HK40081977B - Electro-optic displays, and methods for driving same - Google Patents

Description

Electro-optic displays and methods for driving electro-optic displays

Citation of relevant applications

This application relates to and claims priority to U.S. Provisional Application 63/032,721, filed May 31, 2020.

The full disclosure of the above application is incorporated herein by reference.

Technical Field

This invention relates to a method for driving an electro-optic display. More specifically, this invention relates to a driving method for reducing pixel edge artifacts and/or image persistence in an electro-optic display.

Background Technology

Electro-optic displays typically have a backplane with multiple pixel electrodes, each defining a pixel of the display; conventionally, a single common electrode extends across a large number of pixels, and the entire display is typically positioned on opposite sides of the electro-optic medium. Individual pixel electrodes can be driven directly (i.e., individual conductors can be provided to each pixel electrode), or they can be driven in an active matrix manner familiar to those skilled in the art of backplane technology. Since adjacent pixel electrodes will typically be at different voltages, they must be separated by inter-pixel gaps of finite width to avoid electrical short circuits between the electrodes. While at first glance it might appear that the electro-optic medium covering these gaps will not switch when a driving voltage is applied to the pixel electrodes (and indeed, this is often the case for some non-bistable electro-optic media (e.g., liquid crystals), where a black mask is typically provided to hide these non-switching gaps), in the case of many bistable electro-optic media, the medium covering the gaps does switch due to a phenomenon known as "blooming."

Diffusion refers to the tendency of the optical state of an electro-optic medium to change over an area larger than the physical size of the pixel electrode when a driving voltage is applied to the pixel electrode. While excessive diffusion should be avoided (e.g., in high-resolution active matrix displays, it is undesirable to apply a driving voltage to a single pixel causing switching over an area covering several adjacent pixels, as this would reduce the effective resolution of the display), controlled amounts of diffusion are often useful. For example, consider an electro-optic display with black text on a white background, which displays numerical values using a conventional seven-segment array of seven directly driven pixel electrodes for each digit. For example, when displaying 0, six segments are black. Without diffusion, the gaps between the six pixels would be visible. However, by providing controlled amounts of diffusion, such as as described in U.S. Patent No. 7,602,374, which is incorporated herein by reference, the gaps between pixels can be made black, making the digits more aesthetically pleasing. However, diffusion can lead to a problem known as "edge ghosting."

The diffused region is not uniformly white or black, but typically a transitional region where the medium's color changes from white through various shades of gray to black as one moves across the diffused region. Therefore, edge ghosting will typically be an area of varying gray levels rather than a uniform gray area, yet still visible and objectionable, especially since the human eye has a good ability to detect gray areas in a monochrome image (where each pixel is assumed to be pure black or pure white). In some cases, asymmetric diffusion can lead to edge ghosting. "Asymmetric diffusion" refers to the phenomenon in certain electro-optic media (e.g., the electrophoretic medium encapsulated in copper chromite/titanium dioxide as described in U.S. Patent No. 7,002,728, which is incorporated herein by reference in its entirety) that diffusion is "asymmetric," meaning that more diffusion occurs during the transition from one extreme optical state of a pixel to the other than during the transition in the opposite direction; in the media described in this patent, generally, diffusion is greater during the black-to-white transition than diffusion occurs during the white-to-black transition.

Therefore, a similar driving method is needed to reduce ghosting or diffusion effects.

Summary of the Invention

Therefore, on the one hand, the subject matter disclosed herein provides a method for driving an electro-optic display having multiple display pixels, the method may include detecting a white-to-white grayscale transition on a first pixel, and determining whether a threshold number of primary neighbors of the first pixel have not undergone a white-to-white grayscale transition, or whether the first pixel is a color pixel, and applying a first waveform.

In some embodiments, the driving method may further include determining whether the next grayscale of all four major neighbors of the first pixel is white and whether the current grayscale of at least one major neighbor of the first pixel is not white, and applying a second waveform.

In another embodiment, the driving method may also include determining whether the next grayscale of all four major neighbors of the first pixel is white and whether at least one major neighbor of the first pixel has a white-to-white grayscale transition and is a colored pixel, and applying a second waveform.

In another embodiment, the driving method may include determining whether the next grayscale of all four major neighbors of the first pixel is white and whether at least one major neighbor of the first pixel has a non-white current grayscale and an empty previous pixel transition, and applying a second waveform.

In another embodiment, the driving method may include determining whether the next grayscale of all four major neighbors of the first pixel is white and whether at least one major neighbor of the first pixel has a white-to-white grayscale transition and is a colored pixel, and applying a second waveform.

In some embodiments, the first waveform may include a first component configured to drive the first pixel to an optical black state.

In some other embodiments, the first waveform may include a second component configured to drive the first pixel to an optical white state.

In some embodiments, the second waveform may include a top cutoff pulse.

In some other embodiments, the second waveform may include a rotating pulse.

On the other hand, the subject matter presented herein provides an alternative method for driving an electro-optic display, which may include mapping the colors of a source image to a color-mapped image for the electro-optic display, identifying color pixels from the color-mapped image and marking the color pixels with indicators, and using the identification data of the color pixels as input to a waveform generation algorithm.

In some embodiments, the driving method may further include performing color filter array mapping on a color-mapped image.

In another embodiment, the driving method may further include generating a waveform from a waveform generation algorithm for the next state image.

In yet another embodiment, the driving method may also include using the generated waveform as the current state image of the next state image.

Attached Figure Description

Figure 1 is a circuit diagram showing the electrophoresis display;

Figure 2 shows the circuit model of the electro-optic imaging layer;

Figure 3 shows a cross-sectional view of an electro-optic display with a color filter array;

Figure 4A illustrates an exemplary clearing waveform according to the subject matter disclosed herein;

Figure 4B shows an exemplary T WW transition waveform according to the subject matter disclosed herein;

Figure 5 is a flowchart illustrating the first algorithm for driving the display;

Figure 6 is a flowchart illustrating the second algorithm for driving the display; and

Figure 7 illustrates the process of rendering an image on a monitor.

Detailed Implementation

This invention relates to methods for driving electro-optic displays (particularly bistable electro-optic displays), and to apparatus for such methods. More specifically, this invention relates to driving methods that can allow for reduction of ghosting and edge effects, as well as reduction of flickering, in such displays. The invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays, in which one or more types of charged particles are present in a fluid and move through the fluid under the influence of an electric field to alter the appearance of the display.

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

The term "gray state" is used here in its conventional meaning in the imaging field, referring to a state between the two extreme optical states of a pixel, but not necessarily a black-and-white transition between those two extremes. For example, several patents and publications of IENK, discussed below, describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate "gray state" actually a pale blue. In fact, as already mentioned, a change in optical state may not be a color change at all. The terms "black" and "white" may be used below to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochrome" may be used below to refer to a driving scheme that only drives pixels to their two extreme optical states, without an intermediate gray state.

In the sense that a material has a solid outer surface, some electro-optic materials are solid, although the material may and often does indeed have internal spaces filled with liquid or gas. For convenience, such displays using solid electro-optic materials may be referred to as "solid-state electro-optic displays" below. Therefore, the term "solid-state electro-optic display" includes rotating dual-color component displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

The terms “bistable” and “bistable” are used herein in their conventional meaning in the art, referring to a display comprising display elements having first and second display states, at least one optical characteristic of which differs such that, after any given element is driven to present its first or second display state using an addressing pulse of finite duration, the state will persist for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse terminates. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays supporting grayscale are stable not only in their extreme black and white states but also in intermediate gray states, as are some other types of electro-optical displays. This type of display is aptly referred to as “multistable” rather than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

The term "impulse" is used here in its conventional sense, referring to the integral of voltage with respect to time. However, some bistable electro-optic dielectrics are used as charge converters, and for such dielectrics, an alternative definition of impulse can be used: the integral of current with respect to time (which equals the total applied charge). The appropriate definition of impulse should be used depending on whether the dielectric is used as a voltage-time impulse converter or a charge-impulse converter.

Much of the following discussion focuses on methods for driving one or more pixels of an electro-optic display via a transition from an initial grayscale to a final grayscale (which may be different from or the same as the initial grayscale). The term "waveform" will be used to describe a curve of the entire voltage over time used to achieve the transition from a particular initial grayscale to a particular final grayscale. Typically, such a waveform will include multiple waveform elements; where these elements are substantially rectangular (i.e., a given element includes the application of a constant voltage over a time period); the 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 grayscales of a particular display. A display may utilize more than one drive scheme; for example, as taught in the aforementioned U.S. Patent No. 7,012,600, the drive scheme may need to be modified according to parameters such as the temperature of the display or the time it has been operating during its lifetime, and thus the display can provide multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this way may be referred to as a "set of related drive schemes." As described in several of the aforementioned MEDEOD applications, more than one driving scheme can be used simultaneously in different areas of the same display, and a group of driving schemes used in this manner can be referred to as a "group of simultaneous driving schemes".

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

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

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

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

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

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

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

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

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

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

(e) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

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

(g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564.

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

(i) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015/0277160; and applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent Application Publication Nos. 2015/0005720 and 2016/0012710; and

(j) A method for driving a display; see, for example, U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7, 242,514； 7,259,744； 7,304,787； 7,312,794； 7,327,511； 7,408,699； 7,453,445； 7,492,339； 7,528,822； 7,545,358； 7,583,251； 7,602,374； 7,612,760； 7,679,599； 7,679,813； 7,683,606； 7,688,297； 7,729,039； 7,733,311； 7,733,335； 7,787,169； 7,859,7 42; 7,952,557; 7,956,841; 7,982,479; 7,999,787; 8,077,141; 8,125,501; 8,139,050; 8,174,490; 8,243,013; 8,274,472; 8,289,250; 8,300,006; 8,305,341; 8,314,784; 8,373,649; 8,384,658; 8,456,414; 8,462,102; 8,537,105; 8,558,783; 8,558,785; 8 ,558,786； 8,558,855； 8,576,164； 8,576,259； 8,593,396； 8,605,032； 8,643,595； 8,665,206； 8,681,191； 8,730,153； 8,810,525； 8,928,562； 8,928,641； 8,976,444； 9,013,394； 9,019,197； 9,019,198； 9,019,318； 9,082,352；9,171,508； 9,218,773； 9,224,3 38; 9,224,342; 9,224,344; 9,230,492; 9,251,736; 9,262,973; 9,269,311; 9,299,294; 9,373,289; 9,390,066; 9,390,661; and 9,412,314; and U.S. Patent Application Publication Nos. 2003/0102858; 2004/0246562; 2005/0253777; 2007/0070032; 2007/0076289; 2007/0091418; 2007/0103427; 2007/ 0176912; 2007/0296452; 2008/0024429; 2008/0024482; 2008/0136774; 2008/0169821; 2008/0218471; 2008/0291129; 2008/0303780; 2009/0174651; 2009/0195568; 2009/0322721; 2010/0194733; 2010/0194789; 2010/0220121; 2010/0265561; 2010/0283804; 2011/00633 14; 2011/0175875; 2011/0193840; 2011/0193841; 2011/0199671; 2011/0221740; 2012/0001957; 2012/0098740; 2013/0063333; 2013/0194250; 2013/0249782; 2013/0321278; 2014/0009817; 2014/0085355; 2014/0204012; 2014/0218277; 2014/0240210; 2014/02403 73; 2014/0253425; 2014/0292830; 2014/0293398; 2014/0333685; 2014/0340734; 2015/0070744; 2015/0097877; 2015/0109283; 2015/0213749; 2015/0213765; 2015/0221257; 2015/0262255; 2016/0071465; 2016/0078820; 2016/0093253; 2016/0140910; and 2016/0180777.

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 polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even without a discrete capsule film associated with each individual droplet; see, for example, 2002/0131147 above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

One related type of electrophoretic display is the so-called "micro-unit electrophoretic display." In a micro-unit electrophoretic display, charged particles and suspended fluid are not encapsulated within microcapsules, but rather held within multiple cavities formed within a carrier medium (e.g., a polymer film). See, for example, International Application Publication No. WO 02/01281 and U.S. Application Publication No. 2002/0075556, both assigned to Sipix Imaging, Inc.

Many of the aforementioned Einkel and MIT patents and applications also consider microcell electrophoretic displays and polymer dispersion electrophoretic displays. The term "encapsulated electrophoretic display" can refer to all such display types, and can also be collectively referred to as "microcavity electrophoretic display" to encompass the morphology of the entire wall.

Another type of electro-optic display is the electrowetting display developed by Philips, described in Hayes, R. A. et al., “Video-Speed Electronic Paper Based on Electrowetting,” Nature, 425, 383-385 (2003). As shown in co-pending application sequence No. 10/711,802, filed October 6, 2004, this electrowetting display can be fabricated to be bistable.

Other types of electro-optic materials can also be used. Of particular interest are bistable ferroelectric liquid crystal displays (FLCs), which are known in the art and exhibit residual voltage behavior.

While electrophoretic media can be opaque (because, for example, in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in reflective mode, some electrophoretic displays can be made to operate in so-called "shutter mode," in which one display state is substantially opaque and the other is transmissive. See, for example, U.S. Patent Nos. 6,130,774 and 6,172,798 and U.S. Patent Nos. 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays can also operate in shutter mode.

High-resolution displays can include addressable, individual pixels that are independent of interference from adjacent pixels. One way to obtain such pixels is to provide an array of nonlinear elements (such as transistors or diodes), with at least one nonlinear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode used to address a pixel is connected to an appropriate voltage source via the associated nonlinear element. When the nonlinear element is a transistor, the pixel electrode can be connected to the drain of the transistor, and this arrangement will be used in the description below, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. In a high-resolution array, pixels can be arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. The sources of all transistors in each column can be connected to a single column electrode, while the gates of all transistors in each row can be connected to a single row electrode; furthermore, the source-to-row and gate-to-column arrangements can be reversed as needed.

The display can be written line by line. Row electrodes are connected to a row driver that applies voltage to selected row electrodes, for example, to ensure that all transistors in the selected row are turned on, while applying voltage to all other rows, for example, to ensure that all transistors in the unselected rows remain off. Column electrodes are connected to a column driver that applies voltage to various column electrodes, the voltage being selected to drive the pixels in the selected rows to their desired optical state. (The aforementioned voltage is relative to a common front electrode, which may be positioned on the opposite side of the electro-optic medium from the nonlinear array and extend across the entire display. As is known in the art, voltage is relative and is a measurement of the charge difference between two points. One voltage value is relative to another voltage value. For example, zero voltage (“0V”) means there is no voltage difference relative to another voltage.) After a pre-selection interval called the “row 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.

However, in use, certain waveforms may generate residual voltages on the pixels of the electro-optic display, and as is evident from the discussion above, these residual voltages produce several unwanted optical effects, which are generally undesirable.

As described herein, a “shift” in an optical state associated with an addressing pulse refers to a situation where a particular addressing pulse is first applied to an electro-optic display resulting in a first optical state (e.g., a first grayscale), and the same addressing pulse is subsequently applied to the electro-optic display resulting in a second optical state (e.g., a second grayscale). Since the voltage applied to a pixel of the electro-optic display during the application of the addressing pulse comprises the sum of the residual voltage and the addressing pulse voltage, the residual voltage may cause a shift in the optical state.

The "drift" of the optical state of a display over time refers to the change in the optical state of an electro-optic display when the display is at rest (e.g., during a period when no addressing pulse is applied to the display). Since the optical state of a pixel may depend on the pixel's residual voltage, and the residual voltage of a pixel may decay over time, residual voltage can cause the optical state to drift.

As mentioned above, "ghosting" refers to the situation where traces of a previous image remain visible after an electro-optic display has been rewritten. Residual voltage can cause "edge ghosting," a type of ghosting in which the outline (edge) of a portion of the previous image remains visible.

Exemplary EPD

Figure 1 illustrates a schematic diagram of a pixel 100 of an electro-optic display according to the subject matter presented herein. Pixel 100 may include an imaging film 110. In some embodiments, the imaging film 110 may be bistable. In some embodiments, the imaging film 110 may include, but is not limited to, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles.

An imaging film 110 may be disposed between the front electrode 102 and the rear electrode 104. The front electrode 102 may be formed between the imaging film and the front of the display. In some embodiments, the front electrode 102 may be transparent. In some embodiments, the front electrode 102 may be formed of any suitable transparent material, including but not limited to indium tin oxide (ITO). The rear electrode 104 may be formed opposite to the front electrode 102. In some embodiments, a parasitic capacitance (not shown) may be formed between the front electrode 102 and the rear electrode 104.

Pixel 100 may be one of a plurality of pixels. These pixels may be arranged in a two-dimensional array of rows and columns to form a matrix, such that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. In some embodiments, the matrix of pixels may be an “active matrix” in which each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 may be coupled between a back electrode 104 and an addressing electrode 108. In some embodiments, the nonlinear circuit element 120 may include diodes and/or transistors, including but not limited to metal-oxide-semiconductor field-effect transistors (MOSFETs). The drain (or source) of the MOSFET may be coupled to the back electrode 104, the source (or drain) of the MOSFET may be coupled to the addressing electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106 configured to control the activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET coupled to the rear electrode 104 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET coupled to the address electrode 108 will be referred to as the source of the MOSFET. However, those skilled in the art will recognize that in some embodiments, the source and drain of the MOSFET may be interchanged.)

In some embodiments of the active matrix, the addressing electrodes 108 of all pixels in each column may be connected to the same column electrode, and the driver electrodes 106 of all pixels in each row may be connected to the same row electrode. The row electrodes may be connected to a row driver that can select one or more rows of pixels by applying a voltage sufficient to activate the nonlinear circuit elements 120 of all pixels 100 in the selected row. The column electrodes may be connected to a column driver that can apply a voltage suitable for driving the pixel to a desired optical state on the addressing electrodes 108 of the selected (activated) pixel. The voltage applied to the addressing electrodes 108 may be relative to the voltage applied to the front electrode 102 of the pixel (e.g., approximately zero volts). In some embodiments, the front electrodes 102 of all pixels in the active matrix may be coupled to a common electrode.

In some embodiments, the pixels 100 of the active matrix can be written row by row. For example, a row driver can select a row of pixels, and a column driver can apply a voltage to the pixel corresponding to the desired optical state of the pixel row. After a pre-selection interval known as "row address time," the selected row can be deselected, another row can be selected, and the voltage on the column driver can be changed so that another row of the display is written.

Figure 2 shows a circuit model of an electro-optic imaging film 110 according to the subject matter presented herein, the electro-optic imaging layer 100 being disposed between a front electrode 102 and a rear electrode 104. Resistors 202 and capacitors 204 may represent the resistance and capacitance of the electro-optic imaging film 110, the front electrode 102, and the rear electrode 104, including any adhesive layer. Resistors 212 and capacitors 214 may represent the resistance and capacitance of the laminated adhesive layer. Capacitor 216 may represent the capacitance that may be formed between the front electrode 102 and the rear electrode 104, for example, at the interface contact region between layers, such as the interface between the imaging layer and the laminated adhesive layer and/or the interface between the laminated adhesive layer and the backplane electrode. The voltage Vi of the imaging film 110 across a pixel may include the residual voltage of the pixel.

In use, it is desirable for electro-optic displays, as shown in Figures 1 and 2, to update subsequent images without flickering on the display's background. However, a direct approach using null transitions in image updates targeting background-to-background (e.g., white-to-white or black-to-black) waveforms can lead to the creation of edge artifacts, such as diffusion. In black and white electro-optic displays, edge artifacts can be simplified top-off waveforms as shown in Figures 4A and 4B. However, maintaining color quality and contrast can sometimes be challenging in electro-optic displays, such as electrophoretic displays (EPDs), which use colors generated using a color filter array (CFA).

Figure 3 shows a cross-sectional view of a CFA-based color EPD according to the subject matter disclosed herein. As shown in Figure 3, the color electrophoretic display (generally labeled 300) includes a backplate 302 carrying a plurality of pixel electrodes 304. An inverted front-plane laminate may be laminated to the backplate 302, which may include a monochromatic electrophoretic dielectric layer 306 having black and white extreme optical states, an adhesive layer 308, a color filter array 310 having red, green, and blue regions aligned with the pixel electrodes 304, a substantially transparent conductive layer 312 (generally formed of indium tin oxide), and a front protective layer 314.

In practice, in CFA-based color EPD, any colored region in the image will cause modulation of the pixels following each CFA element. For example, optimal red can be obtained when the red CFA pixel is turned on (e.g., becomes white) and the green and blue CFA pixels are turned off (e.g., become black). Any diffusion into white pixels can lead to a reduction in the chroma and brightness of red. Some algorithms are explained in more detail below, in which the aforementioned edge artifacts (e.g., diffusion) can be identified and reduced without sacrificing color saturation.

EPD driving solution

In some applications, displays may use a “Direct Update” driving scheme (“DUDS”). DUDS may have two or more gray levels, typically fewer than a gray-scale driving scheme (“GSDS”). GSDS can handle transitions between all possible gray levels, but the most important feature of DUDS is that its transitions are handled by a simple unidirectional drive from the initial gray level to the final gray level. This differs from the “indirect” transitions commonly used in GSDS, where, at least in some transitions, a pixel is driven from the initial gray level to an extreme optical state and then in the opposite direction to the final gray level. In some cases, the transition can be achieved by driving from the initial gray level to an extreme optical state, then to the opposite extreme optical state, and then to the final extreme optical state—for example, see the driving scheme shown 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 can be about two to three times the saturation pulse length (where the "saturation pulse length" is defined as the time period sufficient to drive the pixels of the display from one extreme optical state to another at a specific voltage), or about 700-900 milliseconds, while the maximum update time of DUDS is equal to the saturation pulse length, or about 200-300 milliseconds.

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

Secondly, a phenomenon known as "diffuse" occurs when an undriven pixel is adjacent to an updating pixel. The driving of the driven pixel causes a change in the optical state over an area slightly larger than the driven pixel, and this area encroaches into the area of the adjacent pixel. This diffuse itself manifests as an edge effect along the edge of an undriven pixel adjacent to the driven pixel. A similar edge effect occurs when using region updates (where only specific areas of the display are updated, such as the area used to display an image), except that the edge effect of region updates occurs at the boundaries of the updated area. Over time, such edge effects become visually distracting and must be eliminated. To date, such edge effects (and the effect of color drift in undriven white pixels) have typically been removed by using a single GC update at regular intervals. Unfortunately, using such random GC updates reintroduces the problem of "flickering" updates, and in fact, the flickering of the update can be amplified by the fact that flickering updates occur only at long intervals.

Edge artifact reduction

In practice, several driving methods or algorithms can be used to reduce optical edge artifacts in pixels. For example, pixels undergoing a white-to-white transition and their primary neighboring pixels undergoing a non-empty transition can be identified first, and based on the number of such primary pixels undergoing this transition, a full clearing waveform, as shown in Figure 4A, can be applied to the pixels undergoing the white-to-white transition. Determining the exact number of neighboring primary pixels before applying the full clearing waveform can be designed to achieve optimal display quality for a specific application. As shown in Figure 4A, the full clearing or "F" waveform can include two complete long pulses designed to drive the display pixel to black and/or white. For example, a first portion 402 configured to drive the display pixel to black for 18 frames with an amplitude of 15 volts, followed by a second portion 404 configured to drive the display pixel to white for 18 frames with an amplitude of 15 volts.

The following are some driving methods and/or algorithms that can be adopted to reduce pixel edge artifacts.

Method 1

For all pixels in any order:

If the pixel grayscale transition is not white→white (W→W), then the standard GL transition is applied;

otherwise,

If at least the major neighbor of the SFT has not undergone a grayscale transformation from white to white or is a color image pixel (isColorImagePixel), then apply the F W→W transformation;

otherwise,

If the next grayscale of all four primary neighbors is white, and (at least one primary neighbor's current grayscale is not white or at least one primary neighbor is a (W→W grayscale transition and is a color image pixel)), then apply the T W→W transition.

Otherwise, use the empty (GL)W→W transformation.

Finish

In this driving method, a marker or indicator (e.g., "is a color image pixel") is used to identify the display pixels (i.e., color display pixels) in the source image (or alternatively, in the color-mapped image) that are color pixels. In some embodiments, the color pixel may be a non-white pixel in the source image. In fact, when the EPD changes from a white input image to a pure red area input image, each pixel under the red CFA may require a white-to-white transition. Therefore, these pixels will be applied a full clear or F W→W transition waveform, such as the waveform shown in Figure 4A. In another embodiment, another indicator (e.g., SFT) can be used to determine whether a full clear or F W→W transition waveform is applied, depending on how many primary or adjacent pixels do not undergo a white-to-white transition. The exact threshold of SFT (e.g., SFT=3 or 2, etc.) can be varied and determined based on specific display conditions. All other pixels that do not undergo a white-to-white transition can be applied a globally restricted or GL-driven scheme or mode white transition (i.e., empty) waveform. Furthermore, a T W→W transition (i.e., rotated T) waveform can be applied to pixels that are marked or indicated as color pixels. For example, if the next grayscale of all four primary neighbors of a pixel is white, and the current grayscale of at least one primary neighbor is not white, or if at least one primary neighbor has a white-to-white grayscale transition and is a colored pixel under CFA, then a T white-to-white transition is applied. It should be understood that this driving method does not require knowledge of the current waveform state of the current image, but only the grayscale state of the current input image.

Figure 4B illustrates an exemplary T W→W transition waveform 406. This T W→W transition waveform 406 may include a variable number of rotating pulses 410 having variable positions within the waveform 406, and a variable number of top cutoff pulses 408 having variable positions relative to the rotating pulses 410 within the waveform 406. In some embodiments, a single top cutoff pulse 408 corresponds to a white frame driven at an amplitude of -15 volts, while the rotating pulses 410 may include a frame driven to black at 15 volts and a frame driven to white at -15 volts. The rotating pulses 410 themselves may be repeated multiple times, as shown in Figure 4B, while the top cutoff pulses 408 may precede, follow, and/or occur between the rotating pulses 410.

Referring now to Figure 5, in practice, for all pixels of the electro-optical display, if the grayscale transition of the display pixel is not W→W (i.e., white to white), as shown in step 502, then a waveform from the standard GL driving scheme or driving mode is applied, as shown in step 504; otherwise, in step 506, if at least SFT's major neighbors of this display pixel have not undergone a white to white grayscale transition, or are marked by the "is a color image pixel" indicator (i.e., the particular display pixel is a color image in the source image (or alternatively in the color-mapped image)). If the next grayscale of all four primary neighbors of the displayed pixel is white, and the current grayscale of at least one primary neighbor is not white or at least one primary neighbor has a white-to-white grayscale transition and is marked as a “color image pixel” pixel (i.e., a color pixel), then the T W→W transition waveform (e.g., Figure 4B) is applied, see step 512; otherwise, in step 514, the empty GL W→W transition waveform is applied.

In some embodiments, a previous image state or a pixel state from a previous pixel transition can be added to the algorithm to determine which transition waveform to apply, as shown in the driving method or algorithm below and in Figure 6. This algorithm can be used to filter out pixels that have already undergone a non-empty transition in the previous image update, rather than applying a rotation waveform.

Method 2

For all pixels in any order:

If the pixel grayscale transition is not W→W, then apply the standard GL transition;

otherwise,

If at least the major neighbors of the SFT have not undergone a white-to-white grayscale transformation or are color image pixels, then apply the F W→W transformation;

otherwise,

If the next grayscale of all four primary neighbors is white, and (at least one primary neighbor's current grayscale is not white and the previous pixel transition is empty) or at least one primary neighbor is (W→W grayscale transition and is a color image pixel), then apply the T W→W transition.

Otherwise, use the empty (GL)W→W transformation.

Finish

The second method is similar to Method 1 above, but it takes into account the image grayscale state from the currently displayed image. For pixels that have already undergone a non-empty transition in the currently displayed image, the rotation waveform will not be applied to subsequent images. This method may result in lower power consumption for the EPD.

Referring now to Figure 6, in practice, for all pixels of the electro-optical display, if the grayscale transition of the display pixel is not W→W (i.e., white to white), as shown in step 602, then a waveform from the standard GL driving scheme or driving mode is applied, as shown in step 604; otherwise, in step 606, if at least SFT number of the primary neighbors of the display pixel have not undergone a white-to-white grayscale transition, or are marked by the "is a color image pixel" indicator (i.e., the particular display pixel is a color pixel in the source image (or alternatively in the color-mapped image), then an F W→W transition waveform (e.g., Figure 4A) is applied, see step 608; otherwise, in step 610, if the next grayscale of all four primary neighbors of the display pixel is white, and the current grayscale of at least one primary neighbor is not white and its previous pixel transitions to empty, or at least one primary neighbor has a white-to-white grayscale transition and is marked as "is a color image pixel," then a T W→W transition waveform (e.g., Figure 4B) is applied, see step 612; otherwise, an empty GL W→W transition waveform is applied in step 614.

In some embodiments, preferably, before rendering the image on the display, display pixels are identified as color pixels and marked with the indicator "is a color image pixel". Referring now to FIG7, prior to the quantization step 708, at the display controller capable of controlling the operation of the bistable electro-optic display, color pixels can be identified and marked with the indicator "is a color image pixel" 704. In operation, the image or source image 700 can first be processed by a color mapping algorithm 702 associated with the controller. The color mapping algorithm 702 can be configured to process the source image 700 into a color-mapped image 720 to suit the colors available for a particular display in order to obtain the best color visual effect on this particular display. Subsequently, color pixels in the color-mapped image 720 can be identified and marked as "is a color image pixel" 704 and input into algorithm 710. It should be understood that this identification and marking occurs prior to the CFA mapping step 706 and the image dithering and quantization steps 708. The image is then displayed using the waveform of algorithm 710, which can be assigned to the display pixels. Then, in the waveform step 712, the waveform of the display image 720 can be sent to EPD 716. In some embodiments, these waveforms 712 can be recycled to algorithm 710 as input (i.e., waveforms for the current state image 714) to generate waveforms for the next image state.

It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the foregoing description as a whole should be interpreted as exemplary rather than restrictive.

Claims (8)

1. A method for driving an electro-optic display having a plurality of display pixels, wherein the display is a color display having a color filter array for generating colors, the method comprising: Detect the white-to-white grayscale transition on the first pixel; and Determine the threshold number of primary neighbors of the first pixel in the four main directions that have not undergone a grayscale transition from white to white, or whether the first pixel is a color pixel, and apply the first waveform if the threshold number is met or if the first pixel is a color pixel; The first waveform includes a first component configured to drive the first pixel to an optical black state and a second component configured to drive the first pixel to an optical white state. 2. The method of claim 1, further comprising determining whether the next grayscale of all four major neighbors of the first pixel is white and whether the current grayscale of at least one major neighbor of the first pixel is not white, and, if so, applying a second waveform, wherein the second waveform includes a top cutoff pulse and/or a rotation pulse. 3. The method of claim 1, further comprising determining whether the next grayscale of all four major neighbors of the first pixel is white and whether at least one major neighbor of the first pixel has a white-to-white grayscale transition and is a color pixel, and, if so, applying a second waveform, wherein the second waveform includes a top cutoff pulse and/or a rotation pulse. 4. The method of claim 1, further comprising determining whether the next grayscale of all four major neighbors of the first pixel is white and whether at least one major neighbor of the first pixel has a non-white current grayscale and an empty previous pixel transition, and, if so, applying a second waveform, wherein the second waveform includes a top cutoff pulse and/or a rotation pulse. 5. An electro-optic display configured to perform the method of claim 1, comprising a rotating dual-color component, an electrochromic or electrowetting material. 6. The electro-optic display of claim 5, comprising an electrophoretic material containing a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. 7. The electro-optic display according to claim 6, wherein the charged particles and the fluid are confined within a plurality of capsules or microcells. 8. The electro-optic display of claim 6, wherein the charged particles and the fluid exist in the form of a plurality of discrete droplets, the discrete droplets being surrounded by a continuous phase comprising a polymer material.