(19) O)
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`Europaisches Patentamt
`
`European Patent Office
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`Office européen des brevets
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`(11)
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`EP 1 424 672 A1
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`(12)
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`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`02.06.2004 Bulletin 2004/23
`
`(51) Intcl.7; GO9G 3/20
`
`(21) Application number: 02447233.4
`
`(22) Dateoffiling: 29.11.2002
`
`
`(84) Designated Contracting States:
`AT BE BG CH CY CZ DE DK EE ES FIFR GB GR
`IE ITLILU MC NLPTSESKTR
`
`Designated Extension States:
`AL LT LV MK RO SI
`
`(72) Inventors:
`¢ Matthijs, Paul
`9810 Eke (BE)
`* Kimpe, Tom
`9000 Gent (BE)
`
`(71) Applicant: BARCO NLV.
`8500 Kortrijk (BE)
`
`(74) Representative: Bird, William Edward etal
`Bird Goen & Co.,
`Klein Dalenstraat 42A
`3020 Winksele (BE)
`
`(54)
`
`Method and devicefor correction of matrix display pixel non-uniformities
`
`The present invention relates to a system and
`(57)
`method for correction of the non-uniformity of pixel light-
`output behaviour present in matrix addressed electronic
`display devices.
`The present invention provides a method for correc-
`tion of nonuniformities of display elements (pixels or
`sub-pixels) in a matrix display, the display being drive-
`able between a maximum and a minimum brightness.
`The method comprises: storing characterisation data
`characterising the light-output response, i.e. luminance
`and/or colour response, of individual display elements
`of the matrix display, the characterisation data repre-
`senting light-outputs of an individual display element as
`a function ofits drive signals, and the characterisation
`
`data being classified into a pre-set number of catego-
`ries, the pre-set numberbeing less than the number of
`display elements in the display and greater than one,
`the characterisation data of at least two display ele-
`ments being assigned to one of the categories, and the
`light-outputs/drive signals relationships represented by
`at least two characterisation data in two different cate-
`
`gories crossing over within the maximum and minimum
`brightness of the display. The method furthermore com-
`prises pre-correcting, in accordancewith the character-
`isation data in the relevant categories, drive signals of
`individual display elements so as to obtain a pre-deter-
`mined spatial light-output of display elements, to there-
`by display an image.
`
`
`
`Printed by Jouve, 75001 PARIS (FR)
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`EP1424672Al
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`Yi
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`EP 1 424 672 A1
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`Description
`
`Technical field of the invention
`
`[0001] The present invention relates to a system and
`method for correction, for example real-time correction,
`of the non-uniformity of pixel
`light-output behaviour
`present in matrix addressed electronic display devices
`such as plasma displays, liquid crystal displays,
`light
`emitting diode (LED) and organic light emitting diode
`(OLED) displays used in projection or direct viewing
`concepts.
`[0002]
`It applies to emissive, transmissive, reflective
`and trans-reflective display technologies fulfilling the
`feature that each pixel is individually addressable.
`
`Background of the invention
`
`[0003] Atpresent, most matrix based display technol-
`ogies are in its technological infancy compared to long
`established electronic image forming technologies such
`as Cathode Ray Tubes. As a result, many domains of
`image quality deficiency still exist and cause problems
`for the acceptance of these technologies in certain ap-
`plications.
`[0004] Matrix based or matrix addresseddisplays are
`composedof individual image forming elements, called
`pixels (Picture Elements), that can be driven (or ad-
`dressed)individually by proper driving electronics. The
`driving signals can switch a pixel to a first state, the on-
`state (luminance emitted, transmitted or reflected), to a
`second state, the off-state (no luminance emitted, trans-
`mitted or reflected). see for example EP-011 7335 which
`describes an LCD. For some displays, one stable inter-
`mediate state betweenthe first and the second state is
`used - see EP-0462619 which also describes an LCD.
`
`For still other displays, one or more intermediate states
`between the first and the second state (modulation of
`the amountof luminance emitted, transmitted or reflect-
`ed) are used - see EP-011 7335. A modification of these
`designs attempts to improve uniformity by using pixels
`made up ofindividually driven sub-pixel areas and to
`have most of the sub-pixels driven either in the on- or
`off-state - see EP-0478043 which also describes an
`
`LCD. One sub-pixel is driven to provide intermediate
`states. Due to the fact that this sub-pixel only provides
`modulation of the grey-scale values determined by se-
`lection of the binary driven sub-pixels the luminosity var-
`iation over the display is reduced.
`[0005]
`A known image quality deficiency existing with
`these matrix based technologies is the unequal light-
`output response of the pixels that make up the matrix
`addresseddisplay consisting of a multitude of such pix-
`els. More specifically, identical electric drive signals to
`various pixels may lead to different light-output of these
`pixels. Current state of the art displays havepixel arrays
`ranging from a few hundred to millions of pixels. The
`observedlight-output differences between (even neigh-
`
`bouring) pixels is as high as 30%(as obtained from the
`formula (minimum luminance - maximum luminance) /
`minimum luminance).
`[0006]
`These differences in behaviour are caused by
`various production processes involved in the manufac-
`turing of the displays, and/or by the physical construc-
`tion of these displays, each of them being different de-
`pending on the type of technologyof the electronic dis-
`play under consideration. As an example, for liquid crys-
`tal displays (LCDs), the application of rubbing for the
`alignment of the liquid crystal (LC) molecules, and the
`colour filters used, are large contributors to the different
`luminance behaviour of various pixels. The problem of
`lack of uniformity of OLED displays is discussed in US-
`20020047568. Such lack of uniformity may arise from
`differencesin the thin film transistors used to switch the
`
`pixel elements.
`[0007] This phenomenon of non-uniform light-outout
`response of a plurality of pixels is disturbing in applica-
`tions where imagefidelity is required to be high, such
`as for example in medical applications, where lumi-
`nancedifferences of about 1% are supposed to have a
`meaning. The unequal light-output responseof the pix-
`els superimposes an additional, disturbing and unwant-
`ed random image on the required or desired image, thus
`reducing the SNR of the resulting image.
`[0008]
`EP-0755042 describes a method and device
`for providing uniform luminosity of a field emission dis-
`play (FED). Non-uniformities of luminance characteris-
`tics in a FED are compensated pixel by pixel. This is
`done by storing a matrix of calibration values, one value
`for each pixel. These calibration values are determined
`by apreviously measured emission efficiency of the cor-
`responding pixels. These calibration values are used for
`correcting the level of the signal that drives the corre-
`sponding pixel. 16 different calibration values are pro-
`posed.
`‘It is a disadvantage of the method described
`[0009]
`in EP-0755042thata linear approach is applied, i.e. that
`a same calibration value is used to correct a drive signal
`of a given pixel, independent of whether a high or a low
`luminance has to be provided. However, pixel
`lumi-
`nancefor different drive signals of a pixel depends on
`physical features of the pixel, and those physical fea-
`tures may not be the same for high or low luminance
`levels. Therefore, pixel non-uniformityis different at high
`or low levels of luminance, and if corrected by applying
`to apixel drive signal asame calibration value independ-
`ent of the drive value correspondsto a high or to a low
`luminancelevel, non-uniformities in the luminance are
`still observed.
`
`Summaryofthe invention
`
`It is an object of the present invention to pro-
`[0010]
`vide a system and a method for correction of non-uni-
`formities in light-output, i.e. in luminosity and/or colour,
`of display elements of a matrix cisplay.
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`EP 1 424 672 A1
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`[0011]=It is a further object of the present invention to data from images captured from individual display ele-
`
`overcome the disadvantages of the prior art solution
`ments. Generating the characterisation data may com-
`mentioned above.
`prise building a display element profile map represent-
`ing characterisation data for each display elementof the
`matrix display. Building a display element profile map
`may comprise storing the display element characterisa-
`tion data in a storage device such as a memory.
`[0017] The pre-correcting may either be carried out in
`real-time or off-line.
`
`[0012] The above objectives are accomplished by a
`method and device according to the present invention.
`[0013] The present invention provides a method for
`correction of non-uniformities of display elements in a
`matrix display. Display elements may be pixels or sub-
`pixels. The method comprises: storing characterisation
`data characterising the non-linear
`light-output
`re-
`sponse, i.e. luminance and/or colour response, ofindi-
`vidual display elements of the matrix display, the char-
`acterisation data representing light-outouts of an indi-
`vidual display element as a function of its drive signals,
`and the characterisation data being classified into a pre-
`set number of categories, the pre-set number being less
`than the number of display elements in the display and
`greater than one, and the characterisation data of at
`least two display elements being assignedto one of the
`categories; and pre-correcting, in accordance with the
`characterisation data in the relevant categories, drive
`signals of individual display elements so as to obtain a
`pre-determined spatial light-output of display elements,
`to thereby display an image. Obtaining a pre-deter-
`mined spatial light-output may comprise compensating
`for unequal light output between different display ele-
`ments, so that, whenall display elements are driven with
`a same level of a drive signal, then all lignht-outputs are
`the same, and the displayed image looks uniform over
`the display. Alternatively, obtaining a pre-determined
`spatial light-output may comprise obtaining a second
`pre-determined non-uniform light-output behaviour of
`display elements, which second light-outoput behaviour
`is different from a first pre-determined non-uniform light-
`output behaviour generated by the non-uniformities of
`the display elements in the matrix display. This may be
`used to pre-correct for non-uniformities of post-process-
`ing systems that are addedto the display, such as, but
`notlimited to, optical systems such as lensesin case of
`projectors, tiled displays, screen magnification lenses,
`etc.
`
`[0014] The non-linear light-output response of a dis-
`play element may comprise its luminance response and/
`or its colour response.
`[0015] The matrix display may be driveable between
`a maximum and a minimum brightness. According to the
`presentinvention, the light-outputs/drive signals rela-
`tionships represented by at least two characterisation
`data in two different categories may be crossing over
`within the maximum and minimum brightnessofthe dis-
`play, i.e. at certain drive levels the light-output response
`of a first pixel is higher than the light-output response of
`a second pixel, while at other drive levels the light-output
`response of the second pixel
`is higher than the light-
`output response ofthe first pixel. This situation cannot
`be dealt with by the prior art solution of EP-0755042.
`[0016]
`A method according to the present invention
`may further comprise generating the characterisation
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`[0018] The present invention also provides a system
`for characterising the light-output response, i.e. lumi-
`nance and/or colour response, of each individual display
`elementof a matrix display, and uses this characterisa-
`tion to pre-correct the driving signals to that display in
`order to obtain that pre-determined drive signals to pre-
`determined display elements generate a pre-deter-
`mined spatial light-output.
`[0019] A system for correction of non-uniformities of
`light-output, i.e. luminance and/or colour, of display el-
`ementsin a matrix display is provided. The method com-
`prises a characterising device for generating character-
`isation data for every individual display element of the
`matrix display by establishing a non-linear relationship
`between light-outputs of each display element and the
`corresponding drive signals, a classifying device for
`classifying the characterisation data into a pre-set
`number of categories, the pre-set number of categories
`being larger than one and smaller than the total number
`of display elements in the display and the characterisa-
`tion dataof at least two display elements being assigned
`to one of the categories; and a correction device for pre-
`correcting, in accordancewith the characterisation data
`in the relevant categories, driving signals to the display
`elements to obtain that pre-determined drive signals to
`pre-determined display elements generate a pre-deter-
`mined spatial light-output of said display elements to
`thereby display an image. The pre-correction may be
`such that equivalent drive signals to different display el-
`ements generate equivalent
`luminance behaviour of
`said display elements. Alternatively, the pre-correction
`may be so as to obtain a pre-determined non-uniform
`light-output behaviour of display elements which is dif-
`ferent from the first non-uniform light-outout behaviour
`generated bythe display elements in the matrix display.
`[0020] This may be used to pre-correct for non-uni-
`formities of post-processing systems that are added to
`the display, such as, but not limited to, optical systems
`such as lenses in case of projectors, tiled displays,
`screen magnification lenses, etc.
`[0021] The characterising device can take various
`forms. The purpose of the characterising deviceis to de-
`fine the light-output response for each individual display
`elementof the matrix addressed display. The light-out-
`put responseis a relationship, e.g. under the form of a
`curve, between a display element's drive signal, and
`that display element's light-output behaviour. Said light-
`output behaviour can be caused by any optical process
`affecting visual light, be it for example, but not limited
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`EP 1 424 672 A1
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`as to be able to storeit and useit in real time correction
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`thereto, reflection, emission, transmission or a combi-
`of the drive applied to the display elements.
`nation of said processes, or an electrical process indi-
`[0028]
`Fromthe light-output response curves, said al-
`rectly defining the optical response of the system.
`gorithms extract key parameters that define the re-
`[0022] The characterising device may comprise an
`sponse of the display elements such as offset, gain,
`image capturing device for generating an image of the
`maximum. Another approach is to extract a limited set
`display elements of the matrix display. The image cap-
`of (light-output; DDL) points of the light-output response
`turing device may comprise for example a scanner, a
`curvethat allow a reconstruction of the original light-out-
`camera, a CCD or photodiode, with adequate spatial
`put response curve. Yet another algorithm will classify
`resolution comparedto the spatial resolution of the ma-
`the measuredlight-output response of a display element
`trix display that needs to be characterised, in order to
`to a limited set of allowed "typical" display elementlight-
`identify the individual display elements. Image process-
`output responses by approximating the actual response
`ing hardware also needs to have enough luminance
`with the best matching "typical" response. All algorithms
`sensitivity and resolution in order to give a precise quan-
`(or a combination of these algorithms) mentioned have
`tisation of the light-output emitted by the display ele-
`in common thatthe vast amountof display element char-
`ments. The image capturing device allows to capture im-
`acterisation data is compressed and prepared to a use-
`agesfrom the individual display elements of the display,
`able format, called the display element profile map
`and this for a variety of test images. The test images are
`(PPM) which is compatible to real time hardware com-
`chosen in a particular wayto allow extraction of the light-
`pensation schemes.
`output response data of display elements later in the
`process.
`[0029] The PPM is describing the relation between
`the input and output of the transfer function of the cor-
`[0023] Thecharacterising device may comprise a dis-
`rection device or transformation system. The input to
`play elementlocation identifying device for identifying
`this correction device are the uncorrected drive signals
`the actual location of individual display elements of the
`defining the light-output of the display elements. The
`matrix display.
`output are the corrected drive signals to the display el-
`[0024] The characterising device described above
`ements. The transformation circuit is implemented in
`delivers various electronic images of arrays of display
`hardware and designed such that transformation (e.g.
`elements. Algorithms isolate the image of each individ-
`correction) of the drive signals can happenin real time,
`ual display element and quantitatively assign a light-out-
`put value to these pixels.
`this is at the pixel frequency of the system under con-
`30
`sideration.
`[0025]_If images of various test images are combined,
`and light-output values of individual display elements
`[0030] Fora good understanding, it is remarked that
`are listed in this way, a non-linearlight-output response
`only the transformation of the display element drive sig-
`curve of each individual display element can be ob-
`nals described in the previous paragraph needs to hap-
`tained. As explained before, the light-output response
`pen in real time. All other processes described (image
`curvewill fix the relationship between the light-outputof
`capturing, defining the PCD and PPM) can happen "off-
`one individual display element as a function ofits drive
`line" in a non real time fashion using infactory methods.
`signal. The drive signal can be expressed using any
`[0031] The characterising device may comprise a
`physical quantity giving a relationship with the intensity
`light-output value assigning device for assigning one
`of the drive applied to the display element. This is tech-
`light-output value to each display element of the matrix
`nology dependent: it is voltage in case of LCD, and cur-
`display.
`rent in case of LED displays. As a generic representa-
`[0032] The present invention furthermore provides a
`tion of said physical quantity digital driving level (DDL)
`matrix display device for displaying an image. The de-
`may be used, which is proportional to current or voltage
`vice comprises: a plurality of display elements, a mem-
`drive and is defined by a digital to analog conversion
`ory for storing characterisation data for every individual
`process.
`display element of the matrix display, the characterisa-
`The actual light-output response curve allows
`[0026]
`tion data representing a relationship between light-out-
`to calculate a drive curve required to obtain alinearlight-
`puts of a display element and its corresponding drive
`output response (or any other desired response) of the
`signals, the characterisation data being divided into a
`display element under consideration. The obtained
`pre-set numberof categories, the number of categories
`drive curvethatwill yield a linear and equal response of
`being less than the number of display elements in the
`an individual display elementis called the display ele-
`matrix display and greater than one and the character-
`ment characterisation data (PCD) of that display ele-
`isation data of at least two display elements being as-
`ment.
`signedto one of the categories; and a correction device
`for pre-correcting, in accordance with the characterisa-
`tion data of the relevant categories, driving signals to
`the display elements so as to obtain a pre-determined
`spatial light-output of the display elements. The correc-
`tion device maybe such thatat least one drive signal to
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`[0027] The PCD of eachindividual display element
`may contain a lot of information that, given its format
`and quantity of data, is not practically applicable for ad-
`aptation of the drive signals. A set of algorithms is used
`to condense or compress the characterisation data so
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`at least two different display elements generates equiv-
`alent luminance behaviour of said two different display
`elements to thereby display an image. Alternatively,if
`the non-uniformities of the display elements in the matrix
`display generatea first non-uniform light-output behav-
`iour of the display elements, the pre-correction may be
`so as to obtain a second pre-determined non-uniform
`light-output behaviour of display elements different from
`the first pre-determined non-uniform light-output behav-
`jour,
`
`[0033] The present invention also provides a control
`unit for use with a system for correction of non-uniform-
`ities of light-output of display elements of a matrix dis-
`play for displaying an image, the matrix display device
`comprising a plurality of display elements. The control
`unit comprises a memory for storing characterisation
`data for every individual display element of the matrix
`display, the characterisation data representing a non-
`linear relationship between light-outputs of a display el-
`ement and its corresponding drive signals, the charac-
`terisation data being divided into a pre-set number of
`categories, the number of categories being less than the
`number of display elements in the matrix display and
`greater than one and the characterisation data of at least
`two display elements being assigned to one of the cat-
`egories. The control unit also comprises means for pre-
`correcting, in accordancewith the characterisation data
`of the relevant categories, driving signals to the display
`elements so as to obtain a pre-determined spatial light-
`outputof the display elements. The pre-determined spa-
`tial light-output maybe suchthatat least one drive signal
`to at
`least two different display elements generates
`equivalent light-output behaviour of said two different
`display elements. Alternatively, ifthe non-uniformities of
`the display elements in the matrix display generate a
`first non-uniform light-output behaviour of the display el-
`ements, the pre-determined spatial lignt-output may be
`such that a second pre-determined non-uniform light-
`output behaviour of display elements different from the
`first pre-determined non-uniform light-output behaviour
`is obtained.
`
`[0034] The present invention furthermore provides a
`computer program product for executing any of the
`methods of the present invention when executed on a
`computing device associated with a system for correc-
`tion of non-uniformities of luminanceof display elements
`in a matrix display. The present invention also provides
`a machine readable data storage device storing the
`computer program productof the present invention. The
`present
`invention also provides transmission of the
`computer program productof the present invention over
`a local or wide area telecommunications network.
`
`[0035] These and other characteristics, features and
`advantages of the presentinvention will become appar-
`ent from the following detailed description, taken in con-
`junction with the accompanying drawings, which illus-
`trate, by way of example, the principles of the invention.
`This description is given for the sake of example only,
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`Inthe different figures, the same referencefig-
`[0037]
`ures refer to the same or analogous elements.
`
`Description of illustrative embodiments
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`[0038] Thepresent invention will be described with re-
`spect to particular embodiments and with reference to
`certain drawings but the invention is not limited thereto
`but only by the claims. The drawings described are only
`schematic and are non-limiting. Inthe drawings, the size
`of some of the elements may be exaggerated and not
`drawn on scale for illustrative purposes. Where the term
`"comprising" is used in the present description and
`claims, it does not exclude other elements or steps.
`[0039]
`Inthe present description, the terms "horizon-
`tal" and "vertical" are used to provide a co-ordinate sys-
`tem and for ease of explanation only. They do not need
`to, but may, refer to an actual physical direction of the
`device.
`
`[0040] Amatrix addressed display comprises individ-
`ual display elements.
`In the present description, the
`term "display elements"is to be understood to comprise
`any form of element which emits light or through which
`light is passed or from whichlight is reflected. A display
`element may therefore be an individually adressable el-
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`withoutlimiting the scope of the invention. The reference
`figures quoted below refer to the attached drawings.
`
`Brief description of the drawings
`
`[0036]
`
`° a
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`T19707107
`omse
`7270
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`illustrates a matrix display having greyscale
`1
`g.
`xels with equal luminance.
`g. 2 illustrates a matrix display having greyscale
`xels with unequal luminance
`g. 3 illustrates a greyscale LCD based matrix dis-
`ay having unequal luminancein subpixels.
`ig. 4 illustrates a first embodiment of an image cap-
`ring device, the image capturing device compris-
`g a flatbed scanner.
`g. 5 illustrates a second embodimentof an image
`apturing device, the image capturing device com-
`rising a CCD camera and a movementdevice.
`g. 6 schematically illustrates an embodiment of an
`gorithm to identify matrix display pixel locations.
`g. 7 shows an example of a luminance response
`urve of an individual pixel, the curve being con-
`structed using eleven characterisation points.
`Fig. 8 is a block-schematic diagram of signal trans-
`formation according to the present invention.
`Fig. 9 illustrates the signal transformation of the di-
`gram of Fig. 8.
`g. 10is agraph showing different examplesof pix-
`response curves.
`g. 11 illustrates an embodimentof a correction cir-
`cuit.
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`ement of an emissive, transmissive, reflective or trans-
`reflective display. Display elements may be pixels, e.g.
`in a greyscale LCD, as well as sub-pixels, a plurality of
`sub-pixels forming one pixel. For example three sub-pix-
`els with a different colour, such as a red sub-pixel, a
`green sub-pixel and a blue sub-pixel may together form
`one pixel in a colour LCD. Wheneverthe word "pixel"is
`used, it is to be understood that the same may hold for
`sub-pixels, unless the contrary is explicitly mentioned.
`[0041]
`The invention will be described with reference
`to flat panel displays but is not limited thereto. It is un-
`derstood that a flat panel display does not have to be
`exactly flat but includes shaped or bent panels. A flat
`panel display differs from display such as a cathode ray
`tube in that it comprises a matrix or array of "cells" or
`"pixels" each producing or controlling light over a small
`area. Arrays of this kind are called fixed format arrays.
`There is a relationship between the pixel of an image to
`be displayed and a cell of the display. Usually this is a
`one-to-one relationship. Each cell may be addressed
`and driven separately. It is not considered a limitation
`on the present invention whether the flat panel displays
`are active or passive matrix devices. The array of cells
`is usually in rows and columnsbut the presentinvention
`is not limited thereto but may include any arrangement,
`e.g. polar or hexagonal. The invention will mainly be de-
`scribed with respect to liquid crystal displays but the
`presentinvention is more widely applicable to flat panel
`displays of different types, such as plasma displays,
`filed emission displays, EL-displays, OLED displays,
`etc.
`In particular the present invention relates not only
`to displays having an arrayoflight emitting elements but
`also displays having arrays of light emitting devices,
`whereby each device is made up of a number ofindivid-
`ual elements. The displays may be emissive, transmis-
`sive, reflective, or trans-reflective displays.
`[0042]
`Further the method of addressing and driving
`the pixel elements of an array is not considereda limi-
`tation on the invention. Typically, each pixel elementis
`addressed by means of wiring but other methods are
`known and are useful with the invention, e.g. plasma dis-
`charge addressing (as disclosed in US 6,089,739) or
`CRIT addressing.
`[0043]
`A matrix addressed display 2 comprises indi-
`vidual pixels. These pixels 4 can take all kinds of
`shapes, e.g. they can take the forms of characters. The
`examples of matrix displays 2 given in Fig.
`1 to Fig. 3
`have rectangular or square pixels 4 arranged in rows
`and columns. Fig. 1 illustrates an image of a perfectdis-
`play 2 having equal luminance response in all pixels 4
`when equally driven. Every pixel 4 driven with the same
`signal renders the same luminance. In contrast, Fig. 2
`and Fig. 3 illustrate different cases wherethe pixels 4 of
`the displays 2 are also driven by equal signals but where
`the pixels 4 render a different luminance, as can be seen
`by the different grey values in the different drawings.
`The spatial distribution of the luminance differences of
`the pixels 4 can be arbitrary.
`It is also found that with
`
`many technologies, this distribution changes as function
`of the applied drive to the pixels indicating different re-
`sponse relationships for the pixels 4. For a low drive sig-
`nal leading to low luminance, the spatial distribution pat-
`tern can differ from the pattern at higher driving signal.
`[0044]
`In orderto be able to correct matrix display pix-
`el non-uniformities, in a first aspect of the present inven-
`tion the ligth-output of each individual pixel has to be
`known, and thus detected.
`[0045] The present invention provides a vision meas-
`urement system, a set-up for automated, electronic vi-
`sion of the individual pixels of the matrix addressed dis-
`play, i.e. for measuring the light-output, e.g. luminance;
`emitted or reflected (depending on the type of display)
`by individual pixels 4, using a vision measurement set-
`up. The vision measurement system comprises an im-
`age capturing device 6, 12 and possibly a movement
`device 5 for moving the image capturing device 6, 12
`and the display 2 with respect to each other. Two em-
`bodiments are given as an example, although other
`electronic vision implementations may be possible
`reaching the same result: an electronic image of the pix-
`els.
`
`[0046] According to afirst embodiment, as represent-
`ed in Fig. 4, the matrix addressed display 2 is placed
`with its light emitting side against an image capturing
`device, for example is placed face down on a flat bed
`scanner 6. The flat bed scanner 6 may be a suitably
`modified documentor film Scanner. The spatial resolu-
`tion of the scanner6 is So as to allow for adequate vision
`of the individual pixels 4 of the display 2 undertest. The
`sensor 8 and image processing hardwareofthe flat bed
`scanner 6 also have enough luminancesensitivity and
`resolution in order to give a precise quantisation of the
`luminance emitted by the pixels 4. For an emissive dis-
`play 2, the light source 10 or lamp of the scanner 6 is
`switched off: the luminance measured is emitted by the
`display2 itself. For a reflective type of display 2, the light
`source 10 or lamp of the scanner 6 is switched on: the
`light emitted by the display 2 is light from the scanner's
`light source 10, modulated by the reflective properties
`of the display 2, and reflected, and is subsequently
`measured by the sensor 8 of the scanner 6.
`[0047] The outputfile of the image capturing device,
`in the embodiment described scanner 6, is an electronic
`image file giving a detailed picture of the pixels 4 of the
`complete electronic display 2.
`[0048] According to a second embodimentofthe vi-
`sion measurement system, as illustrated in Fig. 5, an
`image capturing device, such as e.g. a high resolution
`CCD camera 12, is used to take a picture of the pixels
`4 of the display 2. The resolution of the CCD camera 12
`is so as to allow adequate definition of the individual pix-
`els 4 of the display 2 to be characterised. In the current
`state of the art of CCD cameras, it is not possible to im-
`age large matrix displays 2 at once. As an example, high
`resolution electronic displays 2 with an image diagonal
`of more than 20" require that the CCD camera 12 and
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`11
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`EP 1 424 672 A1
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`12
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`the display 2 are moved with respect to each other, e.g.
`the CCD camera 12 is scanned(in X-Y position) over
`the image surface of the display 2, or vice versa: the
`display 2 is scanned over the sensor area of t