Patent Publication Number: US-8988453-B2

Title: Stereoscopic image display device and driving method thereof

Description:
This application claims the benefit of Korean Patent Application No. 10-2011-0059162 filed on Jun. 17, 2011, which is hereby incorporated by reference. 
     BACKGROUND 
     1. Field 
     This document relates to a stereoscopic image display device and a driving method thereof. 
     2. Related Art 
     A stereoscopic image display device is classified into a stereoscopic technique and an autostereoscopic technique. 
     The stereoscopic technique is implemented using parallax images of left and right eyes having the most reliable three dimensional effects. The stereoscopic technique is classified into a glasses method and a non-glasses method, both of which are commercialized. The glasses method displays left and right parallax images on a direct-view liquid crystal display panel or projector in a time-divisional manner by changing polarization direction of the left and right parallax images, and implements a stereoscopic image using polarization glasses or liquid-crystal shutter glasses. In general, the non-glasses method is a method which obtains a stereoscopic image by separating the optical axes of left and right parallax images using an optical plate such as a parallax barrier and the like. 
     As described above, the most important factors for displaying the stereoscopic image on the stereoscopic image display device are color temperature and luminance components according to an exposure of a camera in the obtaining state of the image. 
     However, the prior stereoscopic image display device processes and outputs a synthesized image of left-eye and right-eye images in the same processing manner. For this reason, the prior stereoscopic image display device causes a competition phenomenon between the left-eye and right-eye images and thereby reduces the display quality of the stereoscopic image when the color property values of the left-eye and right-eye images are different from each other in an intermediate image processing state after obtaining the stereoscopic image. Accordingly, faces with this situation, clearly further improvement is required. 
     SUMMARY 
     According to an exemplary embodiment of this document, there is provided a stereoscopic image display device including: an image divider unit for dividing a stereoscopic image into a left-eye image and a right-eye image; an image correction unit for correcting color temperature for the left-eye and right-eye images and correcting the brightness for the color-temperature-corrected left-eye and right-eye images; an image synthesis unit for synthesizing the left-eye and right-eye images; and an image display panel for displaying the stereoscopic image on the basis of the stereoscopic image outputted through the image synthesis unit. 
     According to an exemplary embodiment of this document, there is provided a method for driving a stereoscopic image display device including: an image dividing step of dividing a stereoscopic image into a left-eye image and a right-eye image; an image correcting step of correcting color temperature for the left-eye and right-eye images and correcting the brightness for the color-temperature-corrected left-eye and right-eye images; an image synthesizing step of synthesizing the left-eye and right-eye images; and an image outputting step of outputting the synthesized image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompany drawings, which are comprised to provide a further understanding of the invention and are incorporated on and constitute a part of this specification illustrate implementations of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a schematic structure diagram of a stereoscopic image display device; 
         FIG. 2  is an exemplary circuit structure diagram of a sub-pixel; 
         FIG. 3  is a schematic structure diagram of an image display panel; 
         FIG. 4  is a view for explaining a 3D image expression method; 
         FIG. 5  is a schematic block diagram of an image processing unit according to one embodiment of the present invention; 
         FIG. 6  is a detailed block diagram of an image processing unit illustrated in  FIG. 5 ; 
         FIG. 7  is a flow chart for schematically explaining a method for driving a stereoscopic image display device according to one embodiment of the present invention; and 
         FIG. 8  is a flow chart for specifically explaining the driving method of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail implementations of the invention examples of which are illustrated in the accompanying drawings. 
     Hereinafter, an implementation of this document will be described in detail with reference to the attached drawings. 
       FIG. 1  is a schematic structure diagram of a stereoscopic image display device and  FIG. 2  is an exemplary circuit structure diagram of a sub-pixel. 
     As shown in  FIGS. 1 and 2 , a stereoscopic image display device includes an image processing unit SBD, a timing control unit TCN, a driving unit DRV, a liquid crystal display panel LCD, a pattern retarder PRF, and glasses GLS. 
     The image processing unit SBD generates a normal image (hereinafter, 2D image) in a two-dimensional mode 2D mode and generates a stereoscopic image (hereinafter, 3D image) in a three-dimensional mode. The image processing unit SBD supplies timing signals such as a vertical synchronous signal Vsync, a horizontal synchronous signal Hsync, a data enable signal DE, a main clock Main Clock, and the like and a 2D or 3D image to the timing control unit TCN. 
     The image processing unit SBD generates and processes a corresponding image in the 2D mode or 3D mode selected according to a choice of a user inputted through a user interface and supplies the processed image to the timing control unit TCN. The user interface includes a user input unit such as an On Screen Display (OSD), a remote controller, a keyboard, a mouse, and the like. Hereinafter, the image processing unit SBD which is selected in the 3D mode and supplies the 3D image to the timing control unit TCN will be explained. 
     The timing control unit TCN receives the 3D image including a left-eye image and a right-eye image received from the image processing unit SBD. The timing control unit TCN alternately supplies the left-eye and right-eye images at a frame frequency of at least 120 Hz to the driving unit DRV. In addition, the timing control unit TCN supplies a control signal corresponding to the image to the driving unit DRV. 
     The driving unit DRV includes a data driving part connected to data lines to supply data signals and a gate driving part connected to gate lines to supply gate signals. The data driving part included in the driving unit DRV converts digital type left-eye and right-eye images to analog type left-eye and right-eye images under the control of the timing control unit TCN and supplies the converted images to the data lines. In addition, the gate driving part included in the driving unit DRV sequentially supplies the gate signals to the gate lines under the control of the timing control unit TCN. 
     A LCD panel LCD receives the gate signals and the data signals from the driving unit DRV and displays the 2D or 3D image. The LCD panel includes a Thin Film Transistor (TFT) substrate in which TFTs and capacitors and the like are formed and a color filter substrate in which a color filter and a black and the like are formed. A sub-pixel SP including a liquid crystal layer formed between the TFT substrate and the color filter substrate. 
     The sub-pixels SP include a red sub-pixel, a green sub-pixel, a blue sub-pixel and the like. As shown in  FIG. 2 , a general circuit structure of one sub-pixel includes a TFT, a storage capacitor Cst, and a liquid crystal layer Clc. The TFT includes a source electrode connected to a data line DL to which a data signal is supplied and a gate electrode connected to a gate line GL to which a gate signal is supplied. The storage capacitor Cst and the liquid crystal layer Clc are connected to the drain electrode of the TFT and receive a common voltage supplied through a common voltage line Vcom. The liquid crystal layer Clc is driven by a difference between a data voltage supplied to a pixel electrode  1  and a common voltage supplied to a common electrode  2 . The common electrode is formed on the color substrate in a vertical field drive method such as a Twisted Nematic TN mode and a Vertical Alignment VA mode. The common electrode and the pixel electrode  1  are formed on the TFT substrate in a horizontal field drive method such as an In Plane Switching (IPS) mode and a Fringe Field Switching (FFS) mode. 
     A liquid crystal mode of a LCD panel LCD can be formed in any modes as well as the TN mode, the VA mode, the IPS mode, and the FFS mode. A lower polarization plate POL 1  and an upper polarization plate POL 2  are attached to the TFT substrate and the color filter substrate of the LCD panel LCD, respectively. The LCD panel can display the image by the light provided from a backlight unit BLU. 
     The backlight unit BLU is driven by the control of the image processing unit SBD or the timing control unit TCN to provide the light for the LCD panel LCD. The backlight unit BLU includes a light source for emitting the light, a light guide plate for guiding the light emitted from the light source to the LCD panel, an optical member for diffusing and collecting the light emitted from the light guide plate, and the like. 
     The backlight unit BLU is formed with an edge type, a dual type, a quad type, a direct type, and the like. The edge type is a type wherein the light source is arranged in one side of the LCD panel LCD. The dual type is a type wherein the light sources are arranged opposite to each other at both sides of the LCD panel LCD. The quad type is a type wherein the light sources are arranged in four directions of the LCD panel LCD. The direct type is a type wherein the light source is arranged at a lower part of the LCD panel LCD. 
     The pattern retarder PRF mixes the left-eye and right-eye images displayed on the LCD panel in a line-by-line and displays the mixed image in an interlace manner. To achieve the above, the pattern retarder PRF separates the image displayed on the LCD panel by polarizing an odd-numbered line in a right source polarization and polarizing an even-numbered line in a left source polarization (or otherwise). 
     The glasses GLS play a role of dividing the image outputted through the pattern retarder into the left-eye and right-eye images. The glasses GLS are selected as polarization glasses in which polarization characteristics of a left-eye glass and a right-eye glass are opposite to each other. Accordingly, only the left-eye image passes through the left-eye glass LEFT and only the right-eye image passes through the right-eye glass RIGHT. 
     As described above, the backlight unit BLU, the LCD panel LCD, and the pattern retarder PRF are integrated devices for displaying the image and are thus defined as an image display panel PNL in the description of the present invention. 
     Meanwhile, in the above description, the panel including the backlight unit BLU and the LCD panel LCD is described as an example but only the panel for displaying the image like an organic electroluminescent display panel, a plasma panel, and a field emission display panel is possible. However, for the sake of convenient explanation, the present invention will be described on the basis of the LCD panel LCD. 
     Hereinafter, the detailed explanation will focus on the schematic structure of the image display panel and the expression of the 3D image in the image display panel. 
       FIG. 3  is a schematic structure diagram of the image display panel and  FIG. 4  is a view for explaining a 3D image expression method. 
     As described in  FIGS. 3 and 4 , the image display panel PNL includes the LCD panel LCD for displaying the image and the pattern retarder PRF which is attached to a display surface of the LCD panel LCD and divides the image into the left-eye image and the right-eye image in each frame. The backlight unit is omitted therein. 
     The pattern retarder includes a first film FL 1 , a second film FL 2 , black matrixes BM, a retarder liquid crystal layer PLC, and a λ/4 plate PQWP. The first film FL 1  and the second film FL 2  are attached to each other and the black matrixes BM and the retarder liquid crystal layer PLC are formed therebetween. The black matrixes BM are positioned between the first film FL 1  and the second film FL 2  and are separated in the horizontal direction of the LCD panel liquid crystal and are divided to be positioned in a boundary area between the sub-pixels SP. The λ/4 plate PQWP is attached to one surface of the second film FL 2  through which the image received through the LCD panel is outputted. 
     The pattern retarder PRF divides the image displayed on the LCD panel by polarizing the odd-numbered line in the right source polarization R and the even-numbered line in the left source polarization L (or otherwise). 
     The stereoscopic image display device is a stereoscopic image display device using the pattern retarder PRF. In the stereoscopic image display device, the pattern retarder PRF separately outputs the left-eye image and the right-eye image when the left-eye image and the right-eye image are alternately displayed on the LCD panel. 
     Accordingly, a user sees the left-eye image through the left-eye glass LEFT in a first frame [n] and sees the right-eye image through the right-eye glass LIGHT in a second frame [n+1]. Through the above manner, the left-eye image and the right-eye image are alternately displayed on a time axis and the user can appreciate the 3D image through the glasses GLS. 
     Meanwhile, as described above, the most important factors for displaying the 3D stereoscopic image on the stereoscopic image display device are color temperature and luminance components according to an exposure of a camera in the obtaining state of the image. 
     Accordingly, the exemplary embodiment of the invention derives a parameter for color correction by extracting main factors of colors from the obtained left-eye and right-eye images. And, a part which causes a competition phenomenon between the images through the correction for the left-eye and right-eye images is compensated within a permissible error range. Accordingly, the stereoscopic image display device can express the colors considering the peripheral environment, can obtain a 3D color characteristic similar to a processed result for the 2D image, and can improve picture quality. 
     In the description of the prevent invention, the stereoscopic image display device using the pattern retarder is explained as an example. However, the present invention can commonly used in the stereoscopic image display device using various compositions such as shutter glasses, a liquid crystal lens, a lenticular lens, shutter glasses, and the like. 
     Hereinafter, the image processing unit SBD as a main part of the stereoscopic image display device according to one embodiment of the present invention will be explained in detail. 
       FIG. 5  is a schematic block diagram of an image processing unit according to one embodiment of the present invention and  FIG. 6  is a detailed block diagram of an image processing unit illustrated in  FIG. 5 . 
     As shown in  FIGS. 5 and 6 , the image processing unit SBD according to one embodiment of the present invention includes an image divider unit  110 , an image correction unit  130 , and an image synthesis unit  150 . The normal 3D image is inputted as the type of RGB. Thus, as an example of the embodiment of the present invention, the image processing unit SBD includes an image conversion unit  120  for normalizing the RGB type left-eye and right-eye images inputted through the image processing unit SBD in a CIE XYZ color space, converting the CIE XYZ color space into a CIE Yxy color space, and transferring the converted images to the image correction unit and an image inverse-conversion unit  140  for inversely-converting the left-eye and right-eye images brightness-corrected through the image correction unit  130  into the RGB type images again and transferring the inversely-converted images to the image synthesis unit  150 . 
     The image divider unit  110  divides the 3D image into the left-eye and right-eye images. The 3D image is the synthesized state of the left-eye and right-eye images. Accordingly, the image divider unit  110  divides the RGB type synthesized 3D image into the left-eye and right-eye images and transfers the left-eye and right-eye images to the image conversion part unit so as to efficiently correct the images by using the left-eye and right-eye images. 
     The image conversion unit  120  normalizes the divided left-eye and right-eye images in the CIE XYZ color space, converting the CIE XYZ color space into the CIE Yxy color space, and transferring the converted images to the image correction unit  130 . 
     The image correction unit  130  corrects the color temperature for the left-eye and right-eye images and corrects the brightness for the color-temperature-corrected left-eye and right-eye images. More specifically, the image correction unit  130  corrects the color temperature according to whether a white color difference between the left-eye and right-eye images satisfies a reference color difference threshold value. And the image correction unit  130  corrects the brightness according to whether the brightness difference between the color-temperature-corrected left-eye and right-eye images satisfies the reference brightness threshold value. 
     To achieve the above, the image correction unit  130  includes a color difference derivation part  131 , a color temperature correction part  132 , a brightness difference deduction part  133 , and a brightness correction part  134 . The color difference derivation part  131  derives the white color difference between the left-eye and right-eye images by deriving a white area for the left-eye and right-eye images. The color temperature correction part  132  corrects the color temperature according to whether the derived white color difference satisfies the reference color difference threshold value. The bright difference derivation part  133  detects the brightness difference between the color-temperature-corrected left-eye and right-eye images. The brightness correction part  134  corrects the brightness according to whether the detected brightness difference satisfies the reference brightness threshold value. 
     The color temperature correction part  132  corrects the color temperature for only one of the left-eye and right-eye images when the derived white color difference dissatisfies the reference color difference threshold value. 
     The brightness correction part  134  corrects the brightness by multiplying the color-temperature-corrected left-eye and right-eye images by a gain. The brightness correction part  134  corrects the brightness on the basis of a relational expression of 0≦gain&lt;2. 
     The image inverse-conversion unit  140  inversely converts the brightness-corrected left-eye and right-eye images into the RGB type images again and transfers the inversely-converted images to the image synthesis unit  150 . The left-eye and right-eye images are divided by the image correction unit  130  and are corrected in the state which converted into the CIE Yxy color space. Accordingly, the image inverse-conversion unit  140  inversely converts the brightness-corrected left-eye and right-eye images into the RGB type images again. 
     The image synthesis unit  150  synthesizes the left-eye and right-eye images. As the images transmitted from the image inverse-conversion unit  140  is divided by the image divider unit  130 , the image synthesis unit  150  synthesizes the left-eye and right-eye images again to output the brightness-corrected left-eye and right-eye images as the synthesized RGB type 3D image. 
     As described above, as the color temperature and the brightness of the 3D image are corrected by an image processing state of the image processing unit SBD, the image display panel displays the 3D image on the basis of the corrected 3D image. 
       FIG. 7  is a flow chart for schematically explaining a method for driving a stereoscopic image display device according to one embodiment of the present invention and  FIG. 8  is a flow chart for specifically explaining the driving method of  FIG. 7 . 
     As shown in  FIG. 7 , the method for driving the stereoscopic image display device according to one embodiment of the present invention includes: an image dividing step S 210  of dividing the inputted 3D image into the left-eye and right-eye images; an image correcting step S 220  of correcting the color temperature for the left-eye and right-eye images and correcting the brightness for the color-temperature-corrected left-eye and right-eye images; and an image synthesizing step S 230  of synthesizing the left-eye and right-eye images. 
     The method for driving the stereoscopic image display device according to one embodiment of the present invention, particularly the method for processing the image by the image processing unit will be explained in detail. 
     As shown in  FIGS. 7 and 8 , the 3D image is normally inputted as the RGB type image. Accordingly, the image dividing step S 210  includes the step S 211  of dividing the inputted RGB type 3D image into the left-eye and right-eye images and the step S 213  of normalizing the left-eye and right-eye images in the CIE XYZ color space and converting the CIE XYZ color space into the CIE Yxy color space. The image correcting step S 220  includes the steps S 211 -S 228  of correcting the brightness from a color difference deriving step to process the image. The image synthesizing step S 230  includes the step S 231  of inversely converting the brightness-corrected left-eye and right-eye images into the RGB type images and the step S 233  of synthesizing the left-eye and right-eye images. 
     First, the inputted RGB type 3D image is divided into the left-eye image and the right-eye image S 211 . 
     Next, the divided left-eye and right-eye images are converted into the CIE Yxy color space S 213 . To achieve the above, the left-eye image and the right-eye image are normalized in the CIE XYZ color space by the mathematical expression 1 and are converted into the CIE Yxy color space by the mathematical expression 2. 
     
       
         
           
             
               
                 
                     
                 
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     As described above, the conversion method is the method based on ITU standard and the method for converting the RGB type left-eye and right-eye images into the CIE Yxy color space. In the mathematical expression 1, RGB is a linear value. In the mathematical expression 2, the color space expressed as Yxy is widely used as the usage for substantially expressing the colors and a color distribution table thereof is normal and is thus omitted. 
     Next, a white area of each of the converted left-eye and right-eye images is derived S 221 . 
     The white area of each of the converted left-eye and right-eye images is derived by mathematical expressions 3 and 4. The relationship between a white color temperature curve value yw and an offset value offset y corresponds to the mathematical expression 3 and the area derived from the white area can be set by differently setting relevant values (0.015, 25). The white color temperature curve value yw for deriving the white area is derived by the mathematical expression 4.
 
offset  y&lt;y   w ±0.015, and  Y&gt; 25  [Mathematical Expression 3]
 
 y   w =−3 x   w   2 +2.870 x   w −0.275  [Mathematical Expression 4]
 
     Next, the white area is derived and a white color difference between the left-eye and right-eye images is derived S 223 . The white color difference between the left-eye and right-eye images Δxy is derived by an absolute value for an average of the left-eye image average(xy Left ) and an average of the right-eye image average(xy Right ) like the mathematical expression 5.
 
Δ xy =|average( xy   Left )−average( xy   Right )|  [Mathematical Expression 5]
 
     Next, the color temperature is corrected according to whether the derived white color difference Δxy satisfies the reference colors threshold value Δxy TH  S 225 . At this time, the derived white color difference is compared with the reference colors threshold value Δxy TH  S 224 . The brightness difference is derived when the derived white color difference Δxy does not satisfy the reference color difference threshold value Δxy TH  S 226 . The color temperature is corrected when the derived white color difference Δxy dissatisfies the reference colors threshold value Δxy TH  S 225 . The comparison between the derived white color Δxy and the reference color threshold value Δxy TH  can be expressed as Δxy&gt;Δxy TH . 
     Meanwhile, in the color temperature correction process S 225  only one selected from the left-eye image and the right-eye image is corrected. In the present invention, like the following mathematical expression 6, the correction for only the right-eye image is described as an example. The mathematical expression 6 expresses a white right-eye X W   R /white left-eye X W   L  correction matrix for an input (X in , Y in , Z in ) considering an output (X out , Y out , Z out ) in a color temperature correction process 
     
       
         
           
             
               
                 
                     
                 
               
               
                 
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     Next, the brightness difference between the color-temperature-corrected left-eye and right-eye images is derived S 226 . The brightness difference between the color-temperature-corrected left-eye and right-eye images can be derived from an absolute value difference between a left-eye luminance average average(Y Left ) and a right-eye luminance average average(Y Right ) like the following mathematical expression 7. That is, the brightness difference between the color-temperature-corrected left-eye and right-eye images can be derived by using Average Picture Level (APL).
 
Δ Y =|average( Y   Left )−average( Y   Right )|  [Mathematical Expression 7]
 
     Next, the brightness is corrected according to whether the detected brightness difference satisfies the reference brightness threshold value S 225 . At this time, the detected brightness difference ΔY is compared with the reference brightness threshold value Y TH  S 227 . The Yxy is converted to the RGB without correction when the detected brightness difference ΔY satisfies the reference brightness threshold value S 231 . The brightness of the left and right images is corrected when the detected brightness difference dissatisfies the reference brightness threshold value Y TH  S 228 . The comparison between the detected brightness difference ΔY and the reference brightness threshold value Y TH  can be expressed as ΔY&gt;T TH . 
     Meanwhile, in the brightness correction process S 228  for the left and right images, at least one of the left-eye image and the right-eye image are corrected. In the present invention, only the right-eye image is corrected as an example like the following mathematical expression. As shown in the mathematical expression 8, in the brightness correction process S 228  for the left and right images, the brightness can be corrected by multiplying the color-temperature-corrected right-eye image Y Right  by the gain. At this time, the gain has a relational expression of 0≦gain&lt;2.
 
 Y   Right =gain× Y   Right ,0≦gain&lt;2  [Mathematical Expression 8]
 
     The brightness is corrected on the basis of the above relational expression since the corrected color is differently formed in comparison with the desired color when the range of the gain is wide in the color temperature correction process. More correctly, the brightness correction part  134  can correct the brightness of the left-eye and right-eye images within a range of saturation values on the basis of the relational expression 1≦gain&lt;1.5. 
     Next, the brightness-corrected left-eye and right-eye images are inversely converted into the RGB type S 231 . The brightness-corrected left-eye and right-eye images can be completed by inversely performing the color space conversion performed through the mathematical expression 1 like the following mathematical expression 9. In the mathematical expression 9, the inversely converted RGB is the linear value and the inversely converted method is the method based on the ITU D65 standard. 
     
       
         
           
             
                 
             
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                             0.430574 
                           
                           
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     Next, the left-eye and right-eye images are synthesized S 233 . The left-eye and right-eye images are synthesized and are displayed as the 3D image on the image display panel. 
     As described above, the present invention can express the colors considering the peripheral environment by preventing the competition phenomenon between the images through the correction for the left-eye and right-eye images and can improve the picture quality by obtaining the 3D characteristics similar to the processed result of the 2D image when wearing the glasses. In addition, the present invention can appreciate the convenient image by using a peculiar image processing method for maximizing the color picture quality and reduces the 3D image manufacturing cost and easily propagates 3D contents by easily performing the prior 3D image correction process using the post-processing. 
     The foregoing implementations and advantages are merely exemplary and are not to be construed as limiting this document. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing implementations is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.