(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0012821 A1
`(43) Pub. Date:
`Jan. 20, 2005
`Kanai
`
`US 20050012821A1
`
`(54)
`
`DISPLAY DEVICE, METHOD OF
`MANUFACTURING DISPLAY DEVICE,
`INFORMATION PROCESSING APPARATUS,
`CORRECTION VALUE DETERMINING
`METHOD, AND CORRECTION VALUE
`DETERMINING DEVICE
`
`(75)
`
`Inventor: Izumi Kanai, Tokyo (JP)
`
`Correspondence Address:
`FITZPATRICK CELLA HARPER & SCINTO
`30 ROCKEFELLER PLAZA
`NEW YORK, NY 10112 (US)
`
`Assignee: CANON KABUSHIKI KAISHA,
`TOKYO (JP)
`
`Appl. No.:
`
`10/890,192
`
`Filed:
`
`Jul. 14, 2004
`
`Foreign Application Priority Data
`
`(73)
`
`(21)
`(22)
`(30)
`
`Jul. 15, 2003
`Jul. 2, 2004
`
`.. 2003-274993
`(JP)
`(JP) .................................... .. 2004-196394
`
`Publication Classi?cation
`
`(51) Int. Cl? ................................................... ..H04N 5/202
`(52) Us. 01. ............................................................ ..348/189
`
`(57)
`
`ABSTRACT
`
`Adisplay device includes a plurality of display elements and
`a correction circuit Which outputs signals obtained by per
`forming correction on input signals to the respective display
`elements, and the correction circuit performs the correction
`so that a spatial frequency distribution of luminance
`obtained by driving the respective display elements by using
`the signals obtained by performing the correction on the
`input signals indicative of predetermined luminance
`becomes a spatial frequency distribution in Which a prede
`termined frequency component is reduced from among
`frequency components contained in a spatial frequency
`distribution of luminance obtained by driving the respective
`display elements Without performing the correction on the
`input signals indicative of the predetermined luminance and
`at least a portion of frequency components loWer than the
`predetermined frequency component is left.
`
`,
`5
`
`OPARATION
`PART
`
`/2D
`
`CCD
`CAMERA
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 1 0f 14
`
`US 2005/0012821 A1
`
`Fig.1A
`
`300 D/
`
`RECEIVING
`DEVICE
`
`200
`/\/
`
`DISPLAY DEVICE
`
`OPA RATION
`PART
`
`“I
`
`10
`
`/20
`
`CCD
`CAMERA
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 2 0f 14
`
`US 2005/0012821 A1
`
`11. ‘P m
`
`LUMINANCE
`
`GRADATION
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 3 0f 14
`
`US 2005/0012821A1
`
`Fig.3
`
`99
`
`97
`
`93
`
`96 108 111 107
`
`89
`
`96
`
`91 101 111 95 105
`
`90 101 96 107 108 99 104
`
`103 98 101 100 111 112 109
`
`97 105 104 104 110 102 101
`
`103 108 95 108 92 106 113
`
`103 99
`
`90 104 103 103 94
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 4 of 14
`
`US 2005/0012821 Al
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`O v
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`
`Patent Application Publication Jan. 20, 2005
`
`Sheet 5 0f 14
`
`US 2005/0012821 A1
`
`Fig.5
`
`99 99
`
`99
`
`99 100 100 100
`
`99
`
`99 99 99 100 100 100
`
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`
`99 99 100 100 100
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`
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`99 100 100 100
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`
`99
`
`99
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 6 0f 14
`
`US 2005/0012821 A1
`
`Fig.6
`
`
`
`DISCRIMINATION THRESHOLD
`
`
`
`LUMINANCE UNEVENNESS
`
`SPATIAL FREQUENCY
`
`

`
`Patent Application Publication Jan. 20, 2005
`
`Sheet 7 0f 14
`
`US 2005/0012821 A1
`
`Fig.7
`
`1.02 1.06 1.03 0.93
`
`1.11
`
`1.03 1.09 0.98
`
`0.9
`
`1.1
`
`0.98 1.03 0.93 0.93
`
`0.96 1.01 0.98 0.99
`
`0.9
`
`1.02 0.94 0.95 0.95
`
`0.96 0.92 1.04 0.92 1.09
`
`0.96
`
`1.1
`
`0.95 0.97
`
`0.93
`
`0.95
`
`0.96
`
`0.92
`
`0.99
`
`0.88
`
`1.06
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 8 0f 14
`
`US 2005/0012821 A1
`
`com
`
`2:
`
`HONVNIWITI
`
`mwmm
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 9 0f 14
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 10 0f 14
`
`US 2005/0012821 A1
`
`Fig.10
`
`100 100 100 100 100 100 100
`
`100 100 100 100 100 100 100
`
`100 100 100 100 100 100 100
`
`100 100 100 100 100 100 100
`100 100 100 100 100 100 100
`
`100 100 100 100 100 100 100
`
`100 100 100 100 100 100 100
`
`

`
`Patent Application Publication Jan. 20, 2005
`
`Sheet 11 0f 14
`
`US 2005/0012821 A1
`
`Fig.11
`
`1.01 1.03 1.08 1.04 0.93 0.9 0.93
`
`1.12 1.04
`
`1.1
`
`0.99 0.9
`
`1.05 0.95
`
`1.11 0.99 1.04 0.93 0.93 1.01 0.96
`
`0.97 1.02 0.99
`
`0.9
`
`0.89 0.92
`
`1.03 0.95 0.96 0.96 0.91 0.98 0.99
`
`0.97 0.93 1.05 0.93 1.09 0.94 0.88
`
`0.97 1.01 1.11 0.96 0.97 0.97 1.06
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 12 0f 14
`
`US 2005/0012821 A1
`
`Fig.12A
`
`Fig.12B
`
`LUMINANCE
`
`CORRECTION EXAMPLE 2
`
`320
`
`640
`PIXEL NO.
`
`960
`
`1280
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 13 0f 14
`
`US 2005/0012821 A1
`
`Fig.13
`
`LUMINANCE
`
`INJECTED CHARGE AMOUNT
`
`

`
`Patent Application Publication Jan. 20, 2005 Sheet 14 0f 14
`
`US 2005/0012821 A1
`
`Fig.14
`
`LUMINANCE
`
`l
`
`. h
`
`A
`W I ' '
`
`1201 LUMINANCE TARGET VALUE
`(UNIFORM ON THE ENTIRE
`SURFACE)
`
`4
`
`l l
`
`I
`
`\l
`
`VIII/WI, 11200 LUMINANCE DISTRIBUTION
`
`I ALONG A CERTAIN ROW
`PIXEL P
`
`POSITION
`
`

`
`US 2005/0012821 A1
`
`Jan. 20, 2005
`
`DISPLAY DEVICE, METHOD OF
`MANUFACTURING DISPLAY DEVICE,
`INFORMATION PROCESSING APPARATUS,
`CORRECTION VALUE DETERMINING METHOD,
`AND CORRECTION VALUE DETERMINING
`DEVICE
`[0001] This application claims priority from Japanese
`Patent Application No.2003-274993 ?led Jul. 15, 2003 and
`No.2004-196394 ?led Jul. 2, 2004, Which are hereby incor
`porated by reference.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 1. Field of the Invention
`
`[0003] The present invention relates to a display device
`having a plurality of display elements, and more particularly,
`to a method of correcting luminance unevenness of the
`display device.
`[0004] 2. Description of the Related Art
`[0005] Individual display elements such as electron emit
`ting devices have small differences in their element charac
`teristics produced in a manufacturing process or the like.
`Accordingly, if a display device is produced by using such
`display elements, there is the problem that these differences
`in characteristic appear as luminance unevenness.
`
`[0006] A method of correcting this luminance unevenness
`by correcting a driving signal has heretofore been proposed.
`Speci?cally, JP-A-2000-122598 discloses a construction
`Which performs correction in the luminance unevenness of
`a display element on an initial change and a temporal
`change.
`[0007] In the existing method of correcting a driving
`signal, a correction value is set so that a luminance target
`value (in this speci?cation, luminance obtained by ideal
`correction is called a luminance target value) becomes
`uniform.
`
`[0008] HoWever, there occurs the problem that if the
`luminance target value is made uniform, a correction amount
`becomes large.
`
`SUMMARY OF THE INVENTION
`
`[0009] Accordingly, the invention has been made to solve
`the above-described problem of the related art, and realiZes
`a construction capable of providing suitable display While
`restraining a correction amount.
`
`[0010] Therefore, the invention provides a display device
`Which includes a plurality of display elements and a correc
`tion circuit Which outputs signals obtained by performing
`correction on input signals to the respective display ele
`ments. The correction circuit performs the correction so that
`a spatial frequency distribution of luminance obtained by
`driving the respective display elements by using the signals
`obtained by performing the correction on the input signals
`indicative of predetermined luminance becomes a spatial
`frequency distribution in Which a predetermined frequency
`component is reduced (there is also a case Where the
`predetermined frequency component is omitted) from
`among frequency components contained in a spatial fre
`quency distribution of luminance obtained by driving the
`respective display elements Without performing the correc
`
`tion on the input signals indicative of the predetermined
`luminance and at least a portion of frequency components
`loWer than the predetermined frequency component is left.
`[0011] The invention provides a display device Which
`includes a plurality of display elements and a correction
`circuit Which outputs signals obtained by performing cor
`rection on input signals to the respective display elements.
`A spatial frequency distribution of luminance obtained by
`driving the respective display elements by using the signals
`obtained by performing the correction on the input signals
`indicative of predetermined luminance is a spatial frequency
`distribution in Which at least some frequency components
`are reduced from among frequency components contained in
`a spatial frequency distribution of luminance obtained by
`driving the respective display elements Without performing
`the correction on the input signals indicative of the prede
`termined luminance. The spatial frequency distribution of
`luminance obtained by driving the respective display ele
`ments by using the signals obtained by performing the
`correction on the input signals indicative of the predeter
`mined luminance contains a predetermined frequency com
`ponent Which is not a 0. The spatial frequency distribution
`of luminance obtained by driving the respective display
`elements by using the signals obtained by performing the
`correction on the input signals indicative of the predeter
`mined luminance has, on a higher-frequency side than the
`predetermined frequency component, a frequency compo
`nent Which is reduced by the correction in an amount greater
`than the predetermined frequency component.
`[0012] The frequency component Which is reduced by the
`correction in an amount greater than the predetermined
`frequency component also includes a component in Which
`the frequency component is set to a 0 by the correction.
`[0013] The invention also provides an information pro
`cessing apparatus Which includes the above-described dis
`play device and a receiving device Which receives informa
`tion to be displayed on the display device.
`[0014] The invention also provides a method of determin
`ing correction values to correct driving data for driving a
`plurality of display elements for displaying an image. The
`method includes a step of acquiring data having a correlation
`to luminance by driving a display element in accordance
`With image data for measuring, a step of performing con
`version of the data having the correlation to the acquired
`luminance into spatial frequency data, a step of reducing a
`predetermined high-frequency component While leaving at
`least a predetermined loW-frequency component from
`among the spatial frequency data, and calculating a spatial
`frequency component of a luminance target value, a step of
`acquiring a luminance target value by performing the
`inverse conversion of the conversion on the spatial fre
`quency data on the luminance target value, and a step of
`calculating a correction value for driving data for driving the
`display element, on the basis of the luminance target value.
`[0015] The step of calculating the spatial frequency of the
`luminance target value suitable includes a step of comparing
`a frequency component of the spatial frequency data With a
`spatial frequency component of a luminance unevenness
`discrimination threshold and selecting the smaller value as
`the spatial frequency component of the luminance target
`value. The step of calculating the correction value suitably
`includes a step of dividing the luminance target value by the
`acquired data having the correlation to luminance.
`
`

`
`US 2005/0012821 A1
`
`Jan. 20, 2005
`
`[0016] The step of calculating the spatial frequency of the
`luminance target value suitably includes a step of reducing
`a predetermined loW-frequency component from among
`frequency components of the spatial frequency data, setting
`a frequency component eXcept the predetermined loW-fre
`quency component to a 0, and selecting the frequency
`component as the spatial frequency component of the lumi
`nance target value, and the step of calculating the correction
`value suitably includes a step of dividing the luminance
`target value by the acquired data having the correlation to
`luminance.
`
`[0017] The invention also provides a correction value
`determining device for correcting driving data for driving a
`plurality of display elements. The correction value deter
`mining device includes indeX data acquiring means for
`acquiring data having a correlation to luminance by driving
`a display element in accordance With image data for mea
`suring, an indeX data conversion circuit for performing
`conversion of the acquired data having the correlation to
`luminance into spatial frequency data, a luminance target
`value spatial frequency component computing circuit for
`reducing a predetermined high-frequency component While
`leaving at least a predetermined loW-frequency component
`from among the spatial frequency data, and calculating a
`spatial frequency component of a luminance target value, a
`spatial frequency component inverse conversion circuit for
`performing the inverse conversion of the conversion on the
`spatial frequency data on the luminance target value, and a
`correction value calculation circuit for calculating a correc
`tion value for driving data for driving the display element,
`on the basis of the luminance target value obtained by the
`spatial frequency component inverse conversion circuit.
`
`[0018] The luminance target value spatial frequency com
`ponent computing circuit suitably has a function for com
`paring a frequency component of the spatial frequency data
`With a spatial frequency component of a luminance uneven
`ness discrimination threshold and selecting the smaller value
`as the spatial frequency component of the luminance target
`value, and the correction value calculation circuit suitably
`has a function for dividing the luminance target value
`obtained by the spatial frequency component inverse con
`version circuit by the acquired data having the correlation to
`luminance, and calculating the correction value.
`
`[0019] The luminance target value spatial frequency com
`ponent computing circuit suitably has a function for reduc
`ing a predetermined frequency component from among
`frequency components of the spatial frequency data, setting
`a frequency component eXcept the predetermined frequency
`component to a 0, and selecting the frequency component as
`the spatial frequency component of the luminance target
`value. The correction value calculation circuit suitably has a
`function for calculating the correction value by dividing the
`luminance target value obtained by the spatial frequency
`component inverse conversion circuit by the acquired data
`having the correlation to luminance, and calculating the
`correction value.
`
`[0020] According to the invention, it is possible to reduce
`a correction amount by leaving some frequency components
`from among frequency components of luminance uneven
`ness. It is also possible to realiZe a construction Which does
`not easily alloW luminance unevenness to be visible in spite
`of the reduced correction amount, particularly by leaving
`
`(maintaining or reducing) at least a portion of frequency
`components loWer than a predetermined frequency compo
`nent When the predetermined frequency component is
`deleted from the frequency components of the luminance
`unevenness. In addition, it is possible to realiZe a construc
`tion Which restrains a correction amount by leaving (main
`taining or reducing), Without completely deleting, a prede
`termined frequency component from among frequency
`components of luminance unevenness, as Well as Which does
`not easily alloW the luminance unevenness to be visible, by
`more greatly reducing frequency components higher than
`the predetermined frequency component.
`[0021] Namely, it is possible to realiZe a construction
`Which does not easily alloW luminance unevenness to be
`visible in spite of a reduced correction amount, by adopting
`a construction Which reduces or deletes some frequency
`components from among frequency components of lumi
`nance unevenness, and by selecting, as the frequency com
`ponents to be reduced or deleted, frequency components of
`higher frequency than at least one of frequency components
`to be maintained Without being reduced or to be maintained
`While being reduced. Namely, it is preferable to select at
`least components of higher frequency than a predetermined
`frequency as the frequency components to be reduced or
`deleted.
`
`[0022] The luminance unevenness mentioned herein can
`be measured by driving individual display elements on the
`basis of input signals (signals having the same value)
`indicative of predetermined luminance. The spatial distri
`bution of luminance obtained When no correction is per
`formed can be obtained by a plurality of display elements
`being respectively driven by signals having the same value,
`Whereas the spatial distribution of luminance obtained When
`a correction is performed can be obtained by the respective
`display elements being driven by signals obtained by cor
`recting the signals having the same value.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0023] FIGS. 1A and 1B are circuit block diagrams of an
`embodiment;
`[0024] FIG. 2 is a graph shoWing a gradation-luminance
`characteristic of PWM;
`
`[0025] FIG. 3 is a vieW shoWing a luminance distribution
`obtained When no correction is performed;
`
`[0026] FIG. 4A is a vieW shoWing DCT conversion of the
`luminance distribution shoWn in FIG. 3;
`
`[0027] FIG. 4B is a vieW tWo-dimensionally representing
`a visual characteristic;
`[0028] FIG. 4C is a vieW shoWing frequency components
`of luminance target values;
`[0029] FIG. 5 is a vieW shoWing luminance target values;
`[0030] FIG. 6 is a graph representing a visual character
`istic;
`[0031] FIG. 7 is a vieW representing correction values;
`
`[0032] FIG. 8A shoWs a luminance distribution obtained
`When no correction is performed;
`
`[0033] FIG. 8B shoWs a luminance distribution obtained
`along a certain roW When no correction is performed;
`
`

`
`US 2005/0012821 A1
`
`Jan. 20, 2005
`
`[0034] FIG. 8C shows a luminance distribution obtained
`When a correction is performed according to this embodi
`ment;
`[0035] FIG. 8a' shoWs a luminance distribution obtained
`along a certain roW When a correction is performed accord
`ing to this embodiment;
`[0036] FIG. 9A is a vieW shoWing DCT conversion of the
`luminance distribution shoWn in FIG. 3;
`
`[0037] FIG. 9B is a vieW tWo-dimensionally representing
`a visual characteristic;
`[0038] FIG. 9C is a vieW shoWing frequency components
`of luminance target values;
`[0039] FIG. 10 is a vieW shoWing luminance target values;
`[0040] FIG. 11 is a graph representing correction values;
`[0041] FIG. 12A shoWs a luminance distribution obtained
`When a correction is performed according to this embodi
`ment;
`[0042] FIG. 12B shoWs a luminance distribution obtained
`along a certain roW When a correction is performed accord
`ing to this embodiment;
`[0043] FIG. 13 is a vieW aiding in describing a saturation
`characteristic of a phosphor; and
`
`[0044] FIG. 14 is a vieW aiding in describing a problem
`occurring When a target luminance is made uniform.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0045] FIG. 1A is a block diagram shoWing an informa
`tion processing apparatus according to the invention. The
`information processing apparatus includes a display device
`200 and a receiving device 300 Which receives information
`to be displayed on the display device 200.
`
`[0046] The receiving device 300 may use appropriate
`devices such as a television tuner Which receives broadcast
`signals such as ground Waves and satellite Waves, a set top
`boX (STB) used in cable television, and an interface device
`Which receives communication signals via a netWork. The
`receiving device 300 and the display device 200 may be
`respectively accommodated in different cases, or they may
`also be accommodated in the same case.
`
`[0047] FIG. 1B is an explanatory vieW including circuit
`blocks of a correction value determining device according to
`the invention. Reference numeral 1 denotes a correction
`circuit, reference numeral 2 denotes a correction value
`generating part, reference numeral 3 denotes a multiplier,
`reference numeral 4 denotes an operation part, and reference
`numeral 5 denotes a table Which stores correction values
`(storage means; speci?cally, a memory can be used. As the
`memory, a semiconductor memory can be suitably adopted,
`and a memory using a storage medium Which stores mag
`netic information can also be used.) Reference numeral 6
`denotes a sWitch, reference numeral 10 denotes a modula
`tion circuit, reference numeral 11 denotes a scanning signal
`generating circuit, reference numeral 12 denotes a display
`panel, reference numeral 13 denotes a display element,
`reference numeral 14 denotes a vertical Wiring, reference
`numeral 15 denotes a horiZontal Wiring, and reference
`numeral 20 denotes an unevenness measuring part. The
`
`display device 200 according to the invention includes the
`correction circuit 1, the correction value generating part 2,
`the multiplier 3, the operation part 4, the table 5, the sWitch
`6, the modulation circuit 10, the scanning signal generating
`circuit 11, the display panel 12, the display elements 13, the
`vertical Wirings 14, and the horiZontal Wirings 15.
`
`[0048] (How of Signals)
`
`[0049] A broadcast Wave such as a television signal is
`decoded by a decoder Which is not shoWn, and is converted
`into digital RGB signals after having been subjected to
`processing such as Y-C separation. A PC signal, if it is an
`analog signal, is converted into digital RGB signals after
`having been subjected to AD conversion and the like. In
`FIG. 1B, image data d1 denotes these digital RGB signals.
`Speci?cally, a signal outputted from the receiving device
`300 shoWn in FIG. 1A is inputted to the multiplier 3 as the
`image data d1. As the image data d1, not only the digital
`RGB signals but also various signals can be inputted. For
`eXample, in the case Where the receiving device 300 Which
`receives a luminance signal and color-difference signals is
`used, a luminance signal and color-difference signals may
`also be inputted to the correction circuit 1 from the receiving
`device 300. HoWever, since the RGB signals are suitable as
`the input to the correction circuit 1, if the receiving device
`300 is a device Which receives signals other than the RGB
`signals, the receiving device 300 preferably has a circuit
`Which converts its received signal into the RGB signals.
`
`[0050] The image data d1 is inputted to the correction
`circuit 1. The correction circuit 1 includes the correction
`value generating part 2 having the operation part 4 and the
`table 5, the multiplier 3 Which multiplies a correction value
`d4 outputted from the correction value generating part 2 by
`the image data d1, and the sWitch 6 Which effects sWitching
`betWeen measuring data d6 outputted from the correction
`value generating part 2 and an output d5 of the multiplier 3.
`
`[0051] Image data d2 outputted from the correction circuit
`1 is inputted to the modulation circuit 10, and the modula
`tion circuit 10 performs predetermined modulation on the
`image data d2. After that, the image data d2 is outputted to
`the display elements 13 through a driving circuit as driving
`signals, and is displayed on the display elements 13 as an
`image.
`[0052] (Display Panel)
`[0053] The display panel 12 Will be described beloW. The
`display panel 12 has a construction in Which the display
`elements 13 are arranged in matriX form. One display
`element corresponds to any one color of R, G and B that
`constitutes one pixel.
`
`[0054] This embodiment adopts a display element of the
`type Which performs electron emission through the applica
`tion of a voltage to an electron emitting device and causes
`a phosphor corresponding to the electron emitting device to
`emit light, but other types of display elements Which emit
`light by voltage application, such as organic EL elements
`and plasma emission elements, may also be adopted.
`
`[0055] In this embodiment, the display panel 12 has a
`resolution of WXGA (1,280><768). In this case, 1,280><3
`(RGB)><768Ethree million display elements are arranged as
`the display elements 13.
`
`

`
`US 2005/0012821 A1
`
`Jan. 20, 2005
`
`[0056] These display elements 13 are respectively con
`nected to the intersections of the vertical Wirings 14 and the
`horizontal Wirings 15 Which are arranged in matrix form.
`The vertical Wirings 14 are connected to the modulation
`circuit 10, While the horiZontal Wirings 15 are connected to
`the scanning signal generating circuit 11.
`[0057] In this embodiment, the driving method of the
`display panel 12 is passive matrix line sequential driving.
`First, a certain roW of the display panel 12 is selected during
`one horiZontal scanning period of video. A scanning signal
`is applied to the selected roW from the scanning signal
`generating circuit 11 through the corresponding one of the
`horiZontal Wirings 15. In this manner, the scanning signal is
`applied to the display elements connected to the selected
`roW, i.e., 1,280><3 (RGB) display elements.
`[0058] In the meantime, the modulation circuit 10 outputs
`driving signals for the respective display elements (3,840
`display elements) of the selected roW at the same time during
`one selected horiZontal scanning period. The driving signals
`are respectively supplied to the display elements through the
`vertical Wirings 14.
`[0059] Each of the display elements 13 emits light only
`When the above-mentioned scanning signal and driving
`signal are applied at the same time, but does not emit light
`When either one of the scanning signal and the driving signal
`is applied. Accordingly, the 3,840 display elements of the
`selected roW are driven by predetermined driving signals
`and emit light at predetermined luminance. During the next
`one horiZontal scanning period, the next roW is selected, and
`3,840 display elements of the selected roW emit light at
`predetermined luminance in a manner similar to those of the
`previous roW.
`
`[0060] In this embodiment, the modulation method of
`images is pulse Width modulation (PWM). This is intended
`to realiZe gradation representation by changing the pulse
`Width of a voltage to be applied to each display element
`during one horiZontal scanning period. Namely, as the
`gradation of image data becomes larger, the pulse Width of
`applied voltage is made larger to cause a display element to
`emit brighter light. Conversely, as the grayscale of image
`data becomes smaller, the pulse Width of applied voltage is
`made smaller to cause a display element to emit darker light.
`
`[0061] A gradation-luminance characteristic due to PWM
`is shoWn in FIG. 2. As shoWn in FIG. 2, When PWM is
`performed, the gradation-luminance characteristic becomes
`an approximately linear characteristic. In the case of PWM,
`the display elements are made to emit light at predetermined
`luminance, and the time of emission of the display elements
`is modulated. HoWever, in the technical ?eld of display
`devices, even in such a case, the extent of brightness Which
`is obtained as a result is often called luminance in consid
`eration of the case of amplitude modulation, and such usage
`is also adopted in this patent application.
`[0062] (Unevenness Measuring Part)
`[0063] In this embodiment, on the assumption that the
`distribution of unevenness varies during the use of the
`display device 200, the display device 200 is provided With
`a function capable of correcting unevenness in accordance
`With an instruction of a user or the like. The unevenness
`measuring part 20 of this embodiment uses a CCD camera.
`The unevenness measuring part 20 receives an instruction
`
`from the correction value generating part 2, and measures
`the luminance of each of the display elements 13 (the
`luminance of each of the approximate three million display
`elements). During this luminance measurement, the entire
`surface of the display device 200 is made to emit light With
`the same image data, and the luminance of the entire surface
`is collectively measured by the unevenness measuring part
`20. OtherWise, if the resolution of the CCD camera is
`insufficient, the display surface of the display device 200
`may be divided into a plurality of areas so that the luminance
`can be measured a plurality of times.
`
`[0064] Measured luminance data d20 is sent to the cor
`rection value generating part 2, and the correction value
`generating part 2 creates a correction value by calculation.
`
`[0065] In this embodiment, it is assumed that the uneven
`ness measuring part 20 measures luminance; namely, data of
`measured luminance is obtained as data having a correlation
`to luminance. HoWever, data having a correlation to lumi
`nance does not need to be data obtained by directly mea
`suring luminance, and may be any other kind of data that has
`a correlation to luminance, for example, the number of
`emission electrons of each display element or the amount of
`current ?oWing through each display element. Accordingly,
`the invention is not limited to a construction Which has the
`unevenness measuring part 20 like a CCD camera outside
`the display device 200, and can also be applied to a
`construction in Which a display device has an unevenness
`measuring part inside itself.
`
`[0066] (Correction Circuit)
`[0067] The correction circuit 1 Will be described beloW.
`The correction circuit 1 includes the correction value gen
`erating part 2 having the operation part 4 and the table 5, the
`multiplier 3 Which multiplies the correction value d4 out
`putted from the correction value generating part 2 by the
`image data d1, and the sWitch 6 Which effects sWitching
`betWeen the measuring data d6 outputted from the correction
`value generating part 2 and the output d5 of the multiplier 3.
`
`[0068] The correction value d4 for correcting the lumi
`nance unevenness of the display panel 12 is stored in the
`table 5. In accordance With a synchroniZing signal d3, the
`correction value d4 is read from the table 5 and outputted to
`the multiplier 3. The synchroniZing signal d3 is the same
`signal as a synchroniZing signal for the image data d1.
`Accordingly, image data of a predetermined pixel can be
`multiplied by a correction value corresponding to the pixel.
`In FIG. 1, the image data d1 is shoWn by one line, but
`actually includes 3-line data for RGB respectively. Simi
`larly, the correction value d4 also includes 3-line data for
`RGB respectively.
`
`[0069] In the multiplier 3, the respective data for RGB of
`the image data d1 are multiplied by the corresponding RGB
`correction values of the correction value d4. The multiplier
`3 provides the output data d5.
`
`[0070] Symbol d6 denotes measuring image data. In this
`embodiment, the measuring image data d6 is assumed to be
`totally-White, 1/2 grayscale data (for example, 128 grayscale
`levels, if a full grayscale is made of 255 levels).
`
`[0071] Incidentally, the signal d6 need not necessarily be
`supplied from the correction value generating part 2, and
`
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`US 2005/0012821 A1
`
`Jan. 20, 2005
`
`may also be directly supplied to the modulation circuit 10 as
`measuring image data Which is externally created.
`[0072] The sWitch 6 is a sWitch for effecting switching
`betWeen the image data d5 and d6. The sWitch 6 selects and
`outputs the image data d5 When a general television image
`or PC image is to be displayed. The sWitch 6 selects and
`outputs the measuring image data d6 When luminance
`unevenness is to be measured by the unevenness measuring
`part 20. This sWitching is performed by control signals from
`the correction value generating part 2.
`[0073] During the display of a general television image or
`PC image, the correction value generating part 2 outputs the
`correction value d4. HoWever, When the correction value d4
`is to be updated, the correction value generating part 2
`outputs the measuring image data d6 and issues a measure
`ment instruction to the unevenness measuring part 20. Then,
`on the basis of the measured luminance data d20, the
`operation part 4 performs operation processing Which Will
`be described later, and calculates data. Then, the correction
`value stored in the table 5 is updated With this data.
`[0074] In the above description, the unevenness measuring
`part 20 corresponds to index data acquiring means. The
`operation part 4 corresponds to an index data conversion
`circuit, a luminance target value spatial frequency compo
`nent computation circuit, a spatial frequency component
`inverse-conversion circuit, and a correcti