Abstract:
A driving system and method for liquid crystal display is disclosed. The system stores only the driving values corresponding to specific grayscale values of pixels on a current frame and specific grayscale values of pixels on a previous frame. The stored driving values are then used by an operation processing unit of the system to calculate out driving values to be applied to the current frame. Moreover, the system is provided with a logic judging unit for preventing the noises of the frame from being overdriven.

Description:
This application claims priority of Application No. 096125384 filed in Taiwan R.O.C on Jul. 12, 2007, under 35 U.S.C. §119; the entire contents of all of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a liquid crystal display and, more particularly, to an image driving system of a liquid crystal display and method for the same. 
     2. Brief Description of the Related Art 
     A liquid crystal display (LCD) displays images by applying fluctuating electric field to the liquid crystal to orientate the liquid crystal molecules and thus to modulate the light transmission through the liquid crystal. However, the orientation of the liquid crystal molecules does not simultaneously change with a change of an electric field. Thus, the response speed for displaying an image by a LCD is always lower than that by a typical cathode ray tube (CRT). This causes a serious delay problem when dynamic video images are displayed. 
     In view of this, a high speed image driving scheme is used to drive a liquid crystal display. The scheme applying higher voltages to each pixel can speed up the response of the liquid crystal molecules, such that the liquid crystal molecules can tilt to preset directions in a frame period. 
       FIG. 1  is a timing chart schematically shows difference in responses to an applied pixel voltage under an ordinary scheme and a high speed scheme. The horizontal axis represents time, and the vertical axis represents the pixel voltage. Under an ordinary scheme, during a frame period T, the pixel voltage, designated as numeral  1 , is changed from V 1  to V 2 , and the transmittance of the pixel that changes as a result of the voltage variation is designated as numeral  2 . Comparatively, under a high speed driving scheme, during a frame period T, the pixel voltage, designated as numeral  1 ′, is changed from V 1  to V 2 ′, and the transmittance of the pixel that changes as a result of the voltage variation is designated as numeral  2 ′. Obviously, the response time based on a high speed scheme is shorter. 
     The high speed image driving scheme of a liquid crystal display can refer to a U.S. Pat. No. 5,495,265. As shown in  FIG. 2 , a typical high speed image driving system  10  for a liquid crystal display reads and compares pixel data of a current frame G n  and a previous frame G n-1 , and uses a look-up table to obtain driving values according to the result of the comparisons, and applies the driving values to the pixels to generate a corrected frame G n′ . Apparently, the high speed image driving system  10  needs two memories, one of which is a frame buffer  101  and the other is a mapping table  102 . 
     The frame buffer  101  is used for storing pixel data of a current frame G n , and outputting pixel data of a previous frame G n-1 . The mapping table  102  is used for storing driving values in correspondence with grayscale values of each pixel datum. Specifically, the mapping table  102  is in a matrix form that records driving values in correspondence with grayscale values of pixel data of the current frame and the previous frame. Typically, the buffer  101  needs to have a capacity capable of storing  24 , i.e. 3×8, bits of grayscale values for each RGB pixel data, and the mapping table  102  needs to have a capacity capable of storing 3×28×28 numbers of high speed driving values for each RGB pixel data. 
     In this way, the high speed driving scheme is heavily loaded with the high cost memory of a liquid crystal display. Furthermore, the high speed driving scheme also causes amplification of the noises on displaying images, and badly influences image quality. 
     SUMMARY OF THE INVENTION 
     In view of the above problems, the present invention proposed a driving system for a liquid crystal display, which effectively compensates the response of liquid crystals in display with the needed capacity of memories being minimized, and thus eliminates bad effect caused by image noises. 
     The driving system for a liquid crystal display according to the invention comprises a first memory, a second memory, a third memory, an operation processing unit and a logic judging unit. It is known that sensitivity of a naked eye to high speed dynamic image would decline, and which becomes a basis of the proposed driving system. The first memory is used to store pixel data of a current frame. The second and the third memory are used to store specific grayscale values of the pixel data of the current frame and the previous frame, respectively. The operation processing unit is used to perform an interpolation operation to obtain driving values corresponding to grayscale values of pixel data of the current frame and grayscale values of pixel data of the previous frame. Moreover, a logic judging unit is added to prevent image noises from being over amplified. 
     In one embodiment of the invention, the first memory of the invention is used to store pixel data of a current frame and output pixel data of a previous frame. Each pixel datum includes a plurality of c-bit grayscale values, where “c” is a positive integer. Therefore, the first memory stores c-bit grayscale values of pixel data of the current frame, and outputs the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the previous frame, where “A” is a positive integer less than “c”. On the other hand, the second memory of the invention stores driving values corresponding to half part of the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the current frame and the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the previous frame. Further, the third memory of the invention stores driving values corresponding to another half part of the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the current frame and the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the previous frame. 
     At first, the operation processing unit of the invention reads the least significant “B” bits of grayscale values W from the c-bit grayscale values of a pixel data of the current frame, a first driving value X stored in the second memory, and a second driving value Y stored in the third memory, where “B” is a positive integer. Then, the operation processing unit performs an interpolation operation to obtain a third driving value Z, where value Z is between X and Y. The logic judging unit of the invention reads pixel data of the current frame and the pixel data of the previous frame, and judges if a difference of the c-bit grayscale values of the pixel data of the current frame and of the pixel frame is less than a specific value. 
     The driving system of the invention is advantageous in low cost by having memories of less capacity and better display image due to remove of image noises. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a timing chart schematically shows comparison responses to an applied pixel voltage under an ordinary scheme and a high speed scheme, wherein the horizontal axis represents the time and the vertical axis represents the pixel voltage. 
         FIG. 2  is a block diagram schematically showing a typical high speed driving scheme of a liquid crystal display. 
         FIG. 3  is a block diagram schematically showing a driving system of a liquid crystal display according to one embodiment of the invention. 
         FIG. 4A  is a matrix schematically showing driving values that are in correspondence with grayscale values of pixel data from a current frame and a previous frame. 
         FIG. 4B  is a matrix schematically showing driving values that are in correspondence with grayscale values at odd columns of a current frame and odd rows of a previous frame in  FIG. 4A . 
         FIG. 5  is a flow chart schematically showing steps for implementing the driving system of a liquid crystal display according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An image driving system and method for a liquid crystal display according to the invention are described as follows. The conceptual aspects of the image driving system and method are explained with concrete embodiments. However, the invention is not limited to these embodiments, and various modifications thereof are considered to be encompassed thereby. 
     Referring to  FIG. 3 , an image driving system  20  for a liquid crystal display according to one embodiment of the invention includes a frame buffer  201 , a first mapping table memory  2021 , a second mapping table memory  2022 , an operation processing unit  203 , and a logic judging unit  204 . 
     The frame buffer  201  is used to receive and temporarily store pixel data of a current frame F n , and to output pixel data of a previous frame F n-1 . Herein, each pixel datum includes a plurality of c-bit grayscale values, such as 8-bit grayscale values of original R (red), G(green), and B(blue) colors. Of course, “c” can be any positive integer. Specifically, the frame buffer  201  stores the c-bit grayscale values of each pixel datum of the current frame F n , and outputs the most significant “A” bits of the c-bit grayscale values of each pixel datum of the previous frame F n-1 , wherein “A” is a positive integer less than “c”. For example, “c” and “A” are 8 and 5, respectively. 
     The first mapping table memory  2021  is used to store driving values corresponding to half the most significant “A” bits of grayscale values of any pixel data in the current frame F n , and the most significant “A” bits of grayscale values of the same pixel data of the previous frame F n-1 . The second mapping table memory  2022  is used to store driving values corresponding to another half the most significant “A” bits of grayscale values of the same pixel data of the current frame F n , and the most significant “A” bits of grayscale values of the same pixel data of the previous frame F n-1 . In this way, the first mapping table memory  2021  and the second mapping table memory  2022  each stores 2 (a−1) ×2 a  driving values. 
     In one embodiment, the first mapping table memory  2021  of the invention stores driving values corresponding to the most significant “A” bits of grayscale values of any pixel data in the current frame F n  that are in odd columns, and the most significant “A” bits of grayscale values of the same pixel data of the previous frame F n-1 . Meanwhile, the second mapping table memory  2022  stores driving values corresponding to the most significant “A” bits of grayscale values of the same pixel data of the current frame F n  that are in even columns, and the most significant “A” bits of grayscale values of the same pixel data of the previous frame F n-1 . 
     The operation processing unit  203  is used to read the least significant “B” bits of grayscale values W of any pixel data of the current frame F n , a first driving value X stored in the first mapping table memory  2021 , and a second driving value Y stored in the second mapping table memory  2022 , and therefore perform an interpolation calculation to output a third driving value Z between X and Y. In one embodiment, “B” is a positive integer satisfying the equation “B”=“c”−“A”, and Z satisfies the equation Z=(½ B )·[X·(2 B −W)+Y·W]. For example, “B” is 3 when “c” and “A” are 8 and 5, respectively. 
     The logic judging unit  204  is used to read pixel data of the current frame F n  and the pixel data of the previous frame F n-1 , and determine if a difference of grayscale values of the pixel data of the current frame F n  and the previous frame F n-1  is less than a specified value. Generally, a zero or small difference between grayscale values of pixel data of the current frame and previous frame is caused by noises, therefore the driving system  20  would take the driving values corresponding to grayscale values of the pixel data of the current frame as what is required for adjusting the driving voltage for a corrected frame F n ′. 
     Referring to  FIGS. 4A and 4B , the mapping tables stored in the first mapping table memory  2021  and the second mapping table memory  2022  are in matrix form as shown, respectively. Referring to  FIG. 4A , an original mapping table  90  is a 2 4 ×2 4  matrix, where the transverse shows all 4-bit grayscale values of a pixel data of the current frame, and the vertical shows all 4-bit grayscale values of the same pixel data of the previous frame. Meanwhile, a crossing position of any one grayscale value in the transverse and any one grayscale value in the vertical corresponds to a driving value. Referring to  FIG. 4B , the mapping table  91  is formed by selecting only half the grayscale values from the transverse and half the grayscale values from the vertical of the original mapping table  90 . In other words, the transverse of the mapping table  91  is a 2 3 ×2 3  matrix, where the transverse shows the most significant 3 bits of grayscale values of a pixel data of the current frame, and the vertical shows the most significant 3 bits of grayscale values of the same pixel data of the previous frame. 
     In addition, we can further select driving values that are only corresponds to the odd or even grayscale values of the pixel data of the current frame and the grayscale values of the same pixel data of the previous frame to form an odd or even mapping table. 
     Therefore, driving values corresponding to an odd portion of grayscale values of the most significant “A” bits of each c-bit pixel data of the current frame F n  and all portion of grayscale values of the same pixel data of the previous frame are similar to that shown by numeral  911  in  FIG. 4B . The driving values corresponding to an even portion of grayscale values of the most significant “A” bits of each c-bit pixel data of the current frame F n  and all portion of grayscale values of the same pixel data of the previous frame are similar to that shown by numeral  912  in  FIG. 4B . 
     As shown, we can have a sampling mapping table in matrix including 2 (c−k) ×2 (c−k)  driving values corresponding to pixel data of the current frame and the same pixel data of the previous frame from the original mapping table storing 2 c ×2 c  driving values by sampling one from 2 k . Moreover, the sampling mapping table can be divided into two sub-sampling mapping table such as odd and even mapping tables each recording only 2 (c−k−1) ×2 (c−k)  driving values. For example, when “k” is 3 and “c” is 8, we can have a sampling mapping table of 2 5 ×2 5  driving values and an odd mapping table and an even mapping table of 2 4 ×2 5  driving values, respectively. Therefore, these driving values can be stored in memories with less capacity than ever used. 
     Referring to  FIG. 3  and  FIG. 5 , the driving system  20  of a liquid crystal display according to one embodiment of the invention is implemented by the following steps. 
     step  501 : receiving c-bit grayscale values of pixel data of a current frame F, and storing the grayscale values in a frame buffer  201 , wherein “c” is a positive integer. 
     step  502 : reading the most significant “A” bits of grayscale values from the c-bit grayscale values of pixel data of the current frame F n , and of the previous frame F n-1 , wherein “A” is a positive integer less than “c”. 
     step  503 : reading and judging a difference between the c-bit grayscale values of pixel data of the current frame and of the previous frame via a logic judging unit  204 ; when the difference isn&#39;t less than a specific value, then go to step  504 , when the difference is less than a specific value, then go to step  507 . 
     step  504 : looking up a first mapping table stored in the first mapping table memory  2021  to find out a first driving value X, and looking up a second mapping table stored in the second mapping table memory  2022  to find out a second driving value Y. 
     step  505 : reading the least “B” bits of grayscale values W from the c-bit grayscale values of pixel data of the current frame F n , the first driving value X, and the second driving value Y; and performing a interpolation calculation to obtain a third driving value Z via the operation processing unit  203 , wherein Z is between X and Y and satisfies Z=(½ B )·[X·(2 B −W)+Y·W]. 
     step  506 : outputting and serving the third driving value Z as driving values for adjusting driving voltages for a corrected frame F n ′. 
     step  507 : outputting driving values corresponding to grayscale values of pixel data of the current frame, serving as driving values for adjusting the driving voltages for the corrected frame F n ′. 
     In this way, the response of liquid crystal molecules can be speeded up, and the memory capacity of a frame butter unit  201  of the driving system  20  of the liquid crystal display can be saved. The side effect caused by enlarged noises can also be lowered. 
     It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms during which the appended claims are expressed. For example, the mapping tables in the mapping table memory  2021  and  2022  are not limited to the illustrated odd or even mapping tables, but can be others for affording information to do calculation. The above-mentioned numbers “A”, “B”, “c”, and “k” can also be modified according to demand.