Abstract:
A plasma display panel drive art capable of restraining a contour noise in a picture displayed on a PDP and reducing a maximum power consumption. The drive art allows one frame to be consisted of a plurality of sub fields each having a different weighting value for brightness so as to display a video signal of gray scale. The plurality of the sub fields are differently arranged along with a distribution of logical values in the video data for one frame, thereby dividing the one frame into a display interval and a non-display interval. Also, the plurality of the sub fields are equal to sub fields without a sub field having a least weighting value for the brightness.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method capable of preventing an appearance of contour noise at which it is driven a plasma display panel in a pulse width modulation to implement a gray scale of picture and an apparatus thereof. 
     2. Related Art of the Invention 
     Recently, the plasma display panel, hereinafter PDP, attracts public attention as a display device of slim and light weight. Generally, it uses a modulation allowing the times of emitting light to be proportioned to the video signal in order to display a video signal (for example, a television signal) on the PDP. In detail, the video signal is digitized and each frame period is divided into sub-field periods corresponding to the bit number of a video data digitized. At each sub-field period, the emitting light causes by the times relative to a weighting value of each bit of the digital video data to perform the gray scale display. 
     Actually, in the case that a picture is displayed in 256 gray scales on the basis of a video data of 8 bits, one frame interval, in which each picture element on the PDP is displayed, is divided into 8 sub field periods SF 1  to SF 8 . Each sub field period SF 1  to SF 8  is separated again into a reset period RP, an addressing period AP and a display period SP, and the display period SP has the weighting value increasing at a ratio of 1:2:4: . . . :128 according to the sub field periods. The reset period RPP and the addressing period AP come in for a share of each sub field period to be same regardless of the sub field periods. For example, the reset period RPP and the addressing period AP have the term of 1.5 ms, respectively. In such a PDP driving method, the sub field periods opposite to each bit of the video data are proceeded in a fixed sequence, for example SF 1 →SF 2 →SF 3 →SF 4 →SF 5 →SF 6 →SF 7 →SF 8 , as shown in FIG.  1 . Due to this, a display term and a non-display term appear in one frame period such a manner of a mixed-up state according to the logical value of the pixel data, as shown in FIG.  2 . In other words, the display and non-display terms existed in the frame period are arranged in a variety of patterns according the logical value of the pixel data. 
     As described above, since the sub field periods are proceeded in the fixed sequence, there is generated a contour noise in the picture displayed by the conventional PDP drive method. Actually, the PDP driven by the conventional PDP drive method of PWM system becomes to display the picture depending on the total quantity of the lights emitted during each sub field period. The integration characteristics of the lights is not identified with a visual characteristics accepted by the eyes of human. Due to this, the contour noise is generated in the picture on the PDP. The contour noise appears in the shape of a black stripe or a white stripe on the PDP which displays continuously two frames (or two pictures) having gray scale levels different from each other. In other words, in the case that two gray scale levels such as 127 and 128, 63 and 64,31 and 32 and so on, which allow the emitting light patterns of two frames to be entirely different from each other, are continuously displayed, the contour noise is generated. If the gray scale level of two continuous frames is changed from 128 to 127, the difference of brightness between two frames (or two pictures) is small but a time lag between the emitting patterns of two frames is enlarged to elongate the moving distance of emitting light point. In this case, there is generated the black stripe on the PDP displaying continuously the two frames because the eyes of the human does not follow the emitting point. Also, when the gray scale level of two continuous frames is changed from 128 to 127, the contour noise of the white stripe appears on the PDP displaying continuously the two frames due to the reason as described above. Such a contour noise is generated more when an object of complexion moves. In other words, the contour noise appears more in moving picture that the face or body of human moves. Further, when a color picture is displayed, it is lost a color balance by the contour noise. Furthermore, the contour noise is generated further more by the distribution of the display and non-display terms arranged in one frame period. Consequently, the quality of the picture displayed by the conventional PDP drive method is reduced largely by the contour noise. Also, the conventional PDP drive method consumes a great amount of power since a sustaining signal must be supplied continuously in the non-display term due to the distribution of the display and non-display terms. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a PDP drive method and apparatus which is capable of restraining a contour noise in a picture displayed on a PDP. 
     Another object of the present invention provides a PDP drive method and apparatus which is capable of restraining a contour noise in a picture displayed on a PDP and reducing a power consumption. 
     In order to achieve these and other objects of the invention, a PDP drive method according to one aspect of the present invention allows one frame to be consisted of a plurality of sub fields each having a different weighting value for a brightness so as to display a video signal of gray scale. The sub fields are differently arranged along with a distribution of logical values in the video data for one frame, thereby dividing the one frame into a display interval and a non-display interval. 
     In a PDP drive method according to another aspect of the present invention, the plurality of the sub fields are equal to sub fields without a sub field having a least weighting value for the brightness, respectively. 
     Further, a PDP drive apparatus according to still another aspect of the present invention includes: signal input means for receiving a video signal; address drive means for driving address electrodes on the plasma display panel depending on the video signal from the signal input means; a frame memory connected between the signal input means and the address drive means, the frame memory storing temporarily the video signal; sustain drive means for driving sustain electrodes on the plasma display panel; and control means for controlling the sustain drive means to allow one frame to be consisted of a plurality of sub fields each having a different weighting value for a brightness so as to display a video signal of gray scale and to divide a frame period into a display interval and a non-display interval. 
     Furthermore, a PDP drive apparatus according to still another aspect of the present invention includes: signal input means for receiving a video signal; address drive means for driving address electrodes on the plasma display panel depending on the video signal from the signal input means; a frame memory connected between the signal input means and the address drive means, the frame memory storing temporarily the video signal; sustain drive means for driving sustain electrodes on the plasma display panel to allow one frame to be consisted a plurality of sub fields each having a different weighting value for a brightness; and control means for controlling the sustain drive means to allow one frame to be consisted of a plurality of sub fields without a sub field having a least weighting value for the brightness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic view showing a drive sequence according to a conventional PDP drive method; 
     FIG. 2 is a schematic view showing the case of video signal driven by the conventional PDP drive method; 
     FIG. 3 is a schematic view showing a PDP drive apparatus according to an embodiment of the present invention; 
     FIG. 4 is a schematic view explaining the case of a drive sequence performed by the PDP drive apparatus shown in FIG. 3; and 
     FIG. 5 is a schematic view representing the case of a video signal driven by the PDP drive apparatus shown in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 3, there is shown a PDP drive apparatus of an embodiment according to the present invention. The PDP drive apparatus includes a frame memory  12  and a data driver  14  connected in serial between an input line  11  and a PDP  10 , and a sustain waveform generator  18  and a sustain driver  20  connected serially between a scan data generator  16  and the PDP  10 . A video data having pixel signals of n bits (for example, 8 bits) is applied to the frame memory  12  coupled with the input line  11 . The frame memory  12  transmits the video data from the input line  11  to the data driver  14  for one frame. Then, in the video data transmitted from the frame memory  12  to the data driver  14 , there are continuously arranged pixel signals of single bit corresponding to the weighting value of sub field. For example, if the PDP  10  is driven during the sub field period having the weighting value of “128”, the pixel signals having a most significant bit are continuously arranged in the video data to be applied to the data driver  14 . To this end, the frame memory  12  includes a single port memory adaptive to store the video data for two frames or a dual port memory capable of storing the video data for one frame. The data driver  14  drives address electrodes on the PDP  10  depending on the video data from the frame memory  12 . 
     The scan data generator  16  produces a variety of frame scan pattern according to the distribution of logical values of the pixel signals for one frame, which is stored in the frame memory  12 . The frame scan pattern output from the scan data generator  16  is changed every frame unit. On the other hand, the scan data generator  16  can generate the frame scan pattern varied every line unit. In this case, the frame scan pattern is selected according to the distribution of the logical values of the pixel signal for one line. In order to generate the frame scan pattern, the scan data generator  16  stores a plurality of the frame scan patters in accordance with the distribution of the logical value of the pixel signals for one frame or one line. Each frame scan pattern stored in the scan data generator  16  includes sub fields SF 2  to SF 8 , as shown in FIG.  4 . The sub fields are arranged regardless of order of the weighting values to reduce a contour noise. In FIG. 4, each frame scan pattern does not include a least significant sub field (hereinafter, first sub field SF 1 ). The first sub field SF 1  corresponding to the pixel signal of a least significant bit has a most short period. Such a first sub field SF 1  affects largely to the generation of contour noise, while does not affect a gray scale level. Therefore, the first sub field SF 1  is eliminated such that the contour noise is largely reduced on the picture displayed by the PDP  10 . Also, in the frame scan pattern, a most significant sub field SF 8  (hereinafter a eighth sub field SF 8 ) is arranged in such a manner of dividing into two. In other words, the most significant sub field SF 8  having the weighting value of 128 for the display period is divided into a pre-sub field SF 8   a  and a post-sub field SF 8   b.  The pre and post sub fields SF 8   a  and SF 8   b  each has the weighting value of 64 for the display period. The pre-sub field SF 8   a  is positioned between the fourth and sixth sub fields SF 4  and SF 6 , and the post-sub field SF 8   b  is inserted between the fifth and third sub field SF 5  and SF 3 . Further, the location of each sub field SF 2  to SF 8 , which are arranged in one frame period with the sequence of SF 2 , SF 4 , SF 8   a,  SF 6 , SF 7 , SF 5 , SF 8   b  and SF 3  as shown in FIG. 4, is randomly changed according to the distribution of the logical values of the pixel signals. Since the location of each sub field SF 2  to SF 8  is randomly changed, the frame scan pattern is separated into the display and non-display intervals as shown in FIG.  5 . In this case, the scan data generator  16  disables the sustain waveform generator  18  not to generate a sustain waveform during the non-display interval. Therefore, a driving interval of PDP  10  and a non-driving interval appear in the frame period by once. As a result, in the PDP drive apparatus of an embodiment according to the present invention, the power consumption is greatly reduced. Also, the scan data generator  16  controls a read operation of the frame memory  12  for the video data. In detail, the scan data generator  16  addresses the storing regions of the frame memory  12  to oppose the video data read out from the frame memory  12  to the frame scan pattern. Thus, the frame memory  12  reads out a video data corresponding to each sub field SF 2  to SF 8  by one frame or one line. Generated is a sustain driving signal in sustain waveform generator  18  which receives the frame scan pattern from the scan data generator  16 . The sustain driving signal has the waveform varied along with the frame scan pattern. The sustain driver  20  responds to the sustain driving signal from the sustain waveform generator  18  and drives the sustain electrodes on the PDP  10 . 
     In the PDP drive apparatus of the embodiment according to the present invention, there is included a controller  22  connected commonly to the frame memory  12  and the scan data generator  16 . The controller  22  controls the write operation of the frame memory  12  and detects the distribution of the logical values of the pixel signals for one frame. Also, the controller  22  applied the detected distribution of the logical values of the pixel signals to the scan data generator  16  to vary the frame scan pattern output from the scan data generator  16  according to the frame. Further, the controller  22  controls the read timing of the frame memory  12  on the basis of the frame scan pattern output from the scan data generator  16 . On the other hand, the controller  22  can detect a distribution of the logical values of the pixel signals on each line among the video data stored in the frame memory  12 . In this case, the scan data generator  16  provides with a frame scan pattern varied according to the lines on the PDP  10 . Accordingly, the lines on the PDP  10  are driven respectively by the frame scan pattern that the sub fields SF 2  to SF 8  are arranged differently in each line. 
     As described above, in a PDP drive apparatus of an embodiment according to the present invention, sub fields are differently arranged along with the distribution of logical values of pixel signals to separate one frame period into a display term and a non-display term. Also, the PDP drive apparatus of the embodiment according to the present invention distributes and arranges an arbitrary sub field, such as a most significant sub field interval corresponding to a most significant bit of the pixel signal, in such a manner of dividing two portions. Accordingly, the PDP drive apparatus restrains the generation of contour noise in a picture displayed on a PDP and reduces the power required driving the PDP. Further, in the PDP drive apparatus of the embodiment according to the present invention, there is reduced more and more the contour noise in the picture displayed on the PDP because of eliminating a least significant sub field period for the least significant bit of the pixel signal. 
     Although the present invention has been explained by the embodiments shown in the drawing hereinbefore, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather than that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.