames is sequentially displayed from an upper portion to a lower portion of the screen according to time when a V-sync start signal STV is input twice. 
     The timing diagram  220  of an output period of a 3D image illustrates a timing diagram when a 3D image of one frame is converted to four frames including a left image, a black image, a right image, and a black image. The timing diagram  230  of an output period of a 3D image illustrates a timing diagram when a 3D image of one frame is converted to four frames including a left image, a left image, a right image, and a right image so that the 3D image of one frame is output at a frequency of 240 Hz. The images including four frames are synchronized with a V-sync signal at a frequency of 240 Hz and are alternately output. 
     According to the timing diagram  240  of a turn-on/off period of the backlight unit, the light sources are turned on from a time point when a frame is output on the LCD panel according to a V-sync signal and irradiate light to the LCD panel while frames are consecutively being output thereon. 
     Referring to the timing diagrams  250  and  260  of the opening/closing periods of the shutter glasses, a left eye shutter glass and a right eye shutter glass are repeatedly and alternately open or closed during a left image output period and a right image output period, respectively. As a result, a user may view a 3D image. 
       FIGS. 3A and 3B  illustrate an edge-type backlight unit  300  in which light sources are disposed on upper and lower edges, according to an exemplary embodiment. 
     The upper light source unit includes upper light sources  310  and the lower light source unit includes lower light sources  320 . The upper and lower light sources  310  and  320  are disposed on upper and lower edges of the edge-type backlight unit  300 , respectively. The backlight control unit  140  of the LCD device  100  controls the upper light sources  310  of the upper light source unit and the lower light sources  320  of the lower light source unit of the edge-type backlight unit  300  separately. In detail, the backlight control unit  140  may control turning on and off the upper light sources  310  and the lower light sources  320  in synchronization with a V-sync signal. 
     In  FIG. 3A , the upper light sources  310  are turned on, and the lower light sources  320  are turned off, and thus an upper portion  352  of a screen of an LCD device  350  is bright, and a lower portion  354  of the screen of the LCD device  350  is dark. In  FIG. 3B , the upper light sources  310  are turned off, and the lower light sources  320  are turned on, and thus the upper portion of the screen of the LCD device  350  is dark, and the lower portion  354  of the screen of the LCD device  350  is bright. 
       FIGS. 4A and 4B  illustrate an edge-type backlight unit  400  in which light sources are disposed on upper and lower edges and left and right edges, according to an exemplary embodiment. 
     In the edge-type backlight unit  400 , an upper light source unit includes upper light sources  410  disposed on an upper edge of the backlight unit  400 , and upper light sources  411  and  412  disposed on left and right edges of the backlight unit  400 . The lower light source unit includes lower light sources  420  disposed on a lower edge of the backlight unit  400  and lower light sources  421  and  422  disposed on left and right edges of the backlight unit  400 . The backlight control unit  140  of the LCD device  100  may separately control the upper light sources  410 ,  411 , and  412  disposed on the upper edge and upper portions of the left and right edges, and the lower light sources  420 ,  421 , and  422  disposed on the lower edge and lower portions of the left and right edges. The backlight control unit  140  may control turning on and off the upper light sources and lower light sources in synchronization with a V-sync signal. 
     In  FIG. 4A , the upper light sources  410 ,  411 ,  421  are turned on, and the lower light sources  420 ,  421 ,  422  are turned off, and thus an upper portion of a screen of an LCD device  450  is bright, and a lower portion of the screen of the LCD device  450  is dark. In  FIG. 4B , the upper light sources  410 ,  411 ,  421  are turned off, and the lower light sources  420 ,  421 ,  422  are turned on, and thus the upper portion of the screen of the LCD device  450  is dark and the lower portion  354  of the screen of the LCD device  450  is bright. 
       FIG. 5  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to an exemplary embodiment. 
     A timing diagram  520  of an output period of a 3D image, timing diagrams  530  and  540  of a turn-on/off period of the light sources of the edge-type backlight unit  120 , and timing diagrams  550  and  560  of an opening/closing period of the shutter glasses of the LCD panel  110  are synchronized with a timing diagram  510  of a V-sync start signal STV. 
     According to the timing diagram  520  of an output period of a 3D image, four frames including a left image, a black image, a right image, and a black image that are converted to correspond to one frame of a 3D image are alternately output on the LCD panel  110  at a frequency of 240 Hz. As discussed above, the LCD screen displays according to the data holding characteristics of the LCD device  100  the left image, the right image, and the black image which are synchronized with a V-sync start signal STV and output on the LCD panel  110 . A method of controlling turning on and off the light sources by the backlight control unit  140  is described in detail below. 
     In a section  521 , a cross-talk is generated over the entire screen due to a previous image that is left due to data holding characteristics of the LCD device  100 , and thus the backlight control unit  140  turns off the upper light source unit and the lower light source unit of the edge-type backlight unit  120 . 
     In a section  523 , the previous image is left due to the data holding characteristics of the LCD device  100  on a lower portion of a screen. The backlight control unit  140  turns on the upper light source unit of the edge-type backlight unit  120 . 
     In a section  525 , a next image is output on the upper portion of the screen. The backlight control unit  140  turns off the upper light source unit and turns on the lower light source unit. 
     In a section  527 , since a next image is displayed over the entire screen, the backlight control unit  140  turns off the upper light source unit and the lower light source unit. 
     According to the timing diagrams  550  and  560  of the opening/closing period of the shutter glasses, while a left image is being output, the shutter glass for a left image is open and the shutter glass for a right eye is closed in synchronization with a V-sync start signal. Also, while the right image is being output, the shutter glass for the right eye is controlled to be open, and the shutter glass for a left image is controlled to be closed in synchronization with a V-sync start signal. 
     Although one set including four frames that are converted to correspond to one frame is described above, if all the frames are controlled in the above-described manner, the cross-talk due to left and right images that are adjacent to each other may be prevented or eliminated. 
       FIG. 6  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment. 
     A timing diagram  620  of an output period of a 3D image, timing diagrams  630  and  640  of a turn-on/off period of the light sources of the edge-type backlight unit  120 , and timing diagrams  650  and  660  of an opening/closing period of the shutter glasses of the LCD panel  110  are synchronized with a timing diagram  610  of a V-sync start signal STV. 
     In a section  621 , a cross-talk is generated over the entire screen due to a previous image that is left due to the data holding characteristics of the LCD device  100 , and thus the backlight control unit  140  turns off the upper light source unit and the lower light source unit of the edge-type backlight unit  120 . 
     In a section  622 , the previous image is left due to the data holding characteristics of the LCD device  100  on a lower portion of a screen. The backlight control unit  140  turns on only the upper light source unit of the edge-type backlight unit  120 . 
     In a section  625 , a ratio of a left image and a right image that mixedly exist on the screen is smaller than a predetermined threshold. The backlight control unit  140  turns on the upper light source unit and the lower light source unit. The method of controlling the light sources of the edge-type backlight light unit  120  is similar to that of  FIG. 5  except that a control section such as the section  625  is inserted. 
     In a section  627 , a next image is output on an upper portion of a screen. The backlight control unit  140  turns off the upper light source unit of the edge-type backlight unit  120  and maintains the lower light source unit of the edge-type backlight unit  120  turned on. 
     In a section  629 , a next image is displayed over the entire screen. The backlight control unit  140  turns off the upper light source unit and the lower light source unit. 
     According to the timing diagrams  650  and  660  of the opening/closing period of the shutter glasses, the shutter glass for a left image and the shutter glass for a right image are open or closed in synchronization with a V-sync start signal STV as shown by the timing diagrams  650  and  660 . 
       FIG. 7  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment. 
     A timing diagram  720  of an output period of a 3D image, timing diagrams  730  and  740  of a turn-on/off period of the light sources of the edge-type backlight unit  120 , and timing diagrams  750  and  760  of an opening/closing period of the shutter glasses of the LCD panel  110  are synchronized with a timing diagram  710  of a V-sync start signal STV. 
     Referring to the timing diagram  720  of an output period of a 3D image, a left image, a right image, a right image, and a left image, a left image, a right image and a right image are output. That is, four frames including a left image, a left image, a right image, and a right image that are converted to correspond to one frame of a 3D image are alternately output on the LCD panel  110  at a frequency of 240 Hz. As discussed above, the LCD screen displays according to the data holding characteristics of the LCD display  110  the left image and the right image which are synchronized with a V-sync start signal STV and output on the LCD panel  110 . A method of controlling turning on and off the light sources of the edge-type backlight unit  120  by the backlight control unit  140  is described in detail below. 
     In a section  721 , a cross-talk is generated over the entire screen due to a previous image that is left due to the data holding characteristics of the LCD device  100 , and thus the backlight control unit  140  turns off the upper light source unit and the lower light source unit of the edge-type backlight unit  120 . 
     In a section  723 , the previous image is left due to the data holding characteristics of the LCD device  100  on a lower portion of a screen. The backlight control unit  140  turns on only the upper light source unit of the edge-type backlight unit  120 . 
     In a section  725 , a next image is output on an upper portion of the screen. The upper light source unit of the edge-type backlight unit  120  is turned off, and the lower light source unit of the edge-type backlight unit  120  is turned on. 
     In a section  727 , a next image is output on the entire screen. The upper light source unit and the lower light source unit of the edge-type backlight unit  120  are turned off. 
     According to the timing diagrams  750  and  760  of the opening/closing period of the shutter glasses, the shutter glass for a left image is open and the shutter glass for a right image is closed if a first frame, which is output first in synchronization with a V-sync start signal, contains the left image. Also, if a first frame, which is output first, contains the right image, the shutter glass for a right image is controlled to be open and the shutter glass for a left image is controlled to be closed in synchronization with a V-sync start signal. 
     One set including four frames that are converted to correspond to one frame is described above, but if all the frames are controlled in the above-described manner, the cross-talk due to left and right images that are adjacent to each other may be prevented or eliminated. 
       FIG. 8  illustrates a method of synchronizing a 3D image output period of an LCD panel, a turn-on/off period of light sources of a backlight unit, and an opening/closing period of shutter glasses, according to another exemplary embodiment. 
     A timing diagram  820  of an output period of a 3D image, timing diagrams  830  and  840  of a turn-on/off period of the light sources of the edge-type backlight unit  120 , and timing diagrams  850  and  860  of opening/closing periods of the shutter glasses of the LCD panel  110  are synchronized with a timing diagram  810  of a V-sync start signal STV. 
     As discussed above, the LCD screen displays according to the data holding characteristics of the LCD device  100  four frames of the left image, the left image, the right image, and the right image, which are converted to correspond to one frame of a 3D image according to the timing diagram  820  of a 3D image output period, synchronized with a V-sync start signal STV at a frequency of 240 Hz, and output on the LCD panel  110 . A method of turning on and off the light sources of the edge-type backlight unit  120  by the backlight control unit  140  is described in detail below. 
     In a section  821 , a cross-talk is generated over the entire screen due to a previous image that is left due to the data holding characteristics of the LCD device  100 , and thus the backlight control unit  140  turns off the upper light source unit and the lower light source unit of the edge-type backlight unit  120 . 
     In a section  823 , the previous image is left due to the data holding characteristics of the LCD device  100  on a lower portion of a screen. The backlight control unit  140  turns on only the upper light source unit of the edge-type backlight unit  120 . 
     In a section  825 , a ratio of a left image and a right image that mixedly exist on the screen is smaller than a predetermined threshold. The backlight control unit  140  turns on the upper light source unit and the lower light source unit. The method of controlling the light sources of the edge-type backlight light  120  is similar to that of  FIG. 7  except that a control section such as the section  825  is inserted. 
     In a section  827 , a next image is output on an upper portion of a screen. The backlight control unit  140  turns off the upper light source unit of the edge-type backlight unit  120  and maintains the lower light source unit of the edge-type backlight unit  120  turned on. 
     In a section  829 , a next image is displayed over the entire screen. The backlight control unit  140  turns off the upper light source unit and the lower light source unit. 
     According to the timing diagrams  850  and  860  of the opening/closing periods of the shutter glasses, the shutter glass for a left image and the shutter glass for a right image are open or closed in synchronization with a V-sync start signal as shown by the timing diagrams  850  and  860 . 
     To summarize,  FIGS. 5 and 6  illustrate the diagrams when a 3D image of one frame is converted to one set including a left image, a black image, a right image, and a black image, and  FIGS. 7 and 8  illustrate the diagrams when a 3D image of one frame is converted to one set including a left image, a left image, a right image, and a right image. 
     Also, in  FIGS. 5 and 7 , turn-on/off periods of the light sources of the edge-type backlight unit light  120  may be divided into six sections, and in  FIGS. 6 and 8 , turn-on/off periods of the light sources of the edge-type backlight unit light  120  may be divided into eight sections. 
     That is, in  FIGS. 5 and 7 , a period T 1  during which one of a left image and a right image of a 3D image is output on the LCD panel  110  and a black image is output on the LCD panel  110  is divided into six sections. The upper light source unit is controlled to be turned on in a second section S 2  and a third section S 3 , and turned off in a first section S 1 , a fourth section S 4 , a fifth section S 5 , and a sixth section S 6 . The lower light source unit is controlled to be turned on in the fourth section S 4  and the fifth section S 5  and turned off in the first section S 1 , the second section S 2 , the third section S 3 , and the sixth section S 6 . 
     The controlling during each period T 1  is repeated periodically for each frame group including one of the left image and the right image and the black image, shown in  FIGS. 5 and 7 . 
     In  FIGS. 6 and 8 , a period T 3  during which one of a left image and a right image of a 3D image is output on the LCD panel  110  and a next image of another type is output on the LCD panel  110  is divided into eight sections. The upper light source unit may be controlled to be turned on in a second section S 2 , a third section S 3 , a fourth section S 4 , and a fifth section S 5 , and turned off in a first section S 1 , a sixth section S 6 , a seventh section S 7 , and an eighth section S 8 . The lower light source unit may be controlled to be turned on in the fourth section S 4 , the fifth section S 5 , the sixth section S 6 , and the seventh section S 7 , and turned off in the first section S 1 , the second section S 2 , the third section S 3 , and the eighth section S 8 . 
     The controlling during each period T 3  is repeated for each frame group including a left image or a right image, a black image and a control section, shown in  FIGS. 6 and 8 . 
       FIG. 9  illustrates a flowchart illustrating a method of controlling an LCD device including an edge-type backlight unit, according to an exemplary embodiment. 
     In operation  910 , turn-on and turn-off periods of the upper light source unit and the lower light source unit of an edge-type backlight unit are controlled to be synchronized with an output period of a 3D image displayed on an LCD panel. 
     Light sources of the edge-type backlight unit include the upper light source unit and the lower light source unit. The upper light source unit may include one or more light sources disposed at an upper edge of the edge-type backlight unit, and the lower light source unit may include one or more light sources disposed at a lower edge of the edge-type backlight unit. The light sources of the edge-type backlight unit may further include light sources that are disposed at left and right edges of the edge-type backlight unit. Accordingly, the upper light source unit of the edge-type backlight unit may include one or more upper light sources disposed at an upper edge and one or more light sources disposed at upper left and right edges of the edge-type backlight unit. The lower light source unit of the edge-type backlight unit may include one or more lower light sources disposed at a lower edge and one or more light sources disposed at lower left and right edges of the edge-type backlight unit. 
     As a current image is output on an upper portion of a screen and a previous image is still left at a lower portion of the screen, the controlling of the light sources of the edge-type backlight unit may include turning on the upper light source unit and turning off the lower light source unit, and turning off the upper light source unit and turning on the lower light source unit when a next image starts to be output on the upper portion of the screen and a current image is output on the lower portion of the screen. 
     Also, the controlling of the light sources of the edge-type backlight unit may include turning-off the upper light source unit and the lower light source unit if a ratio of a current image and a previous image that mixedly exist over the entire screen is a predetermined threshold or greater, and turning on the upper light source unit and the lower light source unit if the ratio of a current image and a previous image that mixedly exist over the entire screen is smaller than the predetermined threshold. 
     The controlling of the light sources of the edge-type backlight unit may be synchronized with a period in which a 3D image is output on the LCD panel by using a V-sync signal of an LCD device. 
     The method of controlling an LCD device may further include controlling the LCD panel such that a left image and a right image of the 3D image are alternately output. One frame of the 3D image may be converted to four frames in order of a left image, a black image, a right image, and a black image or to four frames in order of a left image, a left image, a right image, and a right image, and be output at a frequency of 240 Hz. The images may be sequentially output from an upper portion to a lower portion of the LCD panel. 
     According to exemplary embodiments, the light sources of the edge-type backlight unit are controlled so that an area where a left image and a right image are mixedly output on the LCD panel is not viewed by the viewer, thereby preventing the cross-talk. 
     Exemplary embodiments can be implemented as computer programs and can be implemented in general-use digital computers that execute the programs using a computer-readable recording medium. Examples of the computer-readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.), optical recording media (e.g., CD-ROMs, or DVDs), etc. 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.