Electro-optical display having a color filter array for reducing visible texture patterns in a displayed image
Patent Information
- Application Number
- KR1020267028168
- Authority / Receiving Office
- KR · KR
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-03-06
- Filing Date
- 2025-03-06
- Publication Date
- 2026-09-21
Smart Images
Figure P1020267028168_ABST
Abstract
Description
Technology Field
[0001] Cross-reference regarding related applications
[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 561,909, filed March 6, 2024, titled “Electro-Optic Displays with Color Filter Arrays for Reducing Visible Texture Patterns in Displayed Images,” the entirety of which is incorporated herein by reference. Background Technology
[0003] The present invention relates to an electro-optical display and a color filter array used in such a display configured to reduce a visible texture pattern in a displayed image.
[0004] The term “electro-optic,” as applied to materials or displays, is used herein in the customary sense in the field of imaging technology to refer to a material having at least first and second display states with at least one optical property that is different, and which changes from its first display state to its second display state by the application of an electric field to the material. The optical property is typically a color that can be perceived by the human eye, but it may also be another optical property such as optical transmittance, reflectance or luminescence, or, in the case of a machine-readable display, a pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible light range.
[0005] The terms bistable and bistable are used herein in the customary sense in the art to refer to a display comprising a display element having first and second display states having at least one optical characteristic that is different, so as to refer to a display in which, after any given element is driven, its first or second display state is assumed by an addressing pulse of finite duration, and after the addressing pulse is terminated, said state is to be sustained at least several times, e.g., at least four times, which is the minimum duration of the addressing pulse required to change the state of the display element. For example, U.S. Patent No. 7,170,670 describes that some particle-based electrophoretic displays capable of grayscale are stable in their extreme grayscale states as well as in intermediate grayscale states, and the same is true for some other types of electro-optical displays. While it is appropriate to call this type of display “multi-stable” rather than bistable, for convenience, the term “bistable” is used herein to encompass both bistable and multi-stable displays.
[0006] There are various types of electro-optical displays, one of which is a rotating bichromatic element display as described, for example, in U.S. Patent Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071; 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791. (This type of display is often referred to as a “rotating bichromatic ball” display, but the term “rotating bichromatic element” is preferred as more accurate because in some of the aforementioned patents, the rotating element is not spherical.) Such displays use a plurality of small bodies (typically spherical or cylindrical) having two or more sections with different optical properties and an internal dipole. These bodies are suspended within liquid-filled vacuoles within a matrix, and the vacuoles are filled with liquid to allow the bodies to rotate freely. By applying an electric field to the display, the appearance of the display is changed, thereby rotating the body into various positions and changing which section of the body is visible through the viewing surface. This type of electro-optical medium is typically bistable.
[0007] Another type of electro-optical display uses an electrochromic medium, such as a nanochromic film comprising an electrode formed of at least partially semiconducting metal oxide and a plurality of reversibly color-changing dye molecules attached to the electrode, see, for example, O'Regan, B., et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patent Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.
[0008] Another type of electro-optical display is the electro-wetting display developed by Philips and described in Hayes, RA, et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 demonstrates how such an electro-wetting display can be made bistable.
[0009] Another type of electro-optical display is the particle-based electrophoretic display (EPD), in which multiple charged particles move through a suspension fluid under the influence of an electric field. Electrophoretic displays have been the subject of intensive research and development for many years. Compared to liquid crystal displays, these displays can possess properties such as good brightness and contrast, a wide viewing angle, state bistable, and low power consumption.
[0010] As mentioned above, the electrophoretic medium requires the presence of a suspended fluid. In most conventional electrophoretic media, this suspended fluid is a liquid, but the electrophoretic medium can be produced using a gaseous suspended fluid; see, for example, Kitamura, T., et al., Electrical toner movement for electronic paper-like display, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., Toner display using insulative particles charged triboelectrically, IDW Japan, 2001, Paper AMD4-4. Also see European patent applications 1,429,178; 1,462,847; and 1,482,354; and international applications WO 2004 / 090626; WO 2004 / 079442; WO 2004 / 077140; WO 2004 / 059379; See WO 2004 / 055586; WO 2004 / 008239; WO 2004 / 006006; WO 2004 / 001498; WO 03 / 091799; and WO 03 / 088495. These gas-based electrophoretic media appear to be susceptible to the same type of problem as liquid-based electrophoretic media due to particle sedimentation, for example, when the medium is used in an orientation that allows such sedimentation, such as when the medium is placed in a vertical plane. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of the gas suspension fluid compared to the liquid case enables faster sedimentation of electrophoretic particles.
[0011] As mentioned above, electrophoretic media require the presence of a fluid. In most conventional electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using a gaseous fluid; see, for example, Kitamura, T., et al., Electrical toner movement for electronic paper-like display, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., Toner display using insulative particles charged triboelectrically, IDW Japan, 2001, Paper AMD4-4. Also see U.S. Patent Nos. 7,321,459 and 7,236,291. These gas-based electrophoretic media appear to be susceptible to the same type of problem as liquid-based electrophoretic media due to particle precipitation when the medium is used in an orientation that allows such precipitation, for example, in a display where the medium is placed in a vertical plane. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of gaseous suspensions compared to liquids enables faster sedimentation of electrophoretic particles.
[0012] Numerous patents and applications assigned to or in the names of MIT (Massachusetts Institute of Technology) and E Ink Corporation describe various technologies used for encapsulated electrophoresis and other electro-optical media. These encapsulated media comprise numerous small capsules, each capsule comprising an inner phase containing electrophoretic transport particles in a fluid medium and a capsule wall surrounding the inner phase. Typically, the capsules themselves are immobilized within a polymerizable binder to form a coherent layer positioned between two electrodes. The technologies described in these patents and applications include the following:
[0013] (a) Electrophoretic particles, fluids and fluid additives; see, e.g., U.S. Patent No. 7,002,728;
[0014] (b) capsules, binders, and encapsulation processes; see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719;
[0015] (c) Microcell structure, wall material and method for forming a microcell; see, e.g., U.S. Patent Nos. 7,072,095 and 9,279,906;
[0016] (d) a method for filling and sealing microcells; see, for example, U.S. Patent No. 7,715,088 and U.S. Patent Application Publication No. 2002 / 0188053;
[0017] (e) Films and subassemblies comprising electro-optical materials; see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564;
[0018] (f) backplanes, adhesive layers and other auxiliary layers and methods used in displays; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;
[0019] (g) Color formation and color adjustment; see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564;
[0020] (h) a method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;
[0021] (i) Applications of displays; see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348; and
[0022] (j) non-electrophoretic displays as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of encapsulation and microcell technology other than displays; see, e.g., U.S. Patent Application Publications No. 2015 / 0005720 and 2016 / 0012710.
[0023] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium may be replaced by a continuous phase, and thus the electrophoretic medium may produce a so-called polymer-dispersed EPD comprising multiple discrete droplets of the electrophoretic fluid and a continuous phase of the polymerizable material, and that the discrete droplets of the electrophoretic fluid within such a polymer-dispersed EPD may be regarded as capsules or microcapsules even if the discrete capsule membrane is not associated with each individual droplet; refer, for example, to the aforementioned U.S. Patent No. 6,866,760. Accordingly, for the purposes of this application, such a polymer-dispersed electrophoretic medium is considered a subspecies of an encapsulated electrophoretic medium.
[0024] A related type of EPD is the so-called microcell EPD. In a microcell EPD, charged particles and fluids are not encapsulated within microcapsules but are instead retained within a carrier medium, typically within a plurality of cavities formed within a polymerizable film. For example, see U.S. Patent Nos. 6,672,921 and 6,788,449.
[0025] Electrophoretic media are often opaque (e.g., because in many electrophoretic media, particles substantially block the transmission of visible light through a display) and operate in a light absorption mode or a light reflection mode. However, electrophoretic devices can also be manufactured to operate in a so-called "shutter mode" in which one display state is substantially opaque and one display state is substantially light-transmitting. For example, see the aforementioned U.S. Patent Nos. 6,130,774 and 6,172,798, and U.S. Patent Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but depend on variations in electric field intensity, can also operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optical displays can also operate in shutter mode. In particular, when this "shutter mode" electrophoretic device is configured on a transparent substrate, it is possible to control the transmission of light through the device.
[0026] Encapsulated or microcell electrophoretic displays typically do not suffer from the problems caused by clustering and deposition failure modes of traditional electrophoretic devices and offer additional advantages, such as the ability to print or coat displays on various flexible and rigid substrates. (The use of the word “print” is intended to include all forms of printing and coating, including but not limited to pre-measurement coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, and curtain coating; roll coatings such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition; and other similar techniques.) Thus, the resulting display can be flexible. Additionally, because the display medium can be printed (using various methods), the display itself can be manufactured at a low cost.
[0027] Other types of electro-optical media may also be used in the display of the present invention.
[0028] Many types of electro-optical media are essentially monochrome in the sense that any given medium has two extreme optical states (white state (WS) and dark state (DS)) and a gray level range between the two extreme optical states. The two extreme optical states do not necessarily have to be black and white. For example, one extreme optical state could be white and the other dark blue, so the intermediate gray level would be various shades of blue, or one extreme optical state could be red and the other blue, so the intermediate gray level would be various shades of purple.
[0029] Today, there is an increasing demand for full-color displays, even for small portable displays. For example, most displays on mobile phones today are full-color. To provide a full-color display using a monochrome medium, it is necessary to utilize a color filter array (CFA) through which the display can be viewed, or to provide regions of different electro-optical media capable of displaying different colors adjacent to each other.
[0030] CFAs have been known to generate undesirable visible texture patterns associated with the arrangement of CFA filter stripes. There is a need for improved CFAs for electro-optical displays that reduce these visible texture patterns.
[0031] A color electro-optical display according to one aspect of the present invention comprises an electro-optical material layer having a viewing side facing a viewer, a light-transmitting electrode on the viewing side of the electro-optical material layer, an array of pixel electrodes on the opposite side of the electro-optical material layer, and a color filter array disposed on the viewing side of the electro-optical material layer. The pixel electrodes can each be independently addressed to drive a corresponding portion of the electro-optical material on the viewing side of the electro-optical material layer between a first substantial white optical state and a second substantial black or dark optical state by applying a driving voltage to an adjacent portion of the electro-optical material layer associated therewith. The color filter array comprises an array of pixels, wherein each of the pixels has at least three color filter elements or subpixels. Each of the at least three color filter elements has a different color and is aligned with a different pixel electrode among the pixel electrodes, so that the color of any color filter element is visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material into a substantially white optical state. The color of the color filter element is not visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material into a substantially black optical state. The colors of the color filter elements within the color filter array are configured to have the same lightness or a lightness difference of 10L* or less to substantially eliminate a visible color filter array texture pattern in the displayed image.
[0032] In one or more embodiments, the colors of the color filter elements in the color filter array have a luminance contrast of less than 1.6.
[0033] In one or more embodiments, the colors of the color filter elements in the color filter array are red, green, and blue.
[0034] In one or more embodiments, the colors of the color filter elements in the color filter array are approximately 45L * Up to about 55L * It has a brightness value.
[0035] In one or more embodiments, the electro-optical material layer is monochrome.
[0036] In one or more embodiments, the electro-optical material layer comprises an encapsulated electrophoretic medium.
[0037] In one or more embodiments, the encapsulated electrophoretic medium may comprise an electrophoretic medium encapsulated in microcapsules or microcups.
[0038] In one or more embodiments, the electro-optical material layer comprises charged pigment particles dispersed in a non-polar solvent. In one or more embodiments, the charged pigment particles comprise black and white pigment particles. In another embodiment, the charged pigment particles comprise blue and white pigment particles.
[0039] In one or more embodiments, the electro-optical material layer is bistable. Brief explanation of the drawing
[0040] The patent or application file includes at least one drawing in color. A copy of the patent or patent application publication containing the color drawing(s) will be provided by the office upon request and payment of the necessary fees. Figure 1a is a schematic cross-sectional view of a typical electrophoretic display in which an electrophoretic medium is encapsulated in microcapsules. Figure 1b is a schematic cross-sectional view of a typical electrophoretic display in which an electrophoretic medium is encapsulated in a microcell. FIG. 1c is a schematic cross-sectional view of a representative electrophoretic display comprising an electrophoretic layer containing oppositely charged black and white particles coupled to CFA between the electrophoretic layer and the viewer. Figure 1d is a typical RGBW (red-green-blue-white) color filter array pattern that can be used with a CFA-enabled color electrophoretic display. The dashed lines define "pixels" for the purpose of defining pixels in the image. Each pixel of the RGBW CFA contains independently controllable red, green, and blue partially transmissive filter parts known as "subpixels." The clear (aka white) subpixel helps improve white and bright colors in the image. Beneath each subpixel is an independently controllable pixel electrode. Figure 1e shows a typical RGB (red-green-blue) color filter array pattern that can be used with a CFA-based color electrophoretic display. The dashed lines define "pixels" for the purpose of defining pixels in the image. Each pixel of the RGB CFA includes independently controllable red, green, and blue partially transparent filter portions known as "subpixels." The portion surrounding each subpixel is transparent to enhance white and bright colors in the image (also known as partial fill CFA) and has a higher overall resolution than in Figure 1d. Beneath each subpixel is an independently controllable pixel electrode. FIG. 2a illustrates an exemplary subpixel array of a CFA. FIG. 2b illustrates the reflective luminance of a CFA. Figures 3a and 3b show the CIELAB color reflected by CFA RGB subpixels as a function of CFA printing ink concentration, respectively b * vs a * and L * vs C *This is the graph shown in the diagram. (L * represents lightness, and C * represents saturation, and a * is the red / green coordinate, and b * is the yellow / blue coordinate.) Figure 4 shows the brightness L of an RGB subpixel in a white state relative to the relative amount of CFA printing ink. * This is a graph representing . Figures 5a, 5b, 5c, and 5d represent Table 1, Table 2, Table 3, and Table 4, respectively. Specific details for implementing the invention
[0041] According to one aspect of the present invention, a reflective electro-optical display comprises a CFA having a filter primary color of matched brightness to reduce a visible texture pattern in a displayed image.
[0042] FIGS. 1A and 1B illustrate representative electrophoretic displays (101, 102) in which an electrophoretic medium is encapsulated in a microcapsule and a microcell, respectively. FIG. 1C illustrates an electrophoretic display (103) comprising a CFA (190). As illustrated, each electrophoretic display (101, 102, 103) comprises an upper transparent electrode (110), an electrophoretic medium (120), and a lower electrode layer (130) comprising pixel electrodes of an active matrix of pixels controlled, for example, by a thin-film transistor (TFT). As illustrated in FIGS. 1A and 1B, the electrophoretic medium (120) of the display (101, 102) comprises oppositely charged white and black particles (121, 122). The CFA display (103) of FIG. 1c also includes an encapsulated electrophoretic medium (120) having oppositely charged particles of black and white. FIG. 1d is a typical RGBW color filter array pattern that may be included in the CFA display (103). Color elements may be provided directly onto an upper transparent electrode (110), which may be, for example, indium-tin-oxide (ITO). Such CFA films are available from Toppan Printing (Japan). Alternatively, color filter elements may be applied to the electrophoretic medium (120) using an inkjet or other precision printing process. See U.S. Patent No. 10,209,556. In FIG. 1d and FIG. 1e, the dashed lines define "pixels" for the purpose of defining pixels in the image. In Fig. 1d, each pixel of the RGBW CFA includes red, green, blue, and transparent subpixels that can be independently controlled to enhance white in an image and render not only brighter colors but also darker colors.In FIG. 1e, each pixel of the RGB CFA contains independently controllable red, green, and blue subpixels, and the area around each subpixel is transparent to enhance white and bright colors in the image (also known as partial fill CFA). In practice, the CFA pattern of FIG. 1e is preferred over the pattern of FIG. 1d because each image pixel is slightly smaller and, consequently, a higher resolution can be achieved for the same number of PPIs (pixel electrodes per inch), typically 100 to 400 PPIs, more commonly 150 to 300 PPIs.
[0043] The electrophoretic medium (120) is typically compartmentalized by the walls of microcapsules (126) or microcells (127). An optional adhesive layer (140) may be placed adjacent to any of the layers, but is typically adjacent to the electrode layer (110 or 130). A given electrophoretic display may have more than one adhesive layer (140), but generally only one layer. The entire display stack is placed on a substrate (150) which may be rigid or flexible. The display may also typically include a protective layer (160) that simply protects the upper electrode (110) from damage, or may surround the entire display to prevent water ingress, etc. The display may also include a sealing layer (180) as needed. The adhesive layer may include a primer component to improve adhesion to the electrode layer (110), or a separate primer layer may be used. Structures and component parts of electrophoretic displays, pigments, adhesives, electrode materials, etc. are described in many patents and patent applications disclosed by E Ink Corporation, such as U.S. Patents 6,922,276; 7,002,728; 7,072,095; 7,116,318; 7,715,088; and 7,839,564, all of which are incorporated herein by reference in their entirety.
[0044] Although improvements have been achieved using CFA-based displays, it has been found that CFAs can generate visible textures associated with an array of CFA filters, for example, horizontally or vertically oriented RGB filter stripes generate textures of horizontal or vertical lines. The visibility of these lines depends on the resolution of the display and the viewing distance, both of which are related to the contrast sensitivity function (CSF) of the human visual system (HVS). For example, if a display includes a TFT backplane with a resolution of 300 PPI (pixels per inch) and a CFA with three primary (RGB) filters, its intrinsic subpixel resolution is 300 PPI, but its color resolution is only 100 PPI. When viewing the display at a viewing distance of 12 inches, a 300 PPI subpixel resolution corresponds to a spatial frequency of 31.4 cycles / degree on the viewer's retina, and a 100 PPI color resolution corresponds to a spatial frequency of 10.5 cycles / degree, which is close to the maximum luminance contrast sensitivity. As a result, the CFA pattern can be very clearly visible, especially when displaying white or bright achromatic gray colors.
[0045] Several methods for reducing the visual impact of CFA texture patterns are known in the art, including methods to increase display resolution beyond the visibility limit of the CSF and methods to find CFA arrays where the texture is less visible. Increasing the resolution of the CFA requires a corresponding increase in TFT backplane resolution and is effective only when retinal color resolution or higher spatial frequencies are reached, which corresponds to a color resolution of 447 PPI at a 12-inch viewing distance and 326 PPI at an 18-inch viewing distance, with the corresponding subpixel resolution being three times these resolutions. Examples of such displays include the Apple Retina® display, which has 26 μm subpixels corresponding to a color resolution of 326 PPI and a subpixel resolution of 978 PPI. However, current electrophoretic color displays with CFAs have a subpixel resolution of only about 300 PPI, because increasing the resolution further increases blooming and optical crosstalk. Consequently, a modified CFA subpixel array, which uses a CFA pattern with a staggered arrangement of short striped RGB or Bayer-type RGB patterns, becomes the preferred method for softening textures. However, in each of these CFA patterns, the texture lines are tilted from the horizontal and vertical directions at an angle corresponding to the CFA array, for example, 45 degrees for the staggered RGB pattern illustrated in FIG. 2a, rather than in the horizontal or vertical direction. When the reflective luminance differs between the red, green, and blue subpixels as exemplified in FIG. 2b, the texture becomes very visible because the luminance channel of human vision is the most sensitive to textures. Furthermore, some CFA arrays can make rendering text and images more difficult and may result in unwanted text and image artifacts. Therefore, there is a need for an improved CFA for electro-optical displays that reduces visible texture patterns.
[0046] According to one aspect of the present invention, a reflective electro-optical display comprises a CFA having CFA subpixels of matched brightness to reduce a visible texture pattern in a displayed image. It has been found that reducing the luminance contrast between CFA subpixels reduces the visibility of the CFA texture. Reducing the luminance contrast is less expensive than other methods of texture mitigation, such as modifying the CFA pattern or increasing the subpixel resolution. By this, the CFA design can be optimized for the best text and image rendering rather than texture mitigation.
[0047] According to one or more embodiments, Kubelka-Munk modeling of CFA RGB filter primary colors is used to determine and adjust luminance contrast between CFA subpixels. In one example, solid regions of R, G, and B filter inks are inkjet printed onto an electrophoretic black and white (B&W) panel at a defined default ink density, and the spectral reflectance of each filter primary color region is such that when the B&W panel is switched to a white state (WS). After being measured as such, with the B&W panel switched to the black or dark state (DS) It was measured again as. The measurement was performed using a Konica-Minolta CM 3700a spectrophotometer with a hemispherical-diffuse geometry including specular reflection. By measuring the spectral reflectance of the blank panel region switched to WS and then measuring it again when switched to DS, the reference spectral reflectance required for the Kubelka-Munk calculation was obtained. and ...was provided. From four measurements—filter primary colors on WS and DS, and blank-referenced WS and DS—scatter (for a set of wavelengths (380, 10, 730) nm) using the solution of the Kubelka-Munk equation for the translucent case [Georg A. Klein, Industrial Color Physics, Springer (2010), chapter 5.3] ) and absorption( The spectral coefficient of ) was calculated:
[0048]
[0049] Therefore, using the determined spectral coefficients of scattering and absorption, filter ink concentration on the background panel switched to WS or DS and ink layer thickness Spectral reflectance of each filter primary color as a function of It can be predicted as follows:
[0050]
[0051] Figures 3a and 3b show the CIELAB color reflected by the CFA RGB primary colors as a function of CFA printing ink concentration. * vs a * Diagram (Fig. 3a) and brightness L * Alternative saturation C * This is illustrated in the diagram (Fig. 3b). The squares within the diagram correspond to the same amount of default ink application for the R, G, and B filters.
[0052] The L* versus C* diagram (Fig. 3b) shows that the green filter primary color is significantly brighter than the red and blue filter primary colors. Table 1 (Fig. 5a) provides luminance data for the same amount of default ink application for the R, G, and B filters. The green primary color is 58L * It has a brightness of, and the red and blue primary colors are 45.8L each * and 47L* It has the brightness of . 10L * The difference in brightness between the above CFA primary colors corresponds to a luminance contrast of at least 1.6, which results in obstructive visible diagonal texture lines as shown in FIGS. 2a and 2b. These figures illustrate a CFA display having a Bayer filter array with staggered RGB subpixels. FIG. 2a illustrates the subpixel array of the CFA, and FIG. 2b illustrates the reflected luminance. As shown in FIG. 2a, the green subpixel was significantly brighter than the red and blue subpixels, leading to a difference in luminance between the CFA primary colors, which appears as a texture of diagonal stripes.
[0053] The solid lines in FIGS. 3a and 3b represent the Kubelka-Munk calculation results of Equation (2), namely the lightness, hue angle, and saturation (L) of each filter primary color. * , h and C * It shows how ) changes depending on the CFA printing ink concentration relative to the default amount. Default concentration The density dependence of filter brightness upon reflection on contrast WS is illustrated in Fig. 4. The squares within the diagram indicate the default equal ink amounts for R, G, and B.
[0054] To match the reflected luminance or brightness of the three filter primary colors, each L * The concentration of the filter ink can be increased until this matches. The amount of change is L shown in Fig. 4. * It can be determined from the concentration dependence of. L of the filter base color *There are various ways to match it, for example, by increasing the concentration of green ink and / or decreasing the concentration of red and blue ink. Since this will also result in changes in color angle and saturation as illustrated in FIG. 3a, the CIELAB color gamut volume in reflection mode must be considered. If front lighting is present, the color gamut volume in emission mode must also be considered. This is illustrated in the following example:
[0055] Example 1
[0056] In the first example, only the concentration of the green filter ink is increased by 2.51 times, while the red and blue inks remain unchanged. This results in the brightness of the green primary color subpixel being 58L, as shown in Table 2 (Fig. 5b). * 47.1L * Lower it to . Compared to the initial filter primary color in Table 1, the darker green primary color slightly improves the color gamut volume in emission mode (front light on), but decreases in reflection mode (front light off).
[0057] Example 2
[0058] In the second example, the concentration of the green filter ink is doubled, and the amounts of red and blue inks are reduced by 0.5 and 0.79 times, respectively. This reduces the brightness of all three primary color subpixels by approximately 50L * It is matched in this way, which will remove the texture associated with the CFA pattern (see Table 3 (Fig. 5c)). However, compared to the initial filter primary colors in Table 1, the color gamut volume is reduced in both emission mode (front light on) and reflection mode (front light off). Making the CFA primary colors brighter is similar to mixing more white into the primary colors, which results in brighter and more desaturated colors along with a reduced color gamut volume overall.
[0059] Example 3
[0060] A third example having closely matched filter base colors and improved emission and reflection chromatic gamut volumes is shown in Table 4 (Fig. 5d). In addition to increasing the amount of green filter ink by 2.51 times, the amount of blue ink is also increased by 1.26 times to change its color angle from cyan to blue for a better emission chromatic gamut volume without loss of reflection chromatic gamut volume.
[0061] Therefore, the Kubelka-Munk measurement and model adjust the luminance or brightness (L) between inkjet-printed CFA subpixels by adjusting the amount of ink printed for each filter. * It can be used to equalize ). L between CFA primary colors * Leveling the difference removes the major components of the CFA texture that appear as horizontal, vertical, or diagonal lines. Adjusting the filter brightness can also be used to improve the hue of primary colors, such as blue, which are strongly dependent on ink density. According to various embodiments of the present invention, the method of removing CFA texture is less costly and more feasible than methods of increasing the subpixel resolution of a display and other known methods of reducing texture visibility.
[0062] It will be apparent to those skilled in the art that numerous changes and modifications are possible to the specific embodiments of the invention described above. Accordingly, the foregoing description is illustrative and should not be interpreted in a limiting sense, and the invention is defined by the appended claims.
Claims
Claim 1 A color electro-optical display comprises: an electro-optical material layer having a viewing side facing a viewer; a light-transmitting electrode on the viewing side of the electro-optical material layer; and an array of pixel electrodes on the side of the electro-optical material layer opposite to the viewing side, wherein each of the pixel electrodes is independently addressable to drive a corresponding portion of the electro-optical material on the viewing side of the electro-optical material layer between a first substantial white optical state and a second substantial black optical state by applying a driving voltage to an adjacent portion of the electro-optical material layer associated therewith. A color electro-optical display comprising: a color filter array disposed on the viewing side of the electro-optical material layer, wherein the color filter array comprises an array of pixels, wherein each of the pixels has at least three color filter elements, each of the at least three color filter elements has a different color, and each color filter element is aligned with a different pixel electrode among the pixel electrodes, such that the color of any color filter element is visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material into a substantial white optical state, and the color of any color filter element is not visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material into a substantial black optical state; wherein the colors of the color filter elements within the color filter array have the same brightness or have a brightness difference of 10L* or less to substantially eliminate a visible color filter array texture pattern. Claim 2 A color electro-optical display according to claim 1, wherein the colors of the color filter elements in the color filter array have a luminance contrast of less than 1.
6. Claim 3 A color electro-optical display according to claim 1 or claim 2, wherein the colors of the color filter elements in the color filter array are red, green, and blue. Claim 4 In any one of claims 1 to 3, the colors of the color filter elements in the color filter array are 45L * Up to 55L * A color electro-optical display having a brightness value. Claim 5 A color electro-optical display according to any one of claims 1 to 4, wherein the electro-optical material layer is monochrome. Claim 6 A color electro-optical display according to any one of claims 1 to 5, wherein the electro-optical material layer comprises an encapsulated electrophoretic medium. Claim 7 A color electro-optical display according to claim 6, wherein the encapsulated electrophoretic medium comprises an electrophoretic medium encapsulated in microcapsules or microcups. Claim 8 A color electro-optical display according to any one of claims 1 to 7, wherein the electro-optical material layer comprises charged pigment particles dispersed in a non-polar solvent. Claim 9 A color electro-optical display according to claim 8, wherein the charged pigment particles comprise black and white pigment particles. Claim 10 A color electro-optical display according to any one of claims 1 to 9, wherein the electro-optical material layer is bistable. Claim 11 A color electro-optical display according to any one of claims 1 to 10, wherein the colors of the color filter elements each have a given ink concentration configured to provide the same brightness, and each ink concentration is determined using a Kubelka-Munk model. Claim 12 A method for constructing a color electro-optical display comprises the step of depositing a color filter array on an electro-optical display, wherein the electro-optical display comprises: (a) an electro-optical material layer having a viewing side facing a viewer; (b) a light-transmitting electrode on the viewing side of the electro-optical material layer; and (c) an array of pixel electrodes on the side opposite to the viewing side of the electro-optical material layer, wherein each of the pixel electrodes is independently addressable to drive a corresponding portion of the electro-optical material on the viewing side of the electro-optical material layer between a first substantial white optical state and a second substantial black optical state by applying a driving voltage to an adjacent portion of the electro-optical material layer associated therewith, and the color filter array is deposited on the viewing side of the electro-optical material layer, wherein the color filter array comprises an array of pixels, wherein each of the pixels has at least three color filter elements, and each of the at least three color filter elements has a different color, and each color filter element is aligned with a different pixel electrode among the pixel electrodes, so that the color of any color filter element is visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material to the substantial white optical state, and the color of any color filter element is not visible to the viewer when the pixel electrode aligned with the color filter element drives an adjacent portion of the electro-optical material to the substantial black optical state. A method for constructing a color electro-optical display, wherein the colors of the color filter elements within the color filter array have the same brightness or a brightness difference of 10L* or less to substantially eliminate a visible color filter array texture pattern. Claim 13 A method of constructing a color electro-optical display according to claim 12, wherein the colors of the color filter elements in the color filter array have a luminance contrast of less than 1.
6. Claim 14 A method of constructing a color electro-optical display according to claim 12 or claim 13, wherein the colors of the color filter elements in the color filter array are red, green, and blue. Claim 15 In any one of claims 12 to 14, the colors of the color filter elements in the color filter array are 45L * Up to 55L * A method for constructing a color electro-optical display having a brightness value. Claim 16 A method for constructing a color electro-optical display according to any one of claims 12 to 15, wherein the electro-optical material layer is monochrome. Claim 17 A method for constructing a color electro-optical display according to any one of claims 12 to 16, wherein the electro-optical material layer comprises an encapsulated electrophoretic medium. Claim 18 A method of constructing a color electro-optical display according to claim 17, wherein the encapsulated electrophoretic medium comprises an electrophoretic medium encapsulated in microcapsules or microcups. Claim 19 A method for constructing a color electro-optical display according to any one of claims 12 to 18, wherein the electro-optical material layer comprises charged pigment particles dispersed in a non-polar solvent. Claim 20 A method of constructing a color electro-optical display according to claim 19, wherein the charged pigment particles comprise black and white pigment particles. Claim 21 A method for constructing a color electro-optical display according to any one of claims 12 to 20, wherein the electro-optical material layer is bistable. Claim 22 A method for constructing a color electro-optical display according to any one of claims 12 to 21, wherein the colors of the color filter elements each have a given ink concentration configured to provide the same brightness, and each ink concentration is determined using the Kubelka-Munk model.