Abstract:
A method and an apparatus capable of increasing the video depths depending on the video content of each line in order to provide a maximum of color gradation for each given scene shall be proposed. For this purpose there is disclosed an apparatus for driving a display device including input means for receiving a digital value as video level for each pixel or cell of a line of the display device, reference signalling means for providing at least one reference driving signal and driving means for generating a driving signal on the basis of the digital value and the at least one reference driving signal. The apparatus further includes adjusting means for adjusting the at least one reference driving signal in dependence of the digital values of at least a part of the line.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for driving a display device including the steps of providing a digital value as video level for each pixel or cell of a line of the display device, providing at least one reference driving signal and generating a driving signal on the basis of the digital value and the at least one reference driving signal. Furthermore, the present invention relates to a respective apparatus for driving a display device.  
       BACKGROUND OF THE INVENTION  
       [0002]     The structure of an active matrix OLED (organic light emitting display) or AMOLED is well known. According to  FIG. 1  it comprises: 
        an active matrix  1  containing, for each cell (one pixel includes a red cell, a green cell and a blue cell), an association of several TFTs T 1 , T 2  with a capacitor C connected to an OLED material. Above the TFTs the capacitor C acts as a memory component that stores a value during a part of the video frame, this value being representative of a video information to be displayed by the cell  2  during the next video frame or the next part of the video frame. The TFTs act as switches enabling the selection of the cell  2 , the storage of a data in the capacitor C and the displaying by the cell  2  of a video information corresponding to the stored data;     a row or gate driver  3  that selects line by line the cells  2  of the matrix  1  in order to refresh their content;     a column or source driver  4  that delivers the data to be stored in each cell  2  of the current selected line; this component receives the video information for each cell  2 ; and     a digital processing unit  5  that applies required video and signal processing steps and that delivers the required control signals to the row and column drivers  3 ,  4 .        
 
         [0007]     Actually, there are two ways for driving the OLED cells  2 . In a first way, each digital video information sent by the digital processing unit  5  is converted by the column drivers  4  into a current whose amplitude is directly proportional to the video level. This current is provided to the appropriate cell  2  of the matrix  1 . In a second way, the digital video information sent by the digital processing unit  5  is converted by the column drivers  4  into a voltage whose amplitude is proportional to the square of the video level. This current or voltage is provided to the appropriate cell  2  of the matrix  1 .  
         [0008]     However, in principle, an OLED is current driven so that each voltage based driven system is based on a voltage to current converter to achieve appropriate cell lighting.  
         [0009]     From the above, it can be deduced that the row driver  3  has a quite simple function since it only has to apply a selection line by line. It is more or less a shift register. The column driver  4  represents the real active part and can be considered as a high level digital to analog converter.  
         [0010]     The displaying of a video information with such a structure of AMOLED is symbolized in  FIG. 2 . The input signal is forwarded to the digital processing unit that delivers, after internal processing, a timing signal for row selection to the row driver synchronized with the data sent to the column driver  4 . The data transmitted to the column driver  4  are either parallel or serial. Additionally, the column driver  4  disposes of a reference signalling delivered by a separate reference signalling device  6 . This component  6  delivers a set of reference voltages in case of voltage driven circuitry or a set of reference currents in case of current driven circuitry. The highest reference is used for the white and the lowest for the smallest gray level. Then, the column driver  4  applies to the matrix cells  2  the voltage or current amplitude corresponding to the data to be displayed by the cells  2 .  
         [0011]     In order to illustrate this concept, the example of a voltage driven circuitry will be taken in the rest of this document. The driver of this example uses 8 reference voltages named V 0  to V 7  and the video levels are built as explained in the following table 1.  
                         TABLE 1                           Gray level table from voltage driver            Video level   Grayscale voltage level                0   V7        1   V7 + (V6 − V7) × 9/1175        2   V7 + (V6 − V7) × 32/1175        3   V7 + (V6 − V7) × 76/1175        4   V7 + (V6 − V7) × 141/1175        5   V7 + (V6 − V7) × 224/1175        6   V7 + (V6 − V7) × 321/1175        7   V7 + (V6 − V7) × 425/1175        8   V7 + (V6 − V7) × 529/1175        9   V7 + (V6 − V7) × 630/1175       10   V7 + (V6 − V7) × 727/1175       11   V7 + (V6 − V7) × 820/1175       12   V7 + (V6 − V7) × 910/1175       13   V7 + (V6 − V7) × 998/1175       14   V7 + (V6 − V7) × 1086/1175       15   V6       16   V6 + (V5 − V6) × 89/1097       17   V6 + (V5 − V6) × 173/1097       18   V6 + (V5 − V6) × 250/1097       19   V6 + (V5 − V6) × 320/1097       20   V6 + (V5 − V6) × 386/1097       21   V6 + (V5 − V6) × 451/1097       22   V6 + (V5 − V6) × 517/1097       . . .   . . .           V1 + (V0 − V1) × 2278/3029       251    V1 + (V0 − V1) × 2411/3029       252    V1 + (V0 − V1) × 2549/3029       253    V1 + (V0 − V1) × 2694/3029       254    V1 + (V0 − V1) × 2851/3029       255    V0                  
 
         [0012]     Table 1 illustrates the obtained output voltages (gray scale voltage levels) from the voltage driver for various input video levels. For instance, the reference voltages of Table 2 are used.  
                                           TABLE 2                           Example of voltage references                Reference Vn   Voltage (V)                            V0   3           V1   2.6           V2   2.2           V3   1.4           V4   0.6           V5   0.3           V6   0.16           V7   0                      
 
         [0013]     Then, the grayscale voltage levels of following Table 3 depending on video input levels according to Table 1 and Table 2 are obtained:  
                             TABLE 3                           Example of gray level voltages                Video level   Grayscale voltage level                        0    0.00 V            1   0.001 V            2   0.005 V            3   0.011 V            4    0.02 V            5   0.032 V            6   0.045 V            7    0.06 V            8   0.074 V            9   0.089 V           10   0.102 V           11   0.115 V           12   0.128 V           13    0.14 V           14   0.153 V           15   0.165 V           16   0.176 V           17   0.187 V           18   0.196 V           19   0.205 V           20   0.213 V           21   0.221 V           22   0.229 V           . . .   . . .           250    2.901 V           251    2.919 V           252    2.937 V           253    2.956 V           254    2.977 V           255     3.00 V                      
 
         [0014]     As can be seen in the previous paragraph current AMOLED concepts are capable of delivering 8-bit gradation per color. This can be further enhanced by using more advanced solutions like improvements on analog sub-fields.  
         [0015]     In any case, there will be the need in the future of displays having more video-depth. This trend can be seen in the development of transmission standards based on 10-bit color channels. At the same time, various display manufacturers like PDP makers are claiming providing displays with more than 10-bit color-depth.  
       SUMMARY OF THE INVENTION  
       [0016]     The object of the present invention is to provide a method and an apparatus capable of increasing the video depth depending on the video content of each line in order to provide a maximum of color gradation for a given scene. I.e., a line content picture enhancement shall be provided.  
         [0017]     According to the present invention this object is solved by a method for driving a display device including the steps of 
        providing a digital value as video level for each pixel or cell of a line of said display device,     providing at least one reference driving signal and     generating a driving signal on the basis of said digital value and said at least one reference driving signal, as well as     adjusting said video level and said at least one reference driving signal in dependence of the digital values of at least a part of said line.        
 
         [0022]     Furthermore, there is provided an apparatus for driving a display device including 
        input means for receiving a digital value for each pixel or cell of a line of said display device,     reference signalling means for providing at least one reference driving signal and     driving means for generating a driving signal on the basis of said digital value and said at least one reference driving signal, as well as     adjusting means for adjusting said video level and said at least one reference driving signal in dependence of the digital values of at least a part of said line.        
 
         [0027]     Preferably, the display device is an AMOLED or a LCD. Especially, these display concepts can be improved by the above described method or apparatus.  
         [0028]     The reference driving signal may be a reference voltage or a reference current. Each of these driving systems can profit from the present invention.  
         [0029]     According to a further preferred embodiment, a maximum digital value of at least the part of a line is determined and when adjusting the reference driving signals, they are assigned to digital values between a minimum digital value, which is to be determined or is predetermined, and a maximum digital value. By this way, the whole range of gray scale levels is used for the video input of one line.  
         [0030]     A further improvement can be obtained when determining a histogram of the digital values of at least the part of a line and adjusting the reference driving signals on the basis of this histogram. This results in an enhanced picture line-dependent gradation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     Exemplary embodiments of the invention are illustrated in the drawings showing in:  
         [0032]      FIG. 1 a  circuit diagram of an AMOLED electronic according to the prior art;  
         [0033]      FIG. 2 a  possible OLED display structure according to the prior art;  
         [0034]      FIG. 3 a  sequence of the movie “Zorro” and a corresponding line analysis diagram;  
         [0035]      FIG. 4 a  sequence of a Colombia movie and a corresponding line analysis diagram;  
         [0036]      FIG. 5 a  histogram of line  303  from the sequence “Zorro”;  
         [0037]      FIG. 6 a  histogram of line  303  with optimized reference voltages and  
         [0038]      FIG. 7 a  block diagram of a hardware embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0039]     The main idea behind the inventive concept is based on the fact that in a video scene, the whole video dynamic range is not used on a large part of the scene.  FIGS. 3 and 4  show typical examples for frames of different dynamics.  FIG. 3  shows a dark picture of the movie “Zorro”. The picture has the format 4:3 with 561 lines. On the right hand side of  FIG. 3  the maximum video level of each line is plotted.  
         [0040]      FIG. 4  shows a picture of a Colombia film. The picture has the format 16:9 with 267 lines. The right hand side diagram of  FIG. 4  illustrates that nearly each line is driven with a maximum video level.  
         [0041]     Together,  FIGS. 3 and 4  show that for some sequences there are strong differences in the vertical distribution of video levels. The most differences are located in dark scenes with some luminous content as illustrated by the sequence “Zorro”.  
         [0042]     On the other hand, it is important to notice that in dark scenes the eye is much more sensitive to picture gradation. Therefore, an optimization of picture gradation for dark scenes while keeping luminous scenes quite stable would have a positive effect on the global picture quality.  
         [0043]     As already explained, the main idea is to perform a picture line-dependent gradation by optimizing the driver reference signalling (voltage or current) to the maximum of video levels available in a line. For instance, in the sequence “Zorro” of  FIG. 3 , the maximum video level for line  303  is  128 . Therefore, if nothing is done, from the 8-bit of available gradations ( 0  to  255 ), only 7 are used for this line ( 0  to  128 ). However, according to the present invention, the 8-bit gradation for video levels between  0  and  128  will be used. In order to do that, the reference signalling of the driver is adjusted to these 129 levels. In the present example of a voltage driven system the maximum voltage level will be adjusted to the  129 / 256  of the original one and all other voltages accordingly. This is illustrated in following Table 4:  
                                           TABLE 4                           Example of adjusted voltage references for line 303            Reference Vn   Line 303 Voltage (Vn)   Original Voltage (Vrefn)                    V0   1.5   3       V1   1.3   2.6       V2   1.1   2.2       V3   0.7   1.4       V4   0.3   0.6       V5   0.15   0.3       V6   0.08   0.16       V7   0   0                  
 
         [0044]     More generally, a complex function can be applied to the reference signalling under the form S n =f(Sref n ;MAX(Line)) where MAX(Line) represents the maximum video level used for a given line and Srefn the reference signaling (either voltage or current). This function can be implemented by means of LUT or embedded mathematical functions.  
         [0045]     In the example shown in Table 4, all voltages have been modified using the same transformation  
         V   n     =         (       Vref   n     -     Vref   7       )     ⨯       MAX   ⁡     (   Line   )       255       +     Vref   7           
 
 where Vref 0  represents the threshold voltage. This is the simplest transformation that can be used for voltage driven system since the gamma function is applied inside the OLED according to the proportionality L(x,y)∝I(x;y)=k×(V(x;y)−V th ) 2  where L(x;y) represents the luminance of the pixel located at (x;y) and I(x,y) the current provided to this pixel. Indeed in a first approach, it is intended to have L(x,y)∝k×(Video(x;y)) 2  if one could afford to have a gamma of 2 instead of a gamma of 2.2. In this case it is easy to understand that if the Video level dynamic is modified by a factor p, then it is sufficient to modify the voltages by the same factor. In all other cases, like gamma different from 2 or current driven systems where no inherent gamma is existing a more complex transformation is mandatory for the voltage adjustment since the voltages are no more proportional to the video values. 
 
         [0046]     For instance, in a current driven system there is L(x,y)=k×(I−I th ) but ideally it should be L(x,y)∝(Video(x;y)) 2.2 . Then, a gamma transfer function of 2.2 is needed between the video level and the applied intensity. So if the video level is divided by 2, the provided intensity must be divided by 4.59 since  
           L   ⁡     (     x   ,   y     )       ∝       (       Video   ⁢           ⁢     (     x   ;   y     )       2     )     2.2       =           (     Video   ⁢           ⁢     (     x   ;   y     )       )     2.2       2   2.2       .         
 
         [0047]     The same is true for a voltage driven system and a real gamma of 2.2 is aimed. In this case, there is a transformation of 1.1 between video and voltages under the form V(x,y)∝Video(x;y) 1.1  that is needed in order to have finally: 
 
 L ( x,y )∝( V ( x;y )− V   th ) 2 ∝(Video( x;y ) 1.1 ) 2 =Video( x;y ) 2.2  
 
         [0048]     In that case, if the maximum video is divided by 2, the voltages must be divided by 2 1.1 =2.14.  
         [0049]     Such a transformation is quite complex and it is often difficult to be computed on-chip. Therefore, the ideal solution is to use a LUT containing 255 inputs, each one dedicated to a maximum value. The output can be on 8-bit or more in order to define the adjusting factor. Ideally, 10-bit is mandatory.  
         [0050]     Reverting to the example of the current driven system, if the maximum amplitude per line is 128, the output of the 256×10-bit LUT will be 225. Then the voltages will be multiplied by 225 and divided by 1024 to obtain the factor 4.59. Here, it is very difficult to perform a division in hardware excepted if a 2 m  divider is used that is simply a shift register. Indeed, dividing by 1024 corresponds to a shift by 10. Therefore the multiplication coefficients are always based on a 2 p  divider. Some further examples for such a LUT are given in Table 5 below.  
                                           TABLE 5                           Example of LUT for reference signalling adjustment                LUT (Voltage   LUT (current           driven)   driven)       MAX (Line)   power of 1.1   power of 2.2                    96   350   119       97   354   122       98   358   125       99   362   128       100   366   131       101   370   133       102   374   136       103   378   139       104   382   142       105   386   145       106   390   148       107   394   152       108   398   155       109   402   158       110   406   161       111   410   164       112   414   168       113   418   171       114   422   174       115   426   178       116   431   181       117   435   184       118   439   188       119   443   191       120   447   195       121   451   199       122   455   202       123   459   206       124   463   210       125   467   213       126   472   217       127   476   221       128   480   225       129   484   229       130   488   233       131   492   237       132   496   241       133   500   245       134   505   249       135   509   253       136   513   257       137   517   261       138   521   265                  
 
         [0051]     In parallel to that the video levels must be modified accordingly to benefit of the enhanced gradation. In that case  
         L   out     =       L   in     ⨯     255     MAX   ⁡     (   Line   )               
 
 applies. Here also the transformation should be better implemented via a LUT with 256 inputs corresponding to the 256 possible values for MAX(Line) and an output corresponding to a coefficient on 10-bit or more. 
 
         [0052]     In the previous paragraph, a simple solution is shown based on adjusting the reference signalling range to the maximal available video level in a line. A more advanced concept would lead in an optimization of the gradation between the more used video levels. Such enhanced concept of picture line-dependent gradation will be based on a histogram analysis performed on each line. The example of the sequence “Zorro” and the line  303  shall be taken from such histogram analysis with the previous approach for voltage adjustment.  
         [0053]      FIG. 5  shows in a histogram analysis the repartition of video levels for the line  303  of the sequence “Zorro” ( FIG. 3 ). The vertical lines represent the new adjusted voltages from the first embodiment presented in connection with Table 4. The reference voltages are represented according to the example from Table 1 and the video level is adjusted according to the equation  
         V   n     =         (       Vref   n     -     Vref   0       )     ⨯       MAX   ⁡     (   Line   )       255       +       Vref   0     .             
         [0054]     Now, for all examples simply a gamma of 2 shall be used. For this case, the new correspondence between video levels and voltages is shown in Table 6.  
                             TABLE 6                           Adjusted gray level table from voltage driver                Video level   Grayscale voltage level                        0   V7            0.5   V7 + (V6 − V7) × 9/1175            1   V7 + (V6 − V7) × 32/1175            1.5   V7 + (V6 − V7) × 76/1175            2   V7 + (V6 − V7) × 141/1175            2.5   V7 + (V6 − V7) × 224/1175            3   V7 + (V6 − V7) × 321/1175            3.5   V7 + (V6 − V7) × 425/1175            4   V7 + (V6 − V7) × 529/1175            4.5   V7 + (V6 − V7) × 630/1175            5   V7 + (V6 − V7) × 727/1175            5.5   V7 + (V6 − V7) × 820/1175            6   V7 + (V6 − V7) × 910/1175            6.5   V7 + (V6 − V7) × 998/1175            7   V7 + (V6 − V7) × 1086/1175            7.5   V6            8   V6 + (V5 − V6) × 89/1097            8.5   V6 + (V5 − V6) × 173/1097            9   V6 + (V5 − V6) × 250/1097            9.5   V6 + (V5 − V6) × 320/1097            10   V6 + (V5 − V6) × 386/1097            10.5   V6 + (V5 − V6) × 451/1097            11   V6 + (V5 − V6) × 517/1097           . . .   . . .           125.5   V1 + (V0 − V1) × 2278/3029           126   V1 + (V0 − V1) × 2411/3029           126.5   V1 + (V0 − V1) × 2549/3029           127   V1 + (V0 − V1) × 2694/3029           127.5   V1 + (V0 − V1) × 2851/3029           128   V0                      
 
         [0055]     As it can be seen on  FIG. 5 , the maximum of video levels are located between level  15  (V 5 ) and level  95  (V 2 ) but this is not the location where the finest gradation is obtained. However, the finest gradation is obtained when reference voltages are near together. This example shows that the gradation obtained with this driver with voltages computed according to the first embodiment is not optimized to this particular line structure.  
         [0056]     Therefore, according to a further embodiment there is provided an adaptation of the video transformation and voltage levels to adjust finest gradation where the maximum of video levels are distributed. In order to implement this concept, a first table is needed representing the driver behavior, which means the number of levels represented by each voltage. This is illustrated in Table 7 for the example of Table 1. A full voltage reference table for the driver chosen as example is given in Annex 1.  
                                           TABLE 7                           Example of voltage references video rendition                Reference Vn   Amount of levels                            V7   0           V6   15           V5   16           V4   32           V3   64           V2   64           V1   32           V0   32                      
 
         [0057]     It is generally known that a histogram of a picture represents, for each video level, the number of times this level is used. Such a histogram table is computed for a given line and described as HISTO[n], where n represents the possible video levels used for the input picture (at least 8 bit or more). In order to simplify the exposition, an input signal limited to 8-bit (256 discrete levels) will be taken.  
         [0058]     Now, the main idea is based on a computation of video level limits for each voltage. Such a limit represents the ideal number of pixels that should be coded inside each voltage. Ideally, this will be based on a percentage of the number of pixels per line. For example, for a display with 720 pixels per lines (720×3 cells) the voltage V 5  should be used to encode at least 720×3×16/255=135 cells. Based on this assumption the following Table 8 is obtained.  
                                           TABLE 8                           Example of voltage references limitation                Amount of   Limit with       Reference Vn   levels   320 cells                    V7   0   0       V6   15   127       V5   16   135       V4   32   271       V3   64   542       V2   64   542       V1   32   271       V0   32   271                  
 
         [0059]     The limits of this table are stored in an array LIMIT[k] with LIMIT[ 0 ]=0, LIMIT[ 1 ]=127, . . . , LIMIT[ 7 ]=271.  
         [0060]     Now, for each line following exemplary computation is performed:  
                                                   LevelCount = 0           Range = 1           For (l=0; l&lt;255; l++)           {             LevelCount = LevelCount + HISTO[l]             If (LevelCount &gt; LIMIT[Range])             {               LevelCount = 0               LEVEL_SELECT[Range]=l               Range++             }           }                      
 
         [0061]     From this computation a table of video levels LEVEL_SELECT[k] results that represents the video level at the transition between the voltage k- 1  and k. The results for line  303  are given in Table 9 below, which is based on Annex 2.  
                                                           TABLE 9                           Results of analysis for line 303                Level   Occurrence   Accumulation   Decision                             0   27   27   Range 1            1   13   40   Range 1            2   1   41   Range 1            3   2   43   Range 1            4   3   46   Range 1            5   4   50   Range 1            6   3   53   Range 1            7   0   53   Range 1            8   1   54   Range 1            9   1   55   Range 1           10   2   57   Range 1           11   0   57   Range 1           12   5   62   Range 1           13   7   69   Range 1           14   4   73   Range 1           15   8   81   Range 1           16   9   90   Range 1           17   19   109   Range 1           18   29   138   Range 2           19   50   188   Range 2           20   35   223   Range 2           21   37   260   Range 2           22   24   284   Range 3           23   26   310   Range 3           . . .   . . .           116    0   2149   Range 7           117    2   2151   Range 7           118    1   2152   Range 7           119    0   2152   Range 7           120    1   2153   Range 7           121    0   2153   Range 7           122    0   2153   Range 7           123    2   2155   Range 7           124    0   2155   Range 7           125    1   2156   Range 7           126    1   2157   Range 7           127    2   2159   Range 7           128    1   2160   Range 7                      
 
         [0062]     Table 9 shows that: 
        Levels [ 0 - 17 ] are used in Range  1 →voltage V 6 →LEVEL_SELECT[ 1 ]=18     Levels [ 18 - 21 ] are used in Range  2 →voltage V 5 →LEVEL_SELECT[ 2 ]=22     Levels [ 22 - 31 ] are used in Range  3 →voltage V 4 →LEVEL_SELECT[ 3 ]=32     Levels [ 32 - 40 ] are used in Range  4 →voltage V 3 →LEVEL_SELECT[ 4 ]=41     Levels [ 41 - 51 ] are used in Range  5 →voltage V 2 →LEVEL_SELECT[ 5 ]=52     Levels [ 52 - 60 ] are used in Range  6 →voltage V 1 →LEVEL_SELECT[ 6 ]=61     Levels [ 61 - 128 ] are used in Range  7 →voltage V 0 →LEVEL_SELECT[ 7 ]=128 
 
 LEVEL_SELECT[ 0 ]=0. 
       
 
         [0070]     The result is illustrated in  FIG. 6  showing a possible optimization of the voltages repartition according to the video levels repartition. The example of algorithm used here for this optimization should be seen as an example since other computations with similar achievements are possible. Indeed, it could be better to reduce a bit more the gap V 1  to V 0  in the above example. This can be achieved by a more complicated system.  
         [0071]     As soon as the optimal voltages repartition for a given line is defined, two types of adjustment should be performed to display a correct but improved picture: 
        First the adaptation of the voltages themselves—this computation is similar to the computation done in the previous embodiment. In that case the following equation applies:  
         V   n     =         (       Vref   n     -     Vrefr     n   -   1         )     ⨯     (               LEVEL_SELECT   ⁡     [   n   ]       -               LEVEL_SELECT   ⁡     [     n   -   1     ]               LIMIT   ⁡     [   n   ]         )       +     V     n   -   1             
    with n≧1     Then, the modification of the video levels to suit the new voltages distribution. In that case for a level located in Range n the luminance value is:  
         L   out     =         (       L     i   ⁢           ⁢   n       -     LEVEL_SELECT   ⁡     [     n   -   1     ]         )     ⨯     (       LIMIT   ⁡     [   n   ]                 LEVEL_SELECT   ⁡     [   n   ]       -               LEVEL_SELECT   ⁡     [     n   -   1     ]               )       +     
     ⁢           ⁢     TRANS   ⁡     [     n   -   1     ]             
       
 
         [0075]     With the table transition being an accumulation of the LIMIT[k] values so that  
         TRANS   ⁡     [   k   ]       =       ∑     p   =   0       p   =   k       ⁢       LIMIT   ⁡     [   k   ]       .           
 
 Consequently, one gets TRANS[ 0 ]=0, TRANS[ 1 ]=16, TRANS[ 1 ]=32, TRANS[ 2 ]=64, TRANS[ 3 ]=128, TRANS[ 4 ]=192, TRANS[ 5 ]=224 and TRANS[ 6 ]=256. 
 
         [0076]     The results of the previous computations are given in Tables 10 and 11 below:  
                                           TABLE 10                           Computed new voltages for line 303                Vref   Vline 303                        V7   0.00 V   0.00 V       V6   0.16 V   0.19 V       V5   0.30 V   0.23 V       V4   0.60 V   0.32 V       V3   1.40 V   0.43 V       V2   2.20 V   0.57 V       V1   2.60 V   0.68 V       V0   3.00 V   1.52 V                  
 
         [0077]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                   
               
               
                 Computed new video levels for line 303 
               
             
          
           
               
                   
                 Lin 
                 Lout 
               
               
                   
                   
               
             
          
           
               
                   
                  0 
                 0 
               
               
                   
                  1 
                 0.833333 
               
               
                   
                  2 
                 1.666667 
               
               
                   
                  3 
                 2.5 
               
               
                   
                  4 
                 3.333333 
               
               
                   
                  5 
                 4.166667 
               
               
                   
                  6 
                 5 
               
               
                   
                  7 
                 5.833333 
               
               
                   
                  8 
                 6.666667 
               
               
                   
                  9 
                 7.5 
               
               
                   
                 10 
                 8.333333 
               
               
                   
                 11 
                 9.166667 
               
               
                   
                 12 
                 10 
               
               
                   
                 13 
                 10.83333 
               
               
                   
                 14 
                 11.66667 
               
               
                   
                 15 
                 12.5 
               
               
                   
                 16 
                 13.33333 
               
               
                   
                 17 
                 14.16667 
               
               
                   
                 18 
                 15 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                 116  
                 249.2687 
               
               
                   
                 117  
                 249.7463 
               
               
                   
                 118  
                 250.2239 
               
               
                   
                 119  
                 250.7015 
               
               
                   
                 120  
                 251.1791 
               
               
                   
                 121  
                 251.6567 
               
               
                   
                 122  
                 252.1343 
               
               
                   
                 123  
                 252.6119 
               
               
                   
                 124  
                 253.0896 
               
               
                   
                 125  
                 253.5672 
               
               
                   
                 126  
                 254.0448 
               
               
                   
                 127  
                 254.5224 
               
               
                   
                 128  
                 255 
               
               
                   
                   
               
             
          
         
       
     
         [0078]     As already explained the complex computations are most of the cases replaced by LUTs. In the situation of the video level adjustment described as:  
         L   out     =         (       L     i   ⁢           ⁢   n       -     LEVEL_SELECT   ⁡     [     n   -   1     ]         )     ⨯     (       LIMIT   ⁡     [   n   ]                 LEVEL_SELECT   ⁡     [   n   ]       -               LEVEL_SELECT   ⁡     [     n   -   1     ]               )       +     
     ⁢           ⁢     TRANS   ⁡     [     n   -   1     ]             
 
         [0079]     A 8-bit LUT takes as input the value LEVEL_SELECT[n]−LEVEL_SELECT[n−1] and delivers a certain factor (more than 10-bit resolution is mandatory) to perform the division. The rest are only multiplications and additions that can be done in real time without any problem.  
         [0080]     As already said, the example is related to a simple gamma of 2 in a voltage driven system to simplify the exposition. For a different gamma or for a current driven system, the computations must be adjusted accordingly by using adapted LUTs.  
         [0081]      FIG. 7  illustrates an implementation of the inventive solution. The input signal  11  is forwarded to a line analysis block  12  that performs for each input line the required parameters extraction like the highest video level per line or even histogram analysis. This block  12  requires a line memory to delay the whole process of a line. Indeed, the results of the line analysis are obtained only at the end of the line but the modifications to be done on this line must be performed on the whole line.  
         [0082]     After the analysis and the delay of the line, the video levels are adjusted in a video adjustment block  13 . Here the new video levels Lout are generated on the basis of the original video levels Lin. The video signal with the new video levels is input to a standard OLED processing unit.  14 . Column driving data are output from this unit  14  and transmitted to a column driver  15  of an AMOLED display  16 . Furthermore, the standard OLED processing unit  14  produces row driving data for controlling the row driver  17  of the AMOLED display  16 .  
         [0083]     Analysis data of line analysis block  12  are further provided to a voltage adjustment block  18  for adjusting a reference voltages being provided by a reference signalling unit  19 . This reference signalling unit  19  delivers reference voltages Vref n  to the column driver  15 . For adjusting the reference voltages, the voltage adjustment block  18  is synchronized onto the row driving unit  17 .  
         [0084]     The control data for programming the specific reference voltages are forwarded from voltage adjustment block  18  to the reference signalling unit  19 . The adaptation of the voltages as well as that of the video levels is done on the basis of LUTs and computation.  
         [0085]     In case of a current driven system, the reference signalling is performed with currents and block  18  takes care of a current adjustment.  
         [0086]     The invention is not limited to the AMOLED screens but can also be applied to LCD displays or other displays using reference signalling means.  
                                                   Annex 1 - Full driver voltage table            Level   Voltage                    0   V7       1   V7 + (V6 − V7) × 9/1175       2   V7 + (V6 − V7) × 32/1175       3   V7 + (V6 − V7) × 76/1175       4   V7 + (V6 − V7) × 141/           1175       5   V7 + (V6 − V7) × 224/           1175       6   V7 + (V6 − V7) × 321/           1175       7   V7 + (V6 − V7) × 425/           1175       8   V7 + (V6 − V7) × 529/           1175       9   V7 + (V6 − V7) × 630/           1175       10   V7 + (V6 − V7) × 727/           1175       11   V7 + (V6 − V7) × 820/           1175       12   V7 + (V6 − V7) × 910/           1175       13   V7 + (V6 − V7) × 998/           1175       14   V7 + (V6 − V7) × 1086/           1175       15   V6       16   V6 + (V5 − V6) × 89/1097       17   V6 + (V5 − V6) × 173/           1097       18   V6 + (V5 − V6) × 250/           1097       19   V6 + (V5 − V6) × 320/           1097       20   V6 + (V5 − V6) × 386/           1097       21   V6 + (V5 − V6) × 451/           1097       22   V6 + (V5 − V6) × 517/           1097       23   V6 + (V5 − V6) × 585/           1097       24   V6 + (V5 − V6) × 654/           1097       25   V6 + (V5 − V6) × 723/           1097       26   V6 + (V5 − V6) × 790/           1097       27   V6 + (V5 − V6) × 855/           1097       28   V6 + (V5 − V6) × 917/           1097       29   V6 + (V5 − V6) × 977/           1097       30   V6 + (V5 − V6) × 1037/           1097       31   V5       32   V5 + (V4 − V5) × 60/           1501       33   V5 + (V4 − V5) × 119/           1501       34   V5 + (V4 − V5) × 176/           1501       35   V5 + (V4 − V5) × 231/           1501       36   V5 + (V4 − V5) × 284/           1501       37   V5 + (V4 − V5) × 335/           1501       38   V5 + (V4 − V5) × 385/           1501       39   V5 + (V4 − V5) × 434/           1501       40   V5 + (V4 − V5) × 483/           1501       41   V5 + (V4 − V5) × 532/           1501       42   V5 + (V4 − V5) × 580/           1501       43   V5 + (V4 − V5) × 628/           1501       44   V5 + (V4 − V5) × 676/           1501       45   V5 + (V4 − V5) × 724/           1501       46   V5 + (V4 − V5) × 772/           1501       47   V5 + (V4 − V5) × 819/           1501       48   V5 + (V4 − V5) × 866/           1501       49   V5 + (V4 − V5) × 912/           1501       50   V5 + (V4 − V5) × 957/           1501       51   V5 + (V4 − V5) × 1001/           1501       52   V5 + (V4 − V5) × 1045/           1501       53   V5 + (V4 − V5) × 1088/           1501       54   V5 + (V4 − V5) × 1131/           1501       55   V5 + (V4 − V5) × 1173/           1501       56   V5 + (V4 − V5) × 1215/           1501       57   V5 + (V4 − V5) × 1257/           1501       58   V5 + (V4 − V5) × 1298/           1501       59   V5 + (V4 − V5) × 1339/           1501       60   V5 + (V4 − V5) × 1380/           1501       61   V5 + (V4 − V5) × 1421/           1501       62   V5 + (V4 − V5) × 1461/           1501       63   V4       64   V4 + (V3 − V4) × 40/2215       65   V4 + (V3 − V4) × 80/2215       66   V4 + (V3 − V4) × 120/           2215       67   V4 + (V3 − V4) × 160/           2215       68   V4 + (V3 − V4) × 200/           2215       69   V4 + (V3 − V4) × 240/           2215       70   V4 + (V3 − V4) × 280/           2215       71   V4 + (V3 − V4) × 320/           2215       72   V4 + (V3 − V4) × 360/           2215       73   V4 + (V3 − V4) × 400/           2215       74   V4 + (V3 − V4) × 440/           2215       75   V4 + (V3 − V4) × 480/           2215       76   V4 + (V3 − V4) × 520/           2215       77   V4 + (V3 − V4) × 560/           2215       78   V4 + (V3 − V4) × 600/           2215       79   V4 + (V3 − V4) × 640/           2215       80   V4 + (V3 − V4) × 680/           2215       81   V4 + (V3 − V4) × 719/           2215       82   V4 + (V3 − V4) × 758/           2215       83   V4 + (V3 − V4) × 796/           2215       84   V4 + (V3 − V4) × 834/           2215       85   V4 + (V3 − V4) × 871/           2215       86   V4 + (V3 − V4) × 908/           2215       87   V4 + (V3 − V4) × 944/           2215       88   V4 + (V3 − V4) × 980/           2215       89   V4 + (V3 − V4) × 1016/           2215       90   V4 + (V3 − V4) × 1052/           2215       91   V4 + (V3 − V4) × 1087/           2215       92   V4 + (V3 − V4) × 1122/           2215       93   V4 + (V3 − V4) × 1157/           2215       94   V4 + (V3 − V4) × 1192/           2215       95   V4 + (V3 − V4) × 1226/           2215       96   V4 + (V3 − V4) × 1260/           2215       97   V4 + (V3 − V4) × 1294/           2215       98   V4 + (V3 − V4) × 1328/           2215       99   V4 + (V3 − V4) × 1362/           2215       100   V4 + (V3 − V4) × 1396/           2215       101   V4 + (V3 − V4) × 1429/           2215       102   V4 + (V3 − V4) × 1462/           2215       103   V4 + (V3 − V4) × 1495/           2215       104   V4 + (V3 − V4) × 1528/           2215       105   V4 + (V3 − V4) × 1561/           2215       106   V4 + (V3 − V4) × 1593/           2215       107   V4 + (V3 − V4) × 1625/           2215       108   V4 + (V3 − V4) × 1657/           2215       109   V4 + (V3 − V4) × 1688/           2215       110   V4 + (V3 − V4) × 1719/           2215       111   V4 + (V3 − V4) × 1750/           2215       112   V4 + (V3 − V4) × 1781/           2215       113   V4 + (V3 − V4) × 1811/           2215       114   V4 + (V3 − V4) × 1841/           2215       115   V4 + (V3 − V4) × 1871/           2215       116   V4 + (V3 − V4) × 1901/           2215       117   V4 + (V3 − V4) × 1930/           2215       118   V4 + (V3 − V4) × 1959/           2215       119   V4 + (V3 − V4) × 1988/           2215       120   V4 + (V3 − V4) × 2016/           2215       121   V4 + (V3 − V4) × 2044/           2215       122   V4 + (V3 − V4) × 2072/           2215       123   V4 + (V3 − V4) × 2100/           2215       124   V4 + (V3 − V4) × 2128/           2215       125   V4 + (V3 − V4) × 2156/           2215       126   V4 + (V3 − V4) × 2185/           2215       127   V3       128   V3 + (V2 − V3) × 31/2343       129   V3 + (V2 − V3) × 64/2343       130   V3 + (V2 − V3) × 97/2343       131   V3 + (V2 − V3) × 130/           2343       132   V3 + (V2 − V3) × 163/           2343       133   V3 + (V2 − V3) × 196/           2343       134   V3 + (V2 − V3) × 229/           2343       135   V3 + (V2 − V3) × 262/           2343       136   V3 + (V2 − V3) × 295/           2343       137   V3 + (V2 − V3) × 328/           2343       138   V3 + (V2 − V3) × 361/           2343       139   V3 + (V2 − V3) × 395/           2343       140   V3 + (V2 − V3) × 429/           2343       141   V3 + (V2 − V3) × 463/           2343       142   V3 + (V2 − V3) × 497/           2343       143   V3 + (V2 − V3) × 531/           2343       144   V3 + (V2 − V3) × 566/           2343       145   V3 + (V2 − V3) × 601/           2343       146   V3 + (V2 − V3) × 636/           2343       147   V3 + (V2 − V3) × 671/           2343       148   V3 + (V2 − V3) × 706/           2343       149   V3 + (V2 − V3) × 741/           2343       150   V3 + (V2 − V3) × 777/           2343       151   V3 + (V2 − V3) × 813/           2343       152   V3 + (V2 − V3) × 849/           2343       153   V3 + (V2 − V3) × 885/           2343       154   V3 + (V2 − V3) × 921/           2343       155   V3 + (V2 − V3) × 958/           2343       156   V3 + (V2 − V3) × 995/           2343       157   V3 + (V2 − V3) × 1032/           2343       158   V3 + (V2 − V3) × 1069/           2343       159   V3 + (V2 − V3) × 1106/           2343       160   V3 + (V2 − V3) × 1143/           2343       161   V3 + (V2 − V3) × 1180/           2343       162   V3 + (V2 − V3) × 1217/           2343       163   V3 + (V2 − V3) × 1255/           2343       164   V3 + (V2 − V3) × 1293/           2343       165   V3 + (V2 − V3) × 1331/           2343       166   V3 + (V2 − V3) × 1369/           2343       167   V3 + (V2 − V3) × 1407/           2343       168   V3 + (V2 − V3) × 1445/           2343       169   V3 + (V2 − V3) × 1483/           2343       170   V3 + (V2 − V3) × 1521/           2343       171   V3 + (V2 − V3) × 1559/           2343       172   V3 + (V2 − V3) × 1597/           2343       173   V3 + (V2 − V3) × 1635/           2343       174   V3 + (V2 − V3) × 1673/           2343       175   V3 + (V2 − V3) × 1712/           2343       176   V3 + (V2 − V3) × 1751/           2343       177   V3 + (V2 − V3) × 1790/           2343       178   V3 + (V2 − V3) × 1829/           2343       179   V3 + (V2 − V3) × 1868/           2343       180   V3 + (V2 − V3) × 1907/           2343       181   V3 + (V2 − V3) × 1946/           2343       182   V3 + (V2 − V3) × 1985/           2343       183   V3 + (V2 − V3) × 2024/           2343       184   V3 + (V2 − V3) × 2064/           2343       185   V3 + (V2 − V3) × 2103/           2343       186   V3 + (V2 − V3) × 2143/           2343       187   V3 + (V2 − V3) × 2183/           2343       188   V3 + (V2 − V3) × 2223/           2343       189   V3 + (V2 − V3) × 2263/           2343       190   V3 + (V2 − V3) × 2303/           2343       191   V2       192   V2 + (V1 − V2) × 40/1638       193   V2 + (V1 − V2) × 81/1638       194   V2 + (V1 − V2) × 124/           1638       195   V2 + (V1 − V2) × 168/           1638       196   V2 + (V1 − V2) × 213/           1638       197   V2 + (V1 − V2) × 259/           1638       198   V2 + (V1 − V2) × 306/           1638       199   V2 + (V1 − V2) × 353/           1638       200   V2 + (V1 − V2) × 401/           1638       201   V2 + (V1 − V2) × 450/           1638       202   V2 + (V1 − V2) × 499/           1638       203   V2 + (V1 − V2) × 548/           1638       204   V2 + (V1 − V2) × 597/           1638       205   V2 + (V1 − V2) × 646/           1638       206   V2 + (V1 − V2) × 695/           1638       207   V2 + (V1 − V2) × 745/           1638       208   V2 + (V1 − V2) × 795/           1638       209   V2 + (V1 − V2) × 846/           1638       210   V2 + (V1 − V2) × 897/           1638       211   V2 + (V1 − V2) × 949/           1638       212   V2 + (V1 − V2) × 1002/           1638       213   V2 + (V1 − V2) × 1056/           1638       214   V2 + (V1 − V2) × 1111/           1638       215   V2 + (V1 − V2) × 1167/           1638       216   V2 + (V1 − V2) × 1224/           1638       217   V2 + (V1 − V2) × 1281/           1638       218   V2 + (V1 − V2) × 1339/           1638       219   V2 + (V1 − V2) × 1398/           1638       220   V2 + (V1 − V2) × 1458/           1638       221   V2 + (V1 − V2) × 1518/           1638       222   V2 + (V1 − V2) × 1578/           1638       223   V1       224   V1 + (V0 − V1) × 60/3029       225   V1 + (V0 − V1) × 120/           3029       226   V1 + (V0 − V1) × 180/           3029       227   V1 + (V0 − V1) × 241/           3029       228   V1 + (V0 − V1) × 304/           3029       229   V1 + (V0 − V1) × 369/           3029       230   V1 + (V0 − V1) × 437/           3029       231   V1 + (V0 − V1) × 507/           3029       232   V1 + (V0 − V1) × 580/           3029       233   V1 + (V0 − V1) × 655/           3029       234   V1 + (V0 − V1) × 732/           3029       235   V1 + (V0 − V1) × 810/           3029       236   V1 + (V0 − V1) × 889/           3029       237   V1 + (V0 − V1) × 969/           3029       238   V1 + (V0 − V1) × 1050/           3029       239   V1 + (V0 − V1) × 1133/           3029       240   V1 + (V0 − V1) × 1218/           3029       241   V1 + (V0 − V1) × 1304/           3029       242   V1 + (V0 − V1) × 1393/           3029       243   V1 + (V0 − V1) × 1486/           3029       244   V1 + (V0 − V1) × 1583/           3029       245   V1 + (V0 − V1) × 1686/           3029       246   V1 + (V0 − V1) × 1794/           3029       247   V1 + (V0 − V1) × 1907/           3029       248   V1 + (V0 − V1) × 2026/           3029       249   V1 + (V0 − V1) × 2150/           3029       250   V1 + (V0 − V1) × 2278/           3029       251   V1 + (V0 − V1) × 2411/           3029       252   V1 + (V0 − V1) × 2549/           3029       253   V1 + (V0 − V1) × 2694/           3029       254   V1 + (V0 − V1) × 2851/           3029       255   V0                  
 
         [0087]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Annex 2 - Histogram of line 303 from sequence “Zorro” 
               
             
          
           
               
                   
                 Level 
                 Occurrence 
               
               
                   
                   
               
             
          
           
               
                   
                 0 
                 27 
               
               
                   
                 1 
                 13 
               
               
                   
                 2 
                 1 
               
               
                   
                 3 
                 2 
               
               
                   
                 4 
                 3 
               
               
                   
                 5 
                 4 
               
               
                   
                 6 
                 3 
               
               
                   
                 7 
                 0 
               
               
                   
                 8 
                 1 
               
               
                   
                 9 
                 1 
               
               
                   
                 10 
                 2 
               
               
                   
                 11 
                 0 
               
               
                   
                 12 
                 5 
               
               
                   
                 13 
                 7 
               
               
                   
                 14 
                 4 
               
               
                   
                 15 
                 8 
               
               
                   
                 16 
                 9 
               
               
                   
                 17 
                 19 
               
               
                   
                 18 
                 29 
               
               
                   
                 19 
                 50 
               
               
                   
                 20 
                 35 
               
               
                   
                 21 
                 37 
               
               
                   
                 22 
                 24 
               
               
                   
                 23 
                 26 
               
               
                   
                 24 
                 19 
               
               
                   
                 25 
                 23 
               
               
                   
                 26 
                 12 
               
               
                   
                 27 
                 24 
               
               
                   
                 28 
                 26 
               
               
                   
                 29 
                 23 
               
               
                   
                 30 
                 25 
               
               
                   
                 31 
                 31 
               
               
                   
                 32 
                 56 
               
               
                   
                 33 
                 54 
               
               
                   
                 34 
                 64 
               
               
                   
                 35 
                 61 
               
               
                   
                 36 
                 78 
               
               
                   
                 37 
                 42 
               
               
                   
                 38 
                 59 
               
               
                   
                 39 
                 61 
               
               
                   
                 40 
                 75 
               
               
                   
                 41 
                 78 
               
               
                   
                 42 
                 61 
               
               
                   
                 43 
                 41 
               
               
                   
                 44 
                 55 
               
               
                   
                 45 
                 52 
               
               
                   
                 46 
                 43 
               
               
                   
                 47 
                 48 
               
               
                   
                 48 
                 42 
               
               
                   
                 49 
                 42 
               
               
                   
                 50 
                 46 
               
               
                   
                 51 
                 45 
               
               
                   
                 52 
                 28 
               
               
                   
                 53 
                 29 
               
               
                   
                 54 
                 27 
               
               
                   
                 55 
                 26 
               
               
                   
                 56 
                 28 
               
               
                   
                 57 
                 25 
               
               
                   
                 58 
                 25 
               
               
                   
                 59 
                 33 
               
               
                   
                 60 
                 39 
               
               
                   
                 61 
                 38 
               
               
                   
                 62 
                 38 
               
               
                   
                 63 
                 25 
               
               
                   
                 64 
                 23 
               
               
                   
                 65 
                 12 
               
               
                   
                 66 
                 11 
               
               
                   
                 67 
                 22 
               
               
                   
                 68 
                 13 
               
               
                   
                 69 
                 5 
               
               
                   
                 70 
                 4 
               
               
                   
                 71 
                 5 
               
               
                   
                 72 
                 6 
               
               
                   
                 73 
                 13 
               
               
                   
                 74 
                 8 
               
               
                   
                 75 
                 3 
               
               
                   
                 76 
                 7 
               
               
                   
                 77 
                 6 
               
               
                   
                 78 
                 4 
               
               
                   
                 79 
                 2 
               
               
                   
                 80 
                 2 
               
               
                   
                 81 
                 2 
               
               
                   
                 82 
                 4 
               
               
                   
                 83 
                 5 
               
               
                   
                 84 
                 3 
               
               
                   
                 85 
                 3 
               
               
                   
                 86 
                 6 
               
               
                   
                 87 
                 2 
               
               
                   
                 88 
                 1 
               
               
                   
                 89 
                 3 
               
               
                   
                 90 
                 2 
               
               
                   
                 91 
                 0 
               
               
                   
                 92 
                 3 
               
               
                   
                 93 
                 0 
               
               
                   
                 94 
                 1 
               
               
                   
                 95 
                 1 
               
               
                   
                 96 
                 0 
               
               
                   
                 97 
                 1 
               
               
                   
                 98 
                 0 
               
               
                   
                 99 
                 1 
               
               
                   
                 100 
                 0 
               
               
                   
                 101 
                 0 
               
               
                   
                 102 
                 0 
               
               
                   
                 103 
                 1 
               
               
                   
                 104 
                 1 
               
               
                   
                 105 
                 1 
               
               
                   
                 106 
                 0 
               
               
                   
                 107 
                 2 
               
               
                   
                 108 
                 0 
               
               
                   
                 109 
                 0 
               
               
                   
                 110 
                 1 
               
               
                   
                 111 
                 1 
               
               
                   
                 112 
                 0 
               
               
                   
                 113 
                 1 
               
               
                   
                 114 
                 0 
               
               
                   
                 115 
                 0 
               
               
                   
                 116 
                 0 
               
               
                   
                 117 
                 2 
               
               
                   
                 118 
                 1 
               
               
                   
                 119 
                 0 
               
               
                   
                 120 
                 1 
               
               
                   
                 121 
                 0 
               
               
                   
                 122 
                 0 
               
               
                   
                 123 
                 2 
               
               
                   
                 124 
                 0 
               
               
                   
                 125 
                 1 
               
               
                   
                 126 
                 1 
               
               
                   
                 127 
                 2 
               
               
                   
                 128 
                 1 
               
               
                   
                 129 
                 0 
               
               
                   
                 130 
                 0 
               
               
                   
                 131 
                 0 
               
               
                   
                 132 
                 0 
               
               
                   
                 133 
                 0 
               
               
                   
                 134 
                 0 
               
               
                   
                 135 
                 0 
               
               
                   
                 136 
                 0 
               
               
                   
                 137 
                 0 
               
               
                   
                 138 
                 0 
               
               
                   
                 139 
                 0 
               
               
                   
                 140 
                 0 
               
               
                   
                 141 
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