111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20100020002Al
`
`(19) United States
`c12) Patent Application Publication
`Van Woudenberg et al.
`
`(10) Pub. No.: US 2010/0020002 A1
`Jan. 28, 2010
`(43) Pub. Date:
`
`(54) SCANNING BACKLIGHT FOR LCD
`
`(86) PCT No.:
`
`PCT/IB05/54377
`
`(75)
`
`Inventors:
`
`Roe! Van Woudenberg, Eindhoven
`(NL); Hendrikus Willem Groot
`Hulze, Eindhoven (NL); Jeroen
`Hubert Christoffel Jacob Stessen,
`Eindhoven (NL); Aleksandar Sevo,
`Eindhoven (NL); Gerben Johan
`Hekstra, Eindhoven (NL); Hendrik
`Jan Blankers, Oss (NL); Vedran
`Kovacevic, Eindhoven (NL);
`Jeroen Den Breejen, Eindhoven
`(NL)
`
`Correspondence Address:
`PHILIPS
`INTELLECTUAL PROPERTY &
`STANDARDS
`P.O. BOX 3001
`BRIARCLIFF MANOR, NY 10510 (US)
`
`(73) Assignee:
`
`KONINKLIJKE PHILIPS
`ELECTRONICS, N.V.,
`EINDHOVEN (NL)
`
`(21) Appl. No.:
`
`11/722,194
`
`(22) PCT Filed:
`
`Dec. 22, 2005
`
`§ 371 (c)(l),
`(2), ( 4) Date:
`Jun.20,2007
`Foreign Application Priority Data
`
`(30)
`
`(EP) .................................. 04106987.3
`Dec. 27, 2004
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`G09G 3136
`(52) U.S. Cl. ........................................................ 345/102
`
`(57)
`
`ABSTRACT
`
`A method for displaying images on a display having backlight
`is disclosed, where the images is updated periodically with a
`period. The method comprises the steps of: generating a sig(cid:173)
`nal with a pulse pattern for each period depending on the
`contents of an image to be displayed in that period; and
`activating backlight in accordance with the signal. Further, a
`display (100) comprising a display panel (102) and a back(cid:173)
`light unit, wherein the backlight unit comprises a controller
`(104) and a lighting device is disclosed. The controller (104)
`is arranged to generate a control signal, and the lighting
`device is arranged to provide backlight to the display panel
`(102) according to the control signal, wherein the control
`signal comprises a pulse pattern depending on contents of
`displayed images.
`
`_,..,..-
`
`_,--
`
`102
`105
`
`f.--1 04
`
`100
`
`106 --
`108 --
`
`SONY 1006
`Page 1
`
`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 1 of 7
`
`US 2010/0020002 A1
`
`f-__,--
`
`102
`
`.......--
`
`105
`
`--1 04
`
`FI G.l
`
`106 .........
`
`108 .........
`
`100
`
`226
`
`212
`
`214
`
`--~~ ~~--,
`,
`
`'
`
`I
`I
`I
`\
`\
`
`~~-7-
`
`\
`\
`I
`I
`I
`
`...
`
`~-7-~
`
`206 222
`
`220 208
`
`228
`
`FIG.2
`
`Page 2
`
`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 2 of 7
`
`US 2010/0020002 A1
`
`400
`
`Determine contents
`
`402
`
`Generate backlight control signal
`
`404
`
`Generate backlight
`
`FIG.3
`
`FIG.4
`
`Page 3
`
`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 3 of 7
`
`US 2010/0020002 A1
`
`500
`
`Generate signal with 1st pattern
`
`502
`
`Generate signal with intermediate
`pattern
`
`YES
`
`506
`
`Generate signal with 2nd pattern
`
`FIG.S
`
`Page 4
`
`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 4 of 7
`
`US 2010/0020002 A1
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`Page 5
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`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 5 of 7
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`US 2010/0020002 A1
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`Page 6
`
`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 6 of 7
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`US 2010/0020002 A1
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`Page 7
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`

`

`Patent Application Publication
`
`Jan. 28, 2010 Sheet 7 of 7
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`US 2010/0020002 A1
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`Page 8
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`

`

`US 2010/0020002 AI
`
`Jan.28,2010
`
`1
`
`SCANNING BACKLIGHT FOR LCD
`
`TECHNICAL FIELD
`
`[0001] The present invention relates to a method and a
`display, wherein backlight is generated depending on con(cid:173)
`tents of displayed images.
`
`BACKGROUND OF THE INVENTION
`
`[0002] LCD (Liquid Crystal Display) panels suffer from
`motion blur due to their sample-and-hold nature, i.e. the LC
`(Liquid Crystal) remains in the same state after addressing
`during a whole frame. When displayed objects move, as is the
`case in e.g. TV images, this causes a blurred image of the
`objects on the retina of a viewer. In US 2004/0012551 A, it is
`disclosed a means to drive the data for the value correspond(cid:173)
`ing to a present frame display data. By comparing with pre(cid:173)
`vious frame of display data, the display data in the present
`frame that have changes are then over emphasized and written
`into the LCD driver with more than the amount of change to
`the picture element data. Further, a backlight control means to
`control the lighting delay time, the lighting time width, the
`lighting time interval and the number of times of lighting
`within one frame of a LCD backlighting is disclosed. How(cid:173)
`ever, there is a need for improved backlight control to avoid a
`flickering image.
`
`SUMMARY OF THE INVENTION
`
`[0003]
`It is therefore an object of the present invention to
`provide an improved method for displaying images on a dis(cid:173)
`play, and an improved display.
`[0004] The above object is achieved according to a first
`aspect of the present invention by a method for displaying
`images on a display having backlight, wherein the images are
`updated periodically with a period. The method comprises the
`steps of: generating a signal with a pulse pattern for each
`period depending on contents of an image to be displayed in
`that period; and activating the backlight in accordance with
`said signal.
`[0005] An advantage of this is that the backlighting is
`depending on the contents of the displayed images for pro(cid:173)
`viding an image that is experienced as less flickering.
`[0006] The backlight may comprise a plurality of lighting
`units and each lighting unit is associated with a part of the
`display, wherein the steps of generating a signal and activat(cid:173)
`ing backlight are separately adapted to each of the parts.
`[0007] An advantage of this is that an image comprising
`contents with very different contents in different parts is
`improved in each part.
`[0008] The pulse pattern may comprise a plurality of pulses
`for each period when contents of the displayed image com(cid:173)
`prise relatively high brightness.
`[0009] An advantage of this is that a viewer often experi(cid:173)
`ences a bright image as more flickering, but this is compen(cid:173)
`sated for by increasing the backlighting frequency for such
`images.
`[0010] The term "relatively high brightness" should in this
`context be construed to be a brightness essentially higher than
`an average brightness of an average image.
`[0011] The plurality of pulses may be symmetrical during
`said period when contents of displayed images comprise low
`changes between subsequent images.
`[0012] An advantage of this is optimal reduced flickering
`when an image is relatively static, i.e. when a viewer would
`experience flickering the most, and the equal distribution
`would not introduce any blurring.
`
`[0013] The plurality of pulses may be asymmetrical during
`said period when contents of displayed images comprise high
`changes between subsequent images.
`[0014] An advantage of this is reduced flickering, and
`counteracting blurring by distributing the pulses asymmetri(cid:173)
`cally when there is a lot of motion in the image.
`[0015] The pulse pattern may comprise one pulse for each
`period when contents of displayed images comprise high
`changes between subsequent images and relatively low
`brightness.
`[0016] The term "relatively low brightness" should in this
`context be construed to be a brightness essentially lower than
`an average brightness of an average image.
`[0017] An advantage of this is optimized counteracting of
`blurring, while there is little or no experienced flickering due
`to low brightness.
`[0018] By symmetrical pulses, it is meant that the pulse in
`each half of the frame period is symmetrical in effective
`brightness and position, and for higher multiples of fre(cid:173)
`quency, for each corresponding fraction of frame period. By
`asymmetrical pulses, it is meant that the pulse in each half of
`the frame period is symmetric in effective brightness and/or
`position, and for higher multiples of frequency, for each cor(cid:173)
`responding fraction of frame period. Effective brightness
`depend on pulse amplitude and/or width.
`[0019] Where contents change, the method may further
`comprise the steps of: generating said signal with a first
`pattern; generating said signal with intermediate patterns; and
`generating said signal with a second pattern, wherein said
`intermediate patterns are such that an average value of said
`signal is kept constant upon a transition from said first pattern
`to said second pattern.
`[0020] An advantage of this is a seamless transition from
`one backlighting pattern to another, without any brightness
`dips or peaks. This is particularly advantageous when transi(cid:173)
`tion from one backlighting pattern to another is performed
`within a single image, i.e. from one part to another.
`[0021] Where the first pattern is a single pulse for each
`period, and the second pattern is two symmetrical pulses, the
`intermediate patterns may be two pulses with different effec(cid:173)
`tive pulse brightnesses. Where the first pattern is two sym(cid:173)
`metrical pulses, and the second pattern is a single pulse for
`each period, the intermediate patterns may be two pulses with
`different effective pulse brightnesses. An aggregated effec(cid:173)
`tive pulse brightness of said pulses within each period may be
`constant.
`[0022] An advantage of this is an efficient way to seam(cid:173)
`lessly transition from one backlighting scheme to another.
`[0023] The above object is achieved according to a second
`aspect of the present invention by a display comprising a
`display panel and a backlight unit, wherein the backlight unit
`comprises a controller and a lighting device, wherein the
`controller is arranged to generate a control signal, and the
`lighting device is arranged to provide backlight to the display
`panel according to the control signal, wherein the control
`signal comprises a pulse pattern depending on contents of
`displayed images.
`[0024] The backlight unit may comprise a plurality oflight(cid:173)
`ing devices, and each lighting device is associated with a part
`of the display, and the control signal is separately adapted to
`each of the parts.
`[0025] The advantages of the second aspect of the present
`invention are essentially the same as those of the first aspect.
`
`Page 9
`
`

`

`US 2010/0020002 AI
`
`Jan.28,2010
`
`2
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0026] The above, as well as additional objects, features
`and advantages of the present invention, will be better under(cid:173)
`stood through the following illustrative and non-limiting
`detailed description of preferred embodiments of the present
`invention, with reference to the appended drawings, wherein:
`[0027] FIG. 1 illustrates a display according to an embodi(cid:173)
`ment of the present invention;
`[0028] FIG. 2 is a mode transition diagram showing tran(cid:173)
`sition between two modes via intermediate modes;
`[0029] FIG. 3 is a mode transition diagram showing tran(cid:173)
`sition between modes related to image contents;
`[0030] FIG. 4 is a flow chart illustrating a method according
`to an embodiment of the invention;
`[0031] FIG. 5 is a flow chart illustrating a method for mode
`transition;
`[0032] FIGS. 6-20 are pulse diagrams; and
`[0033] FIG. 21 illustrates a display according to another
`embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`[0034] FIG.1 illustrates a display 100 comprising a display
`panel102. The display panel102, which can be a LCD (Liq(cid:173)
`uid Crystal Display) panel, is provided with backlighting 105.
`The backlighting 105 can for example comprise one or more
`light sources (not shown), such as light emitting diodes
`(LEDs) or gas discharge lamps. The backlight is flashed,
`either for the entire panel 102 or, preferably, by scanning
`backlight segments of the panel 102. Thus, an LC cell is
`illuminated only for a certain fraction of the frame time. A
`backlight controller 104, which is connected to the backlight(cid:173)
`ing 105 of the panel102, controls backlight flashing. To avoid
`large area flicker, the backlight controller 104 provides a
`backlight control signal which is dependent on an image
`displayed on the panel102. Therefore, the backlight control(cid:173)
`ler 104 is connected to a display controller 106, which in turn
`receives image data from an image data source 108. It should
`be noted that this description is for illustrative purpose, and
`both the backlight controller 104 and the display controller
`106 can be a common video controller, or divided between
`two or more units, which provide the same function as the
`backlight and display controllers 104, 106. The data source
`108 can be a TV decoder, a DVD player, a computer, or any
`other means providing images to be viewed on the display
`100.
`[0035] An effective way to reduce large area flicker and
`achieving motion blur reduction would be to drive the panel at
`a higher refresh rate and use motion-compensated video up(cid:173)
`conversion to achieve a higher video rate with smooth motion.
`For an LCD it is however not possible to increase refresh rate
`above 75-80Hz. Moreover, it is very expensive to up-convert
`video signals with motion compensation. The present inven(cid:173)
`tion provides a less expensive way to achieve less flicker and
`less motion blurring.
`[0036] To achieve this, the backlight is operated at double
`refresh frequency, or a higher multiple. This introduces a
`higher frequency brightness modulation, which is far above
`the flicker threshold, even for a white image.
`
`[0037] To provide a clearer view in examples provided
`below, FIGS. 6-20 illustrate a plurality of pulse patterns in
`pulse diagrams, which will be referred to in the description of
`the embodiments. It should be noted that the pulse diagrams
`show principles, from which the artisan is able to understand
`the spirit of the invention according to the embodiments pre(cid:173)
`sented below, and pulse shapes, widths, amplitudes and posi(cid:173)
`tions, as well as ways of transition from one pulse pattern to
`another via intermediate pulse patterns, are simplified to
`avoid obscuring the basic ideas of the present invention.
`[0038] FIG. 6 is a pulse diagram illustrating a single pulse
`per frame period, i.e. one pulse is provided for each period of
`refresh of the display. The effective brightness produced by
`the pulse, by controlling a light generating means, or regard(cid:173)
`ing the pulse as an output of the light generating means, is
`dependent on the pulse width and the amplitude of the pulse.
`[0039] FIG. 7 is a pulse diagram illustrating a symmetrical
`double pulse, i.e. there is provided two pulses for each frame
`period and the pulses in each half of the frame period is
`symmetrical in effective brightness and position.
`[0040] FIG. 8 is a pulse diagram illustrating an asymmetri(cid:173)
`cal double pulse, which pulses are symmetric in position, but
`asymmetric in effective brightness, i.e. there are two pulses
`for each frame period that are symmetric in position, but the
`pulse in each half of the frame period is asymmetric in effec(cid:173)
`tive brightness. Thus, the double pulse, considered as a
`whole, is asymmetric.
`[0041] FIG. 9 is a pulse diagram illustrating an asymmetri(cid:173)
`cal single pulse, where the pulse is asymmetrical in sense of
`position.
`[0042] FIG. 10 is a pulse diagram illustrating an asym(cid:173)
`metrical double pulse where the pulse pattern is asymmetrical
`in sense of effective brightness, since the amplitudes of the
`pulsed differ.
`[0043] FIG.ll is a pulse diagram illustrating a double pulse
`pattern, where the two pulses are close together to achieve a
`lighting effect relatively similar to a single pulse pattern as
`illustrated in FIG. 6, and are therefore referred to as a quasi(cid:173)
`single pulse.
`[0044] FIG.12 is a pulse diagram illustrating a double pulse
`pattern, where the two pulses provide very different effective
`brightness by having very different pulse widths. Also with
`this pattern, a lighting effect relatively similar to a single
`pulse pattern as illustrated in FIG. 9 is achieved, and is there(cid:173)
`fore also referred to as a quasi-single pulse. FIG.13 illustrates
`an even more extreme quasi-single pulse pattern, where two
`pulses are very different in both pulse width and amplitude.
`[0045] FIG. 14 is a pulse diagram illustrating a transition
`between two pulse patterns, where a brightness peak occurs at
`the transition. During a period, here marked by a bracket, the
`average pulse width and amplitude are higher than over other
`periods, and a brightness peak can be experienced by a
`v1ewer.
`[0046] FIG. 15 is a pulse diagram illustrating a transition
`between two pulse patterns, where a brightness dip occurs at
`the transition. During a period, here marked by a bracket, the
`average pulse width and amplitude are lower than over other
`periods, and a brightness dip can be experienced by a viewer.
`[0047] FIG. 16 is a pulse diagram illustrating a first pulse
`pattern with eight symmetrical pulses, and a transition to
`another pulse pattern with three symmetrical pulses via an
`intermediate pulse pattern, which is asymmetrical and com(cid:173)
`prises five pulses.
`
`Page 10
`
`

`

`US 2010/0020002 AI
`
`Jan.28,2010
`
`3
`
`[0048] FIG. 17 is a pulse diagram illustrating a transition
`from a quasi -single pulse pattern, similar to that illustrated in
`FIG. 12, to a symmetrical pulse pattern, similar to that illus(cid:173)
`trated in FIG. 7, via an intermediate pulse pattern, here illus(cid:173)
`trated similar to the quasi -single pulse pattern as illustrated in
`FIG. 11. It should be noted that a transition via intermediate
`pulse patterns normally comprises more patterns to achieve a
`seamless transition, and FIG. 17 illustrates the principle to
`avoid a brightness peak, which would occur as illustrated in
`FIG. 14.
`[0049] FIG. 18 illustrates the use of intermediate pulse
`patterns when a transition is to be made to a more extreme
`pulse pattern.
`[0050] FIG. 19 illustrates transition from a single pulse
`pattern to a double pulse pattern via a quasi-single pulse
`pattern as intermediate pulse pattern.
`[0051] FIG. 20 is a pulse diagram illustrating an instanta(cid:173)
`neous transition without intermediate pulse patterns when a
`scene shift is occurring. This is possible, since brightness dips
`or peaks would not be visible at a scene shift. Thus, no
`transition using intermediate pulse patterns is needed.
`[0052] The operation will be described with an example
`using double pulses in a display refresh period, i.e. double
`frequency, but the same principle applies for three or more
`pulses in a period, i.e. higher multiples of frequency.
`[0053] For a perfect flicker reduction, these two pulses need
`to be spaced exactly half a frame distance apart and to have
`the exactly the same brightness, i.e. symmetrical pulses as
`illustrated in FIG. 7, resulting in a pure double frequency
`backlight pulsing. It is observed for 50 Hz display refresh and
`double flashing, flicker is already visible when the two pulses
`differ 0.5% in brightness at a total display brightness of 500
`cd/m2 and for 60 Hz display refresh and double flashing,
`flicker is visible at 3.5% difference in brightness between the
`pulses.
`[0054] The lamps are preferably operated at a fixed current.
`Therefore, the backlight brightness modulation is preferably
`done using pulse width modulation. The pulses can also com(cid:173)
`prise a series of even higher frequency pulses, i.e. the modu(cid:173)
`lation can be done by pulse number modulation of pulse
`trains. Further, the amplitude of the pulses can be modulated,
`and a combination of the above mentioned backlight modu(cid:173)
`lation techniques can be applied.
`[0055] Flicker is most visible in bright scenes with little or
`no motion, although flicker also is visible in bright scenes
`with a lot of motion, but in the latter case, motion blur prob(cid:173)
`lems increase. For example, when a bright scene with some or
`a lot of motion is paused, flicker becomes more visible, but
`motion blur problems, of course, disappear. Therefore, the
`backlight is operated in double pulse mode, with the two
`pulses in the frame exactly spaced at half a frame distance,
`and with exactly the same brightness for the two pulses, when
`the flicker problem is the most apparent.
`[0056] When there is some or a lot of motion in the scene,
`it is only needed to introduce a bit ofhigher frequency content
`in the brightness modulation. Therefore, backlight is operated
`with two pulses spaced at half a frame distance, but with
`different brightness of the pulses. A first pulse, half a frame
`period earlier than the second pulse takes care of reducing the
`flicker to a large extent, while it is sufficiently low in bright(cid:173)
`ness not to cause a clear double image or to cause blur. The
`second pulse gives the main brightness.
`[0057] Alternatively, two pulses of same brightness can be
`moved closer together, as illustrated in FIG. 11, to improve
`
`moving image quality compared to distributing the pulses at
`half frame period distance and at the same time having some
`higher frequencies in the display brightness to reduce flicker.
`The reduction of motion blur is now due to that the two
`illuminated images in this case of asymmetrically distributed
`pulses are closer in time.
`[0058] By asymmetrically distributed pulses, it is meant
`that the pulse in each half of the frame period is asymmetric
`in effective brightness and position, and for higher multiples
`of frequency, for each corresponding fraction of frame period.
`[0059]
`It is observed that for a total duty cycle of 40%, the
`flicker of a 25% to 7 5% pulse ratio is the same as of two pulses
`of 20% duty cycle each separated by approximately 2h of a
`frame period, center to center. It is also observed that moving
`image quality is very similar for these two cases for both
`natural scenes and edge quality.
`[0060] When there is little or no motion and the scene is not
`too bright, it is preferable to use the asymmetrical pulse
`distribution. However, in this case it is not critical and the
`backlight mode can be chosen arbitrarily, preferably in a way
`to avoid mode change.
`[0061] When there is a lot of motion and the scene is not too
`bright, no flicker reduction is needed, and a single or quasi(cid:173)
`single pulse backlight operation can be used to achieve best
`performance for scenes with a lot of motion.
`[0062] FIG. 2 is a mode transition diagram showing tran(cid:173)
`sition between two modes 200, 202 via intermediate modes
`206, 208. If a direct transition to another mode is performed
`instantaneously, the effect could be that there is a larger gap
`between the last pulse of the first mode and the first pulse of
`the second mode, causing a brightness dip due to that the
`average value of the pulses temporarily dips, as illustrated in
`FIG. 15, or that there is a smaller gap between the last pulse of
`the first mode and the first pulse of the second mode, causing
`a brightness peak, as illustrated in FIG. 14. To avoid these
`backlight dips or peaks during change of backlight mode,
`intermediate modes 206, 208 are formed to achieve a seam(cid:173)
`less transition.
`[0063] To illustrate this, the operation will be described for
`double pulse as in the example above in relation to FIG. 1, i.e.
`double frequency, but as above, the same principle applies for
`three or more pulses, i.e. higher multiples of frequency. For an
`illustrative example, transition is to be performed between a
`single pulse mode 200 to a symmetrical double pulse mode
`202. This can for example be the case when a scene with low
`brightness and a lot of motion changes to high brightness and
`little or no motion.
`[0064] A first transition 210 is performed to a first interme(cid:173)
`diate mode 206. This mode can be a double pulse mode with
`asymmetrical pulses, e.g. a pulse width ratio of 5% to 95%,
`and only a small distance between the pulses, i.e. a double
`pulse pattern that is relatively similar to the single pulse
`pattern. A second transition 212 is then performed to a second
`intermediate mode (not shown) with two pulses with less
`asymmetry, and then further transitions to intermediate
`modes with more and more symmetry to a transition 214 to a
`last intermediate mode 208 where the pulse width ratio
`between the pulses is almost 50% to 50% and the distance
`between the pulses is almost a half frame distance, center to
`center. A last transition 216 is performed is performed to the
`symmetrical double pulse mode 202, where the pulse width
`ratio is exactly 50% to 50%, and the distance between the
`pulses is exactly a half frame distance, center to center. The
`transition between the modes 200, 202 is then complete, and
`
`Page 11
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`

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`US 2010/0020002 AI
`
`Jan.28,2010
`
`4
`
`performed such that a viewer do not experience any dips or
`peaks in brightness. The transitions 210,212,214,216 can be
`performed between each frame, or between each couple of
`frames.
`[0065] Alternatively, the transition is performed, as illus(cid:173)
`trated in FIG. 19, by forming a quasi-single pulse pattern with
`two pulses with equal effective brightness, and then separat(cid:173)
`ing the pulses in one or more steps to get to the symmetrical
`pulse pattern.
`[0066] The same applies with transition from symmetrical
`double pulse mode 202 to single pulse mode 200 via inter(cid:173)
`mediate modes 208, 206 and transitions 218, 220, 222, 224.
`[0067] This example illustrated transition between single
`pulse mode and symmetrical double pulse mode. The same
`principle applies between other modes, e.g. between single
`pulse mode and asymmetrical double pulse mode, and
`between symmetrical and asymmetrical double pulse modes.
`Further, the principle is also applicable to multi pulse modes.
`The general principle of the transitions is to insert intermedi(cid:173)
`ate modes that gradually change the pulse patterns from one
`mode to another to avoid brightness dips or peaks.
`[0068] When there is a change of scene, a transition can be
`made directly from the first mode 200 to the second mode 202
`by a direct transition 226, and from the second mode 202 to
`the first mode 200 by a direct transition 228. A control signal,
`from e.g. the display controller, would enable the backlight
`controller to do such direct transitions 226, 228.
`[0069] FIG. 3 is a mode transition diagram showing tran(cid:173)
`sitions 300,302,304,306,308,310 between modes 312,314,
`316 related to image contents. Each of the transitions 300,
`302, 304, 306,308,310 can comprise intermediate modes, as
`illustrated in FIG. 2. Three modes 312, 314, 316 are illus(cid:173)
`trated as an example, e.g. single pulse mode 312, asymmetri(cid:173)
`cal double pulse mode 314, and symmetrical double pulse
`mode 316. However, more modes can be comprised, e.g.
`different quasi-single pulse modes, asymmetrical modes, and
`modes with three or more pulses.
`[0070] FIG. 4 is a flow chart illustrating a method according
`to an embodiment of the invention. In a content determination
`step 400, the contents of the image is determined. Contents
`can comprise brightness of the image or a part of the image,
`and presence of motion in the image. A backlight control
`signal is generated in a backlight generation step 402 in
`dependence on the determined contents. Examples of this
`dependence is described above. Backlight is then activated
`based upon the backlight control signal in a backlight gen(cid:173)
`eration step 404. The backlight is activated with a backlight
`driver driving lamps or LEDs.
`[0071] FIG. 5 is a flow chart illustrating a method for mode
`transition. In a first pattern signal generation step 500, a
`backlight control signal with a first pattern is generated. A
`signal with an intermediate pattern relatively similar to the
`first pattern is generated in an intermediate pattern signal
`generation step 502. In a determination step 504 it is deter(cid:173)
`mined if more intermediate patterns should be inserted. This
`can be dynamically determined or determined from a pre(cid:173)
`defined transition procedure. If further patterns are to be
`inserted, the method returns to the intermediate pattern signal
`generation step 502. Otherwise, the method continues with a
`second pattern signal generation step 506 where the back(cid:173)
`lighting is operated in the second mode, and the transition is
`ready.
`[0072] FIG. 21 illustrates a display 2100 comprising a dis(cid:173)
`play panel2102. The display panel2102, which can be a LCD
`
`(Liquid Crystal Display) panel, is provided with a plurality of
`backlighting units 2105. Each of the backlighting units 2105
`can for example comprise one or more lighting units, such as
`light emitting diodes (LEDs) or gas discharge lamps. The
`backlight is flashed, either for the entire panel2102 or, pref(cid:173)
`erably, by scanning backlight units 2105. Thus, an LC cell is
`illuminated only for a certain fraction of the frame time.
`Backlight controllers 2104, which are connected to the back(cid:173)
`lighting units 2105 of the panel 2102, controls backlight
`flashing. To avoid large area flicker, the backlight controllers
`2104 provide backlight control signals which are dependent
`on an image displayed on an associated part of the panel21 02.
`Therefore, the backlight controllers are connected to a display
`controller 2106, which in turn receives image data from an
`image data source 2108. It should be noted that this descrip(cid:173)
`tion is for illustrative purpose, and both the backlight control(cid:173)
`lers 2104 and the display controller 2106 can be a common
`video controller, or divided between two or more units, which
`provide the same function as the backlight and display con(cid:173)
`trollers 2104, 2106. The data source 2108 can be a TV
`decoder, a DVD player, a computer, or any other means
`providing images to be viewed on the display 2100.
`[0073]
`In some cases, image contents are segmented, e.g. a
`cloudy, bright sky at top and at bottom a dark ground, with
`sharp letters in subtitles. Therefore, in some cases, it is desir(cid:173)
`able to segment the driving of the backlight accordingly, i.e.
`by backlight units 2165 associated to the part of the image to
`be shown on the display 2100. The present invention is also
`applicable to this. Thus, the backlighting is not only improved
`for each type of image, the backlighting is also improved for
`each part of the image associated to backlight units 2105. To
`be able to implement this, there is a few things to consider.
`[0074] Analysis of the image is performed for each part of
`the image, where the part can be defined by a part illuminated
`by a certain lighting unit, or a part comprising a certain type
`of image contents.
`[0075] To avoid unwanted effects at borders between parts
`of the image, the transition between a pulse pattern in one part
`to another part is treated similar to the transition between a
`first and a second backlight pattern described above. If there
`is a moving object at a border between two parts of the image,
`the different effects of the different pulse patterns are reduced
`by crosstalk between the backlighting units associated with
`the pulse patterns.
`[0076]
`It can be noted that driving the backlighting in
`double pulse modes, or multi pulse modes, will in some cases
`produce more light than with single pulse, although the same
`total pulse duration. An explanation to this is that a switch-off
`time for a backlight nnit last longer than a switch-on time.
`This is the case for some types of backlight units, and the
`opposite effect can be observed for other types of backlight
`units. The difference in lighting can, as described above, be
`prevented by using quasi-single pulse patterns. As an alterna(cid:173)
`tive to quasi-single pulse patterns, single pulse patterns,
`which provides some additional time for reactive components
`to settle and thus a somewhat sharper image, can be used, but
`with a compensation factor added to the pulse to equalize to a
`quasi-single, double, or multi pulse pattern. It is preferable to
`have a look-up table, with compensation factors for different
`pulse patterns for the actual light source or sources, from
`which compensation factors are used to enable seamless tran(cid:173)
`sitions between different pulse patterns, especially when used
`in neighboring partitions of an image.
`
`Page 12
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`US 2010/0020002 AI
`
`Jan.28,2010
`
`5
`
`[0077] However, when a seamless transition is to be made
`between single and dual or multi pulse patterns, the following
`procedure can be used:
`i) If the double o