Method for reducing image artifacts during partial update of electrophoretic display

Abstract

A method for driving an electro-optic display to reduce visible artifacts is described. Such a method includes driving additional pixels by providing paired sets of drive instructions, where a boundary between driven and un-driven areas would otherwise cause an artifact, thereby allowing the un-driven areas to be driven while maintaining the desired (un-driven) optical state.

Description

[0001] Citation of relevant applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 108,852, filed November 2, 2021. All patents and publications disclosed herein are incorporated herein by reference in their entirety. Technical Field

[0003] This invention relates to methods for driving electro-optic displays, particularly bistable electro-optic displays, and to apparatus for such methods. More specifically, the invention relates to driving methods that can allow for reduction of "ghosting," "blooming," or other edge effects during partial updates of the display. The invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays, wherein one or more types of charged particles are present in a fluid and move through the fluid under the influence of an electric field to alter the appearance of the display. These methods are broadly applicable to bistable electro-optic media, where, advantageously, a large portion of the image remains unupdated while a smaller portion of the image undergoes optical changes. Background Technology

[0004] The term "electro-optic," used in this document to refer to materials or displays, is used in its conventional meaning in the field of imaging. It refers to a material having a first display state and a second display state, where at least one optical property differs between the first and second display states, and the material is changed from its first display state to its second display state by applying an electric field. While the optical property is typically color perceptible to the human eye, it can be another optical property, such as light transmission, reflection, emission, or, in the case of displays used for machine reading, a pseudocolor in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0005] The term "gray state" is used here in its conventional meaning in the imaging field, referring to a state between the two extreme optical states of a pixel, but not necessarily a black-and-white transition between those two extremes. For example, several patents and publications of IENK, mentioned below, describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate gray state actually a 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 white and dark blue states mentioned above. The term "monochrome" may be used below to refer to a driving scheme that drives pixels only to their two extreme optical states without an intermediate gray state.

[0006] 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, wherein at least one optical property of the first and second display states differs such that, after any given element is driven to present its first or second display state using an addressing pulse of finite duration, the state will persist 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 after the addressing pulse terminates. 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 intermediate gray states, as are some other types of electro-optic displays. This type of display is aptly referred to as “multistable” rather than bistable; however, for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0007] The term "impulse" as used here conventionally means the integral of voltage with respect to time. However, some bistable electro-optic dielectrics are used as charge converters, and with such dielectrics, an alternative definition of impulse can be used: the integral of current with respect to time (equal to the total applied charge). The appropriate definition of impulse should be used depending on whether the dielectric is used as a voltage-time impulse converter or a charge-impulse converter.

[0008] The majority of the discussion below will focus on methods for driving one or more pixels of an electro-optic display by transitioning from an initial gray level to a final gray level (which may or may not differ from the initial gray level). The term "waveform" will be used to refer to the entire voltage-time curve used to achieve the transition from a particular initial gray level to a particular final gray level. Typically, such a waveform will consist of multiple waveform elements; where these elements are substantially rectangular (i.e., where a given element involves the application of a constant voltage over a period of time); these elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to achieve all possible transitions between gray levels of a particular display. A display may use more than one drive scheme; for example, U.S. Patent No. 7,012,600 above teaches that the drive scheme may need to be modified based on parameters such as the temperature of the display or the operating time of the display during its lifespan, so a display may have multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this way may be referred to as a "set of related drive schemes." As described in the aforementioned MEDEOD applications, more than one driving scheme can be used simultaneously in different areas of the same display, and a group of driving schemes used in this way can be referred to as a "group of synchronous driving schemes".

[0009] Several types of electro-optic displays are known. One type of electro-optic display is the rotating bicolor component type, as described, for example, in U.S. Patent Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071, 6,055,091, 6,097,531, 6,128,124, 6,137,467, and 6,147,791 (although this type of display is often referred to as a "rotating bicolor sphere" display, the term "rotating bicolor component" is preferred as it is more accurate because in some of the patents mentioned above, the rotating component is not spherical). This display uses a number of small bodies (typically spherical or cylindrical) and internal dipoles, said bodies comprising two or more parts with different optical properties. These bodies are suspended within liquid-filled bubble chambers within a matrix, the bubble chambers being filled with liquid to allow the bodies to rotate freely. The appearance of a display is altered by applying an electric field to the display, thereby rotating the subject to various positions and changing which part of the subject is seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0010] Another type of electro-optic display uses electrochromic media, such as those in the form of nanochromic films, which include electrodes formed at least partially of semiconductor metal oxides and multiple dye molecules attached to the electrodes capable of reversing color changes; see, for example, O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patent Nos. 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0011] Another type of electro-optic display is the electrowetting display developed by Philips, described in Hayes, RA et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be manufactured in a bistable manner.

[0012] Electro-optic displays, a type of display that has been the subject of intensive research and development for many years, are particle-based electrophoretic displays, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays can offer advantages such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, long-term image quality issues have hindered their widespread use. For example, the particles constituting an electrophoretic display are prone to settling, resulting in a short lifespan for these displays.

[0013] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be generated using a gaseous fluid; see, for example, Kitamura, T. et al., “Electronic toner movement for electronic paper-like display”, IDW Japan, 2001, Paper HCS 1-1, and Yamaguchi, Y. et al., “Toner display using insulative particles charged triboelectrically”, IDW Japan, 2001, Paper AMD4-4. See also U.S. Patent Nos. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in a direction that allows particle settling, such as in signs where the media are arranged in a vertical plane, they are susceptible to the same type of problems as liquid-based electrophoretic media due to the same particle settling. In fact, particle sedimentation is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the lower viscosity of gaseous suspensions allows electrophoretic particles to settle more quickly compared to liquids.

[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. These encapsulated media comprise a plurality of small capsules, each capsule comprising an inner phase and a capsule wall surrounding the inner phase, wherein the inner phase contains electrophoretically movable 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) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0018] (d) Backplanes, adhesive layers and other auxiliary layers in displays, and methods thereof; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0019] (e) Color formation and color adjustment; see, for example, U.S. Patent No. 7,075,502; and U.S. Patent Application Publication No. 2007 / 0109219;

[0020] (f) A method for driving a display; see the above MEDEOD application;

[0021] (g) Applications of displays; see, for example, U.S. Patent No. 7,312,784 and U.S. Patent Application Publication No. 2006 / 0279527; and

[0022] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921; 6,950,220; and 7,420,549; and U.S. Patent Application Publication No. 2009 / 0046082.

[0023] 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 if no discrete capsule membrane is associated with each individual droplet; see, for example, the aforementioned 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.

[0024] 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 within microcapsules, but rather held within multiple cavities formed within a carrier medium (typically a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging.

[0025] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in reflective mode, many electrophoretic displays can be fabricated to operate in a so-called "shutter mode," in which one display state is substantially opaque and the other is transmissive. See, for example, U.S. Patent Nos. 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 No. 4,418,346. Other types of electro-optic displays are also capable of operating in shutter mode. In the multi-layered structure of a full-color display, an electro-optic medium operating in shutter mode may be useful; in such a structure, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0026] Encapsulated electrophoretic displays are generally unaffected by the clustering and sedimentation failure modes of conventional electrophoretic apparatus and offer more beneficial effects, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The term "printing" is used to include all forms of printing and coating, including but not limited to: pre-metering coating such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coating such as roller blade 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 displays can be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0027] Other types of electro-optic media can also be used in the display of this invention.

[0028] The bistable or multistable behavior of particle-based electrophoretic displays, and other electro-optic displays exhibiting similar behavior (hereafter referred to as "impulse-driven displays" for convenience), contrasts sharply with conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bistable or multistable; instead, they act as voltage converters, so applying a given electric field to a pixel in such a display produces a specific gray level at that pixel, regardless of the gray level previously present at that pixel. Furthermore, liquid crystal displays are driven in only one direction (from nontransmissive or "dark" to transmissive or "bright"), and the reverse transition from a brighter state to a darker state is achieved by reducing or eliminating the electric field. Finally, the gray levels of pixels in an LC display are insensitive to the polarity of the electric field, only to its magnitude; in fact, for technical reasons, commercial LC displays often frequently reverse the polarity of the driving field. In contrast, bistable electro-optic displays act as impulse converters in a first-order approximation, so the final state of a pixel depends not only on the applied electric field and the time of application but also on the state of the pixel before the application of the electric field.

[0029] Regardless of whether the electro-optic medium used is bistable, to achieve a high-resolution display, the individual pixels of the display must be addressable without interference from adjacent pixels. One way to achieve this is to provide an array of nonlinear elements (such as transistors or diodes), with at least one nonlinear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode of 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 arrangement will be assumed in the following description, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Typically, 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 specified row and a specified column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; again, the source-to-row and gate-to-column assignments are conventional but essentially arbitrary and can be reversed if desired. Row electrodes are connected to row drivers, which essentially ensures that only one row is selected at any given time. That is, a voltage is applied to the selected row electrode to ensure all transistors in the selected row are turned on, while voltages are applied to all other rows to ensure all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply voltages to the individual column electrodes selected to drive the pixels in the selected row to their desired optical state. (These voltages are 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 across the entire display.) After a preselection interval known as the “line 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 to the display. This process is repeated to write to the entire display row by row.

[0030] At first glance, the ideal approach to addressing such impulse-driven electro-optic displays might seem to be the so-called "general grayscale image stream," where the controller schedules each write of the image so that each pixel transitions directly from its initial grayscale level to its final grayscale level. However, writing images to impulse-driven displays inevitably introduces some errors. Some of these errors encountered in practice include:

[0031] (a) Previous state dependence; for at least some electro-optic media, the impulse required to switch a pixel to a new optical state depends not only on the current and desired optical state, but also on the previous optical state of the pixel.

[0032] (b) Dwell time dependence; for at least some electro-optic media, the impulse required to switch a pixel to a new optical state depends on the time the pixel spends in its various optical states. The exact nature of this dependence is not yet clear, but in general, the longer a pixel remains in its current optical state, the more impulse is required.

[0033] (c) Temperature dependence; the impulse required to switch a pixel to a new optical state depends largely on temperature.

[0034] (d) Humidity dependence; for at least some types of electro-optic media, the impulse required to switch a pixel to a new optical state depends on the ambient humidity.

[0035] (e) Mechanical uniformity; the impulse required to switch a pixel to a new optical state may be affected by mechanical variations in the display, such as thickness variations in the electro-optic medium or associated laminating adhesive. Other types of mechanical non-uniformity may be caused by unavoidable variations between different manufacturing batches of the medium, manufacturing tolerances, and material variations.

[0036] (f) Voltage error; The actual impulse applied to the pixel will inevitably differ slightly from the theoretically applied impulse because there is an unavoidable small error in the voltage provided by the driver.

[0037] Grayscale image streams generally suffer from an "error accumulation" phenomenon. For example, suppose temperature dependence causes an error of 0.2L* in the positive direction of each transition (where L* has the usual CIE definition:

[0038] L* = 116(R / R0) 1 / 3 –16,

[0039] Where R is reflectance and R0 is the standard reflectance value. After fifty transitions, this error will accumulate to 10L*. Perhaps more realistically, assume the average error per transition (expressed as the difference between the display's theoretical and actual reflectance) is ±0.2L*. After 100 consecutive transitions, the pixel will show an average deviation of 2L* from its expected state; for some types of images, this deviation is noticeable to the average observer.

[0040] This error accumulation phenomenon applies not only to temperature-induced errors but also to all types of errors listed above. Such errors can be compensated for, but with limited accuracy, as described in the aforementioned U.S. Patent No. 7,012,600. For example, temperature errors can be compensated for using a temperature sensor and a lookup table, but the temperature sensor has limited resolution and may read a temperature slightly different from that of the electro-optic medium. Similarly, previous state dependencies can be compensated for by storing previous states and using a multidimensional transition matrix, but the controller memory limits the number of states that can be recorded and the size of the transition matrix that can be stored, thus limiting the accuracy of this compensation.

[0041] Therefore, general grayscale image streams require very precise control of the applied impulse to produce good results, and experience has shown that, given the current state of electro-optical display technology, general grayscale image streams are not feasible in commercial displays.

[0042] In some cases, it may be desirable to use multiple driving schemes for a single display. For example, a display supporting more than two grayscale levels can use a grayscale driving scheme (“GSDS”) and a monochrome driving scheme (“MDS”). GSDS can handle transitions between all possible grayscale levels, while MDS handles transitions between only two grayscale levels, providing a faster display rewrite than GSDS. MDS is used when all pixels changed during a display rewrite only handle transitions between the two grayscale levels used by MDS. For example, U.S. Patent No. 7,119,772 describes a display in the form of an e-book or similar device capable of displaying grayscale images as well as a monochrome dialog box that allows the user to input text related to the displayed image. When the user inputs text, a fast MDS is used to quickly update the dialog box, providing the user with rapid confirmation of the input. On the other hand, a slower GSDS is used when the entire grayscale image displayed on the display changes.

[0043] Alternatively, the display can use both GSDS and a "direct update" driving scheme ("DUDS"). DUDS can have two or more gray levels, typically fewer than GSDS, but the most important feature of DUDS is that the transition from the initial gray level to the final gray level is handled by a simple unidirectional driver, rather than the "indirect" transition often used in GSDS, where, at least in some transitions, the pixel is driven from the initial gray level to an extreme optical state and then in the opposite direction to the final gray level; in some cases, the transition can be achieved by driving from the initial gray level to an extreme optical state, then to the opposite extreme optical state, and finally to the final extreme optical state, see, for example, the driving scheme shown in Figures 11A and 11B of U.S. Patent No. 7,012,600. Therefore, the update time of current electrophoretic displays in grayscale mode can be about two to three times the length of the saturation pulse (where the "length of the saturation pulse" is defined as the time period sufficient to drive the pixels of the display from one extreme optical state to another at a specific voltage) or about 700-900 milliseconds, while the maximum update time of DUDS is equal to the length of the saturation pulse, or about 200-300 milliseconds.

[0044] However, variations in driving schemes are not limited to differences in the number of gray levels used. For example, driving schemes can be categorized into global driving schemes and partial update driving schemes. In a global driving scheme, driving voltage is applied to every pixel (possibly the entire display or a defined portion thereof) in the area where a global update driving scheme (more accurately called a "globally complete" or "GC" driving scheme) is applied. In a partial update driving scheme, driving voltage is applied only to pixels undergoing a non-zero transition (i.e., a transition where the initial and final gray levels differ from each other), but no driving voltage is applied during zero transitions (where the initial and final gray levels are the same). An intermediate form of driving scheme (specified as a "globally restricted" or "GL" driving scheme) is similar to a GC driving scheme, except that no driving voltage is applied to pixels undergoing a zero, white-to-white transition. For example, in a display used as an e-book reader displaying black text on a white background, there are many white pixels, especially between page margins and text lines, which remain unchanged from one page of text to the next; therefore, not rewriting these white pixels significantly reduces the noticeable "flickering" of the display rewriting. However, some problems still exist in this type of GL-driven scheme. First, as discussed in detail in some of the aforementioned MEDEOD applications, bistable electro-optic media are generally not perfectly bistable; pixels in an extreme optical state gradually drift towards intermediate gray levels over time periods ranging from minutes to hours. In particular, pixels driven as white slowly drift towards lighter gray. Therefore, if, in a GL-driven scheme, white pixels are allowed to remain undriven after multiple page turns while other white pixels (e.g., those that form parts of text characters) are driven, the newly updated white pixels will be slightly brighter than the undriven ones, and eventually, the difference will become noticeable even to untrained users.

[0045] Secondly, a phenomenon known as "blooming" occurs when an undriven pixel is adjacent to a pixel being updated. The driving of the driven pixel causes a change in the optical state over an area slightly larger than the driven pixel, and this area encroaches on the area of ​​adjacent pixels. This blooming manifests as an edge effect along the edge of the undriven pixel adjacent to the driven pixel. A similar edge effect occurs when using region updates (where only a specific area of ​​the display is updated, such as to display an image), except that the edge effect occurs at the boundary of the area being updated. Over time, this edge effect becomes visually distracting and must be eliminated. To date, such edge effects (along with the color drift effect of undriven white pixels) have generally been eliminated by using GC updates periodically. Unfortunately, using such occasional GC updates reintroduces the problem of "flickering" updates; in fact, since flickering updates occur only at very long intervals, the flickering of updates can be exacerbated.

[0046] This invention relates to reducing or eliminating the problems discussed above while still avoiding flicker updates as much as possible. However, an additional complexity arises in attempting to solve these problems: the need for overall DC balancing. As discussed in many of the aforementioned MEDEOD applications, if the driving scheme used is not substantially DC balanced (i.e., if the algebraic sum of the impulses applied to the pixels does not approach zero during any series of transitions starting and ending at the same gray level), it can adversely affect the electro-optical characteristics and operational lifespan of the display. See in particular U.S. Patent No. 7,453,445, which discusses the DC balancing problem in a so-called “heterogeneous loop” involving transitions performed using more than one driving scheme. A DC-balanced driving scheme ensures that the total net impulse bias is bounded (for a finite number of gray states) at any given time. In a DC-balanced driving scheme, each optical state of the display is assigned an impulse potential (IP), and the individual transitions between optical states are defined such that the net impulse of the transition is equal to the difference in impulse potentials between the initial and final states of the transition. In a DC-balanced driving scheme, it is required that any round-trip net impulse is substantially zero. Summary of the Invention

[0047] Therefore, in one aspect, the present invention provides a method for reducing or eliminating edge artifacts. Specifically, the method aims to eliminate such artifacts, also known as partial updates, that occur along the straight edge between driven and undriven pixels without special adjustment. In this method, at least two sets of control instructions are programmed for each optical state. During a partial update, some pixels adjacent to the updated pixel but needing to maintain their current optical state are updated simultaneously with the updated pixel using alternating sets of paired instructions. Thus, pixels that do not need updating but are at risk of artifacts can maintain their optical state and avoid artifacts. Furthermore, by alternating between sets of paired instructions, it is not necessary to track the previous state of a given pixel. If it is adjacent to the updated pixel, most of the artifacts will be cleared after two updates. Driving adjacent pixels in this way greatly reduces the visibility of edge artifacts (e.g., flooding), because any edge artifacts occurring along the edge defined by the additional pixels are less noticeable than without these methods.

[0048] In all methods of the present invention, the display can use any type of electro-optic medium discussed above. Thus, for example, an electro-optic display may include a rotating dual-color component or an electrochromic material. Alternatively, the electro-optic display may include an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. The charged particles and the fluid may be confined within a plurality of capsules or microunits. Alternatively, the charged particles and the fluid may exist as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid may be a liquid or a gas.

[0049] In another aspect, a method for driving a bistable electro-optic display including a controller is provided. The bistable electro-optic display has a pixel matrix arranged in rows and columns. The matrix includes: primary pixels undergoing a transition from a first optical state to a second optical state; secondary pixels adjacent to the primary pixels, wherein the secondary pixels undergo a transition from a third optical state to a fourth optical state; and tertiary pixels adjacent to the secondary pixels, the secondary pixels being located in a row or column between the primary pixels and the tertiary pixels, wherein the tertiary pixels do not undergo optical state transitions. The resulting driving method includes: a) providing a first update from the controller to the bistable electro-optic display, including providing a first waveform to the primary pixel, a third waveform to the secondary pixel, and a fifth waveform to the tertiary pixel; and b) providing a second update from the controller to the bistable electro-optic display, including providing a second waveform to the primary pixel, a fourth waveform to the secondary pixel, and not providing a waveform to the tertiary pixel, wherein the first optical state and the second optical state differ in color or grayscale, while the third optical state and the fourth optical state are the same in color and grayscale.

[0050] In some embodiments, the third, fourth, and fifth waveforms all produce the same optical state. In some embodiments, the method further includes c) providing a third update from the controller to the bistable electro-optic display, including providing a sixth waveform to the primary pixels, providing a third waveform to the secondary pixels, and not providing a waveform to the tertiary pixels. In some embodiments, the bistable electro-optic display is an electrophoretic display. In some embodiments, the electrophoretic display includes an electrophoretic medium comprising at least three different types of electrophoretic particles. In some embodiments, the electrophoretic display includes an electrophoretic medium disposed in a microcapsule layer. In some embodiments, the electrophoretic display includes an electrophoretic medium disposed in microcells. In some embodiments, the bistable electro-optic display includes a color filter array. In some embodiments, the bistable electro-optic display includes at least 10 primary pixels, at least 10 secondary pixels, and at least 10 tertiary pixels. In some embodiments, the primary pixels define the edges of the image displayed on the bistable electro-optic display. In some embodiments, the bistable electro-optic display includes at least 1000 pixels. In some embodiments, 20% or less of the pixels are primary pixels (number of primary pixels / total number of pixels). In some embodiments, the bistable electro-optic display is capable of producing at least 16 different colors or grayscale levels. In some embodiments, the bistable electro-optic display is capable of producing at least 32 different colors. Attached Figure Description

[0051] Figure 1 This illustrates how a small group of pixels on a display can be affected differently during partial updates, in this case, a drop-down menu on a fixed image.

[0052] Figure 2A A first method is shown for updating a set of pixels in a small area of ​​a display that has undergone a partial update.

[0053] Figure 2B A second method is shown for updating a set of pixels in a small area of ​​a display that has undergone a partial update.

[0054] Figure 3 An exemplary waveform update of six adjacent pixels undergoing three updates is shown, wherein, according to the invention, different pixels receive different waveforms. Detailed Implementation

[0055] The method of this invention aims to reduce or eliminate edge artifacts that occur along the straight edge between driven and undriven pixels. The human eye is particularly sensitive to linear edge artifacts, especially those that extend along rows or columns of a display. In this method, multiple pixels located near the edge between the driven and undriven regions are actually driven, such that any edge effects caused by the transition are hidden or otherwise minimized.

[0056] As mentioned above, partial updates are typically used when only a portion of an image needs updating, such as dropdown menus, scrolling text, or simplified animations. Figure 1 An example is shown where a dropdown menu advances over an existing image. As the dropdown menu advances, a subset 100 of pixels in a small area of ​​the display undergoes different color transitions. For example, some pixels will brighten from dark, while others will not change their optical state. Some pixels will be adjacent to the pixels being updated, while others will be far enough away that they are unlikely to be affected by update artifacts (such as bloom or ghosting). For illustrative purposes, the subset 100 of pixels has been magnified by 120, allowing for a better understanding of the... Figure 2A and Figure 2B The phenomenon.

[0057] One problem with partial updates is that pixels adjacent to the updated pixel may actually change color due to the driving force of neighboring pixels (e.g., due to the presence of a nearby electric field), i.e., bloom. Furthermore, while bloom during partial updates can cause blurry edges in monochrome devices, it is more noticeable in color displays, such as advanced color electrophoresis paper. Similar amounts of flooding in the medium will cause a shift in the actual color of neighboring pixels. Most users do not welcome this color shift. This color shift is particularly noticeable when dithering is used in the next image and some pixels in dithering mode have the same color as pixels in the currently displayed image. This effect can be so strong that it results in a noticeable loss of color.

[0058] In the actual update of the display, if a pixel in image I2 has not changed compared to image I1, the controller will not update that pixel (i.e., provide a new set of voltages based on the lookup voltage list). However, to avoid the artifacts discussed above, it is preferable to use a new waveform that achieves the same color state to update some pixels near the pixel being updated. Comparison Figure 2A and Figure 2B .like Figure 2AAs shown, even if only the top-right pixel 210 is being updated, the updated stray electric field lines from pixel 210 will cause flooding 225 in the surrounding pixels because the electro-optical medium associated with these pixels "sees" the voltage from the updated pixel 210, even if the surrounding pixels maintain a constant voltage. By implementing the techniques described below, the flooding can be substantially erased in one or two subsequent updates, as... Figure 2B As shown.

[0059] In examples of ACeP-type electrophoretic displays (i.e., four-particle electrophoretic media comprising white, cyan, yellow, and magenta particles), the typical waveforms have a 5-bit lookup table: that is, 32 different possible colors. However, usually only 16 different colors are sufficient, allowing the reproduction of waveforms in 16 different colors. In such a system, for example, waveforms 1 and 2 are both assigned to black, waveforms 3 and 4 both produce blue, and so on, until waveforms 31 and 32, which are both white, are reached. Each waveform in each of these pairs has the same voltage list.

[0060] Copying the same waveform to a different "color" allows, for example, a white pixel adjacent to an updated pixel in the first image (waveform 32) to be subsequently assigned waveform 31 in the second image. When implemented as described herein, the controller updates all pixels associated with the image, as well as some neighboring pixels that would otherwise not be updated in a partial update. Nevertheless, these pixels do not change their optical state because they transition between waveforms of the same color. However, since they are actually being updated, these pixels will have any bloom due to the erasure of nearby switching pixels. The same logic can be applied to reduce artifacts in monochrome displays, for example, by using a 4-bit lookup table and creating 8 unique gray levels using 8 pairs of waveforms for each gray level.

[0061] This technique can be implemented by starting with an image region and marking it with the elements to be added (such as menus or sliders). During this composition, the region where the new element is added can be examined, and pixels that have undergone self-transformation can be identified. To force the controller to update these pixels, the solution is to change the state of the pixels in the next state image to a mirror state, i.e., another state with the same meaning. Note that the current state of a pixel can be any parity bit (even or odd) because we do not know whether such a replacement has occurred before, but by alternating between pairs of waveforms during various desired updates, pixels that have not been updated maintain the correct optical state.

[0062] It should be noted that the state labeling scheme with parity states described above is merely an example; the same purpose can be achieved using many different definitions of equivalent states. For instance, if the standard states are defined as 1-16, then the equivalent states can be defined as states 17-32 in any random order. Clearly, the scheme most easily implemented in a given controller design should be chosen. This method is not limited to 16 states, but the only requirement is that the controller can manage twice the number of nominal states.

[0063] The described method can also be used for "fade-in / fade-out" updates, where a series of intermediate images are provided between the first image I1 and the second image I2, or typically I1->2[1] to I1->2[n]. In each of these intermediate images, from image I1 to image I2, only a selected portion of the image region is changed. For example, in I1->2(1), there may be 10% of the pixels that are as they are in I2, while 90% of the pixels remain as they are in I1. When a partial update is requested, the controller will update only 10% of the I2 pixels. In I1->2(2), the next 10% is updated, and so on. For example, when we reach I1->2(10), the image update is complete.

[0064] Similar to the example above of new edges in the dropdown menu, many updated pixels will be adjacent to other pixels that actually change between I1 and I2. As mentioned above, unupdated (e.g., white) pixels will experience edge fields from adjacent updates and will change color from the desired (e.g., white) state. To prevent this, image I1 cannot have the same state as image I2, even if they have the same color. This can be achieved by assigning two lookup tables for the same color in the waveform and providing alternative lookup tables during fade-in and fade-out processes. In some cases, "undriven" pixels will therefore be updated 2-3 times during the transition to maintain a consistent color in the unupdated areas.

[0065] Returning to the accompanying drawings, the effects of the method of this invention can be clearly seen. For example... Figure 1 As shown, Figure 1 A subset of 100 pixels will be updated. For illustrative purposes, six pixels in a two-row, three-column configuration will be discussed; however, the invention is broadly applicable to any number of pixels, where the target update (e.g., a first-level pixel) typically creates the edge of the image being updated on a field of another color or grayscale level. For illustrative purposes, pixels are numbered 1-6. Figure 2A The pixel numbers are enclosed in circles. For simplicity, not all pixels are numbered.

[0066] In the conventional approach, updating pixel 210 (alone) from color 1 to color 2 would simply be a matter of the controller implementing lookup table 2, such as... Figure 2A As shown. Since pixel 210 (i.e., pixel number 3) is intentionally updated with state changes, pixel 210 is a primary pixel. Because adjacent (secondary) pixels (pixels 2, 5, 6) are not updated, all adjacent (secondary) pixels will experience a certain amount of flooding 225, which may be detrimental to the user experience. In other words, if not updated, all adjacent pixels 220, 230, and 240 are at risk of flooding, similar to... Figure 2A (Importantly, for illustrative purposes, pixels 250 and 260 (i.e. Figure 2A Pixels 1 and 4 in the image are not adjacent pixels, but rather third-level pixels, and there is generally no risk of flooding when updating pixel 210. However, see [link to relevant documentation]. Figure 2B Since pixel 220 and pixel 210 are updated at the same time, pixel 220 maintains the same optical state as before, but without floodlight 225.

[0067] In different embodiments, and for comparison purposes, the update may switch each secondary pixel to the same first or second waveform on each update. For example, as Figure 2B As shown, pixels 230 and 240 may already be in a state implemented through lookup table 1B, even if another secondary pixel (22) is in a state of lookup table 1A. Since pixels 230 and 240 are not updated when all "A" states switch to "B" states, an update of the primary pixel (210) may cause flood pixels 230 and 240, as Figure 2B The set of intermediate pixels is shown. However, after an additional update, this time from "B" to "A", the flood 225 has been cleared, causing updating pixels 210, 220, 230, and 240 to result in some (but not so much flood) 225, as... Figure 2B As shown. The advantage of this method is that the controller does not need to track the actual state of each pixel. Instead, after two updates, all secondary pixels should have been updated at least once, allowing any unwanted flooding to be removed. In other words, for each subsequent update, the optical state of the primary pixels can be advanced without comparing those updated states with the updated states of the secondary pixels. Finally, all primary and secondary pixels (i.e., 210, 220, 230, and 240) are updated from lookup table XB to lookup table XA, thus removing flooding and preserving image realism.

[0068] Figure 3 Further illustration of the invention is shown below, with exemplary waveforms provided by the controller to each of pixels 1-6. It will be understood that... Figure 3The waveform is a generalized form and does not correspond to a specific color or grayscale level. Furthermore, the waveforms sent by the controller to individual pixels are typically more complex and may include elements such as pre-wipe pulses, DC balancing pulses, and post-drive cleanup pulses. Additionally, Figure 3 The waveforms shown are a generalized representation of voltage changes over time and typically include both positive and negative voltages.

[0069] The pixels under discussion start from a common starting point (denoted as "0"). During the first update, the controller sends a first waveform to the main electrode, causing the primary pixel to change its optical state. Simultaneously, the secondary and tertiary pixels are updated with the third and fifth waveforms, respectively. In the second update, the primary pixel is updated by the controller with a different second waveform, while the secondary pixel is updated with the same fourth waveform as the third. However, the tertiary pixel does not receive any update; this typically occurs in direct update refreshes, where only the pixel used to change its optical state is updated. As a result, the primary pixel transitions from a first optical state to a second optical state; that is, the optical state of the primary pixel after the first update is different from the optical state after the first update. However, during the second update, the optical states of the secondary and tertiary pixels are the same. However, since the secondary pixel actually receives the waveform from the controller, pixels adjacent to the primary pixel "flicker," allowing them to maintain the correct optical state without ghosting. In some embodiments, a further third update can be provided, whereby the primary and / or secondary pixels receive yet another waveform. Typically, for both primary and secondary pixels, the third update will be the waveform of one of the previous update states, usually the previous update state. This ensures that all floodlight is removed from the secondary pixels.

[0070] As can be readily apparent from the foregoing description, many methods of the present invention require or implement desired modifications to prior art display controllers. The present invention requires a small amount of additional power compared to a lower-power direct update, but the overall viewer experience is improved. Of course, displays implementing the present invention consume significantly less power than those updating all pixels on each update, as is achieved in full update mode. Various modifications to the display controller can be used to allow for the storage of transition information. For example, an image data table that typically stores the grayscale level of each pixel in the final image can be modified to store one or more additional bits specifying the category to which each pixel belongs. For instance, an image data table that previously stored 4 bits per pixel to indicate which of the 16 grayscale levels the pixel would represent in the final image can be modified to store 5 bits per pixel, with the most significant bit of each pixel defining which of the two states (black or white) the pixel would represent in a monochrome intermediate image. Clearly, if the intermediate image is not monochrome, or if more than one intermediate image is used, it may be necessary to store more than one additional bit per pixel.

[0071] Alternatively, different image transitions can be encoded into different waveform patterns based on the transition state map. For example, waveform pattern A would cause a pixel to undergo a transition to a white state in the intermediate image, while waveform pattern B would cause a pixel to undergo a transition to a black state in the intermediate image. Since each individual transition in waveform pattern A and waveform pattern B is identical, simply delayed by the length of their respective first pulses, the same result can be achieved using a single waveform. Here, the second update (the global update in the previous paragraph) delays the length of the first waveform pulse. Image 2 is then loaded into the image buffer and a global update is performed using the same waveform. The rectangular region requires the same degrees of freedom.

[0072] Another option is to use a controller architecture with separate final image buffers and initial image buffers (which are loaded alternately with consecutive images), and additional memory space for optional state information. These provide a pipelined operator that can perform various operations on each pixel while considering the initial, final, and additional states of each pixel's nearest neighbors, as well as their effects on the pixel under consideration. The operator computes a waveform table index for each pixel and stores it in a separate memory location, and optionally modifies the pixel's saved state information. Alternatively, a memory format can be used, thereby concatenating all storage buffers into a single large word for each pixel. This reduces the number of times each pixel is read from different memory locations. Furthermore, a 32-bit word with a frame count timestamp field is proposed to allow arbitrary access to the waveform lookup table for any pixel (per-pixel pipeline). Finally, a pipelined structure for the operator is proposed where three image rows are loaded into a fast access register to allow efficient data shifting into the operator structure.

[0073] Frame count timestamps and pattern fields are used to create unique indicators in the pattern lookup table to provide the illusion of a per-pixel pipeline. These two fields allow each pixel to be assigned to one of 15 waveform patterns (allowing a pattern state to indicate no action on the selected pixel) and one of 8196 frames (currently far exceeding the number of frames required to update a display). This increased flexibility, achieved by extending the waveform index from 16 bits in existing controller designs to 32 bits, comes at the cost of display scanning speed. In a 32-bit system, each pixel must be read from memory at twice the number of bits, and the controller's memory bandwidth (the rate at which data can be read from memory) is limited. This limits the rate at which the panel can be scanned because the entire waveform table index must be read for each scan frame (now each pixel consists of a 32-bit word).

[0074] A memory and controller architecture that meets this requirement reserves a (region) bit in the image buffer memory to specify any pixel contained within that region. The region bit acts as a "gatekeeper" for modifying the update buffer and assigning lookup table numbers. The region bit can actually comprise multiple bits that can be used to indicate separate, simultaneously updatable, arbitrarily shaped regions that can be assigned different waveform patterns, thus allowing the selection of arbitrary regions without creating new waveform patterns.

[0075] Of course, the above description of using alternating pairwise instruction sets to remove flooding along image edges in a device containing partial updates can be extended to consider other factors that may affect flooding performance, such as previous state information (grayscale, color, jitter), device temperature, device age, front illumination intensity, or spectrum. It is well known that some electro-optic media exhibit memory effects, and for such media, it is desirable to consider not only the initial state of each pixel when generating the output signal, but also (at least) the first previous state of the same pixel. In this case, alternating state instructions would become multidimensional lookup tables. In some cases, it may be desirable to consider more than one previous state per pixel, resulting in lookup tables with three, four, five, six, or seven or more dimensions.

[0076] From a formal mathematical perspective, the implementation of such a method can be viewed as including an algorithm that, given information about the initial state, final state, and (optionally) previous states of the electro-optic pixel, and information about the physical state of the display (e.g., temperature and total operating time), produces a function V(t) that can be applied to the pixel to achieve a transition to the desired final state. From this formal viewpoint, the controller of the present invention can essentially be considered a physical embodiment of this algorithm, acting as an interface between the device wishing to display information and the electro-optic display.

[0077] Ignoring physical state information for the time being, the algorithm is encoded in the form of a lookup table or transition matrix according to the present invention. This matrix will have one dimension for the desired final state and for each other state used in the computation (the initial state and any previous states). The elements of the matrix will contain the function V(t) to be applied to the electro-optic medium. In the alternating pairwise instruction set approach, each V(t) may have an alternative V(t) that takes into account, for example, the previous state or temperature, but allows the controller to efficiently update neighboring pixels to maintain the correct optical state, thereby avoiding unwanted flooding.

[0078] The elements of a lookup table or transition matrix can take many forms. In some cases, each element may comprise a single number. For example, an electro-optic display may use a high-precision voltage modulation driver circuit capable of outputting a large number of different voltages above and below a reference voltage, and simply apply the desired voltage to the pixel within a standard predetermined period. In this case, each entry in the lookup table may simply have the form of a signed integer specifying which voltage to apply to a given pixel. In other cases, each element may comprise a series of numbers associated with different portions of a waveform. For example, embodiments of the invention using a single prepulse waveform or a double prepulse waveform are described below, and specifying such waveforms necessarily requires several numbers associated with different portions of the waveform. Alternatively, pulse length modulation can be implemented by applying a predetermined voltage to the pixel during selected sub-scan cycles of multiple sub-scan cycles during a full scan. In such embodiments, the elements of the transition matrix may have the form of a series of bits specifying whether a predetermined voltage is to be applied during each sub-scan cycle of the relevant transition.

[0079] It will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted as illustrative rather than restrictive.

Claims

1. A method for driving a bistable electro-optic display including a controller, the bistable electro-optic display having a pixel matrix arranged in rows and columns, the pixel matrix comprising: The first-level pixel undergoes a transition from the first optical state to the second optical state. The secondary pixels adjacent to the primary pixel, wherein the secondary pixels undergo a transition from a third optical state to a fourth optical state, and The tertiary pixel adjacent to the secondary pixel, wherein the secondary pixel is located between the primary pixel and the tertiary pixel in a row or column, and wherein the tertiary pixel does not undergo an optical state transition. The method includes: a) Providing a first update from the controller to the bistable electro-optic display, including providing a first waveform to the primary pixels, a third waveform to the secondary pixels, and a fifth waveform to the tertiary pixels; and b) Providing a second update from the controller to the bistable electro-optic display, including providing a second waveform to the primary pixels, providing a fourth waveform to the secondary pixels, and not providing a waveform to the tertiary pixels. The first waveform and the second waveform are different, and the third waveform and the fourth waveform are the same. Thus, the first optical state and the second optical state are expected to be different in color or grayscale, while the third optical state and the fourth optical state are expected to be the same in color and grayscale.

2. The method according to claim 1, wherein, The third, fourth, and fifth waveforms all produce the same optical state.

3. The method of claim 1, further comprising c) providing a third update from the controller to the bistable electro-optic display, including providing a sixth waveform to the primary pixels, providing a third waveform to the secondary pixels, and not providing a waveform to the tertiary pixels.

4. The method according to claim 1, wherein, The bistable electro-optic display is an electrophoretic display.

5. The method according to claim 4, wherein, The electrophoretic display includes an electrophoretic medium comprising at least three different types of electrophoretic particles.

6. The method according to claim 4, wherein, The electrophoretic display includes an electrophoretic medium arranged in a microcapsule layer.

7. The method according to claim 4, wherein, The electrophoretic display includes an electrophoretic medium arranged in microcells.

8. The method according to claim 1, wherein, The bistable electro-optic display includes a color filter array.

9. The method according to claim 1, wherein, The bistable electro-optic display includes at least 10 primary pixels, at least 10 secondary pixels, and at least 10 tertiary pixels.

10. The method according to claim 9, wherein, The first-level pixel defines the edge of the image displayed on the bistable electro-optic display.

11. The method according to claim 9, wherein, The bistable electro-optical display includes at least 1000 pixels.

12. The method according to claim 11, wherein, The ratio of the number of first-level pixels to the total number of pixels is 20% or less.

13. The method according to claim 1, wherein, The bistable electro-optic display can produce at least 16 different colors or gray levels.

14. The method according to claim 1, wherein, The bistable electro-optic display can produce at least 32 different colors.

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