USRE45209E1 - Display device comprising an adjustable light source - Google Patents

Display device comprising an adjustable light source Download PDF

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USRE45209E1
USRE45209E1 US14/080,212 US200514080212A USRE45209E US RE45209 E1 USRE45209 E1 US RE45209E1 US 200514080212 A US200514080212 A US 200514080212A US RE45209 E USRE45209 E US RE45209E
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brightness level
level
pixels
gray
dimmed
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Nalliah Raman
Gerben Johan Hekstra
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Koninklijke Philips NV
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Koninklijke Philips NV
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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
    • G09G3/34—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 by control of light from an independent source
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • G09G3/3413—Details of control of colour illumination sources
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • 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
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • G09G3/342—Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/36—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 by control of light from an independent source using liquid crystals
    • 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
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0271—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
    • 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
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/0646—Modulation of illumination source brightness and image signal correlated to each other
    • 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
    • G09G2320/0666—Adjustment of display parameters for control of colour parameters, e.g. colour temperature
    • 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
    • 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
    • G09G3/34—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 by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • G09G3/342—Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
    • G09G3/3426—Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines the different display panel areas being distributed in two dimensions, e.g. matrix

Definitions

  • the invention relates to a display device comprising an adjustable light source, a display panel with display pixels for modulating light originating from the light source and processing circuitry coupled to the display panel and the adjustable light source.
  • EP 1,111,578A1 discloses a display device with a passive light modulation part and a light source.
  • a video signal is provided to the passive light modulation part for generating an image.
  • the amplitude of the video signal is dynamically adjustable based on a detected minimum, maximum and average brightness value of the video signal.
  • the brightness of the light source is adjustable in such a way that the image displayed on the passive light modulation part after the dynamic adjusting of the amplitude does not vary visually from an average brightness level for each frame of the video signal. It is a disadvantage of the known display device that this adjustment of the amplitude and the corresponding adjustment of the brightness of the light source do not provide for all images the best possible rendering of these images on the light modulation part.
  • the display device comprises an adjustable light source; a display panel with display pixels for modulating light originating from the light source; and processing circuitry coupled to the display panel and the adjustable light source, the processing circuitry having an input for receiving an input signal representing gray levels of pixels of an image to be displayed on the display panel and comprising:
  • the dimmed brightness level of the light source is determined. This enables the selection of a value that the light source is able to provide, thereby taking into account, for example, operating conditions or limitations of dynamic variations of the light source.
  • the processing circuitry adapts the input signal taking into account the selected brightness level. This sequence enables the selection of a matching combination for each image of a dimmed brightness level and an adapted input signal.
  • the prior art disclosed in EP 1,111,578A1 firstly determines the adaptation of the amplitude of the input signal and thereafter determines the dimmed brightness level so as to match a brightness level of the input signal.
  • U.S. Pat. No. 5,717,422 discloses a display with a light source providing light to a light modulation part.
  • a control is present for controlling the intensity of the light source as function of a brightness characteristic of an image to be displayed, while nothing is disclosed about adapting an input signal coupled to the modulation part in correspondence with the controlling of the intensity of the light source.
  • U.S. Pat. No. 6,631,995 discloses a device with a light source and a light control device. Via a video signal amplifier a light modulation panel is driven in such a way that the contrast of an image to be displayed by the device has a desired value. Via a light-control device, controlling the amount of light provided by the light source to the modulation panel, the image to be displayed is corrected such that the brightness of the displayed image corresponds with a desired value. So, this prior art, firstly determines the desired contrast, and then to what extent to control the amount of light provided by the light source.
  • the means for selecting is adapted to select the dimmed brightness level in dependence on a number of occurrences of a gray level corresponding to a brightness of display pixels above the dimmed brightness level and/or a number of occurrences of a gray level corresponding to a brightness level of display pixels below a predetermined brightness level.
  • this invention provides generally a further dimming of the light source, resulting in an improved discemability of the dark gray levels corresponding to brightness levels near the minimum brightness level at the expense of some clipping of the gray levels corresponding to brightness levels near the dimmed brightness level.
  • the predetermined level may be a fixed level, or, more preferably, an adjustable level, which is determined in dependence on the dimmed brightness level.
  • the predetermined brightness level is formed by the maximum contrast ratio of the display panel and the dimmed brightness level, preferably by dividing the dimmed brightness level by the contrast ratio.
  • the dimmed brightness level it is important to take into account the resulting minimum brightness level that can be reproduced, as gray levels corresponding to a brightness level below this minimum obtainable brightness level are not correctly reproduced on the display device.
  • a suitable range of values is 50% to 150% of the ratio of the dimmed brightness level and contrast ratio, particularly a range of 80% to 100%.
  • FIG. 1 shows a block diagram of an embodiment of the display device according to the invention
  • FIGS. 2A to 2C show various backlight configurations which may be applied in the display device according to the invention
  • FIG. 3 shows a graph of the output luminance of the display panel versus the gray levels of the input signal of the display device illustrating the operation of an embodiment of the display device according to the invention
  • FIG. 4 shows another graph of the output luminance of the display panel versus the gray levels of the input signal of the display device illustrating the operation of another embodiment of the display device according to the invention
  • FIG. 5 shows a block diagram of an embodiment of processing circuitry applied in the display device according to the invention.
  • FIG. 6 shows a flow diagram of an embodiment according to the invention
  • FIG. 7 shows a part of an image comprising a matrix of rows i and columns j of pixels
  • FIG. 8 shows an embodiment of an interpolation approach to obtain soft clipping according to the invention
  • FIG. 9 shows a block diagram of an embodiment of the display device according to the invention with feedback.
  • FIG. 10 shows a graph of the output gray levels of the output signal as function of the gray levels of the input signal.
  • An embodiment of the display device DD according to the invention as shown in FIG. 1 comprises an adjustable light source BL, a display panel DP with pixels for modulating light LB originating from the light source BL, and processing circuitry P.
  • the processing circuitry P is coupled to the display panel DP and to the adjustable light source BL and has an input for receiving an input signal V 1 representing an image to be displayed on the display panel DP.
  • the image may be represented by a matrix of rows and columns of pixels.
  • the input signal represents a sequence of images.
  • the input signal comprises sequences of parts of images, for example, even and odd fields of a video frame, then the image is to be interpreted also as such an even or odd field.
  • the processing circuitry P comprises means for selecting a dimmed brightness level Lbdim of the light source BL in dependence on brightness levels, hereinafter also called gray levels, of pixels of the image to be displayed.
  • the means for selecting may be hardware selection circuitry S as shown in FIG. 1 or may be realized with software or a combination of both.
  • the means for selecting processes the input signal V 1 and selects the dimmed brightness level Lbdim, thereby substantially minimizing an error function as will be explained later on.
  • the selection circuitry S provides a light source drive signal BLD for adapting the brightness level LB of the light source BL to the dimmed brightness level Lbdim.
  • the processing circuitry P further comprises means for adapting the input signal V 1 in dependence on the selected dimmed brightness level LBdim.
  • the means for adapting may be hardware adaptation circuitry A as shown in FIG. 1 or may be realized with software or a combination of both.
  • the selection circuitry S provides an adaptation drive signal AD to the adaptation circuitry A in dependence on the selected dimmed brightness level Lbdim.
  • the adaptation circuitry A adapts the input signal V 1 , thereby talking into account the adaptation drive signal AD and any other transformations required to adapt the input signal V 1 to an output signal V 2 , suitable for driving the display panel DP.
  • transformations may include, amongst others, gamma correction, adaptation of the input signal V 1 to transmission characteristics of the display panel DP, and/or adaptation of color components of the input signal V 1 to the primary colors of the display panel DP.
  • the output signal V 2 driving the display panel DP in combination with the brightness level of the light LB from the light source BL, determines the light output L of each of the pixels of the display panel.
  • the input signal V 1 may be analog or digital; it may represent monochrome images or color images.
  • the input signal may comprise a separate luminance signal in combination with color information or may comprise color components, for example in the form of an RGB signal with a red color component R, a green color component G and a blue color component B.
  • the light source BL may be a single lamp backlight unit BL 1 with one lamp L 1 as shown in FIG. 2A for illuminating the whole display panel DP.
  • it may be a multiple lamp backlight unit BL 2 with a plurality of lamps L 1 , L 2 , L 3 , L 4 , each directed to illuminate a corresponding region R 1 , R 2 , R 3 , R 4 of the display panel DP.
  • Each of the lamps L 1 , L 2 , L 3 , L 4 may be dimmed simultaneously with a substantially same amount or may be dimmed separately with a different amount and/or at different moments in time.
  • the effect of dimming one of the lamps L 1 , L 2 , L 3 , L 4 for a particular one of the regions R 1 , R 2 , R 3 , R 4 may result in a change of brightness levels in another region which overlaps with this particular region.
  • the change of brightness levels may be corrected by adapting the output signal V 2 , such that this adaptation counteracts the changes. If one or more of the regions R 1 , R 2 , R 3 , R 4 correspond, for example, to a horizontal (or vertical) black bar in an image to be displayed, the corresponding lamp L 1 ; L 2 ; L 3 ; L 4 may be turned off completely.
  • FIG. 2C Another alternative, as shown in FIG. 2C , is a multicolor backlight unit BL 3 with a plurality of color lamps LC 1 , LC 2 of different color, the color lamps LC 1 , LC 2 directed to illuminate a same region of the display panel DP.
  • the light source may also be formed by alterations (for example of number, type or positions of lamps) and/or combinations of above mentioned backlight units.
  • the number of lamps may be equal to the number of pixels.
  • a backlight unit having one or more lamps providing a substantially constant brightness, while dimming of the light is obtained by means of a light shutter, which controls the amount of light to be passed on from the lamps to the display panel DP.
  • the light shutter may comprise parts which are controllable separately, so that the amount of light can be controlled per part of the area to be illuminated.
  • the lamps may be any type of lamp, like fluorescent lamps, LEDs, or OLEDs.
  • the display panel DP as shown in FIG. 1 may be a Liquid Crystal Display panel (LCD panel) or any other light-modulating panel, for example a panel with movable micro mirrors as used in a projector with Digital mirror Devices.
  • the LCD panel may be a transmissive LCD panel for modulating the light passing through the panel as shown in FIG. 1 or a reflective LCD that modulates the light reflected by the panel (not shown) or a transflective LCD which is capable of modulating; both the transmitted and the reflected light.
  • the display panel DP may be applied in a display product PR, for example, a television set, a monitor, a portable computer (laptop), a PDA or mobile phone equipped with a display.
  • these products include signal processing circuitry SPC for processing signals received via an input terminal IN to convext convert them into the input signal V 1 of the display module.
  • the input terminal IN may be an antenna terminal or a connector via which a base band signal is received.
  • the product PR may be a direct view display panel allowing a user to watch images on the display or a projection based system allowing the user to watch images projected from the display panel via an optical system on a screen.
  • the projection system may be a rear or a front projection system.
  • FIG. 3 illustrating an embodiment with a digital monochrome input signal V 1 , representing gray levels x of the pixel of the image.
  • the adaptation circuitry A may be designed to deliver an output signal V 2 , which results in a light output L of a display pixel as function of the gray level x of that corresponding pixel in the input signal according to the first curve C 1 .
  • the light output L would be proportional to the gray level x from a zero gray level (black level) to a maximum available gray level x max (white level).
  • the contrast ratio CR of a display panel such as an LCD panel, is limited to a value in the order of magnitude of 100 to 200.
  • the lowest brightness that can be represented is Lbmax/CR. This means that gray levels with a value below a threshold level x thres are not correctly displayed on the display panel DP: all dark gray values from 0 to x thres will have the light output Lbmax/CR.
  • a further improvement of the reproduction of dark gray levels is obtained up to a minimum gray level, being the dimmed threshold level X thresd which is smaller than x thres .
  • This dimmed threshold level x thresd corresponds to the minimum brightness level Lbdim/CR. This improvement is obtained at the expense of clipping of gray levels above a level x 1 corresponding to the dimmed brightness level Lbdim.
  • the input signal V 1 may include a gamma pre-correction function Gs(Ls) which is provided by a source from which the image is obtained.
  • the term Ls represents the brightness of the image at the source.
  • the display panel DP may have a gamma characteristic Gd that is different from the pre-correction function Gs.
  • a A look-up table may be applied to determine the adapted gray level x′ as function of the gray level x.
  • the light BL may be dimmed. If the image contains many bright pixels with gray values close to x max and no values below x thres , then the light source BL may be driven to its maximum value Lbmax. When an image contains very few pixels with a gray level above x 1 and many pixels with a gray level below x thres , then the light source BL is preferably driven to the dimmed brightness level Lbdim.
  • the dimmed brightness level Lbdim and the corresponding gray level x 1 may be determined dynamically for subsequent images (or per region of each of the subsequent images in case a multiple lamp backlight unit BL 2 is applied).
  • an image contains both pixels with gray levels above x 1 and below x thres , deterioration of the displayed image is inevitable and a compromise is necessary.
  • an error function is applied which corresponds to the amount of deterioration of the displayed image. By selecting for each image a dimmed brightness level Lbdim which results in a minimum value of this error function, the deterioration is minimized.
  • the error function includes a number of occurrences of gray levels x corresponding to a brightness level L above the dimmed brightness level Lbdim and/or a number of occurrences of gray levels x corresponding to a brightness level L below a predetermined brightness level, which preferably corresponds to the minimum brightness level Lbdim/CR.
  • An embodiment of the error function E Tot (x 1 ) is given by the formula:
  • Dividing by the total number of pixels may be omitted, as this number is the same for all terms in the summation and results merely in the resulting error function to be scaled with the number of pixels.
  • the weighting functions f(x), g(x) may be substantially equal to one, giving an equal weight to each of the gray levels above x 1 or below x thresd .
  • the weighting functions may take into account information about pixels surrounding pixels with a same gray level x as explained in further detail below.
  • FIG. 7 shows a part of an image comprising a matrix of rows i and columns j of pixels. Each pixel is identified by a combination of a row index i and a column index j.
  • the indices i, j are determined for pixels having this gray level x.
  • the weight factor f ij is determined for each of the pixels with the thus determined indices i, j. This weight factor f ij is determined taking into account the gray level of pixels surrounding the pixel with indices i, j.
  • the row indices i of the surrounding pixels range SP from a lowest value of i minus an integer value i 1 up to and including a highest value of i plus an integer value i 2 .
  • the column indices j of the surrounding pixels range from a lowest value of j minus an integer value j 1 up to and including a highest value of j plus an integer value j 2 .
  • the pixel with indices i, j is of course to be excluded from the surrounding pixels SP.
  • a suitable method to determine this weight factor f ij is to sum differences d(k 1 ,k 2 ) in gray levels between the surrounding pixels SP with indices k 1 , k 2 and the pixel with indices i, j.
  • the weight factor may be expressed as:
  • the value f ij is calculated for each of the pixels having the gray value x.
  • the final weight function f(x) associated with the gray level x may be the largest value f ij found for the pixels with this value of x.
  • f(x) may be the sum of all weight factors f ij found for the pixels with this value of x.
  • the term (x ⁇ x 1 ) represents the deviations of the displayed gray value from the gray value x of the input signal, hence is a measure for the amount of clipping.
  • FIG. 4 Another embodiment with soft clipping is illustrated in FIG. 4 .
  • the light output L as function of the gray level x is shown with x max being the maximum gray level.
  • the first curve C 1 shows again the curve for an ideal panel.
  • a fourth curve C 4 illustrates the soft clipping for a dimmed brightness level Lbdim.
  • the fourth curve C 4 follows substantially the first curve C 1 , similar to the third curve C 3 as shown in FIG. 3 .
  • the difference with the third-curve C 3 is that below the gray level x 3 the relation of the light output L versus the gray level x is gradually flattened.
  • the gray level x approaches zero, the light output approaches the minimum brightness level Lbdim/CR.
  • the embodiments illustrated in FIGS. 3 and 4 may have look-up tables. These look-up tables comprise for each gray level of the input signal V 1 a corresponding value of the gray level of the output signal V 2 .
  • the display panel DP is driven with these corresponding gray values of the output signal V 2 , the light output L follows a curve as function of the gray level x as programmed in the look-up table.
  • Whether soft clipping is applied or not may be made dependent on the amount of errors introduced in the light output L as function of the gray levels of the input signal V 1 . These errors result from clipping of the gray levels in the range from zero to x thresd and from x 1 to x max as, for example, is illustrated with the third curve C 3 in FIG. 3 .
  • the known method in the field of computer graphics of Bezier Curves may be applied as smoothing algorithm, in particular the quadratic form of the Bezier Curve.
  • This quadratic form is simply a linear interpolation of the linear interpolation between three control points P 0 , P 1 , and P 2 as shown in FIG. 8 .
  • the algorithm given below is iterated, indicated by the integers h and t, for a number of samples m on the smooth Bezier curve of the output signal V 2 .
  • the output gray levels y of the output signal V 2 as function of the gray levels x of the input signal V 1 are shown in FIG. 10 .
  • the curve C 4 corresponds to the curve C 4 shown in FIG. 4 , however now the relation with the output signal is shown instead of the relation with the light output L.
  • the output gray levels y have been given the same indices as the corresponding gray levels x.
  • the algorithm is:
  • the number of samples m may be selected to be equal to the number of gray levels between x max and x 2 .
  • P 0 y thresd
  • P 1 y thresd
  • P 2 y 3
  • the value y 3 may be 2*y thresd , resulting in a number of samples m equal to x 3 .
  • the processing circuitry P may be realized as shown in the block diagram of FIG. 5 .
  • the selection circuitry S is adapted to select the dimmed brightness level Lbdim for which the sum of the error functions of each of the color component R 1 , G 1 , B 1 is minimized.
  • the gray levels of the color components R 1 , G 1 , B 1 are to be interpreted as the amplitude levels of the color components R 1 , G 1 , B 1 .
  • the sum may be determined based on a weighted addition of the error functions. The weighting may be based on the brightness contribution of each of the color components R 1 , G 1 , B 1 .
  • the selection circuitry S provides the light source drive signal BLD, which adjusts the light source BL to the selected dimmed brightness level Lbdim.
  • the selection circuitry also provides the adaptation drive signal AD.
  • the adaptation circuitry A adapts the gray levels (amplitudes) of each of the color components in respective color component adjustment circuits AR, AG, AB. Due to the dimming the colors in dark gray areas of the image are reproduced more correctly as the amplitudes corresponding to these dark gray levels of each of the color components are discernable in the displayed image.
  • further transformations may take place in the adaptation circuitry A. In case the display panel DP has primary colors differing from the primary colors of the input signal V 1 and/or a different number of primary colors, then also the transformation from the primary colors of the input signal V 1 to the primary colors of the display panel DP may be included.
  • FIG. 6 A further embodiment is illustrated with the flow diagram shown in FIG. 6 :
  • the smoothing as described in the fifth step M 5 may be set to respond faster to an increase of the dimmed brightness level Lbdim(n) during subsequent images. This may be achieved by selecting a different constant q during the increase.
  • the advantage is, that clipping in white areas is reduced for images with white areas following a sequence of dark images.
  • the relatively slow response during a decrease of the dimmed brightness level Lbdim(n) for subsequent images ensures that flickering of the displayed image is avoided.
  • the smoothing may also take into account lamp parameters, for example at what rate a lamp is able to change its light output, or any limitations required to ensure an adequate lifetime of a lamp.
  • the smoothing may also take into account actual operating conditions or historical operating conditions of a lamp.
  • FIG. 9 shows a block diagram of an embodiment of the display device according to the invention, which uses feedback.
  • the diagram is the same as the one shown in FIG. 1 , except that the input for the selection circuitry S is now the output signal V 2 .
  • This means a feedback loop is present, wherein the selection circuitry S determines a dimmed brightness level Lbdim(n) for an n th image of a sequence of images and a corresponding adaptation drive signal AD on the basis of gray levels of the output signal V 2 corresponding to the (n ⁇ 1) th image.
  • the display panel When dimming the light source BL and simultaneously compensating for the dimming by adapting the input signal V 1 , the display panel operates at a higher transmission (or reflection) rate. Especially for LCD panels, at this higher transmission rate the viewing angle increases. This means that dimming in combination with adapting the input signal V 1 as described hereinbefore has the additional advantage of improving the viewing angle for the dimmed images. Moreover a lamp of the light source requires less power when dimmed, so power is saved when dimming is applied. At the same time the lifetime of the lamp may be extended.
  • a further advantage is, that when the amount of dimming takes into account the operating limits of the light source, it is possible to select firstly the amount of dimming which the light source is able to follow, and then to determine the corresponding adaptation of the input signal V 1 . So, any mismatch, caused by the fact that the light source is not able to follow the requested brightness changes of subsequent images, is avoided, thereby avoiding picture quality deterioration.

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PL1733372T3 (pl) 2019-11-29
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US8059082B2 (en) 2011-11-15
US20080238840A1 (en) 2008-10-02
CN1934614A (zh) 2007-03-21
TR201910283T4 (tr) 2019-08-21
EP1733372B1 (de) 2019-05-15
KR20070005637A (ko) 2007-01-10
JP4937108B2 (ja) 2012-05-23
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ES2738001T3 (es) 2020-01-17
WO2005093703A1 (en) 2005-10-06

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