Abstract:
A 3D filter includes a first area having a plurality of even numbered and odd numbered alternating lines, each line having an equal height, the even numbered lines formed with a first polarization characteristic, a first dummy line formed outside of the first area and adjacent to a first line of the 3D filter, the first dummy line having a height greater than a height of a single line, the odd numbered lines formed with a second polarization characteristic, a second dummy line formed outside of the first area and adjacent to a last line of the 3D filter, the second dummy line having a height greater than the height of a single line, the first dummy line formed with a polarization characteristic opposite to a polarization characteristic of a first line in the first area, and the second dummy line formed with a polarization characteristic opposite to a polarization characteristic of a last line in the first area.

Description:
This application claims the benefit of Korea Patent Application No. 10-2010-0035184 filed on Apr. 16, 2010, the entire contents of which are incorporated herein by reference as if fully set forth herein. 
     BACKGROUND 
     1. Field of the Invention 
     This document relates to a stereoscopic image display and an alignment method thereof. 
     2. Related Art 
     An image display device implements 3D images using a stereoscopic technique and an autostereoscopic technique. 
     The stereoscopic technique uses binocular parallax images which produce large stereoscopic effects, and may or may not have a corresponding set of lenses or eyeglasses for viewing by the user. In the type of system using eyeglasses, binocular parallax images are displayed on a direct view display panel or by a projector by changing polarization directions. Alternatively, using temporal division, polarization eyeglasses or liquid crystal shutter eyeglasses may be used to implement stereoscopic images. In the type of system not using eyeglasses, the stereoscopic images are implemented by dividing optical axes of binocular parallax images, where optical plates, such as parallax barriers, are provided at front and rear surfaces of a display panel. 
     To mass-produce the stereoscopic image display devices, it is necessary to efficiently align a display device and a 3D filter, which is disposed on the display device and divides light from the display device into light corresponding to left eye images and light corresponding to right eye images. 
     A method of aligning a parallax barrier with a display panel has been proposed in Korean Patent No. 10-0709728, where separate eyeglasses are not used. In this method, as shown in  FIG. 1 , two cameras CAM 1  and CAM 2  disposed at a predetermined distance from the display panel  1  and from the parallax barrier  2 , take stereoscopic images displayed on the display panel  1 . The display panel  1  and the parallax barrier  2  are repeatedly realigned while checking the division state of left eye images and right eye images until reaching a predetermined alignment reference state. 
     However, in a method of aligning a display panel with a 3D filter by a worker who views images displayed on the display panel based on luminosity, or in a method that determines whether or not stereoscopic images are divided over a predetermined reference value in a system using two cameras, power data and test pattern data must be provided to the display panel so as to display the images. Therefore, using such related art alignment techniques, it is difficult to numerically quantify the degree of alignment or misalignment, equipment cost is high, and productivity is low. 
     In a known method of aligning a display panel with a 3D filter in the eyeglass type stereoscopic image display device, a worker wears polarization eyeglasses, drives a display panel placed at a certain distance, determines an alignment degree between the display panel and the 3D filter through luminosity, and repeats the above-described operation until images displayed on the display panel are properly viewed. The assignee of the present application has proposed, in Korean Patent No. 10-0939214, a alignment system and method of stereoscopic image display devices which can automatically align the 3D filter with the display panel in the eyeglass type and solve the problems disclosed in Korean Patent No. 10-0709728. In this method, alignment marks are formed in a display panel and a 3D filter, the alignment marks are checked by a vision system, and thereby the display panel and the 3D filter can be aligned with each other without driving the display panel. Also, an alignment state can be quantified by checking an alignment state of the alignment marks. 
     The 3D filter may have a known tolerance or variation. In this case, because an accumulated error increases as the distance increase from the alignment reference positions (alignment marks) during the alignment of the display panel with the 3D filter, an alignment error accumulates. As a result, up and down viewing angles in the stereoscopic image display device may be narrowed due to the tolerance or variation of the 3D filter. 
     SUMMARY 
     According to an exemplary embodiment, a 3D filter includes a first area having a plurality of even numbered and odd numbered alternating lines, each line having an equal height, the even numbered lines formed with a first polarization characteristic, a first dummy line formed outside of the first area and adjacent to a first line of the 3D filter, the first dummy line having a height greater than a height of a single line, the odd numbered lines formed with a second polarization characteristic, a second dummy line formed outside of the first area and adjacent to a last line of the 3D filter, the second dummy line having a height greater than the height of a single line, the first dummy line formed with a polarization characteristic opposite to a polarization characteristic of a first line in the first area, and the second dummy line formed with a polarization characteristic opposite to a polarization characteristic of a last line in the first area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a diagram illustrating a method of aligning a parallax barrier in a related art stereoscopic image display device; 
         FIG. 2  is a diagram illustrating a stereoscopic image display device according to an embodiment of the invention; 
         FIG. 3  is a diagram illustrating an alignment system of the stereoscopic image display device according to the embodiment of the invention; 
         FIG. 4  is a diagram illustrating an ideal alignment state of a display panel with a 3D filter when alignment marks are formed at one side edges of the display panel and the 3D filter; 
         FIG. 5  is a diagram illustrating a poor alignment of the display panel with the 3D filter due to tolerance of the 3D filter when the alignment marks are formed at one side edges of the display panel and the 3D filter; 
         FIG. 6  is a diagram illustrating a phenomenon where up and down viewing angles are narrowed due to the accumulated alignment error as shown in  FIG. 5 ; 
         FIG. 7A  is a plan view illustrating alignment marks formed at central portions of longitudinal edges of the 3D filter; 
         FIG. 7B  is a sectional view illustrating alignment marks formed at central portions of longitudinal edges of the 3D filter; 
         FIG. 8  is a diagram illustrating alignment marks formed at central portions of longitudinal edges of each of the display panel and the 3D filter; 
         FIG. 9  is a diagram illustrating up and down viewing angle of a stereoscopic image display device where the display panel and the 3D filter are aligned with each other using the alignment marks as shown in  FIGS. 7A to 8 ; 
         FIG. 10  is a diagram illustrating a 3D filter according to another embodiment of the invention; 
         FIG. 11A  is an exemplary diagram illustrating an image of the boundary regions of the 3D filter in  FIG. 10 , taken by cameras; 
         FIG. 11B  is an exemplary diagram illustrating an image of the boundary region of the 3D filter in  FIG. 10 , taken by cameras; 
         FIG. 12A  is an exemplary diagram illustrating an alignment state of the display filter shown in  FIG. 7A  and the 3D filter shown in  FIG. 10 ; and 
         FIG. 12B  is an exemplary diagram illustrating camera movement when the 3D filter is aligned on the display panel. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification. In the following description, when a detailed description of well-known functions or configurations is determined to be unnecessary the understanding of the invention, such description will be omitted. 
     In the following embodiments, alignment indicia portions are defined as reference position marking points for aligning a display panel and a 3D filter, and are formed in plurality in each of the display panel and the 3D filter. The alignment indicia portions may be implemented by alignment marks and/or dummy retarder patterns like the following embodiments. 
     Referring to  FIG. 2 , a stereoscopic image display device according to an embodiment of this document comprises a display  10 , a 3D filter  20 , and polarization glasses  30 . 
     The display panel  10  may be implemented by display panels of flat display devices such as a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electroluminescence device (EL), an electrophoresis display (EPD), and so on. Hereinafter, the display panel  10  will be described by exemplifying a display panel of the liquid crystal display. 
     The display panel  10  comprises a lower transparent substrate provided with a thin film transistor (TFT) array, an upper transparent substrate provided with a color filter array, and a liquid crystal layer interposed between the substrates. In the lower transparent substrate, a polarization film is attached to the rear surface facing a backlight unit, and an alignment layer for setting a pretilt angle of the liquid crystal is formed at a surface contacting with the liquid crystal layer. In the upper transparent substrate, a polarization film  11  is attached to the front surface facing the 3D filter  20 , and an alignment layer is formed at a surface contacting with the liquid crystal layer. 
     The lower transparent substrate is provided with data lines supplied with data voltages, gate lines (or scan lines) which intersect the data lines and are sequentially supplied with gate pulses (scan pulses) synchronized with the data voltages, TFTs formed at the intersections of the data lines and the gate lines, and pixel electrodes respectively connected to the TFTs. The data lines are arranged in the longitudinal direction (y axis direction) of the display panel  10  and the gate lines are arranged in the transverse direction (x axis direction) of the display panel  10 . The liquid crystal layer is driven by electric fields generated by the pixel electrodes applied with the data voltages and common electrodes applied with common voltages. The common electrodes are disposed on the upper transparent substrate in a vertical electric field driving type such as a TN (twisted nematic) mode and a VA (vertical alignment) mode, and are disposed on the lower transparent substrate along with the pixel electrodes in a horizontal electric field type such as an IPS (in plane switching) mode and an FFS (fringe field switching) mode. 
     The display panel  10  displays data for 2D input images in a 2D mode where data is not separated according to left and right viewing. Rather, in such a 2D mode, each pixel displayed corresponds to the image exactly. The display panel  10  also displays left eye image data L and right eye image data R for 3D input images in the form of a line by line presentation in a 3D mode. For example, as shown in  FIG. 2 , the left eye image data L may be displayed in odd numbered lines of the display panel  10 , and the right eye image data R may be displayed in even numbered lines of the display panel  10 . The polarization film  11  is attached between the upper transparent substrate of the display panel  10  and the 3D filter  20 . The polarization film  11  transmits only a linearly polarized light, which is transmitted through the liquid crystal layer and incident on the polarization film  11 . 
     The 3D filter  20  is attached onto the polarization film  11  of the display panel  10 . The 3D filter  20  shown in  FIG. 2  exemplifies a retarder, which delays a phase of light by λ/4 using a birefringence medium. The 3D filter  20  includes first retarder patterns  20 A corresponding to the odd numbered lines of the display panel  10  and second retarder patterns  20 B corresponding to the even numbered lines of the display panel  10 . Light absorption axes of the first retarder pattern  20 A and the second retarder pattern  20 B are perpendicular to each other. The first retarder pattern  20 A, which is aligned with and faces the odd numbered line, converts a light from the odd numbered line into a light undergoing left-circular polarization (or right-circular polarization). The second retarder pattern  20 B, which is aligned with and faces the even numbered line, converts a light from the even numbered line into a light undergoing right-circular polarization (or left-circular polarization). 
     A left lens of the polarization eyeglasses  30  includes a polarization filter, which passes only a light having undergone left-circular polarization (or right-circular polarization) therethrough, and a right lens of the polarization eyeglasses  30  includes a polarization filter which passes only a light having undergone right-circular polarization (or left-circular polarization) therethrough. A viewer wearing the polarization eyeglasses  30  views only left eye images with the left eye and only right eye images with the right eye to sense images displayed on the display panel  10  as stereoscopic images. The viewer may view 2D images in the 2D mode without wearing the eyeglasses. 
     In order to align the display panel  10  with the 3D filter  20 , two or more alignment marks are formed in the display panel  10 . Also, alignment marks are formed in the 3D filter so as to correspond to the alignment marks in the display panel  10 . 
       FIG. 3  shows an alignment system of the stereoscopic image display device according to the embodiment of this document. 
     In  FIG. 3 , the alignment system comprises a vision system, an image analysis unit  51 , a controller  52 , an alignment driver  53 , and an xyθ table  54 . 
     The display panel  10  provided with alignment marks  12  is placed on the xyθ table  54 . The 3D filter  20  provided with alignment marks  22  is aligned on the display panel  10  in planar relation. 
     The vision system comprises two or more cameras  41  facing the alignment marks  22  in the display panel side, polarization filters  42  disposed between camera lenses and the 3D filter, and a camera transfer driver  55  which transfers the cameras  41  in an x-axis direction and in a y-axis direction, as shown in  FIG. 3 . The polarization filters  42  transmit specific polarization light towards the cameras  42 . The polarization filters  42  may be omitted. The camera transfer driver  55  drives a two-axial robot or a two-axial guide equipped with the cameras  41  and moves the cameras  41  in the x-axis direction or in the y-axis direction under the control of the controller  52 . 
     The image analysis unit  51  or controller performs analog-digital conversion for data output from the cameras  41 , and performs imaging processing for the digital data so as to clearly show images for the alignment marks. The controller  52  calculates an error between a reference point and a center point of each alignment mark obtained by the cameras  41  (axial misalignment). The controller  52  calculates an error between center points of the alignment marks  12  formed in the display panel  10  and center points of the alignment marks  22  formed in the 3D filter and facing them. The alignment driver  53  moves the X-Y table  54  where the display panel  10  is placed such that the error values from the controller  52  become “0.” The alignment driver  53  may be separate from the controller  52  or may be combined into a signal component. Note that the X-Y table may support and move either the display panel  10  or the 3D filter  20 , or both. It is immaterial to the scope of this invention which component is moved as long as the alignment error is minimized when the display panel  10  and the 3D filter  20  are moved relative to each other. 
     The xyθ table  54  supports the display panel  10  under the display panel  10 . The xyθ table  54  moves the substrate of the display panel  10  in the x-axis and y-axis directions by the alignment driver  53  and rotates the display panel in the 0 direction. 
     An alignment of the display panel  10  with the 3D filter  20  described below may be performed in a state where the display panel  10  is not driven. 
       FIG. 4  is a diagram illustrating an ideal alignment state of the display panel  10  with the 3D filter  20  when the alignment marks  12  and  22  are formed at one side edge of the display panel and the 3D filter.  FIG. 5  is a diagram illustrating poor alignment of the display panel with the 3D filter caused by tolerance of the 3D filter when the alignment marks are formed at only one side edge of the display panel and the 3D filter. 
     If the 3D filter  20  is aligned with the display panel  10  with respect to the alignment marks  12  and  22  formed at the upper ends of the 3D filter having no tolerance, as shown in  FIG. 4 , all the lines of the display panel  10  and the 3D filter  30  can be aligned with each other in accordance with a design value without an alignment error. However, generation of errors in the 3D filter  20  is unavoidable in the manufacturing process thereof. In  FIGS. 4 and 5 , the reference numeral  14  denotes an active region which displays 2D images and 3D images in the display panel  10 . The active region of the display panel  10  includes pixels arranged in a matrix. The reference numeral  24  denotes an active region of the 3D filter  20 , which corresponds to the active region  14  of the display panel  10  and in which the first retarder pattern  20 A and the second retarder pattern  20 B are alternately arranged in the longitudinal direction. 
     When the 3D filter  20  having tolerance is aligned with the display panel  10 , if they are aligned with each other with respect to the alignment marks  12  and  22  formed at the upper end (or lower end) of the 3D filter  20 , and at the upper end (or lower end) of the display panel  10 , due to accumulation of an alignment error, the alignment error increases as the distance increases from the alignment marks  12  and  22 , as shown in  FIG. 5 . When the alignment error increases relative to the position of the alignment marks  12  and  22 , the up and down viewing angles for viewing 3D images are narrowed, as shown in  FIG. 6 . According to a preferred embodiment, to minimize an accumulated tolerance when the 3D filter  20  is aligned with the display panel  10 , as shown in  FIGS. 7A to 8 , the alignment marks are formed at central portions of opposite longitudinal (or lateral) edges of each of the display panel  10  and the 3D filter  20 . Although the alignment marks are preferably located at the center of the corresponding longitudinal or lateral edge, the alignment marks need not be placed at the exact center or midpoint of the corresponding edges, and some variation may exist. For example, in one embodiment, the alignment marks may be located at substantially a midpoint, but may vary by about 15% of the total length of the lateral edge. For example, if the lateral edge is 50 cm in length, the exact midpoint is 25 cm from a corner, and thus the location of the alignment mark may be located at plus or minus 7.5 cm from the exact midpoint. 
     When the alignment marks  12  and  22  are positioned at the central portions of the longitudinal edges and the vicinity thereof of the display panel  10  and the 3D filter  20  as shown in  FIGS. 7A to 8 , if the alignment marks  12  and  22  overlap each other as designed to align the display panel  10  with the 3D filter  20 , it is possible to minimize an accumulated value of alignment error which increases in the farther side from the alignment marks in the stereoscopic image display device. This is because the alignment error is evenly distributed upwards and downwards with respect to the alignment marks  12  and  22  as shown in  FIG. 8 . Therefore, when the alignment marks  12  and  22  are formed at the central portion of the longitudinal or lateral edges of each of the display panel  10  and the 3D filter  20 , and the alignment marks  12  and  22  overlap each other to align the display panel  10  with the 3D filter  20 , the up and down viewing angles for viewing 3D images, as shown in  FIG. 9 , can be widened in a horizontally symmetrical manner about a center of a display screen. 
       FIG. 10  is a plan view illustrating another embodiment of the 3D filter  20 . 
     Referring to  FIG. 10 , the 3D filter  20  comprises first retarder patterns  20 A formed at the odd numbered lines PR#1, PR#3, . . . , PR#n−1, second retarder patterns  20 B formed at the even numbered lines PR#2, PR#4, . . . , PR#n, a first dummy retarder pattern  20 C formed on the first retarder pattern  20 A positioned at the uppermost end, and a second dummy retarder pattern  20 D formed under the second retarder pattern  20 B positioned at the lowermost end. 
     The height (or width) of the first dummy retarder pattern  20 C is set to be greater than that of each of the first and second retarder patterns  20 A and  20 B so as to be easily differentiated from the first and second retarder patterns  20 A and  20 B in the active region. A polarization characteristic of the first dummy retarder pattern  20 C may be set to be the same as that of the second retarder pattern  20 B. The height of the second dummy retarder pattern  20 D is set to be greater than that of each of the first and second retarder patterns  20 A and  20 B so as to be easily differentiated from the first and second retarder patterns  20 A and  20 B in the active region. A polarization characteristic of the second dummy retarder pattern  20 D may be set to be the same as that of the first retarder pattern  20 A. Therefore, the first retarder patterns  20 A and the second dummy retarder pattern  220 D convert incident light into left circularly polarized light (or right circularly polarized light). 
     When the 3D filter shown in  FIG. 10  is aligned with the display panel  10 , the cameras  41  of the vision system capture two or more boundary regions A, B, C and D where the dummy retarder patterns  20 C and  20 D are seen along with the first and second retarder patterns  20 A and  20 B in the active region. The polarization filters  42  disposed between the cameras  41  and the 3D filter  20  may transmit specific polarization light, for example, right circularly polarized light (or left circularly polarized light). 
     If the upper cameras  41  capture the upper boundary regions A and B through the polarization filters  42 , since only the right circularly polarized light or the left circularly polarized light enters the cameras  41  through the polarization filters  42 , as shown in  FIG. 11A , an image where the first dummy retarder pattern  20 C and DUM 1  and the second retarder pattern  20 B and PR#2 are seen bright, whereas the first retarder pattern  20 A is seen dark is obtained. In addition, if the lower cameras  41  capture the lower boundary regions C and D through the polarization filters  42 , since only the right circularly polarized light or the left circularly polarized light enters the lower cameras  41  through the polarization filters  41 , as shown in  FIG. 11B , an image where the second dummy retarder pattern  20 D and DUM 1  and the first retarder pattern  20 B and PR#n−1 are seen dark, whereas the second retarder pattern  20 B is seen bright is obtained. Through this comparison of the images obtained by the vision system, it is possible to reduce the accumulated alignment error and also to confirm the first and second retarder patterns  20 A and  20 B aligned with the lines of the display panel  10  in a tilted state in the θ direction. 
     When the display panel  10  is aligned with the 3D filter  20 , the central alignment marks  12  and  22  may be used along with the dummy retarder patterns  20 C and  20 D formed at the upper and lower ends of the 3D filter  20 . For example, as shown in  FIG. 12A , an image of the boundary regions A, B, C and D of the 3D filter is obtained using the cameras  41  and the polarization filter  42 , and an alignment state of the 3D filter  20  with the display panel  10  is confirmed by analyzing the image, thereby preliminarily correcting the alignment state. Successively, as shown in  FIG. 12B , an image of the central alignment marks  12  and  22  is obtained by moving the cameras  41  in the y-axis direction, and thus the alignment state can be secondarily corrected. 
     The display panel  10  has been described mainly based on the liquid crystal display in the above embodiment, but may be implemented using any suitable flat display panel device, such as a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electroluminescence device (EL), an electrophoresis display (EPD), and so on. 
     As described above, according to this document, the alignment marks are formed at substantially the central portions of each of the 3D filter and the display panel, and the alignment marks overlap each other to align the 3D filter with the display panel, thereby distributing an accumulated tolerance upwards and downwards with respect to the alignment marks. As a result, it is possible to widen the up and down viewing angles of the stereoscopic image display device by minimizing the amount of alignment error accumulated when the 3D filter having tolerance is aligned with the display panel. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.