Patent Publication Number: US-8125502-B2

Title: Method for driving a pixel by generating an over-drive grey level and driver thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for driving a pixel by an over-drive grey level and related driver, and more particularly, to a method for driving a pixel by a corresponding over-drive grey level generated from mathematical operation and related driver. 
     2. Description of the Prior Art 
     Please refer to  FIG. 1 .  FIG. 1  is a diagram illustrating a raw over-drive table for looking up over-drive grey levels to over-drive a pixel with the corresponding over-drive grey level looked up in the raw over-drive table. Generally, for enhancing response time of liquid crystal particles in a Liquid Crystal Display (LCD), manner of over-driving is used when liquid crystal particles are driven. The liquid crystal particles of one pixel of the LCD can be driven with a corresponding over-drive grey level according to the original grey levels for the pixel in a current frame and the frame previous to the current frame. An appropriate over-drive grey level can be looked up in the over-drive table as illustrated in  FIG. 1  and is used to drive the pixel for enhancing the response time of the pixel. As shown in  FIG. 1 , F 1  (column) represents the original grey level for one pixel in one frame (the previous frame), and F 2  (row) represents the original grey level for the pixel in the frame next to the frame (the current frame). Under the condition that one color is divided into 256 grey levels (8 bits), the raw over-drive table sizes up to 256×256×256 bits (equals to 32 Kbytes). However, a normal driving chip for LCD cannot afford that big size to store all the data of the over-drive grey levels. 
     Please refer to  FIG. 2 .  FIG. 2  is a diagram illustrating an over-drive table after reduction. As shown in  FIG. 2 , the data in the table of  FIG. 2  are reduced by decreasing the resolution of the table of  FIG. 1  and abandoning some data in the table of  FIG. 1 . For example, if the original grey level for one pixel in the previous frame falls in the range between the grey levels “0”˜“32”, and the original grey level for that pixel in the current frame falls in the range between the grey levels “32”˜“64”, the corresponding over-drive grey level is grey level “0”. In this way, the over-drive table of  FIG. 2  can be reduced to 8×8×256 bits (64 bytes), which is obviously much smaller than the raw over-drive table of  FIG. 1 . However, the reduction from the table of  FIG. 1  to the table of  FIG. 2  results in insufficiently over-driving, decreasing the response time of the liquid crystal particles, and distortion in the displayed frames. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for generating an over-drive grey level to drive a pixel. The method comprises (a) according to an original grey level for the pixel in a previous frame, providing a corresponding over-drive function, and (b) 
     generating the over-drive grey level according to an original grey level for the pixel in a current frame and the corresponding over-drive function. The previous frame is a frame previous to the current frame. 
     The present invention further provides a driver for generating an over-drive grey level to drive a pixel. The driver comprises a function providing device for providing a corresponding over-drive function according to an original grey level for the pixel in a previous frame, and an over-drive-grey-level generating device for generating the over-drive level according to an original grey level for the pixel in a current frame and the corresponding over-drive function. The previous frame is a frame previous to the current frame. 
     The present invention further provides a method for generating an over-drive grey level to drive a pixel. The method comprises (a) according to an original grey level for the pixel in a previous frame, an original grey level for the pixel in a current frame, and an over-drive function, generating the over-drive grey level. The previous frame is a frame previous to the current frame. 
     The present invention further provides a driver for generating an over-drive grey level to drive a pixel. The driver comprises an over-drive-grey-level generating device for generating the over-drive level according to an original grey level for the pixel in a previous frame, an original grey level for the pixel in a current frame, and an over-drive function, and a pixel driving device for driving the pixel with the over-drive grey level. The previous frame is a frame previous to the current frame. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a raw over-drive table. 
         FIG. 2  is a diagram illustrating an over-drive table after reduction. 
         FIG. 3  is a diagram illustrating the relation between the over-drive grey level for a pixel to display in the current frame and the original grey level for the pixel in the current frame. 
         FIG. 4  is a flowchart of the method according to the first embodiment of the present invention. 
         FIG. 5  is a driver according to the first embodiment of the present invention. 
         FIG. 6  is a flowchart illustrating a method according to the second embodiment of the present invention. 
         FIG. 7  is a diagram illustrating a driver according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Therefore, the present invention provides a method to replace the conventional method for over-driving with the lookup table. In this way, the size of the over-drive table needed in the present invention can be efficiently reduced. 
     Please continue referring to  FIG. 2 . When the original grey level of a pixel in the previous frame falls within the range from “32” to “64” (the second column), the over-drive grey levels corresponding to different original grey levels for the pixel in the current frame stored in the table of  FIG. 2  are “0”, “32”, “70”, “109”, “149”, “186”, “219”, “245”, and “255”. According to a first embodiment of the present invention, under the condition that an original grey level of a pixel in the previous frame is known (ranging from “32” to “64”, for example), the relation between an original grey level and an over-drive grey level for the pixel in the current frame can be described with a cubic equation in one unknown. The equation is described as follows:
 
OD( X )= aX   3   +bX   2   +cX+d   (1),
 
where OD(X) represents the over-drive grey level, X represents the original grey level for the pixel in the current frame. In equation (1), coefficients “a”, “b”, “c”, and “d” can be derived from the known over-drive grey pixels “0”, “32”, “70”, “109”, “149”, “186”, “219”, “245”, and “255”, shown in the second column of the table in  FIG. 2 . The manner to derive the coefficients “a”, “b”, “c”, and “d” from the known over-drive grey levels can be, for example, regression. Thus, in this embodiment, a predetermined set of the coefficients “a”, “b”, “c”, and “d” for the equation (1) corresponds to a set of known over-drive grey levels for a known original grey level of a pixel in a previous frame (for example, the second column of the table in  FIG. 2 ). However, the set of the values of the coefficient “a”, “b”, “c”, and “d” for one known original grey level of a pixel in a previous frame is possibly same as the set of the values of the coefficient “a”, “b”, “c”, and “d” for another known original grey level for the pixel in the previous frame.
 
       FIG. 3  is a diagram illustrating the relation between the over-drive grey level for a pixel to display in the current frame and the original grey level for the pixel in the current frame. As shown in  FIG. 3A , if one color is divided into 256 grey levels (8 bits), when the original grey level of a pixel in a previous frame is “0”, the relation between the over-drive grey level for a pixel to display in the current frame and the original grey level for the pixel in the current frame can be described as a first function. As shown in  FIG. 3B , if one color is divided into 256 grey levels (8 bits), when the original grey level of a pixel in a previous frame is “255”, the relation between the over-drive grey level for a pixel to display in the current frame and the original grey level for the pixel in the current frame can be described as a second function. As shown in  FIG. 3C , if one color is divided into 256 grey levels (8 bits), when the original grey level for a pixel in a previous frame is “128”, the relation between the over-drive grey level for a pixel to display in the current frame and the original grey level for the pixel in the current frame can be described as a third function. 
     In the first embodiment of the present invention, after all sets of coefficients “a”, “b”, “c”, and “d” corresponding to each original grey level for the pixel in the previous frame are generated, all sets of the coefficients “a”, “b”, “c”, and “d” are stored into a memory device. That is, the store space in this embodiment are only required for all the sets of the coefficients “a”, “b”, “c”, and “d”. When the original grey level for the pixel in the previous frame is received, the corresponding values for the coefficients of the equation (1) can be looked up from the memory device. For example, when the original grey level for the pixel in the previous frame is “0”, the corresponding values for the coefficients of the equation (1) respectively are a (0) , b (0) , c (0) , and d (0) , and thus the equation (1) can be expressed as: OD(X)=a (0) X 3 +b (0) X 2 +c (0) X+d (0) , as shown in  FIG. 3A , and the coefficients a (0) , b (0) , c (0) , and d (0)  are stored in the memory device of the present invention. In this way, the over-drive grey level for the pixel in the current frame, in the condition that the original grey level for the pixel in the previous frame is “0”, can be generated according to the original level for the pixel in the current frame and the equation (1) with the coefficients a (0) , b (0) , c (0) , and d (0)  as shown in  FIG. 3A ; the over-drive grey level for the pixel in the current frame, in the condition that the original grey level for the pixel in the previous frame is “255”, can be generated according to the original level for the pixel in the current frame and the equation (1) with the coefficients a (255) , b (255) , c (255) , and d (255)  as shown in  FIG. 3B ; the over-drive grey level for the pixel in the current frame, in the condition that the original grey level for the pixel in the previous frame is “128”, can be generated according to the original level for the pixel in the current frame and the equation (1) with the coefficients a (128) , b (128) , c (128) , and d (128)  as shown in  FIG. 3C . 
     In the first embodiment of the present invention, since each set of the coefficients “a”, “b”, “c”, and “d” corresponding an original grey level for the pixel in the previous frame is different from another, the relation between the original grey level for the pixel in the previous frame and the set of the coefficients can be further found. In other words, the coefficients “a”, “b”, “c”, and “d” can be further expressed as functions a(Y), b(Y), c(Y), and d(Y) respectively for the variable “Y”, where Y represents the original grey level for the pixel in the previous frame. 
     Therefore, a second embodiment of the present invention is further derived according to the description above. More particularly, the second embodiment of the present invention further expresses the over-drive table of  FIG. 2  with a cubic equation in two unknowns. The equation is expressed as follows:
 
OD (X,Y) =( e ) X   3   Y   3 +( f ) X   3   Y   2 +( g ) X   3   Y +( h ) X   3 +( i ) X   2   Y   3 +( j ) X   2   Y   2 +( k ) X   2   Y +( l ) X   2 +( m ) XY   3 +( n ) XY   2 +( o ) XY +( p ) X +( q ) Y   3 +( r ) Y   2 +( s ) Y +( t )  (2),
 
where “e”, “f”, “g”, “h”, “i”, “j”, “k”, “l”, “m”, “n”, “o”, “p”, “q”, “r”, “s”, and “t” are coefficients of the equation (2), Y represents the original grey level for the pixel in the previous frame, X represents the original grey level for the pixel in the current frame, and OD (X,Y)  represents the over-drive grey level for the pixel in the current frame. In this way, for any original grey levels for the pixel in the previous frame and in the current frame, after the coefficients “e”, “f”, “g”, “h”, “i”, “j”, “k”, “l”, “m”, “n”, “o”, “p”, “q”, “r”, “s”, and “t” for the equation (2) are obtained, the looking-up-in-the over-drive-table step is no longer needed, which means the over-drive table is not required for over-driving as well, and the corresponding over-drive grey level for the pixel in the current frame can be derived from the equation (2) according to the original grey level for the pixel in the previous frame (the unknown Y) and the original grey level for the pixel in the current frame (the unknown X).
 
     Please refer to  FIG. 4 .  FIG. 4  is a flowchart of the method  400  according to the first embodiment of the present invention. The steps are described as follows: 
     Step  401 : Start; 
     Step  402 : According to the original grey level for the pixel in the previous frame, provide a corresponding over-drive function; 
     Step  403 : Input the original grey level for the pixel in the current frame to the corresponding over-drive function provided in step  402  in order to generate a corresponding over-drive grey level for the pixel to display in the current frame; 
     Step  404 : Drive the pixel with the over-drive grey level generated in step  403 ; 
     Step  405 : End. 
     Step  402 , according to the original grey level for the pixel in the previous frame, finds corresponding coefficients of a cubic equation in one unknown such as equation (1) from the memory device. 
     Step  403  inputs the original grey level for the pixel in the current frame to the function generated from the step  402 . In this way, the desired over-drive grey level for the pixel to display in the current frame can be obtained. 
     Step  404  drives the pixel with the over-drive grey level generated from step  403  for completing over-driving the pixel. 
     Please refer to  FIG. 5 .  FIG. 5  is a driver  500  according to the first embodiment of the present invention. As shown in  FIG. 5 , the driver  500  comprises a function providing device  510 , an over-drive-grey-level generating device  520 , and a pixel driving device  530 . The function providing device  510 , according to the original grey level for the pixel in the previous frame, provides a corresponding over-drive function. The function providing device  510  comprises a coefficient storing device for storing the predetermined coefficients of the corresponding over-drive function. The corresponding over-drive function can be a cubic equation in one unknown. Thus, the function providing device  510  can look up the predetermined coefficients, required for the cubic equation in one unknown, in the coefficient storing device  511 . The over-drive-grey-level generating device  520 , according to the original grey level for the pixel in the current frame and the provided over-drive function, generates a corresponding over-drive grey level for the pixel to display in the current frame. The pixel driving device  530  uses the over-drive grey level generated from the over-drive-grey-level generating device  520  to drive the pixel in order to achieve over-driving purpose. 
     Please refer to  FIG. 6 .  FIG. 6  is a flowchart illustrating a method  600  according to the second embodiment of the present invention. The steps are described as follows: 
     Step  601 : Start; 
     Step  602 : Input the original grey levels respectively for the pixel in the previous frame and the current frame to an over-drive function for generating a corresponding over-drive grey level for the pixel to display in the current frame; 
     Step  603 : Use the over-drive grey level generated in step  602  to drive the pixel; 
     Step  604 : End. 
     Step  602  inputs the original grey levels respectively for the pixel in the previous frame and the current frame to a cubic equation in two unknown such as equation (2) for generating a corresponding over-drive grey level for the pixel to display in the current frame. Then step  603  uses the over-drive grey level generated in step  602  to drive the pixel in order to achieve over-driving purpose. 
     Please refer to  FIG. 7 .  FIG. 7  is a diagram illustrating a driver  700  according to the second embodiment of the present invention. As shown in  FIG. 7 , the driver  700  comprises an over-drive-grey-level generating device  710  and a pixel driving device  720 . The over-drive-grey-level generating device  710  receives the original grey levels respectively for the pixel in the previous frame and the current frame, and then inputs the received grey levels to an over-drive function. The over-drive function used by the over-drive-grey-level generating device  710  can be a cubic equation in two unknowns, and the coefficients of the cubic equation in two unknowns are derived from a predetermined over-drive table. The pixel driving device  720  utilizes the over-drive grey level generated from the over-drive-grey-level generating device  710  to drive the pixel in order to achieve over-driving purpose. 
     To sum up, the method and the driver provided by the present invention effectively utilizes mathematical operation to generate over-drive grey levels required for the pixel so that the required memory space can be greatly reduced, providing great convenience. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.