EP1624438B1 - Method and apparatus for power level control and/or contrast control of a display device - Google Patents

Method and apparatus for power level control and/or contrast control of a display device Download PDF

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Publication number
EP1624438B1
EP1624438B1 EP05106877A EP05106877A EP1624438B1 EP 1624438 B1 EP1624438 B1 EP 1624438B1 EP 05106877 A EP05106877 A EP 05106877A EP 05106877 A EP05106877 A EP 05106877A EP 1624438 B1 EP1624438 B1 EP 1624438B1
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Prior art keywords
picture
contrast
intensity
refn
display device
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German (de)
French (fr)
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EP1624438A1 (en
Inventor
Sebastien Weitbruch
Dennis Cota
Philippe Le Roy
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THOMSON LICENSING
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Thomson Licensing SAS
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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/066—Adjustment of display parameters for control of contrast
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/02—Details of power systems and of start or stop of display operation
    • G09G2330/021—Power management, e.g. power saving
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/16—Calculation or use of calculated indices related to luminance levels in display data

Description

  • The present invention relates to a method and an apparatus for controlling the power level and/or the contrast in a display device having a plurality of luminous elements corresponding to the colour components of the pixels of a picture, wherein the luminance generated by each of said luminous element is based on the intensity of the signal supplied to the luminous element.
  • More specifically, the invention is closely related to organic light emitting displays (OLED).
    • Background
  • A high peak-white luminance is always required to achieve a good contrast ratio in every display technologies even with ambient light conditions and, for every kind of active displays, more peak white luminance corresponds to a higher power that flows in the electronic of the display. Therefore, if no specific management is done, the enhancement of the peak luminance for a given electronic efficacy will introduce an increase of the power consumption.
  • The main idea behind every kind of power management concept associated with peak white enhancement is based on the variation of the peak-luminance depending on the picture content in order to stabilize the power consumption to a specified value. This concept is shown in Figure 1. When the picture load is low, the peak luminance is high and when the picture load is high, the peak luminance is low. The concept described on this figure enables to avoid any overloading of the power supply of the display panel as well as a maximum contrast for a given picture.
  • Such a concept suits very well to the human visual system. When the picture load is low, the contrast ratio is high and when the picture is high, the human eye is dazzled and is less sensitive to contrast ratio. So, for a full-white picture, the contrast ratio can be lower than for a peak-white picture.
  • In the case of cathode Ray Tubes (CRTs), the power management is based on a so called ABL function (Average Beam-current Limiter), which is implemented by analog means and which decreases video gain as a function of the average luminance of the pictures.
  • In the case of an organic light-emitting diode display, also called OLED display, the luminance as well as the power consumption is directly linked to the current that flows through each cell. Currently, there is no power level control means for stabilizing the power consumption to a target value.
  • In the other hand, in such a display device, the contrast is adjusted by a video scaler acting on the video signal. If the video signal is coded on 8 bits and if the contrast should be reduced by 50%, the video signal is rescaled leading to a video signal with only a 7 bit resolution. So, there is a loss of video resolution.
  • Otherwise, US 2003/218583 discloses a method of controlling the power consumption of an organic electroluminescent display with luminescing elements of red, green and blue. This method comprises measuring the power consumption via a so-called summation data detection circuit, and controlling the power consumption by changing the luminescing time period according to the measured data.Otherwise, US 2003/218583 discloses a method of controlling the power consumption of an organic electroluminescent display with luminescing elements of red, green and blue. This method comprises measuring the power consumption via a so-called summation data detection circuit, and controlling the power consumption by changing the luminescing time period according to the measured data.
  • EP-A-1 310 935 discloses a method for controlling the brightness of a display device. A brightness suppression coefficient is calculated for adjusting the emission brightness of the display panel in accordance with the average brightness of the image to be displayed. This coefficient is so calculated as to have such a relationship that the emission brightness of the display panel is decreased for a higher average brightness of the image. It is coupled with a scene changeover detection circuit to change rapidly the display brightness when a scene change over is detected and to change slowly the display brightness when no scene change over is detected. So, the emission brightness adjustment is done by changing a brightness component of the video signal or by changing the drive voltage of the electron emitting devices or by changing the acceleration voltage.
  • EP-A-1 310 935 discloses a method for controlling the brightness of a display device. A brightness suppression coefficient is calculated for adjusting the emission brightness of the display panel in accordance with the average brightness of the image to be displayed. This coefficient is so calculated as to have such a relationship that the emission brightness of the display panel is decreased for a higher average brightness of the image. It is coupled with a scene changeover detection circuit to change rapidly the display brightness when a scene change over is detected and to change slowly the display brightness when no scene change over is detected. So, the emission brightness adjustment is done by changing a brightness component of the video signal or by changing the drive voltage of the electron emitting devices or by changing the acceleration voltage.
  • Furthermore, an image display device wherein a pixel has a light emitting element for emitting light in accordance with a luminance level of an image signal to be input and a luminance adjustment method thereof already has been disclosed according to EP 1469449 A1 .
    • Invention
  • The invention is set forth in claims 1 and 6. The present invention proposes a new method and apparatus for controlling the power level and/or the contrast in display devices having a plurality of luminous elements, wherein the luminance generated by each of said luminous element is based on the intensity of the signal supplied to the luminous element and the power level and/or contrast for each picture is controlled by adjusting the intensity of the signal to be supplied to each luminous element.
  • The basic idea of this invention is to supply the luminous elements of the display device with a signal whose intensity is based on reference signals and to modify the level of these reference signals for adjusting the intensity of the signals supplied to the luminous elements.
  • So, the invention relates to a method for controlling the power level and/or the contrast in a display device having a plurality of luminous elements corresponding to the colour components of the pixels of a picture, wherein the luminance generated by each of said luminous elements is based on the intensity of the signal supplied to the luminous element and the power level and/or contrast for each picture is controlled by adjusting the intensity of the signal to be supplied to each luminous element, characterized in that the intensity of the signal to be supplied to each luminous element is based on reference signals and in that the adjustment of the signal intensity is made by adjusting the level of the reference signals.
  • By this method, the resolution of the video signal supplied to the luminous elements is not modified.
  • For controlling the power level, the method further comprises the two following steps:
    • calculating, for each picture received by the display device, a parameter representative of the power needed by the display device for displaying said picture; this parameter is for example the average power level; and
    • adjusting the intensity of the signal to be supplied to each luminous element in order that the power needed by the display device for displaying said picture is lower than a target value.
  • For controlling the contrast of the pictures displayed by the display device, the method further comprises the following steps :
    • calculating an adjustment factor to be applied to the intensity of the picture signal supplied to the luminous elements in order that the resulting contrast is equal to a required contrast, and
    • applying said adjustment factor to said reference signals.
  • In a preferred embodiment, a non linear transformation is applied to reference signals, before adjustment of the signal intensity, in order to increase the amplitude of the low-amplitude reference signals. To compensate this transformation, the inverse transformation is applied to the picture signal.
  • The invention concerns also an apparatus for controlling the power level and/or the contrast in a display device having a plurality of luminous elements corresponding to the colour components of the pixels of a picture, wherein the luminance generated by each of said luminous elements is based on the intensity of the signal supplied to the luminous element and the power level and/or contrast for each picture is controlled by adjusting the intensity of the signal to be supplied to each luminous element, characterized in that the intensity of the signal to be supplied to each luminous element is based on reference signals and in that it comprises adjustment means for modifying the signal intensity by adjusting the level of the reference signals.
  • For controlling the power level, the apparatus further comprises calculation means for calculating, for each picture received by the display device, a parameter representative of the power needed by the display device for displaying said picture, and in that the adjustment means adjusts the level of the reference signals in order that the power needed by the display device for displaying each picture is lower than a target value. The calculation means calculates for example, for each picture received by the display device, the average power level of said picture.
  • For controlling the contrast of the pictures displayed by the display device, the apparatus further comprises calculation means for calculating an adjustment factor to be applied to the intensity of the signal supplied to the luminous elements in order that the resulting contrast is equal to a required contrast, and in that the adjustment means applies said adjustment factor to said reference signals.
  • For these two applications, the apparatus comprises a frame memory for storing a picture before transmitting it to the display device.
  • In a preferred embodiment, the adjustment means of the apparatus comprises means for applying a non linear transformation to reference signals in order to increase the amplitude of the low-amplitude reference signals and the apparatus comprises means for applying the inverse transformation to the picture signal.
  • Lastly, the invention concerns also a display device comprising
    • a plurality of organic light emitting diodes,
    • signal processing means for processing the picture signal received by the display device,
    • driving means for driving said plurality of organic light emitting diodes according to the signal processed by the signal processing means,
    • reference signalling means for outputting reference signals to the driving means, and
    • an apparatus as defined above which is integrated to the signal processing means.
    Brief description of the drawings
  • Exemplary embodiments of the invention are illustrated in the drawings and in more detail in the following description.
  • In the figures :
    • Fig.1
    shows the variation of the peak luminance versus the picture load in a display device ;
    Fig.2
    shows the structure of the control electronic in a OLED display;
    Fig.3
    shows the variations of reference voltages according to picture load in a basic embodiment of the invention;
    Fig.4
    shows the variations of reference voltages according to picture load in an improved embodiment of the invention; and
    Fig.5
    shows the structure of the control electronic in a OLED display used for implementing the method of the invention;
    Description of preferred embodiments
  • The invention is described in relation to a OLED display with an active matrix where each luminous element of the display is controlled via an association of several thin-film transistors (TFTs). The general structure of the electronic for controlling the OLED elements is illustrated by figure 2. It comprises :
    • an active matrix 1 containing, for each OLED element, an association of several thin-film transistors with a capacitor connected to the OLED material of the luminous element; the capacitor acts as a memory component that stores the value of the luminous element during a certain part of the frame; the thin-film transistors act as switches enabling the selection of the luminous element, the storage of the capacitor and the lighting of the luminous element; in the present structure, the value stored in the capacitor determines the luminance produced by the luminous element;
    • at least one row driver 2 that selects line by line the luminous elements of the display in order to refresh their content,
    • at least one column driver 3 that delivers the value or content to be stored in each luminous element of the current selected line; this component receives the video information for each luminous element;
    • a digital processing and driving unit 4 that applies required video and signal processing steps to the video input signal and that delivers the required signals to the row and column drivers.
  • Actually, there are two ways for driving the OLED elements:
    • in a current driven concept, the digital video information sent by the digital processing and driving unit 4 is converted by the column driver 3 in a current amplitude that is supplied to the luminous element via the active matrix 1;
    • in a voltage driven concept, the digital video information send by the digital processing and driving unit 4 is converted by the column driver 3 in a voltage amplitude that is supplied to the luminous element via the active matrix 1; but, even so, it should be noticed that an OLED element is a current driven so that each voltage based driving unit is based on a voltage to current converter to achieve appropriate lighting.
  • The column driver 3 represents, with the digital processing and driving unit 4, the real active part of the electronic and can be considered as a high-level digital to analog converter. The row driver 2 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 functioning of said electronic is the following : the input video signal is forwarded to the digital processing and driving unit 4 that delivers, after internal processing, a timing signal for row selection to the row driver 2 synchronized with the data sent to the column driver 3. Depending on the used column driver 3, the data are sent either in a parallel way or in a serial way. Additionally, the column driver 3 is equipped with a reference signaling device 5 for delivering reference signals. More precisely, this device 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 being used for the highest gray level (white) and the lowest for the smallest gray level. These reference signals are used by the column driver 3 for generating the signal to be supplied to the OLED element.
  • An example of reference signals is given below for a voltage driven circuitry. Eight reference voltages named V0 to V7 are used : V ⁢ 0 = 3 ⁢ V
    Figure imgb0001
     V ⁢ 1 = 2 , 6 ⁢ V
    Figure imgb0002
     V ⁢ 2 = 2 , 2 ⁢ V
    Figure imgb0003
     V ⁢ 3 = 1 , 4 ⁢ V
    Figure imgb0004
     V ⁢ 4 = 0 , 6 ⁢ V
    Figure imgb0005
     V ⁢ 5 = 0 , 3 ⁢ V
    Figure imgb0006
     V ⁢ 6 = 0 , 16 ⁢ V
    Figure imgb0007
     V ⁢ 7 = 0 ⁢ V
    Figure imgb0008
  • The different gray levels can be defined as given by the following table. The whole table is given by the annex 1.
    gray level gray level voltage Gray level voltage
    0 V7 0.00V
    1 V7+(V6-V7)x9/1175 0.001V
    2 V7+(V6-V7)x32/1175 0.005V
    3 V7+(V6-V7)x76/1175 0.011V
    4 V7+(V6-V7)x141/1175 0.02V
    5 V7+(V6-V7)x224/1175 0.032V
    6 V7+(V6-V7)x321/1175 0.045V
    7 V7+(V6-V7)x425/1175 0.06V
    8 V7+(V6-V7)x529/1175 0.074V
    9 V7+(V6-V7)x630/1175 0.089V
    10 V7+(V6-V7)x727/1175 0.102V
    11 V7+(V6-V7)x820/1175 0.115V
    12 V7+(V6-V7)x910/1175 0.128V
    13 V7+(V6-V7)x998/1175 0.14V
    14 V7+(V6-V7)x1086/1175 0.153V
    15 V6 0.165V
    16 V6+(V5-V6)x89/1097 0.176V
    ... ... ...
    252 V1+(V0-V1)x2549/3029 2.937V
    253 V1+(V0-V1)x2694/3029 2.956V
    254 V1+(V0-V1)x2851/3029 2.977V
    255 V0 3.00V
  • Of course, these voltage levels are converted into current before being supplied to the OLED elements. For deducing a luminance value from these voltages, it will be assumed in the rest of the present specification that a 3V voltage applied to an OLED element corresponds to a 400cd/m2 luminance and that it represents the maximal luminance that can be displayed by the screen of the display device. This value is given as an example.
  • For a 4/3 screen with a 6.5" ( =16.25cm) diagonal (size = 13cm x 9.75cm) and an efficacy for the OLED material around 14Cd/A, the surface of the screen is 13x9.75 = 126.75cm2 and the current density is 40000/14000 = 2.86mA/cm2. So, the total current needed by the panel is 126.75x2.86 = 362.1 mA.
  • This current value can be considered as too high. For example, it is sought a maximum current value of 80mA.
  • According to the invention, the luminance of the display panel is adjusted in order that the current value necessary for displaying the picture is lower than a maximum current value.
  • The power of the incoming picture is first evaluated and the luminance of the panel is then adjusted in order to limit the power consumption of the panel to the maximum current value.
  • A first step of the inventive method consists in evaluating the power of the incoming picture to decide which luminance should be used for a white level. The computation of the picture power is done by computing the Average Power Level (APL) of the picture through the following function: APL l x y = 1 C × L ⋅ ∑ x , y l x y
    Figure imgb0009
    where I(x,y) represents the video level of the pixel with coordinates x, y in the picture, C is the number of elements columns of the screen and L is the number of elements lines of the screen.
  • In the present specification, the APL value of a picture will be expressed as a percentage of white surface in the picture for clarity and simplicity reasons.
  • In a second step, the maximal luminance of the screen is determined for different percentages of white surface as shown in the following table. In the case of a maximum current value of 80 mA, the luminance of a full white image (100% white surface) for the above-mentioned 4/3 screen is: 80 ⋅ 14 ⋅ 10 - 3 126.75 ⋅ 10 - 4 = 88.363 cd / m ⁢ 2.
    Figure imgb0010
    Surface (white) Luminance (Cd/m2) Power (mA)
    100.00% 88.363 Cd/m2 80.00 mA
    97.50% 90.629 Cd/m2 80.00 mA
    95.00% 93.014 Cd/m2 80.00 mA
    92.50% 95.527 Cd/m2 80.00 mA
    90.00% 98.181 Cd/m2 80.00 mA
    87.50% 100.986 Cd/m2 80.00 mA
    85.00% 103.956 Cd/m2 80.00 mA
    82.50% 107.107 Cd/m2 80.00 mA
    80.00% 110.454 Cd/m2 80.00 mA
    77.50% 114.017 Cd/m2 80.00 mA
    75.00% 117.817 Cd/m2 80.00 mA
    72.50% 121.88 Cd/m2 80.00 mA
    70.00% 126.233 Cd/m2 80.00 mA
    67.50% 130.908 Cd/m2 80.00 mA
    65.00% 135.943 Cd/m2 80.00 mA
    62.50% 141.381 Cd/m2 80.00 mA
    60.00% 147.272 Cd/m2 80.00 mA
    57.50% 153.675 Cd/m2 80.00 mA
    55.00% 160.66 Cd/m2 80.00 mA
    52.50% 168.31 Cd/m2 80.00 mA
    50.00% 176.726 Cd/m2 80.00 mA
    47.50% 186.027 Cd/m2 80.00 mA
    45.00% 196.362 Cd/m2 80.00 mA
    42.50% 207.913 Cd/m2 80.00 mA
    40.00% 220.907 Cd/m2 80.00 mA
    37.50% 235.634 Cd/m2 80.00 mA
    35.00% 252.465 Cd/m2 80.00 mA
    32.50% 271.886 Cd/m2 80.00 mA
    30.00% 294.543 Cd/m2 80.00 mA
    27.50% 321.32 Cd/m2 80.00 mA
    25.00% 353.452 Cd/m2 80.00 mA
    22.50% 392.724 Cd/m2 80.00 mA
    20.00% 400.00 Cd/m2 72.429 mA
    17.50% 400.00 Cd/m2 63.375 mA
    15.00% 400.00 Cd/m2 54.321 mA
    12.50% 400.00 Cd/m2 45.268 mA
    10.00% 400.00 Cd/m2 36.214 mA
    7.50% 400.00 Cd/m2 27.161 mA
    5.00% 400.00 Cd/m2 18.107 mA
    2.50% 400.00 Cd/m2 9.054 mA
  • As the luminance is in this example limited to 400 cd/m2, the power consumption for the picture with a white surface percentage inferior to 22 % is inferior to 80 mA. The maximal contrast ratio is obtained for a 22% white surface percentage and is equal to 4.5.
  • According to an important characteristics of the invention, the luminance of the screen is adjusted by modifying the value of the reference levels Vn, n ∈ [0,...,7] defined above. The luminance LUM of the screen can be approximated by a quadratic function of the applied voltage V: LUM x ; y = 44 × V x ; y 2 .
    Figure imgb0011
  • This formula is given as an example. The following table gives the different voltage values for the reference voltage V0 :
    Surface (white) V0 Luminance (Cd/m2)
    100.00% 1.41 V 88.363 Cd/m2
    97.50% 1.43 V 90.629 Cd/m2
    95.00% 1.45 V 93.014 Cd/m2
    92.50% 1.47 V 95.527 Cd/m2
    90.00% 1.49 V 98.181 Cd/m2
    87.50% 1.51 V 100.986 Cd/m2
    85.00% 1.53 V 103.956 Cd/m2
    82.50% 1.55 V 107.107 Cd/m2
    80.00% 1.58 V 110.454 Cd/m2
    77.50% 1.6 V 114.017 Cd/m2
    75.00% 1.63 V 117.817 Cd/m2
    72.50% 1.66 V 121.88 Cd/m2
    70.00% 1.69 V 126.233 Cd/m2
    67.50% 1.72 V 130.908 Cd/m2
    65.00% 1.75 V 135.943 Cd/m2
    62.50% 1.78 V 141.381 Cd/m2
    60.00% 1.82 V 147.272 Cd/m2
    57.50% 1.86 V 153.675 Cd/m2
    55.00% 1.9 V 160.66 Cd/m2
    52.50% 1.95 V 168.31 Cd/m2
    50.00% 2.0 V 176.726 Cd/m2
    47.50% 2.05 V 186.027 Cd/m2
    45.00% 2.1 V 196.362 Cd/m2
    42.50% 2.16 V 207.913 Cd/m2
    40.00% 2.23 V 220.907 Cd/m2
    37.50% 2.3 V 235.634 Cd/m2
    35.00% 2.38 V 252.465 Cd/m2
    32.50% 2.47 V 271.886 Cd/m2
    30.00% 2.58 V 294.543 Cd/m2
    27.50% 2.69 V 321.32 Cd/m2
    25.00% 2.82 V 353.452 Cd/m2
    22.50% 2.97 V 392.724 Cd/m2
    20.00% 3.0 V 400.00 Cd/m2
    17.50% 3.0 V 400.00 Cd/m2
    15.00% 3.0 V 400.00 Cd/m2
    12.50% 3.0 V 400.00 Cd/m2
    10.00% 3.0 V 400.00 Cd/m2
    7.50% 3.0 V 400.00 Cd/m2
    5.00% 3.0 V 400.00 Cd/m2
    2.50% 3.0 V 400.00 Cd/m2
  • The other reference levels, V1 to V7, can be adjusted in a linear way from the reference level V0. For example, the reference level Vn for a given average power level APL can then be computed as follows : Vn APL = V ⁢ 0 APL × Vn 0 % V ⁢ 0 0 %
    Figure imgb0012
  • The following table gives the voltage values of all the reference levels V0 to V7 for different APL :
    Surface (white) V0 V1 V2 V3 V4 V5 V6 V7
    100.00% 1.41 V 1.22 V 1.03 V 0.66 V 0.28 V 0.14 V 0.08 V 0.0 V
    97.50% 1.43 V 1.24 V 1.05 V 0.67 V 0.29 V 0.14 V 0.08 V 0.0 V
    95.00% 1.45 V 1.25 V 1.06 V 0.68 V 0.29 V 0.14 V 0.08 V 0.0 V
    92.50% 1.47 V 1.27 V 1.08 V 0.68 V 0.29 V 0.15 V 0.08 V 0.0 V
    90.00% 1.49 V 1.29 V 1.09 V 0.69 V 0.3 V 0.15 V 0.08 V 0.0 V
    87.50% 1.51 V 1.31 V 1.11 V 0.7 V 0.3 V 0.15V 0.08 V 0.0 V
    85.00% 1.53 V 1.33 V 1.12 V 0.71 V 0.31 V 0.15V 0.08 V 0.0 V
    82.50% 1.55 V 1.35 V 1.14 V 0.72V 0.31 V 0.16 V 0.08 V 0.0 V
    80.00% 1.58 V 1.37 V 1.16 V 0.74 V 0.32 V 0.16 V 0.08 V 0.0 V
    77.50% 1.6 V 1.39 V 1.18 V 0.75 V 0.32 V 0.16 V 0.09 V 0.0 V
    75.00% 1.63 V 1.41 V 1.19 V 0.76 V 0.33 V 0.16 V 0.09 V 0.0V
    72.50% 1.66 V 1.44 V 1.21 V 0.77 V 0.33 V 0.17 V 0.09 V 0.0 V
    70.00% 1.69 V 1.46 V 1.24 V 0.79 V 0.34 V 0.17 V 0.09 V 0.0 V
    67.50% 1.72V 1.49 V 1.26 V 0.8 V 0.34 V 0.17 V 0.09 V 0.0 V
    65.00% 1.75 V 1.52 V 1.28 V 0.82 V 0.35 V 0.17 V 0.09 V 0.0 V
    62.50% 1.78 V 1.55 V 1.31 V 0.83 V 0.36 V 0.18 V 0.1 V 0.0 V
    60.00% 1.82 V 1.58 V 1.34 V 0.85 V 0.36 V 0.18 V 0.1 V 0.0 V
    57.50% 1.86 V 1.61 V 1.36 V 0.87 V 0.37 V 0.19 V 0.1 V 0.0 V
    55.00% 1.9 V 1.65 V 1.39 V 0.89 V 0.38 V 0.19 V 0.1 V 0.0 V
    52.50% 1.95 V 1.69 V 1.43 V 0.91 V 0.39 V 0.19 V 0.1 V 0.0 V
    50.00% 2.0 V 1.73 V 1.46 V 0.93 V 0.4 V 0.2 V 0.11 V 0.0 V
    47.50% 2.05 V 1.77 V 1.5 V 0.96 V 0.41 V 0.2 V 0.11 V 0.0 V
    45.00% 2.1 V 1.82 V 1.54 V 0.98 V 0.42 V 0.21 V 0.11 V 0.0 V
    42.50% 2.16 V 1.88 V 1.59 V 1.01 V 0.43 V 0.22 V 0.12 V 0.0 V
    40.00% 2.23V 1.93 V 1.64 V 1.04 V 0.45 V 0.22 V 0.12 V 0.0 V
    37.50% 2.3 V 2.0 V 1.69 V 1.08 V 0.46 V 0.23 V 0.12 V 0.0 V
    35.00% 2.38 V 2.07 V 1.75 V 1.11 V 0.48 V 0.24 V 0.13 V 0.0 V
    32.50% 2.47 V 2.14 V 1.81 V 1.15V 0.49 V 0.25 V 0.13 V 0.0 V
    30.00% 2.58 V 2.23 V 1.89 V 1.2 V 0.52 V 0.26 V 0.14 V 0.0 V
    27.50% 2.69 V 2.33 V 1.97 V 1.26 V 0.54 V 0.27 V 0.14 V 0.0 V
    25.00% 2.82 V 2.45 V 2.07 V 1.32 V 0.56 V 0.28 V 0.15 V 0.0 V
    22.50% 2.97V 2.58 V 2.18 V 1.39 V 0.59 V 0.3 V 0.16 V 0.0 V
    20.00% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    17.50% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    15.00% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    12.50% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    10.00% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    7.50% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    5.00% 3.0 V 2.6 V 2.2 V 1.4 V 0.6 V 0.3 V 0.16 V 0.0 V
    2.50% 3.0 V 2.6 V 2.2 V 1.4 V 0.6V 0.3 V 0.16 V 0.0 V
  • Figure 3 shows curves illustrating this table and showing the variations of the reference voltages for the percentages of white surface 5%, 10%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%.
  • A problem can appear when the voltage references related to the lowest gray levels are very low, which is the case in the above table for the reference voltages V5 and V6 when the picture load is high. Actually, in a voltage driven system, if the voltage is too low, the error (coming from the mismatch between neighbouring luminous elements) becomes higher than the required precision and the information is lost. In a current driven system, the problem is different. In such a system, the lower the current is, the longer it takes to load the capacitance of the luminous element. So, if the required current is too low, the writing time of the luminous element will be too long for a video application.
  • In the present example, the voltage values below 0.16V (bold values in the above table) can create a precision error. So, as an improvement, it is proposed to modify the reference voltages V1 to V7 in a non-linear way according to the reference level V0. The voltage values for the reference voltage V0 is kept constant while the other ones are modified by a non-linear mathematical transformation f(x,y,z) as followed: Vn APL = f V ⁢ 0 APL ; Vn 0 % ; V ⁢ 0 0 % .
    Figure imgb0013
  • An example of the result of such a transformation is given in the next table:
    Surface (white) V0 V1 V2 V3 V4 V5 V6 V7
    100.00% 1.41 V 1.35V 1.26V 0.97 V 0.5 V 0.27 V 0.16 V 0.0 V
    97.50% 1.44 V 1.38 V 1.28 V 0.97 V 0.5 V 0.27 V 0.16 V 0.0 V
    95.00% 1.47 V 1.4 V 1.3 V 0.98 V 0.5 V 0.27V 0.16 V 0.0 V
    92.50% 1.51 V 1.43 V 1.32 V 0.99 V 0.5 V 0.27 V 0.16 V 0.0 V
    90.00% 1.54 V 1.45 V 1.34 V 1.0 V 0.51 V 0.27 V 0.16 V 0.0 V
    87.50% 1.57 V 1.48 V 1.36 V 1.01 V 0.51 V 0.27 V 0.16 V 0.0 V
    85.00% 1.61 V 1.51 V 1.38 V 1.02 V 0.51 V 0.27 V 0.16 V 0.0 V
    82.50% 1.65 V 1.54 V 1.4 V 1.03 V 0.51 V 0.27 V 0.16 V 0.0 V
    80.00% 1.68 V 1.57 V 1.42 V 1.04 V 0.51 V 0.27 V 0.16 V 0.0 V
    77.50% 1.72 V 1.6 V 1.45 V 1.05V 0.52 V 0.27 V 0.16 V 0.0 V
    75.00% 1.76 V 1.63 V 1.47 V 1.06 V 0.52 V 0.28 V 0.16 V 0.0 V
    72.50% 1.81 V 1.66 V 1.5 V 1.07 V 0.52 V 0.28 V 0.16 V 0.0 V
    70.00% 1.85 V 1.7 V 1.52 V 1.09 V 0.53 V 0.28 V 0.16 V 0.0 V
    67.50% 1.9 V 1.73 V 1.55 V 1.1 V 0.53 V 0.28 V 0.16 V 0.0 V
    65.00% 1.94 V 1.77 V 1.58 V 1.11 V 0.53 V 0.28 V 0.16 V 0.0 V
    62.50% 1.99 V 1.81 V 1.61 V 1.12V 0.53 V 0.28 V 0.16 V 0.0 V
    60.00% 2.04 V 1.85 V 1.64V 1.14V 0.54 V 0.28 V 0.16 V 0.0 V
    57.50% 2.1 V 1.89 V 1.67V 1.15V 0.54 V 0.28 V 0.16 V 0.0 V
    55.00% 2.15 V 1.94 V 1.7V 1.17V 0.55V 0.28 V 0.16 V 0.0 V
    52.50% 2.21 V 1.98 V 1.73V 1.18V 0.55 V 0.28 V 0.16 V 0.0 V
    50.00% 2.27 V 2.03 V 1.77V 1.2V 0.55 V 0.29 V 0.16 V 0.0 V
    47.50% 2.33 V 2.08 V 1.81 V 1.22 V 0.56 V 0.29 V 0.16 V 0.0 V
    45.00% 2.4 V 2.13 V 1.85V 1.24V 0.56 V 0.29 V 0.16 V 0.0 V
    42.50% 2.47 V 2.18 V 1.89 V 1.25 V 0.57 V 0.29 V 0.16 V 0.0 V
    40.00% 2.54 V 2.24 V 1.93 V 1.27 V 0.57 V 0.29 V 0.16 V 0.0 V
    37.50% 2.61 V 2.29 V 1.97 V 1.29 V 0.57 V 0.29 V 0.16 V 0.0 V
    35.00% 2.68 V 2.35 V 2.01 V 1.31 V 0.58 V 0.29 V 0.16 V 0.0 V
    32.50% 2.76 V 2.41 V 2.06 V 1.33V 0.58 V 0.3V 0.16 V 0.0 V
    30.00% 2.83 V 2.47 V 2.1 V 1.35V 0.59 V 0.3 V 0.16 V 0.0 V
    27.50% 2.9 V 2.52 V 2.14V 1.37V 0.59 V 0.3 V 0.16 V 0.0 V
    25.00% 2.96 V 2.57 V 2.18V 1.39V 0.6 V 0.3 V 0.16 V 0.0 V
    22.50% 3.0 V 2.6V 2.2V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    20.00% 3.0 V 2.6 V 2.2V 1.4V 0.6 V 0.3V 0.16 V 0.0 V
    17.50% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3V 0.16 V 0.0 V
    15.00% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    12.50% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    10.00% 3.0 V 2.6 V 2.2V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    7.50% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    5.00% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
    2.50% 3.0 V 2.6 V 2.2 V 1.4V 0.6 V 0.3 V 0.16 V 0.0 V
  • Figure 4, to be compared with Figure 3, illustrates these new variations of voltage references V0 to V7 by curves. After this transformation, there are almost no more differences for the reference voltages V6 and V7 between the different APL values.
  • This non linear transformation f applied to the reference voltages V1 to V7 should be compensated by an inverse transformation f-1 in the video signal processing chain of the device. With such transformations (f and f-1), it is possible to obtain an optimized power management without introducing too much difficulties in the low level gradations (low voltages/low currents).
  • A circuit implementation of the digital processing and driving unit 4 to be used the power level control method of the invention is given at figure 5.
  • An input picture is forwarded to a power evaluation block 41 that performs the computation of the APL level of the input picture. The APL value is transmitted to a power management block 42. Since the result of this computation can be only made after a complete frame, the input picture should be then stored in a frame memory 43, for example a DDRAM, in order to dispose of one frame delay. This memory can be inside or outside the unit 4.
  • Based on this APL value, an appropriate set of reference signals Refn is chosen for instance from a Look Up Table and sent to the Reference Signaling Unit 5 via a programming bus. Advantageously, a non-linear transformation f is integrated in these signals. As indicated previously, these reference signals can be reference voltages or reference currents. This programming should occur during the vertical blanking in order not to disturb the displayed picture.
  • In parallel to that, a non-linear transfer function f-1 (it can be a mathematical function or a Look Up Table) which is the inverse of the transformation integrated in the chosen set of reference signals Refn is chosen and is applied to the delayed picture by a block 44. The picture after processing is sent to a standard OLED processing block 45 and then to a standard OLED driving block 46 for finally driving the display with the current picture information.
  • The method of the invention can be used for controlling the contrast of the pictures displayed by the display device. In that case, the method consists in calculating an adjustment factor that is to be applied to the intensity of the signal supplied to the luminous elements in order to make the contrast go from a present value to a required value. This adjustment factor is then applied to the reference signals.
  • For example, for reducing the contrast by 50%, the reference signals are decreased from 50%.
    • Annexe 1
  • 0 V7 0.00V 50 V5+(V4-V5)×957/1501 0,487V
    1 V7+(V6-V7)×9/1175 0,001V 51 V5+(V4-V5)×1001/1501 0,496V
    2 V7+(V6-V7)×32/1175 0,004V 52 V5+(V4-V5)×1045/1501 0,505V
    3 V7+(V6-V7)×76/1175 0,01V 53 V5+(V4-V5)×1088/1501 0,514V
    4 V7+(V6-V7)×141/1175 0,019V 54 V5+(V4-V5)×1131/1501 0,523V
    5 V7+(V6-V7)×224/1175 0,03V 55 V5+(V4-V5)×1173/1501 0,532V
    6 V7+(V6-V7)×321/1175 0,043V 56 V5+(V4-V5)×1215/1501 0,541V
    7 V7+(V6-V7)×425/1175 0,057V 57 V5+(V4-V5)×1257/1501 0,55V
    8 V7+(V6-V7)×529/1175 0,071V 58 V5+(V4-V5)×1298/1501 0,559V
    9 V7+(V6-V7)×630/1175 0,084V 59 V5+(V4-V5)×1339/1501 0,567V
    10 V7+(V6-V7)×727/1175 0,097V 60 V5+(V4-V5)×1380/1501 0,576V
    11 V7+(V6-V7)×820/1175 0,11V 61 V5+(V4-V5)×1421/1501 0,584V
    12 V7+(V6-V7)×910/1175 0,122V 62 V5+(V4-V5)×1461/1501 0,593V
    13 V7+(V6-V7)×99811175 0,133V 63 V4 0,601V
    14 V7+(V6-V7)×1086/1175 0,145V 64 V4+(V3-V4)×40/2215 0,615V
    15 V6 0,157V 65 V4+(V3-V4)×80/2215 0,628V
    16 V6+(V5-V6)×89/1097 0,167V 66 V4+(V3-V4)×120/2215 0,641V
    17 V6+(V5-V6)×173/1097 0,177V 67 V4+(V3-V4)×160/2215 0,654V
    18 V6+(V5-V6)×250/1097 0,186V 68 V4+(V3-V4)×200/2215 0,667V
    19 V6+(V5-V6)×320/1097 0,194V 69 V4+(V3-V4)×240/2215 0,681V
    20 V6+(V5-V6)×386/1097 0,202V 70 V4+(V3-V4)×280/2215 0,694V
    21 V6+(V5-V6)×451/1097 0,21V 71 V4+(V3-V4)×320/2215 0,707V
    22 V6+(V5-V6)×517/1097 0,217V 72 V4+(V3-V4)×360/2215 0,72V
    23 V6+(V5-V6)×585/1097 0,225V 73 V4+(V3-V4)×400/2215 0,734V
    24 V6+(V5-V6)×654/1097 0,233V 74 V4+(V3-V4)×440/2215 0,747V
    25 V6+(V5-V6)×723/1097 0,241V 75 V4+(V3-V4)×480/2215 0,76V
    26 V6+(V5-V6)×790/1097 0,249V 76 V4+(V3-V4)×520/2215 0,773V
    27 V6+(V5-V6)×855/1097 0,257V 77 V4+(V3-V4)×560/2215 0,787V
    28 V6+(V5-V6)×917/1097 0,264V 78 V4+(V3-V4)×600/2215 0,80V
    29 V6+(V5-V6)×977/1097 0,271V 79 V4+(V3-V4)×640/2215 0,813V
    30 V6+(V5-V6)×1037/1097 0,278V 80 V4+(V3-V4)×680/2215 0,826V
    31 V5 0,285V 81 V4+(V3-V4)×719/2215 0,839V
    32 V5+(V4-V5)×60/1501 0,298V 82 V4+(V3-V4)×758/2215 0,852V
    33 V5+(V4-V5)×119/1501 0,31V 83 V4+(V3-V4)×796/2215 0,865V
    34 V5+(V4-V5)×176/1501 0,322V 84 V4+(V3-V4)×834/2215 0,877V
    35 V5+(V4-V5)×231/1501 0,334V 85 V4+(V3-V4)×/2215 0,889V
    36 V5+(V4-V5)×284/1501 0,345V 86 V4+(V3-V4)×/2215 0,902V
    37 V5+(V4-V5)×335/1501 0,356V 87 V4+(V3-V4)×944/2215 0,914V
    38 V5+(V4-V5)×385/1501 0,366V 88 V4+(V3-V4)×980/2215 0,925V
    39 V5+(V4-V5)×434/1501 0,376V 89 V4+(V3-V4)×1016/2215 0,937V
    40 V5+(V4-V5)×483/1501 0,387V 90 V4+(V3-V4)×1052/2215 0,949V
    41 V5+(V4-V5)×532/1501 0,397V 91 V4+(V3-V4)×1087/2215 0,961V
    42 V5+(V4-V5)×580/1501 0,407V 92 V4+(V3-V4)×1122/2215 0,972V
    43 V5+(V4-V5)×628/1501 0,417V 93 V4+(V3-V4)×1157/2215 0,984V
    44 V5+(V4-V5)×676/1501 0,427V 94 V4+(V3-V4)×/2215 0,996V
    45 V5+(V4-V5)×724/1501 0,438V 95 V4+(V3-V4)×1226/2215 1,007V
    46 V5+(V4-V5)×772/1501 0,448V 96 V4+(V3-V4)×1260/2215 1,018V
    47 V5+(V4-V5)×819/1501 0,458V 97 V4+(V3-V4)×1294/2215 1,029V
    48 V5+(V4-V5)×866/1501 0,468V 98 V4+(V3-V4)×1328/2215 1,04V
    49 V5+(V4-V5)×912/1501 0,477V 99 V4+(V3-V4)×1362/2215 1,052V
    100 V4+(V3-V4)×1396/2215 1,063V 150 V3+(V2-V3)×777/2343 1,581V
    101 V4+(V3-V4)×1429/2215 1,074V 151 V3+(V2-V3)×813/2343 1,593V
    102 V4+(V3-V4)×1462/2215 1,085V 152 V3+(V2-V3)×849/2343 1,604V
    103 V4+(V3-V4)×1495/2215 1,096V 153 V3+(V2-V3)×885/2343 1,616V
    104 V4+(V3-V4)×1528/2215 1,107V 154 V3+(V2-V3)×921/2343 1,627V
    105 V4+(V3-V4)×1561/2215 1,118V 155 V3+(V2-V3)×958/2343 1,639V
    106 V4+(V3-V4)×1593/2215 1,128V 156 V3+(V2-V3)×995/2343 1,651V
    107 V4+(V3-V4)×1625/2215 1,139V 157 V3+(V2-V3)×1032/2343 1,663V
    108 V4+(V3-V4)×1657/2215 1,149V 158 V3+(V2-V3)×1069/2343 1,674V
    109 V4+(V3-V4)×1688/2215 1,16V 159 V3+(V2-V3)×1106/2343 1,686V
    110 V4+(V3-V4)×1719/2215 1,17V 160 V3+(V2-V3)×1143/2343 1,698V
    111 V4+(V3-V4)×1750/2215 1,18V 161 V3+(V2-V3)×1180/2343 1,71V
    112 V4+(V3-V4)×1781/2215 1,19V 162 V3+(V2-V3)×1217/2343 1,722V
    113 V4+(V3-V4)×1811/2215 1,20V 163 V3+(V2-V3)×1255/2343 1,734V
    114 V4+(V3-V4)×1841/2215 1,21V 164 V3+(V2-V3)×1293/2343 1,746V
    115 V4+(V3-V4)×1871/2215 1,22V 165 V3+(V2-V3)×1331/2343 1,758V
    116 V4+(V3-V4)×1901/2215 1,23V 166 V3+(V2-V3)×1369/2343 1,77V
    117 V4+(V3-V4)×1930/2215 1,24V 167 V3+(V2-V3)×1407/2343 1,782V
    118 V4+(V3-V4)×1959/2215 1,249V 168 V3+(V2-V3)×1445/2343 1,794V
    119 V4+(V3-V4)×1988/2215 1,259V 169 V3+(V2-V3)×1483/2343 1,806V
    120 V4+(V3-V4)×2016/2215 1,268V 170 V3+(V2-V3)×1521/2343 1,819V
    121 V4+(V3-V4)×2044/2215 1,277V 171 V3+(V2-V3)×1559/2343 1,831V
    122 V4+(V3-V4)×2072/2215 1,287V 172 V3+(V2-V3)×1597/2343 1,843V
    123 V4+(V3-V4)×2100/2215 1,296V 173 V3+(V2-V3)×1635/2343 1,855V
    124 V4+(V3-V4)×2128/2215 1,305V 174 V3+(V2-V3)×1673/2343 1,867V
    125 V4+(V3-V4)×2156/2215 1,314V 175 V3+(V2-V3)×1712/2343 1,879V
    126 V4+(V3-V4)×2185/2215 1,324V 176 V3+(V2-V3)×1751/2343 1,892V
    127 V3 1,334V 177 V3+(V2-V3)×1790/2343 1,904V
    128 V3+(V2-V3)×31/2343 1,344V 178 V3+(V2-V3)×1829/2343 1,917V
    129 V3+(V2-V3)×64/2343 1,354V 179 V3+(V2-V3)×1868/2343 1,929V
    130 V3+(V2-V3)×97/2343 1,365V 180 V3+(V2-V3)×1907/2343 1,942V
    131 V3+(V2-V3)×130/2343 1,375V 181 V3+(V2-V3)×1946/2343 1,954V
    132 V3+(V2-V3)×163/2343 1,386V 182 V3+(V2-V3)×1985/2343 1,966V
    133 V3+(V2-V3)×196/2343 1,396V 183 V3+(V2-V3)×2024/2343 1,979V
    134 V3+(V2-V3)×229/2343 1,407V 184 V3+(V2-V3)×2064/2343 1,992V
    135 V3+(V2-V3)×262/2343 1,417V 185 V3+(V2-V3)×2103/2343 2,004V
    136 V3+(V2-V3)×295/2343 1,428V 186 V3+(V2-V3)×2143/2343 2,017V
    137 V3+(V2-V3)×328/2343 1,438V 187 V3+(V2-V3)×2183/2343 2,03V
    138 V3+(V2-V3)×361/2343 1,449V 188 V3+(V2-V3)×2223/2343 2,042V
    139 V3+(V2-V3)×395/2343 1,46V 189 V3+(V2-V3)×2263/2343 2,055V
    140 V3+(V2-V3)×429/2343 1,471V 190 V3+(V2-V3)×2303/2343 2,068V
    141 V3+(V2-V3)×463/2343 1,481V 191 V2 2,081V
    142 V3+(V2-V3)×497/2343 1,492V 192 V2+(V1-V2)×40/1638 2,09V
    143 V3+(V2-V3)×531/2343 1,503V 193 V2+(V1-V2)×81/1638 2,10V
    144 V3+(V2-V3)×566/2343 1,514V 194 V2+(V1-V2)×124/1638 2,11V
    145 V3+(V2-V3)×601/2343 1,525V 195 V2+(V1-V2)×168/1638 2,121V
    146 V3+(V2-V3)×636/2343 1,536V 196 V2+(V1-V2)×213/1638 2,131V
    147 V3+(V2-V3)×671/2343 1,548V 197 V2+(V1-V2)×259/1638 2,142V
    148 V3+(V2-V3)×706/2343 1,559V 198 V2+(V1-V2)×306/1638 2,153V
    149 V3+(V2-V3)×741/2343 1,57V 199 V2+(V1-V2)×353/1638 2,165V
    200 V2+(V1-V2)×401/1638 2,176V 250 V1+(V0-V1)×2278/3029 2,756V
    201 V2+(V1-V2)×450/1638 2,188V 251 V1+(V0-V1)×2411/3029 2,773V
    202 V2+(V1-V2)×499/1638 2,199V 252 V1+(V0-V1)×2549/3029 2,79V
    203 V2+(V1-V2)×548/1638 2,211V 253 V1+(V0-V1)×2694/3029 2,808V
    204 V2+(V1-V2)×597/1638 2,223V 254 V1+(V0-V1)×2851/3029 2,828V
    205 V2+(V1-V2)×646/1638 2,234V 255 V0 2,85V
    206 V2+(V1-V2)×695/1638 2,246V
    207 V2+(V1-V2)×745/1638 2,258V
    208 V2+(V1-V2)×795/1638 2,27V
    209 V2+(V1-V2)×846/1638 2,282V
    210 V2+(V1-V2)×897/1638 2,294V
    211 V2+(V1-V2)×949/1638 2,307V
    212 V2+(V1-V2)×1002/1638 2,319V
    213 V2+(V1-V2)×1056/1638 2,332V
    214 V2+(V1-V2)×1111/1638 2,345V
    215 V2+(V1-V2)×1167/1638 2,359V
    216 V2+(V1-V2)×1224/1638 2,372V
    217 V2+(V1-V2)×1281/1638 2,386V
    218 V2+(V1-V2)×1339/1638 2,40V
    219 V2+(V1-V2)×1398/1638 2,414V
    220 V2+(V1-V2)×1458/1638 2,428V
    221 V2+(V1-V2)×1518/1638 2,442V
    222 V2+(V1-V2)×1578/1638 2,457V
    223 V1 2,471V
    224 V1+(V0-V1)×60/3029 2,478V
    225 V1+(V0-V1)×120/3029 2,486V
    226 V1+(V0-V1)×180/3029 2,493V
    227 V1+(V0-V1)×241/3029 2,501V
    228 V1+(V0-V1)×304/3029 2,509V
    229 V1+(V0-V1)×369/3029 2,517V
    230 V1+(V0-V1)×437/3029 2,526V
    231 V1+(V0-V1)×507/3029 2,534V
    232 V1+(V0-V1)×580/3029 2,544V
    233 V1+(V0-V1)×655/3029 2,553V
    234 V1+(V0-V1)×732/3029 2,563V
    235 V1+(V0-V1)×810/3029 2,572V
    236 V1+(V0-V1)×889/3029 2,582V
    237 V1+(V0-V1)×969/3029 2,592V
    238 V1+(V0-V1)×1050/3029 2,602V
    239 V1+(V0-V1)×1133/3029 2,613V
    240 V1+(V0-V1)×1218/3029 2,623V
    241 V1+(V0-V1)×1304/3029 2,634V
    242 V1+(V0-V1)×1393/3029 2,645V
    243 V1+(V0-V1)×1486/3029 2,657V
    244 V1+(V0-V1)×1583/3029 2,669V
    245 V1+(V0-V1)×1686/3029 2,682V
    246 V1+(V0-V1)×1794/3029 2,695V
    247 V1+(V0-V1)×1907/3029 2,71V
    248 V1+(V0-V1)×2026/3029 2,724V
    249 V1+(V0-V1)×2150/3029 2,74V

Claims (10)

  1. Method for controlling the power level and/or the contrast in a display device having a plurality of luminous elements corresponding to the colour components of the pixels of a picture, wherein the luminance generated by each of said luminous elements is based on the intensity of the signals supplied to the luminous element and the power level and/or contrast for each picture is controlled by adjusting the intensity of the signals to be supplied to each luminous element, wherein the intensity of the signals to be supplied to the luminous elements is based on a plurality of analog reference signals (Refn), and wherein the power level and/or contrast is controlled by adjusting the intensity of said analog reference signals (Refn) based on an average power level of said picture and characterized in that a non-linear transformation is applied to the reference levels and the inverse transformation (f-1) is applied to the picture signal for using instead of reference levels (Vn) below a predetermined value (0.16V) said predetermined value (0.16V) or a value above said predetermined value (0.16V) for said analog reference signals (Refn) to avoid reference levels (V5, V6) having a value between zero and below the predetermined value (0.16V) to avoid precision errors.
  2. Method according to claim 1, characterized in that, for the controlling the contrast of the pictures displayed by the display device, it further comprises the following steps :
    - calculating an adjustment factor to be applied to the intensity of the picture signal supplied to the luminous elements in order that the resulting contrast is equal to a required contrast, and
    - applying said adjustment factor to the analog reference signals (Refn)
  3. Method according to one of claims 1 or 2, characterized in that, before adjustment of the signal intensity, the non linear transformation (f) is applied to reference signals(Refn) in order to increase the amplitude of the low-amplitude reference signals (Refn) and the inverse transformation (f-1) is applied to the picture signal to adapt further reference levels related to a certain percentage of white surface in the picture.
  4. Method according to one of claims 1 to 3, characterized in that the luminous elements are organic light emitting display diodes.
  5. Method according to one of claims 1 to 4, characterized in that the analog reference signals (Refn) are reference voltages or reference currents.
  6. Apparatus for controlling the power level and/or the contrast in a display device having a plurality of luminous elements corresponding to the colour components of the pixels of a picture, wherein the luminance generated by each of said luminous elements is based on the intensity of the signals supplied to the luminous element and the power level and/or contrast for each picture is controlled by adjusting the intensity of the signals to be supplied to each luminous element, and wherein the intensity of the signals to be supplied to the luminous elements is based on a plurality of analog reference signals(Refn) characterized in that it comprises adjustment means (42) for controlling the power level and/or contrast by adjusting the intensity of the reference signals (Refn) based on an average power level of said picture and wherein
    a non-linear transformation is applied to the reference levels, provided by a reference signalling unit (5), for providing instead of reference levels (Vn) below a predetermined value (0.16V) said predetermined value (0.16V) or a value above said predetermined value (0.16V) for avoiding reference levels (V5, V6) having a value above zero and below the predetermined value (0.16V) and means (44) for applying the inverse transformation (f-1) to the picture signal are provided to avoid precision errors.
  7. Apparatus according to claim 6, characterized in that, for controlling the contrast of the pictures displayed by the display device, it further comprises calculation means for calculating an adjustment factor to be applied to the intensity of the signal supplied to the luminous elements in order that the resulting contrast is equal to a required contrast, and in that the adjustment means (42) applies said adjustment factor to the analog reference signals
    (Refn)
  8. Apparatus according to one of claims 6 or 7, characterized in that it comprises a frame memory (43) for storing a picture before transmitting it to the display device.
  9. Apparatus according to claim 6 or 7, characterized in that the adjustment means (42) comprises means for applying the non linear transformation (f) to reference signals (Refn) and means (44) for applying the inverse transformation (f-1) to the picture signal.
  10. Display device comprising
    - a plurality of organic light emitting diodes (1),
    - signal processing means (4) for processing the picture signal received by the display device,
    - driving means (2, 3) for driving said plurality of organic light emitting diodes (1) according to the signal processed by the signal processing means (4),
    - reference signalling means (5) for outputting analog reference signals (Refn) to the driving means (3),
    characterized in that said signal processing means (4) comprises an apparatus according to any of claims 6 to 9 .
EP05106877A 2004-07-29 2005-07-26 Method and apparatus for power level control and/or contrast control of a display device Active EP1624438B1 (en)

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EP04291945A EP1622119A1 (en) 2004-07-29 2004-07-29 Method and apparatus for power level control and/or contrast control of a display device
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WO2004040542A1 (en) * 2002-10-31 2004-05-13 Sony Corporation Image display and color balance adjusting method therefor

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JP3658362B2 (en) * 2001-11-08 2005-06-08 キヤノン株式会社 Video display device and control method thereof
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