Patent Publication Number: US-2011050742-A1

Title: Backlight unit, display apparatus and method of controlling backlight unit

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0082558, filed on Sep. 2, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     One or more embodiments relate to a backlight unit having excellent three-dimensional effects of an image, a display apparatus, and a method of controlling the backlight unit. 
     2. Description of the Related Art 
     A backlight unit is used as a light source for many applications including, but not limited to, display devices used in notebook computers, desktop computers, liquid crystal display (LCD)-TVs, mobile communication terminals, etc. For example, an LCD device, which is a flat panel display device, is a light-receiving type display device that does not emit light itself so as to form an image. Thus, a backlight unit is necessary in such an LCD device. In general, a backlight unit is disposed on the back surface of a display device so as to emit light. 
     The backlight unit may be classified based on the alignment of a light source. For example, a direct light type backlight unit emits light from a plurality of light sources installed right under the LCD device onto an LCD panel and an edge light type backlight unit emits light from a light source installed on a side wall of a light guide panel (LGP) onto an LCD panel. As a light source, a cold cathode fluorescent lamp (CCFL) is generally, but not always, used in the backlight unit. Further, a light emitting diode (LED) may also be used instead of the CCFL. 
     SUMMARY 
     An illustrative embodiment provides a backlight unit having excellent three-dimensional effects on an image. 
     An illustrative embodiment also provides a display apparatus having excellent three-dimensional effects on an image. 
     An illustrative embodiment also provides a method of controlling the backlight unit having excellent three-dimensional effects on an image. 
     According to an illustrative embodiment, there is provided a backlight unit including: light emitting devices for emitting light; an image depth information extraction unit for extracting image depth information from an image signal; a brightness calculator for calculating brightness from the image depth information; and a controller for controlling the brightness of the light emitting devices according to the calculated brightness. 
     The light emitting devices may be controlled in a block unit including a plurality of adjacent light emitting devices. 
     The controller may control the brightness of the light emitting devices by adjusting a voltage applied to the light emitting devices. 
     The controller may control the brightness of the light emitting devices using pulse width modulation (PWM). 
     The brightness calculator may partition an image into a plurality of regions and calculates the brightness of each region. 
     The brightness calculator may calculate the brightness such that as the image depth increases, the brightness decreases, and as the image depth decreases, the brightness increases. 
     According to another illustrative embodiment, there is provided a display apparatus including: an image board for generating an image signal; a display panel for displaying an image according to the image signal generated by the image board; light emitting devices for emitting light to the display panel; an image depth information extraction unit for extracting image depth information from the image signal from the image board; a brightness calculator for calculating the brightness from the image depth information; and a controller for controlling the brightness of the light emitting devices according the calculated brightness. 
     According to another illustrative embodiment, there is provided a method of controlling a backlight unit, the method including: extracting image depth information from an image signal; calculating the brightness of a plurality of image regions according to the image depth information; and controlling the brightness of the light emitting devices so as to correspond to the calculated brightness. 
     The calculating the brightness may include using a look-up table corresponding to the image depth information. 
     The extracting the image depth information may include partitioning an image depth distribution area into a plurality of regions. 
     The controlling the brightness of the light emitting devices may include partitioning an image into a plurality of regions, and calculating the brightness of each region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages will become more apparent by describing illustrative embodiments in detail with reference to the attached drawings, in which: 
         FIG. 1  schematically illustrates a layered structure of a display apparatus according to an illustrative embodiment; 
         FIG. 2  is a block diagram of a display apparatus according to an illustrative embodiment; 
         FIG. 3A  shows an image used in a display apparatus according to an illustrative embodiment; 
         FIGS. 3B ,  3 C, and  3 D are images for describing a process of extracting depth information and brightness information from the image of  FIG. 3A ; 
         FIG. 4  schematically shows a backlight unit according to an illustrative embodiment; and 
         FIG. 5  is a flowchart illustrating a method of controlling the backlight unit, according to an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a backlight unit, a display apparatus, and a method of controlling the backlight unit according to illustrative embodiments will be described more fully with reference to the accompanying drawings. 
       FIG. 1  schematically illustrates a layered structure of a display apparatus  100  according to an illustrative embodiment.  FIG. 2  is a block diagram of the display apparatus  100  according to an illustrative embodiment. 
     Referring to  FIGS. 1 and 2 , the display apparatus  100  includes a backlight unit  10  for emitting light, and a display panel  70  which uses light emitted by the backlight unit  10  to display an image. 
     The display panel  70  may be, but is not limited to, a liquid crystal display (LCD) panel. The display panel  70 , which includes pixel units that each include a thin film transistor and an electrode, displays an image by transmitting an electric field to each pixel of the display panel  70  according to an image signal input by an image board  20 , and modulates light emitted by the backlight unit  10 . 
     The backlight unit  10  may include light emitting devices  15  and a controller  28  that controls the light emitting devices  15 . The light emitting devices  15  may be, but is not limited to, a light emitting diode (LED). A diffusion plate  40  for uniformly diffusing light emitted by the light emitting devices  15  to be incident into the display panel  70  and a prism sheet  50  for guiding light to the display panel  70  by adjusting an optical path may be disposed between the light emitting devices  15  and the display panel  70 . A polarization improving film  60  may be disposed between the prism sheet  50  and the display panel  70  to improve light efficiency by improving polarization. However, the layered structure of the display apparatus  100  is not limited to that shown in  FIG. 1 , and a variety of layers may be disposed between the light emitting devices  15  of the backlight unit  10  and the display panel  70 . 
     The backlight unit  10  may include light emitting devices  15  that are two-dimensionally aligned on a substrate  12  and the controller  28  that controls the light emitting devices  15 . The substrate  12  may include a printed circuit board (PCB) substrate. 
     Referring to  FIG. 2 , when the image board  20  outputs an image signal, the image signal is input to a display panel driving unit  22  and an image depth information extraction unit  24 . The display panel driving unit  22  generates a display panel driving signal according to the image signal to operate the display panel  70 . According to the display panel driving signal, the display panel  70  is operated by an on-off switch of each pixel. The display panel driving unit  22  may include information about a voltage applied to each pixel of the display panel  70 . For example, the transmittance of light emitted by the light emitting devices  15  of the backlight unit  10  may be controlled by adjusting the voltage applied to each pixel of the display panel  70  so as to represent an image in gray scale. 
     The image depth information extraction unit  24  extracts image depth information from the image signal output by the image board  20 . For example, if the image signal includes a two-dimensional image and image depth information, the image depth information extraction unit  24  may extract the image depth information without calculating the image depth. In a stereoscopic image, the image depth is calculated from the image signal. For example, the image depth information may be extracted from a two-dimensional image by mixing predetermined depth models according to color information of an input image. Such a method is disclosed in Pseudo 3D Image Generation width Simple Depth Models, 2005 IEEE. The image depth information may be extracted from a stereoscopic image by calculating a disparity map by comparing feature points such as edges, lines, and corners. Such a method is disclosed in Edge-Preserving Directional Regularization Technique For Disparity Estimation of Stereoscopic Images, IEEE Transaction on Consumer Electronics, Vol. 45, No. 3, August 1999, pp. 804-810. 
     For example, when the image shown in  FIG. 3A  is displayed, the image depth information extracted from the image of  FIG. 3A  is shown in  FIG. 3B . As image depth decreases, the image appears closer to white in color, and as image depth increases, the image appears closer to black in color. In other words, as the distance between an observer and the image decreases, the image appears closer to white in color, and as the distance between the observer and the image increases, the image appears closer to black in color. 
       FIG. 3C  is an image partitioned into a plurality of regions, for example, a first region L 1 , a second region L 2 , and a third region L 3 , according to the image depth information. When the image of  FIG. 3A  is compared with the image depth distribution of  FIG. 3C , the lake shown in  FIG. 3A , which is the closest to the observer, corresponds to the first region L 1  of  FIG. 3C , a region in the middle of the image corresponds to the second region L 2 , and the sky, which is the farthest from the observer, corresponds to the third region L 3 . For example, a part of the image in the first region L 1  may have first image depth information, and a part of the image in the second region L 2  may have second image depth information and a part of the image in the third region L 3  may have third image depth information. In this regard, if a resolution of the image depth is referred to as a bit, the first region L 1 , the second region L 2 , and the third region L 3  may be shown in gray scale. For example, the image depth information of each region may be distributed in gray scale between white (255) and black (0). 
     The image depth distribution area may be partitioned into a plurality of regions according to the number of light emitting devices  15 . For example, the image depth information extraction unit  24  may partition the image into a plurality of brightness distribution regions A as shown in  FIG. 3D , and may extract depth information of each brightness distribution region A using an averaging operation. 
     After the depth information is extracted by the image depth information extraction unit  24 , a brightness calculator  26  calculates a brightness corresponding to each piece of depth information. The brightness calculator  26  may include a look-up table corresponding to each piece of depth information. The brightness calculator  26  may include a reference value for calculating brightness according to the depth information. Based on the reference value, a region in which brightness is required to be adjusted may be extracted. 
     According to the brightness obtained by the brightness calculator  26 , the controller  28  controls the brightness of the light emitting devices  15 . The light emitting devices  15  may be each independently electrically operated, and the brightness of the light emitting devices  15  may be controlled based on the brightness distribution. For example, if an image has a brightness distribution as shown in  FIG. 3C , the brightness of the light emitting devices  15  located in a region corresponding to the first region L 1  is controlled to L 1   b , the brightness of the light emitting devices  15  located in a region corresponding to the second region L 2  is controlled to L 2   b , and the brightness of the light emitting devices  15  located in a region corresponding to the third region L 3  is controlled to L 3   b . In this regard, when the depth of each region satisfies the relation of the depth of the first region L 1 &lt;the depth of the second region L 2 &lt;the depth of the third region L 3 , the brightness of light emitting devices corresponding to each region may be controlled to satisfy the relation of L 1   b &gt;L 2   b &gt;L 3   b.    
     The light emitting devices  15  may be each independently controlled. Alternatively, as shown in  FIG. 4 , a block B including a plurality of adjacent light emitting devices  15  may be controlled. 
     The light emitting devices  15  may be two-dimensionally aligned on the substrate  12  as shown in  FIG. 4  and partitioned into a plurality of blocks B, wherein the blocks B may be each independently controlled. The plurality of blocks B may correspond to, for example, the brightness distribution regions A of the brightness calculator  26  as shown in  FIG. 3D . The number of light emitting devices  15  contained in the blocks B is not limited.  FIG. 4  shows four light emitting device  15  in blocks B, but  FIG. 4  is merely an illustrative embodiment. 
     The light emitting devices  15  may be disposed on a PCB substrate  12  and have a circuit by which current is supplied independently to the light emitting devices  15 . The controller  28  may control current supplied to, or voltage applied to, each of the light emitting devices  15  using a digital-to-analog (D/A) converter. Or, the brightness of the light emitting devices  15  may be controlled by adjusting current supplied to, or voltage applied to, the light emitting devices  15  of each block B using a D/A converter. For example, the perspective of an image may be improved by supplying relatively greater or less current to the light emitting devices  15  located in the regions with high brightness than to the light emitting devices  15  located in the regions with low brightness, and thus three-dimensional effects of the image may be improved. 
     Alternatively, the controller  28  may control the brightness of the light emitting devices  15  using a pulse width modulation (PWM). 
     According to an illustrative embodiment, the light emitting devices  15  may each be a multi-chip light emitting device including a plurality of light emitting diodes that emit lights having at least two wavelength ranges and are formed in a single package. Light having different wavelengths emitted by a light emitting diode chip are totally reflected internally to create a white light. The number of light emitting diode chips of each wavelength and the alignment thereof may vary according to a range for a desired color temperature in consideration of the amount of light emitted by the light emitting diode chip of each wavelength. As described above, since the size of the multi-chip light emitting device is not significantly changed when compared with that of the single-chip light emitting device, the volume of the multi-chip light emitting device is also not changed substantially. In addition, since color-mixing for the color white is performed in the light emitting devices  15 , the space for the color-mixing is significantly reduced, thereby decreasing the thickness of the backlight unit  10 . 
     The light emitting devices  15  may each also be a single-chip light emitting device, and light emitting devices  15  emitting lights having different wavelengths may be alternately aligned. For example, a first light emitting device emitting a light having a first wavelength, a second light emitting device emitting a light having a second wavelength, and a third light emitting device emitting a light having a third wavelength may be disposed on the PCB substrate  12  and separated by a predetermined distance. In this regard, only one first light emitting device, one second light emitting device, and one third light emitting device are alternately aligned herein. However, if an amount of one of the lights having different wavelengths is required to be increased; two chips for emitting the light may be continuously aligned. For example, the amount of green light may be increased by aligning a red light emitting device, a green light emitting device, a green light emitting device, and a blue light emitting device. 
     Alternatively, the light emitting devices  15  may constitute a single chip including fluorescent materials. A white light may be emitted by mixing light emitted from the single chip and light emitted from the fluorescent material excited by light emitted from the single chip. The fluorescent materials for light emitting devices to form a white light are well known in the art, and thus description thereof will be omitted herein. 
       FIG. 5  is a flowchart illustrating a method of controlling the backlight unit  10 , according to an illustrative embodiment. 
     In operation S 10 , an image signal is generated in the image board  20  ( FIG. 1 ), and in operation S 15 , image depth information is extracted from the image signal. 
     The brightness of the image is calculated from the image depth information in operation S 20 . As image depth increases, the brightness decreases, and as image depth decreases, the brightness increases. The brightness calculator  26  may include a look-up table or a reference value corresponding to the image depth information to calculate the brightness information. The brightness calculator  26  may partition the image into a plurality of brightness distribution regions. In operation S 25 , the brightness of the light emitting devices  15  in regions corresponding to the plurality of brightness distribution regions are controlled according to the calculated image brightness. The brightness may be controlled according to the image depth to improve three-dimensional effects. A method of controlling the brightness of the light emitting device may be classified into a method of controlling the brightness of each of the light emitting devices  15  and a method of controlling the brightness of a block including a plurality of the light emitting devices  15 . 
     As described above, the backlight unit  10  and the display apparatus  100  using the backlight unit  10  control the brightness of the light emitting devices  15  according to the image depth information to improve three-dimensional effects. The three-dimensional effects may be improved by processing the image signal without using a separate device. Furthermore, since the brightness of the light emitting devices  15  is controlled by the perspective of the image, power consumption may be reduced compared with light emitting devices maintaining a constant brightness. According to an illustrative embodiment of the method of controlling the backlight unit  10 , the light emitting devices  15  are controlled by extracting the image depth information from the image signal and extracting the brightness of the image from the image depth information. Thus, three-dimensional effects based on the perspective of the image may be improved. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.