Patent Publication Number: US-7221347-B2

Title: Apparatus and method to improve a response speed of an LCD

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Application No. 2002-19478 filed Apr. 10, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus and method to operate a liquid crystal display (LCD), and more particularly, to an apparatus that rejects an error due to noise in a digital image signal to improve a response speed of an LCD, and a method therefor. 
   2. Description of the Related Art 
   As size and weight of personal computers (PCs) and televisions (TVs) reduce continuously, light and compact displays devices have been developed. As a result, flat-panel type displays such as liquid crystal displays (LCDs), have appeared and are replacing the conventional cathode ray tubes (CRTs). 
   The LCD is a display device that produces a desired image signal by applying an electric field to a liquid material that has anisotropic permittivity and is injected between two substrates. An amount of light transmitted to the two substrates is adjusted by controlling an intensity of the applied electric field. 
   Liquid crystals used in LCDs present a hold-type physical property. In other words, a state of the liquid crystals corresponding to current data is maintained until next data is input. A response speed of the liquid crystals indicates how fast the liquid crystals change according to input data. Most LCD panels have the response speed faster than 1/60 seconds, which corresponds to a speed of one frame per 16.6 ms. Accordingly, as shown in  FIG. 1 , a long period of time corresponding to several frames is necessary between intermediate levels of a general image until the liquid crystal reaches an appropriate voltage in response to the input data. For this reason, ghost, a reduction in a dynamic contract ratio, and blurring edges occur in moving-image display devices such as TVs, digital TVs or DVD players, thereby deteriorating image quality. 
     FIG. 2  is a block diagram of a conventional apparatus to improve the LCD response speed, which prevents deterioration of the image quality. Input digital image data is temporarily stored in a buffer  200  in conjunction with a frame memory  201 . Current image data D n  stored in the buffer  200  and previous image data D n-1  stored in the frame memory  201  are input to a comparator  202 . The comparator  202  compares a gradation of the current image data D n  and a gradation of the previous image data D n-1  at a same pixel position. If the gradation of the current image data D n  and the gradation of the previous image data D n-1  are the same, the comparator  202  outputs data D n ′ that has a response speed of the gradation of the current data D n . If the gradation of the current image data D n  is larger than the gradation of the previous image data D n-1 , the comparator  202  outputs the data D n ′ that has a gradation larger than that of the current data D n . On the contrary, if the gradation of the current image data D n  is smaller than the gradation of the previous image data D n-1 , the comparator  202  outputs the data D n ′ that has a gradation smaller than that of the current data D n . A controller  203  controls reading or writing data from or to all blocks. 
   However, the use of the apparatus to improve the response speed of  FIG. 2  leads the LCD to be sensitive to every kind of noise. In this case, noise on a screen, which is not serious in the LCD having slow response speed, grows worse after improving the response speed, thereby causing serious deterioration of the image quality. 
   SUMMARY OF THE INVENTION 
   Various aspects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   In accordance with the above and other aspects of the present invention, there is provided an apparatus to improve a response speed of an LCD, the apparatus that rejects errors due to noise in a digital image signal to improve the response speed of the LCD. 
   In accordance with the above and other aspects of the present invention, there is provided a method of improving a response speed of an LCD, where errors are rejected due to noise in a digital image signal to improve the response speed of the LCD. 
   In accordance with the above and other aspects of the present invention, there is provided an apparatus to improve a response speed of an LCD, the apparatus including: a noise rejection unit to reject noise in current digital image data and previous digital image data at a same pixel position as in the current digital image data; and a comparator to compare the current digital image data and the previous digital image data of which noises are rejected within a reference value, to change the current digital image data based on a comparison result, and to output a result indicative thereof. 
   The noise rejection unit includes: a first low-pass filter (LPF) to reject a noise in the current digital image data; and a second LPF to reject the noise in the previous digital image data at the same pixel position as in the current digital image data. 
   The comparator includes a look up table (LUT) to hold gradation data that changes a response speed of the current digital image data. 
   The comparator accesses the LUT to output the current digital image data when a difference between gradations of the current digital image data and the previous digital image data, of which the noise is rejected, is smaller than the reference value. 
   The comparator compares the gradation of the current digital image data and the gradation of the previous digital image data, changes the current digital image data and outputs the result, when the difference between the gradations of the current digital image data and the previous digital image data of which the noise is rejected, is larger than the reference value. 
   The comparator accesses the LUT to increase the gradation of the current digital image data and outputs the result when the difference between the gradations of the current digital image data and the previous digital image data, of which the noise is rejected, is larger than the reference value and the gradation of the current digital image data is larger than the gradation of the previous digital image data. Also, the comparator accesses the LUT to decrease the gradation of the current digital image data and outputs the result when the difference between the gradation of the current digital image data and the previous digital image data, of which the noise is rejected, is larger than the reference value and the gradation of the current digital image data is smaller than the gradation of the previous digital image data. 
   In accordance with the above and other aspects of the present invention, there is provided an apparatus to improve a response speed of an LCD, including: a buffer receiving digital image data and outputting first current image data; a first noise rejection unit rejecting noise in the first current image data and outputting second current image data where noise is rejected; a frame memory storing the first current image data and outputting first previous image data, which precedes the first current image data; a second noise rejection unit outputting second previous image data indicative of noise rejected from the first previous image data; a comparator comparing gradations of the first current image data, the second current image data, the first previous image data, and the second previous image data to output the digital image data having the improved response speed. 
   In accordance with the above and other aspects of the present invention, there is provided a method of improving response speed of an LCD, the method including: rejecting noise in previous digital image data at a same pixel position as current digital image data; comparing a difference between gradations of the current digital image data and the previous digital image data with a reference value and outputting a result indicative thereof; and accessing an LUT storing gradation data that changes a response speed, to change the current digital image data based on the result. 
   When accessing the LUT, the LUT is accessed to output the current digital image data when the difference between the gradations of the current digital image data and the previous digital image data, of which the noise is rejected, in is smaller than the reference value. 
   When accessing the LUT, the gradation of the current digital image data is compared with the gradation of the previous digital image data, the gradation of the current digital image data is changed based on the comparison result, and the result is output when the difference between the gradations of the current digital image data and the previous digital image data, of which the noise is rejected, is larger than the reference value. 
   The LUT is accessed to increase the gradation of the current digital image data and output the result, when the difference between the gradations of the current digital image data and the previous digital image data, of which the noise is rejected, is larger than the reference value and the gradation of the current digital image data is larger than the gradation of the previous digital image data. Also, the LUT is accessed to decrease the gradation of the current digital image data and output the result, when the difference between the gradations of the current digital image data and the previous digital image data, of which the noise is rejected, is larger than the reference value and the gradation of the current digital image data is smaller than the gradation of the previous digital image data. 
   In accordance with the above and other aspects of the present invention, there is provided a method to improve a response speed of an LCD, including: outputting first current image data based on digital image data; rejecting noise in the first current image data and outputting second current image data indicative thereof; outputting first previous image data preceding the first current image data; rejecting noise in the first previous image data and outputting second previous image data indicative thereof; comparing a gradation of the second current image data and a gradation of the second previous image data; and outputting the digital image data having a same response speed as the first current image data when a difference between the gradations of the second current image data and the second previous image data is smaller than a reference value. 
   In accordance with the above and other aspects of the present invention, there is provided a method to improve a response speed of an LCD, including: outputting first current image data based on digital image data; rejecting noise in the first current image data and outputting second current image data indicative thereof; outputting first previous image data preceding the first current image data; rejecting noise in the first previous image data and outputting second previous image data indicative thereof; comparing a gradation of the second current image data and a gradation of the second previous image data; and determining whether the gradation of the first current image data is larger than the gradation of the first previous image data when a difference between the gradations of the second current image data and the second previous image data is larger than a reference value. 
   These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a graph illustrating a characteristic curve of a conventional liquid crystal display (LCD); 
       FIG. 2  is a block diagram of a structure of a conventional apparatus to improve response speed; 
       FIG. 3  is a block diagram of the structure of an apparatus to improve the response speed, according to an embodiment of the present invention; 
       FIG. 4  is a graph illustrating a characteristic curve of the LCD having the improved response speed, according to an embodiment of the present invention; and 
       FIG. 5  is a flow chart illustrating a method to improve the response speed of the LCD, according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. 
     FIG. 3  is a block diagram of a structure of an apparatus to improve a response speed of an LCD, according to an embodiment of the present invention. The apparatus includes a buffer  300 , a first noise rejection unit  301 , a frame memory  302 , a second noise rejection unit  303 , a comparator  304 , a look up table (LUT)  304 - 1 , and a controller  305 .  FIG. 4  is a graph illustrating a characteristic curve of the LCD having the improved response speed.  FIG. 5  is a flow chart illustrating a method to improve the response speed of the LCD according to an embodiment of the present invention. The method includes, at operation  500 , outputting data D n ′ where noise is rejected by passing current image data D n  through a low-pass filter (LPF). 
   At operation  501 , the method outputs data D n-1 ′ where the noise is rejected by passing previous image data D n-1  through the LPF at a same pixel position of the current image data D n . At operation  502 , the method compares the data D n ′ and the data D n-1 ′ where noises are rejected. At operation  503 , the method checks whether a difference between gradations of the data D n ′ and the data D n-1 ′ is smaller than a reference value, which is gradation data stored in the LUT  304 - 1 . At operation  504 , the method outputs data D n ″ that has the same response speed as the current data D n  and, at 2  operation  505 , the method checks whether the gradation of the current data D n  is larger than the gradation of the data D n-1 . At operation  506 , the method outputs data D n ″ that has the response speed faster than that of the current image data D n  by accessing an LUT. At operation  507 , the method outputs data D n ″ that has the response speed slower than that of the current image data D n  by accessing the LUT. 
   Hereinafter, the apparatus to improve the response speed, according to an embodiment of the present invention, will be described in detail with reference to  FIGS. 3 and 4 . Here, the buffer  300  temporarily stores an input digital image data. 
   The first noise rejection unit  301  includes a low-pass filter (LPF), and rejects the noise contained in the image data D n  output from the buffer  300 . The first noise rejection unit  301  receives the image data D n  and outputs the image data D n ′. 
   The frame memory  302  stores the current image data D n  output from the buffer  300  and outputs the previous image data D n-1 , which precedes the current image data D n , in response to a control signal from the controller  305 . 
   The second noise rejection unit  303  also includes an LPF, and outputs image data D n-1 ′ indicative of the noise rejected from the previous image data D n-1 . 
   The comparator  304  receives and compares the current image data D n , the current image data D n ′ that has the noise rejected, the previous image data D n-1  having a same pixel position as the current image data D n , and the previous image data D n-1 ′ that has the noise rejected. Thereafter, the comparator  304  outputs the current image data D n ″ having an improved response speed. The comparator  304  includes the LUT  304 - 1  that holds the gradation data that changes the response speed of the current digital image data and outputs the gradation data that changes the gradation of the current image data D n . 
   The comparator  304  compares a difference between gradations of the current image data D n ′ and previous image data D n-1 ′ where the noises are rejected with the reference value, and outputs the image data D n ″ having the same response speed as the current image data D n , when the difference is smaller than the reference value. Here, D n ″ denotes the same current image data D n . 
   On the contrary, if the difference is larger than the reference value, the comparator  304  compares the gradation of the current image data D n  and the gradation of the previous image data D n-1 , changes the response speed of the current image data D n , i.e., changes the gradation, and outputs the current image data D n . When the gradation of the current image data D n  is larger than that of the previous image data D n-1 , the comparator  304  accesses the LUT  304 - 1  and outputs the image data D n ″ having the response speed faster than the current digital image data D n . Here, D n ″ denotes the current image data D n  having the increased gradation. When the gradation of the current image data D n  is smaller than that of the previous image data D n-1 , the comparator  304  accesses the LUT  304 - 1  and outputs the image data D n ″ with the response speed slower than that of the current digital image data D n . Here, D n ″ denotes the current image data D n  with the reduced gradation. 
   Referring to  FIG. 4 , (a) illustrates an LCD ideal response, (b) illustrates an LCD actual response, and (c) illustrates the LCD response after applying the inventive embodiment. In detail, the response in (c) is obtained by comparing the gradation of the image signal where the noise is rejected with the reference value and the gradation of the image signal is improved based on the compared result. The response in (c) is approximately closer to the LCD ideal response in (a) than the LCD actual response in (b), thereby correcting image distortion. 
     FIG. 5  is a flow chart illustrating the method of improving the response speed. At operation  500 , the current image data D n  is passed through the LPF  301  to reject noise therein and is output as the D n ′. 
   At operation  501 , the previous image data D n-1  is passed through the LPF  301 , the same pixel position as the current image data D n , so as to cancel the noise in the previous image data D n-1  and is output as data D n-1 ′. At operation  502 , the comparator  304  compares the gradation of the current image data D n ′ and the gradation of the previous image data D n-1 ′. At operation  503 , the comparator  304  checks if the difference between the gradations of the current image data D n ′ and previous image data D n-1 ′ is smaller than the reference value. 
   If it is determined at operation  503  that the difference is smaller than the reference value, at operation  504 , the image data D n ″ that has the same response speed as the current image data D n  is output. Here, D n  denotes the same current image data D n . 
   If it is determined at operation  503  that the difference is larger than the reference value, at operation  505 , the comparator  304  checks whether the gradation of the current image data D n  is larger than that of the previous image data D n-1 . 
   When the difference between the gradations of the current image data D n ′ where the noise is rejected and the previous image data D n-1 ′ where the noise is rejected is larger than the reference value and the gradation of the current image data D n  is larger than the previous image data D n-1 , at operation  506 , the LUT  304 - 1  is accessed to output image data D n ″ that has a larger response speed than the current image data D n . Here, D n ″ denotes the current image data where gradation is increased. 
   When the gradation difference is larger than the reference value and the gradation of the current image data D n ′ is smaller than the gradation of the previous image data D n-1 ′, at operation  507 , the LUT  304 - 1  is accessed to output the image data D n ″ of which the response speed is slower than the current image data D n . Here, D n ″ denotes the current image data D n  having the reduced gradation. 
   As described above, according to the present invention, image distortion due to noise, which is a problem in existing methods to improve a response speed, can be solved. Further, the response speed of an LCD is improved, thereby reducing an occurrence of ghost and blurring edges to a desired level. 
   The various features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.