CA1331408C - Apparatus and method for additive/subtractive pixel arrangement in color mosaic displays - Google Patents
Apparatus and method for additive/subtractive pixel arrangement in color mosaic displaysInfo
- Publication number
- CA1331408C CA1331408C CA000603226A CA603226A CA1331408C CA 1331408 C CA1331408 C CA 1331408C CA 000603226 A CA000603226 A CA 000603226A CA 603226 A CA603226 A CA 603226A CA 1331408 C CA1331408 C CA 1331408C
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- Canada
- Prior art keywords
- panel
- image
- pixel units
- liquid crystal
- red
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
- G02F1/13475—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell
Abstract
ABSTRACT
A liquid crystal display unit is described in which a first panel of pixel elements is used to control red and green portions of a displayed image using an additive technique while a second panel, having pixels aligned with the first panel pixels, controls the blue portion of the image through subtractive techniques. The resulting display system can provide enhanced brightness, resolution and color characteristics. The display system makes use of the fact that the eye is less sensitive to blue radiation for several visual parameters. As a result of the deceased sensitivity, the second (blue) panel can operate with less stringent requirements.
A liquid crystal display unit is described in which a first panel of pixel elements is used to control red and green portions of a displayed image using an additive technique while a second panel, having pixels aligned with the first panel pixels, controls the blue portion of the image through subtractive techniques. The resulting display system can provide enhanced brightness, resolution and color characteristics. The display system makes use of the fact that the eye is less sensitive to blue radiation for several visual parameters. As a result of the deceased sensitivity, the second (blue) panel can operate with less stringent requirements.
Description
/r 1 3 3 4 ~
APPARATUS AND METHOD FOR ADDITIVE~SUBTRACTIVE
PIXEL ARRANGEMENT IN COLOR MOSAIC DISPLAYS ~ ~;
BACKGROUND OF THE INV~NTION
1. Fleld of the Inventlon : .
:~ This lnventlon rela~es generally to flat panel color . ;~
dlsplays and, more partlcularly, to dlsplays ln WhlCh the lmage is the result of a mosalc o~ pixel regions.
APPARATUS AND METHOD FOR ADDITIVE~SUBTRACTIVE
PIXEL ARRANGEMENT IN COLOR MOSAIC DISPLAYS ~ ~;
BACKGROUND OF THE INV~NTION
1. Fleld of the Inventlon : .
:~ This lnventlon rela~es generally to flat panel color . ;~
dlsplays and, more partlcularly, to dlsplays ln WhlCh the lmage is the result of a mosalc o~ pixel regions.
2. Description of the_Related Art Llquld crystal mosalc dlsplay technology ls belng developed as a posslble successor to color cathode ray tubes :~
(CRTs) in many display applications, lncludlng those appllca-tlons ln the avlonlcs fleld. Thls technology offers lmportant advantages such as higher rellablllty along wlth reduced power, r~-e .nd _ ~g~t 3u~ ~ ~e cu r nt ~ B
^ -2- ~ 331~
state of development of the liquid crystal technology, capability of this technology for the rendering of an image falls short of the image capability achievable using CRT technology. This invention addresses three specific problem areas still remaining in liquid crystal mosaic displays:
-~ color definition; image resolution; and display brightness. In terms of color definition, the liquid ~; crystal mosaic display color rendition suffers from effects similar to those okserved on a misaligned CRT
.. ~ :
~ display tube. The primary hues, the red, green and -j~ blue colors, do not blend properly. A white line, for example, appears to have multicolored fringes, symptomatic of deficient color synthesis. Part of the problem can be attributed to the symbol generator , ~ .
which controls the formation of graphics on the flat panel. However, part of the problem can also be ~;`
attributed to the display itself, a contribution addressed by this invention.
In terms of image resolution, graphic symbols and lines appear excessively jagged or discontinuous on color mosaic displays, especially when compared with lines drawn on calligràphic color ~CRT systems.
Again part of the image resolution problem can be attributed to the symbol génerator whlle the display panel itself also provides a contribution. A major part o~ the c~ontribution from the display panel is ~ - .
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the result of the presence of blue pixels as part of the display pixel mosaic. Referring now to Fig. lA, the low degree of spatial sensitivity that the human visual system has for blue light as compared to the other primary colors is illustrated. The eye's peak response to blue light occurs at about one half the frequency of peak response for the red radiation and half again the frequency for green radiation. This ` result indicates that blue radiation contributes only a minor amount to image shape and spatial detail. As a result, blue pixels on the display surface of the panel tend to degrade the overall resolution capability~ of color mosaic displays, a feature addressed by the present invention.
15With respect to display brightness, the origin of the problem can be attributed to both the pixel arrangement of the panel and the current backlight ~;"
~6"` ~ technology used in liquid crystal displays. The ; backlight ~technology includés the lamp and the 20 electronics controlling the backlight lamp. The chief figure of merit for achieving a given level of brightness is how much power is needed to achieve that ! brightness level. Research is Ibeing aggressively pursued to make backlight technology ~ 25 more e~ficient.
;~ The present invention,~ however, addresses the brightness problem from a different perspective. Once 1~
~ . .
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~ 3 3 1 ~
again, the pixel arrangement on the surface of the flat panel display can account for a considerable portion of the problem. Blue pixels contribute little to the total perceived luminance of the panel display. The photopic response of the eye accounts for this phenomenon. Figure lB illustrates that red and green radiation provide a larger contribution to perceived brightness than blue radiation. Blue radiation can typically provide only about a ten ~
;lO percent contribution to the overall brightness of the ~ -panel.
Referring next to Figure 2, the effect of having blue pixels occupyin~ space in the pixel arrangement is shown. Wherever a blue pixel is present, the effect on the pattern of pixels is to occlude the perceivable luminance passing through the display surface. No appreciabIe contribution to luminance capability is available at ~the sites of the blue pixels. As a result, these blue pixel regions of Figure 2 can be considered as black regions. These regions occupy thirty percent of useful area in a typical RedjGreen/Blue (RGB) pixel mosaic 1,. f : ' 'I arrangement.
-In order to compete successfully with the cathode~ray tube technology in a multiplicity of applications, the liquid crystal mosaic displays must ~` evolve to the point where they efficiently achieve ~ . :.~ . . .
:, , 1~ ! . . . -5 64159-1080 ~
,, - . , enough brightness to prevent bright sunæhine from washlng out dlsplayed ~nformatlon. Addltlonally, they must also exhibit ~ -~
higher resolutlon and lmproved color mlxture attributes for , . .
hlgher ~uality imagery to be dlsplayed. Achievlng these goals has proven dlfflcult ln the past.
A wlde range of technlques have been lmplemented ln flat panel dlsplay technology to allevlate the problems des- ~ -crlbed above. Listed below ls a descrlptlon of the prlncipal approaches for ~olving color deflnltlon, lmage resolutlon and display brlghtness problems ln the liquid crystal mosaic dis-plays.
~; Generally, color lmage synthesls in llquld crystal ; mosalc dlsplays use elther addltlve or subtractlve technlques.
Additive technlques use spatlal proximity, temporal super- ; ~-posltlon or spatlal superposltlon technlques to mix prlmary hues lnto dlfferent colors. Additlve spatlal proxlmlty methods are the most common approach used ln llquld crystal flat panel technology. Flgure 3 lllustrates the baslc technlque of spa~
tial proxImlty. Small dots (plxels) of prlmary colors, typl- !`~"'~.''~''.'"'' '`'"' cally red, green and blue, are evenly dlspersed across the ~; surface of the flat panel dlsplay. If the dots (pixels) are ~ -small enough and close enough, then the eye fuses or --~
. ' ,', ',. .' `
. ;
.' ~..~'::
i,--,:., -6- 1 3 3 1 ~ ~ 8 integrates the contribution of each color dot together with its neighbors. The additive method can achieve enhanced resolution by making the pixels smaller and more densely packed. Additionally, the differently colored pixels can be arranged into different patterns, in hopes of striking a better fit with the characteristics of the human visual system.
Full color imagery is therefore perceived. Excellent resolution can result because each pixel is capable of full color control and full luminance control.
Additive spatial proximity, the method generally preferred throughout the industry, suffers three serious drawbacks, outlined above in the problem discussion. Color definition is faulty in the case o~ computer generated imayery (unless signal processing methods are usedj resulting in color . ~
`~ fringing and rainbows effects. As the pixels are ;~ made smaller, color integration is improved but light output~is worsened because a~ greater percentage of the~ primary display area gets consumed by address lines and interconnecting conductors. In addition, blue ~oontributes very little to perceived brightness yet consumes typically one quarter to~one third thb ;~ ~ ~ active ~disp1ay area as indicated previously. Blue also detracts from ~resolution capability, limiting `` ~`~ edge definition and image sharpness. ~ The three ~ ~ principall problems with this approach then are~
::
. :~ :
. ~:
,: ";
,~
,, :
_7_ 1 3 3 1 ~ ~ g ' poor color integration and 2) wasked luminance and 3) wasted resolution. -~
In additive temporal superposition methods, the primary hues are rapidly sequenced before the eye.
Figure 4 shows one possible sequence. First, the red portion of the image is flashed on the flat panel display, then the green portion of the image is ; flashed on the flat panel display and, a short time later, the blue portion of the image is flashed on the flat~panel display. Successful color synthesis ~; using this temporal additive technique depends on the limited temporal frequency response of human vision.
If the sequencing; occurs rapidly ~enough, the eye `~
cannot discern the separate primary hues, but, 15 instead, perceives their overàll integrated image. ~-Temporal superposition suffers ~rom smearing effects, jitter and image instability as the observer shifts his viewing posit~ion rapidly ~ or vibration induces similar motion.;~In addition,~todays liquid crystal ~ma~erials exhibit such slow optical response times, rapid~tempora~l~soquenoing using them is virtually impossible.
In additive spatial `superposition methods~
separate ~images,~ each comprised of only one primary ;25 hue, are`optically fused into one full color image.
Typically three images~, corresponding to red, green and blue hues, are~used. These separate images are;
~:
: ~
` ' u~ :
(CRTs) in many display applications, lncludlng those appllca-tlons ln the avlonlcs fleld. Thls technology offers lmportant advantages such as higher rellablllty along wlth reduced power, r~-e .nd _ ~g~t 3u~ ~ ~e cu r nt ~ B
^ -2- ~ 331~
state of development of the liquid crystal technology, capability of this technology for the rendering of an image falls short of the image capability achievable using CRT technology. This invention addresses three specific problem areas still remaining in liquid crystal mosaic displays:
-~ color definition; image resolution; and display brightness. In terms of color definition, the liquid ~; crystal mosaic display color rendition suffers from effects similar to those okserved on a misaligned CRT
.. ~ :
~ display tube. The primary hues, the red, green and -j~ blue colors, do not blend properly. A white line, for example, appears to have multicolored fringes, symptomatic of deficient color synthesis. Part of the problem can be attributed to the symbol generator , ~ .
which controls the formation of graphics on the flat panel. However, part of the problem can also be ~;`
attributed to the display itself, a contribution addressed by this invention.
In terms of image resolution, graphic symbols and lines appear excessively jagged or discontinuous on color mosaic displays, especially when compared with lines drawn on calligràphic color ~CRT systems.
Again part of the image resolution problem can be attributed to the symbol génerator whlle the display panel itself also provides a contribution. A major part o~ the c~ontribution from the display panel is ~ - .
`1 ~
il ` .
1 :
~ _3_ ~ 3 ~
the result of the presence of blue pixels as part of the display pixel mosaic. Referring now to Fig. lA, the low degree of spatial sensitivity that the human visual system has for blue light as compared to the other primary colors is illustrated. The eye's peak response to blue light occurs at about one half the frequency of peak response for the red radiation and half again the frequency for green radiation. This ` result indicates that blue radiation contributes only a minor amount to image shape and spatial detail. As a result, blue pixels on the display surface of the panel tend to degrade the overall resolution capability~ of color mosaic displays, a feature addressed by the present invention.
15With respect to display brightness, the origin of the problem can be attributed to both the pixel arrangement of the panel and the current backlight ~;"
~6"` ~ technology used in liquid crystal displays. The ; backlight ~technology includés the lamp and the 20 electronics controlling the backlight lamp. The chief figure of merit for achieving a given level of brightness is how much power is needed to achieve that ! brightness level. Research is Ibeing aggressively pursued to make backlight technology ~ 25 more e~ficient.
;~ The present invention,~ however, addresses the brightness problem from a different perspective. Once 1~
~ . .
`I I' 'i ~ '' ~
~ 3 3 1 ~
again, the pixel arrangement on the surface of the flat panel display can account for a considerable portion of the problem. Blue pixels contribute little to the total perceived luminance of the panel display. The photopic response of the eye accounts for this phenomenon. Figure lB illustrates that red and green radiation provide a larger contribution to perceived brightness than blue radiation. Blue radiation can typically provide only about a ten ~
;lO percent contribution to the overall brightness of the ~ -panel.
Referring next to Figure 2, the effect of having blue pixels occupyin~ space in the pixel arrangement is shown. Wherever a blue pixel is present, the effect on the pattern of pixels is to occlude the perceivable luminance passing through the display surface. No appreciabIe contribution to luminance capability is available at ~the sites of the blue pixels. As a result, these blue pixel regions of Figure 2 can be considered as black regions. These regions occupy thirty percent of useful area in a typical RedjGreen/Blue (RGB) pixel mosaic 1,. f : ' 'I arrangement.
-In order to compete successfully with the cathode~ray tube technology in a multiplicity of applications, the liquid crystal mosaic displays must ~` evolve to the point where they efficiently achieve ~ . :.~ . . .
:, , 1~ ! . . . -5 64159-1080 ~
,, - . , enough brightness to prevent bright sunæhine from washlng out dlsplayed ~nformatlon. Addltlonally, they must also exhibit ~ -~
higher resolutlon and lmproved color mlxture attributes for , . .
hlgher ~uality imagery to be dlsplayed. Achievlng these goals has proven dlfflcult ln the past.
A wlde range of technlques have been lmplemented ln flat panel dlsplay technology to allevlate the problems des- ~ -crlbed above. Listed below ls a descrlptlon of the prlncipal approaches for ~olving color deflnltlon, lmage resolutlon and display brlghtness problems ln the liquid crystal mosaic dis-plays.
~; Generally, color lmage synthesls in llquld crystal ; mosalc dlsplays use elther addltlve or subtractlve technlques.
Additive technlques use spatlal proximity, temporal super- ; ~-posltlon or spatlal superposltlon technlques to mix prlmary hues lnto dlfferent colors. Additlve spatlal proxlmlty methods are the most common approach used ln llquld crystal flat panel technology. Flgure 3 lllustrates the baslc technlque of spa~
tial proxImlty. Small dots (plxels) of prlmary colors, typl- !`~"'~.''~''.'"'' '`'"' cally red, green and blue, are evenly dlspersed across the ~; surface of the flat panel dlsplay. If the dots (pixels) are ~ -small enough and close enough, then the eye fuses or --~
. ' ,', ',. .' `
. ;
.' ~..~'::
i,--,:., -6- 1 3 3 1 ~ ~ 8 integrates the contribution of each color dot together with its neighbors. The additive method can achieve enhanced resolution by making the pixels smaller and more densely packed. Additionally, the differently colored pixels can be arranged into different patterns, in hopes of striking a better fit with the characteristics of the human visual system.
Full color imagery is therefore perceived. Excellent resolution can result because each pixel is capable of full color control and full luminance control.
Additive spatial proximity, the method generally preferred throughout the industry, suffers three serious drawbacks, outlined above in the problem discussion. Color definition is faulty in the case o~ computer generated imayery (unless signal processing methods are usedj resulting in color . ~
`~ fringing and rainbows effects. As the pixels are ;~ made smaller, color integration is improved but light output~is worsened because a~ greater percentage of the~ primary display area gets consumed by address lines and interconnecting conductors. In addition, blue ~oontributes very little to perceived brightness yet consumes typically one quarter to~one third thb ;~ ~ ~ active ~disp1ay area as indicated previously. Blue also detracts from ~resolution capability, limiting `` ~`~ edge definition and image sharpness. ~ The three ~ ~ principall problems with this approach then are~
::
. :~ :
. ~:
,: ";
,~
,, :
_7_ 1 3 3 1 ~ ~ g ' poor color integration and 2) wasked luminance and 3) wasted resolution. -~
In additive temporal superposition methods, the primary hues are rapidly sequenced before the eye.
Figure 4 shows one possible sequence. First, the red portion of the image is flashed on the flat panel display, then the green portion of the image is ; flashed on the flat panel display and, a short time later, the blue portion of the image is flashed on the flat~panel display. Successful color synthesis ~; using this temporal additive technique depends on the limited temporal frequency response of human vision.
If the sequencing; occurs rapidly ~enough, the eye `~
cannot discern the separate primary hues, but, 15 instead, perceives their overàll integrated image. ~-Temporal superposition suffers ~rom smearing effects, jitter and image instability as the observer shifts his viewing posit~ion rapidly ~ or vibration induces similar motion.;~In addition,~todays liquid crystal ~ma~erials exhibit such slow optical response times, rapid~tempora~l~soquenoing using them is virtually impossible.
In additive spatial `superposition methods~
separate ~images,~ each comprised of only one primary ;25 hue, are`optically fused into one full color image.
Typically three images~, corresponding to red, green and blue hues, are~used. These separate images are;
~:
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3, ~ ' ~:;
-8- 1331~
formed from three separate image sources. The output images of these three sources are then fused by optics into one full color image to be viewed by the observer (cf. Figure 5). Excellent resolution is typical of this approach because each pixel is capable of full color and full luminance control.
Brightness can also be high since three image forming sources are operated in parallel. Additive spatial superposition techniques suffer from complexity problems and performance difficulties. These systems al~o tend to be prohibitively large for many applications, especially those of the aerospace : :,~::
market. Cost generally rises due to the ~act that three separate imaging devices are needed. Then additional hardware must~be used to combine the three :
images. Frequently, this hardware must be extremely precise and rigid to maintain color purity.
;In subtractive display apparatus (illustrated in Fig.~ 6), white (broad band) radiation is passed through ~ suGcessive layers of complimentary ~color filters,~each layer being electrically controlled for absorbing a~well-defined;region of the spectrum.~ By modulating the~ voltage applied to each layer, different portions of the white light spectrum can be 25~ ~occluded or, in~the alternative, be allowed to pass .~, , .
throùgh unimpeded. This spectral control, the ~ ability to withdraw selectively different portions of .''~ ' ~
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' 331~8 ~ :
the spectrum, can be used to synthesize full color imagery. Resolution can be excellent with this approach because full color control is available at the site of each pixel. Subtractive methods suffer from an expected higher cost, parallax effects and ;~ complex methods for color control. At least three and possibly four separate liquid crystal panels are needed to make a subtractive superpositional liquid crystal display. Currently, this additional complexity is viewed as too costly. In addition, parallax can be troublesome using this technique. As the viewing angle is changed with respect to the display, each layer o~ pixels in the panel is viewed from a slightly different position. Pixels on different layers of the display will be observed to move with respect to each other. Lines can vary ~ substantially in perceived thickness, due to head ,:: , motion alone. Effects such as these, which are functions of viewing angle,~are unacceptable for many (e.g., aerospace) appl~lca~ions. Finally, color control~has proven to be particularly troublesome to date. Experiments indicate that, unless better dyes, backlighting or even a fourth layer can be deveiopedl, colors~ cannot be tracked~ over a broad range of ambient lighting conditions. The difficulty lies in ::: ~
the complex interrelationships between hue and ~` luminance. One interferes with the other in a i ' :
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non-linear manner which currently has proven very difficult to predict.
A need has therefore been felt for a liquid crystal display unit that provides increased display brightness, increased image resolution and better color reproduction.
FEATURES OF THE INVENTION
It is an object of the present invention to provide an improved color display device.
10It is a feature of the present invention to provide an improved flat-panel mosaic display device.
It is a further feature of the present invention to provide for green and red color components by spatial proximity of pixels while the blue color component is provided by pixel subtraction.
It is another featùre of the present invention to provide a mosaic display device in which a first panel tranamittlng red ~and ~green light through a c~ mosaic~ of ~ piYels have a second panel allgned ` 20~ therewith through which blue Iight is transmitted in~
a~mosaic;of pixels.
SUMMARY OF THE INVENTION
The~ àforementioned ~and other ~features ~arè
accomplished,;~according~to the present~invention, by providing a~liquid crystal~display system in which a irst panel has liquid crystal pixel elements that control the transmission of red iand green image `.
;~
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~ - 1 1 1 3 3 ~ 64159-10~0 "~, .. .. .
components and a secon~ panel, aligned with the ~lrst panel for which llquid crystal plxel elements control the transmlssion blue lmage components therethrouyh. The first panel controls ~.'s; ` ' . :
~ the red and green color components by addltive spatlal proxlml-..i,.,.`
ty technlques. The second panel controls the blue lmage compo-nent by æubtractlve techniques. Because of the reduced sensi-tlvlty of the eye to blue color components, the pixel array o~
the second panel can have dimlnlshed resolutlon and can have a ~i~, dlminlshed refresh rate compared to the ~lrst panel.
In accordance wlth the present lnventlon there is ~-~
provlded a liquid crystal dlsplay system comprlslng:
flrst panel means for controlllng transmlsslon of red ~; and green image components therethrough; and second panel means for controlllng transmisslon of blue image components therethrough, said second panel compo~
nents being aligned wlth sald red and green image components.
In accordance with the present invention there is -further provlded the method of displaying an lmage, æaid method comprlsing the steps of:
controllably transmitting blue image components -through a second panel ln response to white llght applied -~
thereto; and cohtrollably transmittlng red and green image compo- ;`~ i nents through a first panel, said second panel recelving light from sald second panel.
In accordance wlth the present inventlon, there is `~
further provlded a liquid crystal dlsplay system for providlng an lmage, sald system comprislng~
a source of optlcal radiation; i -`
'' '~ ' .`' ' ~; ::. , .: .
: ~ 331~
lla 64159-1080 a second panel lncluding flrst plurallty of pixel unlts responslve to control signals ~or transmittln~ blue color components of sald lmage along With refl and green components of ~-~
sald optlcal radiation~ and a flrst panel havlng a second and thlrd plurality of plxel unlts responsive to control slgnals, said second plurali- ~;
ty of pixels transmittlng blue radlation and red color image components ln response to radiatlon transmitted through said ~; second panel, sald third plurallty of plxel unlts transmlttlng blue radiatlon and green color lmage components ln response to radlatlon transmltted through sald second panel.
These and other features of the lnvention wlll be understood upon readlng of the ~ollowlng descrlption along with the drawlngs.
BRIEF DESCRIPTION OF T~E DRAWINGS
;~; Flgure lA illustrates the eye's lower spatial fre-quency for blue as compared to other prlmary colors.
Flgure lB lllustrates the reduced sensitlvity to blue radlation as compared to radIation of the other prlmary colors.
; 20 Figure 2 lllustrates the reglons (blue plxels) that do not contrlbute to the mosalc dlsplay luminance.
;; Flgure 3 lllustrates how the eye lntegrates neighbor- -lng pixels to provlde a full color spectrum from prlmary hues. ~ ~
~. i...~.
-12- ~31~
Figure 4A and Figure 4B illustrate temporal integration of a sequence of primary color images to provide a complete image. ;
Figure 5 is a block cliagram illustrating the development of an image using spatial superposition of image portions.
; Figure 6 illustrates a controllable filter for creating a color image by removing selected portion ~-;
. ..
of broad band optical transmission passing ; ~ lO therethrough.
Figure 7 is a schematic diagram of a first panel of an additive/subtractive display panel of the present invention.
Figure 8A illustrates the passband - 15 characteristics of a magenta filter; Figure 8B shows -the passband characteristics of a cyan filter; and 8C
illustrates the passband characteristics of dichroic filter for transmitting blue light.
Figure 9 is a schematic diagram of a second panel of~ the~ additive/subtractive display of the present invention.
Figure~ 10 is a cross-sectional view of the additive~subtractive display system according to the~
, , present invention. ;
Figure ~ll is a table illustrating the colors available with the additive/subtractive display panel F~ of Fig. lOo ~ :
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~-13- 1 33l 4~
Figure 12 is a CIE diagram illustrating the colors that can be achi~ved using the additive subtractive display system of the present invention.
DESC~IPTION OF THE PREFERRED EMBODIMEN~
1. Detailed Descri~tion of the Fiqures Referring now to Fig. 7, a first panel 1 of the additive/subtractive display is shown. The liquid ~
crystal ~display has an MxN matrix of pixels, each ~ ;
pixel being addressed by one of M column conductors 10 and one of N row conductors. The M column conductors ~--~- .
are selected by x-axis column bus drive unit 2 in response to groups of address signals, Wx, and the N
row conductors are selected by y-row bus drive unit 3 $n response to groups of address signals, Wy. The lntersection~of act1vated aolumn oonductors and an activated ~row conductor activates the associated pixels~a}ong the row. Either actiVe~matrix methods ~-or~ multiplexing methods can be used to activate the pixels,~techniqùes~known in the related art. In the 20 ~ ;active~matrix;approach, active~devioes such as thin film transistors;or metal insulator metal~diodes are used as~ switohlng~ or non-linear devices to control~
thè storage~ of ohargè aoross~ each pixel.l ~In multiplexing ~m t:hods,~ ~no~active device is present.
25 ~The~relationships of voltage signals on row bus lines with~respect~to~voltages present on colùmn~bus lines ~controls charge~storage aoross each pixel which in ; ~
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:~; ' ` ~ .
~ ' . '`,'''', -14- ~ 331~
turn controls the state of the pixel (liquid crystal) optically active material. This method depends on the sharp electro-optical threshold of the liquid crystal material itself rather than on the threshold behavior of intervening electronic devices used in active matrices.
Still referring to Fig. 7, the color pixel arrangement of the top layer of the additive subtractive display is illustrated. Pixels of one complimentary primary hue, (magenta filter) pixel 4, for example, are distributed in a checkerboard pattern with pixels of another complimentary primary hue (cyan filter) pixel 5. The checkerboard pattern is~ used by; way of example and is not meant to be ;-~
~limiting. The opticàl passband characteristics of the magenta and cyan filters are shown in Fig. 8A and 8B. No blue primary hue pixels are present in the pixel pattern of the top surface. The use of only magenta and cyan filter pixels leads to the 20~ ~re901ution and brightness advantages described `~
earlier in the~disclosure.
Re~ferring next to Fig. 9, the second panel 6 of the 'additive/subtractive display is shown.l The matrix~is shown with half the number (M/2 x N/2) of 25 rows and columns used in the first panel 1. This ~;~
degraded~resolution is possible because of the lower -spatial resolution capability human vision has for .
-15- 1331~
blue light modulation as compared to red and green light modulation. Except for this spatial resolution difference, the drive units and address waveforms used for second panel 6 can be identical to those used for the first panel 1. Another difference is possible, however. The refre4h rate of images displayed on the second panel 6 can be lowered relative to the refresh rate of the first panel 1 because human vision is less sensitive to blue light in terms of temporal resolution as well as spatial resolution. When red/green images are displayed on a display device whose images decay with time, the ;red/green images need to be refreshed periodically at ~-~
a typidal frequency of 60Hz. This critical fusion 15 ~frequency allows the eye~to integrate ~the flashing ;;~
images~ nto~a~ateady sceDe sbsent of flicker or image deoay.~Blue light~images c D be seen without flicker ~`
at much lower refresh ~frequencies, lOHz~ for example.
This~phenomenon can be~;used to have~ the overall 2Q~ ~effect~o~ ~lowering the~drive requirements for the blue~color~portion of the system.
Y` ~ Still referring ;to~ Fig. 9, the color pixel `~
arrangem-nt~of~the~ ~bottom layer 6 ls~shown.' Each pixel 7~controls~he pa~ssage~of~ blue llght~ through 25~ th-~display.~ Each pixel;can block blue light from passing~through or,~alternatively, can be energized so blue~ light can~`pass through unimpeded. In order , , . ~:
~:..::
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~.
l v to accomplish this, a guest host dichroic liquid crystal material (Merck ZLI2010 for example) is used.
The passband characteristics of this liquid crystal material are shown in Fig. 8c. The passband spectral characteristic is variable and is a function of applied voltage. If voltage of one value is applied, then the passband is g as shown by Fig. 8c. No blue light is allowed to be transmitted. Other spectral components ~red and green), however, can pass through freely, giving this filter a yellow hue when placed before a broad band light source (white light).
When, on the other hand, another appropriate voltage is applied, then all wavelengths, including blue, are ~allowed to pass freely through the dichroic material.
The passband is shown by dotted line 8 plus solid line 9 in Fig. 8c. Therefore, if the second panel 6 is placed before a broad band (white) light source and all the plxels are activated with the appropriate voltage, then the light passed through the second panel 6 ~appears blue-white instead of yellow. To ;obtain~whlte,~one half the pixels in the lower layer ~are activated.~ This activation provides an improved balance of the blue contribution to the overall spectral output. The ability of the bottom layer 6 ~to modulate blue light~on a pixel by pixel basis, yet pass ~other spectral~components ~lS used together with the first panel 1 to produce full color images.
.
~ -17- 1 3 3 1 ~ ~ ~
Referring next to Fig. ~0, the cross section o~
a total additive/subtractive display unit 100 incorporating both the first panel l (of Fig. 7) and the second panel 6 (of Fig. g) is shown. The additive/subtractive display unit 100 inaludes a glass plate 14 and a glas?e plate 13 which enclose a region 16 containing dichroic material combined with a liquid crystal material. The glass plate 13 and filter plate 15, which includes a mosaic of magenta and cyan~ filters, enclose a region ~12 containing a liquid crystal. ~Pixel control devices 10 in region 16 and pixel control devices 11 in region 12 are also -shown. m ose~pixel control devices lO~and ll can be active matrix control~devices (thin film transistors 15~ or metal/insulator/metal~ dlodes for~example) or, alternatively~,~ can~represent the intersection points `~
of~the~row/column~eleotrodes of multiplexed display technology~describad above. The blue control devises lO~;are~;shown~;~with~twice the spaoing and, therefore, 20- ~half`the~resolution~of~the red/green control devices This~redùce~d:~olement~;~spacing~refleots~ the physical differences ~of human vision resolution for r-solving~ colors ~ ~ dedcribed ~ previdusly.
Altornàtively,~`~the~ resolution oP~the second~panel 6 ~ ~ ~ 7'.
~can~bè~identicàl to;that of the~;first~panel l. ~This n cQnfiguration~ has~ the~ effect~ of~adding ~ a~higher degree~of~fault tolerance capability in~addition to : ~:
1 3 ~
increased blue light resolution capability. Several blue panel control devices and their associated blue pixels can be activated simultaneously in this configuration to cover the same area as a lower resolution blue control pixel. ~herefore, some measure of redundancy or immunity to local failure can be achieved. The blue panel control devices lo provide control over each pixel, enabling the additive/aubtractive display to control the passage of blue light over the area of each cell or pixel 7 of Fig. 9 in the matrix of the second panel 6. Each pixel can either permit white light or yellow light to pass through the second panel 6 to the first panel ; 1. The red/green control devices 11 control the passage of light through the top layer 1. The red/green control devices determine whether any light is free to pass through the red-blue (magenta) 4 and green-blue (cyan) 5 filters located on the color filter ~surface of the top panel 1. Consequently, this layer not~only;controls hue but, significantly, controls brightness. Each pixel can be controlled to rPnder gray shades as well as hue. This capability builds on the advantageous methods for renderin~ gray shades established~by additive technology and avoids the distinctly~ complex luminance/chrominance interrelationships manifest in subtractive ` technology, alone.
!
-19- 133~
Re~erring next to Fig. 11, the operating ~:
conditions of pixels in each panel needed to produce :-the display colors listed is shown. For example, if a black pixel 12 is desired, then the condition of ' the second panel 6 is inconsequential because any :light passing through this panel will be blocked by ~-~
the off condition of the magenta and cyan pixels in ;~-' :: :the first panel I. If a white region 13 is desired, ':~
:then one half of the pixels of the second panel 6 10 must be in the~pass "yellow plus blue" (white) state '-and the magenta 4 and cyan 5 pixels in first panel l ;~
Y~:
must be fully ON. Although the panel in actuality '''~
: produces~ only discrete magenta and cyan pixels in '.
this state, the~eye fuses them into white because of ::' the close proximity of these hues.: For this fusion to be successful,:the pixels must be small enough and .:.
close enough~to fall within the:intogration zone of '';
tho eye.~:In order to produco a rod region 14, tho second~ panel ~ must be placed in the yeIlow or minus `::-blue:~stato 9 shown~in~Fig.~8. ~Tho magenta pixels 4 in~:'tho~first panol~l must~bo ON and the cyan ~pixels 5~in tho~dosirod~region;must~be placed in the OFF i~
~`~c~ ;stat~
Roforrlng~next~ to ~Fig. 12, a CIE`color chart '~'' 25~ `illustrating ::the rango of colors which can be ~`
producod:by gray level control of all pixels. If the `:: ` ~blue control pixels 7 of the second panel 6 are '~
, . !
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-20- 1331~8 varied from the pass blue state 8 plus 9 (all wavelengths are passed yielding white) to the block blue state 9, then each magenta pixel 4 moves from the magenta state to red along line 15 and each cyan pixel 5 moves from cyan to green along line 16 shown in Fig. 12. If blue is blocked entirely by pixels on ~; ~ layer 6, and if the cyan pixels 5 are ON and the magenta pixels are varied along a continuum from OFF
to ON, then colors along line segment 17 will be ;10 produced, ending in yellow when the resultant green and red pixels are finally integrated by the eye.
Conversely, if blue is again blocked by the second panel 6, but, this time, the magenta pixels 4 are fully ON and the cyan~plxels 5 are varled from OFF to 15 ~ ON, then~ colors along~ line segment ~8 will be produced. Again the~final color is yel}ow. When all pixels are~allowed~to vary from one extreme state to the other,~all~the colors` within region 19 oan be produced.~ In-~addition, by taking ~advantage of 20 ~additive methods, luminance can be varied as well.
Images;~ can; bè ~shaded,~ shaped and contoured in much the ~same ; manner ~ as is used with additive juxtaposition mechanisms. It is the red/green pixels .:: ~ - : .
of~additive methods~which provide the brightness and ; 25 ~shape~informa~ion. SimilarIy, it is the magenta/cyan pixels of the ~;additlve/subtractive display system which provide the same kind of information.
.,':' ';:
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~::
-21- 1 3 3 ~ ~g 2. operation of the Preferred Embodiment The present invention differs from prior art by tailoring the panel in better accord with the human visual system. Specifically, the invention addresses 5 the fact that human vision relies almost exclusively ~
on non-blue light, the red colors and the green ~ ;
colors, for spatial and intensity information. ~ ;
Further, the invention takes into account the fact ;~
, ~,.
that the eye uses blue light energy almost `
10 exclusively for chromatic information alone. Because -~
..
~; blue light contributes very little to spatial detail and brightness, the invention removes blue light control from the principal display surface and dedicates~ this surface to the brighter and more resolvable red and green pixels. To achieve a wide range of colors, blue light control is placed behind the principal imaging layer, using techniques ; developed recently for the subtractive ` superpositional approach. Together, these two image 20~ planes add~ and subtract light to synthesize higher resolution, higher brightness images with a broad range of colors. The invention combines the ' I ' simpIicity ànd~ superior luminance control o~ onè
approach (additive juxtaposition) with the resolution enhancement of the second~ approach (superpositional subtractive).
By taking better advantage of the human visual ~ ': , ,;
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~ ' .. ,., . , ' ` ' ' ' ' ~ ' ' . ' " ! ' -` 133~40~ 1 system, the display system of the present invention produces up to one third more luminance and resolution capability than predominant methods without incurring the volume and complexity cost of the other methods. Blue pixel control, useful for color synthesis, but wasteful for brightness and image sharpness, is relegated to a secondary surface.
This control leaves the primary display surface free to display the highly useful red and green pixels.
These two display surfac~es are sandwiched together into one compact flat panel display. Because imagery ~ -is not rapidly sequenced as a fuDction of primary hue, the lnv-ntion does not suffer from the temporal anomalies of~ temporal superposition approaches.
Because lt does~;not~require recomblnation optics, it has a size advantage over spatial superposition methods. Finally, because it is primarily an additlve display and uses~ only two~imaging layers with blue on~the~aecondary layer, it delivers more 20~ manageable luminance-~ and color control, less complexity ~ ànd parallax~ stability than the subtractive approach. ~ ~
' - The forego1ng ~;description is included to illustrate the~operation~of~the preferred embodiment and is not meant to limit the scope of the invention.
The scope of the invention~is to be limited only by the ~following~ ~claims. From the foregoing .~ :
~.~
:;
. .
: 1 3 3 1 ~ ~ 8 description, many variations will be apparent to those skilled in the art that would yet be ~
'':
encompassed by the spirit and scope of the invention.
: ' ~
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-8- 1331~
formed from three separate image sources. The output images of these three sources are then fused by optics into one full color image to be viewed by the observer (cf. Figure 5). Excellent resolution is typical of this approach because each pixel is capable of full color and full luminance control.
Brightness can also be high since three image forming sources are operated in parallel. Additive spatial superposition techniques suffer from complexity problems and performance difficulties. These systems al~o tend to be prohibitively large for many applications, especially those of the aerospace : :,~::
market. Cost generally rises due to the ~act that three separate imaging devices are needed. Then additional hardware must~be used to combine the three :
images. Frequently, this hardware must be extremely precise and rigid to maintain color purity.
;In subtractive display apparatus (illustrated in Fig.~ 6), white (broad band) radiation is passed through ~ suGcessive layers of complimentary ~color filters,~each layer being electrically controlled for absorbing a~well-defined;region of the spectrum.~ By modulating the~ voltage applied to each layer, different portions of the white light spectrum can be 25~ ~occluded or, in~the alternative, be allowed to pass .~, , .
throùgh unimpeded. This spectral control, the ~ ability to withdraw selectively different portions of .''~ ' ~
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the spectrum, can be used to synthesize full color imagery. Resolution can be excellent with this approach because full color control is available at the site of each pixel. Subtractive methods suffer from an expected higher cost, parallax effects and ;~ complex methods for color control. At least three and possibly four separate liquid crystal panels are needed to make a subtractive superpositional liquid crystal display. Currently, this additional complexity is viewed as too costly. In addition, parallax can be troublesome using this technique. As the viewing angle is changed with respect to the display, each layer o~ pixels in the panel is viewed from a slightly different position. Pixels on different layers of the display will be observed to move with respect to each other. Lines can vary ~ substantially in perceived thickness, due to head ,:: , motion alone. Effects such as these, which are functions of viewing angle,~are unacceptable for many (e.g., aerospace) appl~lca~ions. Finally, color control~has proven to be particularly troublesome to date. Experiments indicate that, unless better dyes, backlighting or even a fourth layer can be deveiopedl, colors~ cannot be tracked~ over a broad range of ambient lighting conditions. The difficulty lies in ::: ~
the complex interrelationships between hue and ~` luminance. One interferes with the other in a i ' :
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.,,.~ ,", .. , . -~
3314~ ~
non-linear manner which currently has proven very difficult to predict.
A need has therefore been felt for a liquid crystal display unit that provides increased display brightness, increased image resolution and better color reproduction.
FEATURES OF THE INVENTION
It is an object of the present invention to provide an improved color display device.
10It is a feature of the present invention to provide an improved flat-panel mosaic display device.
It is a further feature of the present invention to provide for green and red color components by spatial proximity of pixels while the blue color component is provided by pixel subtraction.
It is another featùre of the present invention to provide a mosaic display device in which a first panel tranamittlng red ~and ~green light through a c~ mosaic~ of ~ piYels have a second panel allgned ` 20~ therewith through which blue Iight is transmitted in~
a~mosaic;of pixels.
SUMMARY OF THE INVENTION
The~ àforementioned ~and other ~features ~arè
accomplished,;~according~to the present~invention, by providing a~liquid crystal~display system in which a irst panel has liquid crystal pixel elements that control the transmission of red iand green image `.
;~
:`: ~
~ `~
~ - 1 1 1 3 3 ~ 64159-10~0 "~, .. .. .
components and a secon~ panel, aligned with the ~lrst panel for which llquid crystal plxel elements control the transmlssion blue lmage components therethrouyh. The first panel controls ~.'s; ` ' . :
~ the red and green color components by addltive spatlal proxlml-..i,.,.`
ty technlques. The second panel controls the blue lmage compo-nent by æubtractlve techniques. Because of the reduced sensi-tlvlty of the eye to blue color components, the pixel array o~
the second panel can have dimlnlshed resolutlon and can have a ~i~, dlminlshed refresh rate compared to the ~lrst panel.
In accordance wlth the present lnventlon there is ~-~
provlded a liquid crystal dlsplay system comprlslng:
flrst panel means for controlllng transmlsslon of red ~; and green image components therethrough; and second panel means for controlllng transmisslon of blue image components therethrough, said second panel compo~
nents being aligned wlth sald red and green image components.
In accordance with the present invention there is -further provlded the method of displaying an lmage, æaid method comprlsing the steps of:
controllably transmitting blue image components -through a second panel ln response to white llght applied -~
thereto; and cohtrollably transmittlng red and green image compo- ;`~ i nents through a first panel, said second panel recelving light from sald second panel.
In accordance wlth the present inventlon, there is `~
further provlded a liquid crystal dlsplay system for providlng an lmage, sald system comprislng~
a source of optlcal radiation; i -`
'' '~ ' .`' ' ~; ::. , .: .
: ~ 331~
lla 64159-1080 a second panel lncluding flrst plurallty of pixel unlts responslve to control signals ~or transmittln~ blue color components of sald lmage along With refl and green components of ~-~
sald optlcal radiation~ and a flrst panel havlng a second and thlrd plurality of plxel unlts responsive to control slgnals, said second plurali- ~;
ty of pixels transmittlng blue radlation and red color image components ln response to radiatlon transmitted through said ~; second panel, sald third plurallty of plxel unlts transmlttlng blue radiatlon and green color lmage components ln response to radlatlon transmltted through sald second panel.
These and other features of the lnvention wlll be understood upon readlng of the ~ollowlng descrlption along with the drawlngs.
BRIEF DESCRIPTION OF T~E DRAWINGS
;~; Flgure lA illustrates the eye's lower spatial fre-quency for blue as compared to other prlmary colors.
Flgure lB lllustrates the reduced sensitlvity to blue radlation as compared to radIation of the other prlmary colors.
; 20 Figure 2 lllustrates the reglons (blue plxels) that do not contrlbute to the mosalc dlsplay luminance.
;; Flgure 3 lllustrates how the eye lntegrates neighbor- -lng pixels to provlde a full color spectrum from prlmary hues. ~ ~
~. i...~.
-12- ~31~
Figure 4A and Figure 4B illustrate temporal integration of a sequence of primary color images to provide a complete image. ;
Figure 5 is a block cliagram illustrating the development of an image using spatial superposition of image portions.
; Figure 6 illustrates a controllable filter for creating a color image by removing selected portion ~-;
. ..
of broad band optical transmission passing ; ~ lO therethrough.
Figure 7 is a schematic diagram of a first panel of an additive/subtractive display panel of the present invention.
Figure 8A illustrates the passband - 15 characteristics of a magenta filter; Figure 8B shows -the passband characteristics of a cyan filter; and 8C
illustrates the passband characteristics of dichroic filter for transmitting blue light.
Figure 9 is a schematic diagram of a second panel of~ the~ additive/subtractive display of the present invention.
Figure~ 10 is a cross-sectional view of the additive~subtractive display system according to the~
, , present invention. ;
Figure ~ll is a table illustrating the colors available with the additive/subtractive display panel F~ of Fig. lOo ~ :
:~ ~
..
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~-13- 1 33l 4~
Figure 12 is a CIE diagram illustrating the colors that can be achi~ved using the additive subtractive display system of the present invention.
DESC~IPTION OF THE PREFERRED EMBODIMEN~
1. Detailed Descri~tion of the Fiqures Referring now to Fig. 7, a first panel 1 of the additive/subtractive display is shown. The liquid ~
crystal ~display has an MxN matrix of pixels, each ~ ;
pixel being addressed by one of M column conductors 10 and one of N row conductors. The M column conductors ~--~- .
are selected by x-axis column bus drive unit 2 in response to groups of address signals, Wx, and the N
row conductors are selected by y-row bus drive unit 3 $n response to groups of address signals, Wy. The lntersection~of act1vated aolumn oonductors and an activated ~row conductor activates the associated pixels~a}ong the row. Either actiVe~matrix methods ~-or~ multiplexing methods can be used to activate the pixels,~techniqùes~known in the related art. In the 20 ~ ;active~matrix;approach, active~devioes such as thin film transistors;or metal insulator metal~diodes are used as~ switohlng~ or non-linear devices to control~
thè storage~ of ohargè aoross~ each pixel.l ~In multiplexing ~m t:hods,~ ~no~active device is present.
25 ~The~relationships of voltage signals on row bus lines with~respect~to~voltages present on colùmn~bus lines ~controls charge~storage aoross each pixel which in ; ~
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`` ~ ' ,',~''' `~ ~
:~; ' ` ~ .
~ ' . '`,'''', -14- ~ 331~
turn controls the state of the pixel (liquid crystal) optically active material. This method depends on the sharp electro-optical threshold of the liquid crystal material itself rather than on the threshold behavior of intervening electronic devices used in active matrices.
Still referring to Fig. 7, the color pixel arrangement of the top layer of the additive subtractive display is illustrated. Pixels of one complimentary primary hue, (magenta filter) pixel 4, for example, are distributed in a checkerboard pattern with pixels of another complimentary primary hue (cyan filter) pixel 5. The checkerboard pattern is~ used by; way of example and is not meant to be ;-~
~limiting. The opticàl passband characteristics of the magenta and cyan filters are shown in Fig. 8A and 8B. No blue primary hue pixels are present in the pixel pattern of the top surface. The use of only magenta and cyan filter pixels leads to the 20~ ~re901ution and brightness advantages described `~
earlier in the~disclosure.
Re~ferring next to Fig. 9, the second panel 6 of the 'additive/subtractive display is shown.l The matrix~is shown with half the number (M/2 x N/2) of 25 rows and columns used in the first panel 1. This ~;~
degraded~resolution is possible because of the lower -spatial resolution capability human vision has for .
-15- 1331~
blue light modulation as compared to red and green light modulation. Except for this spatial resolution difference, the drive units and address waveforms used for second panel 6 can be identical to those used for the first panel 1. Another difference is possible, however. The refre4h rate of images displayed on the second panel 6 can be lowered relative to the refresh rate of the first panel 1 because human vision is less sensitive to blue light in terms of temporal resolution as well as spatial resolution. When red/green images are displayed on a display device whose images decay with time, the ;red/green images need to be refreshed periodically at ~-~
a typidal frequency of 60Hz. This critical fusion 15 ~frequency allows the eye~to integrate ~the flashing ;;~
images~ nto~a~ateady sceDe sbsent of flicker or image deoay.~Blue light~images c D be seen without flicker ~`
at much lower refresh ~frequencies, lOHz~ for example.
This~phenomenon can be~;used to have~ the overall 2Q~ ~effect~o~ ~lowering the~drive requirements for the blue~color~portion of the system.
Y` ~ Still referring ;to~ Fig. 9, the color pixel `~
arrangem-nt~of~the~ ~bottom layer 6 ls~shown.' Each pixel 7~controls~he pa~ssage~of~ blue llght~ through 25~ th-~display.~ Each pixel;can block blue light from passing~through or,~alternatively, can be energized so blue~ light can~`pass through unimpeded. In order , , . ~:
~:..::
~-~: .....
' ~ ~ ' ''''''`'."
~.
l v to accomplish this, a guest host dichroic liquid crystal material (Merck ZLI2010 for example) is used.
The passband characteristics of this liquid crystal material are shown in Fig. 8c. The passband spectral characteristic is variable and is a function of applied voltage. If voltage of one value is applied, then the passband is g as shown by Fig. 8c. No blue light is allowed to be transmitted. Other spectral components ~red and green), however, can pass through freely, giving this filter a yellow hue when placed before a broad band light source (white light).
When, on the other hand, another appropriate voltage is applied, then all wavelengths, including blue, are ~allowed to pass freely through the dichroic material.
The passband is shown by dotted line 8 plus solid line 9 in Fig. 8c. Therefore, if the second panel 6 is placed before a broad band (white) light source and all the plxels are activated with the appropriate voltage, then the light passed through the second panel 6 ~appears blue-white instead of yellow. To ;obtain~whlte,~one half the pixels in the lower layer ~are activated.~ This activation provides an improved balance of the blue contribution to the overall spectral output. The ability of the bottom layer 6 ~to modulate blue light~on a pixel by pixel basis, yet pass ~other spectral~components ~lS used together with the first panel 1 to produce full color images.
.
~ -17- 1 3 3 1 ~ ~ ~
Referring next to Fig. ~0, the cross section o~
a total additive/subtractive display unit 100 incorporating both the first panel l (of Fig. 7) and the second panel 6 (of Fig. g) is shown. The additive/subtractive display unit 100 inaludes a glass plate 14 and a glas?e plate 13 which enclose a region 16 containing dichroic material combined with a liquid crystal material. The glass plate 13 and filter plate 15, which includes a mosaic of magenta and cyan~ filters, enclose a region ~12 containing a liquid crystal. ~Pixel control devices 10 in region 16 and pixel control devices 11 in region 12 are also -shown. m ose~pixel control devices lO~and ll can be active matrix control~devices (thin film transistors 15~ or metal/insulator/metal~ dlodes for~example) or, alternatively~,~ can~represent the intersection points `~
of~the~row/column~eleotrodes of multiplexed display technology~describad above. The blue control devises lO~;are~;shown~;~with~twice the spaoing and, therefore, 20- ~half`the~resolution~of~the red/green control devices This~redùce~d:~olement~;~spacing~refleots~ the physical differences ~of human vision resolution for r-solving~ colors ~ ~ dedcribed ~ previdusly.
Altornàtively,~`~the~ resolution oP~the second~panel 6 ~ ~ ~ 7'.
~can~bè~identicàl to;that of the~;first~panel l. ~This n cQnfiguration~ has~ the~ effect~ of~adding ~ a~higher degree~of~fault tolerance capability in~addition to : ~:
1 3 ~
increased blue light resolution capability. Several blue panel control devices and their associated blue pixels can be activated simultaneously in this configuration to cover the same area as a lower resolution blue control pixel. ~herefore, some measure of redundancy or immunity to local failure can be achieved. The blue panel control devices lo provide control over each pixel, enabling the additive/aubtractive display to control the passage of blue light over the area of each cell or pixel 7 of Fig. 9 in the matrix of the second panel 6. Each pixel can either permit white light or yellow light to pass through the second panel 6 to the first panel ; 1. The red/green control devices 11 control the passage of light through the top layer 1. The red/green control devices determine whether any light is free to pass through the red-blue (magenta) 4 and green-blue (cyan) 5 filters located on the color filter ~surface of the top panel 1. Consequently, this layer not~only;controls hue but, significantly, controls brightness. Each pixel can be controlled to rPnder gray shades as well as hue. This capability builds on the advantageous methods for renderin~ gray shades established~by additive technology and avoids the distinctly~ complex luminance/chrominance interrelationships manifest in subtractive ` technology, alone.
!
-19- 133~
Re~erring next to Fig. 11, the operating ~:
conditions of pixels in each panel needed to produce :-the display colors listed is shown. For example, if a black pixel 12 is desired, then the condition of ' the second panel 6 is inconsequential because any :light passing through this panel will be blocked by ~-~
the off condition of the magenta and cyan pixels in ;~-' :: :the first panel I. If a white region 13 is desired, ':~
:then one half of the pixels of the second panel 6 10 must be in the~pass "yellow plus blue" (white) state '-and the magenta 4 and cyan 5 pixels in first panel l ;~
Y~:
must be fully ON. Although the panel in actuality '''~
: produces~ only discrete magenta and cyan pixels in '.
this state, the~eye fuses them into white because of ::' the close proximity of these hues.: For this fusion to be successful,:the pixels must be small enough and .:.
close enough~to fall within the:intogration zone of '';
tho eye.~:In order to produco a rod region 14, tho second~ panel ~ must be placed in the yeIlow or minus `::-blue:~stato 9 shown~in~Fig.~8. ~Tho magenta pixels 4 in~:'tho~first panol~l must~bo ON and the cyan ~pixels 5~in tho~dosirod~region;must~be placed in the OFF i~
~`~c~ ;stat~
Roforrlng~next~ to ~Fig. 12, a CIE`color chart '~'' 25~ `illustrating ::the rango of colors which can be ~`
producod:by gray level control of all pixels. If the `:: ` ~blue control pixels 7 of the second panel 6 are '~
, . !
`~'`:;` ` ' ' ~,,'.' ` ` .~ ':, :;;::
:`` ~ " ' ",~' , ` ~
~ ....
-20- 1331~8 varied from the pass blue state 8 plus 9 (all wavelengths are passed yielding white) to the block blue state 9, then each magenta pixel 4 moves from the magenta state to red along line 15 and each cyan pixel 5 moves from cyan to green along line 16 shown in Fig. 12. If blue is blocked entirely by pixels on ~; ~ layer 6, and if the cyan pixels 5 are ON and the magenta pixels are varied along a continuum from OFF
to ON, then colors along line segment 17 will be ;10 produced, ending in yellow when the resultant green and red pixels are finally integrated by the eye.
Conversely, if blue is again blocked by the second panel 6, but, this time, the magenta pixels 4 are fully ON and the cyan~plxels 5 are varled from OFF to 15 ~ ON, then~ colors along~ line segment ~8 will be produced. Again the~final color is yel}ow. When all pixels are~allowed~to vary from one extreme state to the other,~all~the colors` within region 19 oan be produced.~ In-~addition, by taking ~advantage of 20 ~additive methods, luminance can be varied as well.
Images;~ can; bè ~shaded,~ shaped and contoured in much the ~same ; manner ~ as is used with additive juxtaposition mechanisms. It is the red/green pixels .:: ~ - : .
of~additive methods~which provide the brightness and ; 25 ~shape~informa~ion. SimilarIy, it is the magenta/cyan pixels of the ~;additlve/subtractive display system which provide the same kind of information.
.,':' ';:
, . ..
~::
-21- 1 3 3 ~ ~g 2. operation of the Preferred Embodiment The present invention differs from prior art by tailoring the panel in better accord with the human visual system. Specifically, the invention addresses 5 the fact that human vision relies almost exclusively ~
on non-blue light, the red colors and the green ~ ;
colors, for spatial and intensity information. ~ ;
Further, the invention takes into account the fact ;~
, ~,.
that the eye uses blue light energy almost `
10 exclusively for chromatic information alone. Because -~
..
~; blue light contributes very little to spatial detail and brightness, the invention removes blue light control from the principal display surface and dedicates~ this surface to the brighter and more resolvable red and green pixels. To achieve a wide range of colors, blue light control is placed behind the principal imaging layer, using techniques ; developed recently for the subtractive ` superpositional approach. Together, these two image 20~ planes add~ and subtract light to synthesize higher resolution, higher brightness images with a broad range of colors. The invention combines the ' I ' simpIicity ànd~ superior luminance control o~ onè
approach (additive juxtaposition) with the resolution enhancement of the second~ approach (superpositional subtractive).
By taking better advantage of the human visual ~ ': , ,;
```` `: `' '", ` ' ''.
~ ' .. ,., . , ' ` ' ' ' ' ~ ' ' . ' " ! ' -` 133~40~ 1 system, the display system of the present invention produces up to one third more luminance and resolution capability than predominant methods without incurring the volume and complexity cost of the other methods. Blue pixel control, useful for color synthesis, but wasteful for brightness and image sharpness, is relegated to a secondary surface.
This control leaves the primary display surface free to display the highly useful red and green pixels.
These two display surfac~es are sandwiched together into one compact flat panel display. Because imagery ~ -is not rapidly sequenced as a fuDction of primary hue, the lnv-ntion does not suffer from the temporal anomalies of~ temporal superposition approaches.
Because lt does~;not~require recomblnation optics, it has a size advantage over spatial superposition methods. Finally, because it is primarily an additlve display and uses~ only two~imaging layers with blue on~the~aecondary layer, it delivers more 20~ manageable luminance-~ and color control, less complexity ~ ànd parallax~ stability than the subtractive approach. ~ ~
' - The forego1ng ~;description is included to illustrate the~operation~of~the preferred embodiment and is not meant to limit the scope of the invention.
The scope of the invention~is to be limited only by the ~following~ ~claims. From the foregoing .~ :
~.~
:;
. .
: 1 3 3 1 ~ ~ 8 description, many variations will be apparent to those skilled in the art that would yet be ~
'':
encompassed by the spirit and scope of the invention.
: ' ~
` ~ . ~:,, :'~ `" '';
~, ... ,.. , ~
Claims (20)
1. A liquid crystal display system comprising:
first panel means for controlling transmission of red and green image components therethrough; and second panel means for controlling transmission of blue image components therethrough, said second panel components being aligned With said red and green image components.
first panel means for controlling transmission of red and green image components therethrough; and second panel means for controlling transmission of blue image components therethrough, said second panel components being aligned With said red and green image components.
2. The liquid crystal display system of Claim 1 wherein said first panel means controls said red and green image components by additive spatial proximity techniques and wherein said second panel means controls said blue image components by subtractive techniques.
3. The liquid crystal display system of Claim 2 wherein image resolution is determined by said red and green image components.
4. The liquid crystal display system of Claim 2 wherein said first panel includes a first plurality of controllable liquid crystal pixel units for controlling transmission of red color components therethrough and wherein said first panel includes a second plurality of controllable liquid crystal pixel units for controlling transmission of green color components therethrough.
5. The liquid crystal display unit of Claim 4 wherein said second panel includes a third plurality of controllable liquid crystal pixel units, each of said third plurality of pixel units aligned with a plurality of first panel pixel units.
6. The liquid crystal display unit of Claim 5 wherein brightness parameters of an image are controlled by said first panel pixel units.
7. The liquid crystal display unit of Claim 6 wherein said first, second and third pluralities of pixel units are controlled using matrix addressing techniques.
8. The method of displaying an image, said method comprising the steps of:
controllably transmitting blue image components through a second panel in response to white light applied thereto; and controllably transmitting red and green image components through a first panel, said second panel receiving light from said second panel.
controllably transmitting blue image components through a second panel in response to white light applied thereto; and controllably transmitting red and green image components through a first panel, said second panel receiving light from said second panel.
9. The method of displaying an image of Claim 8 wherein said first and said second panel include liquid crystal pixel units, a first plurality of pixel units of said first panel controlling transmission red image components, a second plurality of pixel units of said first panel controlling transmission of red image components, the method further comprising the step of visually integrating light through proximate red pixel units and green pixel units.
10. The method of displaying an image of Claim 9 further comprising the step of controlling transmission of light through pixel units of said first panel by address control networks.
11. The method of displaying an image of Claim 10 wherein pixel units of said second panel are at least as large as pixel units of said first panel, said method further comprising the step of aligning said first and said second panel radiation transmitted through a pixel unit of said second panel is transmitted through a plurality of pixel units of said first panel.
12. The method of displaying an image of Claim 11 further comprising the step of controlling a brightness of said image by controlling an amount of radiation transmitted by said first panel.
13. The method of displaying an image of Claim 12 further comprising the step of controlling image resolution by a structure of said red and green pixel units.
14. A liquid crystal display system for providing an image, said system comprising:
a source of optical radiation;
a second panel including first plurality of pixel units responsive to control signals for transmitting blue color components of said image along with red and green components of said optical radiation; and a first panel having a second and third plurality of pixel units responsive to control signals, said second plurality of pixels transmitting blue radiation and red color image components in response to radiation transmitted through said second panel, said third plurality of pixel units transmitting blue radiation and green color image components in response to radiation transmitted through said second panel.
a source of optical radiation;
a second panel including first plurality of pixel units responsive to control signals for transmitting blue color components of said image along with red and green components of said optical radiation; and a first panel having a second and third plurality of pixel units responsive to control signals, said second plurality of pixels transmitting blue radiation and red color image components in response to radiation transmitted through said second panel, said third plurality of pixel units transmitting blue radiation and green color image components in response to radiation transmitted through said second panel.
15. The liquid crystal display system of Claim 14 wherein a brightness of said image is controlled by radiation through said first panel.
16. The liquid crystal display system of Claim 14 wherein said second panel pixel units are at least as large as said first panel pixel units, a second panel pixel unit transmitting radiation transmitted by a plurality of pixel units of said first panel.
17. The liquid crystal display system of Claim 16 wherein said second panel includes a dichroic material and a liquid crystal material along with a first plurality of control elements and said first panel includes a liquid crystal material, a mosaic of red/blue and green/blue filters and a first and second plurality of control elements.
18. The liquid crystal display system of Claim 17 wherein colors of said image are obtained by combining radiation transmitted through a plurality of proximate first panel pixel units.
19. The liquid crystal display system of Claim 18 wherein image resolution is determined by said first panel pixel units.
20. The liquid crystal display system of Claim 19 wherein a white color is provided by activating neighboring green and red pixel units.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/211,827 US4886343A (en) | 1988-06-20 | 1988-06-20 | Apparatus and method for additive/subtractive pixel arrangement in color mosaic displays |
| US07/211,827 | 1988-06-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1331408C true CA1331408C (en) | 1994-08-09 |
Family
ID=22788505
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000603226A Expired - Fee Related CA1331408C (en) | 1988-06-20 | 1989-06-19 | Apparatus and method for additive/subtractive pixel arrangement in color mosaic displays |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4886343A (en) |
| EP (1) | EP0347790B1 (en) |
| JP (1) | JP2797199B2 (en) |
| CA (1) | CA1331408C (en) |
| DE (1) | DE68913084T2 (en) |
| ES (1) | ES2050188T3 (en) |
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-
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- 1989-06-19 DE DE68913084T patent/DE68913084T2/en not_active Expired - Fee Related
- 1989-06-19 EP EP89111071A patent/EP0347790B1/en not_active Expired - Lifetime
- 1989-06-19 ES ES89111071T patent/ES2050188T3/en not_active Expired - Lifetime
- 1989-06-19 CA CA000603226A patent/CA1331408C/en not_active Expired - Fee Related
- 1989-06-20 JP JP1155995A patent/JP2797199B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0347790B1 (en) | 1994-02-16 |
| EP0347790A3 (en) | 1990-08-22 |
| JP2797199B2 (en) | 1998-09-17 |
| EP0347790A2 (en) | 1989-12-27 |
| ES2050188T3 (en) | 1994-05-16 |
| US4886343A (en) | 1989-12-12 |
| JPH02110430A (en) | 1990-04-23 |
| DE68913084T2 (en) | 1994-07-14 |
| DE68913084D1 (en) | 1994-03-24 |
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