Abstract:
The invention relates to a method for processing video pictures data for display on a display device having a plurality of luminous elements corresponding to the pixels of a video picture. The invention is related to every kind of display devices based on the principle of duty cycle modulation (pulse width modulation) of light emission and comprising a data driver. The aim of this method is to reduce the data driver overheating by optimizing the dithering of the pixel values of the video pictures. According to the invention, the pixel values used for dithering are chosen for reducing the state changes between successive bits of subfield code words of adjacent luminous elements.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to a method for processing video pictures data for display on a display device having a plurality of luminous elements corresponding to the pixels of a video picture, the luminous elements being organized in columns and lines, wherein the time of a video frame or field is divided into a plurality of sub-fields during which the luminous elements can be activated for light emission, a sub-field code word corresponding to said plurality of sub-fields being used for encoding the pixels values in which each bit can have either an “OFF” state or an “ON” state such that each luminous element is activated during a subfield when the corresponding bit of sub-field code word has an “ON” state. 
         [0002]    The invention is related to every kind of display devices based on the principle of duty cycle modulation (pulse width modulation) of light emission and comprising at least a data driver. 
       BACKGROUND OF THE INVENTION  
       [0003]      FIG. 1  illustrates the actual structure of a Plasma Display Panel, called hereinafter PDP. Video is sent to a digital board  10  including a PDP controller. This controller is an integrated circuit (IC) that takes care of all PDP relevant signal processing and converts video information into sub-field information. This controller is responsible for sending all power signals to data drivers  11 , line drivers  12  and a common part  13  of the PDP. Line drivers  12  are responsible for selecting, one by one, the lines of cells to be written. Data drivers  11  are responsible for sending bits (0 or 1) on the vertical electrodes of all cells of the current selected lines. Finally, the common part  13  is responsible for generating global signals in combination with line drivers  12  like sustain signals, erase signals, priming signals . . . A PDP cell is present at the crossing point between a vertical electrode coming from a data driver output, a horizontal electrode coming from a line driver output and a horizontal electrode coming from the common part. 
         [0004]    As illustrated by  FIG. 2 , each data driver  11  works as a serial to parallel converter. For a data driver with n outputs, the n data samples Cn,t for a line t are sent serially from the PDP controller  10  to said data driver. The input works at a frequency defined by a clock circuit. On each starting edge of an enable signal ENA, the n outputs of the data driver take the n last input values. In fact when the data Cn,t are sent to the input of the data driver, the outputs take the values Cn,t−1. The enable signal is included in the addressing signal used to activate the current line t−1. The important point is that the input signals are control logic signals (low voltage) whereas the output signals are power signal (high voltage≈60V). The global activity of the data driver is defined by two main parameters:
       the number of changes occurring at the input of the driver during the loading of the data driver, and   the number of changes occurring at the output of the driver from one line to another.       
 
         [0007]    It is also important to notice how these changes are appearing. Indeed if all outputs have the same value and are changing in one time, this is less energy consuming than if each output is different and is changing. 
         [0008]    Then, based on all these assumptions, a critical test pattern called hereinafter chequered pattern can be defined per driver as illustrated by  FIG. 3 . This chequered pattern, which is a bit series always toggling between 0 and 1, introduces an overheating of the data driver and above all when the addressing speed is fast (clk and ENA are high) like for high-resolution displays. If the data driver is overheated a long time (many frames) it can be definitely damaged. Moreover, today, the data drivers are bonded on the PDP glass by using glue and it is almost impossible to remove them in order to perform an exchange. Therefore, if a data driver has been damaged, the whole panel can be thrown away. 
         [0009]    Today, there are mainly three possibilities to avoid such a problem:
       limiting either the addressing speed, or the number of sub-fields used per frame;   using a specific coding that should reduce the situation depicted in  FIG. 3  for standard picture (reducing the toggling inside a codeword),   detecting the critical patterns and reducing the number of sub-fields used during their addressing.       
 
         [0013]    Solutions consisting in detecting chequered patterns in video pictures to be displayed also exist but the problem is not solved because chequered patterns can also be introduced by the dithering operation applied to any pictures. Indeed in case of cell-based dithering as defined in WO 01/71702 and EP 1 262 947, the structure of dithering with a level ½ is exactly the chequered pattern. Such a dithering is illustrated by the following example. In this example, the sub-fields have the following weights: 1-2-3-5-8-13-18-26-39-57-83. The following pixel values can be displayed:
       0: 00000000000   ( . . . )   46: 01011110000   56: 10111101000   ( . . . )   255: 11111111111       
 
         [0020]    The dithering consists in associating to each pixel value V of the picture to be displayed a dithering level L used to dither between two different pixel values V 1  and V 2  that can be coded by the given set of subfields such that V=(1−L)×V 1 +L×V 2  with V 1 &lt;V 2  and L∈[0, 1]. The pixel values can be displayed by a group of adjacent cells (or luminous elements) of the panel or by a same cell on a plurality of frames. In the present case, to render the pixel value V=51, we will use spatial dithering of level ½ with the pixel values V 1 =46 and V 2 =56 So if a uniform gray level with value 51 is to be displayed on the whole panel, the following picture pixel values are displayed during one frame: 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
               
               
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
               
               
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
               
               
                 56 
                 46 
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                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
               
               
                 46 
                 56 
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                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
               
               
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
               
               
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
               
               
                 56 
                 46 
                 56 
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                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
               
               
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
               
               
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
                 56 
                 46 
               
               
                   
               
             
          
         
       
     
         [0021]    The subfield information sent to the data drivers are given by the following tables. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 1 st  sub-field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 2 nd  sub-field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 3 rd  sub-field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 4 th , 5 th  and 6 th  sub-fields 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 7 th  sub-field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 8 th  sub-field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
               
               
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 9 th , 10 th  and 11 th  sub-fields 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0022]    As it can be seen in the previous tables, 5 sub-fields will use a chequered pattern. This means that even with a standard picture, the data driver overheat problem may occur because of dithering. 
       SUMMARY OF THE INVENTION  
       [0023]    It is an object of the present invention to disclose a method and an apparatus reducing the number of chequered patterns in order to prevent the driver overheating. 
         [0024]    According to the invention, this object is solved by selecting appropriate dithering levels for limiting the number of bit changes between the subfield code words of adjacent luminous elements. 
         [0025]    More particularly, the invention concerns a method for processing video pictures data for display on a display device having a plurality of luminous elements corresponding to the pixels of a video picture, the luminous elements being organized in columns and lines, wherein the time of a video frame or field is divided into a plurality of sub-fields during which the luminous elements can be activated for light emission, a sub-field code word corresponding to said plurality of sub-fields being used for encoding the pixels values in which each bit can have either an “OFF” state or an “ON” state such that each luminous element is activated during a subfield when the corresponding bit of sub-field code word has an “ON” state. This method comprises:
       a splitting step for splitting each pixel value of the picture to be displayed into at least first and second split pixel values, each split value being associated to a group of subfields of said plurality of subfields,   a spatial dithering step for associating to each split pixel value V one dithering level L used to dither between two different pixel values V 1  and V 2  that can be coded by the associated group of subfields such that V=(1−L)×V 1 +L×V 2  with V 1 &lt;V 2  and L∈[0, 1],   a coding step for coding the pixel values V 1  and V 2  into sub-field code words, each bit of the sub-field code word having a bit state.       
 
         [0029]    According to the invention, the split pixel values and the dithering levels are selected such that, if the sum of the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the first split pixel value and the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the second split pixel value is greater than or equal to a first threshold, the sum of the absolute differences between the dithering level of each split pixel value and ½ is made greater than a second threshold. Thus, the split values and the dithering levels are selected to avoid that the dithering levels are close to ½ simultaneously, specially when the total number of different states in the sub-field code word (the sum of the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the first split pixel value and the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the second split pixel value) is high. 
         [0030]    Preferably, the second threshold is greater than or equal to ¼. Under the value ¼, the benefits of the invention would not be significant. Preferably, the second threshold is equal to ½ 
         [0031]    In a preferred embodiment, the first threshold is equal to 0. Thus, for all the pixel values, the split pixel values and the dithering levels are selected such that the sum of the absolute differences between the dithering level of each split pixel value and ½ is greater than the second threshold. This aims at reducing in average the data driver current and not only the peak current. 
         [0032]    In other embodiments, the first threshold can be chosen different from 0, for example for reducing only the peak current in the driver circuits. 
         [0033]    The inventive method is particularly adapted to a specific coding called parallel Peak Coding (PPC) wherein
       each pixel value of the picture to be displayed is split into two first and second split pixel values, the first and second split values (a,b) being associated to first and second groups of subfields respectively,   the number of subfields of the first group of subfields is substantially equal to the number of subfields of the second group of subfields, and   the first and second pixel values are substantially equal.       
 
         [0037]    With this coding, the dithering levels are selected as follows:
       the dithering level for the first split pixel value is ½ and the dithering level for the second split pixel value is 0, or   the dithering level for the first split pixel value is 0 and the dithering level for the second split pixel value is ½, or   the dithering level for the first and second split pixel values are different from ½.       
 
         [0041]    The invention concerns also a device for processing video pictures data for display on a display device having a plurality of luminous elements corresponding to the pixels of a video picture, the luminous elements being organized in columns and lines, wherein the time of a video frame or field is divided into a plurality of sub-fields during which the luminous elements can be activated for light emission, a sub-field code word corresponding to said plurality of sub-fields being used for encoding the pixels values in which each bit can have either an “OFF” state or an “ON” state such that each luminous element is activated during a subfield when the corresponding bit of sub-field code word has an “ON” state The device comprises
       splitting means for splitting each pixel value of the picture to be displayed into at least first and second split pixel values, each split value being associated to a group of subfields of said plurality of subfields,   spatial dithering means for associating to each split pixel value V one dithering level L used to dither between two different pixel values V 1  and V 2  that can be coded by the associated group of subfields such that V=(1−L)×V 1 +L×V 2  with V 1 &lt;V 2  and L∈[0, 1], and   coding means for coding the pixel values V 1  and V 2  into sub-field code words, each bit of the sub-field code word having a bit state.       
 
         [0045]    In this device, the splitting means and the spatial dithering means are controlled such that, if the sum of the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the first split pixel value and the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the second split pixel value is greater than or equal to a first threshold, the sum of the absolute differences between the dithering level of each split pixel value and ½ is made greater than a second threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. In the drawings: 
           [0047]      FIG. 1  shows the overall electronic structure of a plasma display panel; 
           [0048]      FIG. 2  shows the global functioning of the data driver of the plasma display panel of  FIG. 1 ; 
           [0049]      FIG. 3  shows the critical data pattern introducing an overheating of the data driver; 
           [0050]      FIG. 4  shows the equivalent number of chequered patterns for every dithering level; 
           [0051]      FIG. 5  shows the equivalent number of chequered patterns for every pixel value between 2 and 232; 
           [0052]      FIG. 6  shows the partition between the first peak and the second peak for all the pixel values between 0 and 255; 
           [0053]      FIG. 7  shows the equivalent number of chequered patterns for every pixel value between 0 and 255 when the inventive method is applied; 
           [0054]      FIG. 8  shows a block diagram of a first possible circuit implementation of the inventive method; and 
           [0055]      FIG. 9  shows a block diagram of a second possible circuit implementation of the inventive method. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0056]    The inventive method proposes to reduce the number of chequered patterns by splitting each pixel value into a plurality of split pixel values and by selecting appropriate pixel values and appropriate dithering levels for these pixel values. 
         [0057]    It is possible to define for every dithering level the equivalent number of chequered pattern (ENCP). A dithering level of ½ on one sub-field corresponds to one chequered pattern (ENCP=1) i.e. when looking at 5 adjacent cells (01010 or 10101) there are 4 transitions (0 to 1 or 1 to 0). For a dithering level of ¼ or ¾, when looking at 5 adjacent cells (00010 or 11101), there are only 2 transitions, so this will be equivalent to a half chequered pattern (ENCP=0.5). The dithering levels of ⅛, ⅜, ⅝ and ⅞ correspond to a fourth of a chequered pattern (ENCP=0.25).  FIG. 4  shows the equivalent number of chequered patterns for every dithering level. 
         [0058]    As mentioned previously, it is proposed to reduce this number of chequered patterns on at least one subfield of the subfields set. The subfields set is divided into two groups of subfields and the number of chequered patterns is reduced at least in one of the two groups. 
         [0059]    The invention will be described with reference to a specific coding called parallel Peak Coding (PPC) using two groups of subfields having substantially the same number of subfields and for which the driver circuit overheating is a big problem. So, the principle of this coding will be first described and the inventive method will follow. 
         [0060]    The general idea of the Parallel Peak Coding is to have almost always the same energy in two packets of light and to encode the code words for these two packets differently so that changes in sub-field code word will not appear in the two packet code words simultaneously. This coding is notably used for reducing the false contour effect with any number of sub-fields. It will be illustrated by a Parallel Peak Coding with 15 sub-fields. Considering a frame comprising 15 sub-fields with the following weights:
       1-2-3-5-7-9-11-14-17-20-24-28-33-38-43       
 
         [0062]    In the parallel peak coding, these sub-fields are organized in two consecutive groups. A part of a sub-field code word is assigned to each group. These two groups of sub-fields are used for generating the two packets of light. The pixel value to be displayed is thus split into two split pixel values: one split pixel value is displayed by the first group of subfields and the other split is displayed by the second group of subfields. 
         [0063]    For example, the odd sub-fields are grouped in a first group, called G 1 , and the even sub-fields are grouped in a second group called G 2 . 
         [0064]    G 1 : 1-3-7-11-17-24-33-43 
         [0065]    G 2 : 2-5-9-14-20-28-38 
         [0066]    Of course, the distribution of the sub-fields between the two groups can be carried out differently. The only condition is that the two groups should comprise sub-fields of different weights. Furthermore, the sub-fields of the group G 1  could be put before or after the sub-fields of the group G 2 . 
         [0067]    Furthermore, a different coding is selected for each group of sub-fields. For example, the following encoding tables can be used:
       for the group G 1  (1-3-7-11-17-24-33-43)       
 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Pixel value 
                 Code word 
                 Code number 
               
               
                   
                   
               
             
             
               
                   
                 value 0: 
                 00000000 
                 Code 0 
               
               
                   
                 value 1: 
                 10000000 
                 Code 1 
               
               
                   
                 value 3: 
                 01000000 
                 Code 2 
               
               
                   
                 value 4: 
                 11000000 
                 Code 3 
               
               
                   
                 value 7: 
                 00100000 
                 Code 4 
               
               
                   
                 value 8: 
                 10100000 
                 Code 5 
               
               
                   
                 Value 10: 
                 01100000 
                 Code 6 
               
               
                   
                 Value 11: 
                 11100000 
                 Code 7 
               
               
                   
                 Value 14: 
                 01010000 
                 Code 8 
               
               
                   
                 Value 15: 
                 11010000 
                 Code 9 
               
               
                   
                 Value 18: 
                 00110000 
                 Code 10 
               
               
                   
                 Value 19: 
                 10110000 
                 Code 11 
               
               
                   
                 Value 21: 
                 01110000 
                 Code 12 
               
               
                   
                 Value 22: 
                 11110000 
                 Code 13 
               
               
                   
                 Value 24: 
                 00101000 
                 Code 14 
               
               
                   
                 Value 25: 
                 10101000 
                 Code 15 
               
               
                   
                 Value 27: 
                 01101000 
                 Code 16 
               
               
                   
                 Value 28: 
                 11101000 
                 Code 17 
               
               
                   
                 Value 29: 
                 10011000 
                 Code 18 
               
               
                   
                 Value 31: 
                 01011000 
                 Code 19 
               
               
                   
                 Value 32: 
                 11011000 
                 Code 20 
               
               
                   
                 Value 35: 
                 00111000 
                 Code 21 
               
               
                   
                 Value 36: 
                 10111000 
                 Code 22 
               
               
                   
                 Value 38: 
                 01111000 
                 Code 23 
               
               
                   
                 Value 39: 
                 11111000 
                 Code 24 
               
               
                   
                 Value 42: 
                 00110100 
                 Code 25 
               
               
                   
                 Value 43: 
                 10110100 
                 Code 26 
               
               
                   
                 Value 45: 
                 01110100 
                 Code 27 
               
               
                   
                 Value 46: 
                 11110100 
                 Code 28 
               
               
                   
                 Value 48: 
                 00101100 
                 Code 29 
               
               
                   
                 Value 49: 
                 10101100 
                 Code 30 
               
               
                   
                 Value 51: 
                 01101100 
                 Code 31 
               
               
                   
                 Value 52: 
                 11101100 
                 Code 32 
               
               
                   
                 Value 53: 
                 10011100 
                 Code 33 
               
               
                   
                 Value 55: 
                 01011100 
                 Code 34 
               
               
                   
                 Value 56: 
                 11011100 
                 Code 35 
               
               
                   
                 Value 59: 
                 00111100 
                 Code 36 
               
               
                   
                 Value 60: 
                 10111100 
                 Code 37 
               
               
                   
                 Value 62: 
                 01111100 
                 Code 38 
               
               
                   
                 Value 63: 
                 11111100 
                 Code 39 
               
               
                   
                 Value 65: 
                 11011010 
                 Code 40 
               
               
                   
                 Value 68: 
                 00111010 
                 Code 41 
               
               
                   
                 value 69: 
                 10111010 
                 Code 42 
               
               
                   
                 value 71: 
                 01111010 
                 Code 43 
               
               
                   
                 value 72: 
                 11111010 
                 Code 44 
               
               
                   
                 value 75: 
                 00110110 
                 Code 45 
               
               
                   
                 value 76: 
                 10110110 
                 Code 46 
               
               
                   
                 value 78: 
                 01110110 
                 Code 47 
               
               
                   
                 value 79: 
                 11110110 
                 Code 48 
               
               
                   
                 value 81: 
                 00101110 
                 Code 49 
               
               
                   
                 value 82: 
                 10101110 
                 Code 50 
               
               
                   
                 value 84: 
                 01101110 
                 Code 51 
               
               
                   
                 value 85: 
                 11101110 
                 Code 52 
               
               
                   
                 value 86: 
                 10011110 
                 Code 53 
               
               
                   
                 value 88: 
                 01011110 
                 Code 54 
               
               
                   
                 value 89: 
                 11011110 
                 Code 55 
               
               
                   
                 value 92: 
                 00111110 
                 Code 56 
               
               
                   
                 value 93: 
                 10111110 
                 Code 57 
               
               
                   
                 value 95: 
                 01111110 
                 Code 58 
               
               
                   
                 value 96: 
                 11111110 
                 Code 59 
               
               
                   
                 value 98: 
                 01011101 
                 Code 60 
               
               
                   
                 value 99: 
                 11011101 
                 Code 61 
               
               
                   
                 value 102: 
                 00111101 
                 Code 62 
               
               
                   
                 value 103: 
                 10111101 
                 Code 63 
               
               
                   
                 value 105: 
                 01111101 
                 Code 64 
               
               
                   
                 value 106: 
                 11111101 
                 Code 65 
               
               
                   
                 value 107: 
                 01011011 
                 Code 66 
               
               
                   
                 value 108: 
                 11011011 
                 Code 67 
               
               
                   
                 value 111: 
                 00111011 
                 Code 68 
               
               
                   
                 value 112: 
                 10111011 
                 Code 69 
               
               
                   
                 value 114: 
                 01111011 
                 Code 70 
               
               
                   
                 value 115: 
                 11111011 
                 Code 71 
               
               
                   
                 value 118: 
                 00110111 
                 Code 72 
               
               
                   
                 value 119: 
                 10110111 
                 Code 73 
               
               
                   
                 value 121: 
                 01110111 
                 Code 74 
               
               
                   
                 value 122: 
                 11110111 
                 Code 75 
               
               
                   
                 value 124: 
                 00101111 
                 Code 76 
               
               
                   
                 value 125: 
                 10101111 
                 Code 77 
               
               
                   
                 value 127: 
                 01101111 
                 Code 78 
               
               
                   
                 value 128: 
                 11101111 
                 Code 79 
               
               
                   
                 value 129: 
                 10011111 
                 Code 80 
               
               
                   
                 value 131: 
                 01011111 
                 Code 81 
               
               
                   
                 value 132: 
                 11011111 
                 Code 82 
               
               
                   
                 value 135: 
                 00111111 
                 Code 83 
               
               
                   
                 value 136: 
                 10111111 
                 Code 84 
               
               
                   
                 value 138: 
                 01111111 
                 Code 85 
               
               
                   
                 value 139: 
                 11111111 
                 Code 86 
               
               
                   
                   
               
             
          
         
       
       
         
           
             for the group G 2  (2-5-9-14-20-28-38) 
           
         
       
     
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Pixel value 
                 Code word 
                 Code number 
               
               
                   
                   
               
             
             
               
                   
                 value 0: 
                 0000000 
                 Code 0 
               
               
                   
                 value 2: 
                 1000000 
                 Code 1 
               
               
                   
                 value 5: 
                 0100000 
                 Code 2 
               
               
                   
                 value 7: 
                 1100000 
                 Code 3 
               
               
                   
                 value 9: 
                 0010000 
                 Code 4 
               
               
                   
                 value 11: 
                 1010000 
                 Code 5 
               
               
                   
                 value 14: 
                 0110000 
                 Code 6 
               
               
                   
                 value 16: 
                 1110000 
                 Code 7 
               
               
                   
                 value 19: 
                 0101000 
                 Code 8 
               
               
                   
                 value 21: 
                 1101000 
                 Code 9 
               
               
                   
                 value 23: 
                 0011000 
                 Code 10 
               
               
                   
                 value 25: 
                 1011000 
                 Code 11 
               
               
                   
                 value 28: 
                 0111000 
                 Code 12 
               
               
                   
                 value 30: 
                 1111000 
                 Code 13 
               
               
                   
                 value 34: 
                 0110100 
                 Code 14 
               
               
                   
                 value 36: 
                 1110100 
                 Code 15 
               
               
                   
                 value 39: 
                 0101100 
                 Code 16 
               
               
                   
                 value 41: 
                 1101100 
                 Code 17 
               
               
                   
                 value 43: 
                 0011100 
                 Code 18 
               
               
                   
                 value 45: 
                 1011100 
                 Code 19 
               
               
                   
                 value 48: 
                 0111100 
                 Code 20 
               
               
                   
                 value 50: 
                 1111100 
                 Code 21 
               
               
                   
                 value 53: 
                 1011010 
                 Code 22 
               
               
                   
                 value 56: 
                 0111010 
                 Code 23 
               
               
                   
                 value 58: 
                 1111010 
                 Code 24 
               
               
                   
                 value 59: 
                 1010110 
                 Code 25 
               
               
                   
                 value 62: 
                 0110110 
                 Code 26 
               
               
                   
                 value 64: 
                 1110110 
                 Code 27 
               
               
                   
                 value 67: 
                 0101110 
                 Code 28 
               
               
                   
                 value 69: 
                 1101110 
                 Code 29 
               
               
                   
                 value 71: 
                 0011110 
                 Code 30 
               
               
                   
                 value 73: 
                 1011110 
                 Code 31 
               
               
                   
                 value 76: 
                 0111110 
                 Code 32 
               
               
                   
                 value 78: 
                 1111110 
                 Code 33 
               
               
                   
                 value 81: 
                 0011101 
                 Code 34 
               
               
                   
                 value 83: 
                 1011101 
                 Code 35 
               
               
                   
                 value 86: 
                 0111101 
                 Code 36 
               
               
                   
                 value 88: 
                 1111101 
                 Code 37 
               
               
                   
                 value 89: 
                 0011011 
                 Code 38 
               
               
                   
                 value 91: 
                 1011011 
                 Code 39 
               
               
                   
                 value 94: 
                 0111011 
                 Code 40 
               
               
                   
                 value 96: 
                 1111011 
                 Code 41 
               
               
                   
                 value 97: 
                 1010111 
                 Code 42 
               
               
                   
                 value 100: 
                 0110111 
                 Code 43 
               
               
                   
                 value 102: 
                 1110111 
                 Code 44 
               
               
                   
                 value 105: 
                 0101111 
                 Code 45 
               
               
                   
                 value 107: 
                 1101111 
                 Code 46 
               
               
                   
                 value 109: 
                 0011111 
                 Code 47 
               
               
                   
                 value 111: 
                 1011111 
                 Code 48 
               
               
                   
                 value 114: 
                 0111111 
                 Code 49 
               
               
                   
                 value 116: 
                 1111111 
                 Code 50 
               
               
                   
                   
               
             
          
         
       
     
         [0070]    All the pixel values can not be achieved. So, the missing pixel values are expressed from the available values by a dithering step. Two independent dithering blocks can be used for the two codes of these two packets of light. 
         [0071]    A way to determine the two split pixel values to be displayed by the two packets of light is given below. If i designates an input pixel value, a the split pixel value assigned to the first group of subfields G 1 , and b the split pixel value assigned to the second group of subfields G 2 , the values a and b can be computed as follows:
       For 0≦i≦1, a=i and b=0.   For 1≦i≦2, a=1 and b=i−1.   For 2≦i≦232, a=i/2 and b=i/2. (232=2×116)   For 232≦i≦255, a=i−116 and b=116.       
 
         [0076]    In PPC, the same light energy is emitted during these two packets of light. In this example, for all levels between 2 and 232, half of this value is expressed by the first peak and the second half by the second peak. So for the input pixel value 140, the two peaks have to express the level 70. They both need dithering to render it because this level is not available with these groups of sub-fields. The first peak will use a dithering level ½ using the pixel values 69 (10111010) and 71 (01111010). The second peak will use a dithering level ½ using the pixel values 69 (1101110) and 71 (0011110). In case of a uniform gray level of 70 in input, the code of the first split pixel value will display a chequered pattern on 2 sub-fields, while the code of the second split pixel value on 3 sub-fields, so in total 5 sub-fields will use a chequered pattern. This means that the data driver could overheat. 
         [0077]    Since the two peaks are working in parallel, the number of sub-field bit changes between two pixel values can be twice as big as when working with only one peak (classical code). For the input levels below 2 and above 232, since the two peaks are not working in parallel, the number of sub-field bit changes will be minimal. 
         [0078]      FIG. 5  shows the equivalent number of chequered pattern for every pixel value between 2 and 232 for the Parallel Peak Coding as defined previously. The equivalent number of chequered patterns for a pixel value is the sum of the ENCPs defined for all its subfields. As it can be seen the equivalent number of chequered patterns for different pixel values displayed by using the Parallel Peak Coding can be quite high (higher than 3 or 4) for some pixel values. 
         [0079]    In one peak, there are maximum 4 sub-field bit changes between the two pixel values used for the dithering. But since the two peaks are working in parallel, these sub-field bit changes add up. When the dithering level is close to ½ on the two peaks, the number of bit changes is maximum for the considered pixel value and can reach 6 or 7. 
         [0080]    The inventive method consists in selecting appropriate split pixel values and dithering levels to reduce the equivalent number of chequered patterns. The invention is described for a dithering step consisting in associating to each split pixel value V one dithering level L used to dither between two different pixel values V 1  and V 2  that can be coded by the given group of subfields such that V=(1−L)×V 1 +L×V 2  with V 1 &lt;V 2  and L∈[0, 1]. According to the invention, the split pixel values and dithering levels are selected such that, if the sum of the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the first split pixel value and the number of bits having a different state in the subfield code word of the pixel value V 1  and the subfield code word of the pixel value V 2  associated to the second split pixel value is greater than or equal to a first threshold, the sum of the absolute differences between the dithering level of each split pixel value and ½ is greater than a second threshold. 
         [0081]    Thus, the split pixel values and the dithering levels are selected such that the two or more split pixel values do not have simultaneously a dithering level close to ½ where the ENCP is maximal (see  FIG. 4 ). 
         [0082]    The second threshold is advantageously equal to or greater than ¼ and is preferably equal to ½. 
         [0083]    The first threshold is preferably equal to 0. Thus, the dithering level is optimized whatever the number of bit changes in the two split pixel values. 
         [0084]    In a variant, the first threshold can be increased to a value greater than 0. For example, it can be equal to 4. So, the optimized selection of the split pixel values and the dithering levels will be done only if the number of bit changes in the two split pixel values is 4 or more. 
         [0085]    In the following description, the first threshold is preferably equal to 0. 
         [0086]    In a specific embodiment, it consists in splitting the set of subfields into at least two groups of subfields and using dithering levels other than ½ for the split pixel values associated to these groups of subfields or using a dithering level of ½ for only one split pixel value and a dithering level of 0 (no dithering) for the other split pixel value. 
         [0087]    For this Parallel Peak Coding (PPC), it consists in using a dithering level of ½ on only one of the two split pixel values or by using a dithering level other than ½ on the two split pixel values. The goal of the inventive method is to maximize the sum of the absolute differences between the dithering level of each split value and ½ (dithering level where the ENCP is maximal). 
         [0088]    The inventive method solution will be now described in detail for Parallel Peak Coding (PPC), i.e. two substantially identical split pixel values (a and b) and two groups of subfields (G 1  and G 2 ) having substantially the same number of subfields. 
         [0089]    As mentioned before, the inventive method for PPC consists in using a dithering level of ½ on only one of the two split pixel values or by using a dithering level other than ½ on the two split pixel values. For example basic pixel values using a dithering level of 0 for at least one of the two split pixel values are first defined. When one split pixel value uses a dithering level ½, the other one is forced to use a dithering level 0 (no dithering). Thus the two split pixel values are not necessarily exactly identical but they are very close. For these basic pixel values, the maximum ENCP is then equal to the number of sub-field bit changes for the split pixel value having a dithering level different from 0. 
         [0090]    More precisely, each basic pixel value is the combination of a split pixel value a displayed during the first peak and a split pixel value b displayed during the second peak. Each split pixel value is either a pixel value without dithering or a pixel value using a dithering level ½. It can not be the combination of two split pixel values using dithering levels ½. From one new pixel value to the next new pixel value, the first split pixel value (respectively the second split pixel value) can either be unchanged if the dithering level is equal to 0 or go from a code using no dithering to a code using a dithering level ½ or inversely. 
         [0091]    Below is given an example of the new Parallel peak Code, called hereinafter matched PPC, made for the 15 Sub-fields presented previously. If we consider two successive code numbers n and n+1 in the encoding table defined previously for the group G 1  or for the group G 2 , the code n½ means that a dithering level of ½ is assigned to the code n and that the pixel value of the code n½ is equal to the sum of half of the value of the code n and half of the value of the code n+1. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 1 st  peak 
                   
                 2 nd  peak 
                 basic 
               
             
          
           
               
                   
                   
                 Pixel 
                   
                 Pixel 
                 pixel 
               
               
                   
                 code 
                 value a 
                 code 
                 value b 
                 value 
               
               
                   
                   
               
             
          
           
               
                   
                  0 
                 0 
                  0 
                 0 
                 0 
               
               
                   
                  0½ 
                 0.5 
                  0 
                 0 
                 0.5 
               
               
                   
                  1 
                 1 
                  0½ 
                 1 
                 2 
               
               
                   
                  1½ 
                 2 
                  1 
                 2 
                 4 
               
               
                   
                  2 
                 3 
                  1½ 
                 3.5 
                 6.5 
               
               
                   
                  2½ 
                 3.5 
                  2 
                 5 
                 8.5 
               
               
                   
                  3 
                 4 
                  2 
                 5 
                 9 
               
               
                   
                  3½ 
                 5.5 
                  2 
                 5 
                 10.5 
               
               
                   
                  4 
                 7 
                  2½ 
                 6 
                 13 
               
               
                   
                  4½ 
                 7.5 
                  3 
                 7 
                 14.5 
               
               
                   
                  5 
                 8 
                  3½ 
                 8 
                 16 
               
               
                   
                  5½ 
                 9 
                  4 
                 9 
                 18 
               
               
                   
                  6 
                 10 
                  4½ 
                 10 
                 20 
               
               
                   
                  6½ 
                 10.5 
                  5 
                 11 
                 21.5 
               
               
                   
                  7 
                 11 
                  5½ 
                 12.5 
                 23.5 
               
               
                   
                  7½ 
                 12.5 
                  6 
                 14 
                 26.5 
               
               
                   
                  8 
                 14 
                  6 
                 14 
                 28 
               
               
                   
                  8½ 
                 14.5 
                  6 
                 14 
                 28.5 
               
               
                   
                  9 
                 15 
                  6½ 
                 15 
                 30 
               
               
                   
                  9½ 
                 16.5 
                  7 
                 16 
                 32.5 
               
               
                   
                 10 
                 18 
                  7½ 
                 17.5 
                 35.5 
               
               
                   
                 10½ 
                 18.5 
                  8 
                 19 
                 37.5 
               
               
                   
                 11 
                 19 
                  8 
                 19 
                 38 
               
               
                   
                 11½ 
                 20 
                  8 
                 19 
                 39 
               
               
                   
                 12 
                 21 
                  8½ 
                 20 
                 41 
               
               
                   
                 12½ 
                 21.5 
                  9 
                 21 
                 42.5 
               
               
                   
                 13 
                 22 
                  9½ 
                 22 
                 44 
               
               
                   
                 13½ 
                 23 
                 10 
                 23 
                 46 
               
               
                   
                 14 
                 24 
                 10½ 
                 24 
                 48 
               
               
                   
                 14½ 
                 24.5 
                 11 
                 25 
                 49.5 
               
               
                   
                 15 
                 25 
                 11 
                 25 
                 50 
               
               
                   
                 15½ 
                 26 
                 11 
                 25 
                 51 
               
               
                   
                 16 
                 27 
                 11½ 
                 26.5 
                 53.5 
               
               
                   
                 16½ 
                 27.5 
                 12 
                 28 
                 55.5 
               
               
                   
                 17 
                 28 
                 12 
                 28 
                 56 
               
               
                   
                 17½ 
                 28.5 
                 12 
                 28 
                 56.5 
               
               
                   
                 18 
                 29 
                 12½ 
                 29 
                 58 
               
               
                   
                 18½ 
                 30 
                 13 
                 30 
                 60 
               
               
                   
                 19 
                 31 
                 13 
                 30 
                 61 
               
               
                   
                 19½ 
                 31.5 
                 13 
                 30 
                 61.5 
               
               
                   
                 20 
                 32 
                 13½ 
                 32 
                 64 
               
               
                   
                 20½ 
                 33.5 
                 14 
                 34 
                 67.5 
               
               
                   
                 21 
                 35 
                 14½ 
                 35 
                 70 
               
               
                   
                 21½ 
                 35.5 
                 15 
                 36 
                 71.5 
               
               
                   
                 22 
                 36 
                 15 
                 36 
                 72 
               
               
                   
                 22½ 
                 37 
                 15 
                 36 
                 73 
               
               
                   
                 23 
                 38 
                 15½ 
                 37.5 
                 75.5 
               
               
                   
                 23½ 
                 38.5 
                 16 
                 39 
                 77.5 
               
               
                   
                 24 
                 39 
                 16½ 
                 40 
                 79 
               
               
                   
                 24½ 
                 40.5 
                 17 
                 41 
                 81.5 
               
               
                   
                 25 
                 42 
                 17½ 
                 42 
                 84 
               
               
                   
                 25½ 
                 42.5 
                 18 
                 43 
                 85.5 
               
               
                   
                 26 
                 43 
                 18 
                 43 
                 86 
               
               
                   
                 26½ 
                 44 
                 18 
                 43 
                 87 
               
               
                   
                 27 
                 45 
                 18½ 
                 44 
                 89 
               
               
                   
                 27½ 
                 45.5 
                 19 
                 45 
                 90.5 
               
               
                   
                 28 
                 46 
                 19½ 
                 46.5 
                 92.5 
               
               
                   
                 28½ 
                 47 
                 20 
                 48 
                 95 
               
               
                   
                 29 
                 48 
                 20 
                 48 
                 96 
               
               
                   
                 29½ 
                 48.5 
                 20 
                 48 
                 96.5 
               
               
                   
                 30 
                 49 
                 20½ 
                 49 
                 98 
               
               
                   
                 30½ 
                 50 
                 21 
                 50 
                 100 
               
               
                   
                 31 
                 51 
                 21½ 
                 51.5 
                 102.5 
               
               
                   
                 31½ 
                 51.5 
                 22 
                 53 
                 104.5 
               
               
                   
                 32 
                 52 
                 22 
                 53 
                 105 
               
               
                   
                 32½ 
                 52.5 
                 22 
                 53 
                 105.5 
               
               
                   
                 33 
                 53 
                 22 
                 53 
                 106 
               
               
                   
                 33½ 
                 54 
                 22 
                 53 
                 107 
               
               
                   
                 34 
                 55 
                 22½ 
                 54.5 
                 109.5 
               
               
                   
                 34½ 
                 55.5 
                 23 
                 56 
                 111.5 
               
               
                   
                 35 
                 56 
                 23½ 
                 57 
                 113 
               
               
                   
                 35½ 
                 57.5 
                 24 
                 58 
                 115.5 
               
               
                   
                 36 
                 59 
                 24½ 
                 58.5 
                 117.5 
               
               
                   
                 36½ 
                 59.5 
                 25 
                 59 
                 118.5 
               
               
                   
                 37 
                 60 
                 25½ 
                 60.5 
                 120.5 
               
               
                   
                 37½ 
                 61 
                 26 
                 62 
                 123 
               
               
                   
                 38 
                 62 
                 26 
                 62 
                 124 
               
               
                   
                 38½ 
                 62.5 
                 26 
                 62 
                 124.5 
               
               
                   
                 39 
                 63 
                 26½ 
                 63 
                 126 
               
               
                   
                 39½ 
                 64 
                 27 
                 64 
                 128 
               
               
                   
                 40 
                 65 
                 27½ 
                 65.5 
                 130.5 
               
               
                   
                 40½ 
                 66.5 
                 28 
                 67 
                 133.5 
               
               
                   
                 41 
                 68 
                 28½ 
                 68 
                 136 
               
               
                   
                 41½ 
                 68.5 
                 29 
                 69 
                 137.5 
               
               
                   
                 42 
                 69 
                 29½ 
                 70 
                 139 
               
               
                   
                 42½ 
                 79 
                 30 
                 71 
                 141 
               
               
                   
                 43 
                 71 
                 30 
                 71 
                 142 
               
               
                   
                 43½ 
                 71.5 
                 30 
                 71 
                 142.5 
               
               
                   
                 44 
                 72 
                 30½ 
                 72 
                 144 
               
               
                   
                 44½ 
                 73.5 
                 31 
                 73 
                 146.5 
               
               
                   
                 45 
                 75 
                 31½ 
                 74.5 
                 149.5 
               
               
                   
                 45½ 
                 75.5 
                 32 
                 76 
                 151.5 
               
               
                   
                 46 
                 76 
                 32½ 
                 77 
                 153 
               
               
                   
                 46½ 
                 77 
                 33 
                 78 
                 155 
               
               
                   
                 47 
                 78 
                 33 
                 78 
                 156 
               
               
                   
                 47½ 
                 78.5 
                 33 
                 78 
                 156.5 
               
               
                   
                 48 
                 79 
                 33½ 
                 79.5 
                 158.5 
               
               
                   
                 48½ 
                 80 
                 34 
                 81 
                 161 
               
               
                   
                 49 
                 81 
                 34 
                 81 
                 162 
               
               
                   
                 49½ 
                 81.5 
                 34 
                 81 
                 162.5 
               
               
                   
                 50 
                 82 
                 34½ 
                 82 
                 164 
               
               
                   
                 50½ 
                 83 
                 35 
                 83 
                 166 
               
               
                   
                 51 
                 84 
                 35½ 
                 84.5 
                 168.5 
               
               
                   
                 51½ 
                 84.5 
                 36 
                 86 
                 170.5 
               
               
                   
                 52 
                 85 
                 36 
                 86 
                 171 
               
               
                   
                 52½ 
                 85.5 
                 36 
                 86 
                 171.5 
               
               
                   
                 53 
                 86 
                 36½ 
                 87 
                 173 
               
               
                   
                 53½ 
                 87 
                 37 
                 88 
                 175 
               
               
                   
                 54 
                 88 
                 37 
                 88 
                 176 
               
               
                   
                 54 
                 88 
                 37½ 
                 88.5 
                 176.5 
               
               
                   
                 54½ 
                 88.5 
                 38 
                 89 
                 177.5 
               
               
                   
                 55 
                 89 
                 38½ 
                 90 
                 179 
               
               
                   
                 55½ 
                 90.5 
                 39 
                 91 
                 181.5 
               
               
                   
                 56 
                 92 
                 39 
                 91 
                 183 
               
               
                   
                 56½ 
                 92.5 
                 39 
                 91 
                 183.5 
               
               
                   
                 57 
                 93 
                 39½ 
                 92.5 
                 185.5 
               
               
                   
                 57½ 
                 94 
                 40 
                 94 
                 188 
               
               
                   
                 58 
                 95 
                 40½ 
                 95 
                 190 
               
               
                   
                 58½ 
                 95.5 
                 41 
                 96 
                 191.5 
               
               
                   
                 59 
                 96 
                 41½ 
                 96.5 
                 192.5 
               
               
                   
                 59½ 
                 97 
                 42 
                 97 
                 194 
               
               
                   
                 60 
                 98 
                 42½ 
                 98.5 
                 196.5 
               
               
                   
                 60½ 
                 98.5 
                 43 
                 100 
                 198.5 
               
               
                   
                 61 
                 99 
                 43 
                 100 
                 199 
               
               
                   
                 61½ 
                 100.5 
                 43 
                 100 
                 200.5 
               
               
                   
                 62 
                 102 
                 43½ 
                 101 
                 203 
               
               
                   
                 62½ 
                 102.5 
                 44 
                 102 
                 204.5 
               
               
                   
                 63 
                 103 
                 44½ 
                 103.5 
                 206.5 
               
               
                   
                 63½ 
                 104 
                 45 
                 105 
                 209 
               
               
                   
                 64 
                 105 
                 45 
                 105 
                 210 
               
               
                   
                 64½ 
                 105.5 
                 45 
                 105 
                 210.5 
               
               
                   
                 65 
                 106 
                 45½ 
                 106 
                 212 
               
               
                   
                 65½ 
                 106.5 
                 46 
                 107 
                 213.5 
               
               
                   
                 66 
                 107 
                 46 
                 107 
                 214 
               
               
                   
                 66½ 
                 107.5 
                 46 
                 107 
                 214.5 
               
               
                   
                 67 
                 108 
                 46½ 
                 108 
                 216 
               
               
                   
                 67½ 
                 109.5 
                 47 
                 109 
                 218.5 
               
               
                   
                 68 
                 111 
                 47½ 
                 110 
                 221 
               
               
                   
                 68½ 
                 111.5 
                 48 
                 111 
                 222.5 
               
               
                   
                 69 
                 112 
                 48½ 
                 112.5 
                 224.5 
               
               
                   
                 69½ 
                 113 
                 49 
                 114 
                 227 
               
               
                   
                 70 
                 114 
                 49 
                 114 
                 228 
               
               
                   
                 70½ 
                 114.5 
                 49 
                 114 
                 228.5 
               
               
                   
                 71 
                 115 
                 49½ 
                 115 
                 230 
               
               
                   
                 71½ 
                 116.5 
                 50 
                 116 
                 232.5 
               
               
                   
                 72 
                 118 
                 50 
                 116 
                 234 
               
               
                   
                 72½ 
                 118.5 
                 50 
                 116 
                 234.5 
               
               
                   
                 73 
                 119 
                 50 
                 116 
                 235 
               
               
                   
                 73½ 
                 120 
                 50 
                 116 
                 236 
               
               
                   
                 74 
                 121 
                 50 
                 116 
                 237 
               
               
                   
                 74½ 
                 121.5 
                 50 
                 116 
                 237.5 
               
               
                   
                 75 
                 122 
                 50 
                 116 
                 238 
               
               
                   
                 75½ 
                 123 
                 50 
                 116 
                 239 
               
               
                   
                 76 
                 124 
                 50 
                 116 
                 240 
               
               
                   
                 76½ 
                 124.5 
                 50 
                 116 
                 240.5 
               
               
                   
                 77 
                 125 
                 50 
                 116 
                 241 
               
               
                   
                 77½ 
                 126 
                 50 
                 116 
                 242 
               
               
                   
                 78 
                 127 
                 50 
                 116 
                 243 
               
               
                   
                 78½ 
                 127.5 
                 50 
                 116 
                 243.5 
               
               
                   
                 79 
                 128 
                 50 
                 116 
                 244 
               
               
                   
                 79½ 
                 128.5 
                 50 
                 116 
                 244.5 
               
               
                   
                 80 
                 129 
                 50 
                 116 
                 245 
               
               
                   
                 80½ 
                 130 
                 50 
                 116 
                 246 
               
               
                   
                 81 
                 131 
                 50 
                 116 
                 247 
               
               
                   
                 81½ 
                 131.5 
                 50 
                 116 
                 247.5 
               
               
                   
                 82 
                 132 
                 50 
                 116 
                 248 
               
               
                   
                 82½ 
                 133.5 
                 50 
                 116 
                 249.5 
               
               
                   
                 83 
                 135 
                 50 
                 116 
                 251 
               
               
                   
                 83½ 
                 135.5 
                 50 
                 116 
                 251.5 
               
               
                   
                 84 
                 136 
                 50 
                 116 
                 252 
               
               
                   
                 84½ 
                 137 
                 50 
                 116 
                 253 
               
               
                   
                 85 
                 138 
                 50 
                 116 
                 254 
               
               
                   
                 85½ 
                 138.5 
                 50 
                 116 
                 254.5 
               
               
                   
                 86 
                 139 
                 50 
                 116 
                 255 
               
               
                   
                   
               
             
          
         
       
     
         [0092]    The missing pixel values (pixel values between two basic pixel values) are generated by interpolation of these basic pixel values. 
         [0093]    It is interesting to see what happens in the two peaks when interpolating the missing pixel values. Each interpolated pixel value is located between two consecutive basic pixel values (a first one and a second one). Depending on the nature of these two basic pixel values (using a ½ dithering or no dithering for the first split pixel value and/or for the second split pixel value), two different cases can be defined (all the others being symmetrical):
       a) the first basic pixel value has one split pixel value using no dithering (code n) and the other one using also no dithering (code p), and the second basic pixel value has one split pixel value using a dithering level ½ (code n ½) and the other one using no dithering (code p). In this case, all the interpolated pixel values between the pixel values corresponding to the codes (n+p) and (n ½+p) will use a dithering only on one split pixel value, the dithering level of this split pixel value being included between 0 and 1.   As an example in the previous table, the interpolated pixel value 200 is generated by the code  61  with a dithering level equal to 113(=⅔×½) for the first split pixel value and the code  43  with no dithering for the second split pixel value. The ENCP is then about 0.66×3 (3 subfield bit changes) for the first split pixel value and 0 for the second split pixel value according to  FIG. 4 . The global ENCP is thus about 2.   b) The first basic pixel value has one split pixel value having a dithering level equal to ½ (code n½) and the other one using no dithering (code p), and the second basic pixel value has one split pixel value using no dithering (code (n+1)) and the other one using a dithering level ½ (code p½). In this case, all the interpolated pixel values between the pixel values corresponding to the codes (n½+p) and ((n+1)+p½) will use dithering on the two split pixel values. But the two dithering levels will be, in a certain sense, complementary (the difference of the two dithering levels will always be equal to ½). For example, one pixel value will use a dithering level ¾ for one split pixel value and ¼ on the other. If the number of sub-field bit changes between code n and code (n+1) is the same than between the code p and (p+1), then all pixel values between the pixel values corresponding to the codes (n½+p) and ((n+1)+p½) will have the same ENCP. In other words, the ENCP between the two new pixel values between the pixel values corresponding to the codes (n½+p) and ((n+1)+p½) will go from the ENCP of one split pixel value to the ENCP of the other split pixel value. It means that the ENCP will smaller than or equal to the biggest ENCP of the two split pixel values).   As an example, the interpolated video value  140  is generated by the code  42  with a dithering level ¼ for the first split pixel value and the code  29  with a dithering level ¾ for the second split pixel value. The ENCP is about 0.5×2 (2 subfield bit changes) for the first split pixel value and 0.5×3 (3 subfield bit changes) for the second split pixel value according to  FIG. 4 . The global ENCP is about 2.5 (instead of 5=1×2+1×3 if a code 42½ is used for the first split pixel value and a code 29½ for the second split pixel value).       
 
         [0098]    This matched PPC remains compatible with the standard PPC implementation since the two split pixel values have substantially the same energy. Only modified look-up tables are needed. 
         [0099]    For all video inputs, the partition between the first and the second split pixel values is shown at  FIG. 6 . In case of standard PPC, the two curves would be identical for all input values between 2 and 232. Here, they are slightly different. But because their differences are very small, the picture quality is substantially the same than with standard PPC. In fact, the picture quality is slightly better because the dithering levels on the two split pixel values are mostly complementary. 
         [0100]    Concerning driver heat,  FIG. 7  shows the equivalent number of chequered patterns for every video input between 2 and 232 when the inventive method is applied. This figure is to be compared with  FIG. 5  related to the standard PPC. The maximum equivalent number of chequered pattern is now reduced to 4. 
         [0101]    The inventive method has been described for the Parallel Peak Coding, i.e. for a coding wherein the subfields are divided into two groups of subfields generating substantially the same light energy and wherein the two split pixel values are substantially equal. It can be extended to other codings wherein the subfields are divided into three or more groups of subfields generating different light energy and wherein the pixel values are thus split into three or more different split pixel values. 
         [0102]    The circuit for implementing the inventive method is the same than the one used for implementing the standard PPC. Only the content of the look-up tables is amended. The driver heat problem is thus solved without extra costs and without loss of quality. 
         [0103]    In  FIG. 8 , a block diagram of a possible circuit implementation for encoding the pixel values into sub-field code word as described above is illustrated. Input R,G,B video data, IN[9:0], coming for example from a video degamma unit, are forwarded to splitting means  20  used for outputting, for each input video data, the split pixel values a and b. These means comprise for example at least two Look-Up Tables (LUTs), one for each split value. In the case of PPC, there are two LUTs, one delivering the split pixel value a and one for delivering the split pixel value b. The split pixel value a (respectively b) is then advantageously transmitted to a dithering block  21  (resp.  31 ) for generating, if need be, values encodable by the subfield group G 1  (resp. G 2 ) as described before. The dithered value is then forwarded to a subfield coding block  22  (resp. 32 ) for outputting the corresponding subfield code word. This sub-field code word will be used by the display panel for driving the lighting period of the cells of the panel. 
         [0104]    It is also possible to use the matched Parallel Peak Code with a frame frequency twice as high. For example, instead of having a 50 Hz video input, it is also possible to have a 100 Hz video input and to use, depending on the parity of the frame (odd or even), the first or the second group of sub-fields (G 1  or G 2 ) and the corresponding encoding table. Of course, it is not limited to 100 Hz; it can also be used for other frequencies like 72, 75, 80, 85, 90 or even 120 Hz.  FIG. 9  is illustrated this possibility. Count is a 1-bit counter, which is incremented at each frame. Depending on its value (0 or 1), the video is encoded with sub-field group G 1  and the encoding table assigned to this first group (case  0 ) or with sub-field group G 2  and the encoding table assigned to this second group (case  1 ). 
         [0105]    The invention has been described for The Parallel Peak Coding (PPC) having a big problem of driver overheating. Of course, the principle of the inventive method can be extended to other codings using at least two groups of subfields.