Abstract:
A display control device for controlling a display panel includes a contents frame rate detector detecting a contents frame rate of an input image data and outputting a repetitive frame number dependent from a display frame rate of the display panel and the detected contents frame rate; a frame memory for storing a level data of a previous frame; and an emulated level generator in communication with the contents frame rate detector and the frame memory. An output level data to the display panel is generated according to the repetitive frame number from the contents frame rate detector, the previous level data from the frame memory and an input level data of the input image data.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a display control device, and more particularly to a display control device for controlling a liquid crystal display. 
     BACKGROUND OF THE INVENTION 
     The response of a liquid crystal display (LCD) is generally slower than the response of a plasma display, and is now improved in an order of several milliseconds to ten more milliseconds so as to trace the early stage of image. In addition to LCD and plasma displays, other displays such as organic electroluminescence (EL) displays, organic light-emitting diode (OLED) displays, field emission displays (FED), surface-conduction electron-emitter display (SED), etc., which have enhanced response speed, are under development. Prior art includes Japanese Patent Publication No. 2006-337448. 
     For a display with a quick response, if the frame rate of the contents themselves to be displayed is relatively low or the frame rate of the displayed image is relatively low due to the displaying mode, detailed flicker that reveals an unsmooth edge or discontinuous action of image, particularly the image of a moving object such as a hand or a leg, may occur. Such detailed flicker does not bother a display with a slow response but does cause problems to the effort in hastening the response speed. 
     For example, a conventional film is taken with 24 frames per second. If the response of a display is much quicker than the rate, an action of an object shown in the display would be suddenly and unnaturally stopped at times. In another example, the frame rate of a one seg TV displayed in for example a mobile phone is about 15 frames per second. The discontinuity of displayed image is even serious when the display is with a high response speed. 
     Enhancing the frame rate of contents may help in alleviating discontinuity, but is not applicable to the case that the contents are fixed and the frame rate is unchangeably low. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a display control device that controls a display with a relatively high response speed to display contents of a relatively low frame rate in order to minimize discontinuity and smoothen displayed image. 
     The present invention provides a display control device for controlling a display panel. The display control device includes a contents frame rate detector detecting a contents frame rate of an input image data and outputting a repetitive frame number dependent from a display frame rate of the display panel and the detected contents frame rate; a frame memory for storing a level data of a previous frame; and an emulated level generator in communication with the contents frame rate detector and the frame memory, generating an output level data to the display panel according to the repetitive frame number from the contents frame rate detector, the previous level data from the frame memory and an input level data of the input image data. 
     In an embodiment, the emulated level generator includes: a plurality of lookup tables corresponding to different repetitive frame numbers, respectively, in which correlating information among the previous level data, the input level data and the output level data are recorded; and a lookup table selector selects one of the lookup tables according to the repetitive frame number from the contents frame rate detector to be referred to so as to determine the output level data corresponding to the previous level data and the input level data. 
     In another embodiment, the emulated level generator is an emulated level operator which includes a counter cyclically counting from 1 to the repetitive frame number, and generates the output level data to the display panel according to the counted value from the counter, the previous level data from the frame memory and the input level data of the input image data. 
     The display control device according to the present invention allows the output level to change gently with time so as to minimize discontinuity and smoothen displayed image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  is a functional diagram illustrating a display control device according to an embodiment of the present invention; 
         FIG. 2  is a table summarizing input and output level changes during a series of frame time points in the embodiment of  FIG. 1 ; 
         FIG. 3  is a plot showing level changes of  FIG. 2  with curves; 
         FIG. 4  is a functional diagram illustrating a display control device according to another embodiment of the present invention; 
         FIG. 5  is a table summarizing input and output level changes during a series of frame time points in the embodiment of  FIG. 4 ; and 
         FIG. 6  is a plot showing level changes of  FIG. 5  with curves. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a display control device according to an embodiment of the present invention. In this embodiment, a conventional LCD panel well known to those ordinary in the art is used with the present display control device and is thus not to be redundantly shown in the figure and described in detail. 
     Receiving an input image data, a contents frame rate detector  10  detects a frame rate of the input image data, e.g. 15 frames/sec for a one seg image or 24 frames/sec for a movie image, and outputs a repetitive frame number Nfrm relative to the 60 frames/sec standard display rate of the display device. Given that the contents frame rate is 30 frames/sec, Nfrm=2; and Given that the contents frame rate is 15 frames/sec, Nfrm=4. 
     The repetitive frame number Nfrm is then inputted into a lookup table (LUT) selector  20  to find a lookup table corresponding to the repetitive frame number Nfrm. For example, a lookup table LUT 1  is selected for Nfrm=2; and another lookup table LUT 2  is selected for Nfrm=4. 
     According to the selected lookup table, an emulated gray level Gemu corresponding to a gray level Gn of the input image and a previous gray level Gn-1 obtained from a frame memory  30  is realized and outputted to the display panel. Meanwhile, the value of the emulated gray level Gemu is stored into the frame memory  30  to replace the value of the previous gray level Gn-1. 
       FIG. 2  illustrates gray level changes with time in an example that the input image is a one seg image, wherein the repetitive frame number Nfrm is 4, and the corresponding lookup table is LUT 2 . Respective input and output gray levels of eleven frame time points  0 ˜ 10  are illustrated. 
     Provided that the input level at the frame time point  0 , i.e. indicative of black, the input level and output level for repetitive four frame time points  0 ˜ 3  are all zero. 
     While entering the frame time point  4 , the input level is changed to 63, i.e. white, and the emulated level value outputted from the lookup table LUT 2  is 8. This level value 8 is stored into the frame memory  30  as a previous level Gn-1 and corresponds to an output level value 32 at the frame time point  5  according to the LUT 2 . Likewise, the output level value is 56 at the frame time point  6 , and the output level value is 63 at the frame time point  7 . 
     In  FIG. 3 , input level changes and output level changes as shown in  FIG. 2  are revealed as curves. As shown, the input level is dramatically changed from black to white gray level when time goes from the frame time point  3  to frame time point  4 . In contrast, the output level gently changes from black to white gray level during the advancement of time from the frame time point  3  to frame time point  7 . In this way, there would not be dramatic level change even if contents with a low frame rate are displayed by a display device with a high response speed. Accordingly, discontinuous action can be minimized and smooth image can be displayed. 
     In another example that the input image is of a film type having the frame rate of 24 frames per second, the repetitive frame number Nfrm is 60/24=2.5, either the lookup table corresponding to the repetitive frame number Nfrm=2 or the lookup table corresponding to the repetitive frame number Nfrm=3 can be used. Alternatively, the lookup table corresponding to Nfrm=2 and the lookup table corresponding to Nfrm=3 can be mixed or alternately used frame by frame so as to further improve display quality. 
     In brief, the above embodiment of the present invention smoothens the displayed image by setting lookup tables varying with repetitive frame numbers, detecting a repetitive frame number, and selecting a lookup table corresponding to the detected repetitive frame number. 
       FIG. 4  illustrates a display control device according to another embodiment of the present invention. In this embodiment, the contents frame rate detector  10  and frame memories  30  similar to those used in the embodiment of  FIG. 1  are used, and in addition, the display control device further includes an emulated level operator  40  in lieu of the LUT selector  20  of  FIG. 1 . In the emulated level operator  40 , a frame counter  41  is disposed. The frame counter  41  accumulatively counts from 1 to the repetitive frame number Nfrm, and then repeats the counting from 1 to the repetitive frame number Nfrm. 
     For calculating level changes, it is set Gemu=Gn-1+(Gn−Gn-1)*k/Nfrm, where k is a counted value of the frame counter  41  and ranged from 1 to the repetitive frame number Nfrm. 
       FIG. 5  illustrates gray level changes with time in an example that the input image is a one seg image, wherein the repetitive frame number Nfrm is 4. Respective input and output gray levels of eleven frame time points  0 ˜ 10  are illustrated. Similar to the embodiment shown in FIG.  2 , the input level is 0 (black) during frame time points  0 ˜ 3  and becomes 83 (white) at the frame time point  4 . 
     Referring back to  FIG. 4 , the emulated level operator  40  calculates the output level value to the display panel based on the value Nfrm from the contents frame rate detector  10 , the gray level Gn of the input image, and the value Gn-1 stored in the frame memories  30 . In this embodiment, the input level value is stored into the frame memory  30  as the value Gn-1 whenever the frame counter  41  counts up to the value Nfrm. For example, in each of the frame time points  0 ˜ 3 , the initial value stored in the frame memory  30  is 0 and the gray level Gn of the input image is also 0, the output level value to the display panel is 0 accordingly (Gemu=0+(0−0)*k/4=0). Afterwards, at the frame time point  4 , the input level value becomes 63, but the level values stored in the frame memory through the frame time point  6  are still 0 because the counted value has not reached the repetitive frame number  4 . Once the counted value reaches 4 at the frame time point  7 , the input level value 63 is stored into the frame memory. 
     The emulated level values at the frame time points  4 ˜ 7  are then calculated based on the formula of Gemu=Gn-1+(Gn−Gn-1)*k/Nfrm, and realized as follows by way of round up or round down or truncation.
 
0+(63−0)×1÷4=16  Frame time point 4
 
0+(63−0)×2÷4=32  Frame time point 5
 
0+(63−0)×3÷4=47  Frame time point 6
 
0+(63−0)×4÷4=63  Frame time point 7
 
The emulated levels are outputted to the panel for display.
 
     The level values stored in the frame memory at the frame time points  8  through  10  are all 63. Accordingly the emulated levels Gemu outputted to the panel are equal to 63+(63−63)*k/Nfrm=63. 
       FIG. 6  shows the gentle change of the output levels while the input levels dramatically changes from black to white gray level. 
     In this embodiment, no lookup table is required. Furthermore, it does not matter if the repetitive frame number is an integer or not. 
     It is understood that the output level may change following a reasonable curve such as a secondary curve, a parabolic curve, etc., even though it changes linearly in this embodiment. 
     To sum up, the display control device according to the present invention helps in displaying contents with a low frame rate smoothly in a display with a high response speed. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.