WO2013019104A1 - Backlight unit device for illuminating an image - Google Patents

Backlight unit device for illuminating an image Download PDF

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Publication number
WO2013019104A1
WO2013019104A1 PCT/NL2012/050501 NL2012050501W WO2013019104A1 WO 2013019104 A1 WO2013019104 A1 WO 2013019104A1 NL 2012050501 W NL2012050501 W NL 2012050501W WO 2013019104 A1 WO2013019104 A1 WO 2013019104A1
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WO
WIPO (PCT)
Prior art keywords
light source
value
width
modulation pulse
driving signal
Prior art date
Application number
PCT/NL2012/050501
Other languages
French (fr)
Inventor
Alain Decraemer
Original Assignee
Tp Vision Holding B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tp Vision Holding B.V. filed Critical Tp Vision Holding B.V.
Publication of WO2013019104A1 publication Critical patent/WO2013019104A1/en

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Classifications

    • 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
    • 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
    • G09G2320/0261—Improving the quality of display appearance in the context of movement of objects on the screen or movement of the observer relative to the screen
    • 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
    • G09G2320/0633—Adjustment of display parameters for control of overall brightness by amplitude modulation of the brightness of the illumination 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
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/064—Adjustment of display parameters for control of overall brightness by time modulation of the brightness of the illumination 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
    • 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
    • G09G2320/0626—Adjustment of display parameters for control of overall brightness
    • G09G2320/0653—Controlling or limiting the speed of brightness adjustment of the illumination 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
    • G09G2320/00—Control of display operating conditions
    • G09G2320/10—Special adaptations of display systems for operation with variable images
    • G09G2320/103—Detection of image changes, e.g. determination of an index representative of the image change
    • 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
    • G09G2320/10—Special adaptations of display systems for operation with variable images
    • G09G2320/106—Determination of movement vectors or equivalent parameters within the image
    • 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
    • G09G2340/00—Aspects of display data processing
    • G09G2340/16—Determination of a pixel data signal depending on the signal applied in the previous frame
    • 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

Definitions

  • Backlight unit device for illuminating an image
  • the present invention relates to a method for controlling a backlight unit device, and more specifically to a method, a backlight unit device, a panel display apparatus and a computer program for illuminating an image formed in a display panel.
  • the images may be displayed using various techniques.
  • One particular technique comprises providing a backlight unit device which provides light to a display panel placed in front of the backlight unit device, which display panel may let more or less light from the backlight unit device through different regions of the display panel in order to display an image in the display panel.
  • the backlight unit may be equipped with various types of light sources, such as Incandescent light bulbs, light-emitting diodes (LEDs), electroluminescent panels (ELPs), Cold Cathode Fluorescent Lamps (CCFLs) or one or more Hot Cathode Fluorescent Lamps (HCFL).
  • the display panel may utilize various technologies, such as Liquid Crystal Display (LCD) technology.
  • WO 2009/145329 Al relates to systems and methods for generating, modifying and applying backlight array driving values.
  • the systems include a motion detector for comparing a first block of a first frame to a corresponding second block of a second frame to determine if motion occurs; a motion map manager for incrementing a motion map variable for a pixel in the second block motion occurs and decrementing the motion map variable when motion does not occur; and a screen generator for creating a backlight modulation screen for the second block, wherein the backlight modulation screen comprises at least one pulse with a pulse width that is dependent on the motion map variable.
  • the prior art devices may have poor image quality and/or high power consumption.
  • the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method for controlling a backlight unit device for illuminating an image formed in a display panel, the backlight unit device comprising a light source, being capable of emitting light in the backlight unit device, the method comprising:
  • Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image
  • the light source driving signal comprises information relating to
  • the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse.
  • 'width of a modulation pulse' is understood a period in time in which there is a non-zero, such as substantial, current passing through the light source.
  • this width may be referred to with respect to frame width, e.g., "50 % PWM", which means that a modulation pulse has a duty cycle of 50 % with respect to the frame width.
  • the light source is driven by a non-zero current during 50 % of the frame width, and in the remaining 50 % the current is substantially zero, such as zero.
  • 'frame width' is understood a period in time corresponding to a full frame of a video sequence.
  • 'backlight unit device' is understood a device which provides light from the back to a display panel which is optically connected to the backlight device.
  • 'display panel' is understood a panel for displaying visual information, such as images, such as frames in a video sequence.
  • a display panel may be embodied in the form of a Liquid Crystal Display (LCD) panel.
  • LCD Liquid Crystal Display
  • image information is understood information regarding an image, such as spatially resolved information comprising information regarding, brightness and color. It is understood that such information may be comprised within the image itself, but may also be comprised within information representing such image, such as a set of digitalized or analogue values representing color and/or brightness in a set of pixels in the image.
  • 'Illumination Value' is understood a value indicative of illumination of at least a pixel in the image. It is understood when referring to Illumination Value, that it is indicative of the required illumination.
  • 'Movement Value' is understood a change in Illumination Value with respect to time, such as with respect to a change from one frame to another, where the frames are meant to be displayed temporally displaced.
  • 'light source driving signal' is understood a signal which enables driving of the light source.
  • the light source driving signal is a signal enabling adjusting a light source current value with respect to time, such as varying the light source current value over time.
  • 'luminous intensity' is understood the actual illumination, i.e., the illumination which is actually delivered by a light source when a current flows through the light source (notice that in this context the current flow may be zero amperes in which case the luminous intensity is also zero).
  • the invention is particularly, but not exclusively, advantageous for controlling a backlight unit device while keeping the power consumption relatively low.
  • the gist of the invention may be seen as keeping the width of the modulation pulse relatively small when this is required (when there is movement) in order to optimize the visually perceived quality, such as to avoid motion blur, and maximizing a width of the modulation pulse when the visually perceived quality does not deteriorate from this (when there is little or no movement).
  • the basic insight of the invention is that while it might be necessary to keep the width of the modulation pulse small and the light source current value high when the Movement Value is high, it might also be possible to do the opposite (when the Motion Value is low, this can be done without deteriorating the visually perceived quality of the displayed image or video sequence) and this can be exploited to save energy, since the light source might need unproportionally much power to yield a given time averaged intensity when this is done over short time.
  • the light source current value must be boosted.
  • the characteristic of, e.g., the LED is not linear (see Fig. 3), the light source current value must be more than doubled.
  • Scanning is used to reduce motion blur, so when there is no or little movement transmitted it is not necessary. Unfortunately, motion is often present and then requires more power consumption than necessary.
  • the idea is to make the width of the modulation pulse of the scanning dependent on the movement detected. For example, when no movement is detected, scanning is not necessary, and PWM can be 100% (i.e., conducting time of the LEDs is equal to the corresponding frame width). When movement exceeds a predetermined threshold, it must be minimal (e.g., a PWM of 50%). In between, it can take intermediate values. In order to compensate for the reduction in time in which current flows through the light sources, current in the light sources must be adapted to compensate loss of time averaged luminous intensity. This is done by increasing the light source current value and thus increase the driving current.
  • a scanning system with good energy efficiency such as optimal energy efficiency. It can be associated with 2D (e.g., direct LED), ID and 0D (e.g., side LED) dimming.
  • 2D e.g., direct LED
  • ID and 0D e.g., side LED
  • the modulation width and light source current value are adapted to the image information, the quality of the displayed image is high, which may be seen as a possible advantage. Furthermore, since the modulation width and light source current value are adapted in order to not have higher light source current value than needed, the power consumption can be kept low, which may also be seen as a possible advantage. Still further, since the method is relatively simple, and can be implemented with correspondingly simply means, the cost may be kept low, which may also be seen as a possible advantage. It may be possible to implement embodiments and/or aspects of the invention in existing backlight unit devices, since the necessary hardware may already be present, and the invention may thus be implemented via a change of software and/or loading of software.
  • the durability may be relatively high, which may also be seen as a possible advantage.
  • the light source in embodiments of the invention may degrade to a smaller extent or at a slower rate than in comparable prior art devices, since in embodiments of the present invention, less energy is dissipated in the light source, and hence less heat is generated, and there is hence less degradation of the light source and/or surrounding components.
  • the backlight unit device comprising a plurality of light sources with spatially distributed individual light sources, and the Illumination Value and/or the Movement Value are spatially resolved, and wherein the step of
  • generating the light source driving signal comprises generating a spatially resolved light source driving signal, the spatially resolved driving signal being determined according to the Illumination Value and the Movement Value and the spatial distribution of the individual light sources,
  • driving the light source according to the light source driving signal further comprises driving individual light sources in the plurality of light sources according to the spatially resolved light source driving signal.
  • spatially distributed is understood that at least two light sources are placed in spatially different positions such as to enable that each of the light sources provide backlight to spatially non-identical regions on the display device.
  • An advantage of having spatially distributed light sources may be, that it enables more specific control of the backlight illumination, for example, if a region in the image which corresponds spatially to a first light source is relatively bright (corresponding to a large Illumination Value) while another region which corresponds to a second light source is relatively dark (corresponding to a small Illumination Value), the light source current value for the second light source can be kept relatively low which may be advantageous both in terms of quality of the displayed image and in terms of energy consumption.
  • the step of generating the light source driving signal comprises
  • a look-up-table which look-up-table connects values of the Movement Value and the Illumination Value with the width of the modulation pulse and the light source current value.
  • Accessing a look-up-table may be advantageous in that it may enable predetermining of appropriate width of the modulation pulse according to the Movement Value and appropriate light source current value according to both of the Illumination Value and the width of the modulation pulse. Thus, during operation, less processing power is required in order to identify appropriate width of the modulation pulse and light source current value which may translate into faster and/or more energy efficient operation.
  • Movement Value may be spatially resolved, such as being a matrix with Movement Values inserted in different entries corresponding to different spatially resolved light sources in the backlight unit device.
  • the width of the modulation pulse can be described as a substantially continuous function, such as a continuous function, of the Movement Value.
  • the width of the modulation pulse may for all Movement Values be set at an optimal value.
  • the width of the modulation pulse can be described as a step-function of the Movement Value. This may provide a simple embodiment, since relatively few possible values of the width of the modulation pulse may be given.
  • a width of a modulation pulse and an light source current value associated with a previous frame of the video sequence and/or a width of a modulation pulse and an light source current value associated with a subsequent frame of the video sequence.
  • time averaged luminous intensity may be relatively high or relatively low across certain time spans, such as when the Movement Value changes, it may be advantageous.
  • a temporal position of the modulation pulse (114) is adjusted relative to the frame of the video sequence. This may provide an alternative means for adjusting the time averaged luminous intensity.
  • the width of the modulation pulse is monotonically decreasing (or put in an alternative formulation: monotonically non-increasing) with increasing motion value for fixed Illumination Value.
  • the width of the modulation pulse does not increase, but it may decrease, be constant. It may also decrease in steps with increasing Motion Value. This may be advantageous in order to ensure that the displayed image quality and energy consumption are both optimized.
  • the light source current value is monotonically increasing (or put in an alternative formulation: monotonically non-decreasing) with decreasing width of the modulation pulse for fixed Illumination Value.
  • this may be expressed as lLSCv(tpWM,l) ⁇ ILSCV (tpWM, 2 ), tpWM,l ⁇ tpWM, 2
  • the light source current value does not increase, but it may decrease, be constant, and it may decrease in steps with increasing Motion Value.
  • the light source current value is non- constant corresponding to
  • This may be advantageous in order to ensure that the displayed image quality and energy consumption are both optimized.
  • the light source current value may be given as a function of the width (tpwivi) of the modulation pulse and the Illumination Value (IV) according to the formula
  • tf ra me is the frame width and IRLOIV is to be understood as the current which must be applied to the light source in order to make the Luminous Intensity equal the Illumination value (as can, e.g., be read off from Fig. 3).
  • a backlight unit device for illuminating an image formed in a display panel, the backlight unit device comprising
  • a light source being capable of emitting light in the backlight unit device, a backlight driving circuitry adapted for
  • the light source driving signal comprises information relating to
  • the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse.
  • This aspect of the invention is particularly, but not exclusively, advantageous in that the method according to the present invention may be implemented by adapting a backlight unit device to carry to carry out the method according to the first aspect.
  • a possible advantage may be that a backlight unit device is provided which enables relatively low power consumption while keeping the displayed image quality in an associated display panel equally good.
  • the reduction in energy consumption for the backlight unit device may amount to 25-30 %, such as more than 30 % (for still pictures).
  • a backlight unit device wherein the light source is a light source which has a relation between input current and luminous intensity which is non-linear, such as the luminous intensity being monotonically increasing with input current, such as the second derivative of luminous intensity with respect to input current is negative at least within a limited range of the input current scale, such as throughout the range of applicable input currents, such as the shape of the relation entail that in order to increase the luminous intensity by increasing the input current, an unproportionally large (relative) increase in input current will have to be applied as compared to the achieved (relative) increase in luminous intensity.
  • a backlight unit device wherein the light source is chosen from the group comprising: a light emitting diode, an incandescent lamp.
  • a display panel apparatus comprising a display panel and the backlight unit device according to the second aspect of the invention.
  • the display panel apparatus is chosen within the group of: A television set, a display panel apparatus for a computer, such as a monitor, a projector.
  • a computer program product being adapted to enable a computer system comprising at least one computer having data storage means associated therewith to operate a processor arranged for receiving image information corresponding to
  • Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image
  • the light source driving signal comprises information relating to
  • the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse.
  • the first, second, third and fourth aspect of the present invention may each be combined with any of the other aspects.
  • Fig. 1 shows a method according to an embodiment of the invention
  • Fig. 2 shows a backlight unit device for illuminating an image formed in a display panel
  • Fig. 3 is a graph showing a correspondence between the relative luminous intensity of the light source and an input current
  • Fig. 4 is a detailed schematic of a specific display panel apparatus according to an embodiment of the invention.
  • Fig. 5 shows a schematic of a look-up-table
  • Fig. 6 shows examples of a light source driving signal
  • Fig. 7 shows further examples of the light source driving signal.
  • Fig. 1 shows a method 100 according to an embodiment of the invention, which method is for controlling a backlight unit device 220 (see Fig. 2) for illuminating an image formed in a display panel 456 (see Fig. 4), the backlight unit device comprising a light source 222 (see Fig. 2), being capable of emitting light in the backlight unit device, the method comprising:
  • Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image
  • generating 110 a light source driving signal 112 for controlling the light source, wherein the light source driving signal comprises information relating to - a width 114 of a modulation pulse, and
  • the width of the modulation pulse is determined according to the Movement Value 108 and the light source current value are determined according to both of the Illumination Value 106 and the width of the modulation pulse.
  • Fig. 2 shows a backlight unit device 220 for illuminating an image formed in a display panel 456, the backlight unit device comprising
  • a light source 222 being capable of emitting light in the backlight unit device, a backlight driving circuitry 224 adapted for
  • the light source driving signal comprises information relating to
  • the width of the modulation pulse is determined according to the Movement Value 108 and the light source current value are determined according to both of the Illumination Value 106 and the width of the modulation pulse.
  • Fig. 3 is a graph showing a correspondence 328 between the relative luminous intensity (RLI) of the light source, which in the present figure is a Light Emitting Diode (LED), and an input current (I) which is given in milliampere (mA).
  • the term 'input current' is used interchangeably with 'light source driving current' .
  • the RLI is given in arbitrary (arb.) units normalized at 20 mA. It can be seen from the graph that the dependence between input current and RLT is non-linear, the RLT is monotonically increasing and that the second derivative of RLT with respect to input current is negative throughout the range of the curve. In consequence, in order to increase the RLT by increasing the input current, an
  • Fig. 4 is a detailed schematic of a specific display panel apparatus according to an embodiment of the invention (which also corresponds to a simplified schematic of a modern LCD TV set), which features a signal processing unit 430 which receives information 432 comprising a video sequence, the signal processing unit demodulates, decodes and processes the information 432 and converts it into a Low- Voltage Differential Signalling (LVDS) signal 434 which is a 50 Hz signal.
  • the LVDS signal 434 is received by a Frame Rate Converter 436.
  • the Frame Rate Converter 436 converts the 50 Hz LVDS signal 434 into a 200 Hz signal 438. By increasing the frequency to 200 Hz, motion blur can be reduced (partially).
  • This particular Frame Rate Converter generates a Movement Value for each frame in the 50 Hz LVDS signal 434, which may be used in order to interpolate the intermediate frames. It is however also contemplated that Movement Values can be generated for each frame in the 200 Hz signal 438.
  • the Frame Rate Converter sends image information 104 to a processing unit 444 via a Serial Peripheral Interface (SPI) bus.
  • the image information 104 comprises an Illumination Value 106 and the Movement Value 108.
  • the Frame Rate Converter also sends corresponding video information 438 to an LCD controller 448 via a V by One bus.
  • the V-by-one is an open standard. It is cost effective because it uses a high speed (3 Ghz) serial bus with a limited number of differential pairs so limited connections.
  • the FRC can be a Trident 94x9S which can output according to the V-by-one standard.
  • the processor receives image information 104 and generates in response driving information 450 corresponding to a light source driving signal (112).
  • the display panel apparatus comprises a plurality of light sources 223, which comprises light sources 222 which are spatially distributed within a backlight panel 454 which lie in a plane being substantially parallel with a plane of a display panel 456, which may be an Liquid Crystal Display (LCD) panel.
  • LCD Liquid Crystal Display
  • the light sources 222 in the present embodiment are Light Emitting Diodes (LEDs).
  • the driving information 450 is received by an LED driver 452 which converts the driving information 450 into the light source driving signal 112 which is sent to the backlight panel 454 in order to control the plurality of light sources 223 in the backlight panel 454.
  • the processor 444 is arranged to generate the light source driving signal 112 which comprises information regarding a width 114 of a modulation pulse and a light source current value 116, based upon the Illumination Value 106 and the Movement Value 108. In the present example, this is done by consulting a look-up-table 448 via an appropriate communications channel 446.
  • the processor may in an exemplary embodiment be a Field Programmable Gate Array (FPGA) and the look-up-table may be comprised within the FPGA.
  • FPGA Field Programmable Gate Array
  • the Illumination Values and the movement vector may be spatially resolved, so as to correspond to different parts of the image.
  • the light source driving signal 112 may be spatially resolved. For example, if light sources 222 are distributed in the backlight panel 454 as indicated in Fig. 4, the Illumination Value and/or the Movement Value may be spatially resolved in order to correspond to a region corresponding to each individual light source.
  • the Illumination Value and/or the Movement Value may be spatially resolved in order to correspond to a resolution of the image, and the processor takes this into account when generating the light source driving signal which can be spatially resolved so as to correspond to the distribution of the light sources.
  • the backlight system is any one of 0D (overall, e.g., side LEDs), ID (line, e.g., individual LED strings) or 2D (two-dimensional resolution).
  • the FPGA will deliver 2 data:
  • Frame Rate Converter 436 (e.g. through the SPI bus), the width of the modulation pulse and the non-linearity coefficient of the specific LED characteristic (such as from Fig. 3).
  • Fig. 5 shows a schematic of a look-up-table 448.
  • the width 112 of the modulation pulse, and the light source current value 114 comprised within the light source driving signal 112 may be given in the look-up-table, which may be a table with entrances given by the Illumination Value 106 and Movement Value 108 comprised within the image information 104.
  • the (required) illumination is given as an Illumination Value IV is given in the top row, while the Movement Value MV is given in the leftmost column.
  • the look-up-table may be stored in a database, such as being accessible to the processor 444. If an FPGA is applied, it may be stored within the FPGA itself.
  • the width of the modulation pulse is maximum, corresponding to, e.g., 100 % of a frame width (Pulse Width Modulation (PWM) is 100%), and the (light source current, corresponding to current in the LEDs) is derived from Fig. 3; for example, an Illumination Value of 0.5 corresponds to a current of 8 mA and an illumination of 1 to a current of 20mA.
  • PWM Pulse Width Modulation
  • PWM Pulse Width Modulation
  • the width of the modulation pulse (PWM) is a linear function of Movement Value.
  • An advantage of having the width of the width of the modulation pulse (PWM) being a continuous function, such as a linear function, of Movement Value may be that it is energy efficient, as it may be optimized so that the light source 222 is often, such as always, driven in a manner where perceived visual quality is not compromised while the energy consumption is kept relatively low.
  • Fig. 6 shows examples of a light source driving signal 112 which span 5 frames of a video sequence.
  • the horizontal axis corresponds to time t and the vertical axis corresponds to light source current value I.
  • the light source current value 672a is relatively low.
  • the last three modulation pulses 663-665 the situation is the opposite, they correspond to frames where the
  • the width 674b of the modulation pulse is small and in this example 50 % of the frame width 660. Furthermore, the light source current value 674a is relatively high (in the present example, the Illumination Values corresponding to all frames are substantially equal).
  • the width of these modulation pulses is large and in this example 100 % of the frame width 660. Furthermore, the light source current value is relatively low (in the present example, the Illumination Values corresponding to all frames are substantially equal).
  • the visually perceived illumination may shortly drop, since in a region 668 the time averaged
  • Relative Luminous Intensity may be relatively small ("perceived illumination dip").
  • the visually perceived illumination may shortly increase, since in a region 688 the time averaged Relative Luminous Intensity may be relatively high ("perceived illumination flash").
  • Fig. 7 shows further examples of the light source driving signal, which may be advantageous for overcoming the perceived illumination dip/flash outlined in connection with Fig. 6.
  • the situation in Fig. 7 is very similar to Fig. 6 so only the differences will be described.
  • a transition modulation pulse 763 has been inserted between the frame with corresponding low Movement Value and the frame with a corresponding high Movement Value.
  • the transition pulse 763 has a different width 773b and light source current value 773a, compared to a normal modulation pulse 766, so that the time averaged Relative Luminous Intensity may be relatively constant.
  • An advantage may be that the observer does not perceive abrupt changes in illumination during in the region 768.
  • a transition modulation pulse 783 has been inserted between the frame with corresponding high Movement Value and the frame with a corresponding low Movement Value.
  • the transition pulse 783 has a different width 793b and light source current value 793a, compared to a normal modulation pulse 786, so that the time averaged Relative Luminous Intensity may be relatively constant.
  • An advantage may be that the observer does not perceive abrupt changes in illumination during in the region 788.
  • both the width (773b, 793b) of the transition modulation pulse and the light source current value (773a, 793a) may depend on the width (672b) of a modulation pulse and an light source current value (672a) associated with a previous frame of the video sequence, and/or the width of a modulation pulse (674b) and light source current value (674a) associated with a subsequent frame of the video sequence.
  • the temporal position of the transition modulation pulse may be adjusted. It may also be possible to have a plurality of transition modulation pulses, such as in a sequence.
  • the present invention relates to a method for controlling a backlight unit device, wherein one or more light sources in the backlight unit device are driven with a current, where the current may vary over time so as to form pulses, and wherein the width of the pulses are adjusted according to the motion content, such as to avoid motion blur, while the height (such as the light source current value) is adjusted so that the luminous intensity of the light sources is not affected by the varying width of the modulation pulses. Since modulation pulses with small widths necessitate an unproportionally large current flow, and hence large energy consumption, the method enables minimum energy consumption while the image quality is not compromised.

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Abstract

The present invention relates to a method for controlling a backlight unit device, wherein one or more light sources in the backlight unit device are driven with a current, where the current may vary over time so as to form pulses, and wherein the width of the pulses are adjusted according to the motion content, such as to avoid motion blur, while the height (such as the light source current value) is adjusted so that the luminous intensity of the light sources is not affected by the varying width of the modulation pulses. Since modulation pulses with small widths necessitate an unproportionally large current flow, and hence large energy consumption, the method enables minimum energy consumption while the image quality is not compromised.

Description

Backlight unit device for illuminating an image
FIELD OF THE INVENTION
The present invention relates to a method for controlling a backlight unit device, and more specifically to a method, a backlight unit device, a panel display apparatus and a computer program for illuminating an image formed in a display panel.
BACKGROUND OF THE INVENTION
In modern television sets the images may be displayed using various techniques.
One particular technique comprises providing a backlight unit device which provides light to a display panel placed in front of the backlight unit device, which display panel may let more or less light from the backlight unit device through different regions of the display panel in order to display an image in the display panel. The backlight unit may be equipped with various types of light sources, such as Incandescent light bulbs, light-emitting diodes (LEDs), electroluminescent panels (ELPs), Cold Cathode Fluorescent Lamps (CCFLs) or one or more Hot Cathode Fluorescent Lamps (HCFL). The display panel may utilize various technologies, such as Liquid Crystal Display (LCD) technology.
WO 2009/145329 Al relates to systems and methods for generating, modifying and applying backlight array driving values. The systems include a motion detector for comparing a first block of a first frame to a corresponding second block of a second frame to determine if motion occurs; a motion map manager for incrementing a motion map variable for a pixel in the second block motion occurs and decrementing the motion map variable when motion does not occur; and a screen generator for creating a backlight modulation screen for the second block, wherein the backlight modulation screen comprises at least one pulse with a pulse width that is dependent on the motion map variable.
The prior art devices may have poor image quality and/or high power consumption.
Hence, it would be advantageous to provide a method, a backlight unit device, a panel display apparatus and/or a computer program for illuminating an image formed in a display panel which yields high quality, durability, low cost and/or energy efficiency. SUMMARY OF THE INVENTION
It is a further object of the present invention to provide an alternative to the prior art.
In particular, it may be seen as an object of the present invention to provide a method, a backlight unit device, a panel display apparatus and/or a computer program that solves the above mentioned problems of the prior art with
Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a method for controlling a backlight unit device for illuminating an image formed in a display panel, the backlight unit device comprising a light source, being capable of emitting light in the backlight unit device, the method comprising:
receiving image information corresponding to
- an Illumination Value, and
- a Movement Value
where the Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image,
generating a light source driving signal for controlling the light source, wherein the light source driving signal comprises information relating to
- a width of a modulation pulse, and
- a light source current value,
controlling the light source according to the light source driving signal, wherein the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse.
By 'width of a modulation pulse' is understood a period in time in which there is a non-zero, such as substantial, current passing through the light source. In this application, this width may be referred to with respect to frame width, e.g., "50 % PWM", which means that a modulation pulse has a duty cycle of 50 % with respect to the frame width. In other words, the light source is driven by a non-zero current during 50 % of the frame width, and in the remaining 50 % the current is substantially zero, such as zero.
By 'frame width' is understood a period in time corresponding to a full frame of a video sequence. By 'backlight unit device' is understood a device which provides light from the back to a display panel which is optically connected to the backlight device.
By 'display panel' is understood a panel for displaying visual information, such as images, such as frames in a video sequence. A display panel may be embodied in the form of a Liquid Crystal Display (LCD) panel.
By 'image information' is understood information regarding an image, such as spatially resolved information comprising information regarding, brightness and color. It is understood that such information may be comprised within the image itself, but may also be comprised within information representing such image, such as a set of digitalized or analogue values representing color and/or brightness in a set of pixels in the image.
By 'Illumination Value' is understood a value indicative of illumination of at least a pixel in the image. It is understood when referring to Illumination Value, that it is indicative of the required illumination.
By 'Movement Value' is understood a change in Illumination Value with respect to time, such as with respect to a change from one frame to another, where the frames are meant to be displayed temporally displaced.
By 'light source driving signal' is understood a signal which enables driving of the light source. In a particular embodiment, the light source driving signal is a signal enabling adjusting a light source current value with respect to time, such as varying the light source current value over time.
By 'a light source current value' is understood the current which flows through the light source.
By 'luminous intensity' is understood the actual illumination, i.e., the illumination which is actually delivered by a light source when a current flows through the light source (notice that in this context the current flow may be zero amperes in which case the luminous intensity is also zero).
The invention is particularly, but not exclusively, advantageous for controlling a backlight unit device while keeping the power consumption relatively low. The gist of the invention may be seen as keeping the width of the modulation pulse relatively small when this is required (when there is movement) in order to optimize the visually perceived quality, such as to avoid motion blur, and maximizing a width of the modulation pulse when the visually perceived quality does not deteriorate from this (when there is little or no movement). The basic insight of the invention, is that while it might be necessary to keep the width of the modulation pulse small and the light source current value high when the Movement Value is high, it might also be possible to do the opposite (when the Motion Value is low, this can be done without deteriorating the visually perceived quality of the displayed image or video sequence) and this can be exploited to save energy, since the light source might need unproportionally much power to yield a given time averaged intensity when this is done over short time.
In modern LCD TV sets, there are now 2D and scanning possibilities. For good scanning performances, a 50% PWM is required. To maintain the same luminous intensity on the backlight although the light sources, such as LEDs, are conducting only half of the time, the light source current value must be boosted. As the characteristic of, e.g., the LED, is not linear (see Fig. 3), the light source current value must be more than doubled.
Scanning is used to reduce motion blur, so when there is no or little movement transmitted it is not necessary. Unfortunately, motion is often present and then requires more power consumption than necessary.
The idea is to make the width of the modulation pulse of the scanning dependent on the movement detected. For example, when no movement is detected, scanning is not necessary, and PWM can be 100% (i.e., conducting time of the LEDs is equal to the corresponding frame width). When movement exceeds a predetermined threshold, it must be minimal (e.g., a PWM of 50%). In between, it can take intermediate values. In order to compensate for the reduction in time in which current flows through the light sources, current in the light sources must be adapted to compensate loss of time averaged luminous intensity. This is done by increasing the light source current value and thus increase the driving current.
In this way, a scanning system with good energy efficiency, such as optimal energy efficiency. It can be associated with 2D (e.g., direct LED), ID and 0D (e.g., side LED) dimming.
Thus, since the modulation width and light source current value are adapted to the image information, the quality of the displayed image is high, which may be seen as a possible advantage. Furthermore, since the modulation width and light source current value are adapted in order to not have higher light source current value than needed, the power consumption can be kept low, which may also be seen as a possible advantage. Still further, since the method is relatively simple, and can be implemented with correspondingly simply means, the cost may be kept low, which may also be seen as a possible advantage. It may be possible to implement embodiments and/or aspects of the invention in existing backlight unit devices, since the necessary hardware may already be present, and the invention may thus be implemented via a change of software and/or loading of software. Still further, since the current flow through the light sources is not higher than needed, the durability may be relatively high, which may also be seen as a possible advantage. The light source in embodiments of the invention may degrade to a smaller extent or at a slower rate than in comparable prior art devices, since in embodiments of the present invention, less energy is dissipated in the light source, and hence less heat is generated, and there is hence less degradation of the light source and/or surrounding components.
According to an embodiment of the invention, there is provided a method, wherein the backlight unit device comprising a plurality of light sources with spatially distributed individual light sources, and the Illumination Value and/or the Movement Value are spatially resolved, and wherein the step of
generating the light source driving signal comprises generating a spatially resolved light source driving signal, the spatially resolved driving signal being determined according to the Illumination Value and the Movement Value and the spatial distribution of the individual light sources,
and wherein the step of
driving the light source according to the light source driving signal, further comprises driving individual light sources in the plurality of light sources according to the spatially resolved light source driving signal.
By 'spatially distributed' is understood that at least two light sources are placed in spatially different positions such as to enable that each of the light sources provide backlight to spatially non-identical regions on the display device. An advantage of having spatially distributed light sources may be, that it enables more specific control of the backlight illumination, for example, if a region in the image which corresponds spatially to a first light source is relatively bright (corresponding to a large Illumination Value) while another region which corresponds to a second light source is relatively dark (corresponding to a small Illumination Value), the light source current value for the second light source can be kept relatively low which may be advantageous both in terms of quality of the displayed image and in terms of energy consumption.
According to another embodiment of the invention, there is provided a method, wherein the step of generating the light source driving signal comprises
accessing a look-up-table, which look-up-table connects values of the Movement Value and the Illumination Value with the width of the modulation pulse and the light source current value. Accessing a look-up-table may be advantageous in that it may enable predetermining of appropriate width of the modulation pulse according to the Movement Value and appropriate light source current value according to both of the Illumination Value and the width of the modulation pulse. Thus, during operation, less processing power is required in order to identify appropriate width of the modulation pulse and light source current value which may translate into faster and/or more energy efficient operation.
According to another embodiment of the invention, there is provided a method, wherein the method further comprising
receiving the video sequence,
performing a comparison between a first characteristic of the frame of the video sequence and a second characteristic of a previous frame of the video sequence,
determining the Movement Value according to a difference between the first characteristic and the second characteristic.
It is understood, that the Movement Value may be spatially resolved, such as being a matrix with Movement Values inserted in different entries corresponding to different spatially resolved light sources in the backlight unit device.
According to another embodiment of the invention, there is provided a method, wherein the width of the modulation pulse can be described as a substantially continuous function, such as a continuous function, of the Movement Value.
This may be advantageous for enabling energy efficient operation of the backlight unit device, since the width of the modulation pulse may for all Movement Values be set at an optimal value. In an alternative embodiment, the width of the modulation pulse can be described as a step-function of the Movement Value. This may provide a simple embodiment, since relatively few possible values of the width of the modulation pulse may be given.
According to another embodiment of the invention, there is provided a method, wherein the width of the modulation pulse depends substantially linearly on the Movement Value. This may be a simple yet effective embodiment.
According to another embodiment of the invention, there is provided a method, wherein the width of the modulation pulse and the light source current value furthermore depend on
a width of a modulation pulse and an light source current value associated with a previous frame of the video sequence, and/or a width of a modulation pulse and an light source current value associated with a subsequent frame of the video sequence.
This may be advantageous, since the time averaged luminous intensity may be relatively high or relatively low across certain time spans, such as when the Movement Value changes, it may be advantageous.
According to another embodiment of the invention there is provided a method, wherein a temporal position of the modulation pulse (114) is adjusted relative to the frame of the video sequence. This may provide an alternative means for adjusting the time averaged luminous intensity.
According to another embodiment of the invention, there is provided a method, wherein the width of the modulation pulse is monotonically decreasing (or put in an alternative formulation: monotonically non-increasing) with increasing motion value for fixed Illumination Value. Mathematically this may be expressed as
tpwM(MVi) < tpwM(MV2), MVi > MV2
Thus, if the Motion Value increases, the width of the modulation pulse does not increase, but it may decrease, be constant. It may also decrease in steps with increasing Motion Value. This may be advantageous in order to ensure that the displayed image quality and energy consumption are both optimized.
According to another embodiment of the invention, there is provided a method, wherein the light source current value is monotonically increasing (or put in an alternative formulation: monotonically non-decreasing) with decreasing width of the modulation pulse for fixed Illumination Value. Mathematically this may be expressed as lLSCv(tpWM,l)≥ ILSCV (tpWM,2), tpWM,l < tpWM,2
Thus, if the width of the modulation pulse increases, the light source current value does not increase, but it may decrease, be constant, and it may decrease in steps with increasing Motion Value. In a particular embodiment, the light source current value is non- constant corresponding to
lLSCv(tpWM,l) > ILSCV (tpWM,2), tpWM,l < tpWM,2
This may be advantageous in order to ensure that the displayed image quality and energy consumption are both optimized.
According to another embodiment of the invention, there is provided a method, wherein the light source current value scales with a product of
a first factor which is inversely proportional with the width of the modulation pulse, and a second factor which is derived from a correspondence between the intensity of the light source and an input current.
In an exemplary embodiment, the light source current value (ILSCV) may be given as a function of the width (tpwivi) of the modulation pulse and the Illumination Value (IV) according to the formula
ILSCV (IV , tpwM)= tframe tpwM * ILI=IV
Where tframe is the frame width and IRLOIV is to be understood as the current which must be applied to the light source in order to make the Luminous Intensity equal the Illumination value (as can, e.g., be read off from Fig. 3).
According to a second aspect of the invention, there is provided a backlight unit device for illuminating an image formed in a display panel, the backlight unit device comprising
a light source being capable of emitting light in the backlight unit device, a backlight driving circuitry adapted for
- receiving image information corresponding to
- an Illumination Value, and
- a Movement Value
associated with a frame of a video sequence corresponding to the image,
- generating an light source driving signal for controlling the light source, wherein the light source driving signal comprises information relating to
- a width of a modulation pulse, and
- an light source current value, and
- driving the light source according to the light source driving signal, wherein the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse.
This aspect of the invention is particularly, but not exclusively, advantageous in that the method according to the present invention may be implemented by adapting a backlight unit device to carry to carry out the method according to the first aspect. A possible advantage may be that a backlight unit device is provided which enables relatively low power consumption while keeping the displayed image quality in an associated display panel equally good. The reduction in energy consumption for the backlight unit device may amount to 25-30 %, such as more than 30 % (for still pictures). According to another embodiment of the invention, there is provided a backlight unit device wherein the light source is a light source which has a relation between input current and luminous intensity which is non-linear, such as the luminous intensity being monotonically increasing with input current, such as the second derivative of luminous intensity with respect to input current is negative at least within a limited range of the input current scale, such as throughout the range of applicable input currents, such as the shape of the relation entail that in order to increase the luminous intensity by increasing the input current, an unproportionally large (relative) increase in input current will have to be applied as compared to the achieved (relative) increase in luminous intensity.
According to another embodiment of the invention, there is provided a backlight unit device wherein the light source is chosen from the group comprising: a light emitting diode, an incandescent lamp.
According to a third aspect of the invention, there is provided provided a display panel apparatus comprising a display panel and the backlight unit device according to the second aspect of the invention. In particular embodiments, the display panel apparatus is chosen within the group of: A television set, a display panel apparatus for a computer, such as a monitor, a projector.
According to a fourth aspect of the invention, there is provided a computer program product being adapted to enable a computer system comprising at least one computer having data storage means associated therewith to operate a processor arranged for receiving image information corresponding to
- an Illumination Value, and
- a Movement Value
where the Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image,
generating driving information corresponding to a light source driving signal for controlling the light source, wherein the light source driving signal comprises information relating to
- a width of a modulation pulse, and
- a light source current value,
the width of the modulation pulse is determined according to the Movement Value and the light source current value are determined according to both of the Illumination Value and the width of the modulation pulse. The first, second, third and fourth aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE FIGURES
The method, backlight unit device, panel display apparatus and computer program for illuminating an image formed in a display panel according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
Fig. 1 shows a method according to an embodiment of the invention,
Fig. 2 shows a backlight unit device for illuminating an image formed in a display panel,
Fig. 3 is a graph showing a correspondence between the relative luminous intensity of the light source and an input current,
Fig. 4 is a detailed schematic of a specific display panel apparatus according to an embodiment of the invention,
Fig. 5 shows a schematic of a look-up-table,
Fig. 6 shows examples of a light source driving signal,
Fig. 7 shows further examples of the light source driving signal.
DETAILED DESCRIPTION OF AN EMBODIMENT
Fig. 1 shows a method 100 according to an embodiment of the invention, which method is for controlling a backlight unit device 220 (see Fig. 2) for illuminating an image formed in a display panel 456 (see Fig. 4), the backlight unit device comprising a light source 222 (see Fig. 2), being capable of emitting light in the backlight unit device, the method comprising:
receiving 102 image information 104 corresponding to
- an Illumination Value 106, and
- a Movement Value 108
where the Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image,
generating 110 a light source driving signal 112 for controlling the light source, wherein the light source driving signal comprises information relating to - a width 114 of a modulation pulse, and
- a light source current value 116,
controlling 118 the light source 222 according to the light source driving signal 112,
the width of the modulation pulse is determined according to the Movement Value 108 and the light source current value are determined according to both of the Illumination Value 106 and the width of the modulation pulse.
Fig. 2 shows a backlight unit device 220 for illuminating an image formed in a display panel 456, the backlight unit device comprising
- a light source 222 being capable of emitting light in the backlight unit device, a backlight driving circuitry 224 adapted for
- receiving image information 104 corresponding to
- an Illumination Value 106, and
- a Movement Value 108
associated with a frame of a video sequence corresponding to the image,
- generating an light source driving signal 104 for controlling the light source 222, wherein the light source driving signal comprises information relating to
- a width 112 of a modulation pulse, and
- an light source current value 114, and
- driving the light source according to the light source driving signal, the width of the modulation pulse is determined according to the Movement Value 108 and the light source current value are determined according to both of the Illumination Value 106 and the width of the modulation pulse.
Fig. 3 is a graph showing a correspondence 328 between the relative luminous intensity (RLI) of the light source, which in the present figure is a Light Emitting Diode (LED), and an input current (I) which is given in milliampere (mA). The term 'input current' is used interchangeably with 'light source driving current' . The RLI is given in arbitrary (arb.) units normalized at 20 mA. It can be seen from the graph that the dependence between input current and RLT is non-linear, the RLT is monotonically increasing and that the second derivative of RLT with respect to input current is negative throughout the range of the curve. In consequence, in order to increase the RLT by increasing the input current, an
unproportionally large increase in input current will have to be applied. For example, in order to double the RLT from 1 to 2 arbitrary units, the current will have to be increased from 20 mA to 55 mA, i.e., more than a doubling of input current. In this example, if nominal current in the LED is 20 mA for nominal illumination, the same illumination with 50% PWM will be reached with a current of 55 mA which is more than the double. The result is a loss of efficiency of 37.5 % (given by (55 mA/2 - 20 mA)/20 mA). Power consumption increases, and temperature increases as more energy is dissipated as heat).
Fig. 4 is a detailed schematic of a specific display panel apparatus according to an embodiment of the invention (which also corresponds to a simplified schematic of a modern LCD TV set), which features a signal processing unit 430 which receives information 432 comprising a video sequence, the signal processing unit demodulates, decodes and processes the information 432 and converts it into a Low- Voltage Differential Signalling (LVDS) signal 434 which is a 50 Hz signal. The LVDS signal 434 is received by a Frame Rate Converter 436. The Frame Rate Converter 436 converts the 50 Hz LVDS signal 434 into a 200 Hz signal 438. By increasing the frequency to 200 Hz, motion blur can be reduced (partially). This particular Frame Rate Converter generates a Movement Value for each frame in the 50 Hz LVDS signal 434, which may be used in order to interpolate the intermediate frames. It is however also contemplated that Movement Values can be generated for each frame in the 200 Hz signal 438. The Frame Rate Converter sends image information 104 to a processing unit 444 via a Serial Peripheral Interface (SPI) bus. The image information 104 comprises an Illumination Value 106 and the Movement Value 108. The Frame Rate Converter also sends corresponding video information 438 to an LCD controller 448 via a V by One bus. The V-by-one is an open standard. It is cost effective because it uses a high speed (3 Ghz) serial bus with a limited number of differential pairs so limited connections. It is meant for video signals also at full HD at 200 Hz. It has been developed by the company "THine electronics" and is used in several consumer integrated circuits. In a specific embodiment of the present invention the FRC can be a Trident 94x9S which can output according to the V-by-one standard. The processor receives image information 104 and generates in response driving information 450 corresponding to a light source driving signal (112). In the present example, the display panel apparatus comprises a plurality of light sources 223, which comprises light sources 222 which are spatially distributed within a backlight panel 454 which lie in a plane being substantially parallel with a plane of a display panel 456, which may be an Liquid Crystal Display (LCD) panel. The light sources 222 in the present embodiment are Light Emitting Diodes (LEDs). The driving information 450 is received by an LED driver 452 which converts the driving information 450 into the light source driving signal 112 which is sent to the backlight panel 454 in order to control the plurality of light sources 223 in the backlight panel 454. The processor 444 is arranged to generate the light source driving signal 112 which comprises information regarding a width 114 of a modulation pulse and a light source current value 116, based upon the Illumination Value 106 and the Movement Value 108. In the present example, this is done by consulting a look-up-table 448 via an appropriate communications channel 446. The processor may in an exemplary embodiment be a Field Programmable Gate Array (FPGA) and the look-up-table may be comprised within the FPGA. In order to take advantage of the plurality of light sources 223 the Illumination Values and the movement vector may be spatially resolved, so as to correspond to different parts of the image. Correspondingly, the light source driving signal 112 may be spatially resolved. For example, if light sources 222 are distributed in the backlight panel 454 as indicated in Fig. 4, the Illumination Value and/or the Movement Value may be spatially resolved in order to correspond to a region corresponding to each individual light source. Alternatively, the Illumination Value and/or the Movement Value may be spatially resolved in order to correspond to a resolution of the image, and the processor takes this into account when generating the light source driving signal which can be spatially resolved so as to correspond to the distribution of the light sources. It is encompassed by the invention that the backlight system is any one of 0D (overall, e.g., side LEDs), ID (line, e.g., individual LED strings) or 2D (two-dimensional resolution).
So in the present embodiment the FPGA will deliver 2 data:
1. a width of a modulation pulse (PWM value) depending on the movement vector,
2. a light source current value depending on: illumination value based on the
Frame Rate Converter 436 (e.g. through the SPI bus), the width of the modulation pulse and the non-linearity coefficient of the specific LED characteristic (such as from Fig. 3).
Fig. 5 shows a schematic of a look-up-table 448. The width 112 of the modulation pulse, and the light source current value 114 comprised within the light source driving signal 112 may be given in the look-up-table, which may be a table with entrances given by the Illumination Value 106 and Movement Value 108 comprised within the image information 104. In the example depicted in Fig. 5 the (required) illumination is given as an Illumination Value IV is given in the top row, while the Movement Value MV is given in the leftmost column. I.e., on vertical axis, the movement value is represented (from 0=no movement to l=maximum movement), and on the horizontal axis, the (required) Illumination Value is represented (from 0=no illumination to l=normalized illumination responding to 20 raA light source current as shown in the example of Fig. 3). The look-up-table may be stored in a database, such as being accessible to the processor 444. If an FPGA is applied, it may be stored within the FPGA itself.
In the table for each set of Movement Value/Illumination Value, there is a corresponding set of values corresponding to width of a modulation pulse and light source current.
When there is no movement (Movement Value = 0), the width of the modulation pulse is maximum, corresponding to, e.g., 100 % of a frame width (Pulse Width Modulation (PWM) is 100%), and the (light source current, corresponding to current in the LEDs) is derived from Fig. 3; for example, an Illumination Value of 0.5 corresponds to a current of 8 mA and an illumination of 1 to a current of 20mA.
In a particular embodiment, when there is maximal movement then the width of the modulation pulse is half of maximum, corresponding to, 50 % of a frame width (Pulse Width Modulation (PWM) is 50%), and the Relative Luminous Intensity (instantaneous) must be multiplied by (100 %/50 %)=2. So for a Illumination Value of 1, the (instantaneous) Relative Luminous Intensity must be 2, and consequently the light source (LED) current must be 55 mA (as derived from Fig. 3). In this way, the complete table can be filled.
In this example, the width of the modulation pulse (PWM) is a linear function of Movement Value. An advantage of having the width of the width of the modulation pulse (PWM) being a continuous function, such as a linear function, of Movement Value may be that it is energy efficient, as it may be optimized so that the light source 222 is often, such as always, driven in a manner where perceived visual quality is not compromised while the energy consumption is kept relatively low.
In an alternative embodiment, it could a step-function. An advantage of this could be that relatively few values would need to be stored in the look-up-table.
Fig. 6 shows examples of a light source driving signal 112 which span 5 frames of a video sequence. The horizontal axis corresponds to time t and the vertical axis corresponds to light source current value I. The figure shows in the top row modulation pulses 661-665, where the first two modulation pulses 661-662 correspond to frames where the corresponding Motion Value = 0, and consequently the width 672b of the modulation pulse is large and in this example 100 % of the frame width 660. Furthermore, the light source current value 672a is relatively low. On the contrary, for the last three modulation pulses 663-665 the situation is the opposite, they correspond to frames where the
corresponding Motion Value = 1, and consequently the width 674b of the modulation pulse is small and in this example 50 % of the frame width 660. Furthermore, the light source current value 674a is relatively high (in the present example, the Illumination Values corresponding to all frames are substantially equal).
In the bottom row of Fig. 6 the situation is the opposite, since the figure shows modulation pulses 681-685, where the first two modulation pulses 681-682 correspond to frames where the corresponding Motion Value = 1, and consequently the width of these modulation pulses is small and in this example 50 % of the frame width 660. Furthermore, the light source current value is relatively high. On the contrary, for the last three modulation pulses 683-685 the situation is the opposite, they correspond to frames where the
corresponding Motion Value = 0, and consequently the width of these modulation pulses is large and in this example 100 % of the frame width 660. Furthermore, the light source current value is relatively low (in the present example, the Illumination Values corresponding to all frames are substantially equal).
For the situation outlined in the top row, a transition from a frame with corresponding low Movement Value to a frame with a corresponding high Movement Value, the visually perceived illumination may shortly drop, since in a region 668 the time averaged
Relative Luminous Intensity may be relatively small ("perceived illumination dip").
Similarly, for the situation outlined in the bottom row, a transition from a frame with corresponding high Movement Value to a frame with a corresponding low
Movement Value, the visually perceived illumination may shortly increase, since in a region 688 the time averaged Relative Luminous Intensity may be relatively high ("perceived illumination flash").
Fig. 7 shows further examples of the light source driving signal, which may be advantageous for overcoming the perceived illumination dip/flash outlined in connection with Fig. 6. The situation in Fig. 7 is very similar to Fig. 6 so only the differences will be described.
In the top row, a transition modulation pulse 763 has been inserted between the frame with corresponding low Movement Value and the frame with a corresponding high Movement Value. The transition pulse 763 has a different width 773b and light source current value 773a, compared to a normal modulation pulse 766, so that the time averaged Relative Luminous Intensity may be relatively constant. An advantage may be that the observer does not perceive abrupt changes in illumination during in the region 768.
In the bottom row, a transition modulation pulse 783 has been inserted between the frame with corresponding high Movement Value and the frame with a corresponding low Movement Value. The transition pulse 783 has a different width 793b and light source current value 793a, compared to a normal modulation pulse 786, so that the time averaged Relative Luminous Intensity may be relatively constant. An advantage may be that the observer does not perceive abrupt changes in illumination during in the region 788.
In both cases both the width (773b, 793b) of the transition modulation pulse and the light source current value (773a, 793a) may depend on the width (672b) of a modulation pulse and an light source current value (672a) associated with a previous frame of the video sequence, and/or the width of a modulation pulse (674b) and light source current value (674a) associated with a subsequent frame of the video sequence. In addition, the temporal position of the transition modulation pulse may be adjusted. It may also be possible to have a plurality of transition modulation pulses, such as in a sequence.
To sum up, the present invention relates to a method for controlling a backlight unit device, wherein one or more light sources in the backlight unit device are driven with a current, where the current may vary over time so as to form pulses, and wherein the width of the pulses are adjusted according to the motion content, such as to avoid motion blur, while the height (such as the light source current value) is adjusted so that the luminous intensity of the light sources is not affected by the varying width of the modulation pulses. Since modulation pulses with small widths necessitate an unproportionally large current flow, and hence large energy consumption, the method enables minimum energy consumption while the image quality is not compromised.
Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS:
1. A method (100) for controlling a backlight unit device (220) for illuminating an image formed in a display panel (456), the backlight unit device comprising a light source (222), being capable of emitting light in the backlight unit device, the method comprising:
receiving (102) image information (104) corresponding to
- an Illumination Value (106), and
- a Movement Value (108)
where the Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image,
generating (110) a light source driving signal (112) for controlling the light source, wherein the light source driving signal comprises information relating to
- a width (114) of a modulation pulse, and
- a light source current value (116),
controlling (118) the light source (222) according to the light source driving signal (112),
wherein
the width of the modulation pulse is determined according to the Movement Value (108) and the light source current value are determined according to both of the Illumination Value (106) and the width of the modulation pulse.
2. The method according to claim 1, wherein the backlight unit device (220) comprising a plurality of light sources with spatially distributed individual light sources, and the Illumination Value and/or the Movement Value are spatially resolved, and wherein the step of
generating the light source driving signal (112) comprises generating a spatially resolved light source driving signal, the spatially resolved driving signal being determined according to the Illumination Value and the Movement Value and the spatial distribution of the individual light sources,
and wherein the step of
- driving the light source (222) according to the light source driving signal, further comprises driving individual light sources in the plurality of light sources according to the spatially resolved light source driving signal.
3. A method according to any of the preceding claims, wherein the step of generating (110) the light source driving signal (112) comprises
accessing a look-up-table (448), which look-up-table connects values of the Movement Value and the Illumination Value with the width of the modulation pulse and the light source current value.
4. A method according to any of the preceding claims, wherein the method further comprising
receiving the video sequence,
performing a comparison between a first characteristic of the frame of the video sequence and a second characteristic of a previous frame of the video sequence,
determining the Movement Value according to a difference between the first characteristic and the second characteristic.
5. A method according to any of the preceding claims, wherein the width (114) of the modulation pulse can be described as a substantially continuous function of the Movement Value (108).
6. A method according to any of the preceding claims, wherein the width (114) of the modulation pulse depends substantially linearly on the Movement Value (108).
7. A method according to any of the preceding claims wherein the width (114) of the modulation pulse and the light source current value (116) furthermore depend on
a width of a modulation pulse and an light source current value associated with a previous frame of the video sequence, and/or
a width of a modulation pulse and an light source current value associated with a subsequent frame of the video sequence.
8. A method according to any of the preceding claims wherein a temporal position of the modulation pulse (114) is adjusted relative to the frame of the video sequence.
9. A method according to any of the preceding claims, wherein the width of the modulation pulse is monotonically decreasing with the increasing motion value for fixed Illumination Value.
10. A method according to any of the preceding claims, wherein the light source current value is monotonically increasing with decreasing width of the modulation pulse for fixed Illumination Value.
11. A method according to any of the preceding claims, wherein the light source current value (116) scales with a product of
a first factor which is inversely proportional with the width (114) of the modulation pulse, and
a second factor which is derived from a correspondence (328) between the intensity of the light source (222) and an input current.
12. A backlight unit device (220) for illuminating an image formed in a display panel (456), the backlight unit device comprising
a light source (222) being capable of emitting light in the backlight unit device,
- a backlight driving circuitry (224) adapted for
- receiving image information (104) corresponding to
- an Illumination Value (106), and
- a Movement Value (108)
associated with a frame of a video sequence corresponding to the image,
- generating an light source driving signal (104) for controlling the light source (222), wherein the light source driving signal comprises information relating to
- a width (112) of a modulation pulse, and
- an light source current value (114), and
- driving the light source according to the light source driving signal, wherein
the width of the modulation pulse is determined according to the Movement Value (108) and the light source current value are determined according to both of the Illumination Value (106) and the width of the modulation pulse.
13. A backlight unit device according to claim 12, wherein the light source (222) is chosen from the group comprising: a light emitting diode, an incandescent lamp.
14. A display panel apparatus comprising a display panel (456) and the backlight unit device (220) according to claim 12.
15. A computer program product being adapted to enable a computer system comprising at least one computer having data storage means associated therewith to operate a processor (444) arranged for
receiving (102) image information (104) corresponding to
- an Illumination Value (106), and
- a Movement Value (108)
where the Illumination Value and the Movement Value are both associated with a frame of a video sequence corresponding to the image,
generating driving information (450) corresponding to a light source driving signal (112) for controlling the light source, wherein the light source driving signal comprises information relating to
- a width (114) of a modulation pulse, and
- a light source current value (116),
wherein
the width of the modulation pulse is determined according to the Movement Value (108) and the light source current value are determined according to both of the Illumination Value (106) and the width of the modulation pulse.
PCT/NL2012/050501 2011-07-14 2012-07-12 Backlight unit device for illuminating an image WO2013019104A1 (en)

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