Improved methods for producing full-color epaper images with low grain

Abstract

An improved method for driving color electro-optic displays (e.g., electrophoretic displays with multi-particle electrophoretic media). When driving between a first image with high color depth (i.e., more than 64 different colors) and a second image with high color depth, the data processing load can be reduced by irradiating the color set in the first image onto a simplified color set. In a preferred embodiment, the electro-optic medium is an electrophoretic medium comprising white particles and subtractive primary color particles of cyan, yellow, and magenta. Images with high color depth appear less grainy and are more appealing to consumers.

Description

Technical Field

[0001] This application claims priority to U.S. Provisional Application No. 63 / 624,778, filed January 24, 2024. All patents and publications disclosed herein are incorporated herein by reference in their entirety. Prior Technology

[0002] Electrophoretic displays (EPDs) change color by modifying the position of one or more charged colored particles relative to a light-transmitting viewing surface. Such EPDs are often called "electronic paper" or "ePaper" because the resulting display has high contrast and is readable in sunlight, much like ink on paper. EPDs are widely used in eReaders because they provide a book-like reading experience, consume little power, and allow users to carry hundreds of books in a lightweight handheld device. These devices are increasingly suitable for displaying out-of-home (OOH) digital content, such as shelf labels, outdoor advertising, and traffic signs.

[0003] For many years, electrophoretic displays have only included two types of charged color particles (black and white). (Of course, the term "color" here includes both black and white.) White particles are typically light-scattering and include, for example, titanium dioxide, while black particles are absorbent throughout the visible spectrum and can include carbon black or absorbing metal oxides (e.g., copper chromite). In its simplest sense, a monochrome electrophoretic display requires only a transparent electrode on the viewing surface, a back electrode, and an electrophoretic medium comprising white and black particles with opposite charges. When a voltage of one polarity is applied, the white particles move to the viewing surface, and when a voltage of the opposite polarity is applied, the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels)—segmented electrodes or an active matrix of pixel electrodes controlled by transistors—a pattern can appear electronically on the viewing surface. The pattern could, for example, be the text of a book.

[0004] Recently, a variety of colors have become commercially available for electrophoretic displays, including tri-color displays (black, white, and red; black, white, and yellow) and quad-color displays (black, white, red, and yellow). Similar to the operation of a black-and-white electrophoretic display, the operation of an electrophoretic display with three or four reflective pigments is similar to that of a simple black-and-white display because the desired color particles are driven to the viewing surface. The driving scheme is far more complex than that of a purely black-and-white display, but the optical function of the particles is ultimately the same.

[0005] Advanced Color Electronic Paper (ACeP™) also contains four types of particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, allowing each pixel to produce thousands of colors. Color processing is functionally equivalent to the printing methods long used in offset and inkjet printers. A given color is produced by using the correct proportions of cyan, yellow, and magenta against a bright white paper background. In the case of ACeP, the relative positions of the cyan, yellow, magenta, and white particles relative to the viewing surface determine the color of each pixel. While this type of electrophoretic display allows for thousands of colors per pixel, careful control of the position of each pigment (50 to 500 nanometers in size) within a working space approximately 10 to 20 micrometers thick is crucial. Clearly, variations in pigment position will result in incorrect color display at a given pixel. Therefore, such a system requires precise voltage control. Further details of this system are available in the following U.S. patents, all of which are incorporated herein by reference: U.S. Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, 10,593,272, and 10,657,869.

[0006] Unsurprisingly, especially when the subject is people or landscapes, having more colors available for display results in better-looking images. Furthermore, it has been found that images with the same pixel resolution but smaller color sets tend to appear "grainy" due to significant color differences between adjacent pixels that differ by only one chromaticity. See also Figure 7. However, having more color depth comes at a cost. Achieving hundreds of different color states using a system like ACeP requires longer waveforms (voltage pulse sequences) so that all color particles are configured in the correct order and with the correct spacing between the white pigment and the top translucent electrode (viewing surface). [A different color state has a different set of coordinates (i.e., L*, a, b values) in the CIELAB color space than another different color (see also Figure 9)]. Moreover, switching between images with a large number of available colors requires large data files and processors capable of quickly identifying and transmitting the required waveforms. For example, a direct transition between a first image with 64 available colors and a second image with 64 available colors requires 64*64=4096 stored waveforms and a processor capable of recognizing and sending the appropriate waveform within approximately 10ms. Processors with this speed are available, but they are typically associated with high-level graphics, artificial intelligence, and cryptocurrency mining. They are also considerably more expensive than mobile electronic processors. Therefore, in e-readers / tablets using color electrophoresis media, a more common approach is to drive the transition from the first image through a neutral state to the second image. The neutral state represents a known initial state, thus simplifying the problem to selecting from the neutral state to each of the 64 available states. Unfortunately, using neutral transition states prolongs the switching time between states and also causes unpleasant color fluctuations as the device "resets" the positions of all particles in the electrophoresis medium.

[0007] The invention described below attempts to reduce the time required for switching between image states while using standard processors and controllers for electrophoretic displays (e.g., available from Ultrachip, Rockchip, and MTK). This invention relates to color electrophoretic displays, and more particularly, but not limited to, electrophoretic displays capable of displaying more than two colors using a single layer of electrophoretic material comprising a plurality of colored particles (e.g., white, cyan, yellow, and magenta particles). In some cases, two of the particles are positively charged, and one (or two) of the particles are negatively charged. In some cases, one particle is positively charged, and three particles are negatively charged. In some cases, one particle is negatively charged, and three particles are positively charged. Furthermore, the type of charge on the surface of these particles and / or the type of polymer functionalized on the surface may vary. These particles may include organic or inorganic pigments or dyes.

[0008] The term "gray state" is used in this document in its conventional sense within imaging technology to refer to the state between two extreme optical states of a pixel, and does not necessarily imply a black-white transition between these two extreme states. For example, several E Ink patents and publications mentioned below describe electrophoretic displays where the extreme states are white and dark blue, such that the intermediate "gray state" is actually light blue. More precisely, as stated, a change in optical state may not be a color change at all. The terms "black" and "white" can be used below to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not black and white at all, such as the aforementioned white and dark blue states.

[0009] The terms "bistable" and "bistability" are used herein in their conventional sense to refer to a display comprising display elements having first and second display states that are different in at least one optical property, and to present either the first or second display state after any given element is driven by an addressing pulse of finite duration, and that state persists at least several times, for example at least four times, after the addressing pulse terminates; the addressing pulse requires a minimum duration to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays with grayscale capabilities are stable not only in their extreme black and white states but also in their intermediate gray states, and so are some other types of electro-optical displays. This type of display may be appropriately called multi-stable rather than bistable, but for convenience, the term "bistable" may be used herein to encompass both bistable and multi-stable displays.

[0010] When used to drive an electrophoretic display, the term "pulse" is used herein to refer to the integral of the voltage applied during the period of driving the display with respect to time.

[0011] Particles that absorb, scatter, or reflect broadband or selected wavelengths of light are referred to herein as colored or pigment particles. Various light-absorbing or light-reflecting materials other than pigments (in the strict sense of that term, insoluble colored materials), such as dyes or photonic crystals, may also be used in the electrophoretic media and displays of the present invention.

[0012] Particle-based electrophoretic displays have been a subject of intensive research and development for several years. In such displays, multiple charged particles (sometimes called pigment particles) move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays offer superior brightness and contrast, wide viewing angles, dual stability, and low power consumption. However, issues concerning the long-term image quality of these displays have hindered their widespread adoption. For example, the particles constituting an electrophoretic display tend to settle, leading to a shorter lifespan for these displays.

[0013] As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, this fluid system is liquid, but a gaseous fluid can be used to produce the electrophoretic medium; 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. See also U.S. Patents 7,321,459 and 7,236,291. When such media are used in an orientation that allows particle settling (e.g., in the presentation of media arranged in a vertical plane), such gas-based electrophoretic media appear to be susceptible to the same type of problems caused by particle settling as liquid-based electrophoretic media. More precisely, 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 allows for faster sedimentation of these electrophoretic particles compared to liquids.

[0014] Numerous patents and applications, assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, describe various techniques used in encapsulation electrophoresis and other electro-optic media. Such encapsulation media comprise a plurality of small capsules, each capsule comprising an internal phase of electrophoretically moving particles contained in a fluid medium and a capsule wall surrounding the internal phase. Typically, these capsules are held in a polymeric binder to form a coherent layer between two electrodes. The techniques described in these patents and applications include: (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; (b) Capsules, binders, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; (c) Microcellular structures, wall materials, and methods of forming microcells; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906; (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088; (e) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564; (f) Backplates, adhesive layers and other auxiliary layers used in displays, and methods thereof; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624; (g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 6,017,584; 6,545,797; 6,664,944; 6,788,452; 6,864,875; 6,914,714; 6,972,893; 7,038,656; 7,038,670; 7,046,228; 7,052,571; 7,075,502; 7,167,155; 7,385,751; 7,492,505; 7,667,684; 7,684,108; 7,791,789; 7,800,813; 7,821,702; 7,839,564; 7,910,175; 7,952,7 90;7,956,841;7,982,941;8,040,594;8,054,526;8,098,418;8,159,636;8,213,076;8,363,299;8,422,116;8,441,714;8,441,716;8,466,852;8 ,503,063;8,576,470;8,576,475;8,593,721;8,605,354;8,649,084;8,670,174;8,704,756;8,717,664;8,786,935;8,797,634;8,810,899;8,830, 559;8,873,129;8,902,153;8,902,491;8,917,439;8,964,282;9,013,783;9,116,412;9,146,439;9,164,207;9,170,467;9,170,468;9,182,646;9,195,111;9,199,441;9,268,191;9,285,649;9,293,511;9,341,916;9,360,733;9,361,836;9,383,623; and 9,423,666; and U.S. Patent Application Publication No. 2008 / 004331 8;2008 / 0048970;2009 / 0225398;2010 / 0156780;2011 / 0043543;2012 / 0326957;2013 / 0242378;2013 / 0278995;2014 / 0055840;2014 / 0078576;2014 / 0340430;2014 / 0340736;2014 / 0362213;2015 / 0103394;2015 / 0118390;2015 / 0124345;2015 / 0198858;2015 / 0234250;2015 / 0268531;2015 / 0301246;2016 / 0011484; 2016 / 0026062; 2016 / 0048054; 2016 / 0116816; 2016 / 0116818; and 2016 / 0140909; (h) A method of driving a display; see, for example, U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7,312 ,794;7,327,511;7,408,699;7,453,445;7,492,339;7,528,822;7,545,358;7,583,251;7,602,374;7,612,760;7,679,599;7,679,813;7,683,60 6;7,688,297;7,729,039;7,733,311;7,733,335;7,787,169;7,859,742;7,952,557;7,956,841;7,982,479;7,999,787;8,077,141;8,125,501;8 ,139,050;8,174,490;8,243,013;8,274,472;8,289,250;8,300,006;8,305,341;8,314,784;8,373,649;8,384,658;8,456,414;8,462,102;8,51 4,168;8,537,105;8,558,783;8,558,785;8,558,786;8,558,855;8,576,164;8,576,259;8,593,396;8,605,032;8,643,595;8,665,206;8,681,1 91;8,730,153;8,810,525;8,928,562;8,928,641;8,976,444;9,013,394;9,019,197;9,019,198;9,019,318;9,082,352;9,171,508;9,218,773; 9,224,338;9,224,342;9,224,344;9,230,492;9,251,736;9,262,973;9,269,311;9,299,294;9,373,289;9,390,066;9,390,661; and 9,412,314;and U.S. Patent Application Publications Nos. 2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0291129; 2008 / 0303780; 2009 / 0174651; 2009 / 0195568; 2009 / 032272 1; 2010 / 0194733; 2010 / 0194789; 2010 / 0220121; 2010 / 0265561; 2010 / 0283804; 2011 / 0063314; 2011 / 0175875; 2011 / 0193840; 2011 / 0193841; 2011 / 0199671; 2011 / 0221740; 2012 / 0001957; 2012 / 0098740; 2013 / 0063333; 2013 / 0194 250;2013 / 0249782;2013 / 0321278;2014 / 0009817;2014 / 0085355;2014 / 0204012;2014 / 0218277;2014 / 0240210;2014 / 0240373;2014 / 0253425;2014 / 0292830;2014 / 0293398;2014 / 0333685;2014 / 0340734;2015 / 0070744;2015 / 00 Patents and applications numbered 97877;2015 / 0109283;2015 / 0213749;2015 / 0213765;2015 / 0221257;2015 / 0262255;2015 / 0262551;2016 / 0071465;2016 / 0078820;2016 / 0093253;2016 / 0140910; and 2016 / 0180777 (these patents and applications may be referred to below as MEDEOD (method for driving an electro-optic display) applications); (i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and (j) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921; and U.S. Patent Application Publication No. 2015 / 0277160; and U.S. Patent Application Publications Nos. 2015 / 0005720 and 2016 / 0012710.

[0015] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer-dispersed electrophoretic display, wherein the electrophoretic medium comprises electrophoretic fluids of a plurality of discrete droplets and a continuous phase of polymeric material, and even without discrete capsule membranes associated with each individual droplet, the electrophoretic fluids of the discrete droplets within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules; see, for example, U.S. Patent No. 6,866,760. Thus, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subtype of encapsulated electrophoretic media.

[0016] One related type of electrophoretic display is the so-called "microcellular electrophoresis display." In a microcellular electrophoresis display, instead of encapsulating charged particles and fluids in microcapsules, they are held in a plurality of cavities formed within a carrier medium (typically a polymeric membrane). See, for example, U.S. Patents 6,672,921 and 6,788,449.

[0017] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles substantially block the transmission of visible light through the display) and operate in reflective mode, some electrophoretic displays can operate in a so-called "shutter mode," in which one display state is substantially opaque and another display state is transparent. See, for example, U.S. Patents 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays (similar to electrophoretic displays but dependent on changes in electric field strength) can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays can also operate in shutter mode. Electro-optic media operating in raster mode can be used in the multilayer structure of a full-color display; in such a structure, at least one layer adjacent to the viewing surface of the display operates in raster mode to expose or hide a second layer farther from the viewing surface.

[0018] An encapsulated electrophoretic display typically does not suffer from the clustering and settling failure modes of conventional electrophoresis apparatus and offers additional advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of the word "printing" is intended to encompass all forms of printing and coating, including but not limited to: pre-metered coatings (e.g., patch die coating, slot or extrusion coating, slide or cascade coating, and curtain coating); roll coating (e.g., knife over roll coating and forward and reverse roll coating); gravel 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.) Jet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques. Therefore, the resulting display can be flexible. Furthermore, because the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

[0019] As described above, the simplest conventional electrophoretic medium essentially displays only two colors. Such an electrophoretic medium uses a single type of electrophoretic particles of a first color in a colored fluid having a second, different color (in this case, the first color is displayed when the particles are adjacent to the viewing surface of the display, and the second color is displayed when the particles are separated from the viewing surface) or uses first and second types of electrophoretic particles with different first and second colors in a colorless fluid (in this case, the first type of particles is displayed when the first color is adjacent to the viewing surface of the display, and the second type of particles is displayed when the second color is adjacent to the viewing surface). Typically, these two colors are black and white. If full-color display is desired, a color filter array can be deposited on the viewing surface of a monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color blending to generate color stimuli. The available display area can be shared among three or four primary colors such as red / green / blue (RGB) or red / green / blue / white (RGBW), and filters can be configured in 1-dimensional (line) or 2-dimensional (2×2) repeating patterns. The selection of other primary colors or more than three primary colors is also known in this art. Sufficiently small three (in the case of RGB display) or four (in the case of RGBW display) subpixels are selected so that at a predetermined viewing distance they visually blend together to form a single pixel with uniform color stimulation ("color mixing"). An inherent drawback of area sharing is that colorants are always present, and colors can only be modulated by switching the corresponding pixel of the lower monochrome display to black or white (turning the corresponding primary color on or off). For example, in an ideal RGBW display, each of the primary colors red, green, blue, and white occupies 1 / 4 of the display area (one of four sub-pixels), and the white sub-pixel is as bright as the monochrome white display below it, and none of these colored sub-pixels is brighter than 1 / 3 of the monochrome white display. The brightness of the white displayed is generally no greater than half the brightness of the white sub-pixel (the white area of ​​the display is created by displaying one white sub-pixel in every four sub-pixels, and each colored sub-pixel having a color form equal to 1 / 3 of a white sub-pixel, so the combination of three colored sub-pixels is no greater than the contribution of a single white sub-pixel). The brightness and saturation of colors are reduced by area sharing and switching colored pixels to black. Area sharing is particularly problematic when mixing yellow, as it is lighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching the blue pixel (1 / 4 of the display area) to black makes the yellow too dark.

[0020] U.S. Patents 8,576,476 and 8,797,634 describe a multicolor electrophoretic display having a single backplane containing independently addressable pixel electrodes and a common transparent front electrode. A plurality of electrophoretic layers are disposed between the backplane and the front electrode. The displays described in these applications are capable of displaying any primary color (red, green, blue, cyan, magenta, yellow, white, and black) at any pixel location. However, using multiple electrophoretic layers located between a single set of addressing electrodes has disadvantages. The electric field experienced by particles in a particular layer is lower than that of a single electrophoretic layer addressed with the same voltage. Furthermore, optical losses in the electrophoretic layer closest to the viewing surface (e.g., caused by light scattering or unwanted absorption) may affect the display of the image formed in the underlying electrophoretic layer.

[0021] Attempts have been made to provide full-color electrophoretic displays using a single electrophoretic layer. For example, U.S. Patent No. 8,917,439 describes a color display comprising an electrophoretic fluid containing one or two types of pigment particles dispersed in a transparent and colorless or colored solvent, the electrophoretic fluid being disposed between a common electrode and a plurality of pixels or driving electrodes. The driving electrodes are configured to expose a background layer. U.S. Patent No. 9,116,412 describes a method for driving a display unit wherein the display unit is filled with an electrophoretic fluid containing two types of charged particles carrying opposite charge polarities and having two contrasting colors. The two types of pigment particles are dispersed in a colored solvent or in a solvent containing uncharged or slightly charged colored particles. This method involves driving the display unit by applying a driving voltage of about 1% to about 20% of the full driving voltage to display the color of the solvent or the color of the uncharged or slightly charged colored particles. U.S. Patents 8,717,664 and 8,964,282 describe an electrophoretic fluid and a method for driving an electrophoretic display. The fluid contains pigment particles of types one, two, and three, all dispersed in a solvent or solvent mixture. Types one and two pigment particles carry opposite charge polarities, while the charge level of type three pigment particles is approximately 50% lower than that of type one or two pigment particles. These three types of pigment particles have different critical voltage levels or different mobilities, or both.

[0022] Electrophoretic displays capable of displaying any color at any pixel location have been described in U.S. Patents 10,475,399 and 10,678,111. In the '399 patent, a display is described in which a white (light-scattering) pigment moves in a first direction when addressed with a low applied voltage and in the opposite direction when addressed with a higher voltage. In the '111 patent, a full-color electrophoretic display is described in which four pigments are used: white, cyan, magenta, and yellow, two of which are positively charged and two are negatively charged. U.S. Patent Publication 2022 / 0082896 describes a full-color electrophoretic display in which four pigments are used: white, cyan, magenta, and yellow, three of which are positively charged and the white pigment is negatively charged. Embodiments of this type of invention are referred to as CMYW embodiments.

[0023] In addition, there are multi-particle display designs in which colored pigments scatter light (i.e., reflect colored particles). U.S. Patent No. 10,339,876 describes this type of display, which has black, white, and red particles capable of displaying three states. Similar display designs containing four pigments can display four different colors, see, for example, U.S. Patent No. 9,922,603, or by using translucent colored particles, such displays can display six colors, see, for example, U.S. Patent No. 11,640,803. Many multi-particle display designs using light-scattering particles include lengthy and “flickering” updates, which some viewers find unattractive. The solutions described below can be used to reduce the “flickering” of updates in such displays and, in some cases, reduce update time. Summary of the Invention

[0024] This document discloses an improved method for driving a full-color electro-optic medium between a first optical state and a second optical state, wherein the electro-optic medium is disposed between first and second electrodes, and the electro-optic medium changes its optical state in response to a voltage sequence applied between the first and second electrodes, wherein the electro-optic medium is capable of generating at least 64 different optical states. The method includes: mapping the first optical state to a simplified color state, wherein the first optical state is one of the at least 64 different optical states, and the simplified color state is one of no more than 16 different colors; identifying a voltage sequence that causes the electro-optic medium to transition from the simplified color state to the second optical state, wherein the second optical state is one of the at least 64 different optical states; and providing the voltage sequence between the first and second electrodes. In some embodiments, the electro-optic medium is capable of generating 128 different optical states. In some embodiments, the simplified color state is one of eight different colors. In some embodiments, the eight different colors are red, green, blue, cyan, yellow, magenta, white, and black. In some embodiments, the mapping step includes matching the first optical state with the simplified color state on a lookup table. In some embodiments, the providing step is performed by a controller. In some embodiments, the electro-optic medium is an electrophoretic medium. In some embodiments, the electrophoretic medium includes a reflective white particle and at least one subtractive color particle, or a reflective white particle and at least one reflective color particle. In some embodiments, the electrophoretic medium includes a fourth type of electrophoretic particle. In some embodiments, two of the particles of these types are negatively charged, and two of the particles of these types are positively charged, or one of the particles of these types is negatively charged, and three of the particles of these types are positively charged, or three of the particles of these types are negatively charged, and one of the particles of these types is positively charged. In some embodiments, the electrophoretic medium is encapsulated in microcapsules or microcells. In some embodiments, the first electrode is a light-transmitting electrode, and the second electrode is a pixel electrode of a pixel electrode active matrix. In some embodiments, the voltage sequence is DC balanced. Simple Explanation of the Diagram

[0025] Figure 1A shows a representative cross-section of a four-particle electrophoretic display, in which the electrophoretic medium is encapsulated in a capsule. The structure of Figure 1A can be used for multi-particle electrophoretic media containing reflective pigment particles and subtractive pigment particles; Figure 1B shows a representative cross-section of a four-particle electrophoretic display, in which the electrophoretic medium is encapsulated within microcells. The structure in Figure 1B can be used for multi-particle electrophoretic media containing both reflective and subtractive pigment particles. Figure 2 illustrates an exemplary equivalent circuit for a single pixel of an electrophoretic display using pixel electrodes coupled to a storage capacitor in an active matrix backplane; Figure 3 is a schematic diagram of an exemplary driving system for controlling the voltage supplied to the pixel electrodes in an active matrix device. The resulting driving voltage can be used to set the optical state of the multi-particle electrophoresis medium; Figure 4 illustrates an exemplary electrophoretic display including a display module. The electrophoretic display also includes a processor, memory, one or more power supplies, and a controller. The electrophoretic display may also include sensors to allow it to adjust operating parameters based on the surrounding environment (e.g., temperature and lighting). Figure 5 illustrates the optimal positions of each of the four groups of particles that produce eight standard colors in a white-cyan-magenta-yellow (WCMY) four-particle electrophoretic display, where white particles are reflective, while cyan, magenta, and yellow particles are absorptive. Figure 6 shows an exemplary push-pull drive scheme for addressing an electrophoretic medium containing three subtractive (cyan, yellow, and magenta) particles and one scattering (white) particle; Figure 7 illustrates the graininess differences between the same images with the same pixel resolution but different color "depths" (i.e., the number of different colors available per pixel); Figure 8 shows a comparison between R1 drive, R2 drive (where waveforms are established / stored for each possible transition between the first and second color states) using a neutral state, and R3 drive (which is the method of the present invention and involves mapping the previous image color state to a simplified color state, thereby greatly reducing the number of waveforms that must be established / stored); Figure 9 illustrates one possible method for mapping a set of available color states to a simplified color. Implementation

[0026] This invention includes a color electro-optic display (e.g., an electrophoretic display with a multi-particle electrophoretic medium) and an improved method for driving the color electro-optic medium. When driving between a first image with high color depth (i.e., more than 64 different colors) and a second image with high color depth, the data processing load can be reduced by mapping the color set in the first image to a simplified color set. In a preferred embodiment, the electro-optic medium is an electrophoretic medium comprising white particles and subtractive primary color particles of cyan, yellow, and magenta. Images with high color depth appear less grainy and are more appealing to consumers.

[0027] The method of this invention is applicable to many different types of electro-optic displays, such as LCD, LED, OLED, rLCD, and EPD. However, the method of this invention is particularly well-suited for electrophoretic displays containing four (or more) particles as discussed in the background art. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into microcellular structures, which are then sealed with a polymer layer. The microcapsules or microcellular layers can be coated or laminated onto a plastic substrate or film with a transparent conductive material coating. Alternatively, microcapsules can be coated onto a transparent substrate or other electrode material using a spraying technique. (See U.S. Patent No. 9,835,925, which is incorporated herein by reference). The resulting assembly can be laminated to a backplane with pixel electrodes using a conductive adhesive. Alternatively, the assembly can be attached to one or more segmented electrodes on a backplane, wherein the segmented electrodes are directly driven.

[0028] The electrophoretic medium used herein comprises charged particles with different colors, reflective or absorptive properties, charge densities, and mobility in an electric field (measured in zeta potential). Particles that absorb, scatter, or reflect broadband or selected wavelengths of light are referred to herein as colored or pigment particles. Various light-absorbing or reflecting materials other than pigments (strictly defined as insoluble colored materials), such as dyes, photonic crystals, quantum dots, etc., may also be used in the electrophoretic medium and display of the present invention. For example, the electrophoretic medium may comprise a fluid; a plurality of first particles and a plurality of second particles dispersed in the fluid, the first and second particles carrying opposite charges, the first particle being a light-scattering particle, and the second particle having one of the subtractive primary colors; and a plurality of third particles and a plurality of fourth particles dispersed in the fluid, the third and fourth particles carrying opposite charges, each of the third and fourth particles having a subtractive primary color different from and different from that of the second particle, wherein the electric field required to separate aggregates formed by the third and fourth particles is greater than the electric field required to separate aggregates formed by any other two types of particles.

[0029] The electrophoretic medium of the present invention may contain any additives used, for example, in electrophoretic media of the prior art described in the E Ink and MIT patents and applications. Thus, for example, the electrophoretic medium of the present invention typically contains at least one charge control agent to control the charge on various particles, and the fluid may have polymers dissolved or dispersed therein, wherein the polymers have a number average molecular weight of more than about 20,000 and are substantially non-absorbable on the particles to improve the bistability of the display, as described in the aforementioned U.S. Patent No. 7,170,670.

[0030] In one embodiment, the present invention uses one light-scattering particle (typically white) and three substantially non-light-scattering particles. Of course, there are no purely light-scattering or purely non-light-scattering particles. The minimum light scattering level of the light-scattering particles used in the electrophoresis of the present invention and the maximum tolerable light scattering level of the substantially non-light-scattering particles may differ slightly, depending on factors such as the exact pigments used, their colors, and the user's or application's ability to tolerate some deviation from the desired color. The scattering and absorption characteristics of the pigment can be evaluated by measuring the diffuse reflectance of a pigment sample dispersed in a suitable matrix or liquid against white and dark backgrounds. Results from such measurements can be interpreted according to some models well known in the art (e.g., one-dimensional Kubelka-Munk processing). In the present invention, preferably, when the white pigment is distributed at approximately 15 vol% isotropically in a 1 μm thick layer containing the white pigment and a liquid with a refractive index less than 1.55, the white pigment exhibits at least 5% diffuse reflectance at 550 nm against a black background. Yellow, magenta, and cyan pigments preferably exhibit diffuse reflectance of less than 2.5% at 650, 650, and 450 nm, respectively, measured against a black background, under the same conditions. (The wavelengths selected above for measuring yellow, magenta, and cyan pigments correspond to the spectral regions of minimum absorption for these pigments.) Colored pigments that meet these criteria are referred to below as “non-scattering” or “substantially non-scattering.” Specific examples of suitable particles are disclosed in U.S. Patent No. 9,921,451, which is incorporated herein by reference.

[0031] Alternative particle groups may also be used, including four groups of reflective particles, or one absorbing particle and three or four different groups of reflective particles, i.e., as described in U.S. Patent Nos. 9,922,603 ​​and 10,032,419, which are incorporated herein by reference. For example, white particles may be formed from inorganic pigments such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, PbSO4, etc., while black particles may be formed from CI pigment black 26 or 28, etc. (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black. Third / fourth / fifth type particles may have colors such as red, green, blue, magenta, cyan, or yellow. Pigments used for this type of particle may include, but are not limited to, CI pigment PR 254, PR 122, PR 149, PG 36, PG 58, PG 7, PB 28, PB 15:3, PY 138, PY 150, PY 155, or PY 20. Specific examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diarylide yellow, or diarylide AAOT yellow.

[0032] As shown in Figures 1A and 1B, electrophoretic displays (101, 102) typically include a top transparent electrode 110, an electrophoretic medium 120, and a bottom electrode 130, the bottom electrode 130 typically being a pixel electrode of a pixel active matrix controlled by a thin-film transistor (TFT). In the electrophoretic medium 120 described herein, four different types of particles 121, 122, 123, and 124 exist; however, more (or fewer) particle groups can be used in the methods and displays described herein. For example, the technology of the present invention can be used for three types of particles, such as white, black, and red, wherein one of the three different types of particles has a lower charge value than the other two types of particles. In some cases, two particles will be positively charged, and one (or two) particles will be negatively charged. In some cases, one particle will be positively charged, and three particles will be negatively charged. In some cases, one particle will be negatively charged, and three particles will be positively charged. The electrophoretic medium 120 is typically divided by the walls 127 of microcapsules 126 or microcells. The optional adhesive layer 140 can be positioned adjacent to any layer; however, it is typically adjacent to the electrode layers (110 or 130). More than one adhesive layer 140 may be present in a given electrophoretic display (105, 106); however, a single layer is more common. The entire display stack is typically disposed on a substrate 150, which may be rigid or flexible. The displays (101, 102) also typically include a protective layer 160, which may simply protect the top electrode 110 from damage, or it may enclose the entire display (101, 102) to prevent water ingress, etc. The electrophoretic displays (101, 102) may also include a sealing layer 180, if desired. In some embodiments, the adhesive layer 140 may contain a primer component to improve adhesion to the electrode layer 110, or a separate primer layer (not shown in FIG. 1B) may be used. The structure and components of electrophoretic displays, including pigments, adhesives, and electrode materials, are described in numerous patents and patent applications published by E Ink, such as U.S. Patent Nos. 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.

[0033] In some embodiments, such as as shown in FIG1A, an electrophoretic display may include a transparent electrode, an electrophoretic medium, and a plurality of back pixel electrodes. To produce, for example, a high-resolution display for displaying images, each pixel electrode 130 is individually addressable without interference from adjacent pixels, allowing the image file to be faithfully reproduced on the display. One way to achieve this is to provide an array of nonlinear elements (e.g., transistors or diodes), wherein at least one nonlinear element is associated with each pixel to produce an "active matrix" display (see FIG2). The addressing or pixel electrode 130 that addresses a pixel is connected to an appropriate voltage source via the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this configuration will be used in the following description; however, it is substantially arbitrary, and the pixel electrode may be connected to the source of the transistor.

[0034] Traditionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of columns and rows, such that any particular pixel is uniquely defined by the intersection of a designated column and a designated row (see Figure 3). The sources of all transistors in each row are connected to a single row electrode, and the gates of all transistors in each column are connected to a single column electrode; similarly, the source-to-column and gate-to-row assignments are conventional but essentially arbitrary and can be reversed if necessary. Column electrodes are typically connected to column drivers (gate drivers, gate controllers), which essentially ensures that only one column is selected at any given time. That is, a selection voltage is applied to the selected column electrode to ensure that all transistors in the selected column are turned on, while a non-selection voltage is applied to all other columns to ensure that all transistors in these non-selected columns remain off. Row electrodes are typically connected to row drivers (source drivers, source controllers), which apply selected voltages to the individual row electrodes to drive the pixels in the selected column to their desired optical state. (The voltage mentioned above is relative to a common front electrode, which is typically located on the side of the electro-optic medium opposite to the nonlinear array and extends throughout the entire display.) After a pre-selection interval called the "line address time," the selected column is deselected, the next column is selected, and the voltage on the row driver is changed to write the next line of the display. This process is repeated to write the entire display column by column. The time between consecutive updates of a particular column in the display is called a "frame." Therefore, a display updating at 60Hz has a frame length of 16 milliseconds. Electrophoretic displays can use various frame times, such as 8 millisecond frames, 12 millisecond frames, 5 millisecond frames, etc. In some cases, the frame is greater than 1 millisecond and less than 30 milliseconds.

[0035] It should be noted that the magnitude of the voltage that can be provided in such column drive may be limited by the material used to fabricate the nonlinear element (e.g., thin-film transistor). In many embodiments, the semiconductor material is silicon, particularly amorphous silicon, which is capable of controlling the drive voltage within approximately ±15V. In other embodiments, the semiconductor of the thin-film transistor can be a metal oxide, such as indium gallium zinc oxide (IGZO), which allows for a wider range of drive voltages, for example, up to ±30V, as described in U.S. Patent Publication No. 2022 / 0084473. This design feature is particularly suitable when the drive waveform is used to classify pigments in a multi-particle system. In such systems, it is advantageous to provide at least five voltage levels (high positive voltage, low positive voltage, zero voltage, low negative voltage, and high negative voltage), and the higher the total voltage, the easier it is to separate the particles. For further details, see U.S. Patent Publication No. 2021-0132459.

[0036] Figure 2 in the accompanying drawings depicts an exemplary equivalent circuit of a single pixel of an electrophoretic display. As shown, the circuit includes a storage capacitor 10 formed between the pixel electrode (element 130 in Figures 1A and 1B) and a capacitor electrode. The electrophoretic dielectric 20 is represented as a capacitor and resistor connected in parallel. In some cases, the direct or indirect coupling capacitance 30 between the gate electrode of the transistor associated with the pixel and the pixel electrode (often referred to as "parasitic capacitance") can generate unwanted noise to the display. Typically, the parasitic capacitance 30 is much smaller than the capacitance of the storage capacitor 10, and when a pixel column of the display is selected or deselected, the parasitic capacitance 30 may generate a small negative offset voltage to the pixel electrode, also known as a kickback voltage, which is typically less than 2 volts. [In some embodiments, to compensate for the unwanted "kickback voltage," a common potential Vcom can be provided to the top plate electrode and capacitor electrode associated with each pixel, such that when Vcom is set to a value equal to the kickback voltage (VKB), each voltage supplied to the display may be offset by the same amount and will not experience a net DC imbalance.]

[0037] In conventional electrophoretic displays using an active matrix backplane, each pixel electrode has an associated capacitor electrode (storage capacitor), such that the pixel electrode and the capacitor electrode form a capacitor. See, for example, International Patent Application WO 01 / 07961. In some embodiments, an N-type semiconductor (e.g., amorphous silicon) can be used to form the transistor, and the "selection" and "non-selection" voltages applied to the gate electrode can be positive and negative, respectively.

[0038] Figure 3 shows additional details of the column-row addressing used in an "active matrix" display. Addressing electrodes, or pixel electrodes, that address a pixel are fabricated on substrate 402 and connected to appropriate voltage sources 404 and 406 via associated nonlinear elements. It should be understood that voltage sources 404 and 406 may originate from different circuit elements, or voltage may be delivered with the aid of a single power supply and power management integrated circuit (PMIC). In some cases, an intervening source controller 420 is used to control the supplied voltage; however, in other embodiments, controller 460 is configured to control the entire addressing process, including coordinating the gate and source lines. It should also be understood that while Figure 3 is a schematic diagram of the layout of the active matrix backplane 400, in reality, the active matrix has depth, and some elements (e.g., TFTs) may actually be located below the pixel electrodes, where vias provide electrical connections from the drain to the pixel electrodes above.

[0039] Traditionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of columns and rows, such that any particular pixel is uniquely defined by the intersection of a designated column and a designated row. The sources of all transistors in each row are connected to a single row (scan) line 406, and the gates of all transistors in each column are connected to a single column (gate) line 408; similarly, the source-to-column and gate-to-row assignments are conventional but essentially arbitrary and can be reversed if necessary. Gate line 408 is optionally connected to a gate controller 430, which essentially ensures that at any given time only one column is selected—that is, a selection voltage is applied to the selected column electrode to ensure that all transistors in the selected column are conducting, while a non-selection voltage is applied to all other columns to ensure that all transistors in these non-selected columns remain non-conducting. Row scan lines 406 are optionally connected to source controllers 420, which apply selected voltages to each scan line 406 to drive the pixels in the selected column to their desired optical state. (These voltages are relative to a common top electrode and are not shown in FIG3.) In conventional driving, after a preselected interval called "line addressing time," the selected column is deselected, the next column is selected, and the voltage on the row driver is changed to write the next line of the display. In "typical" backplane driving, this process is repeated linearly to write the entire display column by column. As shown in FIG3, the time interval between the gate voltage pulses of each frame is typically fixed and represents the rhythm of line-by-line addressing. It is worth noting that the present invention does not implement a uniform interval between the gate voltage pulses for the pixel electrodes of the addressing column.

[0040] The active matrix backplane described in Figure 3 is coupled to an electro-optic medium, such as those shown in Figures 1A and 1B, and is typically sealed to form a display module 55 as shown in Figure 4. This display module 55 becomes the focal point of the electrophoretic display 40. The electrophoretic display 40 typically includes a processor 50 configured to coordinate numerous functions related to the display of content on the display module 55 and to convert "standard" images, such as sRGB images, into a color regime that optimally reproduces the images on the display module 55. Of course, if the electrophoretic display is used as a sensor or counter, the content may be correlated with other inputs. The processor is typically a mobile processor chip manufactured, for example, by Freescale or Qualcomm, but other manufacturers are also known. The processor frequently communicates with non-transitory memory 70, removing image files and / or lookup tables from the non-transitory memory 70 to perform color image conversions as described below. The non-transitory memory 70 may also contain gate drive instructions, such that specific color transitions may require different gate drive modes. The electrophoretic display 40 may have more than one non-transitory memory chip. The non-transitory memory 70 may be flash memory. Once the desired image has been converted for display on the display module 55, specific image instructions are transmitted to a controller 60, which facilitates the transmission of voltage sequences to individual thin-film transistors (as described above). Such voltages are typically derived from more than one power supply 80, which may include, for example, a power management integrated circuit (PMIC). The electrophoretic display 40 may additionally include a communication facility 85, which may be, for example, a Wi-Fi protocol or Bluetooth, and allows the electrophoretic display 40 to receive images and instructions, which may also be stored in memory 70. The electrophoretic display 40 may additionally include more than one sensor 90, which may include temperature sensors and / or light sensors, and such information may be fed to a processor 50 to allow the processor to select an optimal lookup table when the lookup table is indexed for ambient temperature or incident illumination intensity or spectrum. In some cases, multiple components of the electrophoretic display 40 may be embedded in a single integrated circuit. For example, dedicated integrated circuits can implement the functions of processor 50 and controller 60.

[0041] As shown in Figure 5, the advanced color electronic paper electrophoretic composition ACEP (e.g., containing a WCMY particle system) works in principle similarly to printing on bright white paper, because the viewer only sees the colored pigments on the viewing side of the white pigment (i.e., the only pigment that scatters light). In Figure 5, it is assumed that the viewing surface of the display is located at the top (as shown), that is, the user views the display from this direction, and the illumination light also occurs from this direction. In Figure 5, it is assumed that the light-scattering particles are white pigment. These light-scattering white particles form a white reflector, against which any particles above the white particles can be viewed (as shown in Figure 5). A portion of the incident light passes through the subtractive color particles, is reflected from the white particles below the subtractive color particles, passes backward through these particles, and exits from the display. Different portions of the incident light are absorbed by the subtractive color particles. Therefore, the particles above the white particles can absorb various colors, and the color presented to the user is the color produced by the combination of particles above the white particles. Any particles positioned below the white particles (located behind from the user's perspective) are obscured by the white particles and do not affect the displayed color. Since the second, third, and fourth particles are essentially non-light-scattering, their order or arrangement relative to each other is not important, but for the reasons already stated, their order or arrangement relative to the white (light-scattering) particles is crucial.

[0042] More specifically, when cyan, magenta, and yellow particles are below white particles (case [A] in Figure 5), there are no particles above the white particles, and the pixel simply displays white. When a single particle is above a white particle, the color of that single particle is displayed; in cases [B], [D], and [F] of Figure 5, these are yellow, magenta, and cyan, respectively. When two particles are above a white particle, the displayed color is a combination of the colors of those two particles; in Figure 5, in case [C], magenta and yellow particles display red; in case [E], cyan and magenta particles display blue; and in case [G], yellow and cyan particles display green. Finally, when all three colored particles are above white particles (case [H] in Figure 5), all incident light is absorbed by these three subtractive primary color particles, and the pixel displays black.

[0043] A subtractive primary color can be rendered by particles that scatter light, resulting in a display containing two types of light-scattering particles: one white and one colored. However, in this case, the position of the light-scattering colored particles relative to other colored particles covering the white particles becomes important. For example, when rendering black (when all three colored particles are above the white particles), the scattering colored particles cannot be above the non-scattering colored particles (otherwise they would be partially or completely hidden behind the scattering particles, and the color rendered would be the color of the scattering colored particles, not black).

[0044] Figure 5 shows the ideal scenario where the color is uncontaminated (i.e., the light-scattering white particles completely block any particles behind them). In reality, the blocking of white particles may be imperfect, such that particles that would ideally be completely blocked may absorb a small amount of light. This contamination typically reduces the brightness and chromaticity of the resulting color. In the electrophoretic medium of this invention, this color contamination should be minimized to the extent that the resulting color conforms to industry standards of color rendering. A particularly popular standard is SNAP (Newspaper Advertising Production Standard), which specifically specifies the L*, a*, and b* values ​​for each of the eight primary colors mentioned above. (In the following text, "primary color" will be used to refer to the eight colors shown in Figure 5: black, white, three subtractive primary colors, and three additive primary colors.)

[0045] Figure 6 (in simplified form) shows a typical waveform used to drive the aforementioned four-particle WCMY electrophoretic display system. The waveforms in Figure 6 produce only eight different colors, i.e., low color depth. Such waveforms have a "push-pull" structure: that is, they consist of dipoles containing pulses of two opposite polarities. Typically, each dipole has a pulse of voltage V1 applied at time t1, followed by a pulse of voltage V2 applied at time t2. The dipoles reach pulse equilibrium when V1t1 + V2t2 = 0. The amplitude and length of these pulses determine the resulting color. At least five such voltage levels are required. Figure 6 shows high and low positive and negative voltages as well as zero volt. Typically, "low" (L) refers to a range of approximately 5-15V, while "high" (H) refers to a range of approximately 15-30V. Generally, the higher the amplitude of the "high" voltage, the better the color gamut achieved by the display. In some cases, especially where more colors are needed, medium voltages are also included. The "medium" (M) level is typically around 15V; however, the value of M depends to some extent on the composition of the particles and the environment of the electrophoresis medium. Due to the need for more control over the position of individual particles, conversions to achieve a greater total number of colors usually involve longer waveforms.

[0046] It is worth noting that for the dipole waveforms in Figure 6, the dipoles used to provide magenta, yellow, green, and blue are at least approximately pulse-balanced. On the other hand, dipole addressing is not necessary to generate black and white. Simple monopole pulses in either direction would cause the colored and white pigments with opposite charges to move toward and away from the viewing surface, so the display behaves in these cases like a conventional display containing black and white pigments. Furthermore, because these monopole pulses are not DC-balanced, additional charge-clearing pulses must be incorporated into the device drive protocol, for example, at the start or end of image updates that may occur during scrolling text, or at the end of extended unbalanced drive sequences. However, even when the waveform is generally pulse-balanced, dipole addressing can disrupt symmetry. For example, there will be... ,and See, for example, Dukhin AS, Dukhin SS, “Aperiodic capillary electrophoresis method using an alternating current electric field for separation of macromolecules.” Electrophoresis, 2005 Jun;26(11):2149-53. Therefore, as long as the pigment mobility depends on the applied electric field, this waveform will cause overall pigment drift.

[0047] Having more than eight different colors available for image processing (i.e., 16 different colors, 32 different colors, 64 different colors, 128 different colors, 256 different colors, or more) allows electro-optic displays to produce images with less graininess, as shown in Figure 7. In Figure 7, the leftmost image shows the original sRGB image, with 256 levels each for R, G, and B. Using eight different colors to render an image in an ACeP-type electrophoretic display results in the image on the left side of the middle; using 16 different colors results in the image on the right side of the middle; and using 64 different colors results in the image on the far right. With the addition of more colors, the image rendered by the ACeP type is improved. There is less graininess in high-contrast areas (e.g., lightning), while sharpness and vibrancy are improved (e.g., in a scarf). However, as previously mentioned, achieving this higher color density has disadvantages in terms of update time and processor / memory requirements.

[0048] As shown in Figure 8, there are at least three methods for an electro-optic display to switch between a first image (where pixels (i, j) have a first color from a large set, e.g., x out of 64 colors) and a second image (where pixels (i, j) have a second color from a large set, e.g., y out of 64 colors). R1 ​​illustrates a more typical driving scheme using a commercially available electrophoresis controller chip and processor. In R1, the transition occurs via a neutral state, i.e., the first color state is driven to a known configuration (e.g., a fully mixed color, black, white), and then the pixel transitions from the neutral state to the second color state. Therefore, less computational power is required to select and provide waveforms (i.e., the transition from the first state to the neutral state and back only requires storing 64 waveforms). However, this update takes longer and is more "flickering" because all electrophoretic particles must be completely rearranged for each update. R2 represents a more refined solution, but with higher computational costs, thus requiring a more complex (and expensive) controller, processor, memory, etc. R2 uses only one state-state waveform for each initial color to each final color. In a 64-color system, this requires 4096 different waveforms. Compared to R1, R2 converts faster and is more user-friendly (provided the necessary processing power is available).

[0049] R3 illustrates one embodiment of the invention, where the computational transformation from a first image to a second image utilizes a mapping from an initial state to a simplified set of color states for faster, more satisfactory updates, but with fewer total waveforms compared to R2. In R3, the processor or controller maps an initial state with 64 colors to a simplified set of 8 colors. This can be done in several ways. The process is illustrated in Figure 9, where each part of the color sphere (CIELAB space) is folded into a single representative color. Typically, the mapping is done using a lookup table in a memory file, but it can also be done mathematically. It is also possible that the color sphere is not divided into equal volumes, as a color gradient between parts of the color sphere is less necessary for the image set. For example, an autumn landscape might require higher color densities of red, yellow, magenta, and cyan, and lower color densities of green and blue. The result of the mapping is that 8 × 64 = 512 waveforms need to be processed and selected, but 512 waveforms are an order of magnitude smaller than 4096 waveforms. Due to the initial color mapping, the final color may exhibit some "slippage" because the waveform used is not as precise as that selected from 4096 options. However, in practice, noticeable differences are rare. In some cases, using a global reset to ensure all pixels are actually in the correct color state may be appropriate, but such a global reset should be performed cautiously or only when the user initiates the process.

[0050] Having described several aspects and embodiments of the technology of this application, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, those skilled in the art will readily conceive of various other means and / or structures for performing functions and / or obtaining the results and / or more than one advantage described herein, and each of such changes and / or modifications is considered to be within the scope of the embodiments described herein. Those skilled in the art will recognize or be able to determine many equivalents of the specific embodiments described herein using only conventional experimentation. Therefore, it should be understood that the foregoing embodiments are presented by way of example only, and embodiments of the invention may be practiced in ways other than those specifically described within the scope of the appended claims and their equivalents. Furthermore, any combination of two or more features, systems, articles, materials, kits, and / or methods described herein is included within the scope of the invention without contradiction.

[0051] 10: Storage capacitors 20: Electrophoretic medium 30: Coupling capacitor 40: Electrophoresis display 50: Processor 55: Display Module 60: Controller 70: Non-temporary memory 80: Power Supply 85: Communication facilities 90: Sensor 101: Electrophoresis Display 102: Electrophoresis display 110: Top transparent electrode 120: Electrophoretic medium 121: Particle 122: Particle 123: Particles 124: Particles 126: Microcapsules 127: Cell walls 130: Bottom electrode 140: Adhesive layer 150:Substrate 160: Protective layer 180: Sealing layer 400: Active matrix backplane 402:Substrate 404: Voltage Source 406: Voltage Source 408: Single-row (gate) line 420: Intermediate Source Controller 430: Gate Controller 460: Controller

Claims

1. A method for driving an electro-optic medium between a first optical state and a second optical state, wherein the electro-optic medium is disposed between first and second electrodes, and the electro-optic medium changes its optical state in response to a voltage sequence applied between the first and second electrodes, wherein the electro-optic medium is capable of generating at least 64 different optical states, the method comprising: The first optical state is mapped to a simplified color state, wherein the first optical state is one of at least 64 different optical states, and the simplified color state is one of no more than 16 different colors; a voltage sequence is identified that causes the electro-optic medium to transition from the simplified color state mapped from the first optical state to the second optical state, wherein the second optical state is one of the at least 64 different optical states; and the voltage sequence is provided between the first and second electrodes.

2. The method of claim 1, wherein the electro-optic medium is capable of generating 128 different optical states.

3. As in request item 1 or 2, where the simplified color state is one of eight different colors.

4. The method of request item 3, wherein the eight different colors are red, green, blue, cyan, yellow, magenta, white and black.

5. The method of request 1 or 2, wherein the mapping step includes matching the first optical state with the simplified color state on a lookup table.

6. The method of request item 1 or 2, wherein the providing step is performed by a controller.

7. The method of claim 1, wherein the electro-optic medium is an electrophoretic medium.

8. The method of claim 7, wherein the electrophoretic medium comprises a reflective white particle and at least one subtractive color particle or a reflective white particle and at least one reflective (non-white) color particle.

9. The method of claim 8, wherein the electrophoretic medium comprises a fourth type of electrophoretic particle.

10. The method of claim 9, wherein two types of particles of such type are negatively charged and two types of particles of such type are positively charged, or wherein one type of particle of such type is negatively charged and three types of particles of such type are positively charged, or wherein three types of particles of such type are negatively charged and one type of particle of such type is positively charged.

11. The method of any one of claims 7-10, wherein the electrophoretic medium is encapsulated in microcapsules or microcells.

12. The method of claim 1 or 2, wherein the first electrode is a light-transmitting electrode and the second electrode is a pixel electrode of a pixel electrode active matrix.

13. The method of request item 1 or 2, wherein the voltage sequence is DC balanced.

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