Patent Publication Number: US-7218305-B2

Title: Liquid crystal display and computer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a liquid crystal display and a computer, particularly but not limited to, an active matrix liquid crystal display suitable for the display of a dynamic image and a computer suitably used with the liquid crystal display. The present application is based on Japanese Patent Application No. 314274/2000, which is incorporated herein by reference. 
     2. Description of the Related Art 
     Recently, the display screen of a liquid crystal display (LCD) has been enlarged and the definition has been enhanced. A displayed image ranges from a static image as in a liquid crystal display used for a personal computer, a word processor and the like, to a dynamic image as in a liquid crystal display used for TV and the like. Since the compression technology for dynamic images has progressed and a dynamic image can now be also easily handled in a computer, a frequency at which a dynamic image is displayed also increases in a liquid crystal display used for a personal computer and the like. It is conceivable that as LCD is thin, compared with TV provided with a cathode ray tube (CRT), and can be installed without occupying a large place, the ratio of popularization of LCD TVs in the general home will increase in the future. 
       FIG. 1  is a block diagram showing the schematic structure of a liquid crystal display as a related art. In  FIG. 1 , a case that a computer  100  such as a personal computer and a liquid crystal display  110  are separately provided is shown as an example. As shown in  FIG. 1 , gradation data D 100  and synchronism data D 101  are output from the computer  100  to the liquid crystal display  110 . For example, gradation data D 100  means an RGB signal and synchronism data D 101  is data including a vertical synchronizing signal, a horizontal synchronizing signal, a data enable signal (DE) and a clock. 
     The liquid crystal display  110  includes an LCD controller  112 , a liquid crystal display panel  114 , a signal line driving circuit  116 , a scanning line driving circuit  118 , a reference gradation voltage generator  120 , a backlight  122  and an inverter for the backlight  124 . The LCD controller  112  generates gradation data D 110  and a signal side control signal D 111  respectively output to the signal line driving circuit  116  based upon gradation data D 100  and synchronism data D 101  respectively output from the computer  100 . The LCD controller  112  also generates a scanning side control signal D 112  output to the scanning line driving circuit  118  and controls the displayed contents of an image displayed on the liquid crystal display panel  114 . 
     Referring to  FIG. 2 , the structure of the liquid crystal display panel  114  will be described below.  FIG. 2  shows an example of the structure of an active matrix LCD as a related art. Though the first and second glass substrates are not shown in  FIG. 2 , LCD is provided with the first and second glass substrates. On the first glass substrate, n scanning lines  131  (n: natural number) and m signal lines  132  (m: natural number) are arranged in a grid and a thin film transistor (TFT)  133  which is a nonlinear device (a switching device) is provided in the vicinity of each cross-point of the scanning line  131  and the signal line  132 . 
     The gate electrode of TFT  133  is connected to the scanning line  131 , the source electrode is connected to the signal line  132  and the drain electrode is connected to a pixel electrode  134 . The second glass substrate is arranged in a position opposite to the first glass substrate and a common electrode  135  is formed on one surface of the glass substrate by a transparent electrode such as an indium-thin-oxide (ITO) film. Each common electrode  135  is connected to a common electrode driving circuit  136  and the electric potential is set by the common electrode driving circuit  136 . Liquid crystal is filled between the common electrode  135  and the pixel electrode  134  formed on the first glass substrate. 
     The scanning line  131  and the signal line  132  are respectively connected to the scanning line driving circuit  118  and the signal line driving circuit  116 . The scanning line driving circuit  118  executes scanning by sequentially applying high potential to n scanning lines  131  and turns on the TFT  133  connected to each scanning line  131 . Gradation voltage is written to the pixel electrode  134  via turned-on TFT  133  when the signal line driving circuit  116  outputs gradation voltage. The signal line driving circuit  116  outputs gradation voltage according to image data to one of the m signal lines  132  while the scanning line driving circuit  118  turns on the scanning line  131 . The amount of transmitted light is controlled based upon potential difference between the common electrode  135  set to a fixed potential and the gradation voltage written to the pixel electrode  134 . 
     As shown in  FIG. 1 , the liquid crystal display  110  is provided with the backlight  122  and the inverter for the backlight  124  for supplying power to the backlight  122 . As the backlight  122  emits light at fixed luminance in a state in which the liquid crystal display  110  is operated, the amount of transmitted light emitted from the backlight  122  is controlled and display is made according to the above-mentioned operational principle. The reference gradation voltage generator  120  shown in  FIG. 1  supplies reference gradation voltage to the signal line driving circuit  116 . 
       FIG. 3  shows the waveforms of signals output from the scanning line driving circuit  118  and the signal line driving circuit  116 , which are respectively provided to the scanning line  131  and the signal line  132  in the conventional type liquid crystal display. In  FIG. 3 , an x-axis shows time and VG 1  to VGn respectively show the waveform of a scanning signal applied to each scanning line  131 . As shown in  FIG. 3 , high potential is applied to only one scanning line  131  at a time and the scanning signals VG 1  to VGn are signals sequentially output to n scanning lines  131 . VD shows the waveform of a signal output to one signal line  132  and Vcom shows the waveform of a signal applied to the common electrode  135 . In an example shown in  FIG. 3 , the signal strength of the signal VD varies according to each image data, and the signal Vcom has a fixed value and is a signal which does not vary with time. 
     The liquid crystal display of the related art and its driving method are described above. However, in the liquid crystal display of the related art, voltage applied to each pixel electrode  134  is held until the scanning line is selected next, thereby fixing transmitted light for one frame period. In the meantime, CRT sequentially scans using an electronic beam. In case a dynamic image is displayed on this LCD, a problem occurs in that the image quality deteriorates due to causes such as a residual image phenomenon. The cause of this deterioration is thought to be because the speed of a response of liquid crystal material is slow. As a result, when gradation varies, the variation of gradation cannot be completed in one field period and an accumulative response is performed in a few field periods. One approach to preventing this deterioration has involved the research of various liquid crystal materials that enable a high speed response. 
     However, it has been reported that the above-mentioned problems such as the residual image phenomenon are not caused by only the speed of the response of liquid crystal, but are also caused by the methods used to change the image displayed on LCD. Such reports have been made by NHK Broadcast Technical Research Institute and others (for example, refer to pp. 207 and 208 of SC-8-1 at 99&#39; General Meeting of The Institute of Electronics, Information and Communication Engineers). To address the problems caused by the conventional methods used to change the image displayed on LCD, a method of driving CRT and a method of driving LCD will be described and compared below. 
       FIGS. 4A and 4B  show the result of comparison between CRT and LCD in the time response of display light at a certain pixel.  FIG. 4A  shows the time response of CRT and  FIG. 4B  shows the time response of LCD. As shown in  FIG. 4A , CRT is a so-called “impulse display” that emits light only for a few milliseconds since an electronic beam reaches a fluophor on the surface of the tube, while LCD shown in  FIG. 4B  is a so-called “hold-type display” that holds display light for one field period since the writing of data to a pixel is finished until the next writing is started. 
     When a dynamic image is displayed on CRT and LCD respectively having such characteristics, display as shown in  FIGS. 5A and 5B  are made.  FIGS. 5A and 5B  show examples of when a dynamic image is respectively displayed on CRT and LCD,  FIG. 5A  showing the example of CRT, and  FIG. 5B  showing the example of LCD. In  FIGS. 5A and 5B , a circular display object moves in a direction shown by x. As shown in  FIG. 5A , a display object is instantaneously displayed in a position corresponding to time on CRT, while an image before one field remains until immediately before new writing on LCD. 
     In case a person looks at a dynamic image displayed as shown in  FIGS. 5A and 5B , the dynamic image is viewed as shown in  FIGS. 6A and 6B .  FIGS. 6A and 6B  are explanatory drawings for explaining an image viewed by a person when a dynamic image is displayed on CRT and LCD,  FIG. 6A  showing a case of CRT and  FIG. 6B  showing a case of LCD. As shown in FIG.  6 A, when a dynamic image is displayed on CRT, it is never viewed that an image displayed at a certain time is overlapped with an image from before that time. However, when a dynamic image is displayed on LCD, an image currently displayed is viewed in a state in which it, and an image displayed immediately before it, are overlapped due to the visual time integral effect and other effects, causing movement to become dim. 
     Some methods have been proposed for reducing the hold time of the displayed image by inputting voltage corresponding to a black image, prior to inputting voltage according to image data into each pixel electrode  134  of the liquid crystal display panel  114 . Such proposed methods prevent movement from being dim, thereby solving the above-mentioned problems caused when a dynamic image is displayed on LCD.  FIGS. 7A to 7D  are explanatory drawings for explaining a method of preventing movement from being dim by inserting a black image between each image data. This method basically prevents movement from being dim by applying predetermined voltage for black display to liquid crystal for a horizontal blanking period as shown in  FIG. 7A . That is, after an image in one field is displayed, black is displayed on the whole screen and an image in the next field is displayed. However, according to this method, as display time is different for each respective scanning line of the liquid crystal display panel  114 . This difference in display time causes a problem in that luminance difference depends upon the location on the liquid crystal display panel  114  as shown in an example in  FIG. 7C . 
     A method of preventing luminance difference from being caused is proposed in Japanese published unexamined patent applications No. Hei. 9-127917, No. Hei. 10-62811 and Japanese published unexamined patent applications No. Hei. 11-30789.  FIG. 8  shows the structure of a liquid crystal display to solve the problem caused by the method shown in  FIG. 7A . This structure is proposed in the above-mentioned patent application No. Hei. 9-127917. The same reference number is allocated to the same member as that in the liquid crystal display shown in  FIG. 2 . 
     In  FIG. 8 , in addition to the circuit structure shown in  FIG. 2 , a circuit for writing black is newly provided, including: a black signal feeder  140 , a black signal supply line  141 , a scanning line for supplying a black signal  142 , TFT for supplying a black signal  143  and a scanning line driving circuit  144  for driving the scanning line  142  for supplying a black signal. The gate electrode of the TFT for supplying a black signal  143  is connected to the scanning line for supplying a black signal  142 , the source electrode of the TFT for supplying a black signal  143  is connected to the black signal supply line  141  and the drain electrode is respectively connected to the drain electrode of TFT  133  and the pixel electrode  134 . 
     In the liquid crystal display having the above-mentioned configuration, voltage corresponding to black is applied to the pixel electrode  134  in one field, and afterward, voltage according to image data is applied to the pixel electrode  134 . Image data is reset by independently driving each scanning line as described above, and illustrated in the example shown in  FIG. 7B . That is, difference in luminance is prevented by resetting each scanning line independently, inserting black after each image is displayed, instead of resetting all of the scanning lines simultaneously as shown in  FIG. 7A . By resetting the scanning lines as shown in  FIG. 7B , the screen luminance differences can be prevented, as shown by the panel display in  FIG. 7D . 
     However, the deterioration of image quality such as a flicker occurs due to a black screen inserted also in the display of a static image, both in the method shown in  FIGS. 7A and 7C  and in the device shown in  FIG. 8 , even though a hold-type display is suited for the display of the static image. Also, because the brightness of a display screen is reduced when a black screen is inserted, the luminance of the backlight is required to be set to a high value so as to acquire the brightness of the same extent as the brightness acquired in case no black screen is inserted. This increase in the luminescence of the back light increases power consumption, which is also a problem. 
     A liquid crystal display in the present invention may display a dynamic image without dim movement or without the deterioration of luminance. A liquid crystal display in the present invention also may display a static image without needless power consumption or without the deterioration of image quality such as a flicker. Further, a computer suitably used with the liquid crystal display is provided by the illustrative embodiment of the present invention. 
     SUMMARY OF THE INVENTION 
     A first aspect of an illustrative embodiment provides a liquid crystal display comprises a display panel, a back light irradiating said display panel; and a back light control circuit making a brightness of said back light brighter at a first period than at a second period, wherein said display panel displays a dynamic image at said first period, and wherein said display panel displays a static image at said second period. 
     A second aspect of the embodiment provides the liquid crystal display, wherein said back light control circuit controls said back light based on an image discriminating signal indicating an active state at said first period and an inactive state at said second period. 
     A third aspect of the embodiment provides the liquid crystal display comprising, a controller controlling said display panel in response to said image discriminating signal indicating said active state so that at least a part of said display panel displays a reset image. 
     A forth aspect of the embodiment provides the liquid crystal display, wherein said display panel comprises a plurality of cells, and wherein at least a part of said plurality of cells displays a single color as said reset image. 
     A fifth aspect of the embodiment provides the liquid crystal display, wherein said display panel comprises a scanning line, a signal line arranged substantially perpendicular to said scanning line, and a cell arranged at an intersection of said scanning line and said signal line, wherein at least a part of said cell displays a single color as said reset image. 
     A sixth aspect of the embodiment provides the liquid crystal display, wherein said controller activates a first scanning line at a first scanning period and provides an image data to a first signal line, and said controller activates a second scanning line at a second scanning period and provides a reset data to said first signal line, and wherein said first period and said second period are included in a basic period for scanning said scanning line. 
     A seventh aspect of the embodiment provides the liquid crystal display, further comprises at least one of a third scanning line arranged between said first scanning line and said second scanning line. 
     A eighth aspect of the embodiment provides the liquid crystal display, further comprising, an input terminal receiving said image discriminating signal and providing said image discriminating signal to said controller and said back light control circuit. 
     A ninth aspect of the embodiment provides the liquid crystal display, wherein said image discriminating signal indicates said active state when a ratio of an area of said display panel to an area of said dynamic image is larger than a threshold value. 
     A tenth aspect of the embodiment provides the liquid crystal display, wherein said controller receives a dynamic image data at said first period and a static image data at said second period, and wherein said controller controls said display panel to display a dynamic image corresponding to said dynamic image data at said first period and to display said static image corresponding to said static image data at said second period. 
     A eleventh aspect of the embodiment provides the liquid crystal display, further comprising: a computer comprising, a memory storing said threshold value; and a detector and comparator detecting said ratio of said area of said display panel and to said area of said dynamic image, comparing said ratio to said threshold value, and providing said image discriminating signal into said controller and said back light control circuit, wherein said image discriminating signal indicates said active state when said ratio is larger than said threshold value. 
     A twelfth aspect of the embodiment provides the liquid crystal display, wherein said image discriminating signal indicates said inactive state when said ratio is smaller than said threshold value. 
     A thirteenth aspect of the embodiment provides the liquid crystal display, further comprising, an image discriminating unit receiving an image data and providing said image discriminating data indicating said active state into said back light control circuit when said image data comprises a dynamic image data, wherein said dynamic image data corresponds to said dynamic image. 
     A fourteenth aspect of the embodiment provides the liquid crystal display, wherein said image discriminating unit provides said image discriminating data indicating said inactive state into back light control circuit when said image data comprises a static image data, and wherein said static image data corresponds to said static image. 
     A fifteenth aspect of the embodiment provides the liquid crystal display, wherein said image data comprises a first part of said image data corresponding to a first frame and a second part of said image data corresponding to a second frame, and wherein said image discriminating unit comprises a memory storing said first part of said image data at said first frame, and a comparator comparing said first part of said image data with said second part of said image data at said second frame, and detecting that said image data comprises said dynamic image data when said first part of said image data is different from said second part of said image data. 
     A sixteenth aspect of the embodiment provides the liquid crystal display, wherein said comparator detects that said image data comprises said static image data when said first part of said image data is the same as said second part of said image data. 
     A seventeenth aspect of the embodiment provides the liquid crystal display, wherein said image data comprises a first part of said image data corresponding to a first frame and a second part of said image data corresponding to a second frame, and wherein said image discriminating unit divides said first part of said image data into a first plurality of partial data corresponding to a plurality of detecting blocks of said display panel and said second part of said image data into a second plurality of partial data corresponding to a plurality of detecting blocks of said display panel. 
     A eighteenth aspect of the embodiment provides the liquid crystal display, wherein said image discriminating unit comprises a memory storing said first part of said image data at said first frame, and a comparator detecting said first plurality of partial data at said first frame which is different from said second plurality of said second data at said second frame, providing a number of detected said first plurality of partial data at said first frame, and providing said image discriminating signal indicating said active state when said number is larger than a predetermined value. 
     A nineteenth aspect of the embodiment provides the liquid crystal display, wherein said image data comprises a first part of said image data corresponding to a first frame and a second part of said image data corresponding to a second frame, and wherein said image discriminating unit define a first plurality of partial data corresponding to a plurality of detecting points of said display panel in said first part of said image data and a second plurality of partial data corresponding to a plurality of detecting points of said display panel in said second part of said image data. 
     A twentieth aspect of the embodiment provides the liquid crystal display, wherein said image discriminating unit comprises a memory storing said first part of said image data at said first frame, and a comparator detecting said first plurality of partial data at said first frame which is different from said second plurality of said second data at said second frame, providing a number of detected said first plurality of partial data at said first frame, and providing said image discriminating signal indicating said active state when said number is larger than a predetermined value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the illustrative, non-limiting embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing the schematic structure of a conventional type liquid crystal display; 
         FIG. 2  shows an example of the structure of conventional type active matrix LCD; 
         FIG. 3  shows the waveforms of signals output from a scanning line driving circuit  118  and a signal line driving circuit  116  to a scanning line  131  and a signal line  132  in the conventional type liquid crystal display in  FIG. 2 ; 
         FIG. 4A  shows the result of comparison in time response of display light in a pixel of a CRT; 
         FIG. 4B  shows the result of comparison in time response of display light in a pixel of a LCD; 
         FIG. 5A  shows display examples of each image in case a dynamic image is displayed on a CRT; 
         FIG. 5B  shows display examples of each image in case a dynamic image is displayed on a LCD; 
         FIG. 6A  is an explanatory drawing for explaining an image viewed by a person when a dynamic image is displayed on a CRT; 
         FIG. 6B  is an explanatory drawing for explaining an image viewed by a person when a dynamic image is displayed on a LCD; 
         FIG. 7A  is an explanatory drawing for explaining a method of inserting a black image between each image data and preventing dim movement; 
         FIG. 7B  is an explanatory drawing for explaining a method of inserting a black image between each image data and preventing dim movement; 
         FIG. 7C  is an explanatory drawing for explaining a method of inserting a black image between each image data and preventing dim movement; 
         FIG. 7D  is an explanatory drawing for explaining a method of inserting a black image between each image data and preventing dim movement; 
         FIG. 8  shows the structure of a liquid crystal display to solve a problem caused by the method shown in  FIG. 7C ; 
         FIG. 9  is a functional block diagram showing the schematic structure of a liquid crystal display equivalent to a first embodiment of the invention; 
         FIG. 10  shows the structure of a liquid crystal display panel  44  and the waveforms of a part of signals output from a signal line driving circuit  46  and a scanning line driving circuit  48  to the liquid crystal display panel  44 ; 
         FIG. 11  shows the contents instantaneously displayed on the liquid crystal display panel  44  when a dynamic image is displayed; 
         FIG. 12  shows a concrete example of various signals output from an LCD controller  42  to the signal line driving circuit  46  and the scanning line driving circuit  48 ; 
         FIG. 13  is a timing chart showing various signals output from the LCD controller  42  when a static image is displayed; 
         FIG. 14  is a timing chart showing various signals output from the LCD controller  42  when a dynamic image is displayed; 
         FIG. 15  is an explanatory drawing for explaining a principle to judge whether an image displayed on the liquid crystal display panel  44  is a dynamic image or not based upon the area ratio of the liquid crystal display panel  44  and a window; 
         FIG. 16  is a functional block diagram showing the structure of a liquid crystal display equivalent to a third embodiment of the invention; 
         FIG. 17  is a functional block diagram showing the internal structure of an image discriminating circuit  60 ; 
         FIG. 18A  is an explanatory drawing for explaining the operation of the image discriminating circuit; and 
         FIG. 18B  is an explanatory drawing for explaining the operation of the image discriminating circuit. 
     
    
    
     BRIEF DESCRIPTION OF THE EMBODIMENTS 
     The following description of the embodiments discloses specific configurations, features, and operations. However, the embodiments are merely examples of the present invention, and thus, the specific features described below are merely used to more easily describe such embodiments and to provide an overall understanding of the present invention. Accordingly, one skilled in the art will readily recognize that the present invention is not limited to the specific embodiments described below. Furthermore, the descriptions of various configurations, features, and operations of the present invention that would have been known to one skilled in the art are omitted for the sake of clarity and brevity. 
       FIG. 9  is a functional block diagram showing the schematic structure of a liquid crystal display according to a first illustrative, non-limiting embodiment of the present invention. In the first embodiment as shown in  FIG. 9 , a computer  30  such as a personal computer and the liquid crystal display  40  are separately provided. The computer  30  outputs gradation data D 10 , synchronism data D 11  and an image discriminating signal J 1  to the liquid crystal display  40 . 
     The gradation data D 10  and the synchronism data D 11  are respectively similar signals to gradation data D 100  and synchronism data D 101  shown in  FIG. 1 . For example, the gradation data D 10  is an RGB signal, and the synchronism data D 11  is data including a vertical synchronizing signal, a horizontal synchronizing signal, a data enable signal (DE) and a clock. The image discriminating signal J 1  is a signal of one bit showing whether image data (a signal composed of the gradation data D 10  and the synchronism data D 11 ) outputted from the computer  30  to the liquid crystal display  40  is a dynamic image or not. 
     The image discriminating signal J 1  at a high level indicates that image data is a dynamic image and its at a low level indicates that image data is a static image. The image discriminating signal J 1  may be set so that the value is at a high level, for example, when an application for handling a dynamic image is run in the computer  30 . Also, in another example, the value may be set to a high level when the computer  30  comprises a TV tuner and the image data are based upon a signal output from the TV tuner. Further, in another example, the value may be also set manually by a user of the computer  30 . 
     The liquid crystal display  40  includes an LCD controller  42 , a liquid crystal display panel  44 , a signal line driving circuit  46 , a scanning line driving circuit  48 , a reference gradation voltage generator  50 , a backlight  52 , an inverter for the backlight  54  and a backlight control circuit  56 . The LCD controller  42  generates gradation data D 20  and a signal side control signal D 21  outputted to the signal line driving circuit  46 , which are based respectively upon the gradation data D 10  and the synchronism data D 11  outputted from the computer  30 . The LCD controller  42  also generates a scanning side control signal D 22  outputted to the scanning line driving circuit  48  and controls image display contents on the liquid crystal display panel  44 . 
     The liquid crystal display  40  comprises the discriminating signal input terminal  57  for outputting the image discriminating signal J 1 , outputted from the computer  30 , to the LCD controller  42  and the backlight control circuit  56 . 
     The LCD controller  42  controls the signal line driving circuit  46  and a scanning line driving circuit  48 , to define whether a black display is performed or not based upon the image discriminating signal J 1  when a dynamic image is displayed to prevent movement from being dim. The black display causes a deterioration of the luminance in the liquid crystal display panel  44 , without regards to a dynamic image or a static image. The black display is required when the dynamic image is displayed in order to prevent movement from being dim. However, black display is not required when the static image is displayed because no movement is made in a static image. Then, the LCD controller  42  defines whether the gradation data D 10  and the synchronism data D 11  are for the dynamic image or for the static image based upon the image discriminating signal J 1 , and it controls the signal line driving circuit  46  and a scanning line driving circuit  48  so that the black display is not performed and an line-sequential driving is performed when a static image is displayed. 
     The backlight control circuit  56  outputs a control signal for controlling the luminance of light emitted from the backlight  52  for illuminating the rear surface of the liquid crystal display panel  44  to the inverter for the backlight  54  based upon the image discriminating signal J 1  input via the discriminating signal input terminal. Concretely, in case the image discriminating signal J 1  indicates a dynamic image, the luminance of light emitted from the backlight  52  is set to a high value to prevent the deterioration of display luminance caused due to black display for preventing movement from being dim. In the meantime, in case the image discriminating signal shows a static image, the luminance of light emitted from the backlight  52  is set to a low value from the viewpoint of the reduction of power consumption because the LCD controller  42  controls so that black display is not made. The reference gradation voltage generator  50  is similar to the reference gradation voltage generator  120  shown in  FIG. 1 . 
     Next, referring to  FIG. 10 , the structure of the liquid crystal display panel  44  will be described.  FIG. 10  shows the structure of the liquid crystal display panel  44  and the waveforms of a part of signals output from the signal line driving circuit  46  and the scanning line driving circuit  48  to the liquid crystal display panel  44 . The waveforms of the signals shown in  FIG. 10  are those of signals respectively output from the signal line driving circuit  46  and the scanning line driving circuit  48  when a dynamic image is displayed and in the case of a static image, the waveforms of the similar signals to the waveforms shown in  FIG. 3  are output and line-sequential driving is performed. 
     The liquid crystal display panel  44  shown in  FIG. 10  is provided with first and second glass substrates as in the liquid crystal display  114  shown in  FIG. 2 . On the first glass substrate, n scanning lines  2  (n: natural number) and m signal lines  3  (m: natural number) are arranged in a grid, and TFT  4  which is a nonlinear device (a switching device) is provided in the vicinity of each cross-point of a scanning line  2  and a signal line  3 . 
     The gate electrode of TFT  4  is connected to the scanning line  2 , the source electrode is connected to the signal line  3  and the drain electrode is connected to a pixel electrode  5 . The second glass substrate is arranged in a position opposite to the first glass substrate and a common electrode  6  is formed on one surface of the glass substrate by a transparent electrode such as ITO. Liquid crystal is filled between the common electrode  6  and the pixel electrode  5  formed on the first glass substrate. 
     Scanning signals VG 1  to VGn in  FIG. 10  are applied to each of the scanning lines  2 , respectively. A signal VD in  FIG. 10  corresponding to image data is applied to the signal line  3 . As shown in  FIG. 10 , each of the scanning signals VG 1  to VGn includes two scanning line selection periods which are a selection period for image data t 1  and a selection period for black display t 2  in one field. For a selection period for image data t 1 , writing gradation voltage according to image data is loaded to the pixel electrode  5 . For a selection period for black display t 2 , writing voltage according to black display is loaded to the pixel electrode  5 . Gradation voltage according to image data and voltage according to black display are alternately outputted to each signal line  3 . 
     The selection period for black display t 2  which is one characteristic of the first embodiment is corresponding to approximately a half of a conventional scanning line selection period t 3  as shown in  FIG. 10 . For example, scanning line G 1  is selected at the selection period for image data t 1 , and then the scanning line Gj, which is separated from the scanning line G 1  by at least one other scanning line G 2 , is selected for black display at the selection period for black display t 2 . Voltage according to black display is applied to the signal line  3  in the selection period for black display t 2 , a black screen which is called a “reset image” is displayed because liquid crystal capacitance  7  shields light from the backlight  52 . As describe above, scanning line  2  is selected individually for black display, which is so-called “reset driving”, instead of selecting all scanning line for black display at the same time. 
     Next, the operation of the liquid crystal display in the first illustrative embodiment will be described in detail. In the following description, each of plural scanning lines  2  is discriminated using G 1  to Gn and each of signals  3  is discriminated using D 1  to Dm. Suppose that the display of image data is made in the order of the scanning line G 1 , G 2 , - - - and black display is made from the ‘j’th (j: natural number: 1&lt;j≦n) scanning line Gj. 
     First, the scanning line G 1  is selected for the selection period for image data t 1  and in this state, gradation voltage according to image data is applied to the signal line D 1 . TFT  4  connected to the scanning line G 1  is turned on and the display of the liquid crystal capacitance  7  begins to display according to image data. Next, the scanning line Gj is selected for the selection period for black display t 2  and in this state, voltage according to black display is applied to the signal line  3 . When this voltage is applied, TFT  4  connected to the scanning line Gj is turned on and the liquid crystal capacity  7  becomes black. 
     The selection period for black display t 2  of the scanning line Gj elapses, and then the scanning line G 2  is scanned and the similar operation to a case in which the scanning line G 1  is scanned is executed. The scanning line Gj+1 is scanned next to the scanning line G 2  and the similar operation to a case in which the scanning line Gj is scanned is executed. Afterward, similarly, the scanning line  2  is selected in the order of the scanning line G 3 , Gj+2, - - - . A band black screen display area shown in  FIG. 11  is displayed on the liquid crystal display panel  44  by such a driving method. 
       FIG. 11  shows the contents displayed instantaneously on the liquid crystal display panel  44  when a dynamic image is displayed. As shown in  FIG. 11 , in case the selection period for black display t 2  is set to substantially the center of the liquid crystal display panel  44 , one screen is composed of three display areas of a normal image display area A 1 , a black screen display area A 2  and a normal image display area A 3 . As time elapses, the black screen display area A 2  is moved in a direction shown by an arrow D 1  in  FIG. 11 . When the black screen display area A 2  reaches the lower end of the liquid crystal display panel  44 , a part of the black screen display area A 2  is moved to the upper end of the liquid crystal display panel  44 , the area occupied by the black screen display area A 2  at the lower end decreases and the black screen display area A 2  is moved in the direction shown by the arrow D 1 , increasing area occupied by the black screen display area A 2  at the upper end. 
     As described above, in the first illustrative embodiment, black display prevents movement from being dim when a dynamic image is displayed. An interval between the scanning line selected in the selection period for black display t 2  and the scanning line selected in the selection period for image data is equivalent to the black screen display area A 2 . A rate occupied by the black screen display area A 2  on one screen is set to a degree at which dim movement is not identified when a dynamic image is displayed. The black screen display area A 2  is scrolled by one scanning line  2  by making the above-mentioned black display as the normal image display areas A 1  and A 3 . Therefore, luminance is almost similar at any location on the display screen. 
     It is described that the selection period for black display t 2  is set after the selection period for image data t 1 . However, the selection period for image data t 1  may be set after the selection period for black display t 2 . 
     Next, the operation when a dynamic image is displayed and when a static image is displayed will be described, concretely showing gradation data D 20  output from the LCD controller  42  to the signal line driving circuit  46 , and the signal side control signal D 21  and the scanning side control signal D 22  output to the scanning line driving circuit  48 .  FIG. 12  shows a concrete example of various signals output from the LCD controller  42  to the signal line driving circuit  46  and the scanning line driving circuit  48 . Generally, in case a liquid crystal display has a large area according to XGA, the signal line driving circuit  46  and the scanning line driving circuit  48  are composed of plural members.  FIG. 12  shows a case that the scanning line driving circuit  48  shown in  FIG. 9  is composed of three scanning line driving circuits  48   a  to  48   c . The signal line driving circuit  46  is also composed of plural members, however, they are not shown in  FIG. 12 . 
     A scanning side start pulse (STV), a scanning side clock (VCLK) and an output control signal (OE) are output from the LCD controller  42  to each scanning line driving circuit  48   a  to  48   c . Gradation data (Data), a signal side start pulse (STH), a signal side clock (HCLK), a signal output pulse (STB) and a polarity inversion pulse (POL) are output from the LCD controller  42  to the signal line driving circuit  46 . As the LCD controller  42  controls by respectively outputting scanning side start pulses STV 1  to STV 3  to the scanning line driving circuits  48   a  to  48   c  and further, outputting output control signals OE 1  to OE 3 , the scanning line driving circuits  48   a  to  48   c  are separately controlled by the LCD controller  42 . 
     The scanning side start pulses STV 1  to STV 3  are respectively a pulse for instructing each scanning line driving circuit  48   a  to  48   c  to start scanning. That is, the scanning line driving circuit  48   a  starts scanning when the scanning side start pulse STV 1  is input, the scanning line driving circuit  28   b  starts scanning when the scanning side start pulse STV 2  is input, and the scanning line driving circuit  48   c  starts scanning when the scanning side start pulse STV 3  is input. If three scanning line driving circuits  48   a  to  48   c  are provided, one frame period is divided into three and the liquid crystal display panel  44  is scanned from the upside to the downside because the scanning line driving circuits  48   a ,  48   b  and  48   c  scan each divided frame period in the order. 
     The above-mentioned output control signals OE 1  to OE 3  are for controlling whether one scanning line is activated or deactivated in a period for scanning one scanning line, when the scanning line driving circuits  48   a  to  48   c  scan, for example, two scanning lines. That is, in the first embodiment, as described referring to  FIG. 10 , a period in which one scanning line is scanned is divided into the selection period for image data t 1  and the selection period for black display t 2 . A scanning line different from a scanning line activated to apply gradation voltage according to image data in the selection period for image data t 1  is activated to apply voltage according to black display in the selection period for black display t 2 . Therefore, in the selection period for image data t 1 , a scanning line to apply voltage according to black display in the selection period for black display t 2  is required to be deactivated and in the selection period for black display t 2 , a scanning line to apply gradation voltage according to image data in the selection period for image data t 1  is required to be deactivated. The output control signals OE 1  to OE 3  are used to control the above-mentioned activation and inactivation of scanning lines. 
     Next, the operation when a static image is displayed will be described. As described above, when a displayed image is a static image, a value of an image discriminating signal output from the computer  30  shown in  FIG. 9  is at a low level.  FIG. 13  is a timing chart showing various signals output from the LCD controller  42  when a static image is displayed. In  FIG. 13 , signals for one frame if the liquid crystal display panel  44  has 768 scanning lines are shown. VG 1 , VG 257  and VG 513  respectively show the waveforms of scanning signals applied to first, 257th and 513th scanning lines. In case 768 scanning lines are provided, the scanning line driving circuit  48   a  scans the first to the 256th scanning lines, the scanning line driving circuit  48   b  scans the 257th to the 512th scanning lines and the scanning line driving circuit  48   c  scans the 513th to the 768th scanning lines. 
     As shown in  FIG. 13 , when a static image is displayed, scanning side start pulses STV 1  to STV 3  are respectively output to the scanning line driving circuits  48   a  to  48   c  in one frame period only once. Therefore, line-sequential driving is performed by the scanning line driving circuits  48   a  to  48   c . As the control of the activation and inactivation of scanning lines in a period in which one scanning line is scanned is not required in case a static image is displayed, output control signals OE 1  to OE 3  are controlled so that they are always at a low level. As is clear from  FIG. 13 , when a static image is displayed, line-sequential driving is performed. That is, a scanning line is provided with fixed voltage in a period for scanning one scanning line and retained active. 
     When a static image is displayed, an image discriminating signal J 1 , the value of which is at a low level, is also input to the backlight control circuit  56  shown in  FIG. 9 . In this case, the backlight control circuit  56  sets the luminance of light emitted from the backlight  52  to the same extent as the luminance of light emitted from a backlight with which a conventional type liquid crystal display is provided. 
     Next, the operation when a dynamic image is displayed will be described. As described above, in case a displayed image is a dynamic image, a value of an image discriminating signal output from the computer  30  shown in  FIG. 9  is at a high level.  FIG. 14  is a timing chart showing various signals output from the LCD controller  42  when a dynamic image is displayed. In  FIG. 14 , signals for one frame in case the liquid crystal display panel  44  has 768 scanning lines are also shown and VG 1 , VG 257  and VG 513  respectively show the waveforms of scanning signals applied to first, 257th and 513th scanning lines. 
     As shown in  FIG. 14 , when a dynamic image is displayed, scanning side start pulses STV 1  to STV 3  are respectively output to scanning line driving circuits  48   a  to  48   c  twice in one frame period and two scanning lines are scanned at a time. When a dynamic image is displayed, control is required to be performed so that only one of the two scanning lines scanned at a time is activated in a period in which one scanning line is scanned. Therefore, output control signals OE 1  to OE 3  are signals, the cycle of which is set to a half of a period in which one scanning line is scanned, and the phase of which is inverse only once in one frame. It is for the following reasons that the phase of the output control signals OE 1  to OE 3  is inverse only once in one frame. 
     That is, as shown in  FIG. 12 , gradation voltage according to image data and voltage according to black display are alternately supplied to the signal line driving circuit  46  from the LCD controller  42  (refer to STH (Data) shown in  FIG. 14 ). In STH (Data) shown in  FIG. 14 , a location B is a location where voltage according to black display is supplied. In a state in which such a signal is supplied, as voltage applied to the pixel electrode  5  connected to a certain scanning line is required to be switched from gradation voltage according to image data to voltage according to black display and is required to be switched from voltage according to black display to gradation voltage according to image data, the inversion of the phase is made. In other words, to switch the selection period for image data t 1  and the selection period for black display t 2 , phase inversion is made. In an example shown in  FIG. 14 , each polarity of output control signals OE 1  to OE 3  is inverted in locations P 1  to P 3 . In the example shown in  FIG. 14 , black display is made on 256 scanning lines equivalent to one third of 768 scanning lines. 
     When a dynamic image is displayed, an image discriminating signal J 1 , the value of which is at a high level, is also input to the backlight control circuit  56  shown in  FIG. 9 . In this case, the backlight control circuit  56  controls so that the luminance of light emitted from the backlight  52  is set to a higher value than the luminance of light emitted from a backlight with which a conventional type liquid crystal display is provided. As described above, black display is made to prevent dim movement when a dynamic image is displayed. However, as the display luminance of the liquid crystal display panel  44  is deteriorated for black display, the deterioration of the display luminance is prevented by setting the luminance of light emitted from the backlight  52  to a high value. 
     In the above-mentioned embodiment, for the simplification of description, the case that the plural scanning line driving circuits  48   a  to  48   c  are provided and the scanning line connected to one of these circuits is set to the black screen display area A 2  (see  FIG. 11 ) is described. However, the area of the black screen display area A 2  on the display screen of the liquid crystal display panel  44  can be set to an arbitrary value. 
     Next, a second illustrative, non-limiting embodiment of the present invention will be described. In the first illustrative embodiment of the present invention, the display method and the backlight of the liquid crystal display are controlled based upon whether image data is a dynamic image or a static image. In case a dynamic image is displayed, it may be also displayed on a part of the liquid crystal display panel  44 . Dim movement caused in a hold-type display is caused by a difference between the amount of movement of a displayed dynamic image and the following kinetic competence of a person&#39;s eye. Therefore, it has been reported that the degree of dim movement is large when the mount of movement of a dynamic image is large on the liquid crystal display panel  44 , and that the degree of dim movement is small when the amount of the movement of a dynamic image is small on the liquid crystal display panel  44  (refer to pp. 207 and 208 of SC-8-1 at 99&#39; General Meeting of The Institute of Electronics, Information and Communication Engineers). 
     That is, when the dynamic image is displayed in a window, which is not a whole of the liquid crystal display panel  44 , but is a part of the liquid crystal display panel  44 , dim movement is not perceived so much, as long as the part of the liquid display panel  44  is proper size. That is because difference between the amount of the movement of a dynamic image and the following kinetic competence of a person&#39;s eye is small. Then, in the second embodiment of the present invention, the criterion of a display method of a liquid crystal display and the judgment of whether a backlight is controlled or not is based upon the area ratio of a liquid crystal display panel  44  and a window in which a dynamic image is displayed. That is, in case the area ratio of the liquid crystal display panel  44  and a window in which a dynamic image is displayed is a certain threshold or more, an image displayed on the liquid crystal display panel  44  is judged to be a dynamic image and an image discriminating signal J 1  is turned to a high level. In the meantime, in cases when the area ratio of the liquid crystal display panel  44  and a window in which a dynamic image is displayed is smaller than a certain threshold, an image displayed on the liquid crystal display panel  44  is judged to be a static image and the image discriminating signal J 1  is turned to a low level. 
       FIG. 15  explains a principle for judging whether an image displayed on the liquid crystal display panel  44  is a dynamic image or not based upon the area ratio of the liquid crystal display panel  44  and the window. In case a dynamic image is handled by a computer  30 , the processing speed is generally enhanced using an overlay function of hardware. As shown in  FIG. 15 , a reference number  70  denotes VRAM for temporarily storing image data. In VRAM  70 , an on-screen area SC 1  for temporarily storing image data for display and an off-screen area SC 2  for temporarily storing dynamic image information are provided. 
     In case an application that handles a dynamic image is activated, an area R 1  for defining in which position of the liquid crystal display panel  44  a dynamic image stored in the off-screen area SC 2  is displayed is secured in the on-screen area SC 1 . An area R 2  in the on-screen area SC 1  shows a display area of the liquid crystal display panel  44  for example. 
     Data showing key color (for example, black and dark blue) is stored in the area R 1 . In case a dynamic image is displayed, an overlay selection circuit  72  generates the image data Im read in the area R 1  in which data showing key color defined in the on-screen area SC 1  is stored of a dynamic image temporarily stored in the off-screen area SC 2 , and displays the image data Im on the liquid crystal display  40 . The above-mentioned structure is used heretofore to realize the overlay function. 
     In the second illustrative embodiment of the present invention, an area threshold memory for discriminating a dynamic image/a static image  74  and a key color area detecting/comparing circuit  76  are provided in addition to the above-mentioned configuration. The area threshold memory  74  stores a first predetermined threshold value to judge whether an image is a dynamic image or not. The first predetermined threshold value is an area ratio of the liquid crystal display panel  44  and the area R 1  which defines the display area of a dynamic image. The key color area detecting/comparing circuit  76  judges whether an image is a dynamic image or not by detecting the area R 1  data showing key color set in the on-screen area SC 1  is stored, calculating the area ratio of the area R 1  and an area R 2  showing the display area of the liquid crystal display panel  44  and comparing this area ratio with the first predetermined threshold value stored in the area threshold memory  74 , and outputs the result of the judgment as an image discriminating signal J 1 . An image judged to be a dynamic image includes an image in a part of which a dynamic image is included. 
     Next, a liquid crystal display according to a third illustrative, non-limiting embodiment of the present invention will be described.  FIG. 16  is a functional block diagram showing the structure of the liquid crystal display according to the third illustrative embodiment of the present invention. The liquid crystal display shown in  FIG. 16  is provided with an image discriminating circuit  60  for judging whether image data outputted from a computer  30  shows a dynamic image or not. The liquid crystal display shown in  FIG. 16  is different from the liquid crystal display according to the first illustrative embodiment shown in  FIG. 9  in that the image discriminating signal J 1  outputted from the computer  30  shown in  FIG. 9  is omitted. 
     In the first illustrative embodiment shown in  FIG. 9 , as the image discriminating signal J 1  is outputted from the computer  30 , a circuit for judging whether an image is a dynamic image or not is required to be provided in the computer  30 . However, in the third illustrative embodiment, as the liquid crystal display  40  itself is provided with the image discriminating circuit  60  that judges whether an image is a dynamic image or not and the structure of the computer  30  is not required to be changed, the third illustrative embodiment is suitable for device configuration. 
       FIG. 17  is a functional block diagram showing the internal structure of the image discriminating circuit  60 . The image discriminating circuit  60  is provided with a frame memory  62  and a comparison/determination circuit  64 . The frame memory  62  stores image data outputted from the computer  30  for one frame. The comparison/determination circuit  64  compares image data outputted from the computer  30  and image data previous by one frame stored in the frame memory  62  and judges whether an image is a dynamic image or not. 
     Next, the operation of the image discriminating circuit  60  will be described.  FIGS. 18A and 18B  are explanatory drawings for explaining the operation of the image discriminating circuit.  FIG. 18A  shows an example of image data previous by one frame stored in the frame memory  62 .  FIG. 18B  shows an example of the image data of a frame currently outputted from the personal computer  30 . In the example shown in  FIGS. 18A and 18B , a dynamic image of an automobile crossing in front and only movement of the automobile is shown. For such a dynamic image, the comparison/determination circuit  64  judges that image data outputted from the computer  30  is image data showing a dynamic image because image data is different between frames. 
     In the above-mentioned third embodiment, it is judged whether image data is a dynamic image or not based upon whether there is movement in two frames or not. However, the storage capacity of the frame memory  62  may be increased to store the image data of plural frames, and the plural frames may be compared in order to judge whether image data is a dynamic image or not. 
     In the above-mentioned third embodiment, image data is considered to be a dynamic image when there is any movement between frames. Therefore, an image discriminating signal J 1  may be turned to a high level even if a display area where a dynamic image is displayed is so small that it might not necessary to control the LCD controller  112  as described in the first embodiment. Then, a frame may be divided in to a plurality of blocks, which is a detection area, and it may be detected how many detection areas have movement, instead of comparing whole frames. When a number of detection areas which have movement is larger than or equal to a second predetermined threshold value, an image data should be judged to be a dynamic image. 
     A few detection points may be set in the frame for detecting movement, instead of defining detection areas in the frame. When a number of detection points which have movement is larger than or equal to a third predetermined threshold value, an image data should be judged to be a dynamic image. 
     The liquid crystal displays according to the embodiments of the present invention are described above. However, the present invention is not limited to the illustrative embodiments and the present invention may be freely changed in a scope of the present invention. For example, in the above-mentioned embodiments, black display is made by separating a period in which one scanning line is scanned into the selection period for image data t 1  and the selection period for black display t 2  so as to prevent dim movement. However, a method of black display is not limited to this and the embodiment can be also applied to the method described referring to  FIGS. 7A to 7D  and the liquid crystal display provided with the structure shown in  FIG. 8 . The invention is not limited to the case that black is displayed as the reset image and if dim movement can be prevented by displaying a single color as the reset image in a part of image data, the present invention can be applied, and one skilled in the art will readily know that the present invention can be applied to devices containing different layers and materials. Accordingly, other structural configurations may be used, without departing from the spirit and scope of the invention as defined in the claims. 
     As described above, according to the embodiment of the present invention, the luminance control circuit is provided to control the luminance of the backlight based upon whether a display image is a dynamic image or a static image. Therefore, the luminance may not be deteriorated even when a dynamic image is displayed. 
     Further, the display control circuit is provided to control so that a part or the whole of a dynamic image is turned to be a single color for a predetermined time based upon whether a displayed image is a dynamic image or a static image. Therefore, dim movement may be prevented. 
     When a static image is displayed, the display control circuit performs line-sequential driving, instead of turning a part of a static image or a whole of a static image into a single color. Therefore, the deterioration of image quality such as a flicker may be prevented. In addition, the deterioration of display luminance may also be prevented. As a result, as the luminance of the backlight is not required to be set to a high value, wasteful power consumption can be prevented.