Patent Publication Number: US-8115710-B2

Title: Liquid crystal display control circuit for reducing memory size by detecting image edges and saving edge data and method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/596,415, which was filed on Sep. 21, 2005 and is included herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (LCD) control circuit and a control method thereof, and more specifically, to a control circuit and a method thereof that detects image edges of frames to reduce memory size by decreasing saved pixel data when executing the overdriving procedures. 
     2. Description of the Prior Art 
     Liquid crystal display (LCD) panels are mass-produced products applied to the field of computers, monitors, and TVs. The operation principle of an LCD is to vary voltages dropped on two terminals of liquid crystal cells in order to change a twisted angle of the liquid crystal cells. The transparency of the liquid crystal cells is changed for achieving the desired objective of illustrating images. Therefore, accurately and appropriately controlling the voltages between two terminals of liquid crystal cells is a key point for showing images rapidly and clearly. 
     It is well known by those skilled in the art that overdriving procedures are usually executed to reduce response time of the liquid crystal cells as images vary rapidly. Please refer to  FIG. 1 .  FIG. 1  is a block diagram of an LCD control circuit  100  according to the prior art. The control circuit  100  receives a gray level value of every pixel and determines the voltage applied on the two terminals of the liquid crystal cell corresponding to a pixel unit in accordance with the gray level value difference of the pixel unit between a current frame and a previous frame. As  FIG. 1  shows, the control circuit  100  includes a buffer circuit  110 , a frame memory  120 , and a driving-decision circuit  130 . Gray level values D in  of pixels are inputted into the control circuit  100  and then delivered to the driving decision circuit  130  and the frame memory  120  respectively through the buffer circuit  110 . The symbol G n  in the figure shows the data is the gray level value of pixels in the current frame. The frame memory  120  records inputted gray level values and outputs a pre-saved gray level value G n-1  that corresponds to the pixels in the previous frame to the driving decision circuit  130 . Next, the driving decision circuit  130  compares the gray level value G n  of the current frame and the gray level value G n-1  of the previous frame and then compares the difference between these two gray level values with the value saved in a look-up table to determine whether the control circuit  100  has to execute overdriving procedures and therefore whether a corresponding voltage will be dropped on the liquid crystal cells when the overdriving procedure is executed. Finally, the driving-decision circuit  130  outputs a driving voltage setting S out  to a voltage supply circuit to provide the voltage dropped on two terminals of the liquid crystal layer. 
     Because the frame memory  120  has to save gray level values of all pixels in a frame, the memory size needs to be large enough to include the gray level values of all pixels in a frame. However, the larger the memory size is, the more expensive it becomes. 
     SUMMARY OF THE INVENTION 
     It is therefore one of the objectives of the claimed invention to provide a liquid crystal display (LCD) control circuit and a control method, to solve the above-mentioned problems. 
     According to an embodiment of the present invention, an LCD control circuit is disclosed. The control circuit includes an edge-detecting circuit for detecting image edges in each frame of an image data, and outputting an edge data and a non-edge data corresponding to each frame; a memory coupled to the edge-detecting circuit, for saving the edge data of the frame; a driving decision circuit coupled to the edge-detecting circuit and the memory, for generating a driving voltage setting according to the non-edge data of a current frame outputted by the edge-detecting circuit, and generating an overdriving voltage setting according to the edge data of a previous frame saved in the memory and the edge data of the current frame outputted by the edge detecting circuit; and an output device coupled to the driving decision circuit, for outputting the driving voltage setting and the overdriving voltage setting. 
     According to another embodiment of the present invention, an LCD control method is disclosed. The method includes: detecting image edges in each frame of an image data, and outputting an edge data and a non-edge data corresponding to each frame; saving the edge data of the frame; generating a driving voltage setting according to the non-edge data of a current frame and generating an overdriving voltage setting according to the edge data of a previous frame and the edge data of the current frame; and outputting the driving voltage setting and the overdriving voltage setting. 
     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 block diagram of an LCD control circuit according to the prior art. 
         FIG. 2  is a block diagram of the LCD control circuit according to a preferred embodiment of the present invention. 
         FIG. 3  is a block diagram of the weighted circuit shown in  FIG. 2  according to a preferred embodiment of the present invention. 
         FIG. 4  is a flowchart of an LCD control method according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 2 .  FIG. 2  is a block diagram of the LCD control circuit  200  according to a preferred embodiment of the present invention. The control circuit  200  includes an edge-detecting circuit  210 , a frame memory  220 , a driving decision circuit  230 , and a multiplexer  280 , wherein the driving decision circuit  230  consists of a non-edge-driving decision circuit  240 , an edge-driving decision circuit  250 , a storage unit  260 , and a weighted circuit  270 . The operation principle of the control circuit  200  is described in the following. 
     Initially, the gray level values D in  of every pixel in the frame are inputted into the edge-detecting circuit  210 , and the edge-detecting circuit  210  detects edge parts of images in the current frame, then classifies the pixel data of the current frame into edge data and non-edge data. The pixel data of edge parts is classified as the edge data and the pixel data of the other parts is classified as the non-edge data. There are many methods, known by those skilled in the art, for detecting the edge parts of images. For example, by comparing gray level values of a pixel and other neighboring pixels in the same frame, it can be determined that the pixel and other neighboring pixels respectively belong to different objects if the gray level values of these pixels are very different. Therefore, the pixel is classified into the edge part. The edge-detecting circuit  210  outputs the non-edge data G n,n  of the current frame to the non-edge-driving decision circuit  240  positioned in the driving decision circuit  230 , and outputs the edge data G n,e  of the current frame to the frame memory  220  and the edge-driving decision circuit  250 . 
     As frames are continuous, if the object is moving, only pixel data (such as light intensity, color etc.) in the edge part of the image has great variation; in other words, only the liquid crystal layer of these pixels in the edge part has to execute an overdriving voltage setting, whereas the liquid crystal layer of other pixels in the other parts of the frame merely needs to execute a general driving voltage setting. Therefore, the non-edge-driving decision circuit  240  generates the driving voltage setting S n  corresponding to the non-edge part of the current frame according to the non-edge data G n,n  (such as the gray level value of the pixel) of the current frame. 
     The frame memory  220  saves the edge data G n,e  (such as the gray level value of the pixel) of the current frame outputted from the edge-detecting circuit  210 , and then outputs pre-saved edge data G n-1,e  of the previous frame to the edge-driving decision circuit  250 . The edge-driving decision circuit  250  compares two edge data G n,e , G n-1,e  that respectively correspond to the current frame and the previous frame, and accesses a look-up table stored in the storage unit  260  in accordance with the difference between these two edge data in order to determine the voltage setting of the liquid crystal layer. For example, if the difference between the edge data G n,e  of the current frame and the edge data G n-1,e  the previous frame is greater than a threshold value, it means that the edge data varies greatly in these two continuous frames. Hence the look-up table must be accessed to obtain a suitable overdriving voltage setting S e  corresponding to the difference for accelerating the response time of the liquid crystal cells. Please note that because the frame memory  220  only has to save edge data rather than the data of all pixels of the frame, the necessary memory size of the present invention is smaller than the memory size required in the prior art. 
     In a preferred embodiment of the present invention, for avoiding error and increasing stability of the control circuit  200 , the driving voltage setting S n  corresponding to the non-edge part of the current frame and the overdriving voltage setting S e  corresponding to the edge part of the current frame are inputted into a weighted circuit  270 . The weighted circuit  270  references the driving voltage setting S n  of the pixels located at the non-edge part neighboring the image edge part for adjusting an initial overdriving voltage setting S e  of the edge part, and the weighted circuit  270  then generates a modified overdriving voltage setting S M  corresponding to the edge part of the current frame. There are many methods for the weighted circuit  270  to execute the weighted operation. For example, please refer to  FIG. 3 .  FIG. 3  is a block diagram of the weighted circuit  270  shown in  FIG. 2  according to a preferred embodiment of the present invention. The weighted circuit  270  includes a first multiplier  271 , a second multiplier  272 , and an adder  273 . The first multiplier  271  firstly multiplies the driving voltage setting S n  of at least one pixel located at the non-edge part next to the edge part in the current frame with a first weighted factor α to generate a first operating value αS n , wherein the first weighted factor α is a value less than  1 . Next, the second multiplier  272  multiplies the initial overdriving voltage setting S e  of a specific pixel located at the edge part in the current frame with a second weighted factor β to generate a second operating value βS e . Finally, the adder  273  sums up the first operating value αS n  with the second operating value βS e  to generate the modified overdriving voltage setting S M  of the specific pixel. 
     The driving voltage setting S n  and the modified overdriving voltage setting S M  are inputted into a multiplexer  280 . The multiplexer  280  is an output device for outputting the driving voltage setting S n  and the modified overdriving voltage setting S M . As mentioned above, the non-edge part of the current frame can directly use the driving voltage setting S n  to set a voltage supply circuit (not illustrated in the diagram) to provide the voltage dropped on two terminals of the liquid crystal layer, but the edge part has to use the modified overdriving voltage setting S M  to set a voltage supply circuit to provide the voltage dropped on two terminals of the liquid crystal layer. Consequently, the multiplexer  280  selectively switches the driving voltage setting S n  or the modified overdriving voltage setting S M  to be the setting value of the voltage supply circuit according to whether the pixel belongs to the edge part or the non-edge part of the frame. 
     Please refer to  FIG. 4 .  FIG. 4  is a flowchart of an LCD control method according to a preferred embodiment of the present invention. Steps of the control method are described below: 
     Step  410 : Start; 
     Step  415 : Detect edge parts of each frame, then go to step  420  and step  445  sequentially; 
     Step  420 : Output an edge data corresponding to each frame, then go to step  425  and step  430  sequentially; 
     Step  425 : Save the edge data of each frame; 
     Step  430 : Access a look-up table according to a previous frame and a current frame; 
     Step  435 : Determine an overdriving voltage setting corresponding to the edge part of the current frame in accordance with the look-up table; 
     Step  440 : Execute a weighted operation to generate a modified overdriving voltage setting according to the driving voltage setting of the non-edge part and the overdriving voltage setting of the edge part, then go to step  455 ; 
     Step  445 : Output a non-edge data corresponding to each frame; 
     Step  450 : Generate the driving voltage setting of the non-edge part in the current frame according to the non-edge data, then go to step  440  and step  455  sequentially; 
     Step  455 : Output the overdriving voltage setting and the driving voltage setting to set the voltage value; 
     Step  460 : End. 
     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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.