HK1252982B - Methods and apparatus for operating an electro-optic display in white mode - Google Patents

Description

Method and apparatus for operating an electro-optical display in white mode

Citation of Related Applications

This application claims the benefit of provisional application serial number 62/292,829, filed February 8, 2016.

This application is related to U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,116,466; 7,119,772; 7,193,625; 7,202,847; 7,259,744; 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; 7,787,169; 7,952,557; 7,956,841; 7,999,787; 8,077,141; and 8,558,783; U.S. Patent Application Publication No. 20 03/0102858; 2005/0122284; 2005/0253777; 2006/0139308; 2007/0013683; 2007/0091418; 2007/0103427; 2007/0200874; 2008/0024429; 2008/0024482; 2008/0048969; 2008/0129667; 2008/0136774; 2008/0150888; 2008/0291129; 2009/01746 51; 2009/0179923; 2009/0195568; 2009/0256799; 2009/0322721; 2010/0045592; 2010/0220121; 2010/0220122; 2010/0265561; 2011/0285754; 2013/0194250 and 2014/0292830; PCT Published Application No. WO2015/017624; and U.S. Patent Application No. 15/015,822 filed on February 4, 2016.

For convenience, the above patents and applications may be collectively referred to as "MEDEOD" (Method for Driving Electro-Optical Displays) applications. The entire contents of these patents and co-pending applications, as well as all other U.S. patents and published and co-pending applications mentioned below, are incorporated herein by reference.

Technical Field

The present application relates to electro-optical displays and related apparatus and methods.

Background Art

An electro-optic display may be operated by applying a voltage signal to one or more pixels of the electro-optic display.

Summary of the Invention

According to one aspect of the present application, a method of operating an electro-optical display is provided. The method includes detecting a null state transition of a first pixel when transitioning from a first image to a second image. The method also includes determining whether a threshold number of primary neighbors of the first pixel transition from a black state to a white state when transitioning from the first image to the second image, and applying a voltage signal to the first pixel in response to a subsequent transition to a third image, wherein the voltage signal has a waveform configured to generate an optically black state for the first pixel.

According to one aspect of the present application, a display is provided. The display includes an electro-optical display and a driver circuit coupled to the electro-optical display and configured to perform a method. The method includes detecting a null state transition of a first pixel when transitioning from a first image to a second image. The method also includes determining whether a threshold number of primary neighbors of the first pixel transition from a black state to a white state when transitioning from the first image to the second image, and applying a voltage signal to the first pixel in response to a subsequent transition to a third image, wherein the voltage signal has a waveform configured to generate an optically black state for the first pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments of the present application will be described with reference to the following drawings. It should be understood that the drawings are not necessarily drawn to scale. Items appearing in multiple figures are represented by the same reference numerals in all figures in which they appear.

FIG1 is a schematic diagram of a cross-sectional view of one example of an electro-optic display.

FIG. 2A is an exemplary waveform for transitioning a pixel from a black state to a white state.

FIG. 2B is an exemplary waveform for transitioning a pixel from a white state to a black state.

3A and 3B are schematic diagrams illustrating the formation of bright edge artifacts in an image displayed on an electro-optic display.

4 is an exemplary waveform for regenerating a black optical state in an exemplary method of operating an electro-optic display.

5 is a flow chart illustrating an exemplary method of operating an electro-optic display according to some embodiments of the present invention.

6 is a flow chart illustrating an exemplary method of operating an electro-optic display according to some embodiments of the present invention.

7 is a flow chart illustrating an exemplary method of operating an electro-optic display according to some embodiments of the present invention.

FIG. 8A is an exemplary image of text displayed without correction of bright edge artifacts.

8B is an exemplary image of text displayed with correction for bright edge artifacts in accordance with the subject matter presented herein.

9 is a graph of simulated residual voltage on an electro-optical display.

FIG. 10A is an electro-optic display showing a checkerboard pattern.

FIG. 10B shows an electro-optic display with another checkerboard pattern.

FIG. 11 is a graph of measured output reflectivity versus input reflectivity.

12A and 12B are input images to be displayed on an electro-optic display.

FIG. 12C is the resulting image after the electro-optic display has been updated with the images of FIG. 12A and FIG. 12B .

13A through 13D are examples of driving waveforms according to the disclosure presented herein.

14 is a graph of measured output reflectivity versus input reflectivity using the waveforms presented in FIGs. 13A through 13D.

FIG. 15 is the resulting image after updating the electro-optic display using the waveforms presented in FIGs. 13A through 13D .

16 is a table illustrating a set of parameters for estimating pixel blur according to the subject matter presented herein.

FIG17 is a model illustrating one embodiment of dithering processing according to the subject matter disclosed herein.

DETAILED DESCRIPTION

Aspects of the present application relate to utilizing drive signals to reduce the presence of edge artifacts in images displayed on an electro-optical display. One type of edge artifact is the appearance of bright edges in dark areas, such as in the body of text characters displayed in white mode, where the text is in a black state and the background is in a white state. This type of artifact can occur when driving a display using a technique that reduces flicker in a display by not applying a voltage signal (or zero voltage) to pixels that remain in the same state from one image to a subsequent image, which can be considered a "null state transition."

The term "electro-optical," as applied to a material or display, is used herein in its conventional sense in the field of imaging, and refers to a material having first and second display states that differ in at least one optical property, the material being caused to change from its first display state to its second display state by applying an electric field to the material. While the optical property is typically color perceptible to the human eye, it may be another optical property, such as light transmission, reflection, luminescence, or, in the case of displays intended for machine reading, false color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

The term "gray state" is used herein in its conventional sense in the field of imaging, referring to a state between the two extreme optical states of a pixel, but does not necessarily mean a black and white transition between the two extreme states. For example, several of the Iink patents and published applications referred to above describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the display, and should be understood to generally include extreme optical states (which are not limited to black and white), such as the white and dark blue states mentioned above. The term "monochromatic" may be used hereinafter to refer to a drive scheme in which a pixel is driven only to its two extreme optical states, without an intermediate gray state.

Most of the following discussion will focus on methods for driving one or more pixels of an electro-optical display through a transition from an initial gray level (or "gray tone") to a final gray level (which may or may not be different from the initial gray level). The terms "gray state," "gray level," and "gray tone" are used interchangeably herein and include extreme optical states as well as intermediate gray states. Due to limitations such as the discreteness of the drive pulses applied by the frame rate and temperature sensitivity of the display driver, the number of possible gray levels in current systems is typically 2-16. For example, in a black and white display with 16 gray levels, typically, gray level 1 is black and gray level 16 is white; however, the names of the black and white gray levels may be reversed. Here, gray tone 1 will be used to designate black. Gray tone 2 will be a lighter color of black as gray tones fade into gray tone 16 (i.e., white).

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, wherein the first and second display states differ in at least one optical property such that after any given element is driven to assume its first or second display state by an addressing pulse of finite duration, that state persists after termination of the addressing pulse for a time that is at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays that support grayscale can be stable not only in their extreme black and white states, but also in intermediate gray states, as can some other types of electro-optical displays. Such displays are properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" will be used herein to cover both bistable and multistable displays.

The term "impulse" is used herein in the conventional sense of the integral of voltage with respect to time. However, some bistable electro-optical media function as charge converters, and with such media, an alternative definition of impulse may be used, namely the integral of current with respect to time (equal to the total applied charge). Depending on whether the medium functions as a voltage-to-time impulse converter or as a charge-to-impulse converter, the appropriate definition of impulse should be used.

The term "residual voltage" is used herein to refer to a persistent or decaying electric field that may remain in an electro-optical display after an addressing pulse (a voltage pulse used to change the optical state of the electro-optic medium). This residual voltage may cause adverse effects on the image displayed on the electro-optical display, including but not limited to the so-called "ghosting" phenomenon, in which traces of the previous image remain visible after the display has been rewritten. Application 2003/0137521 describes how a direct current (DC) unbalanced waveform can result in the generation of a residual voltage that can be determined by measuring the open-circuit electrochemical potential of a display pixel.

The term "waveform" will be used to refer to the entire voltage versus time curve used to achieve a transition from a particular initial gray level to a particular final gray level. Typically, such a waveform will include multiple waveform elements; where these elements are substantially rectangular (i.e., a given element includes applying a constant voltage for 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 for a particular 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 depending on parameters such as the temperature of the display or the amount of time it has been in operation, and thus a display may be provided with 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." As described in some of the aforementioned MEDEOD applications, more than one drive scheme may also be used simultaneously in different areas of the same display, and a set of drive schemes used in this manner may be referred to as a "set of simultaneous drive schemes."

Several types of electro-optical displays are known. One type of electro-optical display is a rotating two-color component type, such as described 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 generally referred to as "rotating two-color ball" display, the term "rotating two-color component" is preferably more accurate because in some of the above-mentioned patents, the rotating component is not spherical). This display uses many little bodies (usually spherical or cylindrical) and internal dipoles, and the body includes two or more parts with different optical properties. These bodies are suspended in a liquid-filled cavity in the matrix, and the cavity is filled with liquid so that the body can rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the body to various positions and changing which part of the body is seen through the viewing surface. This type of electro-optic medium is typically bistable.

Another type of electro-optical display uses an electrochromic medium, for example, in the form of a nanoelectrochromic film comprising an electrode formed at least in part from a semiconducting metal oxide and a plurality of dye molecules attached to the electrode that are capable of reversible color change; 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. Nanoelectrochromic films of this type are 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.

Another type of electro-optical display is the electrowetting display developed by Philips and described in Hayes, R.A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). It is shown in U.S. Patent No. 7,420,549 that such an electrowetting display can be made bi-stable.

One type of electro-optical display that has been the subject of intensive research and development for many years 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 good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up EPDs tend to settle, resulting in a short service life for these displays.

As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, the 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. Patents No. 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in an orientation that allows particle sedimentation, such as in signs where the media is arranged in a vertical plane, such gas-based electrophoretic media are susceptible to the same problems as liquid-based electrophoretic media due to particle sedimentation. In fact, the particle sedimentation problem is more severe in gas-based electrophoretic media than in liquid-based electrophoretic media because the viscosity of the gaseous suspending fluid is lower than that of the liquid, thus causing the electrophoretic particles to sediment more quickly.

Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and Iink Corporation describe various techniques for encapsulated electrophoretic and other electro-optical media. Such encapsulated media comprise a plurality of small capsules, each of which itself comprises an inner phase containing electrophoretically mobile particles 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 coherent layer positioned between two electrodes. The techniques described in these patents and applications include:

(a) electrophoretic particles, fluids, and fluid additives; see, e.g., U.S. Patent Nos. 7,002,728 and 7,679,814;

(b) capsules, adhesives, and encapsulation processes; see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719;

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

(d) Backplanes, adhesive layers and other auxiliary layers and methods for 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, for example, 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.

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 electrophoretic fluid and a continuous phase of polymer material, and that the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered to be capsules or microcapsules, even though 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-dispersed electrophoretic media are considered to be a subclass of encapsulated electrophoretic media.

A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged particles and fluids are not encapsulated in microcapsules, but rather are held within a plurality of 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, Inc.

Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, the particles substantially block visible light from being transmitted through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode," in which one display state is substantially opaque and one display state 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. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on variations 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 can be used in a multilayer structure for a full-color display; in this structure, at least one layer adjacent to the viewing surface of the display is operated in a shutter mode to expose or conceal a second layer further from the viewing surface.

Encapsulated electrophoretic displays are generally not plagued by the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer additional benefits, 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-metered coating such as patch die coating, slot or extrusion coating, slide or laminate coating, curtain coating; roll coating such as blade coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Thus, the resulting display can be flexible. Additionally, because the display medium can be printed (using a variety of methods), the display itself can be inexpensively manufactured.

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

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 conveniently referred to hereinafter as "impulse-driven displays") stands in stark contrast to conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bi-stable or multi-stable, but rather act as voltage converters, such that applying a given electric field to a pixel of such a display produces a specific grayscale level at the pixel, regardless of the grayscale level that previously existed at the pixel. Furthermore, LC displays can be driven in only one direction (from non-transmissive or "dark" to transmissive or "bright"), with the reverse transition from a lighter state to a darker state being achieved by reducing or eliminating the electric field. Finally, the grayscale level of a pixel of an LC display is insensitive to the polarity of the electric field, only its amplitude, and indeed, for technical reasons, commercial LC displays typically reverse the polarity of the drive field at frequent intervals. In contrast, bi-stable electro-optic displays act as impulse converters, to a first approximation, such that the final state of a pixel depends not only on the applied electric field and the duration of that field application, but also on the state of the pixel before the electric field was applied.

Regardless of whether the electro-optical medium used is bi-stable, to achieve a high-resolution display, the 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 at least one nonlinear element associated with each pixel, creating an "active matrix" display. The addressing or pixel electrode that addresses a pixel is connected to an appropriate voltage source through 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 used in the following description, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Traditionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of a designated row and a designated column. The sources of all transistors in each column are connected to a single column 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 if 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, such as to ensure that all transistors in the selected row are conductive, while a voltage is applied to all other rows, such as to ensure that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to a column driver, which places on each column electrode a voltage selected to drive the pixels in the selected row to their desired optical state. (The above voltages are relative to a common front electrode, which is typically provided on the side of the electro-optical medium opposite the non-linear array and extends 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 so that the next row of the display is written. This process is repeated so that the entire display is written in a row-by-row manner.

Voltage signals applied to adjacent pixels can affect the optical state of empty-state pixels, thereby creating artifacts that can be transmitted to subsequent images. For example, a voltage signal may not be applied to a pixel that remains as part of a text character from one image to a subsequent image because the pixel undergoes a black-to-black-state transition (B→B). This can reduce flicker in the display by applying voltage signals only to pixels that change state between subsequent images. Although flicker may be reduced, bright edge artifacts may be generated by such a drive scheme. For pixels that undergo an empty-state transition, voltage signals applied to adjacent pixels may affect the optical state of the empty-state pixels, for example by affecting the distribution of the electrophoretic medium of the pixel that undergoes an empty-state transition and creating an undesirable change in its optical state. A pixel identified as remaining in the black state during the transition may have a brighter optical state due to one or more adjacent pixels undergoing a black-to-white-state transition. These "blooming events" may occur at the edges of objects displayed in an electro-optical display, such as the edges of text characters, and may continue to subsequent image transitions. Pixels having a brighter optical state may become surrounded by pixels that display a black optical state in subsequent image transitions, thereby forming bright edge artifacts in the image that may be more noticeable to a viewer of the display than if the bright pixels were located at the edge of an object. Accordingly, aspects of the present application relate to identifying pixels that may negatively impact the visual aesthetics of displayed content based on previous transitions of pixels adjacent to a pixel of interest, and applying appropriate correction signals, where appropriate, to reduce or eliminate such negative impacts.

Applicants have recognized that when pixels may contribute to bright edge artifacts, bright edge artifacts can be reduced by identifying pixels undergoing a null state transition and applying a waveform configured to produce an optical state in the pixel. The waveform can be a voltage signal configured to regenerate the optically black state of a pixel that has been or may be made brighter due to a voltage signal applied to an adjacent pixel (e.g., by blurring). Regenerating the optically black state of the pixel can reduce the appearance of bright edges that may occur when the pixel transitions from a non-black state to a black state and an adjacent pixel has undergone a black-to-black state transition. The waveform can include a voltage signal having an amplitude and a duration or time suitable for producing the desired optical state. The voltage signal can be applied over multiple display frames to achieve the desired optical state of the pixel. Examples of suitable waveforms are described in the aforementioned U.S. Patent Application No. 15/015,822, filed on February 4, 2016, which includes a transition waveform referred to as an inversion top pulse ("iTop pulse"), the entire contents of which are incorporated herein by reference.

However, if applied too frequently, such waveforms may cause irreversible damage to the display, affecting the performance of the display and the quality of the displayed image. Accordingly, aspects of the present application relate to methods for selectively applying waveforms to pixels in a manner that appropriately balances the reduction of the appearance of bright edge artifacts and the frequency with which the waveforms are applied. A drive scheme for an electro-optical display may include identifying pixels that undergo a transition to a null state, where the optical state of the pixel is likely to have been affected by a transition of an adjacent pixel. When an adjacent pixel has undergone a transition that may affect the optical state of the null state pixel, a waveform for regenerating the optical state of the null state pixel may be applied. For a display operating in white mode, when an adjacent pixel undergoes a transition that may result in a brighter optical state of the pixel, the drive scheme may apply a waveform for regenerating an optically black state to a pixel designated to remain in a black state. In some embodiments, the waveform is applied to the pixel when one or more of its primary neighbors undergoes a transition from a white state to a black state between subsequent images. In some embodiments, the waveform is applied to the pixel when one or more primary neighbors have a subsequent black state.

The above-described aspects and embodiments and additional aspects and embodiments are further described below. These aspects and/or embodiments may be used alone, all together, or in any combination of two or more, as the present application is not limited in this respect.

A cross-sectional view of an exemplary electrophoretic display architecture is shown in FIG1 . Display 100 includes an electrophoretic medium layer 101 that may include a plurality of capsules 104, each having a capsule wall surrounding a fluid and electrophoretic particles 106 suspended in the fluid. Electrophoretic medium layer 101 is positioned between electrode 102 and pixelated electrodes 110 a, 110 b, 110 c that define pixels of display 100. Electrophoretic particles 106 may be electrically charged and responsive to an electric field created by electrode 102 and one of electrodes 110 a, 110 b, 110 c. Examples of suitable electrophoretic medium layers are described in U.S. Patent Nos. 6,982,178 and 7,513,813, the entire contents of which are incorporated herein by reference.

The display 100 also includes a voltage source 108 coupled to the electrodes and configured to provide drive signals to the electrodes. Although FIG1 illustrates the coupling of the voltage source 108 between electrodes 102 and 110 a, the voltage source 108 can be coupled to electrodes 110 b and 110 c to provide drive signals to multiple pixels of the display 100. The provided voltage then creates an electric field between the electrode 102 and one or more electrodes 110 a, 110 b, 110 c. Thus, the electric field experienced by the electrophoretic medium layer 101 can be controlled by varying the voltage applied to the electrode 102 and the one or more electrodes 110 a, 110 b, 110 c. Varying the voltage applied to a desired pixel can provide control of the pixels of the display. In response to the applied electric field created by the voltage between the electrode 102 and the electrodes 110 a, 110 b, 110 c, the particles 106 within the electrophoretic medium layer 101 can move within their respective capsules 104. Depending on the voltage applied to the electrodes, the grey level of the optical state of the pixel can be controlled.

Voltage source 108 may be coupled to display controller 112. Display controller 112 may include driver circuitry configured to perform the method of operating display 100. Display controller 112 may include a memory configured to store states of one or more pixels of display 100. Current and/or previous states of the pixels may be stored in the memory of display controller 112 in any suitable manner.

Although FIG1 illustrates a microcapsule-type electrophoretic display, various types of displays may be used in accordance with the techniques described herein. In general, electro-optical displays, including microcapsule-type electrophoretic displays, microcell-type electrophoretic displays, and polymer-dispersed electrophoretic image displays (PDEPIDs), may utilize aspects of the present disclosure. Furthermore, although electrophoretic displays represent a suitable type of display according to various aspects of the present disclosure, other types of displays may also utilize one or more aspects of the present disclosure. For example, Gyricon displays, electrochromic displays, and polymer-dispersed liquid crystal displays (PDLCDs) may also utilize aspects of the present disclosure.

Pixels of an electrophoretic display, such as display 100 shown in FIG. 1 , can be driven to different optical states based on an applied voltage signal. The voltage signal used to achieve the optical state of the pixel can depend on the pixel's previous optical state. Depending on the desired state transition of the pixel, the voltage signal can include a negative voltage and/or a positive voltage. In the examples shown in FIG. 2A , 2B , and 4 , a positive voltage is indicated on the y-axis as Vpos and a negative voltage is indicated as Vneg. In some cases, a waveform with a negative voltage, such as waveform 201 shown in FIG. 2A , can drive a pixel of the electrophoretic display from a black state to a white state. A waveform with a positive voltage, such as waveform 202 shown in FIG. 2B , can drive a pixel of the electrophoretic display from a white state to a black state. In FIG. 2A and 2B , the x-axis represents time and the y-axis represents voltage. Although an electrophoretic display can be driven to another grayscale level, using only two grayscale levels can simplify the number and complexity of waveforms used to drive the pixel to transition between different optical states. The use of two gray levels may be particularly suitable for displays with higher resolutions (e.g., greater than 300 dpi, greater than 500 dpi, between 300 dpi and 800 dpi, or any value or range of values within such a range) due to the ability to present text to a viewer at a desired quality level. The techniques for reducing bright edge artifacts as described herein may be applied to electrophoretic displays driven with two gray levels (e.g., a white state and a black state) due to crosstalk between adjacent pixels. For some electrophoretic displays, a voltage signal applied to a pixel may affect a portion of adjacent pixels, such as approximately one-fifth of the adjacent pixels. Crosstalk between pixels may result in blurring events when a pixel undergoing a null transition has an optical state that is affected by an adjacent pixel.

The occurrence of edge artifacts that appear in text displayed on an electrophoretic display is further discussed with reference to Figures 3A and 3B. Figure 3A depicts a first image 302 (Image 1) that includes the letter "x" representing pixels that are currently in a black state. It is assumed here that the previous image of Image 1 includes the letter "l" 304 and a portion of the letter "y" 306, which are shown by the downward diagonal area of Figure 3A. The pixels of the letter "x" that overlap with the letters "l" 304 and "y" 306 of the previous image undergo a black state to black state transition because, in this example, the display operates with the letters and white background as black. These overlapping pixels can remain in the black state by undergoing a null transition between the previous image and Image 1 because no voltage signal is required to change the optical state of these pixels. The pixels of the letters "l" 304 and "y" 306 that do not overlap with the letter "x" undergo a black state to white state transition to create a white background surrounding the letter "x." Although the letters "l" and "y" are shown in the previous image, they are shown in FIG. 3A to illustrate the overlap between the pixels of the letter "x" and the letters "l" 304 and "y" 306 of the previous image.

Applicants have recognized that pixels that experience a null transition (e.g., a black state to black state transition) lacking a voltage signal may experience a blurring event due to the presence of a voltage signal applied to one or more adjacent pixels. An example is pixel 308. Pixels of the letter "x" (such as pixel 308) that are adjacent to one or more pixels experiencing a black state to white state transition may experience a blurring event and appear brighter than the optical black state. Such pixels are represented by the dark gray area within the letter "x." In the resulting image 1 shown in FIG3A , pixels of the letter "x" that appear less dark are located at the edge of the text and adjacent to pixels experiencing a black to white transition. Some pixels of the letter "x" experience a white state to black state transition. These pixels are pixels that do not overlap with the letters "l" 304 and "y" 306 and may appear darker than pixels of the letter "x" adjacent to pixels experiencing a black to white transition.

The brighter pixels within the letter "x" caused by the blur event can be carried over to subsequent images, particularly when the pixels undergo a subsequent null transition. As an example, FIG3B shows an image 310 (Image 2) including the letter "b" having pixels overlapping with the letter "x" of Image 1 that undergo a null transition by remaining in a black state. Because some pixels of the letter "x" appear in a brighter optical state due to the blur, this brighter appearance of these pixels is present in the current image of the letter "b," an example of which is pixel 312. These brighter pixels create areas that appear less dark than other black pixels. Such bright pixels can create the appearance of bright "edges" or "lines" within the image and degrade the quality of the image.

Some embodiments of the present application relate to operating an electrophoretic display in a manner that reduces the appearance of bright edges within a displayed image, such as those shown by pixel 312 in FIG. 3B . Operation of the electrophoretic display may include selectively applying a voltage signal to pixels (e.g., pixel 312) that may contribute to the presence of bright edges. Whether a pixel may contribute to bright edge artifacts can be determined by the previous transitions of the pixel and one or more pixels adjacent to the pixel in question. In a drive scheme where voltage is not applied to pixels undergoing null-state transitions, such pixels may be most likely to contribute to the appearance of bright edge artifacts. When a voltage signal applied to one or more neighboring pixels changes the optical state of the pixel in question, such a pixel may experience a blur event. The number of neighboring pixels may affect the extent of a pixel's blur event, and thus the pixel's optical state. For example, a pixel may have up to four primary neighboring pixels. A moderate blur event may occur when one primary neighbor undergoes a black-to-white transition. A strong blur event may occur when all four primary neighboring pixels undergo a black-to-white transition. A pixel experiencing a strong blur event may appear brighter than a moderate blur event.

By applying a voltage signal to the pixel in question to generate an optical state of the pixel (e.g., a black optical state), the effects of blur events can be reduced. While applying the voltage signal can reduce the occurrence of blurry pixels, applying the voltage signal too frequently can damage the electrophoretic display. The voltage signal can be a waveform that is DC unbalanced and can cause a buildup of residual voltage in the display over time as the waveform is applied. Some embodiments of the present application relate to detecting whether a pixel undergoes a null transition, determining whether a threshold number of primary neighbors of the pixel transition from a black state to a white state during an image transition, and applying the voltage signal to the pixel in a subsequent image transition. The voltage signal can have a waveform configured to generate an optically black state for the pixel.

The type of transition applied to a pixel can be determined by one or more previous waveform states of the pixel and/or other pixels of the display. The current state of the pixel can determine the type of waveform to be applied to the pixel to change or alter the optical state of the pixel. The waveform state can correspond to a desired optical state of the pixel. The previous and/or current states of the pixels in the display can be stored in a display controller or other suitable circuitry configured to perform the method of operating a display, and allow determination of an appropriate subsequent transition based on the previous or current state of the pixel.

The technology of the present application involves associating an indicator state (or I-state) with a pixel that may have experienced a blur event and, therefore, may tend to appear as a bright pixel in a subsequent image if a refresh or correction signal is not applied. A pixel can assume or be assigned an indicator state when it undergoes a black state to black state transition and one or more adjacent pixels undergo a black state to white state transition. These conditions may identify a pixel that has experienced a blur event. The application of a voltage signal suitable for producing an optically black state in the identified "indicator state" pixel can be applied in subsequent transitions to reduce the presence of bright edge artifacts. In this way, the indicator state can refer to a pixel that should have a black optical state but may not appear completely dark due to a blur event from an adjacent pixel. Referring to Figure 3A, pixel 308 can be set to the indicator state because it remains in the black state and has one or more adjacent pixels that undergo a black to white transition. Such a pixel in Figure 3A results in a bright edge appearing in the letter "b" in Figure 3B, such as pixel 312.

According to some embodiments, a voltage signal may be applied to a pixel in the indicated state (I state) to generate an optically black state for the pixel and may be referred to as a "black regeneration waveform." The voltage signal may have a positive voltage value (e.g., Vpos) for a period of time, with the voltage taking any suitable value. An exemplary voltage signal for generating an optically black state is shown as waveform 402 in FIG. 4 . The voltage signal may be applied over multiple display frames to achieve the desired result. This waveform may be referred to as an inversion top pulse (iTop pulse).

A method of operating an electro-optic display may include detecting a null-state transition for one or more pixels and determining whether a threshold number of primary neighbors experienced a black-to-white state transition between a first image and a second image. It should be noted that, in this context, "first" and "second" are not limited to absolute values, but rather are meant to indicate a previous image and a subsequent image. Similarly, "third" image is not an absolute value, but rather indicates an image subsequent to the "second" image, and there may be intermediate images between the "second" and "third" images. When the subsequent state is a black state, a voltage signal or iTop pulse may be applied to the pixel in the indicated state. FIG5 illustrates steps of an exemplary method of operating an electro-optic display according to some embodiments of the present invention. Method 500 may begin with a first image 510, such as the image preceding image 1 in FIG3A , showing "l" 304 and "y" 306. First image 510 may have a set of states for pixels of the display, which may be stored in a display controller, such as display controller 112 in FIG1 . At act 520, second image data is received, such as by display controller 112. The second image data may include optical states of pixels in the display in order to display a second image, such as image 1 in FIG. 3A showing the letter "x." For a given pixel, method 500 proceeds to act 530. If the current state of the pixel is neither in the black (B) state nor in the indicated (I) state, then a standard transition for operating an electrophoretic display is applied by act 560 when the second image is displayed by act 580.

If the current state of the pixel, action 530, is black (B), then method 500 proceeds to action 540, which examines the transitions of the pixel's primary neighbors to determine whether one or more of the primary neighbors are undergoing a black (B) state to a white (W) state transition from the first image to the second image. In some embodiments, action 540 may include determining whether a threshold number (e.g., 1, 2, 3, 4) of the pixel's primary neighbors are transitioning from a black state to a white state. If there are no primary neighbors undergoing a black to white state transition or if the number of primary neighbors undergoing a black to white state transition is below the threshold, then a standard transition for operating an electrophoretic display is applied by action 560 when displaying the second image by action 580. Conversely, if there are one or more primary neighbors undergoing a black to white state transition or if the number of primary neighbors undergoing a black to white state transition is above the threshold, then the state of the pixel is set to an indication (I) state by action 570 to form the second image by action 580. In this manner, the pixel is identified as potentially experiencing a blur event by one or more of its primary neighbors.

If the current state of the pixel at act 530 is in the indicated (I) state, method 500 proceeds to act 550, which determines the next state of the pixel from the data of the second image. If the next state of the pixel is not a black state (e.g., a white state), a standard transition for operating an electrophoretic display is applied by act 560 when the second image is displayed by act 580. If the next state of the pixel is a black (B) state, a black regeneration waveform, such as the black regeneration waveform shown in FIG. 4 , is applied to the pixel by act 590 when the second image is displayed by act 580. In this manner, the black regeneration waveform is applied to those pixels that are identified as having likely experienced a blur event as indicated by being in the indicated (I) state. For example, when starting from image 1 of FIG. 3A to image 2 of FIG. 3B , acts 550 and 590 may occur, for example, for pixel 308.

Additional steps of this method of operating an electro-optical display can provide selectivity for when to apply the black state regeneration waveform. Figure 6 shows the steps of a method 600 according to another embodiment, which includes the additional steps of the method 500 shown in Figure 5. These additional steps provide further selectivity for when to apply the black regeneration waveform in act 590. A pixel having a current state as the indicated (I) state via act 530 and a next state as the black (B) state via act 550 proceeds to step 610 of method 600, which examines the transition type of one or more primary neighbors of the pixel when transitioning to the second image. If one or more primary neighbors transition from the white (W) state to the black (B) state, a black regeneration waveform is applied to the pixel via act 590 when the second image is displayed via act 580. In some embodiments, if the number of primary neighbors transitioning from the white (W) state to the black (B) state is above a threshold, a black regeneration waveform is applied to the pixel. If the pixel does not meet the conditions of act 610, where there are no major neighbors that transition from a white (W) state to a black (B) state or the number of major neighbors that undergo such a transition is below a threshold, the pixel is set to the indication (I) state via act 620. In this way, when one or more major neighbors transition to a black state, the pixel can receive a black regeneration waveform to reduce the likelihood of brighter pixels adjacent to darker pixels, and therefore the visibility of bright edge artifacts to a viewer of the displayed second image. By selectively applying the black regeneration waveform under such conditions, a balance can be achieved between reducing the presence of bright edges and the frequency with which the waveform is applied.

FIG7 illustrates alternative steps that may be implemented when operating an electro-optical display. Method 7 includes additional steps to method 500 shown in FIG5 . These additional steps provide further options for when to apply the black regeneration waveform in act 590. A pixel having a current state of the indicated (I) state via act 530 and a next state of the black (B) state via act 550 proceeds to step 710 of method 700, which examines the next state of one or more primary neighbors of the pixel in the second image. If one or more primary neighbors have a next state of the black (B) state, the black regeneration waveform is applied to the pixel via act 590 when the second image is displayed via act 580. In some embodiments, if the number of primary neighbors that transition to the black (B) state is above a threshold, the black regeneration waveform is applied to the pixel via act 590. If the pixel does not meet the conditions of act 710, where there are no primary neighbors with a next state of the black (B) state or the number of primary neighbors that transition to the black state is below a threshold, the pixel is set to the indicated (I) state via act 720. Method 700 provides an alternative method for selectively applying a black regeneration waveform to pixels to reduce the presence of bright edge artifacts in an image displayed on an electro-optic display.

The techniques described herein can reduce the presence of bright edge artifacts when displaying images such as text on an electro-optical display. FIG8A shows an example image of text displayed on an electro-optical display without using such bright edge correction. There are lighter areas in the text, particularly in the letters "v" and "j." FIG8B shows an example image of the same text displayed on an electro-optical display operated in the manner described herein to reduce the presence of such bright edge artifacts.

The voltage signal used to regenerate the black optical state of the pixel may be DC unbalanced and cause irreversible damage to the display due to the accumulation of residual voltage in the display. The technology of the present application relates to a method of selectively applying a waveform to reduce the accumulation of residual voltage and damage to the display. Figure 9 shows a graph of simulated residual voltage on a display for a display usage scenario in which 4500 subsequent images (e.g., text pages) are displayed on the display using a bright edge correction operation method according to the technology described herein for different types of black regeneration waveforms with reference to an empty state transition waveform 902. If the black regeneration waveform 904 includes 21 frames of a +15V drive signal, then such a waveform can produce a residual voltage of more than 2.5V at the pixel of the display, which may damage the display. However, if the black regeneration waveform 906 includes 6 frames of a +15V drive signal with 4 frames of padding, then such a waveform can produce a residual voltage of less than 0.5V at the pixel, which can be considered an appropriate amount of residual voltage to reduce damage to the display.

Blurred Differences

In addition to the blurring effect described above, the image quality of an electrophoretic display (EPD) can be further affected by the so-called differential blurring effect. Figures 10A and 10B are two checkerboard image patterns that illustrate the difference in blur (or differential blurring) depending on whether the previously displayed image is pure black or pure white, and whether the EPD is updated using a so-called direct update (DU) waveform. The DU waveform updates the EPD in such a way that EPD pixels undergoing black-to-white and white-to-black transitions receive a single drive pulse, with a typical pulse having a duration of approximately 250 ms. In some embodiments, the waveforms presented in Figures 2A and 2B can be used as the DU waveform. All other pixels (not undergoing a transition) receive a null (i.e., null or non-updated) waveform. Thus, the DU waveform is characterized as a 1-bit waveform. Thus, as shown in Figure 10A, a pixel undergoing a black-to-black transition receives a null waveform, while its neighboring pixel undergoing a black-to-white transition receives a DU waveform. Similarly, in Figure 10B, a pixel remaining from white to white receives a null waveform, while its neighboring pixel undergoing a white-to-black transition receives a DU waveform.

As can be seen from Figures 10A and 10B, crosstalk between pixels can cause optical artifacts (i.e., blurring) in which pixels blur over and into their neighbors. As can be understood from a comparison of Figures 10A and 10B, differential blurring occurs when blur characteristics vary depending on the previous image displayed by the pixels of the EPD, where the average reflectivity of the black and white checkerboards is brighter when the previous image is black than when the previous image is white.

FIG11 is a graph of measured output reflectivity versus input reflectivity for 32 different previous states linearly separated in reflectivity between pure black and pure white. In this measurement setup, the previous state is a gray tone rendered by 1-bit dithering using scattered ordered dithering. For example, a previous state for an intermediate gray tone could be a checkerboard with 50% black and 50% white pixels, where each square is a single pixel. From this previous state, the EPD is updated with the DU to another gray tone known as the input reflectivity. This input reflectivity corresponds to the desired gray tone to be displayed. In this setup, the input reflectivity ranges from 0 to 1, where 0 is pure black and 1 is pure white. The output reflectivity is the reflectivity measured on the display based on the final image. Such a curve is called a tone reproduction curve (TRC). As shown in FIG11 , the TRC varies significantly depending on the previous state, primarily due to difference blurring.

In some cases, as shown in FIG12C , the level of difference blur shown in FIG11 can result in significant image ghosting (e.g., image quality up to 10L*), where FIG12A is the first input image and FIG12B is the subsequent image to be displayed on the EPD.

In some embodiments, this ghosting effect can be significantly reduced by setting the EPD pixels to an original or starting optical state (e.g., pure white). In this way, the EPD can be conveniently updated with a DU waveform, where the update time is fast (e.g., 250ms). In use, the update waveform can be designed so that all pixels first become white before entering their final state. Therefore, no matter where they come from, the blur of all pixels will always be the same, effectively eliminating differential blur.

In some embodiments, the drive waveform can be configured so that all pixels complete their transition to white before any pixel begins to transition to black, and each phase or transition of the waveform is aligned in time (e.g., the transitions of the waveform begin and end at the same time). Specifically, for this setting, all pixels complete their transition to white before any pixel begins to transition to black. In effect, it will look like a white page is inserted in any transition from one image to another. It also results in a transition appearance that can be described as "clean" or "calm," as opposed to the "flickering" of a typical GC waveform. This will enable reasonable ghosting performance for 1-bit usage in the EPD.

Figures 13A to 13D show exemplary 1-bit waveforms for four valid transitions: black to white (Figure 13A), black to black (Figure 13B), white to black (Figure 13C), and white to white (Figure 13D). In general, the waveforms can include six adjustable waveform parameters: pI 1 _BB , pI 2 _BB , pI 1 _BW , pI 2 _WB , gap, and fill. Parameters pI 1 _BB and pI 1 _BW correspond to the pulse lengths of the drive to white for black to black and black to white transitions; parameters pI 2 _BB and pI 2 _WB correspond to the pulse lengths of the drive to black for black to black and white to black transitions. These four parameters can be adjusted independently from 50ms to 500ms. The gap parameter corresponds to the time gap between the end of the last drive to white (for black to black or black to white transitions) and the beginning of the first drive to black (for black to black or white to black transitions). The gap parameter can vary between 0 and 100ms. The fill parameter corresponds to the time between the last drive to black and the end of the waveform, and its duration can also vary between 0 and 100ms. In addition, in order to create a very clean transition appearance, the waveform transitions are aligned. In Figures 13A to 13D, the waveforms are shown as left-aligned, which means that the drive to white and the drive to black both start at the same time. However, the waveforms can also be right-aligned, which means that the drive to white and the drive to black both end at the same time. The white to white transition is empty to further reduce the flicker of the waveform and achieve a clean transition appearance. These waveforms can be integrated with other drive algorithms or schemes (such as the E Ink Regal algorithm) to obtain better performance and avoid edge accumulation using the scheme. For example, in some cases, a white to white pixel may receive an empty waveform or a T or F transition determined by the Regal algorithm. The T transition will be correctly placed so that it is located in the drive to white.

In some embodiments, the above parameters can be further adjusted to meet various design goals, such as minimizing ghosting and blurring in waveform regions and optimizing display reliability. Certain parameter combinations can cause the display to experience significant DC imbalance during use. Therefore, it is preferable to control the amount of DC imbalance introduced by this waveform to ensure long-term reliability and avoid display performance degradation over time. As shown in Figure 14, this waveform concept results in a significant reduction in differential blurring.

Compared to the image presented in Figure 12C, employing the waveforms discussed in Figures 13A to 13D provides a result image without ghosting due to a significant reduction in difference blurring. While this waveform configuration results in an update time that is longer than the DU waveform and similar to a typical GC waveform, the waveform alignment produces a very clean and low-flicker transition appearance, making the update transition appear faster and more immediate, especially compared to a typical GC waveform that appears to flicker significantly when displaying an image.

History-dependent fuzzy models

As mentioned above, when two adjacent pixels undergo different transitions, there may be some crosstalk, and they may affect the optical states of their neighbors. This can be considered a "blur" artifact when it takes the form of a net extension of one of the final optical states over the other. Physically, this can take a variety of forms, but in practice it can be summarized as a net increase or decrease in reflectivity compared to the nominal average expected from the two pixel areas. This is most easily expressed as the "effective blur width" (EBW) of the transitioned blur pair, which is a number with units of length that is positive if the net effect is brightening and negative if the net effect is darkening. This EBW value can then be used to predict the delta reflectivity expected from these pixel pairs in certain areas by multiplying the EBW by the difference of the two nominal optical states and the edge density (length/area) of the pair.

Presented in FIG16 is a table of parameters for a dithering model that can be used to: (1) progressively simulate local blur at each display pixel, and (2) modify an error diffusion algorithm that uses the model to appropriately dither the image. In some embodiments, an estimate of the current optical effect of the blur is maintained for each pixel edge in the image. Since there are twice as many edges as pixels, it is convenient to maintain two display-sized (number of pixels) arrays in memory to hold this information. For our purposes, we will call them bloomUp and bloomLeft, which hold estimates of the optical effect caused by blurring with respect to the upward and leftward neighbors of the associated pixel, respectively. If the previous and current states of the display are known, the next bloomUp and bloomLeft arrays can be updated by examining each pair of pixels that straddles a specified edge (up or left) and replacing that value with the value calculated in the table shown in FIG16.

As shown in Figure 16, the parameters αK and αW are the effective blur width (EBW) fractions obtained from system measurements (for black and white pixels respectively) divided by the length of the pixel edge. The parameters β and αKW can be derived from a special experiment in which pixels in a checkerboard are continuously switched and the resulting optical states are measured. This data can then be fit to the model to find the parameters. The β parameter represents the degree to which the previous blur is not erased. In a real example using V320 on a 500dpi panel, we obtained β = 0.54, which means that more than 1/2 of the previous blur effect is still retained after this particular update pair.

It should be understood that the parameters shown in Figure 16 are an exemplary configuration of the model, as these parameters and the exact configuration can be easily adjusted to better suit the user's specific needs. For example, Figure 16 shows the new value x(n+1) of the bloomUp or bloomLeft entry based on the current and next states of the associated blurry pixel pair and the current value x(n). This is derived from the assumption that if the next state of the pair is the same, there is no blur, hence the zero entry. However, even with a blur reduction waveform (e.g., the Regal algorithm/waveform), some edges may still remain in these cases, and this can be included in the model. More generally, each entry in the table shown in Figure 16 can have a formula for the model that includes an erase term and a contribution term.

In use, the parameters presented in FIG16 can be incorporated into the dithering process in at least two ways. The first, simplest approach is to make the quantization decision as usual in error diffusion. Then, once the decision is made, the actual optical effect is calculated by including the results of the blur update model for that decision when calculating the error to be diffused. Since error diffusion is causal and is typically calculated row by row from top to bottom, the outputs (next state and error) of the upper and left neighbors are known, and therefore the bloomUp and bloomLeft values can be updated immediately after the decision is made. The second approach, shown in FIG17 , is to use the blur model directly in the quantizer. In this case, the bloomLeft and bloomUp values are calculated for the two possible output options for the pixel under consideration. They are then used to modify the optical state presented as the quantizer's choice, so the quantizer will look ahead and know which choice will introduce the least error.

Specifically, FIG17 illustrates a dithering system (e.g., an error diffusion algorithm 1704) configured to calculate the gray tone of a display pixel according to the subject matter presented herein. In this configuration, the error diffusion algorithm 1704 can be designed to operate in a loop so that the calculated bloomLeft and bloomUp values can be fed back to the algorithm 1704 to calculate subsequent values. In this manner, the entire system is self-adjusting and continuously updated. Initially, starting bloomLeft and bloomUp values can be calculated using parameters looked up from table 1702, which is similar to the parameter table presented in FIG16. In some embodiments, the starting bloomLeft and bloomUp values can be predetermined experimentally and the initial desired reflectivity value _rB can be provided by a summation algorithm 1706. The summation algorithm 1706 can calculate an offset reflectivity value 1708 to be fed into a quantizer 1710 of the algorithm 1704, which is configured to calculate the bloomLeft and bloomUp values for the next pixel update. In this way, as described above, the grey tone of the display pixels can be continuously adjusted according to the blurring effect of each pixel depending on the previous optical state.

Having thus described several aspects and embodiments of the technology of the present application, it will be understood that various changes, modifications and improvements will readily occur to those of ordinary skill in the art. Such changes, modifications and improvements are intended to fall within the spirit and scope of the technology described in this application. Therefore, it will be understood that the foregoing embodiments are presented by way of example only, and that within the scope of the appended claims and their equivalents, embodiments of the invention may be practiced in a manner different from that specifically described. In addition, any combination of two or more features, systems, articles, materials, kits and/or methods described herein is included within the scope of the present disclosure if such features, systems, articles, materials, kits and/or methods are not inconsistent with each other.

In addition, as described, some aspects can be embodied as one or more methods. The actions performed as part of the method can be sequenced in any suitable manner. Thus, embodiments can be constructed in which the actions are performed in a different order than shown, which can include performing some actions simultaneously, even though shown as sequential actions in the illustrative embodiments.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles "a" and "an" as used herein in the specification and claims, unless explicitly indicated otherwise, should be understood to mean "at least one".

As used herein in the specification and claims, the phrase "and/or" should be understood to mean "one or both" of the elements so conjoined, ie, elements that are present in conjunction in some cases and separately in other cases.

As used herein in the specification and claims, the phrase "at least one" with respect to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but does not necessarily include at least one of each and every element specifically listed in the list of elements, and does not exclude any combination of elements in the list of elements. This definition also allows that elements may optionally be present in addition to the elements specifically identified in the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified.

In the claims and the foregoing description, all transitional words such as "comprises," "includes," "carries," "has," "contains," "involves," "maintains," "consists of," etc. should be understood as open-ended, i.e., meaning including but not limited to. The transitional words "consisting of" and "consisting essentially of" should be closed or semi-closed transitions.

Claims (7)

1. A method of operating an electro-optic display, comprising: When transitioning from a first image to a second image, an empty state transition of the first pixel is detected, wherein an empty state of the first pixel occurs when the first pixel has a black state in the first image and also has a black state in the second image; When transitioning from the first image to the second image, determine whether the primary neighbors of the first pixel, representing a threshold number, transition from a black state to a white state; and In response to a transition to a subsequent image, it is determined whether the subsequent state of the first pixel is a black state and whether the major neighbors of the first pixel in a second threshold number have a next state as a black state; and if an empty state transition of the first pixel is detected when transitioning from the first image to the second image and the major neighbors of the first pixel in a threshold number transition from a black state to a white state, and the subsequent state of the first pixel is a black state and the major neighbors of the first pixel in a second threshold number have a next state as a black state, then a voltage signal is applied to the first pixel, wherein the voltage signal has a waveform configured to generate an optical black state for the first pixel. 2. The method of claim 1, wherein the waveform is applied to the first pixel if the major neighbor of the second threshold of the first pixel changes from a white state to a black state when transitioning to a third image. 3. The method of claim 1, wherein the method further comprises: storing an indication associated with the first pixel if the primary neighbor of the threshold number of the first pixel changes from a black state to a white state when transitioning from the first image to the second image. 4. The method of claim 3, wherein the method further comprises applying the voltage signal to the first pixel during a subsequent image transition, at least in part based on the presence of the indication. 5. A display comprising: Electro-optical displays; A driving circuit, coupled to the electro-optic display and configured to perform a method including the following steps: When transitioning from a first image to a second image, the empty state of the first pixel is detected, wherein the empty state of the first pixel occurs when the first pixel has a black state in the first image and also has a black state in the second image; When transitioning from the first image to the second image, determine whether the primary neighbors of the first pixel, representing a threshold number, transition from a black state to a white state; and In response to a transition to a subsequent image, it is determined whether the subsequent state of the first pixel is a black state and whether the major neighbors of the first pixel in a second threshold number have a next state as a black state; and if an empty state transition of the first pixel is detected when transitioning from the first image to the second image and the major neighbors of the first pixel in a threshold number transition from a black state to a white state, and the subsequent state of the first pixel is a black state and the major neighbors of the first pixel in a second threshold number have a next state as a black state, then a voltage signal is applied to the first pixel, wherein the voltage signal has a waveform configured to generate an optical black state for the first pixel. 6. The display according to claim 5, wherein the threshold number of the primary neighbors is 1. 7. The display of claim 5, wherein the threshold number of the primary neighbors is greater than 1.