I
`4,966,441
`[11] Patent Number:
`[19]
`United States Patent
`Conner
`[45] Date of Patent:
`Oct. 30, 1990
`
`
`6331-1232 3:: gap“! -
`-
`apan .
`53-195524
`3/1938 Japan ,
`-
`98
`J
`.
`3x98: 1:32: _
`63-286819 11/1988 Japan .
`2024443
`i31x1:i:;ld'Kingdom ............ 350/339 F
`OTHER PUBLICATIONS
`Heilmeier et 211.,
`‘:}111§st—I-Ifiollst Interaction; 1\tIem:tic
`Liquid Cryst
`s,
`ew
`ectro— pt1c
`ec ,”
`p-
`_
`.
`;93111eg2Phys1cs Letters, Aug. 1, 1968, vol. 13, No. 3, pp.
`white et
`al_, “New Absol-pfive Mode Reflective
`Liquid_Cl.ysta1 Display Device,” 10111-11111 of Applied
`Physics, vol. 45, No. 11, Nov., 1974, pp. 4718—4723.
`Schef-fer, Terry’ “New Multicolor Liuid Crystal DiS_
`831% 1*” 35°5:1“:%:‘:1::“:,1‘5::°"£:“:1
`,
`’
`rn
`0
`1e
`,
`-
`.
`-
`1
`N:v., 19071;, 1212- 4799513803-
`y
`_
`t
`L-
`-
`d
`(
`‘St °°"t"‘“e °” “X Page)
`-
`___St
`1
`D_ M'11 ,-
`
`P -
`
`E
`
`. _
`A”"”'eJ" 1439"" 0’ Fm" T°“’“5°"d '3‘ T°W“S°“d
`[57]
`ABSTRACT
`d LCD
`I
`.
`1 d
`_
`pan-
`A color display system {no 11 95 two 00 ore
`els operated in conjunction with a colored filter. One of
`the LCDs may be a primary‘ color, such as red, green or
`h LCD
`b ‘t
`1
`t,
`'.
`.
`Ely: aillsgelxiiiaocgrC3:-ellow, rI:s:>)ect€i=vialSy.c $111: :31: filtcfr
`may be in mosaic form and desirably comprises pixels of
`two subtractive primary colors that are chosen to coop-
`crate with the colored panels to yield a full color dis-
`.
`.
`,
`play. The invention s use of only two stacked panels and
`two colored filter elements y1elds a number of perfor-
`mance and design advantages over pI'lOI‘ art full color
`systems that must rely on three stacked panels or three
`colored filter elements.
`
`_
`_
`15 Claims, 5 Drawmg Sheets
`1 0
`
`.
`
`,
`
`. 28,
`
`[54] HYBRID COLOR DISPLAY SYSTEM
`[75]
`Inventor: Arlie R. Conner, Portland, Oreg.
`.
`.
`[73] Assignee:
`In Focus Systems, Inc., Tualatm,
`0133-
`[21] A991‘ N°" 363399
`[22] Filed‘
`J‘"" 7’ 1989
`Related U.S. Application Data
`.
`.
`-
`-
`.
`.
`,
`,C9‘§;‘_‘““‘’‘‘°“‘“‘’*‘" °f 5°’ N° 329938 M“
`[631
`Int. CL5 ................................................ GUZF 1/13
`[51]
`[52] U.S. C1. .................................... 350/335; 350/337;
`350/339 F
`[58] Field of Search ..................... 350/335, 337, 339 F
`1561
`W
`U.S. PATENT DOCUMENTS
`4,006,968 2/1977 Emstoff et al.
`................. 350/339 F
`4,257,682
`3/1981 Suzuki et al.
`350/349
`4,416,514 ll/1983 Plummet .........
`..... 350/335
`1:13::
`.
`am
`,
`,
`........ 340/805
`3/1987 Takeda etal. ..
`4,651,148
`350/339 F X
`1/1989 Van Raalte
`4,798,441
`......... 350/337
`6/1989 Hunahata et al.
`4,838,655
`6/1989 Oishi et al. ............... 350/335 X
`4,842,379
`8/1989 Iwashita et al.
`350/339 F
`4,859,037
`4,877,309 10/1989 Takamatsu .......................... 350/337
`FOREIGN PATENT DOCUMENTS
`50-110295 3/1975
`1313311 -
`50410297
`3/1975 Japan '
`5365049
`5/1978 Japan '
`54-59162
`5/1979 Japan .
`55459415 12/1980 Japan _
`55.121075
`9/1931 Japan ,
`56-140320 11/1981 Japan .
`53-224375 12/1933
`-“Pan -
`59489317 10/1934 Japan ‘
`'
`59-219719 12/1984 Japan .
`0194-426 10/1985 Japan ................................... 350/335
`60-238815 I1/1985 Japan .
`61-100725
`5/1986 Japan .
`62-125328
`6/1987 Japan .
`62_164024
`7/19877
`Japan _
`
`
`
`.
`
`1 /
`1 1
`1
`\
`\
`\
`1
`YELLOW POLARIZER ;—1—————+—1———r—+/
`YELLOW/WHITE MODE LCD
`7./20
`NEUTRAL POLARIZER Fir...
`1‘
`\\
`1
`/“‘
`BLUE/WHITE MODE LCD
`1280 X 480 STN
`;
`,/18
`
`22
`
`16
`
`\
`
`BLUE POLARIZER
`
`COLOR FILTER LAYE
`EXTERNAL TO CELL
`
`l
`\
`26 \
`28 \
`R 12
`’
`CYAN
`MAGENTA
`30A
`K-32
`
`Light from OHP,
`converging into lens
`VALEO EX. 1015_001
`
`VALEO EX. 1015_001
`
`

`
`4,966,441
`
`Page 2
`
`OTHER PUBLICATIONS
`
`Kotani, et al., “Effect of Various Parameters on Matrix
`Display of SBE—Liquid Crystal Cells,” Japan Display
`’86, pp. 384-386.
`Assouline et al., “Two-Color Liquid-Crystal Display,”
`Electronics Letters, Nov. 18, 1971, vol. 7, No. 23, pp.
`699-700.
`Kawachi, et al., “Light Scatteering Chara cteristics in
`Nematic-Cholesteric Mixtures with Positive Dielectric
`Anisotropy”, Japan Journal of Appl. Phy., vol. 17, No.
`. 7, Jul., ’78, pp. 1245-1250.
`Uchida et al., “Bright Dichroic Guest—Host LCDS
`Without a Polarizer,” Proceedings of the SID, vol.
`22/1, 1981, pp. 41-46.
`Yamagishi, et al., “A Multi-Colored Projection Display
`Using Nematic-Cholesteric Liquid Crystal,”
`1988
`IEEE, pp. 204-207.
`
`Mochizuki, et al., “New Nematic-Cholesteric LCD
`Using Hysteresis Behavior,” Proceedings of the SID,
`1985, vol. 26/4, pp. 243-248.
`Sato, et al., “Novel Multicolor Liquid Crystal Display
`Without Color Filter,” Japan Display ’89, pp. 392-395.
`Uchida, T., “Multicolored Liquid Crystal Displays,”
`Optical Engineering, May/Jun. 1984, vol. 23, No. 3, pp.
`247-252.
`
`Schickel, et al., “Deformation of Nematic Liquid Crys-
`tals With Vertical Orientation in Electrical Fields,”
`Applied Physics Letters, vol. 19, No. 10, Nov. 15, 1971,
`pp. 391-393.
`Iijima, et al., “640><40O Pixels Multicolor STN-LCD
`Using Birefringence Effect,” Japan Display ’89, pp.
`300-302.
`
`IBM Corp., “Twisted Nematic Liquid Crystal Replace-
`ment for Overhead Transparency”, IBM, vol. 29, No.
`11, Apr. 1987.
`
`VALEO EX. 1015_002
`
`VALEO EX. 1015_002
`
`

`
`U.S. Patent
`
` Oct. 30, 1990
`
`Sheet 1 of5
`
`4,966,441
`
`10
`
`A
`
`l
`
`5 /\
`
`22
`
`F|G.1
`YELLOW POLARIZER
`15
`YELLOW/\NHlTE MODE LCD
`NEUTRAL POLARIZER H ._ .._\\ _\...__.)___f—/' 20
`BLUENVHITE MODE LCD ../ ‘4
`
`1280 X 480 STN
`
`\
`
`COLOR FILTER LAYER,
`EXTERNAL TO CELL
`
`‘
`
`26 \
`CYAN
`
`28 \
`\
`MAGENTA
`
`12
`
`Light from OHP,
`converging into lens
`
`YELLOWI
`WHITE
`
` FIG. 2
`
`P|XELON<(i°
`
`FIG. 3
`
`"WHITE"
`
`TUNGSTEN ’ |
`
`CYAN
`
`BLUE K’ BLUE
`
`BLACK
`
`3200°K
`OHP LAMP
`
`IMAGENTA
`
`—>
`
`CYAN
`
`GREEN
`
`CYAN
`BLUE -4 BLACK
`BLUE
`MAGENTA
`V REDMAGENTA
`
`(A)
`
`(8)
`
`VALEO EX. 1015_003
`
`VALEO EX. 1015_003
`
`

`
`U.S. Patent
`
`Oct. 30, 1990
`
`Sheet 2 of 5
`
`4,966,441
`
`4
`
`TRANSMISSION SPECTRUM
`
`BLUE MODE
`
`ON+OFF
`
`IDEAL
`
` TRANSMISSION No
`
`400
`
`600
`500
`WAVELENGTH ( nm )
`
`700
`
`|:|G_ 5
`
`4°
`
`TRANSMISSION SPECTRUM
`YELLOWMODE
`
`IDEAL
`
`__.__[______\|___£__)_____________
`1
`ON
`I/I
`ON+OFF
`I
`I
`I
`I
`
`ON
`
`2 so
`9
`$
`E 20
`3
`
`10
`
`<E
`
`OFF
`
`OFF
`
`ACTUAL
`
`ACTUAL
`
`o______L_(___I
`eoo
`4oo
`5oo
`WAVELENGTH (nm)
`
`700
`
`VALEO EX. 1015_004
`
`VALEO EX. 1015_004
`
`

`
`U.S. Patent
`
`Oct. 30, 1990
`
`Sheet 3 of 5
`
`4,966,441
`
`FIG 5
`
`TRANSMISSION SPECTRUM
`CYAN FILTER
`
`80
`
`O) O
`
`TRANSMISSION N-13-00
`
`
`
`400
`
`500
`
`600
`
`700
`
`800
`
`WAVELENGTH ( nm )
`
`‘
`
`FIG. 7
`100
`
`TRANSMISSION SPECTRUM
`MAGENTA FILTER
`
`(I) O
`
`ACTUAL
`
`
`
`TRANSMISSION A07oo
`
`300
`
`400
`
`500
`
`600
`
`700
`
`800
`
`WAVELENGTH ( nm )
`
`VALEO EX. 1015_005
`
`VALEO EX. 1015_005
`
`

`
`US. Patent
`
`Oct. 30, 1990
`
`Sheet 4 of5
`
`4,966,441
`
`
`E W --
`I--'l“'\ I
`495
`0
`WHITE
`‘ ' I
`5°°
`
`IIWVII
`
`' r
`W1-@l-.4
`
`
`4% AP’ 7' —
`-48°
`0 ‘ -4
`
`I-Imu‘. -
`
`7
`
`460
`
`1
`
`0.2
`
`0.3
`
`0.4
`
`o
`
`.5
`
`0.6
`
`0.7
`
`0.8
`
`
`
`VALEO EX. 1015_006
`
`YELLOW
`
`590
`
`C
`
`
`
`VALEO EX. 1015_006
`
`

`
`U.S. Patent
`
`Oct. 30, 1990
`
`Sheet 5 of5
`
`4,966,441
`
`VALEO EX. 1015_007
`
`VALEO EX. 1015_007
`
`

`
`1
`
`HYBRID COLOR DISPLAY SYSTEM
`
`RELATED APPLICATION DATA
`
`4,966,441
`
`2
`from the following detailed description, which pro-
`ceeds with reference to the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`This application is a continuation-in-part of my co-
`pending application Ser. No. 07/329,938, filed Mar. 28,
`1989.
`
`FIELD OF THE INVENTION
`
`The present invention relates to systems for optically
`displaying color images, and more particularly relates
`to a novel color display system that includes a plurality
`of stacked, light-transmissive panels operating in coop-
`eration with a color mosaic filter.
`
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`
`Much effort has been made in recent years to develop
`low power color displays. Such efforts have generally
`employed LCD panels in one of two configurations. In
`the first configuration, a plurality of differently colored
`LCD panels are stacked and illuminated with white
`light. As the light passes through the stacked layers,
`pixels in each panel act as controllable color filters,
`selectively coloring the light exiting the display.
`While the stacked cell approach can provide a full
`color display, it has certain shortcomings. One is the
`requirement of three LCD panels. This large number
`both increases the cost of the display and reduces its
`light transmissivity. Furthermore, the stacking of cells
`often introduces serious parallax problems which se-
`verely limit the usable viewing angle.
`The second approach uses only a single LCD panel,
`but uses it in conjunction with a mosaic color filter. The
`mosaic filter typically has a plurality of red, green and
`blue filter elements, each aligned with a pixel in the
`LCD panel. (The filter is often fabricated as an integral
`part of the LCD assembly.) By controlling the pixels in
`the LCD panel, the display can pass light through se-
`lected areas of the color mosaic filter.
`While the color mosaic technique addresses certain
`shortcomings of the stacked panel approach, it intro-
`duces certain problems of its own. One is that brightness
`is limited because less than a third of the active area
`transmits light for any given color. Another is that pixel
`density must be increased by a factor of three to obtain
`the same resolution as the stacked cell approach. That
`is, to provide a color display with a horizontal resolu-
`tion of 640 colored pixels, for example, the LCD panels
`must have 1920 pixels, 640 each of red, green and blue.
`This introduces fabrication problems that decrease
`yields and increase panel costs.
`To address these shortcomings of the prior art, the
`present invention adopts a hybrid approach in which
`both stacked panels and color mosaic filters are em-
`ployed. Preferably, only two stacked panels are em-
`ployed, minimizing the problems conventionally associ-
`ated with three panel embodiments. Similarly, only two
`color filter elements are used in the color mosaic filter,
`again minimizing the problems conventionally associ-
`ated with the color mosaic approach. The filter colors
`are desirably selected from the subtractive primaries
`(cyan, magenta, yellow) so as to increase light transmis-
`sion. The filter colors and the colors of the two LCD
`panels are selected so that the two technologies cooper-
`ate to provide a full color display.
`The foregoing and additional features and advantages
`of the present invention will be more readily apparent
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`FIG. 1 is a schematic view of a color display subas-
`sembly according to one embodiment of the present
`invention.
`FIG. 2 is a schematic View illustrating correspon-
`dence between a single pixel in a yellow panel with two
`pixels in a blue panel and two pixels in a color mosaic
`filter in the display subassembly of FIG. 1.
`FIG. 3 illustrates the selective coloring of white light
`by the display subassembly of FIG. 1.
`FIG. 4 is a spectral plot showing ideal and actual
`light transmission characteristics for a blue LCD panel
`used in the display subassembly of FIG. 1.
`FIG. 5 is a spectral plot_ showing ideal and actual
`light
`transmission characteristics for a yellow LCD
`panel used in the display subassembly of FIG. 1.
`FIG. 6 is a spectral plot showing ideal and actual
`light transmission characteristics of cyan filter elements
`used in a color mosaic filter in the display subassembly
`of FIG. 1.
`
`FIG. 7 is a spectral plot showing ideal and actual
`light transmission characteristics of magenta filter ele-
`ments used in a color mosaic filter in the display subas-
`sembly of FIG. 1.
`FIG. 8 is a chromaticity diagram illustrating the color
`gamut achieved with the display subassembly of FIG. 1.
`FIG. 9 is a schematic illustration of a first application
`of the present invention.
`FIG. 10 is a schematic illustration of a second appli-
`cation of the present invention.
`FIG. 11 is a schematic illustration of a variation of the
`FIG. 10 system.
`FIG. 12 is a schematic illustration of another varia-
`tion of the FIG. 10 system.
`DETAILED DESCRIPTION
`
`To provide an enabling disclosure without unduly
`lengthening this specification, applicant incorporates by
`reference the disclosures of U.S. Pat. Nos. 4,547,043,
`4,549,174, 4,652,101, 4,709,990 and 4,763,993 which
`each certain fundamental concepts useful in the con-
`struction of a device according to the present invention.
`Before proceeding, it may be helpful to first review
`certain principles of color optics. The primary light
`colors are generally considered to be red, green and
`blue. White light is composed of all three primaries.
`White light with red filtered therefrom (i.e. removed) is
`termed cyan; white light with green filtered therefrom
`is termed magenta; and white light with blue filtered
`therefrom is termed yellow. These latter colors, cyan,
`magenta and yellow, are sometimes termed subtractive
`primary colors, since they denote the absence of one of
`the primary colors.
`Filters selectively attenuate (or “absorb”) light of
`certain colors and pass light of other colors relatively
`unattenuated. A red filter, for example, attenuates blue
`and green light and lets red light pass. Similarly, a blue
`filter attenuates red and green light and lets blue light
`pass. Finally, a green filter attenuates red and blue light
`and lets green light pass. Filters of the primary colors
`thus subtract two primary colors and let the third pass.
`Filters of the subtractive primary colors subtract one
`primary color and let the two others pass. For example,
`a cyan filter attenuates red light and lets blue and green
`
`VALEO EX. 1015_008
`
`VALEO EX. 1015_008
`
`

`
`4,966,441
`
`3
`light pass. Similarly, a magenta filter attenuates green
`light and lets blue and red light pass. Finally, a yellow
`filter attenuates blue light and lets green and red light
`pass.
`These properties are summarized in Table I.
`TABLE I
`Passes
`Absorbs
`Filter
`Red
`Green, Blue
`Red
`Green
`Red, Blue
`Green
`Blue
`Red, Green
`Blue
`Green, Red
`Blue
`Yellow
`Cyan
`Red
`Blue, Green
`
`Magenta
`Green
`Blue, Red
`
`
`
`10
`
`15
`
`20
`
`25
`
`4
`ing the effect of the twist so that all wavelengths of light
`pass through nearly unaffected,
`i.e. still white. (For
`expository convenience, panel 14 is sometimes called
`the “blue” panel and is said to controllably absorb red
`and green [i.e. yellow] light. It will be recognized, how-
`ever, that this and panel 16 must be operated in conjunc-
`tion with associated front and back polarizers to achieve
`the desired coloring effect.)
`The illustrated second panel 16 is similarly tuned to
`operate as a yellow filter (i.e. absorbing blue) when in its
`deselected state and to pass all wavelengths of light (i.e.
`white light) when in its selected state. It is sometimes
`termed the “yellow” panel.
`It may be noted that, unlike most prior art stacked
`panel displays, the illustrated embodiment includes one
`panel of a primary color (i.e. blue) and one panel of a
`subtractive primary color (i.e. yellow). Their coopera-
`tive relationship to yield a full color display is made
`possible by the color mosaic filter 12, as described be-
`low.
`
`In the illustrated embodiment, the yellow panel 16
`includes a plurality of individually controllable pixels
`regularly arrayed in a 640 by 480 matrix. (In FIG. 1,
`each pixel is illustrated by the pair of electrodes 24 that
`defines it.) The blue panel 14 includes twice as many
`pixels, arrayed in a 1280 by 480 matrix. The blue panel
`is cooperatively positioned with the yellow panel so
`that each pixel of the yellow panel is optically superim-
`posed on two pixels of the blue panel.
`The color mosaic filter 12 is comprised of a plurality
`of cyan and magenta filter elements, 26, 28 respectively,
`regularly arrayed in a 1280 by 480 matrix. The color
`mosaic filter is similarly cooperatively positioned with
`the blue and yellow panels 14, 16 so that each pixel of
`the filter is optically superimposed on one pixel of the
`blue panel, and each pair of pixels in the filter is opti-
`cally superimposed on one pixel in the yellow panel.
`The above-described superimposition relationship is
`illustrated in FIG. 2.
`
`The color mosaic filter 12 may be implemented in a
`number of ways. For example, it may comprise a dyed
`acetate or polyester substrate, aligned during fabrica-
`tion with the other layers, or it may comprise the sur-
`face of one of the polarizer plates on which filter dyes
`are offset or screen printed.
`The fabrication of color mosaic filters is more partic-
`ularly detailed, inter alia, in U.S. Pat. Nos. 4,712,874,
`4,770,525, 4,776,671, 4,773,737, 4,752,771, 4,690,511,
`4,458,175 and 4,653,862, the disclosures of which are
`incorporated herein by reference.
`Inoperation, all light passing through the display
`follows one of two different paths 30 or 32 (FIG. 1).
`The first path 30 is through a cyan filter element 26, the
`blue panel 14 and the yellow panel 16. The second path
`32 is similar but starts with passage through a magenta
`filter element 28 and concludes by passing through the
`blue panel and the yellow panel.
`Light following the first path 30 is first stripped of its
`red component (since the cyan mosaic filter element 26
`attenuates red light). The remaining blue and green
`light next passes through the blue panel 14. If this panel
`is in its deselected state, it acts as a blue filter, passing
`only blue light. If this panel is in its selected state, it
`passes both the blue and green light.
`The light exiting the blue panel 14 then enters the
`yellow panel 16. If the yellow panel is in its deselected
`state, it attenuates blue light, so passes no light if the
`
`VALEO EX. 1015_009
`
`it
`counter-intuitive,
`although somewhat
`Again,
`should be remembered that a blue filter does not filter
`out blue light. It passes blue light and blocks light of
`other colors.
`It should further be noted that the human eye is more
`sensitive to certain wavelengths of light than to others.
`The eye’s response (termed “photopic” response) typi-
`cally peaks at about 554 nanometers and diminishes to
`near negligible values around 400 and 700 nanometers.
`For convenience of discussion, the optical spectrum
`is generally segregated into the red, green and blue
`portions by dividing lines at 500 and 600 nanometers.
`(For physiological reasons, a precise dividing line can-
`not be defined.) Using these boundaries, the human eye
`perceives 55% of the energy in white light from the
`green portion of the spectrum (500 to 600 nm.), 30%
`from the red portion (above 600 nm.), and only 15%
`from the blue portion (below 500 nm.). Perfect green,
`red and blue filters thus transmit 55%, 30% and 15% of
`white light, respectively (photopically). Since yellow,
`cyan and magenta are combinations of these colors, it
`can be seen that yellow, cyan and magenta filters trans-
`mit 85%, 70% and 45% of white light, respectively.
`Referring now to FIG. 1, a display device, or subas-
`sembly, 10 according to one embodiment of the present
`invention includes a color mosaic filter 12, two color
`LCD panels 14, 16, and three polarizers 18, 20, 22.
`Panels 14, 16 used in the illustrated embodiment are
`supertwisted nematic LCD panels that are controllably
`colored by exploitation of the birefringence effect. The
`use of birefringence to control color in LCD panels is
`discussed in U.S. Pat. Nos. 3,876,287, 4,097,128,
`4,127,322, 4,394,069, 4,759,612 and 4,786,146, the disclo-
`sures of which are incorporated by reference. Briefly, in
`birefringence color systems, light of different wave-
`lengths is rotated differing amounts as it passes through
`the liquid crystal material. When the exiting light is
`analyzed by a polarizer, certain color components are
`oriented in a direction that passes through the polarizer,
`and other color components are oriented in directions
`that are attenuated or blocked. This selective filtering of 55
`the optical spectrum by the cooperating polarizers pro-
`duces the color effect.
`
`30
`
`35
`
`45
`
`50
`
`In the illustrated embodiment, the birefringent prop-
`erties of the first panel 14 are “tuned” (by choosing the
`thickness (d) of the liquid crystal layer and its optical
`refractive index anistropy (An)) to rotate the polariza-
`tion of incoming red and green light to a direction in
`which it is absorbed by the exiting polarizer when the
`panel is in its deselected (i.e. deenergized) state. The
`panel 14 and polarizers 18 and 20 thus act as a blue filter
`when the panel is deselected. When the panel is in its
`selected (i.e. energized) state, the liquid crystal mole-
`cules nearly align with the electric field, thereby reduc-
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`blue panel was deselected, and passes only green light if
`the blue panel was selected. If the yellow panel is in its
`selected state, it passes all light, so passes blue light if
`the blue panel was deselected, and passes blue and green
`light (i.e. cyan light) if the blue panel was selected.
`Light following the second path 32 is first stripped of
`its green component (since the magenta mosaic filter
`element 28 attenuates green light). The remaining red
`and blue light next passes through the blue panel 14. If
`this panel is in its deselected state, it acts as a blue filter,
`passing only blue light. If this panel is in its selected
`state, it passes both the blue and red light.
`The light exiting the blue panel 14 then enter the
`yellow panel 16. If this yellow panel is in its deselected
`state, it attenuates blue light, so passes no light if the
`blue panel was deselected, and passes only red light if
`the blue panel was selected. If the yellow panel is in its
`selected state, it passes all light, so passes blue light if
`the blue panel was deselected, and passes blue and red
`light (magenta) if the blue panel was selected.
`The colors resulting from these various combinations
`are illustrated in FIG. 3.
`
`Each of the two paths 30, 32 can produce the colors
`black and blue. The double passage of blue is advanta-
`geous because most incandescent illumination has rela-
`tively less blue energy than energy of other colors.
`Thus, the passage of blue light through both paths acts
`to correct a color imbalance normally inherent with
`incandescent lighting. In particular, tungsten “white”
`or 3200“ K is color corrected by this arrangement to
`5600‘ K.
`
`6
`(which are “leaky”) can be used in certain positions to
`pass more light, improving the brightness and allowing
`color balance improvements.
`Panel 14 is illustrated as being blue when in its dese-
`lected state. Light entering it is polarized by an entrance
`polarizer 18. Normally, all colors of light orthogonal to
`the axis of polarizer 18 would be absorbed by the black
`dye of a conventional, neutral polarizer, resulting in an
`immediate loss of 50% of the light. This loss can be cut
`dramatically if the polarizer 18 is dyed blue. Such a
`polarizer still passes the white light parallel to the polar-
`izer’s axis, but additionally passes blue light orthogonal
`to its axis. This additional blue light is permitted to pass
`to the yellow panel 16 and ultimately contributes to the
`overall brightness of the resulting display, instead of
`being absorbed by the first polarizer as is normally the
`case. The losses normally associated with this first po-
`larizer are thus cut by a third (radiometrically). Display
`brightness improves commensurately.
`The same benefit can be achieved at the exiting end of
`the stacked assembly 10. Panel 16 is illustrated as being
`yellow in its deselected state. By dying the polarizer 22
`adjacent thereto yellow, the red and green light that
`would normally be absorbed thereby is allowed to leak
`through, again improving display brightness.
`In addition to the foregoing benefits, colored polariz-
`ers also ease the design requirements of the LCDs with
`which they are associated. While an LCD designer
`must normally be concerned about the performance of a
`panel across the entire spectrum, the use of a colored
`polarizer with the panel renders the performance at
`certain colors irrelevant. For example, in designing the
`blue panel 14, the designer need not worry about its
`performance in the selected and deselected states in the
`blue portion of the spectrum. The blue polarizer 18 will
`cause the panel to pass blue regardless of its state, so the
`designer can focus on optimizing performance in the
`green and red portions of the spectrum. Similarly with
`the yellow polarizer 22. Since this polarizer will cause
`the yellow panel 16 to pass green and red light regard-
`less of its state, the designer can focus on optimizing
`performance of the panel in the blue portion of the
`spectrum.
`Spectrophotometer plots showing the ideal and ac-
`tual light transmission qualities of panels 14 and 16
`(again, considered in conjunction with their associated
`polarizers) are provided in FIGS. 4 and 5, respectively.
`Panels suitable for use as panels 14, 16 are available
`from Kyocera of Kyoto, Japan or may be fabricated
`using known techniques.
`Spectrophotometer plots showing the ideal and ac-
`tual light transmission qualities of cyan and magenta
`filter elements 26, 28 are provided in FIGS. 6 and 7.
`Suitable filter materials or dyes are available from
`Crompton & Knowles, Brewer Science, Kodak Wrat-
`ten, and Lee Colortran International.
`As can be seen from the foregoing curves, neither the
`passage of light of the desired colors nor the attenuation
`of light of undesired colors is perfect in the actual panels
`and filters. However, the resulting effect is more than
`adequate to provide saturated colors throughout the
`human visual area. A chromaticity diagram illustrating
`the color gamut resulting from these imperfect elements
`(using color illumination) is shown in FIG. 8.
`The foregoing discussion has described only one of
`many possible combinations of panel colors and mosaic
`filter colors. Others can readily be devised. Generally
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`Neither of the paths 30 or 32 by themselves can pro-
`duce yellow or white. However, the human eye can
`average adjoining cyan and magenta pixels to perceive
`white, and can average adjoining green and red pixels to
`perceive yellow. The average of the colors of two ad-
`joining pixels is termed the color of a “super pixel,” of
`which there are 640 across the width of the display.
`This arrangement thus can yield the full gamut of color.
`Table II summarizes the foregoing discussion:
`TABLE II
`After
`Yellow
`Panel
`C (wh)
`M (wh)
`G (yel)
`R (yel)
`C (wh)
`B (wh)
`5 (yel)
`Blk (yel)
`B (wh)
`M (wh)
`Blk (yel)
`R (yel)
`B (wh)
`B (wh)
`Blk (yel)
`Blk (yel)
`
`After
`Filter
`Element
`C
`M
`C
`M
`C
`M
`C
`M
`C
`M
`C
`M
`C
`M
`C
`M
`
`After
`Blue
`Panel
`C (wh)
`M (wh)
`C (wh)
`M (wh)
`C (wh)
`B (b)
`C (wh)
`B (b)
`B (b)
`M (wh)
`B (b)
`M (wh)
`B (b)
`B (b)
`B (b)
`B (b)
`
`
`
`Average
`Wh
`
`Y
`
`C
`
`G
`
`M
`
`R
`
`B
`
`Blk
`
`where B is blue, Blk is black, C is cyan, G is green, M
`is magenta, R is red, W is white and Y is yellow, and the
`colors in parentheses indicate whether a panel pixel is in
`its while (selected) or colored (deselected) states.
`The polarizers 18, 20, 22 used in the illustrated em-
`bodiment are needed to analyze the light passing
`through the liquid crystal panels 14, 16 in order to
`achieve perceptible contrast. In prior art display sys-
`tems, the polarizers are usually neutral (i.e., dyed black
`by iodine). In the present invention, colored polarizers
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`speaking, the preferred embodiments are characterized
`as follows:
`
`the first panel has ZN pixels that pass either all colors,
`or only primary color C;
`the second panel has N pixels that pass either all
`colors, or only a color subtractive primary (A+B);
`the color mosaic filter has N pixels that pass the color
`subtractive primary (A+C), and N more pixels
`that pass the color subtractive primary (B+C);
`(where A, B and C are assigned from the primary
`colors red, green and blue).
`Thus, other embodiments include one in which the
`filter elements are colored magenta and yellow, and the
`panels are colored red and cyan; and a second in which
`the filter elements are colored cyan and yellow, and the
`panels are colored green and magenta.
`One advantage of the present invention is this flexibil-
`ity it offers in possible arrangements. If one of these
`embodiments seems unworkable, a design can be opti-
`mized about another one. For example, if it is found that
`a suitable cyan filter cannot be obtained, then a design
`that does not require a cyan filter can be adopted in-
`stead.
`As noted earlier, the illustrated embodiment is advan-
`tageous due to the color correction it offers with incan-
`descent light. However, these other embodiments have
`their own advantages. The embodiment with magenta
`and yellow filter elements, for example, can advanta-
`geously be used to color compensate fluorescent light,
`which is typically weak in the red portion of the spec-
`trum.
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`Referring now to FIG. 9, in a first application 34 of
`the present invention,
`the display subassembly 10 is
`positioned on the transparent projection surface 36 of a
`conventional overhead projector 38. Such projectors
`typically include an illumination bulb 40 and a Fresnel
`lens 42 under the projection surface to produce light
`beams that pass through a transparency and converge
`onto a projection lens assembly 44. (Due to the short
`focal length and high power required of lens 42, this
`lens is often formed by cementing two or more lower
`powered Fresnel lenses together.)
`When display subassembly 10 is used in the FIG. 9
`application, it is desirable to provide a Fresnel lens 46 to
`collimate the converging light from the projection sur-
`face prior to illumination of the display subassembly.
`The light exiting the subassembly is then refocused by a
`lens 48 (which is also desirably in Fresnel form) onto
`the projection lens assembly 44. (Lens 48 here serves
`the same purpose as the Fresnel lens provided under the
`projection surface of the projector in the projector’s
`normal operation, namely to focus light towards the
`projection lens assembly 44.)
`In another embodiment, no auxiliary Fresnel lenses
`are used. Instead, the pixels on the various layers of the
`display subassembly 10 are spaced with different pitches
`so that the pixels align in proper registration with the
`converging light from the projector’s built-in Fresnel
`lenses 44. This arrangement of pixels is shown in FIG. 1.
`A second application 50 of the display assembly of 60
`the present invention is as a backlit screen for a com-
`puter or the like. In this application, shown in FIG. 10,
`the assembly 10 is illuminated with collimated light, and
`a translucent light dispersing material 52, such as a
`ground glass plate or a commercially available diffusion
`material (i.e. Rolux film manufactured by Rosco of Port
`Chester N.Y.) is mounted adjacent the yellow polarizer
`22 to display the resulting color image. The collimated
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`excitation light can be provided from a relatively low
`wattage bulb 54 in conjunction with a thin lens 56.
`In a related embodiment 50’, shown in FIG. 11, a
`direct view display may be illuminated by a fluorescent
`light panel 57. In such embodiment, the display subas-
`sembly 10 is fabricated with an entrance plate 58 on
`which are formed a plurality of microlenses 60, one
`aligned to each pixel. Light incident on one of micro-
`lenses 60, regardless of its orientation, is directed nor-
`mal to the plane of the display subassembly 10 and thus
`passes through the pixels of the component layers in the
`proper alignment.
`The same arrangement may be used on the exiting
`side of the display. In this case, collimated light exiting
`the subassembly 10 is dispersed by microlenses 62
`which permit the color image to be viewed from a wide
`range of angles without parallax effects. The interstitial
`areas 64 between the lenses may be colored black to
`minimize stray light and to improve perceived contrast.
`Alternatively, a simple light dispersing medium such as
`the ground glass plate 52 shown in FIG. 10 can be used.
`In still a further variation 50" of the direct view appli-
`cation of FIG. 10, the light can be collimated by a novel
`arrangement employing a parabolic mirror 66 (desirably
`in Fresnel form) and a micro-venetian blind material 68.
`As shown in FIG. 12, this embodiment is illuminated by
`a pair of linear light sources, such as fluorescent bulbs
`70. These bulbs illuminate a generally flat mirrored
`surface 72 that has facets arranged to provide one axis
`of collimation. The angles of the facets vary with place-
`ment on the surface to simulate a sectioned parabolic
`reflector. Light reflected from this mirrored surface is
`substantially collimated. However, to remove any stray
`off-axis light, a micro-venetian blind material 68, such as
`Light Control Film marketed by 3M Corp, is desirably
`placed between the mirror and the display subassembly.
`This material is a thin plastic film containing closely
`spaced black microlouvers to absorb light misaligned
`with respect to the louvers. By this arrangement, a very
`compact and efficient display can be provided.
`From the foregoing description, it will be recognized
`that the present invention solves many of the problems
`and deficiencies associated with prior art color display
`technologies. In addition to addressing the parallax and
`brightness problems noted earlier, the