Patent Publication Number: US-2013241961-A1

Title: Electrophoretic display device and method for driving the same

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an electrophoretic display device, and more particularly to an electrophoretic display device and a method for driving the same. 
     BACKGROUND OF THE INVENTION 
     Please refer to  FIG. 1 , which illustrates displaying principle of a conventional electrophoretic display device. The electrophoretic display device mainly comprises a first substrate  100 , a second substrate  102 , an electrode layer  104  which is disposed on the first substrate  100 , an electrophoretic layer  106  which is disposed between the first substrate  100  and the second substrate  102 , and a driving circuit  108 . The electrophoretic layer  106  comprises a plurality of charged particles having white charged particles  110  and black charged particles  112 . The white charged particles  110  are positively charged particles, while the black charged particles are negatively charged particles. The driving circuit  108  is utilized for providing data voltages to the electrode layer  104 . A common voltage is applied to another electrode layer (not shown) on the second substrate  102 . The white charged particles  110  and the black charged particles  112  are driven by an electric field formed by the data voltages and the common voltage, so as to change locations of the white charged particles  110  and the black charged particles  112  for displaying images. 
     Please refer to  FIG. 2  and  FIG. 3 .  FIG. 2  illustrates a graph showing a relationship between the driving time and the gray level in the conventional electrophoretic display device.  FIG. 3  illustrates the locations of the white charged particles versus the corresponding gray levels. As shown in  FIG. 2 , when the driving time of the charged particles is short, the gray level is low. When the driving time of the charged particles is long, the gray level is high. Further, as shown in  FIG. 3 , when the white charged particles  110  are further away from the top surface of the electrophoretic display device (i.e. at the lower location in  FIG. 3 ), the gray level is low. When the white charged particles  110  are closer to the top surface of the electrophoretic display device (i.e. at the upper location in  FIG. 3 ), the gray level is high. By changing the locations of the white charged particles  100  to reflect light received from the environment, the electrophoretic display device is capable of showing the color contrast of the white charged particles  100  for displaying the images. The aforesaid displaying principle is known as a total reflective display technology. Thus, the electrophoretic display device does not require a backlight source. 
     A color electrophoretic display device is manufactured by disposing a color filter (CF) on the electrophoretic display device in  FIG. 1 . 
     Please refer to  FIG. 4  and  FIG. 5 .  FIG. 4  illustrates a system architecture of the conventional electrophoretic display device.  FIG. 5  illustrates a conventional lookup table architecture. In the system architecture, a frame buffer  400  is required to store a previous image F(N−1). A current image F(N) and the previous image F(N−1) are inputted to a controller  402 . The controller  402  looks up a gray level data of each frame in the current image F(N) which are required to be provided to an electrophoretic display panel  404  from the lookup table  406 . 
     As shown in  FIG. 5 , when one image of the conventional electrophoretic display device comprises K frames, K lookup tables are required to be stored. In a first frame, a value is obtained by looking up an input gray level (i.e. a gray level of a pixel of the previous image F(N−1)) versus an output gray level (i.e. a gray level of the pixel of the current image F(N−1)) from a first lookup table and provided to the electrophoretic display panel  404 . Then, the values required from a second frame to a K-th frame are obtained by respectively looking up from a second lookup table to a K-th lookup table. 
     Accordingly, when the system architecture is applied to the color electrophoretic display device, a lookup table capacity is equal to 3 (i.e. red, green, blue)×16 (i.e. total input gray levels)×16 (i.e. total output gray levels)×K (i.e. total frames)=768×K bits. An output voltage being outputted by a source driving circuit lasts for 16.7 milliseconds (ms) at a frame rate of 60 Hz (Hertz). Currently, a response time of the charged particles is about 250 ms to 350 ins. Updating a complete image requires 15 to 21 multiples of a frame time (250 ms/16.7 ms to 350 ms/16.7 ms). That is, K is about 15 to 21 frames. Accordingly, the required lookup table capacity of the color electrophoretic display device is between (768×15) and (768×21)=11.52 k bits and 16.13 k bits, and thus the memory cost is too high. 
     Since the required lookup table capacity is too high, only one group of the lookup tables as shown in  FIG. 5  can be stored. It fails to store several groups of the lookup tables for different situations. For instance, different groups of the lookup tables are looked up according to different temperatures. Accordingly, the values which are looked up from the conventional lookup table architecture are not accurate, so that the display quality is poor or color shift phenomenon occurs. 
     Therefore, there is a need for a solution to the above-mentioned problems that the memory cost is too high and the display quality is poor. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide an electrophoretic display device and a method for driving the same, which are capable of decreasing the memory cost and improving the display quality. 
     To achieve the above-mentioned objective, an electrophoretic display device according to an aspect of the present invention is provided. The electrophoretic display device is used for displaying at least one image. The image comprises a plurality of frames. The electrophoretic display device comprises a first electrode layer, a second electrode layer, an electrophoretic layer, and a controller. The first electrode layer has a plurality of pixels formed thereon. The second electrode layer is corresponding to the first electrode layer and electrically coupled to a common voltage. The electrophoretic layer is disposed between the first electrode layer and the second electrode layer and comprises a plurality of charged particles. Each of the pixels is corresponding to several of the charged particles. The controller receives a display data corresponding to the image. The display data comprises a required gray level for each of the pixels. The controller looks up a write-in gray level data of each of the pixels in each of the frames from at least one lookup table according to the required gray level for determining a voltage. The lookup table records the write-in gray level data of each of the pixels in each of the frames from a reference gray level to the required gray level. The voltage is provided to the first electrode layer. An electric field is formed between the first electrode layer and the second electrode layer through each of the pixels for driving the charged particles corresponding to each of the pixels. 
     To achieve the above-mentioned objective, a method for driving an electrophoretic display device according to another aspect of the present invention is provided. The electrophoretic display device comprises a first electrode layer, a second electrode layer corresponding to the first electrode layer, and an electrophoretic layer which is disposed between the first electrode layer and the second electrode layer. The first electrode layer has a plurality of pixels formed thereon. The electrophoretic layer comprises a plurality of charged particles. Each of the pixels is corresponding to several of the charged particles. The electrophoretic display device is used for displaying at least one image. The image comprises a plurality of frames. The method comprises the steps of receiving a display data corresponding to the image, the display data comprising a required gray level for each of the pixels; looking up a write-in gray level data of each of the pixels in each of the frames from at least one lookup table according to the required gray level for each of the pixels, the lookup table recording the write-in gray level data of each of the pixels in each of the frames from a reference gray level to the required gray level; providing a voltage to the first electrode layer according to the write-in gray level data in each of the frames; and providing a common voltage to the second electrode layer, and an electric field being formed between the first electrode layer and the second electrode layer through each of the pixels for driving the charged particles corresponding to each of the pixels. 
     The electrophoretic display device and the method for driving the same according to the present invention are capable of significantly decreasing the lookup table capacity, thereby decreasing the hardware cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates displaying principle of a conventional electrophoretic display device; 
         FIG. 2  illustrates a graph showing a relationship between the driving time and the gray level in the conventional electrophoretic display device; 
         FIG. 3  illustrates the locations of the white charged particles versus the corresponding gray levels; 
         FIG. 4  illustrates a system architecture of the conventional electrophoretic display device; 
         FIG. 5  illustrates a conventional lookup table architecture; 
         FIG. 6  illustrates a system architecture of an electrophoretic display device according to a preferred embodiment of the present invention; 
         FIG. 7  illustrates pixels of an electrophoretic display panel in  FIG. 6 ; 
         FIG. 8  illustrates a timing chart showing the source data signal inputted to the source driving circuit by the controller; and 
         FIG. 9  illustrates a flow chart of a method for driving an electrophoretic display device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 6  and  FIG. 7 .  FIG. 6  illustrates a system architecture of an electrophoretic display device according to a preferred embodiment of the present invention.  FIG. 7  illustrates pixels of an electrophoretic display panel in  FIG. 6 . The electrophoretic display device is utilized for displaying at least one image. The image comprises a plurality of frames. The electrophoretic display device comprises a controller  600 , a power supply unit  602 , a source driving circuit  604 , a gate driving circuit  606 , a memory unit  608 , and the electrophoretic display panel  610 . 
     The electrophoretic display panel  610  comprises a first substrate  612 , a first electrode layer  614 , an electrophoretic layer  616 , a second electrode layer  618 , and a second substrate  620 . In the present embodiment, the first substrate  612  is a thin film transistor (TFT) substrate. The first electrode layer  614  has a plurality of pixels  630  formed thereon and is an indium tin oxide (ITO) layer being manufactured on the first substrate  612 . The second substrate  620  is a color filter substrate. The second electrode layer  618  is an ITO layer being manufactured on the second substrate  620 . The second electrode layer  618  may be regarded as a common electrode layer corresponding to the first electrode layer  614 . An electric field formed between the first electrode layer  614  and the second electrode layer  618  through each of the pixels  630  drives a plurality of charged particles  622  corresponding to each of the pixels  630  to move to different locations for generating different gray levels. The charged particles  622  may be positively charged particles or negatively charged particles. The color of the charged particles  622  may be white or black. 
     When an image is required to be displayed, a display data S D  corresponding to the image is first inputted to the controller  600 . The display data S D  comprises a required gray level for each of the pixels  630 . The controller  600  looks up a write-in gray level data (i.e. a gray level data is required to be written in each of the frames) of each of the pixels  630  in each of the frames from a lookup table  624  stored in the memory unit  608  according to the required gray level, and then outputs a source data signal S SD  to the source driving circuit  604  according to the write-in gray level data which is looked up from the lookup table  624 . Furthermore, the controller  600  outputs a voltage controlling signal S VC  to the power supply unit  602  so as to control an output voltage from the power supply unit  602  according to the display data S D , as well as outputs a gate controlling signal S GC  to the gate driving circuit  606 . 
     The power supply unit  602  outputs a common voltage V COM  to the second electrode layer  618  according to the voltage controlling signal S VC . The source driving circuit  604  selects a required voltage from the power supply unit  602  according to the source data signal S SD . The gate driving circuit  606  selects a required voltage from the power supply unit  602  according to the gate controlling signal S GC . The gate driving circuit  606  and the source driving circuit  604  respectively transform the required voltages selected from the power supply unit  602  into a gate voltage V G  and a source driving voltage V SD . Then, the gate voltage V G  and the source driving voltage V SD  are outputted to TFTs (not shown) of the pixels  630  on the first substrate  612 . The gate voltage V G  is utilized for turning on and off the TFTs. The charged particles  622  in the electrophoretic layer  616  are driven to different locations for generating different gray levels by the electric field being formed by the source driving voltage V SD  and the common voltage V COM  of the second electrode layer  618 . 
     Compared with the conventional lookup table architecture in  FIG. 5 , the capacity of the lookup table  624  can be significantly decreased according to the present invention, thus the cost of the memory unit  608  can be reduced. The following reason will explain how the capacity of the lookup table  624  can be decreased according to the present invention. 
     Owing to the material characteristics of the charged particles  622 , the charged particles  622  have to be driven back to an initial location (i.e. corresponding to a lowest gray level or a highest gray level) for removing a previous gray level data when updating an image. Then, a current gray level data is written in. The charged particles  622  that are driven back to the initial location means that the charged particles  622  are driven back to a black location (i.e. corresponding to the lowest gray level) or a white location (i.e. corresponding to the highest gray level). In fact, when the charged particles  622  are driven back to the black location (i.e. corresponding to the lowest gray level) and then back to the white location (i.e. corresponding to the highest gray level) for several times, the effect of removing the previous gray level data is better. 
     By using the characteristics that the gray level data can be written in only when the charged particles  622  are driven back to the black location (i.e. corresponding to the lowest gray level) or the white location (i.e. corresponding to the highest gray level), the lookup table  624  according to the present invention only requires to record the write-in gray level data in each of the frames from the lowest gray level or the highest gray level to the required gray level. 
     Please refer to the following TABLE 1, which shows the lookup table according to the present invention. If an image is assumed to comprise K frames and be capable of displaying 16 gray levels (i.e. G 0 -G 15 ). Currently, voltages for driving the charged panicles  622  comprise three voltages: +15 volts (V POS ), −15 volts (V NEG ), and 0 volt (V SS ). As a result, a two-bit data is required for representing the three voltages. 
     The write-in gray level data in each of the frames is obtained by experimenting on the charged particles  622 . That is, the charged particles  622  have to be measured to obtain a relationship between the driving time and the gray level, and therefore the write-in gray level data in each of the frames is determined according to the relationship between the driving time and the gray level. For example, when the required gray level is G 13 , the write-in gray level in the frame  1  is D 27 D 26 , while the write-in gray level in the final frame K is D 27′ D 26′ . 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 frame 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 required gray level 
                 1 
                 2 
                 3 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 K 
               
               
                   
               
               
                 G15 
                 D 31 D 30   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 31 ′D 30 ′ 
               
               
                 G14 
                 D 29 D 28   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 29 ′D 28 ′ 
               
               
                 G13 
                 D 27 D 26   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 27 ′D 26 ′ 
               
               
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
               
               
                 G2 
                 D 5 D 4   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 5 ′D 4 ′ 
               
               
                 G1 
                 D 3 D 2   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 3 ′D 2 ′ 
               
               
                 G0 
                 D 1 D 0   
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 . . . 
                 D 1 ′D 0 ′ 
               
               
                   
               
            
           
         
       
     
     Please refer to the following TABLE 2 and TABLE 3. TABLE 2 shows an example of the lookup table according to the present invention. TABLE 3 shows the write-in gray level data versus the voltages. In the present example, the response time of the charged particles  622  is 300 ms and a frame rate is 60 Hz, that is, updating a complete image requires 18 multiples of a frame time (300 ms/16.7 ms=18). The charged particles  622  are assumed to be back to the white location (i.e. the highest gray level). When the required gray level is G 15  (i.e. the highest gray level), the gray level is not required to be changed. Accordingly, the write-in gray level data in the frames  1 - 18  are “10”. It can be seen from TABLE 3 that “10” represents 0 volt, and thus the gray level is not changed. When the required gray level is G 9 , it can be seen from TABLE 2 and TABLE 3 that the write-in gray level data in the frames  1 - 12  are “10” representing 0 volt and the write-in gray level data in the frames  13 - 18  are “01” representing −15 volts. When the required gray level is G 0  (i.e. the lowest gray level), it can be seen from TABLE 2 that the write-in gray level data in the frames  1 - 18  are “01”. This means that −15 volts is required to be inputted in all frames, such that the highest gray level can be changed to the lowest gray level. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 required gray 
                 frame 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 level 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
                 16 
                 17 
                 18 
               
               
                   
               
               
                 G15 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
               
               
                 G14 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
               
               
                 G13 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
               
               
                 G12 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
               
               
                 G11 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
               
               
                 G10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G9 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G8 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G7 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G6 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G5 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G4 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G3 
                 10 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G2 
                 10 
                 10 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G1 
                 10 
                 10 
                 10 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                 G0 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
                 01 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 write-in gray level data 
                 Voltage 
               
               
                   
               
             
            
               
                 00 
                 V POS  (+15 volts) 
               
               
                 01 
                 V NEG  (−15 volts) 
               
               
                 10 
                 V SS  (0 volt) 
               
               
                 11 
                 X 
               
               
                   
               
            
           
         
       
     
     The lookup table capacity of TABLE 2 is equal to 16 (i.e. total gray levels)×18 (i.e. total frames)=288 bits. When TABLE 2 is applied to a color electrophoretic display device in which each pixel comprises a red sub-pixel, a green sub-pixel, and a blue sub-pixel, three lookup tables can be stored for the red sub-pixel, the green sub-pixel, and the blue sub-pixel, respectively. The capacity of the three lookup tables is equal to 288×3=864 bits. For the color electrophoretic display device, the lookup table capacity according to the present invention is only 1/16 of the lookup table capacity in the prior art. 
     Since the lookup table capacity is significantly decreased, a saving of capacity can be used for storing a plurality of lookup tables for different situations. For example, the lookup tables are used for different sub-pixels or different temperatures. As a result, the display quality of the electrophoretic display device can be improved by looking up different lookup tables under different situations. 
     Please refer to  FIG. 6 ,  FIG. 7 , and  FIG. 8 .  FIG. 8  illustrates a timing chart showing the source data signal inputted to the source driving circuit by the controller. In the present embodiment, the source data signal S SD  inputted to the source driving circuit  604  by the controller  600  per time comprises 8 bits. The 8 bits are denoted as D 7 -D 0 . D 7 -D 0  are provided in a clock period as shown in  FIG. 8 . Since each of the pixels  630  requires 2 bits, the gray level data of four pixels  630  are provided by the controller  600  per time. In the timing chart of  FIG. 8 , the write-in time T WRITE  includes the required time for providing the gray level data of all pixels  630  in one complete image by the controller  600 . The gray level data of the pixels  630  are sequentially provided (i.e. not at the same time) by the controller  600 . 
     Please refer to  FIG. 9 , which illustrates a flow chart of a method for driving an electrophoretic display device according to the present invention. The electrophoretic display device comprises a first electrode layer, a second electrode layer corresponding to the first electrode layer, and an electrophoretic layer which is disposed between the first electrode layer and the second electrode layer. The first electrode layer has a plurality of pixels formed thereon. The electrophoretic layer comprises a plurality of charged particles. Each of the pixels is corresponding to several of the charged particles. The electrophoretic layer is used for displaying at least one image. The image comprises a plurality of frames. 
     In step S 900 , a display data corresponding to the image is received. The display data comprises a required gray level for each of the pixels. 
     In step S 910 , a write-in gray level data of each of the pixels in each of the frames is looked up from at least one lookup table according to the required gray level for each of the pixels. The lookup table records the write-in gray level data of each of the pixels in each of the frames from a reference gray level to the required gray level. The reference gray level may be a lowest gray level or a highest gray level. 
     In step S 920 , a voltage is provided to the first electrode layer according to the write-in gray level data in each of the frames. 
     In step S 930 , a common voltage is provided to the second electrode layer. An electric field formed between the first electrode layer and the second electrode layer through each of the pixels drives the charged particles corresponding to each of the pixels. 
     In one embodiment, the write-in gray level data of each of the pixels in each of the frames is looked up from a plurality of lookup tables. The lookup tables are used for different temperatures. In another embodiment, each of the pixels comprises a plurality of sub-pixels. The write-in gray level data of each of the pixels in each of the frames is looked up from a plurality of lookup tables. The lookup tables are used for different sub-pixels. 
     While the preferred embodiments of the present invention have been illustrated and described in detail, various modifications and alterations can be made by persons skilled in this art. The embodiment of the present invention is therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular fol ins as illustrated, and that all modifications and alterations which maintain the spirit and realm of the present invention are within the scope as defined in the appended claims.