Abstract:
A method of displaying a halftone image on a PDP display unit by using a frame division technique, the method comprising selecting display lines whose number is identical to the total number of said divided subfields, addressing for designating pixels of selected display lines to be displayed and displaying each subfield allocated for the said selected display lines; shifting by a predetermined number of display lines from said selected display lines for at least a sustain pulse period unit, selecting display lines, addressing for designating pixels to be displayed and displaying each subfield allocated for the said display lines; and repeating said shifting, said selecting, said addressing and said displaying steps until each of the subfields is completely displayed for all display lines; wherein display lines for which all subfields of one frame have been completely displayed for an idle period. According to the present invention, there is provided a driving method capable of preventing images in two frames from being viewed overlapped to a viewer when displaying a dynamic image by clarifying a boundary between adjacent frames in a multi-scan driving method within a sustaining pulse period.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of driving a plasma display panel and more particularly, to a method of driving an AC-type plasma display panel for displaying a dynamic image without intensity level disturbance and false color contours in a multi-scan driving method within a sustaining pulse period. 
     BACKGROUND OF THE INVENTION 
     Recently, a plasma display panel (referred to as “PDP” hereinafter) has advantageous characteristics capable of being utilized as a direct-view large HDTV display apparatus having large screen size but a small thickness and a wide viewing angle compared to other flat display devices. 
     A PDP is classified into a two-electrode type PDP in which an address discharge and a sustain discharge are performed by two electrodes and a three-electrode type PDP in which an address discharge and a sustain discharge are performed by three electrodes. 
     FIG. 1 is a schematic sectional view of a discharge cell of a typical PDP and FIG. 2 is a plan view of a three-electrode type of PDP. 
     The discharge cell  10  of the three-electrode type PDP  1  comprises two glass plates  12  and  13  arranged to be facing each other. On the first glass plate  13  the first electrode  14  (X electrode) and the second electrode  15  (Y electrode) are formed and arranged parallel to each other. The electrodes function as sustain electrodes. The first and second electrodes  14  and  15  are covered with a dielectric layer  18 . The upper surface of the dielectric layer  18  is covered with a MgO layer  21 , which protects the dielectric layer  18 . 
     On the second glass plate  12  a third electrode  16  is arranged orthogonal to the first and second electrodes  14  and  15 . The third electrode functions as a data electrode. A barrier rib  17  of a lattice or stripe shape is formed between the two glass plates  12  and  13  to define a discharge cell. A phosphor material  19  is coated on the surface of the third electrode and the inner surface of the barrier rib. 
     As shown in FIG. 2, a PDP display device using such three-electrode type PDP comprises a plurality of X electrodes and Y electrodes arranged parallel to each other and wherein Y electrodes are driven independently by separate Y scan driving circuits  4 - 1  to  4 -n coupled to a Y electrode sustain driving circuit and X electrodes are coupled in common and are driven by a common X electrode driving circuit  5 . 
     Data electrodes  16 - 1  to  16 -n arranged to be orthogonal to the X and Y electrodes are driven by a data driving circuit  6 . Also, each of separate Y electrode scan driving circuits  4 - 1  to  4 -n is coupled to the Y electrode sustain driving circuit  3  and generates a scan pulse and sustain pulse. 
     The Y electrode sustain driving circuit  3  generates a sustain discharge pulse and the generated sustain discharging pulse is applied to the Y electrodes  15 - 1  to  15 -n via the separate Y scan driving circuits  4 - 1  to  4 -n. 
     The common X electrode driving circuit  5  generates a sustaining pulse which is applied to the X electrodes. 
     The driving circuits  3 ,  5  and  6  are controlled by a control circuit (not shown) which is in turn controlled sequentially by a synchronization signal and then a display data signal. In FIG. 2, numeral  1  denotes a PDP and numeral  10  denotes a cell constructing the PDP 1 . 
     There have been proposed several driving methods for a multi-gradation display of such plasma display device. As an example, U.S. Pat. No. 5,541,618 (assigned to Fujitsu Limited.) discloses a driving method in which a frame displaying a single picture is divided into a plurality of subfields and each of the subfields is separated in an addressing period and a sustain period and in each of the subfields, after addressing, a sustaining operation is carried out to all display electrodes at the same time. 
     FIG. 3 shows a frame structure illustrating a conventional driving method. When scan lines are 480, a frame of a single picture is divided into eight subfields, and a time taken to perform an addressing operation within a frame of a single picture is approximately 11 to 12 microseconds. 
     Substantially, since a display time (sustaining time) when a viewer can view an image is approximately 5 to 6 microseconds, a display period (sustaining period) that contributes to the brightness of an image is only approximately 30%, resulting in a deterioration of picture brightness. In this case, increasing a frequency of sustain pulse in order to compensate for such deterioration of image brightness can be considered, however, it also causes an increase of the power consumption and a deterioration of driving reliability. 
     The present applicant has suggested a new driving method capable of solving such problems encountered by the conventional driving method (see PCT/KR98/00204 filed in the name of the present applicant). According to a basic feature of the above-suggested driving method, a frame is divided into a plurality of subfields, and display lines corresponding to the total number of the divided subfields are selected. Then, scan pulses corresponding to the total number of the divided subfields are applied sequentially within a single sustain pulse applied to Y scan sustain electrodes and thereby cells of selected display lines to be displayed are designated. Thereafter, the designated cells of selected display lines are displayed by the following sustain pulse. 
     Next, after one sustain pulse period, display lines which are downwardly or upwardly shifted from the above selected display lines by one line are selected. Then, scan pulses corresponding to the total number of the divided subfields are applied sequentially within a single sustain pulse applied to Y scan sustain electrodes and thereby cells of selected display lines to be displayed are designated. Thereafter, the designated cells of selected display lines are displayed by following sustain pulse. Continuously, by repeating the display of the subfields for the display lines by shifting one line as a unit one sustain pulse period until each of the subfields for all display lines are completely displayed, the display for a frame is completed. 
     In this manner, a feature of the above driving method enables scanning of other display lines simultaneously by sustaining them. In order to realize it most suitably, the number of sustain pulses for one frame should be set to be equal to that of the display lines. Also,when selecting display lines, positioning of selected display lines should be determined by considering the number of sustain pulses for each of the subfields. 
     Now, a feature of the above driving method will be described in detail with reference to FIGS. 4 and 5. For convenience of the description, it assumed that a single frame is divided into three subfields (SF 1 , SF 2 , and SF 3 ) and display lines are  7  lines (D 1  to D 7 ). Accordingly, it is possible to establish sustain periods in subfields SF 1 , SF 2 , and SF 3  to  1 ,  2  and  4 , respectively. Also, regarding the position of the display line selected firstly, it is possible to select the display lines D 1 , D 3  and D 7  in consideration of the sustain periods set for the subfields SF 1 , SF 2  and SF 3 . In FIG. 4, S 1  to S 7  represent sustain periods. 
     As shown in FIG. 4, firstly, display lines D 1 , D 3  and D 7  are selected, and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 1 , D 3  and D 7  are executed respectively. Next, selecting display lines D 2 , D 4  and D 1 , which are allocated downwardly by one display line from the above selected display lines D 1 , D 3  and D 7 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 2 , D 4  and D 1  are executed respectively. Next, selecting display lines D 3 , D 5  and D 2 , which are allocated downwardly by one display line from the above selected display lines D 2 , D 4  and D 1 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 3 , D 5  and D 2  are executed respectively. Next, selecting display lines D 4 , D 6  and D 3 , which are allocated downwardly by one display line from the above selected display lines D 3 , D 5  and D 2 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 4 , D 6  and D 3  are executed respectively. Next, selecting display lines D 5 , D 7  and D 4 , which are allocated downwardly by one display line from the above selected display lines D 4 , D 6  and D 3 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 5 , D 7  and D 4  are executed respectively. Next, selecting display lines D 6 , D 1  and D 5 , which are allocated downwardly by one display line from the above selected display lines D 5 , D 7  and D 4 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 6 , D 1  and D 5  are executed respectively. Finally, selecting display lines D 7 , D 2  and D 6 , which are allocated downwardly by one display line from the above selected display lines D 6 , D 1  and D 5 , and then the display of the subfields SF 1 , SF 2  and SF 3  for display lines D 7 , D 2  and D 6  are executed respectively. 
     At this time, the display of a previous frame for each of the display lines is completed together with selecting display lines for displaying the next frame, and then the display of the subfields of the next frame for display lines are executed. Thereby, the display of the subfields of the next frame and the display of the subfields of the previous frame are overlapped at the same time. In FIG. 4, when display lines D 2 , D 4 , D 5  and D 6  display subfields SF 2 , SF 3 , SF 3  and SF 3  of the previous frame, respectively, other display lines D 1 , D 3  and D 7  display subfields SF 1 , SF 2  and SF 3  of the next frame, respectively. 
     FIG. 5 is a pulse waveform diagram applied to each electrode in order to display the frame as shown in FIG. 4, and illustrates a driving in accordance with a select erase scheme. 
     First, display lines D 1 , D 3  and D 7  whose number is identical to that of the divided subfields are selected, and then the display of the subfields SF 1 , SF 2  and SF 3  for the selected display lines D 1 , D 3  and D 7  are executed respectively. In other words, by applying a negative write pulse to Y electrodes (Y 1 , Y 2  and Y 3 ) constituting the selected display lines D 1 , D 3  and D 7  and applying a positive pulse to common X electrodes, a write discharge for all cells of the selected display lines D 1 , D 3  and D 7  is performed. 
     Thereafter, within one sustain period, scan pulses generated from Y scan-driving circuit are sequentially applied to the selected Y electrodes (Y 1 , Y 2  and Y 3 ). At the same time, data pulses generated from the data driving circuit in accordance with input image data to be displayed are applied to the data electrodes. 
     If explaining the above state using a discharging principle, as a result of the above write discharge, (+) wall charge is accumulated on a dielectric layer covering Y electrodes and (−) wall charge is accumulated on a dielectric layer covering common X electrodes. Then, if applying a scan pulse and data pulse thereto, the accumulated wall charge is erased. Accordingly, the wall charge on the display lines applied data pulse is erased. Thus, even though a sustain pulse is applied to the common X electrodes and Y electrodes, sustain discharge between the common X electrodes and Y electrodes is not performed. However, since the wall charge is accumulated on the display line to which no data pulse is applied, sustain discharge is performed. 
     Next, in the next sustain period, the negative write pulses and the positive pulse are applied to the Y electrodes (Y 2 , Y 4 , and Y 1 ) and the common X electrode of display lines D 2 , D 4  and D 1  respectively, which is allocated downwardly by one display line from the above selected display lines D 1 , D 3  and D 7 . Then, scan pulses generated from the Y scan-driving circuit are sequentially applied to the selected Y electrodes (Y 2 , Y 4  and Y 1 ). At the same time, data pulses generated from the data driving circuit in accordance with the input image data to be displayed are applied to the data electrodes. At this time, by applying the write pulses to the Y electrodes (Y 2 , Y 4  and Y 1 ) of the display lines (D 1 , D 3  and D 7 ) which are selected in the next sustain pulse period, the display of the selected display line (D 1 ) in the previous sustain pulse period is finished. As a result, the display of a subfield (SF 1 ) for the selected display line (D 1 ) in the previous sustain pulse period is completed. In this way, setting of each of the subfields to each of the selected display lines is determined in advance in accordance with the position of the display lines selected firstly. 
     Continuously, by repeating the display of the subfields for the selected display lines by shifting one line as an unit of one sustain pulse period until each of the subfields for all display lines is completely displayed, the display for a frame is completed. Finally, the display lines, which have completed all subfields of one frame, will end their sustain discharges by applying a write pulse to display subfields of the next frame. 
     Accordingly, since within the period of one frame, it can perform simultaneously addressing (scan) of another display line during sustain period of one display line, such driving method can perform display with high efficiency. 
     As shown in FIGS. 4 and 5, however, such driving method has a problem that during at least a predetermined time, continuous two frames are displayed simultaneously. That is, as shown in FIG. 5, before finishing completely an image display of the first frame F 1 , an image display of the second frame F 3  is performed. 
     As a result, a mixing display period FH is produced, resulting in an incorrect image display of one frame. Also, there may be caused a problem of image distortion that when displaying a dynamic image, images in two frames are viewed as overlapped to a viewer. 
     In addition, a general driving method is limited to a fixed sequence in which a sequence of driving each of subfields and the number of subfields is predetermined, and these sequences become identical along the time axis. Accordingly, there is frequently caused a repeated occurrence of a specific gray level when displaying a dynamic image. If such occurrence arises in an area in which a bit carrier exists, a low frequency component is generated in the form of a partial flicker, resulting in a deterioration of image quality. 
     Now, the driving method will be described in more detail with reference to FIG.  6 . 
     First, it is assumed that one frame is divided into eight subfields SF 1 , SF 2  . . . SF 8  and sustain pulses are set as 1, 2, 4, 8, 16, 32, 64 and 128, respectively and that thereafter, by combining suitably these subfields, gray level of 2 8 =256 are displayed. 
     The 63rd gray level lights-on all the subfields SF 1  through SF 6  and the 64th gray level lights-on only subfield SF 7 . As shown in FIG. 6, when light on occurs repeatedly at the 63rd gray level and the 64th gray level for every frame, the human eyes view the 127th gray level and the 0 gray level as light on repeatedly every frame. Thus, there occurs the problem that a low frequency component is formed for two adjacent frames and thusly a flicker is generated. 
     Furthermore, if scrolling a display of gray level in the inclined direction of brightness when displaying a dynamic image, a bright line and a dark line occur in a specific gray level and thusly the dynamic image is displayed as a false contour. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a driving method capable of preventing images in two frames from being viewed overlapping to a viewer when displaying a dynamic image by clarifying a boundary between adjacent frames in a multi-scan driving method within a sustaining pulse period. 
     Another object of the present invention is to provide a driving method capable of reducing an occurrence of a flicker and a false contour in a multi-scan driving method. 
     According to the present invention, there is provided a method of displaying a halftone image on a PDP display unit by using a frame division technique that divides each frame of halftone image into subfields with each having specific sustain pulses to provide a specific intensity level, comprising: 
     selecting display lines whose number is identical to the total number of said divided subfields, the position of said selected display lines being determined based on the number of sustain pulses set previously to said each subfields, addressing for designating pixels of selected display lines to be displayed and displaying each subfield allocated for the said selected display lines; 
     shifting by a predetermined number of display lines from said selected display lines as a sustain pulse period unit, selecting display lines, addressing for designating pixels of selected display lines to be displayed and displaying each subfield allocated for the said selected display lines; and 
     repeating said shifting, said selecting, said addressing and said displaying steps until each of the subfields is completely displayed with regard to all display lines; 
     wherein display lines for all subfields of one frame have been completely displayed within an idle period, during which a subfield of the following frame is not displayed. 
     Moreover, the method is characterized in that said idle period is started by applying an erase pulse to the display lines where the display for all subfields has been already completed. 
     Also, the method is characterized in that the positions of the display lines which are firstly selected to display subfields of the following frame after completely displaying a previous frame are determined different from those of display lines which are firstly selected to display subfields of the previous frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein 
     FIG. 1 is a schematic sectional view of a discharge cell of a conventional plasma display panel; 
     FIG. 2 is a plan view of a conventional three electrode type plasma display panel; 
     FIG. 3 is a frame structure explaining a prior art driving method; 
     FIG. 4 is a timing diagram illustrating division of an image frame into subfields adapted for a conventional driving method; 
     FIG. 5 is a pulse waveform diagram applied by each electrode to display a frame in accordance with a conventional method; 
     FIG. 6 is a diagram illustrating a problem encountered by a conventional plasma display panel; 
     FIG. 7 is a timing diagram for displaying subfields between adjacent subfields in accordance with a first embodiment of the present invention; 
     FIG. 8 shows an example of a pulse waveform applied to each electrode in a first embodiment of the present invention; 
     FIG. 9 shows another example of a pulse waveform applied to each electrode in a first embodiment of the present invention; 
     FIGS. 10 a  and  10   b  are timing diagrams for displaying subfields between adjacent subfields in accordance with a second embodiment of the present invention; and 
     FIG. 11 is an example of a pulse waveform diagram applied to application examples of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 7 shows a timing diagram displaying subfields between two adjacent frames illustrating the first embodiment of the present invention. For convenience of a description, it is assumed that one frame divides into three subfields SF 1 , SF 2  and SF 3 , sustain periods in the subfields SF 1 , SF 2  and SF 3  set as  1 ,  2  and  4 , respectively and the number of display lines is  7 . In practice, however, it is possible to divide one frame into six or eight more subfields and constitute display lines to have a conventional number of  480  lines. In FIG. 7, S 1  through S 7  represent the number of sustain pulses. 
     Since sustain periods (pulses) of each of subfields SF 1 , SF 2  and SF 3  are set as  1 ,  2  and  4  respectively, it is possible to select display lines D 1 , D 3  and D 7  in consideration of the sustain periods (pulses) set for each of the subfields SF 1 , SF 2  and SF 3 . Of course, it is possible to select various combinations of display lines (D 2 , D 4  and D 1 ), (D 3 , D 5  and D 2 ), (D 4 , D 6  and D 3 ), (D 5 , D 7  and D 4 ), (D 6 , D 1  and D 5 ) and (D 7 , D 2  and D 6 ). 
     As shown in FIG. 7, the display lines D 1 , D 3  and D 7  are selected in consideration of the sustain pulses set for each of subfields SF 1 , SF 2  and SF 3  in the first sustain pulse period (S 1 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 1 , D 3  and D 7  is performed respectively. Next, the display lines D 2 , D 4  and D 1  which are allocated downwardly by one display line from the above-selected display lines are selected in the second sustain pulse period (S 2 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 2 , D 4  and D 1  is performed respectively. Next, the display lines D 3 , D 5  and D 2  which are allocated downwardly by one display line from the above-selected display lines are selected in the third sustain pulse period (S 3 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 3 , D 5  and D 2  is performed respectively. Next, the display lines D 4 , D 6  and D 3  which are allocated downwardly by one display line from the above-selected display lines are selected in the fourth sustain pulse period (S 4 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 4 , D 6  and D 3  is performed respectively. Next, the display lines D 5 , D 7  and D 4  which are allocated downwardly by one display line from the above-selected display lines are selected in the fifth sustain pulse period (S 5 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 5 , D 7  and D 4  is performed respectively. Next, the display lines D 6 , D 1  and D 5  which are allocated downwardly by one display line from the above-selected display lines are selected in the sixth sustain pulse period (S 6 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 6 , D 1  and D 5  is performed respectively. Next, the display lines D 7 , D 2  and D 6  which are allocated downwardly by one display line from the above-selected display lines are lastly selected in the seventh sustain pulse period (S 7 ). Then, the display of subfields SF 1 , SF 2  and SF 3  for the selected display lines D 7 , D 2  and D 6  is performed respectively. Thereby, the display of one frame is completed. 
     After lastly selecting display lines D 7 , D 2  and D 6 , the previously selected display lines complete sequentially display the subfields SF 1 , SF 2  and SF 3 , respectively. At this time, the display lines, which have sequentially completed the display, do not perform a selection for displaying the next frame. After displaying subfield SF 3  of the lastly selected display line D 6 , the display lines start the display of the next frame. 
     As a result, after the subfields SF 1 , SF 2  and SF 3  corresponding to one frame are completely displayed, there is provided an idle period H at every display line to the extent of at least the largest bit of subfield period. 
     FIG. 8 is a pulse waveform diagram applied to each electrode in order to display a frame as shown in FIG.  7  and shows a driving method in accordance with a selectively erasing process. 
     Firstly, the selecting step of display lines will be described hereafter. As shown in FIG. 8, there is provided with a predetermined negative voltage to the Y electrodes Y 1 , Y 2  and Y 3  constituting the display lines D 1 , D 3  and D 7 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 1 , D 3  and D 7 . As a result, a write discharge to the display lines D 1 , D 3  and D 7  is performed and thereby, the display lines D 1 , D 3  and D 7  are selected. 
     Thereafter, in the addressing step, scan pulses generated from the Y scan-driving circuit are sequentially applied to the selected Y electrodes Y 1 , Y 3  and Y 7  in first sustaining pulse period. At the same time, data pulses generated from the data driving circuit in accordance with image data to be displayed are applied to data electrodes. If the data pulses are applied, a wall charge on the dielectric layer generated by the write discharge is erased. Thus, even if the sustaining pulse is applied, the sustaining discharge is not performed. If the data pulse is not applied, the wall charge cannot be erased. Accordingly, the write discharge in the above selecting step is still maintained. 
     Next, in the sustaining step, there is provided with the sustaining pulse to the Y electrodes (Y 1 , Y 3  and Y 7 ) and the common X electrodes constituting the display lines D 1 , D 3  and D 7 . As the result, the sustaining discharge of the pixels that are designated in the addressing step is performed. 
     Continuously, by selecting the display lines D 2 , D 4  and D 1  which are allocated downwardly by one line from the display lines D 1 , D 3  and D 7  in the second sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 2 , Y 4  and Y 1  constituting the display lines D 2 , D 4  and D 1 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 2 , D 4  and D 1 . As a result, a write discharge to the display lines D 2 , D 4  and D 1  is performed and thereby, the display lines D 2 , D 4  and D 1  are selected. The display line D 1  is selected again among the display lines D 1 , D 3  and D 7  that were selected in the first sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 1  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 2 , D 4  and D 1  are performed sequentially. 
     Continuously, by selecting the display lines D 3 , D 5  and D 2  which are allocated downwardly by one line from the display lines D 2 , D 4  and D 1  in the third sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 3 , Y 5  and Y 2  constituting the display lines D 3 , D 5  and D 2 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 3 , D 5  and D 2 . As a result, a write discharge to the display lines D 3 , D 5  and D 2  is performed and thereby, the display lines D 3 , D 5  and D 2  are selected. The display line D 3  is selected again among the display lines D 1 , D 3  and D 7  that were selected in the first sustaining pulse period, and thereby the display of subfield SF 2  to the display line D 3  is finished. Also, the display line D 2  is selected again among the display lines D 2 , D 4  and D 1  that were selected in the second sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 2  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 3 , D 5  and D 2  are performed sequentially. 
     Continuously, by selecting the display lines D 4 , D 6  and D 3  which are allocated downwardly by one line from the display lines D 3 , D 5  and D 2  in the fourth sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 4 , Y 6  and Y 3  constituting the display lines D 4 , D 6  and D 3 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 4 , D 6  and D 3 . As a result, a write discharge to the display lines D 4 , D 6  and D 3  is performed and thereby, the display lines D 4 , D 6  and D 3  are selected. The display line D 3  is selected again among the display lines D 3 , D 5  and D 2  that were selected in the third sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 3  is finished. Also, the display line D 4  is selected again among the display lines D 2 , D 4  and D 1  that were selected in the second sustaining pulse period, and thereby the display of subfield SF 2  to the display line D 4  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 4 , D 6  and D 3  are performed sequentially. 
     Continuously, by selecting the display lines D 5 , D 7  and D 4  which are allocated downwardly by one line from the display lines D 4 , D 6  and D 3  in the fifth sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 5 , Y 7  and Y 4  constituting the display lines D 5 , D 7  and D 4 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 5 , D 7  and D 4 . As a result, a write discharge to the display lines D 5 , D 7  and D 4  is performed and thereby, the display lines D 5 , D 7  and D 4  are selected. The display line D 4  is selected again among the display lines D 4 , D 6  and D 3  that were selected in the fourth sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 4  is finished. Also, the display line D 5  is selected again among the display lines D 3 , D 5  and D 2  that were selected in the third sustaining pulse period, and thereby the display of subfield SF 2  to the display line D 5  is finished. Also, the display line D 7  is selected again among the display lines D 1 , D 3  and D 7  that were selected in the first sustaining pulse period, and thereby the display of subfield SF 3  to the display line D 7  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 5 , D 7  and D 4  are performed sequentially. 
     Continuously, by selecting the display lines D 6 , D 1  and D 5  which are allocated downwardly by one line from the display lines D 5 , D 7  and D 4  in the sixth sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 6 , Y 1  and Y 5  constituting the display lines D 6 , D 1  and D 5 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 6 , D 1  and D 5 . As a result, a write discharge to the display lines D 6 , D 1  and D 5  is performed and thereby, the display lines D 6 , D 1  and D 5  are selected. The display line D 1  is selected again among the display lines D 2 , D 4  and D 1  that were selected in the second sustaining pulse period, and thereby the display of subfield SF 3  to the display line D 1  is finished. Also, the display line D 5  is selected again among the display lines D 5 , D 7  and D 4  that were selected in the fifth sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 5  is finished. Also, the display line D 6  is selected again among the display lines D 4 , D 6  and D 3  that were selected in the fourth sustaining pulse period, and thereby the display of subfield SF 2  to the display line D 6  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 6 , D 1  and D 5  are performed sequentially. 
     Continuously, by selecting the display lines D 7 , D 2  and D 6  which are allocated downwardly by one line from the display lines D 6 , D 1  and D 5  in the seventh sustaining pulse period, the shifting step is performed. At this time, there is provided with a predetermined negative voltage to the Y electrodes Y 7 , Y 2  and Y 6  constituting the display lines D 7 , D 2  and D 6 . At the same time, there is provided with a positive voltage to the common X electrodes constituting the display lines D 7 , D 2  and D 6 . As a result, a write discharge to the display lines D 7 , D 2  and D 6  is performed and thereby, the display lines D 7 , D 2  and D 6  are selected. The display line D 2  is selected again among the display lines D 2 , D 4  and D 1  that were selected in the third sustaining pulse period, and thereby the display of subfield SF 3  to the display line D 1  is finished. Also, the display line D 6  is selected again among the display lines D 6 , D 1  and D 5  that were selected in the sixth sustaining pulse period, and thereby the display of subfield SF 1  to the display line D 6  is finished. Also, the display line D 7  is selected again among the display lines D 5 , D 7  and D 4  that were selected in the fifth sustaining pulse period, and thereby the display of subfield SF 2  to the display line D 7  is finished. Thereafter, the addressing and sustaining steps for the selected display lines D 7 , D 2  and D 6  are performed sequentially. 
     In the above described process, erase pulses (Pe) generated from the Y electrode scan driving circuit are applied to the Y electrodes after the total number of sustaining pulses of the corresponding frame are applied to every display line, and thereby wall charge accumulated during the sustain discharge is erased. As the result, the display of the corresponding frame for every display line is finished. The erase pulses (Pe) can be applied to the Y electrode within a sustaining pulse period of the Y electrode as shown in FIG.  8  and also immediately after a sustaining pulse is applied to the X electrode as shown in FIG.  9 . The display of the next frame starts after erase pulses (Pe) to all the display lines are applied. 
     Accordingly, an idle period H for all the display lines is from when applying erase pulse to when starting the display of the next frame. That is, the length of the idle period H depends on a display period of a largest bit of subfield SF 3  allocated in the display lines that are lastly selected. Therefore, it is desirable to shorten the idle period H. By dividing the largest bit of subfield into a plurality of subfields, the idle period H can be shortened. 
     FIGS. 10 a  and  10   b  show a driving method in accordance with a second embodiment of the present invention. As explained in FIG. 7, when displaying one frame of an image, three display lines identical to the number of subfields can be selected firstly. Also, the position of display lines selected can be determined as display lines D 1 , D 3  and D 7  with regard to each of subfields SF 1 , SF 2  and SF 3  in a consideration of the sustain periods  1 ,  2  and  4 . At this time, the positioning of the display lines in consideration of sustain periods designated on each subfield is the same as the allocating of each subfield to the display lines. That is, if selecting one display line D 1  of seven display lines and allocating the subfield SF 1  for the display line D 1 , other display line D 7  or D 2  positioned above or below by one line from the display line D 1  should be selected. 
     In practice, even though the display line D 2  is positioned below by one line from the display line D 1 , the selecting of the display line D 2  can be considered in case that the scanning direction moves upwardly. Next, if selecting one display line D 7  of seven display lines and allocating the subfield SF 3  for the display line D 7 , the remaining display line D 3  can be automatically selected, and thereby subfield F 2  for the display line D 3  is allocated. 
     As described above, once the position of the display lines selected firstly is determined in accordance with the number of sustain pulses set to each of the subfields, the displaying order of each of the subfields SF 1 , SF 2  and SF 3  is constantly maintained until the display of one frame is completed. 
     In FIG. 7, there is shown that the position of display lines for displaying a next frame is selected identical to the previous frame. However, in the case that a specific gray level is repeatedly generated when displaying a dynamic image as shown in FIG. 6, a low frequency ingredient occurs in an area in which a bit carry exists. Thus, there is caused a problem that the low frequency ingredient is generated in the form of a partial flicker, resulting in deterioration of image quality. 
     According to the second embodiment of the present invention, in order to solve such problem, the position of display lines selected firstly to display the next frame is different from that of the display lines selected firstly to display the previous frame. 
     For example, as shown in FIG. 10 a , the position of display lines selected firstly in the previous frame are display lines D 1 , D 3  and D 7  allocated to the subfields SF 1 , SF 2  and Sf 3 , respectively. On the other hand, the position of display lines selected firstly in the next frame are display lines D 1 , D 2  and D 4  allocated to the subfields SF 3 , SF 1  and SF 2 , respectively. Likewise, as shown in FIG. 10 b , the position of display lines selected firstly in the next frame are display lines D 2 , D 3  and D 5  allocated to the subfields SF 3 , SF 1  and SF 2 , respectively. 
     In this way, a combination of display lines to be selected initially in a frame can be selected as any one of combinations of n×N!, wherein n is the number of display lines and N is total number of subfields of one frame. Accordingly, a combination of display lines to be selected initially in the next frame can be selected as any one of [n×N!]−1 combinations which excepts the combination selected in the previous frame. According to the second embodiment of the present invention, it is possible to display subfields in a different order at every frame. 
     Until now, even though the driving method according to the present invention was described based on a selective erase process, as shown in FIG. 11, it can be applicable to a selective writing process comprising writing discharge for the display lines selected, erase discharge for erasing wall charge accumulated on a dielectric layer, addressing discharge for designating pixels to be displayed, and sustain discharge for displaying pixels designated. 
     As mentioned above, according to the present invention, since after completing a display of one frame with respect to all display lines, a display for the next frame is initiated, and it is possible to prevent images in two frames being viewed to a viewer in an overlapped shape when displaying a dynamic image. 
     Moreover, even when a specific gray level is repeatedly displayed, since the display order of subfields of every frame varies, the occurrence of a low frequency ingredient can be prevented. Many different embodiments of the present invention can by provided without departing from the spirit and scope of the present invention which is not limited to the specific embodiments described in the specification. Also, the present invention can be applied to various kinds of flat display devices such LCD, FED, EL and the like.