HK1224792B - Methods for driving electro-optic displays - Google Patents

Description

Method for driving an electro-optical display

This application is a divisional application of an application filed on April 11, 2011, with application number 201180018248.5 and invention name “Method for driving an electro-optical display”.

[Para 1] This application relates to 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, 7,116,466, 7,119,772, 7,193,625, 7,202,847, 259,744, 7,304,787, 7,312,794, 7,327,511, 7,453,445, 7,492,339, 7,528,822, 7,545,358, 7,583,251, 7,602,374, 7,612,760, 7,679,599, 7,688,297, 7,729,039, 7,733,311, 7,733,335, and 7,787,169 U.S. Patents and Nos. 2003/0102858, 2005/0122284, 2005/0179642, 2005/0253777, 2005/0280626, 2006/0038772, 2006/0139308, 2007/0013683, 2007/0091418, 2007/0103427, 2007/0200874, 2008/0024429, 2008/0024 482, 2008/0048969, 2008/0129667, 2008/0136774, 2008/0150888, 2008/0165122, 2008/0211764, 2008/0291129, 2009/0174651, 2009/0179923, 2009/0195568, 2009/0256799, and 2009/0322721.

[Para 2] The aforementioned patents and applications may be collectively referred to hereinafter for convenience as "MEDEOD " (Methods for Driving Electro - Optic Displays). The entire contents of these patents and co-pending applications, as well as the entire contents of all other U.S. patents and published and co-pending applications mentioned below, are incorporated herein by reference.

[Para 3] The present invention relates to methods for driving electro-optical displays, in particular bistable electro-optical displays, and to apparatus for use in these methods. More particularly, the present invention relates to driving methods that can allow displays to respond quickly to user input. The invention also relates to methods that can reduce "ghosting" in such displays. The invention is particularly (but not exclusively) intended for use with particle-based electrophoretic displays, in which one or more classes of charged particles are present in a fluid and move through the fluid under the influence of an electric field to change the appearance of the display.

[Para 4] The term "electro-optical" as applied to a material or display is used herein in its conventional sense in imaging technology to refer to a material having first and second display states that differ in at least one optical property, the material being caused to change from the first display state to the second display state by application of an electric field to the material. Although the human eye typically perceives the optical property in terms of color, it may be another optical property, such as light transmission, reflectance, luminescence, or, in the case of displays for machine reading, pseudo-color in the sense of changes in reflectance at electromagnetic wavelengths outside the visible range.

[Para 5] The term "gray state" is used herein in its conventional sense in imaging technology to refer to a state intermediate the two extreme optical states of a pixel, and does not necessarily imply a black-white transition between the two extreme states. For example, some of the E Ink patents and published applications referenced below describe some electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. Indeed, as already mentioned, the change in optical state may not be entirely a color change. The terms "black" and "white" may be used hereinafter 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 hereinafter to refer to a drive scheme that drives pixels only to their two extreme optical states, without intermediate gray states.

[Para 6] The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to a display comprising a display element having first and second display states, the first and second display states differing in at least one optical property and such that after any given element is driven to assume its first or second display state by means of an addressing pulse of finite duration, this state persists after the addressing pulse has terminated for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays with grayscale functionality are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for some other types of electro-optical displays. This type of display is properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" may be used herein to cover both bistable and multistable displays.

[Para 7] The term "pulse" is used herein in its conventional sense of the integral of voltage with respect to time. However, some bistable electro-optical media are used as charge converters, and with such media, an alternative definition of pulse may be used, namely, the integral of current over time (equal to the total applied charge). The appropriate definition of pulse should be used depending on whether the medium is used as a voltage-to-time pulse converter or a charge-to-pulse converter.

[Para 8] Much of the following discussion will focus on methods for driving one or more pixels of an electro-optical display by transitioning from an initial gray level to a final gray level (which may or may not be different from the initial gray level). The term "waveform" is used to refer to the overall voltage versus time curve used to achieve the transition from a specific initial gray level to a specific final gray level. Typically, such a waveform will include multiple waveform elements, where these elements are substantially rectangular (i.e., where a given element includes a stable voltage applied over a period of time), which elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms that are sufficient to achieve all possible transitions between multiple gray levels for a specific display. A display may use more than one drive scheme, for example, the aforementioned U.S. Patent No. 7,012,600 teaches that the drive scheme may need to be modified based on parameters such as the temperature of the display or the amount of time the display has been in operation during its lifetime, and thus a display may have multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this manner may be referred to as a "set of related drive schemes." It is also possible, as described in several of the aforementioned MEDEOD applications, to use more than one drive scheme simultaneously in different areas of the same display, and a group of drive schemes used in this way may be referred to as a "group of simultaneous drive schemes".

[Para 9] Various types of electro-optical displays are known. One type of electro-optical display is a rotating two-color component type, such as those described in U.S. Patents 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 two-color ball" display, the term "rotating two-color component" is more accurate because the rotating components in some of the above-mentioned patents are not spherical). Such displays use a large number of small objects (usually spherical or cylindrical) that have two or more parts and an internal dipole, and these two or more parts have different optical properties. These objects are suspended in liquid-filled cavities within a matrix, and these cavities are filled with liquid so that these objects can rotate freely. The appearance of the display is changed by applying an electric field thereto, thereby rotating the objects to various positions and changing the portion of the objects that is seen through a viewing surface. This type of electro-optical medium is typically bistable.

[Para 10] Another type of electro-optical display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which includes: an electrode formed at least in part of a semiconducting metal oxide; and a plurality of dye molecules capable of reversible color change attached to the electrode, see, for example, O'Regan, B. et al., Nature 1991, 353,737 and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Advanced Materials, 2002, 14(11), 845. This type of nanochromic film is also described in, for example, U.S. Patents 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[Para 11] Another type of electro-optical display is an electro-wetting display, developed by Philips and described in Hayes, R.A. et al., "Video-speed electronic paper based on electro-wetting," Nature, 425, 383-385 (2003). Such an electro-wetting display can be made bi-stable, as shown in U.S. Patent No. 7,420,549.

[Para 12] Electro-optical displays have been the subject of intensive research and development for many years. One type is the particle-based electrophoretic display (EPD), in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), EPDs can offer the following attributes: high brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues with the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up EPDs tend to settle, resulting in a short service life for these displays.

[Para 13] 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 manufactured using a gaseous fluid, for example, see Kitamura, T. et al., "Electrotoner Motion for Electronic Paper-like Displays," IDW Japan, 2001, document HCS1-1, and Yamaguchi, Y. et al., "Toner Display Using Triboelectrically Charged Insulating Particles," IDW Japan, 2001, document AMD4-4. See also U.S. Patents Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media appear to be susceptible to the same type of problems caused by particle settling as liquid-based electrophoretic media when the medium is used in an orientation that allows such settling, such as in a sign where the medium is placed in a vertical plane. Indeed, particle sedimentation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, because the lower viscosity of the gaseous suspending fluid causes electrophoretic particles to sediment more rapidly than the liquid suspending fluid.

[Para 14] Numerous patents and applications assigned to or under the names of MIT and E Ink describe various technologies used in encapsulated electrophoretic and other electro-optical media. Such encapsulated media comprise numerous small capsules, each of which itself comprises an inner phase containing particles electrophoretically moving in a fluid medium, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held in a polymeric binder to form a bonding layer, positioned between two electrodes. The technologies described in these patents and applications include:

(a) electrophoretic particles, fluids, and fluid additives, see, for example, U.S. Pat. Nos. 7,002,728 and 7,679,814;

(b) capsules, adhesives, and encapsulation techniques, see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

(c) Films and subassemblies containing electro-optical materials, see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

(d) Backplanes, adhesive layers, and other auxiliary layers and methods of use in displays, see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;

(e) color formation and color adjustment, see, e.g., U.S. Patent No. 7,075,502 and U.S. Patent Application Publication No. 2007/0109219;

(f) Method for driving a display, see the aforementioned MEDEOD application;

(g) Display applications, see, e.g., U.S. Patent No. 7,312,784 and U.S. Patent Application Publication No. 2006/0279527; and

(h) Non-electrophoretic displays, such as those described in US Patent Nos. 6,241,921, 6,950,220, and 7,420,549, and US Patent Application Publication No. 2009/0046082.

[Para 15] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and wherein the discrete droplets of electrophoretic fluid within such a polymer dispersed electrophoretic display can be treated as capsules or microcapsules, but there is no discrete capsule membrane 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 dispersed electrophoretic media are treated as a subspecies of encapsulated electrophoretic media.

[Para 16] A 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 are retained within multiple cavities formed within a carrier medium, typically a polymeric film. See, for example, U.S. Patents Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.

[Para 17] Although electrophoretic media are typically opaque (e.g., because in many electrophoretic media, particles substantially block visible light from being transmitted through the display) and operate in a reflective mode, many electrophoretic displays can operate in a so-called "shutter mode," in which one display state is substantially opaque and the other is light transmissive. See, for example, U.S. Patents Nos. 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, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optical displays can also operate in a shutter mode. Electro-optical media operating in a shutter mode may be useful in multilayer structures for full-color displays in which at least one layer adjacent to a viewing surface of the display operates in a shutter mode to expose or conceal a second layer further from the viewing surface.

[Para 18] Encapsulated electrophoretic displays typically do not have the aggregation and precipitation failure modes of traditional electrophoretic devices and offer further advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of the word "printing" is intended to include all forms of printing and coating, including but not limited to: pre-set coating, such as patch die coating, slot or extrusion coating, slide or waterfall coating, curtain coating; roller coating, such as roller blade coating, reciprocating roller coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing process; electrostatic printing process; thermal printing process; ink jet printing process; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar technologies.) Therefore, the resulting display can be flexible. In addition, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.

[Para 19] Other types of electro-optical media may also be used in the displays of the present invention.

[Para 20] The bi-stable or multi-stable behavior of particle-based electrophoretic displays and other electro-optical displays that exhibit similar behavior (such displays may be referred to hereinafter for convenience as "impulse-driven displays") stands in stark contrast to the bi-stable or multi-stable behavior of conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bi-stable or multi-stable, but act as voltage converters such that application of a given electric field to a pixel of such a display produces a specific gray level at that pixel, independent of the gray level previously present at that pixel. Furthermore, LC displays are driven in only one direction (from non-transmissive or "dark" to transmissive or "light"), with the opposite transition from a lighter state to a darker state being achieved by reducing or eliminating the electric field. Finally, the gray level of a pixel of an LC display is not sensitive to the polarity of the electric field, only to its magnitude, and indeed, for technical reasons, commercial LC displays typically frequently reverse the polarity of the drive field. In contrast, bistable electro-optical displays act very closely as pulse switches, so that the final state of a pixel depends not only on the applied electric field and the time when the field is applied, but also on the state of the pixel before the field is applied.

[Para 21] Regardless of whether the electro-optical medium used is bi-stable, in order to achieve a high-resolution display, individual pixels of the display must be addressable without interference from neighboring pixels. One way to achieve this is to provide an array of nonlinear elements, such as transistors or diodes, with each pixel associated with at least one nonlinear element, to produce an "active matrix" display. The addressing or pixel electrode that addresses a pixel is connected to a suitable 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, but it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Conventionally, in high-resolution arrays, the pixels are arranged in a two-dimensional array of rows and columns, so that any particular pixel is uniquely identified 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 electrode, while the gates of all transistors in each row are connected to a single row electrode. Again, the assignment of sources to rows and gates to columns is conventional but essentially arbitrary and can be reversed as desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at any given moment, i.e. a voltage is applied to the selected row electrode, thereby ensuring that all transistors in the selected row are conductive; while a voltage is applied to all other rows, thereby ensuring that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to column drivers which apply selected voltages on the respective column electrodes to drive the pixels in the selected row to their desired optical states. (The aforementioned voltages are relative to a common front electrode which is conventionally provided on the side of the electro-optical medium opposite the non-linear array and extending across the entire display.) After a pre-selected interval called the "line address time", the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to cause the next line of the display to be written. This process is repeated so that the entire display is written row by row.

[Para 22] Initially, it seemed that the ideal method for addressing such an impulse-driven electro-optical display would be so-called "normal grayscale image streaming," in which the controller arranges each write of the image so that each pixel transitions directly from its initial grayscale level to its final grayscale level. However, it is inevitable that there are some errors in writing images to impulse-driven displays. Some of these errors encountered in practice include:

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

(b) Dwell time dependence: For at least some electro-optical media, the pulse 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 well understood, but in general, the longer the pixel is in its current optical state, the more pulses are required.

(c) Temperature dependence; the pulse required to switch a pixel to a new optical state depends strongly on the temperature.

(d) Humidity dependence: For at least some types of electro-optical media, the pulse required to switch a pixel to a new optical state depends on the surrounding humidity.

(e) Mechanical inconsistency: The pulse required to switch a pixel to a new optical state can be affected by mechanical variations in the display, such as variations in the thickness of the electro-optic medium or associated lamination adhesive. Other types of mechanical inconsistencies can arise from inevitable variations between different manufacturing batches of the medium, manufacturing tolerances, and material variations.

(f) Voltage Errors; Due to inevitable slight errors in the voltage delivered by the driver, the actual pulse applied to the pixel will inevitably differ slightly from the pulse applied theoretically.

[Para 23] A common grayscale image stream suffers from the phenomenon of “error accumulation”. For example, imagine that the temperature dependence results in a positive error of 0.2L* at each transition (where L* has the usual CIE definition:

L*＝116(R/R ₀ ) ^1/3 -16,

where R is the reflectance and R0 is the value of the standard reflectance. After 50 transitions, this error will accumulate to 10L*. Perhaps more practically, assume that the average error on each transition is ±0.2L*, expressed in terms of the difference between the theoretical and actual reflectance of the display. After 100 consecutive transitions, the pixels will show an average deviation of 2L* from their expected state, a deviation that is very noticeable to the average observer on certain types of images.

[Para 24] This error accumulation phenomenon applies not only to errors due to temperature, but also to all the types of errors listed above. As described in the aforementioned U.S. Patent No. 7,012,600, it is possible to compensate for such errors, but only to a limited degree of accuracy. For example, temperature errors can be compensated by using a temperature sensor and a lookup table, but the resolution of the temperature sensor is limited and the temperature read may be slightly different from the temperature of the electro-optical medium. Similarly, previous state dependencies can be compensated by storing previous states and using a multidimensional transition matrix, but the amount of controller memory limits the number of states that can be recorded and the size of the transition matrix that can be stored, thereby limiting the accuracy of this type of compensation.

[Para 25] Therefore, general grayscale image streaming requires very precise control of the applied pulses to obtain good results, and it is known from experience that general grayscale image streaming is not feasible in commercial displays in the current state of electro-optical display technology.

[Para 26] In some cases, it may be necessary for a single display to use multiple drive schemes. For example, a display with more than two grayscale capabilities may use a grayscale drive scheme ("GSDS") that transitions between all possible grayscale levels and a monochrome drive scheme ("MDS") that transitions between only two grayscale levels, with MDS providing faster display rewrites than GSDS. MDS is used when all pixels that change during the rewrite of the display transition between only two grayscale levels used by the MDS. For example, the aforementioned U.S. Patent No. 7,119,772 describes a display in the form of an electronic book or a similar device that can display a grayscale image and can also display a monochrome dialog box that allows the user to enter text related to the displayed image. When the user is entering text, the fast MDS is used to quickly update the dialog box, thereby providing the user with quick confirmation of the text being entered. On the other hand, when the entire grayscale image displayed on the display is changing, the slower GSDS is used.

[Para 27] Alternatively, the display may use a "direct update" drive scheme ("DUDS") in conjunction with GSDS. A DUDS can have two or more gray levels, typically fewer than a GSDS, but the most important feature of a DUDS is that the transitions are handled by a simple unidirectional drive from an initial gray level to a final gray level, as opposed to the "indirect" transitions often used in GSDS, where in at least some transitions the pixel is driven from an initial gray level to an extreme optical state and then driven in the opposite direction to the final gray level; in some cases, such a transition may be achieved by driving from an initial gray level to an extreme optical state, thereafter to the opposite extreme optical state, and only then reaching the final extreme optical state - see, for example, the drive scheme illustrated in Figures 11A and 11B of the aforementioned U.S. Patent No. 7,012,600. Therefore, the update time of current electrophoretic displays in grayscale mode is about two to three times the saturation pulse length (where "a saturation pulse length" is defined as the time period sufficient to drive a pixel of the display from one extreme optical state to another extreme optical state at a specific voltage), or approximately 700-900 milliseconds, while the maximum update time of DUDS is equal to this saturation pulse length, or approximately 200-300 milliseconds.

[Para 28] However, in some cases, it is necessary to provide an additional drive scheme (hereinafter referred to as the "application update drive scheme" or "AUDS" for convenience) whose maximum update time is even shorter than that of DUDS and therefore less than the saturation pulse length, but such rapid updates compromise the quality of the resulting image. AUDS may be desirable for interactive applications such as drawing on a display using a stylus and a touch sensor, typing on a keyboard, menu selection, and scrolling of text or a cursor. One specific application in which AUDS may be useful is an e-book reader, which simulates a physical book by displaying images of pages turning as the user turns the pages of the e-book (in some cases by making gestures on a touch screen). During this page turning, rapid movement through the relevant pages is more important than the contrast ratio or quality of the image of the turned page, and once the user has selected the page he wants, the image of that page can be rewritten with higher quality using the GSDS drive scheme. Therefore, prior art electrophoretic displays are limited in interactive applications. However, since the maximum update time of AUDS is smaller than the saturation pulse length, the extreme optical state obtainable by AUDS will be different from that of DUDS. In fact, the limited update time of AUDS does not allow the pixel to be driven to the normal extreme optical state.

[Para 29] However, there is an additional challenge with the use of AUDS, namely the need for overall DC balance. As discussed in many of the aforementioned MEDEOD applications, if the drive scheme used is not sufficiently DC balanced (i.e., if the algebraic sum of the pulses applied to the pixel during any series of transitions that begin and end at the same gray level is not close to 0), then the electro-optical properties and operating life of the display may be adversely affected. See in particular the aforementioned U.S. Patent No. 7,453,445, which discusses the problem of DC balance in so-called "heterogeneous loops" involving transitions made using more than one drive scheme. In any display using both GSDS and AUDS, it is impossible for the two drive schemes to be overall DC balanced due to the need for high-speed transitions in AUDS. (In general, it is possible to use GSDS and AUDS simultaneously while still maintaining overall DC balance.) Therefore, there is a need to provide some method of driving a display using both GSDS and AUDS that allows for overall DC balance, and one aspect of the present invention relates to such a method.

[Para 30] A second aspect of the present invention relates to a method for reducing so-called "ghosting" in electro-optical displays. Certain drive schemes for such displays, particularly those designed to reduce display flicker, leave "ghost images" (blurred copies of previous images) on the display. Such ghost images distract the user and reduce perceived image quality, especially after multiple updates. One situation in which such ghost images become a problem is when using an e-book reader to scroll through an e-book, as opposed to jumping between individual pages of a book.

[Para 31-1] Therefore, in one aspect, the present invention provides a first method for operating an electro-optical display using two different drive schemes. In this method, the display is driven using a first drive scheme to a predetermined transitional image. Then, the display is driven using a second drive scheme to a second image different from the transitional image. Thereafter, the display is driven using the second drive scheme to the same transitional image. Finally, the display is driven using the first drive scheme to a third image different from the transitional image and the second image.

[Para 31-2] The method according to [Para 31-1], wherein the first driving scheme is a grayscale driving scheme capable of driving the display to at least four gray levels.

[Para 31-3] The method according to [Para 31-2], wherein the first driving scheme is a grayscale driving scheme capable of driving the display to at least eight gray levels.

[Para 31-4] The method of [Para 31-1], wherein the second drive scheme is an application update drive scheme having fewer grayscale levels than the first drive scheme and having a maximum update time that is less than a saturation pulse length of the display.

[Para 31-5] The method of [Para 31-1], wherein the transition image comprises a single hue applied to all pixels of the display.

[Para 31-6] The method of [Para 31-1], wherein the display is provided with a plurality of transition images, and a display controller is arranged to select a transition image based on an image already present on the display.

[Para 31-7] The method according to [Para 31-1], wherein the display is driven sequentially to a plurality of transition images before driving the display to the second image and/or before driving to the third image.

[Para 31-8] The method according to [Para 31-1], wherein the electro-optical display includes a rotating two-color member or electrochromic material.

[Para 31-9] The method of [Para 31-1], wherein the electro-optical display comprises 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.

[Para 31-10] The method according to [Para 31-9], wherein the charged particles and the fluid are confined within a plurality of cavities or microcells.

[Para 31-11] The method of [Para 31-9], wherein the charged particles and the fluid exist as discrete droplets surrounded by a continuous phase comprising a polymeric material.

[Para 31-12] The method according to [Para 31-9], wherein the fluid is gaseous.

[Para 32] The method of the present invention may be referred to hereinafter as the "transition image" or "TI" method of the present invention. In this method, the first drive scheme is preferably a grayscale drive scheme capable of driving the display to at least 4, and preferably at least 8, gray levels and having a maximum update time greater than the saturation pulse length (as defined above). The second drive scheme is preferably an AUDS having fewer gray levels than the grayscale drive scheme and having a maximum update time less than the saturation pulse length.

[Para 33-1] In another aspect, the present invention provides a second method for operating an electro-optical display using first and second drive schemes different from each other and at least one transition drive scheme different from both the first and second drive schemes, the method comprising, in the following order: driving the display to a first image using the first drive scheme; driving the display to a second image different from the first image using the transition drive scheme; driving the display to a third image different from the second image using the second drive scheme; driving the display to a fourth image different from the third image using the transition drive scheme; and driving the display to a fifth image different from the fourth image using the first drive scheme.

[Para 33-2] The method according to [Para 33-1], wherein the first driving scheme is a grayscale driving scheme capable of driving the display to at least four gray levels.

[Para 33-3] The method according to [Para 33-2], wherein the first driving scheme is a grayscale driving scheme capable of driving the display to at least eight grayscale levels.

[Para 33-4] The method of [Para 33-1], wherein the second drive scheme is an application update drive scheme having fewer grayscale levels than the first drive scheme and having a maximum update time that is less than a saturation pulse length of the display.

[Para 33-5] The method according to [Para 33-1], wherein a first transition drive scheme is used for the transition from the first image to the second image, and a second transition drive scheme different from the first transition drive scheme is used for the transition from the third image to the fourth image.

[Para 33-6] The method according to [Para 33-1], wherein the electro-optical display includes a rotating two-color member or electrochromic material.

[Para 33-7] The method of [Para 33-1], wherein the electro-optical display comprises 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.

[Para 33-8] The method according to [Para 33-7], wherein the charged particles and the fluid are confined within a plurality of cavities or microcells.

[Para 33-9] The method of [Para 33-7], wherein the charged particles and the fluid exist as discrete droplets surrounded by a continuous phase comprising a polymeric material.

[Para 33-10] The method according to [Para 33-7], wherein the fluid is gaseous.

[Para 34] The second method of the present invention differs from the first method in that no transition-specific transition images are formed on the display. Instead, a special transition drive scheme, the characteristics of which are discussed below, is used to achieve the transition between the two primary drive schemes. In some cases, separate transition drive schemes will be required for transitioning from the first image to the second image and from the third image to the fourth image; in other cases, a single transition drive scheme may be sufficient.

[Para 35] In another aspect, the present invention provides a method of operating an electro-optical display in which an image scrolls across the display and wherein a clearing bar is provided between two portions of the scrolling image, the clearing bar scrolling across the display synchronously with the two portions of the image, the writing of the clearing bar being effected so that each pixel over which the clearing bar passes is rewritten.

[Para 36] In another aspect, the present invention provides a method of operating an electro-optical display wherein an image is formed on the display and wherein a cleaning bar is provided that travels across the image on the display such that each pixel over which the cleaning bar passes is rewritten.

[Para 37] In all of the methods of the present invention, the display may use any of the types of electro-optical media discussed above. Thus, for example, the electro-optic display may include a rotating two-color member 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 cavities or microcells. Alternatively, the charged particles and the fluid may be present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. The fluid may be liquid or gaseous.

[Para 38] Figure 1 of the accompanying drawings schematically illustrates a grayscale driving scheme for driving an electro-optical display.

[Para 39] Figure 2 schematically illustrates a grayscale driving scheme for driving an electro-optical display.

[Para 40] Figure 3 schematically illustrates the transition from the grayscale driving scheme of Figure 1 to the monochrome driving scheme of Figure 2 using the transition image method of the present invention.

[Para 41] Figure 4 schematically illustrates a transition opposite to the transition shown in Figure 3.

[Para 42] FIG5 schematically illustrates the transition from the grayscale driving scheme of FIG1 to the monochrome driving scheme of FIG2 using the transition driving scheme method of the present invention.

[Para 43] Figure 6 schematically illustrates a transition opposite to the transition shown in Figure 5.

[Para 44] As already mentioned in one aspect, the present invention provides two different but related methods for operating an electro-optical display using two different drive schemes. In the first of these two methods, the display is first driven to a predetermined transition image using the first drive scheme, and then the display is rewritten to the second image using the second drive scheme. Thereafter, the display is returned to the same transition image using the second drive scheme, and finally the display is driven to a third image using the first drive scheme. In this "transition image" ("TI") drive method, the transition image serves as a known transition image between the first and second drive schemes. It will be appreciated that more than one image can be written to the display using the second drive scheme between two occurrences of the transition image. If the second drive scheme (typically AUDS) is substantially DC balanced, then when the display transitions from the first drive scheme to the second drive scheme and back to the first drive scheme (typically GSDS), the use of the second drive scheme between two occurrences of the same transition image will cause little or no DC imbalance.

[Para 45] Since the same transition image is used for the first to second (GSDS to AUDS) transition and the reverse (second to first) transition, the exact nature of the transition image does not affect the operation of the TI method of the present invention, and the transition image can be selected arbitrarily. Typically, the transition image will be selected to minimize the visual effect of the transition. For example, the transition image can be selected to be pure white or black, or a pure gray tone, or can be patterned in a manner that has some advantageous qualities. In other words, the transition image can be arbitrary, but each pixel of this image must have a predetermined value. It will also be apparent that since both the first and second drive schemes must achieve a change from the transition image to a different image, the transition image must be an image that can be manipulated by both the first and second drive schemes, that is, the transition image must be restricted to a number of gray levels equal to the smaller of the number of gray levels used by the first and second drive schemes. The transition image can be interpreted differently by each drive scheme, but must be processed consistently by each drive scheme. Furthermore, if the same transition image is used for a particular first to second transition and for the immediately subsequent opposite transition, it is not necessary to use the same transition image for each pair of transitions. A plurality of different transition images can be provided, and the display controller can be arranged to select a particular transition image based on, for example, the properties of an image already present on the display, so as to minimize flicker. The TI method of the present invention can also use multiple consecutive transition images to further improve image performance at the expense of slower transitions.

[Para 46] Since DC balance of an electro-optical display needs to be achieved on a pixel-by-pixel basis (i.e., this drive scheme must ensure that each pixel is substantially DC balanced), the TI method of the present invention can be used when only a portion of the display is switched to the second drive scheme, for example, when an on-screen text box is required to display text input from a keyboard, or when an on-screen keyboard is required in which individual keys flash to confirm input.

[Para 47] The TI method of the present invention is not limited to methods that use only GSDS in addition to AUDS. Indeed, in a preferred embodiment of the TI method, the display is arranged to use GSDS, DUDS, and AUDS. In a preferred form of this method, because AUDS has an update time that is less than a saturation pulse, the white and black optical states achieved by AUDS are reduced compared to those achieved by DUDS and GSDS (i.e., the white and black optical states achieved by AUDS are actually very light gray and very dark gray compared to the "true" black and white states achieved by GSDS), and the variability in the optical states achieved by AUDS is increased compared to those achieved by GSDS and DUDS because previous states (history) and dwell time effects lead to unwanted reflectance errors and image artifacts. In order to reduce these errors, the following image sequence is proposed.

The GC waveform will transition from n-bit image to n-bit image.

The DU waveform transitions an n-bit (or less than n-bit) image to an m-bit image, where m<=n.

The AU waveform transitions p-bit image to p-bit image, typically, n=4, m=1, and p=1, or n=4, m=2 or 1, p=2 or 1.

– GC -> Image n-1 – GC or DU -> Transitional image – AU -> Image n – AU -> Image n+1 – AU -> … – AU -> Image n+m-1 – AU -> Image n+m – AU -> Transitional image – GC or DU -> Image n+m+1

[Para 48] From the above, it will be seen that in the TI method of the present invention, AUDS may require little or no tuning and can be much faster than other drive schemes used (GSDS or DUDS). DC balance is maintained by using transition images, and the dynamic range of slower drive schemes (GSDS and DUDS) is maintained. The image quality achieved can be better than without using intermediate updates. Image quality can be improved during AUDS updates because the first AUDS update can be applied to a (transition) image with the desired properties. For stereoscopic images, image quality can be improved by applying AUDS updates to a uniform background. This reduces previous state ghosting. Image quality after the last intermediate update can also be improved by applying GSDS or DUDS updates to a uniform background.

[Para 49] In the second method of the present invention (hereinafter referred to as the "transition drive scheme" or "TDS" method), a transition image is not used, but a transition drive scheme is used, and a single transition using the transition drive scheme replaces the last transition using the first drive scheme (which produces the transition image) and the first transition using the second drive scheme (which transitions from the transition image to the second image). In some cases, two different transition drive schemes may be required depending on the direction of the transition, and in other cases, a single transition drive scheme will be sufficient for transitions in either direction. Note that the transition drive scheme is applied only once to each pixel and is not applied repeatedly to the same pixel, as is the case with the main (first and second) drive schemes.

[Para 50] The TI and TDS methods of the present invention will be explained in more detail without reference to the accompanying drawings, which illustrate the transitions occurring in these two methods in a highly schematic manner. In all the drawings, time increases from left to right, the squares or circles represent gray levels, and the lines connecting these squares or circles represent gray level transitions.

[Para 51] FIG1 schematically illustrates a standard grayscale waveform having N gray levels (N=6 is shown, where the gray levels are represented by squares), with the N x N transitions being illustrated by a line linking the initial gray level of a transition (on the left-hand side of FIG1 ) to the final gray level (on the right-hand side). (Note that it is necessary to provide a zero transition where the initial and final gray levels are the same, as explained in several of the above-mentioned MEDEOD applications, which typically still involve the application of a non-zero voltage period to the associated pixel). Each gray level has not only a specific gray level (reflectance), but also a specific DC offset if the overall drive scheme is DC balanced (i.e., the algebraic sum of the pulses applied to the pixel during any series of transitions starting and ending at the same gray level is substantially zero), as desired. The DC offsets do not necessarily have to be evenly spaced or even unique. So for a waveform with N gray levels, there will be a DC offset corresponding to each of these gray levels.

[Para 52] When a set of drive schemes are DC balanced with each other, the path taken to reach a particular gray level can vary, but the overall DC offset for each gray level is the same. Thus, it is possible to switch drive schemes within a set of drive schemes that are balanced with each other without fear of causing increased DC imbalance, which could be detrimental to certain types of displays discussed in the aforementioned MEDEOD application.

[Para 53] The aforementioned DC offsets are measured relative to each other, i.e., the DC offset of one gray level is arbitrarily set to arbitrary zero, and the DC offsets of the remaining gray levels are measured relative to this arbitrary zero.

[Para 54] Figure 2 is a diagram similar to Figure 1, but showing a monochrome driving scheme (N=2).

[Para 55] If a display has two drive schemes that are not DC balanced with each other (i.e., their DC offsets are different between certain gray levels; this does not necessarily mean that the two drive schemes have a different number of gray levels), it is still possible to switch between the two drive schemes without causing a growing DC imbalance over time. However, special care is required when switching between these drive schemes. The necessary transitions can be achieved using transition images according to the TI method of the present invention. Transitions between the different drive schemes are made using a common gray tone. Whenever switching between modes, the transition must always be made by switching to this common gray level, thereby ensuring that DC balance is maintained.

[Para 56] Figure 3 illustrates this TI method during a transition from the drive scheme shown in Figure 1 to the drive scheme shown in Figure 2, assuming that the two drive schemes are not balanced with each other. The left-hand quarter of Figure 3 shows a conventional grayscale transition using the drive scheme of Figure 1. Thereafter, the first part of the transition drives all pixels of the display to a common grayscale level (illustrated as the top grayscale level in Figure 3) using the drive scheme of Figure 1, while the second part of the transition drives each pixel to the two grayscale levels of the drive scheme of Figure 2 as required using the drive scheme of Figure 2. Therefore, the total length of the transition is equal to the combined length of the transitions in the two drive schemes. If the optical state of this supposedly common grayscale level does not match in the two drive schemes, then some ghosting may occur. Finally, further transitions are achieved using only the drive scheme of Figure 2.

[Para 57] It will be appreciated that although only a single common gray level is shown in FIG3 , there may be multiple common gray levels between the two drive schemes. In this case, any one of the common gray levels may be used for the transition image, and the transition image may be produced simply by driving each pixel of the display to a common gray level. This tends to produce a visually pleasing transition in which one image "melts" into a uniform gray field from which a different image gradually emerges. However, in this case, not all pixels necessarily use the same common gray level; one group of pixels may use one common gray level while a second group of pixels uses a different common gray level; the second part of the transition may still be implemented using the drive scheme of FIG2 as long as the drive controller knows which pixels use which common gray level. For example, the two groups of pixels using different gray levels may be arranged in a checkerboard pattern.

[Para 58] Figure 4 illustrates a transition that is the opposite of the transition shown in Figure 3. The left-hand quarter of Figure 4 shows a conventional monochrome transition using the drive scheme of Figure 2. Thereafter, the first part of the transition uses the drive scheme of Figure 2 to drive all pixels of the display to a common grayscale level (illustrated as the top grayscale level in Figure 4), while the second part of the transition uses the drive scheme of Figure 1 to drive each pixel to the six grayscale levels of the drive scheme of Figure 1 as needed. Therefore, the total length of the transition is still equal to the combined length of the transitions in the two drive schemes. Finally, further grayscale transitions are achieved using only the drive scheme of Figure 1.

[Para 59] Figures 5 and 6 illustrate transitions that are generally similar to the transitions in Figures 3 and 4, respectively, but the transitions in Figures 5 and 6 use the transition drive scheme approach of the present invention rather than the transition image approach. The left-hand third of Figure 5 shows a conventional grayscale transition using the drive scheme of Figure 1. Thereafter, a transition is made directly from the six grayscale levels of the drive scheme of Figure 1 to the two grayscale levels of the drive scheme of Figure 2 using the transition image drive scheme. Thus, although the drive scheme of Figure 1 is a 6x6 drive scheme and the drive scheme of Figure 2 is a 2x2 drive scheme, the transition drive scheme is a 6x2 drive scheme. The transition drive scheme can replicate the common grayscale approach of Figures 3 and 4 as needed, but using a transition drive scheme rather than a transition image allows for greater design freedom, and therefore the transition drive scheme does not need to pass through a common grayscale case. Note that the transition drive scheme is only used for a single transition at any one time, unlike the drive schemes of Figures 1 and 2, which would typically be used for many consecutive transitions. Using a transition drive scheme achieves better optical matching of the grey levels and the length of the transition can be reduced below the sum of the lengths of the individual drive schemes, providing a faster transition.

[Para 60] Figure 6 shows the reverse transition to that shown in Figure 5. If the transition from Figure 2 to Figure 1 is identical to the transition from Figure 1 to Figure 2, then for overlapping transitions (which is not always the case), the same transition drive scheme can be used in both directions; otherwise, two separate transition drive schemes are required.

[Para 61] As described above, another aspect of the present invention relates to a method for operating an electro-optical display using a cleanup bar. In one such method, an image is scrolled across the display and a cleanup bar is provided between two portions of the scrolled image, the cleanup bar being scrolled across the display synchronously with the two adjacent portions of the image, the writing of the cleanup bar being implemented so that each pixel over which the cleanup bar passes is rewritten. In another such method, an image is formed on the display and a cleanup bar is provided, the cleanup bar being advanced across the image on the display so that each pixel over which the cleanup bar passes is rewritten. These two forms of the method may be referred to hereinafter as the "synchronized cleanup bar" and "asynchronous cleanup bar" methods, respectively.

[Para 62] The "cleaning bar" method is primarily (but not exclusively) used to remove or at least mitigate ghosting effects that can occur in electro-optical displays when partial updating or poorly constructed drive schemes are used. One way such ghosting can occur is when the display scrolls, i.e., a series of images on the display are written slightly differently from one another, leaving the impression that an image (e.g., an e-book, web page, or map) that is larger than the display itself is moving across the display. Such scrolling can leave a ghosting streak on the display, and the greater the number of consecutive images displayed, the more severe this ghosting becomes.

[Para 63] In a bi-stable display, a black (or other non-background color) sweeping bar can be added to one or more edges of the image on the screen (in the margin, on the border, or in the seam). This sweeping bar can be located in pixels that are originally on the screen, or if the controller memory holds an image that is larger than the displayed physical image (for example, to speed up scrolling), then the sweeping bar can also be located in pixels that are in software memory but not on the screen. As the displayed image scrolls through the displayed image (such as when reading a long web page), the sweeping bar advances across the image in synchronization with the movement of the image itself, so that the scrolled image leaves the impression of displaying two separate pages rather than curling, and the sweeping bar forces an update of all pixels it advances through, thereby reducing the accumulation of ghosting and similar artifacts as it passes.

[Para 64] A cleanup bar can take a variety of forms, some of which may not be recognizable as a cleanup bar, at least to casual users. For example, a cleanup bar can be used as a delimiter between multiple components in a chat or bulletin board application, so that each component will scroll across the screen with a cleanup bar between each pair of consecutive components, thereby clearing screen artifacts as the chat or bulletin board thread progresses. In such applications, there is typically more than one cleanup bar on the screen at a time.

[Para 65] The cleaning bar can have the form of a simple line that is perpendicular to the direction of scrolling, and the direction of scrolling is usually horizontal. However, many other forms of cleaning bars can be used in the method of the present invention. For example, the cleaning bar can have the form of parallel lines, jagged (sawtooth) lines, diagonal lines, wavy (sinusoidal) lines or dotted lines. The cleaning bar can also have other forms different from lines, for example, the cleaning bar can have the form of a frame around the image, the form of a grid, which can be visible or invisible (this grid can be smaller than the display size or larger than the display size). The cleaning bar can also have the form of a series of discrete points that pass through the display, and these discrete points are strategically placed so that when they scroll through the display, they force each pixel to switch. Although such discrete points are more complicated to implement, they have the advantage of self-masking and are therefore less visible to the user because they are scattered.

[Para 66] The minimum number of pixels in the cleanup bar in the scrolling direction (hereinafter referred to as the "height" of the cleanup bar for convenience) should be at least equal to the number of pixels that the image moves through each time the scrolling image is updated. Therefore, the cleanup bar height can be changed dynamically, and the cleanup bar height will increase when the page scrolling is accelerated, and the cleanup bar height will decrease when the scrolling is slowed down. However, for a simple embodiment, it may be most convenient to set the cleanup bar height to be sufficient to allow the maximum scrolling speed and to keep this height unchanged. Since the cleanup bar is not needed after scrolling stops, the cleanup bar can be removed or retained on the display when scrolling stops. The use of a cleanup bar will typically be most advantageous when using a fast update drive scheme (DUDS or AUDS).

[Para 67] When a scroll bar is in the form of a number of scattered dots, the "height" of the scroll bar must take into account the spacing between the dots. The position of each dot in the scroll direction should be set modulo the number of pixels the image moves during each scroll update, and the result should be in the range of 0 to the number of pixels moved during each scroll update minus 1, and this requirement should be met for each parallel line of pixels in the scroll direction.

[Para 68] The clean-up bar need not be a solid color, but can be patterned. Patterned clean-up bars can add ghosting noise to the background depending on the drive scheme used, thereby better disguising image artifacts. The pattern of the clean-up bar can change depending on the bar position and time. The artifacts produced by using a patterned clean-up bar in space can produce ghosting in a more eye-catching manner. For example, a pattern in the form of a company logo can be used so that the ghosting artifact left behind appears as a "watermark" of this logo, but if the wrong drive scheme is used, then unwanted artifacts will also be produced. The suitability of a patterned clean-up bar can be determined by using a stereo background image to scroll a patterned clean-up bar with the desired drive scheme across the display and determining whether the resulting artifact is desirable or unwanted.

[Para 69] Patterned cleanup bars can be particularly useful when the display uses a patterned background. All the same rules will apply and in the simplest case, a cleanup bar color can be chosen that is different from the background color. Alternatively, two or more cleanup bars of different colors or patterns can be used. A patterned cleanup bar can effectively be the same as a scattered point cleanup bar, but in the scattered point case it is required to be modified so that for each gray tone of the background there is a point on the cleanup bar (of a different color than the particular point on the background being cleaned) so that the position of each cleanup point in the scrolling direction is set to the same range covered by the result of a modulo operation of the number of pixels moved in each scrolling step as the range covered by the result of a modulo operation of the position of the patterned background point in the scrolling direction.

[Para 70] In displays using a striped background, a cleanup bar can use the same gray tone as the striped background, but be one block out of phase with the background. This can effectively hide the cleanup bar so that it can be placed in the background between the text and the image behind it. A textured background with random ghosting from a patterned cleanup bar can mask patterned ghosting from a recognizable image and produce a display that is more attractive to some users. Alternatively, such a cleanup bar can be arranged to leave a ghost of a specific pattern (if a ghosting exists), so that the ghosting becomes a watermark on the display and becomes a useful resource.

[Para 71] Although the previous discussion of a scrubber has focused on a scrubber that scrolls with the image on the display, the scrubber need not scroll in this manner, but rather can be periodically desynchronized with the scrolling or completely independent of the scrolling. For example, the scrubber can operate like a windshield wiper or like a conventional video slide, moving across the display in one direction while the background image remains completely still. Multiple, non-synchronized scrubbers can be used simultaneously or sequentially to scrub portions of the display. The provision of non-synchronized scrubbers in one or more portions of the display can be controlled by the display application.

[Para 72] The cleanup bar need not use the same drive scheme as the rest of the display. If a drive scheme of the same or less length is used for the cleanup bar as for the rest of the display, then implementation is straightforward. If the drive scheme for the cleanup bar is longer (which is likely to be the case in practice), then not all pixels in the cleanup bar will switch at once, but rather a large proportion of the pixels will switch, with non-switching pixels moving around the cleanup bar as well as pixels that are normally switched. The number of non-switching pixels should be large enough so that the normally switched area does not conflict with the cleanup bar area, while the cleanup bar needs to be wide enough so that no pixels are missed as the cleanup bar moves across the screen. The drive scheme for the cleanup bar may be one selected from the drive scheme used for the rest of the display, or it may be a drive scheme specifically adapted to the needs of the cleanup bar. If multiple cleanup bars are used, then they need not all use the same drive scheme.

[Para 73] As will be seen from the foregoing, the cleaning bar method of the present invention can be readily incorporated into many types of electro-optical displays and provides methods of page cleaning that are less visually obtrusive than other methods of page cleaning. Several variations of the cleaning bar method, both synchronized and asynchronous, can be incorporated into a particular display, allowing software or the user to select the method to use based on factors such as user perception of acceptability or the particular program being run on the display.

[Para 74] It will be apparent to those skilled in the art that many changes and modifications may be made in the particular embodiments of the invention described above without departing from the scope of the invention. Therefore, all of the foregoing description is to be interpreted in an illustrative sense rather than a restrictive sense.

Claims (12)

1. A method for operating a bistable electro-optic display using a first driving scheme and a second driving scheme that are different from each other, the method comprising, in the following order: The first driving scheme is used to drive the display to a predetermined transition image; The second driving scheme is used to drive the display to a second image that is different from the transition image; The display is driven to the same transition image using the second driving scheme; and The first driving scheme is used to drive the display to a third image, which is different from both the transition image and the second image. Before driving the display to the second image, the display is sequentially driven to a plurality of transition images. Each transition image is limited to a number of gray levels equal to the smaller of the number of gray levels used by the first driving scheme and the second driving scheme. 2. The method according to claim 1, wherein the first driving scheme is a grayscale driving scheme, and the grayscale driving scheme is capable of driving the display to at least four grayscale levels. 3. The method according to claim 2, wherein the first driving scheme is a grayscale driving scheme, and the grayscale driving scheme is capable of driving the display to at least eight grayscale levels. 4. The method according to claim 1, wherein the second driving scheme is an application update driving scheme, the application update driving scheme having fewer gray levels than the first driving scheme and a maximum update time less than the saturation pulse length of the display. 5. The method of claim 1, wherein the transition image comprises a single hue applied to all pixels of the display. 6. The method of claim 1, wherein the display is equipped with a plurality of transition images, and the display controller is configured to select a transition image based on an image already present on the display. 7. The method of claim 1, wherein the display is sequentially driven to a plurality of transition images before driving the display to the third image. 8. The method of claim 1, wherein the electro-optic display comprises a rotating dual-color component or an electrochromic material. 9. The method of claim 1, wherein the electro-optic display comprises an electrophoretic material comprising a plurality of charged particles placed in a fluid and capable of moving through the fluid under the influence of an electric field. 10. The method of claim 9, wherein the charged particles and the fluid are confined within a plurality of cavities or microcells. 11. The method of claim 9, wherein the charged particles and the fluid exist as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. 12. The method of claim 9, wherein the fluid is gaseous.