An improved method for producing full-color electronic paper images with low graininess

Abstract

An improved driving method for a color electro-optic display (e.g., an electrophoretic display with a multi-particle electrophoretic 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 (i.e., 8 colors). In a preferred embodiment, the electro-optic medium is an electrophoretic medium containing 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

Related applications

[0001] This application claims priority to U.S. Provisional Application No. 63 / 624,778, filed January 24, 2024. All patents and documents disclosed therein are incorporated herein by reference in their entirety. Background 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. These 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 have been widely adopted in e-readers because they offer a book-like reading experience, low power consumption, and allow users to carry libraries containing hundreds of books in lightweight handheld devices. Such devices are increasingly being adapted for displaying outdoor digital content, such as shelf labels, outdoor advertising, and traffic signs.

[0003] For many years, electrophoretic displays have contained only two types of charged colored particles: black and white. (To be clear, the term "colored" as used herein includes both black and white.) White particles are typically light-scattering and contain, for example, titanium dioxide, while black particles are absorbent across the visible spectrum and may contain carbon black or absorbing metal oxides, such as copper chromite. In its simplest sense, a monochrome electrophoretic display requires only a light-transmitting electrode at the viewing surface, a back electrode, and an electrophoretic medium containing 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 comprises controllable regions (pixels)—whether segmented electrodes or an active matrix of pixel electrodes controlled by transistors—a pattern can be electronically rendered at the viewing surface. This pattern could be, for example, text in a book.

[0004] Recently, several color options have become commercially available for electrophoretic displays, including three-color displays (black, white, and magenta; black, white, and yellow) and four-color displays (black, white, magenta, and yellow). Similar to the operation of monochrome electrophoretic displays, electrophoretic displays with three or four reflective pigments operate much like ordinary monochrome displays because the desired colored particles are driven onto the viewing surface. This driving scheme is far more complex than that of monochrome displays, but ultimately, the optical function of the particles is 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 for thousands of colors to be produced at each pixel. The color processing is functionally equivalent to printing methods long used in offset and inkjet printers. A given color is produced by using the correct proportions of cyan, yellow, and magenta on a bright white paper background. In the ACeP instance, the relative positions of the cyan, yellow, magenta, and white particles relative to the viewing surface determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors to be displayed at each pixel, the key lies in precisely controlling the position of each pigment (50 to 500 nanometers in size) within a working space approximately 10 to 20 micrometers thick. Clearly, variations in pigment position will result in an incorrect color being displayed at a given pixel. Therefore, fine voltage control is required for such a system. Further details of this system can be found in the following U.S. patents, all of which are incorporated herein by reference in their entirety: 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, having more colors available for display produces better-looking images, especially when the subject is a person or landscape. Furthermore, it has been found that images with the same pixel resolution but a smaller color set tend to appear "grainy" because significant color differences occur when adjacent pixels differ by only one color level. See also Figure 7 However, greater color depth comes at a cost. Achieving hundreds of different color states using an ACeP-like system requires longer waveforms (voltage impulse sequences) so that all colored particles are arranged in the correct order and spacing relative to the white pigment and the top light-transmitting 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 9Furthermore, switching between images with a large number of available colors requires large data files and processors capable of quickly identifying and sending the required waveforms. For example, a direct transition from a first image with 64 available colors to a second image with 64 available colors requires 64*64 = 4096 stored waveforms and a processor capable of identifying and sending the appropriate waveform within approximately 10ms. Processors with this speed are available, but they are typically associated with high-end graphics, artificial intelligence, and cryptocurrency mining. They are also considerably more expensive than processors used in mobile electronics. Therefore, in e-readers / tablets using color electrophoresis media, it is more common 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 choosing from the neutral state to each of the 64 available states. Unfortunately, using neutral transition states prolongs the switching time between states and can also cause unpleasant color flickering as the device “resets” the positions of all particles in the electrophoresis medium.

[0007] The invention described below seeks to reduce the time required for switching between image states while using standard processors and controllers for electrophoretic displays (e.g., those available from Ultrachip, Rockchip, and MTK). This invention relates to color electrophoretic displays, and more particularly, but not exclusively, to electrophoretic displays capable of displaying more than two colors using a single layer of electrophoretic material comprising multiple colored particles (e.g., white, cyan, yellow, and magenta particles). In some instances, two of the particles will be positively charged, while one (or two) of the particles will be negatively charged. In some instances, one of the particles will be positively charged, while three of the particles will be negatively charged. In some instances, one of the particles will be negatively charged, while three of the particles will be positively charged. Additionally, the types of charges on the particle surfaces and / or the types of polymers functionalized on the surfaces may also differ. These particles may contain organic or inorganic pigments or dyes.

[0008] The term "gray state" is used herein in its conventional meaning in the field of imaging, referring to the state intermediate between the two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, in the electrophoretic displays described in several IENK patents and publications mentioned below, where the extreme states are white and dark blue, the intermediate gray state is actually light blue. In fact, as already mentioned, a change in optical state may not be a color change at all. The terms "black" and "white" may 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 strictly black and white, such as the aforementioned white and dark blue states.

[0009] The terms bistable and bistable are used herein in their conventional sense in the art to refer to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, such that after either given element is driven to present its first or second display state by an addressing pulse of finite duration, the state persists for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays supporting grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, as are some other types of electro-optical displays. Such types of displays are aptly referred to as multistable rather than bistable, but for convenience, the term bistable may be used herein to encompass both bistable and multistable displays.

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

[0011] Particles that absorb, scatter, or reflect light over a wide band or at a selected wavelength are referred to herein as colored particles or pigment particles. Various materials other than pigments (which, strictly speaking, mean insoluble colored materials) that absorb or reflect light, 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 extensively researched and developed for many years. In these 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 advantages such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, long-term image quality issues hinder their widespread use. 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 is a liquid, but gaseous fluids can also be used to generate the electrophoretic medium; see, for example, Kitamura, T., et al., Electro-toner movement for electronic paper-like displays, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., Toner displays using triboelectrically charged insulating particles (IDW Japan, 2001, Paper AMD4-4). See also U.S. Patents 7,321,459 and 7,236,291. When the electrophoretic medium is used in an orientation that allows such sedimentation (e.g., in a sign where the medium is positioned in a vertical plane), such gas-based electrophoretic media appear to be prone to the same type of problems caused by particle sedimentation as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoresis media than in liquid-based electrophoresis media because gaseous suspensions have lower viscosity than liquid suspensions, which causes electrophoretic particles to settle faster.

[0014] Numerous patents and applications transferred to or in the name of MIT and Einkel describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media comprise a plurality of small capsules, each capsule containing an inner phase and a capsule wall surrounding the inner phase, wherein the inner phase contains electrophoretically mobile particles in a fluid medium. Typically, the capsules themselves are held in a polymer binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0015] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0016] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0017] (c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

[0018] (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

[0019] (e) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0020] (f) Backsheets, adhesive layers and other auxiliary layers, and methods for use in displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0021] (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; No. 7,821,702; No. 7,839,564; No. 7,910,175; No. 7,952,790; No. 7,956,841; No. 7,982,941; No. 8,040,594; No. 8,054,526; No. 8,098,418; No. 8,159,636; No. 8,2 No. 13,076; No. 8,363,299; No. 8,422,116; No. 8,441,714; No. 8,441,716; No. 8,466,852; No. 8,503,063; No. 8,576,470; No. 8,576,475; No. 8,593,721; No. 8,605,3 No. 54; No. 8,649,084; No. 8,670,174; No. 8,704,756; No. 8,717,664; No. 8,786,935; No. 8,797,634; No. 8,810,899; No. 8,830,559; No. 8,873,129; No. 8,902,153 No. 8,902,491; No. 8,917,439; No. 8,964,282; No. 9,013,783; No. 9,116,412; No. 9,146,439; No. 9,164,207; No. 9,170,467; No. 9,170,468; No. 9,182,646; No. 9, U.S. Patent Application Publication Nos. 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 Nos. 2008 / 0043318, 2008 / 0048970, 2009 / 0225398, 2010 / 0156780, 2011 / 0043543, 2012 / 0326957, 2013 / 0242378, and 2013 / 0278995.No. 2014 / 0055840; No. 2014 / 0078576; No. 2014 / 0340430; No. 2014 / 0340736; No. 2014 / 0362213; No. 2015 / 0103394; No. 2015 / 0118390; No. 2015 / 0124345; No. 2015 / 0198858; Nos. 2015 / 0234250, 2015 / 0268531, 2015 / 0301246, 2016 / 0011484, 2016 / 0026062, 2016 / 0048054, 2016 / 0116816, 2016 / 0116818, and 2016 / 0140909;

[0022] (h) A method for 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; and 7,202,847. No. 7,242,514; No. 7,259,744; No. 7,304,787; No. 7,312,794; No. 7,327,511; No. 7,408,699; No. 7,453,445; No. 7,492,339; No. 7,528,822; No. 7,545,358; No. 7,5 No. 83,251; No. 7,602,374; No. 7,612,760; No. 7,679,599; No. 7,679,813; No. 7,683,606; No. 7,688,297; No. 7,729,039; No. 7,733,311; No. 7,733,335; No. 7,787,1 No. 69; No. 7,859,742; No. 7,952,557; No. 7,956,841; No. 7,982,479; No. 7,999,787; No. 8,077,141; No. 8,125,501; No. 8,139,050; No. 8,174,490; No. 8,243,013; No. 8,274,472; No. 8,289,250; No. 8,300,006; No. 8,305,341; No. 8,314,784; No. 8,373,649; No. 8,384,658; No. 8,456,414; No. 8,462,102; No. 8,514,168; No. 8,5 No. 37,105; No. 8,558,783; No. 8,558,785; No. 8,558,786; No. 8,558,855; No. 8,576,164; No. 8,576,259; No. 8,593,396; No. 8,605,032; No. 8,643,595; No. 8,665,2 No. 06; No. 8,681,191; No. 8,730,153; No. 8,810,525; No. 8,928,562; No. 8,928,641; No. 8,976,444; No. 9,013,394; No. 9,019,197; No. 9,019,198; No. 9,019,318;Patent Application Publication Nos. 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 Publication Nos. 2003 / 0102858; 2004 / 0246562; 2005 / 0253777; and 2007 / 0091418. No. 2007 / 0103427; No. 2007 / 0176912; No. 2008 / 0024429; No. 2008 / 0024482; No. 2008 / 0136774; No. 2008 / 0291129; No. 2008 / 0303780; No. 2009 / 0174651; No. 200 No. 9 / 0195568; No. 2009 / 0322721; No. 2010 / 0194733; No. 2010 / 0194789; No. 2010 / 0220121; No. 2010 / 0265561; No. 2010 / 0283804; No. 2011 / 0063314; No. 2011 / 017 No. 5875; No. 2011 / 0193840; No. 2011 / 0193841; No. 2011 / 0199671; No. 2011 / 0221740; No. 2012 / 0001957; No. 2012 / 0098740; No. 2013 / 0063333; No. 2013 / 0194250 No. 2013 / 0249782; No. 2013 / 0321278; No. 2014 / 0009817; No. 2014 / 0085355; No. 2014 / 0204012; No. 2014 / 0218277; No. 2014 / 0240210; No. 2014 / 0240373; No. 201 No. 4 / 0253425; No. 2014 / 0292830; No. 2014 / 0293398; No. 2014 / 0333685; No. 2014 / 0340734; No. 2015 / 0070744; No. 2015 / 0097877; No. 2015 / 0109283; No. 2015 / 021 No. 3749; No. 2015 / 0213765; No. 2015 / 0221257; No. 2015 / 0262255; No. 2015 / 0262551; No. 2016 / 0071465; No. 2016 / 0078820; No. 2016 / 0093253; No. 2016 / 0140910;and No. 2016 / 0180777; (these patents and applications may be referred to below as MEDEOD (method for driving an electro-optic display) applications);

[0023] (i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and

[0024] (j) Non-electrophoretic displays, such as those described in U.S. Patent No. 6,241,921; and U.S. Patent Application Publication No. 2015 / 0277160; and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0025] 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 dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer dispersion electrophoretic display can be considered as capsules or microcapsules, even without a discrete capsule membrane associated with each individual droplet; see, for example, U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0026] One related type of electrophoretic display is the so-called microcell electrophoretic display. In a microcell electrophoretic display, charged particles and fluid are not encapsulated in microcapsules, but are held in multiple cavities formed within a carrier medium (typically a polymer membrane). See, for example, U.S. Patents 6,672,921 and 6,788,449.

[0027] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light transmission through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called shutter mode, in which one display state is substantially opaque and the other display state is transmissive. 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. Dielectric electrophoretic 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 may also be able to operate in shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures of full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or conceal a second layer further away from the viewing surface.

[0028] Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic equipment and offer several advantages, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The term "printing" is intended to include all forms of printing and coating, including but not limited to: pre-metering coatings such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coatings such as doctor blade roller coating, forward and reverse roller coating; concave coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; 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 a variety of methods), the display itself can be manufactured inexpensively.

[0029] As described above, most simple existing electrophoretic media essentially display only two colors. Such electrophoretic media either use a single type of electrophoretic particles with a first color in a colored fluid, which has a different second color (in this case, the first color is displayed when the particles are near the viewing surface of the display, and the second color is displayed when the particles are far from the viewing surface), or use first and second types of electrophoretic particles with different first and second colors in a colorless fluid (in this case, the first color is displayed when the first type of particles are near the viewing surface of the display, and the second color is displayed when the second type of particles are near the viewing surface). Typically, these two colors are black and white. If a full-color display is required, an array of color filters can be placed on the viewing surface of a monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color mixing to generate color stimuli. The available display area is shared among three or four primary colors (such as red / green / blue (RGB) or red / green / blue / white (RGBW)), and the color filters can be arranged in a one-dimensional (strip) or two-dimensional (2x2) repeating pattern. Other primary color choices or choices of more than three primary colors are also known in the art. Three (in the case of an RGB monitor) or four (in the case of an RGBW monitor) subpixels are chosen to be small enough that at the intended viewing distance, they visually blend together to form a single pixel with a uniform color stimulus (“color blending”). An inherent drawback of area sharing is that the colorant is always present and can only be modulated by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW monitor, the red, green, blue, and white primary colors each occupy a quarter of the display area (one of the four subpixels), where the white subpixel is as bright as the white of the underlying monochrome display, and the brightness of each colored subpixel is no less than one-third of the brightness of the white of the monochrome display. The brightness of the white color displayed by the entire monitor cannot exceed half the brightness of the white subpixel (the white area of ​​the monitor is generated by displaying one white subpixel out of every four subpixels, plus each colored subpixel in its colored form, each colored subpixel being equivalent to one-third of the white subpixel, so the combined contribution of three colored subpixels does not exceed that of the single white subpixel). By sharing area with colored pixels that have switched to black, the brightness and saturation of the color are reduced. Area sharing is particularly problematic when mixing yellow, as it is brighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching blue pixels (a quarter of the display area) to black makes the yellow too dark.

[0030] U.S. Patents 8,576,476 and 8,797,634 describe multicolor electrophoretic displays with a single backplane containing independently addressable pixel electrodes and a common light-transmitting front electrode. Multiple 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, there are drawbacks to using multiple electrophoretic layers located between a single set of addressable electrodes. The particles in a particular layer experience a lower electric field compared to 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 undesirable absorption) can affect the appearance of the image formed in the underlying electrophoretic layer.

[0031] 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 clean, colorless or colored solvent, the electrophoretic fluid being disposed between a common electrode and multiple pixel or driving electrodes. The driving electrodes are arranged to expose a background layer. U.S. Patent No. 9,116,412 describes a method for driving a display unit 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 dispersed with uncharged or slightly charged colored particles. The method involves driving the display unit to display the color of the solvent or the color of the uncharged or slightly charged colored particles by applying a driving voltage of approximately 1% to 20% of the full driving voltage. 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 first, second, and third types of pigment particles, all of which are dispersed in a solvent or solvent mixture. The first and second types of pigment particles carry opposite charge polarities, and the third type of pigment particles has a charge level approximately 50% lower than that of the first or second types. These three types of pigment particles have different levels of threshold voltage, or different levels of mobility, or both.

[0032] Electrophoretic displays capable of displaying any color at any pixel location have been described in U.S. Patent Nos. 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 high applied voltage. In the '111 patent, a panchromatic electrophoretic display is described in which four pigments are present: white, cyan, magenta, and yellow, two of which are positively charged and two are negatively charged. U.S. Patent Publication No. 2022 / 0082896 describes a panchromatic electrophoretic display in which four pigments are present: white, cyan, magenta, and yellow, three of which are positively charged and the white pigment is negatively charged. Embodiments of this type in the present invention are referred to as CMYW embodiments.

[0033] In addition, there are multi-particle display designs in which colored pigments scatter light (i.e., reflective colored particles). U.S. Patent No. 10,339,876 describes a display of this type with 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

[0034] This document discloses an improved method for driving a panchromatic electro-optic medium between a first optical state and a second optical state, wherein the electro-optic medium is disposed between a first electrode and a second electrode, and the electro-optic medium changes its optical state in response to a voltage sequence applied between the first electrode and the second electrode, wherein the electro-optic medium is capable of generating at least 64 different optical states. The method includes: mapping a first optical state to a simplified color state, wherein the first optical state includes 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 mapped from the first optical state to a second optical state, wherein the second optical state includes one of the at least 64 different optical states; and providing the voltage sequence between the first electrode and the second electrode. 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 includes matching the first optical state and the simplified color state on a lookup table. In some embodiments, the provided steps are performed by a controller. In some embodiments, the electro-optic medium is an electrophoretic medium. In some embodiments, the electrophoretic medium comprises reflective white particles and at least one subchromatic colored particle, or reflective white particles and at least one reflective colored particle. In some embodiments, the electrophoretic medium comprises a fourth type of electrophoretic particles. In some embodiments, two types of particles are negatively charged and two types of particles are positively charged, or one type of particles is negatively charged and three types of particles are positively charged, or three types of particles are negatively charged and one type of particles is positively charged. In some embodiments, the electrophoretic medium is encapsulated in a microcapsule or microcell. In some embodiments, the first electrode is a light-transmitting electrode, and the second electrode is a pixel electrode in a pixel electrode active matrix. In some embodiments, the voltage sequence is DC balanced. Attached Figure Description

[0035] This patent or application document contains at least one color-drawn drawing. A copy of the patent or application publication with the color drawing will be provided by the authorities upon request and payment of the necessary fees.

[0036] Figure 1A This is a representative cross-sectional view of a four-particle electrophoresis display, in which the electrophoretic medium is encapsulated in a capsule. Figure 1A The structure can be used in multi-particle electrophoretic media containing both reflective and hypochromic pigment particles.

[0037] Figure 1B This is a representative cross-sectional view of a four-particle electrophoretic display, in which the electrophoretic medium is encapsulated in microcells. Figure 1B The structure can be used in multi-particle electrophoretic media containing both reflective and hypochromic pigment particles.

[0038] Figure 2 An exemplary equivalent circuit for a single pixel of an electrophoretic display using an active matrix backplane with pixel electrodes coupled to a storage capacitor is shown.

[0039] Figure 3 This is a schematic diagram of an exemplary driving system for controlling the voltage supplied to pixel electrodes in an active matrix device. The resulting driving voltage can be used to set the optical state of a multi-particle electrophoretic medium.

[0040] Figure 4 An exemplary electrophoretic display including a display module is shown. 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 environmental factors such as temperature and lighting.

[0041] Figure 5 The preferred positions for each of the four particle sets to produce eight standard colors are shown in a white-cyan-magenta-yellow (WCMY) four-particle electrophoretic display, where the white particles are reflective and the cyan, magenta and yellow particles are absorptive.

[0042] Figure 6 An exemplary push-pull drive scheme is shown for addressing an electrophoretic medium containing three subchromatic (cyan, yellow, and magenta) particles and one scattering (white) particle.

[0043] Figure 7 The image shows the difference in graininess for the same image with the same pixel resolution but different color "depths" (i.e., the number of different colors available per pixel).

[0044] Figure 8 A comparison is shown between R1 drive (using a neutral state), R2 drive (creating / storing waveforms for each possible transition between a first color state and a second color state), and R3 (which is the method of the present invention, involving mapping previous image color states to simplified color states, thereby greatly reducing the number of waveforms that must be created / stored).

[0045] Figure 9 This paper demonstrates a possible method for mapping the set of available color states to simplified colors. Detailed Implementation

[0046] This invention includes a color electro-optic display, such as 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 containing 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. Because the electrophoretic medium has a degree of tolerance, it provides a simplified set of instructions, i.e., waveforms for driving from 8 color states to 128 color states, which is sufficient for image changes with high color depth (i.e., 128 colors). Therefore, the size of the lookup table for a given set of operating conditions is reduced (e.g., 1024 entries per lookup table compared to 16,384 entries per lookup table), thereby reducing storage requirements and the processing time required to provide updates.

[0047] The method of this invention is applicable to many different types of electro-optic displays, such as LCDs, LEDs, OLEDs, rLCDs, and EPDs. However, the method of this invention is particularly applicable to electrophoretic displays containing four (or more) particles, as discussed in the background section. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into a microcell structure subsequently sealed with a polymer layer. The microcapsules or microcell layers can be coated or laminated onto a plastic substrate or a film with a transparent conductive material coating. Alternatively, microcapsules can be coated onto a light-transmitting substrate or other electrode material using a spraying technique. (See U.S. Patent No. 9,835,925, incorporated herein by reference). The resulting assembly can be laminated to a backplane with pixel electrodes using a conductive adhesive. The assembly can also be attached to one or more segmented electrodes on the backplane, wherein the segmented electrodes are directly driven.

[0048] The electrophoretic medium used herein includes charged particles that differ in color, reflective or absorptive properties, charge density, and mobility in an electric field (measured in zeta potential). Particles that absorb, scatter, or reflect light over a broad wavelength or at selected wavelengths are referred to herein as colored or pigment particles. Various other light-absorbing or reflecting materials (strictly meaning insoluble colored materials in the strict sense of the term), such as dyes, photonic crystals, quantum dots, etc., besides pigments, can also be used in the electrophoretic medium and displays of the present invention. For example, the electrophoretic medium may include 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 particles being light-scattering particles, the second particles 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 having a subtractive primary color different from each other and different from the second particles, 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.

[0049] The electrophoretic medium of the present invention may contain any additives used in prior art electrophoretic media, such as those described in the aforementioned patents and applications of Einkel and MIT. Thus, for example, the electrophoretic medium of the present invention will typically include at least one charge control agent to control the charge on the individual particles, and a fluid therein may dissolve or disperse polymers having a number average molecular weight of more than about 20,000 and substantially not adsorbed onto the particles to improve the bistability of the display, as described in the aforementioned U.S. Patent No. 7,170,670.

[0050] 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 completely light-scattering particles or completely non-light-scattering particles. The minimum light scattering level of the light-scattering particles used in the electrophoretic medium of the present invention, and the maximum tolerable light scattering level of the substantially non-light-scattering particles, may vary depending on factors such as the exact pigments used, their colors, and the user's or application's ability to tolerate deviations from the desired color. The light scattering and absorption characteristics of the pigments can be evaluated by measuring the diffuse reflectance of the pigment sample dispersed in a suitable matrix or liquid on black and white backgrounds. The results of such measurements can be interpreted according to various models well known in the art (e.g., one-dimensional Kubelka-Munk processing). In the present invention, it is preferred that when the white pigment is distributed substantially isotropically at a volume ratio of 15% in a 1-micron thick layer comprising the pigment and a liquid with a refractive index less than 1.55, the diffuse reflectance exhibited at 550 nm, measured against a black background, is at least 5%. Yellow, magenta, and cyan pigments preferably exhibit diffuse reflectance of less than 2.5% at 650 nm, 650 nm, and 450 nm, respectively, measured against a black background under the same conditions. (The measurement wavelengths selected above for 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 hereinafter as “non-scattering” or “substantially non-light-scattering”. Specific examples of suitable particles are disclosed in U.S. Patent No. 9,921,451, which is incorporated herein by reference.

[0051] Alternative particle sets may also be used, including four sets of reflective particles, or one absorbent particle with three or four different sets of reflective particles, as described, for example, in U.S. Patents 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 pigments such as Black 26 or 28 (e.g., manganese iron black spinel or copper chromite black spinel) or carbon black. Third / fourth / fifth type particles may be colors such as red, green, blue, magenta, cyan, or yellow. Pigments for this type of particle may include, but are not limited to, CI pigments PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155, or PY20. Specific examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Powder E-EDS, PV Solid 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, Benzidine Yellow, or Benzidine AAOT Yellow.

[0052] like Figure 1A and Figure 1BAs shown, 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 an active matrix of pixels controlled by thin-film transistors (TFTs). In the electrophoretic medium 120 described herein, four different types of particles 121, 122, 123, and 124 are present, but more (or fewer) particle sets can be used in the methods and displays described herein. For example, the technique of the present invention can be used for a set of three types of particles, such as white, black, and red, wherein one of the three different types of particles has a lower charge than the other two types of particles. In some instances, two particles will be positively charged, while one (or two) particles will be negatively charged. In some instances, one particle will be positively charged, while three particles will be negatively charged. In some instances, one particle will be negatively charged, while three particles will be positively charged. The electrophoretic medium 120 is typically separated by the walls of microcapsules 126 or microunits 127. An optional adhesive layer 140 can be disposed near 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), but more commonly a single layer is used. The entire display stack is typically disposed on a substrate 150, which may be rigid or flexible. The displays (101, 102) typically also 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 the ingress of water, etc. The electrophoretic displays (101, 102) may also include a sealing layer 180 if desired. In some embodiments, the adhesive layer 140 may include a substrate component to improve adhesion to the electrode layer 110, or a separate substrate layer may be used. Figure 1B (Not shown in the image). The structure and components of the electrophoretic display, pigments, binders, electrode materials, etc., are described in numerous patents and patent applications published by Einkel, 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.

[0053] In some embodiments, such as Figure 1A As shown, an electrophoretic display may include light-transmitting electrodes, an electrophoretic medium, and multiple back pixel electrodes. To produce a high-resolution display, such as 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 method to achieve this is to provide an array of nonlinear elements (e.g., transistors or diodes), with each pixel associated with at least one nonlinear element to produce an "active matrix" display. (See also...) Figure 2 The addressing electrode or pixel electrode 130 that addresses a pixel is connected to a suitable voltage source via an associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be used in the following description, although it is essentially arbitrary and the pixel electrode may be connected to the source of the transistor.

[0054] Typically, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely identified by the intersection of a specified row and a specified column. (See also...) Figure 3 In a column, the sources of all transistors are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode. Similarly, source-to-row and gate-to-column assignment is conventional but largely arbitrary and can be reversed if needed. Row electrodes are typically connected to row drivers (gate drivers, gate controllers), which essentially ensure that only one row is selected at any given time. That is, a selection voltage is applied to the selected row electrode to ensure all transistors in the selected row are turned on, while a non-selection voltage is applied to all other rows to ensure all transistors in these unselected rows remain off. Column electrodes are typically connected to column drivers (source drivers, source controllers), which apply selected voltages to different column electrodes to drive the pixels in the selected row to their desired optical state. (The aforementioned voltage is relative to a common front electrode, which is conventionally provided on the side of the electro-optic medium opposite to the nonlinear array and extends throughout the entire display.) After a preselection interval called the “row addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write the next row of the display. This process is repeated, thus writing to the entire display row by row. The time between consecutive updates of a particular row in the display is called a “frame.” Thus, a display updating at 60Hz has a frame of 16 milliseconds. Various frame times are available for electrophoretic displays, such as 8-millisecond frames, 12-millisecond frames, 5-millisecond frames, etc. In some instances, the frame is longer than 1 millisecond and shorter than 30 milliseconds.

[0055] It should be noted that the voltage amplitude available in such row-column drive may be limited by the material of the nonlinear element (e.g., thin-film transistor). In many embodiments, the semiconductor material is silicon, particularly amorphous silicon, which is capable of controlling drive voltages on the order of ±15 V. 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, such as up to ±30 V, as described in U.S. Patent Publication No. US2022 / 0084473. This design feature is particularly relevant for driving waveforms to classify pigments in multi-particle systems. In such systems, it is advantageous to provide at least five voltage levels (high positive, low positive, zero, low negative, high negative), and using a higher total voltage makes it easier to separate particles. For further details, see U.S. Patent Publication No. 2021-0132459.

[0056] The attached diagram Figure 2 An exemplary equivalent circuit for a single pixel of an electrophoretic display is depicted. As shown in the figure, the circuit includes a pixel electrode ( Figure 1A and 1B The storage capacitor 10 is formed between the element 130 in the image and the capacitor electrode. The electrophoretic dielectric 20 is represented as a capacitor and resistor connected in parallel. In some instances, the direct or indirect coupling capacitance 30 between the gate of the transistor associated with a pixel and the pixel electrode (often referred to as "parasitic capacitance") can introduce unwanted noise into the display. Typically, the parasitic capacitance 30 is much smaller than the storage capacitor 10, and when a pixel row of the display is selected or deselected, the parasitic capacitance 30 can cause a small negative offset voltage, also known as a "recoil voltage," to appear on the pixel electrode, which is typically less than 2 volts. [In some embodiments, to compensate for the unwanted "recoil voltage," a common potential V can be provided to the top plane electrode and the capacitor electrode associated with each pixel.] com , so that when V com Set to be related to the recoil voltage V KB When the values ​​are equal, each voltage supplied to the display is offset by the same amount, and no net DC imbalance is produced.

[0057] In conventional electrophoretic displays using an active matrix backplane, each pixel electrode is associated with a 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, N-type semiconductors (e.g., amorphous silicon) can be used to form transistors, and the “select” and “non-select” voltages applied to the gate can be positive and negative, respectively.

[0058] Figure 3Additional details of row and column addressing used in an "active matrix" display are shown. Addressing electrodes, or pixel electrodes (which address one pixel), are fabricated on substrate 402 and connected to appropriate voltage sources 404 and 406 via associated nonlinear elements. It will be understood that voltage sources 404 and 406 may originate from individual circuit elements or may deliver voltage with the assistance of a single power supply and power management integrated circuit (PMIC). In some instances, an intermediate 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... Figure 3 This is a layout diagram of an active matrix backplane 400, but in reality, the active matrix has depth, and some components (such as TFTs) may actually be located below the pixel electrodes, providing electrical connections from the drain to the pixel electrodes above via vias.

[0059] Conventionally, in a high-resolution array, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of a designated row and a designated column. The sources of all transistors in each column are connected to a single column (scan) line 406, while the gates of all transistors in each row are connected to a single row (gate) line 408; similarly, assigning sources to rows and gates to columns is conventional but essentially arbitrary and can be reversed if necessary. Gate lines 408 are optionally connected to a gate controller 430, which essentially ensures that only one row is selected at any given time, i.e., a selection voltage is applied to the selected row electrode to ensure that all transistors in the selected row are turned on, while a non-selection voltage is applied to all other rows to ensure that all transistors in these unselected rows remain off. Column scan lines 406 are optionally connected to a source controller 420, which applies selected voltages to the respective scan lines 406 to drive the pixels in the selected rows to their desired optical state. (The aforementioned voltages are relative to a common top electrode.) Figure 3 (Not shown in the image). In a conventional drive, after a preselection interval called "row addressing time," the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write the next row of the display. In a "typical" backplane drive, this process is repeated linearly, thus writing to the entire display row by row. Figure 3 As shown, the time interval between gate voltage pulses in each frame is typically constant, representing the rhythm of line-by-line addressing. It is worth noting that this invention does not implement a uniform interval between gate voltage pulses for a given pixel electrode addressing line.

[0060] Combination Figure 3 The described active matrix backplane is coupled to an electro-optic medium (e.g., ... Figure 1A and Figure 1B(as shown), and is typically sealed to create display module 55, such as Figure 4 As shown. Such a display module 55 forms the core of the electrophoretic display 40. The electrophoretic display 40 will typically include a processor 50, which is configured to coordinate many functions related to displaying content on the display module 55 and convert “standard” images (e.g., sRGB images) into a color scheme that best reproduces the image on the display module 55. Of course, if the electrophoretic display is used as a sensor or counter, the content may relate to other inputs. The processor is typically a mobile processor chip, such as those made by Freescale or Qualcomm, although other manufacturers are also known. The processor communicates frequently with a non-transitory memory 70, from which it retrieves image files and / or lookup tables to perform the color image conversions described below. The non-transitory memory 70 may also include gate drive instructions, to some extent requiring different gate drive modes for specific color transitions. 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 is converted for display on the display module 55, specific image instructions are sent to a controller 60, which facilitates the transmission of voltage sequences to the respective thin-film transistors (as described above). Such voltages typically originate from one or more power supplies 80, which may include, for example, a power management integrated circuit (PMIC). The electrophoretic display 40 may additionally include communication 85, which may be, for example, a Wi-Fi protocol or Bluetooth, and allow the electrophoretic display 40 to receive images and instructions, which may also be stored in memory 70. The electrophoretic display 40 may additionally include one or more sensors 90, which may include temperature sensors and / or photoelectric sensors, and such information may be fed to processor 50 to allow the processor to select the optimal lookup table based on ambient temperature or incident illumination intensity or spectral index. In some instances, multiple components of the electrophoretic display 40 may be embedded in a single integrated circuit. For example, an application-specific integrated circuit (ASIC) may implement the functions of processor 50 and controller 60.

[0061] like Figure 5 As shown, the advanced color electronic paper electrophoresis composition ACEP (e.g., containing a WCMY particle system) works in principle similar to printing on bright white paper, where the viewer can only see the colored pigments located on the white pigment viewing side (i.e., the pigments that uniquely scatter light). Figure 5 In this example, we assume the viewing surface of the monitor is at the top (as shown in the figure), meaning the user views the monitor from this direction, and the illumination light also enters from this direction. Figure 5 In this context, it is assumed that the light-scattering particles are white pigments. These light-scattering white particles form a white reflector, and any particles located above the white particles (such as...) Figure 5(As shown) are all observed in contrast to this reflector. A portion of the incident light passes through the subtractive particles, is reflected by the white particles below them, then passes back through these particles and exits the display. Another portion of the incident light is absorbed by the subtractive particles. Therefore, the particles above the white particles may absorb various colors, and the color displayed to the user is produced by the combination of particles above the white particles. Any particles positioned below the white particles (behind them from the user's perspective) will be obscured by the white particles and will not affect the displayed color. Because 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.

[0062] More specifically, when cyan, magenta, and yellow particles are located below white particles ( Figure 5 In scenario [A], there are no particles above the white particle, and the pixel simply displays white. When a single particle is above a white particle, the color of that single particle is displayed, i.e. Figure 5 In the middle cases [B], [D], and [F], yellow, magenta, and cyan are displayed, respectively. When two particles are positioned 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 appear red; in case [E], cyan and magenta particles appear blue; and in case [G], yellow and cyan particles appear green. Finally, when all three colored particles are above the white particle ( Figure 5 In the case of [H], all incident light is absorbed by the three subtractive primary color particles, and the pixel displays black.

[0063] It's possible that a subtractive primary color could be represented by a single light-scattering particle, 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 particle relative to other colored particles covering the white particles becomes crucial. For example, when rendering black (when all three colored particles are on top of the white particles), the scattering colored particles cannot be on top of the non-scattering colored particles (otherwise, they would be partially or completely hidden behind the scattering particles, and the color displayed would be the color of the scattering colored particles, not black).

[0064] Figure 5An idealized scenario is illustrated where the color is uncontaminated (i.e., light-scattering white particles completely obscure any particles behind them). In practice, the obscuring of white particles may not be perfect, and therefore a small amount of light may be absorbed by particles that should ideally be completely obscured. This contamination typically reduces both the brightness and chromaticity of the rendered color. In the electrophoretic medium of this invention, this color contamination should be minimized to the extent that the resulting color conforms to industry color reproduction standards. A particularly favored standard is SNAP (Newspaper Advertising Production Standard), which assigns L*, a*, and b* values ​​to each of the eight primary colors mentioned above. (In the following text, "primary color" will be used to refer to...) Figure 5 The eight colors shown are: black, white, three subtractive primary colors, and three additive primary colors.

[0065] Figure 6 Typical waveforms (simplified form) for driving the aforementioned four-particle WCMY electrophoresis display system are shown. Figure 6 The waveforms in the diagram produce only eight different colors, i.e., low color depth. These waveforms have a "push-pull" structure: that is, they consist of a dipole containing two pulses of 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 dipole is impulse-balanced when V1t1 + V2t2 = 0. The amplitude and length of these pulses determine the color obtained. There should be at least five such voltage levels. Figure 6 The diagram shows high, low positive and negative voltages, as well as zero volt. Generally, "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 instances, especially when more colors are required, medium voltages are also included. "Medium" (M) levels are typically around 15V; however, the value of M will depend to some extent on the composition of the particles and the environment of the electrophoretic medium. Achieving a larger total number of colors typically involves longer waveforms because more control over the position of the individual particles is required.

[0066] It is worth noting that, for Figure 6The dipole waveforms used to provide magenta, yellow, green, and blue dipoles are at least approximately impulse-balanced. On the other hand, generating black and white does not necessarily require dipole addressing. A simple monopole pulse along either direction will move the colored and white pigments with opposite charges toward or away from the viewing surface, thus causing the display to behave similarly to a conventional display containing black and white pigments in these cases. Furthermore, because these monopole pulses are not DC-balanced, additional charge-clearing pulses must be incorporated into the device drive protocol, either at the beginning or end of an image update, or at the end of an extended unbalanced drive sequence (which may occur when scrolling text). However, even if the waveform is impulse-balanced overall, dipole addressing can break symmetry. For example, ∫Vdt = 0 and ∫V³dt ≠ 0. See, for example, Dukhin AS, Dukhin SS, “Aperiodic capillary electrophoresis method using an alternating current electric field for separation of macromolecules”, Electrophoresis, June 2005; 26(11):2149-53. Thus, as long as the pigment mobility depends on the applied electric field, this waveform could lead to overall pigment drift.

[0067] Having more than eight different colors available for image processing—that is, 16, 32, 64, 128, 256, or more different colors—enables electro-optic displays to produce images such as... Figure 7 The image shown has less graininess. Figure 7 The leftmost image displayed is a raw sRGB image with 256 levels for each of R, G, and B. The left-middle image is obtained by displaying the image using an ACeP electrophoresis display with 8 different colors, the right-middle image using an ACeP electrophoresis display with 16 different colors, and the rightmost image using an ACeP electrophoresis display with 64 colors. With the addition of more colors, the image presented by the ACeP display is improved. There is less graininess in high-contrast areas (e.g., lightning), and sharpness and vibrancy are enhanced (e.g., in a scarf). However, as mentioned earlier, there are drawbacks in terms of update time and processor / memory requirements for achieving this higher color density.

[0068] There are at least three ways to make an electro-optical display transition between a first image and a second image, where a pixel (i, j) has a first color from a large set (e.g., color x out of 64 colors) and transitions to a second color from another large set (e.g., color y out of 64 colors), such as... Figure 8 As shown, 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, where a first color state is driven to a known configuration (e.g., a fully mixed color, such as black and white), and then the pixel transitions from the neutral state to the second color state. Therefore, less computational power is needed to select and provide waveforms (i.e., only 64 waveforms need to be stored for the transition from the first state to the neutral state and back). However, this update time is longer and more "flickering" because all electrophoretic particles must be completely rearranged with each update. R2 represents a more elegant solution, but it is computationally more expensive, requiring a more complex (and costly) controller, processor, memory, etc. R2 simply uses a state-to-state waveform for each starting color to each final color. In the case of a 64-color system, this requires 4096 different waveforms. Compared to R1, R2 transitions are faster and more user-friendly (provided sufficient processing power is available).

[0069] One embodiment of the invention is illustrated by R3, wherein the computed transition from image 1 to image 2 utilizes a mapping from initial states to a simplified set of color states to allow for faster, more pleasant updates, but with less total waveform than R2. In R3, the processor or controller maps the initial states of 64 colors to a simplified set of 8 colors. This can be accomplished in various ways. The process in Figure 9 The diagram illustrates how each part of the color sphere (CIELAB space) is folded into a single representative color. Typically, mapping is done using a lookup table in a memory file, but it can also be done mathematically. The color sphere may not be divided into equal volumes because the need for color gradations in one part of the color sphere is less than for another for a collection of images. For example, an autumn landscape might require higher color densities in red, yellow, magenta, and cyan, and less in green and blue. The result of this mapping is that 8 x 64 = 512 waveforms need to be processed and selected; however, 512 waveforms are an order of magnitude smaller than 4096 waveforms. Due to the color mapping of the initial state, the final colors may have some "deviation" because the waveforms used are not as precise as those selected from 4096 options. However, in practice, significant differences are rare. In some instances, a global reset might be appropriate to ensure that all pixels are actually in the correct color state, but such a global reset should be done sparingly or only at user startup.

[0070] Having described several aspects and embodiments of the present technology, it should be recognized that various changes, modifications, and improvements will be readily apparent to those skilled in the art. These changes, modifications, and improvements are intended to fall within the spirit and scope of the technology described herein. For example, those skilled in the art will foresee various other means and / or structures for performing the functions described herein and / or obtaining the results and / or one or more advantages described herein, and each of these changes and / or modifications is considered to be within the scope of the embodiments described herein. Those skilled in the art will recognize, or can determine, many equivalents of the specific embodiments described herein using only conventional experimentation. Therefore, it should be understood that the foregoing embodiments are presented as examples only, and that inventive embodiments may be practiced in ways other than those specifically described within the scope of the appended claims and their equivalents. Furthermore, any combination of features, systems, articles, materials, kits, and / or methods described herein is included within the scope of this disclosure if two or more features, systems, articles, materials, kits, and / or methods described herein are not inconsistent with each other.

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 a first electrode and a second electrode, and the electro-optic medium changes the optical state in response to a voltage sequence applied between the first electrode and the second electrode, 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 includes one of the at least 64 different optical states, and the simplified color state is one of no more than 16 different colors; Identify a voltage sequence that causes the electro-optic medium to transition from a simplified color state mapped from the first optical state to a second optical state, wherein the second optical state includes one of the at least 64 different optical states; and The voltage sequence is provided between the first electrode and the second electrode.

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

3. The method according to claim 1 or 2, wherein the simplified color state is one of eight different colors.

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

5. The method according to any of the preceding claims, wherein the mapping includes matching the first optical state and the simplified color state on a lookup table.

6. The method according to any one of the preceding claims, wherein the provided steps are performed by a controller.

7. The method according to any one of the preceding claims, wherein the electro-optic medium is an electrophoretic medium.

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

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

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

11. The method according to any one of claims 7-10, wherein the electrophoretic medium is encapsulated in a microcapsule or microunit.

12. The method according to any one of the preceding claims, wherein the first electrode is a light-transmitting electrode and the second electrode is a pixel electrode in a pixel electrode active matrix.

13. The method according to any one of the preceding claims, wherein the voltage sequence is DC balanced.

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