CN111615724A - Electro-optic display and method for driving an electro-optic display - Google Patents

Abstract

Various methods for driving electro-optic displays to reduce visible artifacts are described. Such a method includes driving an electro-optic display having a plurality of display pixels and controlled by a display controller associated with a host for providing operating instructions to the display controller, the method may include updating the display with a first image, updating the display with a second image subsequent to the first image, processing image data associated with the first image and the second image to identify display pixels having edge artifacts and generate image data associated with the identified pixels, storing the image data associated with the pixels having edge artifacts at memory locations, and initiating a waveform to clear the edge artifacts.

Description

Electro-optic display and method for driving an electro-optic display

Technical Field

The present invention relates to a method for driving an electro-optic display. More particularly, the present invention relates to a driving method for reducing pixel edge artifacts (edge artifacts) and/or image retention in electro-optic displays.

Background

Electro-optic displays typically have a backplane provided with a plurality of pixel electrodes, each pixel electrode defining one pixel of the display; conventionally, a single common electrode extends over a large number of pixels, and typically the entire display is disposed on opposite sides of the electro-optic medium. The individual pixel electrodes may be driven directly (i.e. a separate conductor may be provided to each pixel electrode) or may be driven in an active matrix manner familiar to those skilled in the backplane art. Since adjacent pixel electrodes will typically be at different voltages, they must be separated by an inter-pixel gap of limited width to avoid electrical shorts between the electrodes. Although at first sight it may appear that the electro-optic medium overlying the gaps will not switch when a drive voltage is applied to the pixel electrodes (and indeed this is often the case for some non-bistable electro-optic media, such as liquid crystals, where a black mask is usually provided to hide the non-switching gaps), in the case of many bistable electro-optic media the medium overlying the gaps does switch due to a phenomenon known as "blooming".

Blooming refers to the tendency of application of a drive voltage to a pixel electrode to cause a change in the optical state of the electro-optic medium over an area larger than the physical dimensions of the pixel electrode. While excessive blooming should be avoided (e.g. in a high resolution active matrix display it is undesirable to apply a drive voltage to a single pixel to cause switching in an area covering several adjacent pixels, as this would reduce the effective resolution of the display), a controlled amount of blooming is often useful. Consider, for example, an electro-optic display in black and white which displays values for each digit using a conventional seven-segment array of seven directly driven pixel electrodes. For example, when 0 is displayed, six segments become black. In the absence of blooming, six inter-pixel gaps will be visible. However, by providing a controlled amount of diffusion, such as described in the aforementioned 2005/0062714, the interpixel gaps can be made black, making the numbers more aesthetically pleasing. However, diffusion causes a problem called "edge ghosting".

The diffuse areas are not uniformly white or black but are generally transition areas where the color of the media transitions from white to black through shades of various grays as one moves across the diffuse areas. Thus, edge ghosting will typically be varying gray shaded regions, rather than uniform gray regions, but still visible and objectionable, particularly because the human eye has a good ability to detect gray regions in a monochrome image (where each pixel assumes pure black or pure white).

In some cases, asymmetric diffusion may lead to edge ghosting. "asymmetric dispersion" refers to the phenomenon that dispersion in certain electro-optic media (such as the copper chromite/titania encapsulated electrophoretic media described in U.S. Pat. No.7,002,728) is "asymmetric" in that more dispersion occurs during the transition from one extreme optical state to the other extreme optical state of the pixel than during the transition in the opposite direction; in the media described in this patent, the dispersion is generally greater during the black-to-white transition than during the white-to-black transition.

As such, a driving method capable of reducing the ghost or dispersion effect is desired.

Disclosure of Invention

Accordingly, in one aspect, a method for driving an electro-optic display having a plurality of display pixels and controlled by a display controller associated with a host for providing operating instructions to the display controller may comprise: the method includes updating the display with a first image, updating the display with a second image subsequent to the first image, processing image data associated with the first and second images to identify display pixels having edge artifacts and generate image data associated with the identified pixels, storing the image data associated with the pixels having edge artifacts at memory locations, and initiating a waveform to clear the edge artifacts.

In another embodiment, the subject matter presented herein provides a method for driving an electro-optic display having a plurality of display pixels. The method includes updating the display with a first image, identifying display pixels having edge artifacts after the first image update, applying a waveform designed to remove the artifacts to the identified pixels, and updating another image to the display. In some embodiments, the method may further include determining a display pixel gray scale transition between the first image and the second image. In some other embodiments, the method may include determining a display pixel having a different gray scale than at least one of its primary neighboring pixels, and marking the identified pixel in a memory associated with a controller of the display.

Drawings

Fig. 1 shows a circuit diagram representing an electrophoretic display;

FIG. 2 shows a circuit model of an electro-optic imaging layer;

FIG. 3a illustrates an exemplary specific pulse-to-edge erase waveform for a pixel undergoing a white-to-white transition;

FIG. 3b shows an exemplary specific DC imbalance pulse for erasing a white edge for a pixel undergoing a white-to-white transition;

FIG. 3c illustrates an exemplary specific all-white to white drive waveform;

FIG. 4a illustrates an exemplary specific edge erase waveform for a pixel undergoing a black-to-black transition;

FIG. 4b illustrates an exemplary specific full black to black drive waveform;

FIG. 5a shows a screenshot of a display with a diffuse or ghost effect; and

FIG. 5b illustrates another screen shot of a display with reduction of the effects of blooming or ghosting applied in accordance with the subject matter presented herein; and

fig. 6 shows a sample Global Edge Cleaning (GEC) waveform.

Detailed Description

The present invention relates to a method for driving an electro-optic display, in particular a bi-stable electro-optic display, and to an apparatus for use in such a method. More particularly, the invention relates to a driving method that may allow to reduce "ghosting" and edge effects and to reduce flicker (flashing) in such displays. The invention is particularly, but not exclusively, intended for use with a particle-based electrophoretic display 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 change the appearance of the display.

As applied to materials or displays, the term "electro-optic" is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states differing in at least one optical property, the material being changed from its first display state to its second display state by application of an electric field to the material. Although the optical property is typically a color perceptible to the human eye, it may be another optical property, such as light transmission, reflection, luminescence, or, in the case of a display for machine reading, a false color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range.

The term "gray state" is used herein in its conventional sense in the imaging art to refer to a state intermediate two extreme optical states of a pixel, but does not necessarily imply a black-and-white transition between the two extreme states. For example, several patents and published applications by the incorporated of lngk referred to below describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is effectively pale 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 that are not strictly black and white, such as the white and deep blue states mentioned above. The term "monochromatic" may be used hereinafter to denote a driving scheme in which a pixel is driven only to its two extreme optical states, without an intermediate gray state.

Some electro-optic materials are solid in the sense that the material has a solid outer surface, although the material may, and often does, have a space filled with a liquid or gas inside. For convenience, such displays using solid electro-optic materials may be referred to hereinafter as "solid electro-optic displays". Thus, the term "solid state electro-optic display" includes rotating bichromal member displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to displays comprising display elements having first and second display states differing in at least one optical characteristic 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 will persist for at least several times (e.g. at least 4 times) the minimum duration of the addressing pulse required to change the state of that display element after the addressing pulse has terminated. It is shown in U.S. patent No.7,170,670 that some particle-based electrophoretic displays that support gray scale can be stabilized not only in their extreme black and white states, but also in their intermediate gray states, as well as some other types of electro-optic displays. This type of display is properly referred to as "multi-stable" rather than bi-stable, but for convenience the term "bi-stable" may be used herein to cover both bi-stable and multi-stable displays.

The term "impulse" is used herein in its conventional sense, i.e., the integral of a voltage with respect to time. However, some bistable electro-optic media act as charge converters, and for such media an alternative definition of impulse, i.e. the integral of the current with respect to time (which is equal to the total charge applied) may be used. Depending on whether the medium is used as a voltage-time impulse converter or as a charge impulse converter, a suitable impulse definition should be used.

Much of the discussion below focuses on methods for driving one or more pixels of an electro-optic display by transitioning from an initial gray level to a final gray level (which may be different from or the same as the initial gray level). The term "waveform" will be used to denote the entire voltage versus time curve used to effect a transition from one particular initial gray level to a particular final gray level. Typically, such a waveform will include a plurality of waveform elements; wherein the elements are substantially rectangular (i.e., a given element comprises applying a constant voltage over a period of time); the elements may be referred to as "pulses" or "drive pulses". The term "drive scheme" denotes a set of waveforms sufficient to achieve all possible transitions between gray levels for a particular display. The display may utilize 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 according to parameters such as the temperature of the display or the time it has been operating during its lifetime, and thus the display may be provided with a plurality of different drive schemes for use at different temperatures or the like. A set of drive schemes used in this manner may be referred to as a "set of correlated drive schemes". More than one drive scheme may also be used simultaneously in different regions 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", as described in several of the aforementioned MEDEOD applications.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type, as described in, for example, 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 commonly referred to as a "rotating bichromal ball" display, the term "rotating bichromal member" is preferably more accurate because in some of the patents mentioned above, the rotating member is not spherical). Such displays use a number of small bodies (usually spherical or cylindrical) comprising two or more parts with different optical properties and an internal dipole. These bodies are suspended in liquid-filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed by: an electric field is applied 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 generally bistable.

Another type of electro-optic display uses an electrochromic medium, such as in the form of a nano-electrochromic (nanochromic) film that includes an electrode formed at least in part from a semiconducting metal oxide and a plurality of dye molecules capable of reverse color change attached to the electrode; see, e.g., O' Regan, b. et al, Nature 1991,353,737; and Wood, d., Information Display,18(3),24 (3 months 2002). See also Bach, u. et al, adv.mater, 2002,14(11), 845. Nano-electrochromic films of this type are described, for example, in U.S. patent nos. 6,301,038; 6,870,657, respectively; and 6,950,220. This type of media is also generally bistable.

Another type of electro-optic display is the electro-wetting display developed by Philips, which is described in Hayes, R.A. et al, "Video-Speed Electronic Paper Based on electric wetting", Nature,425,383-385 (2003). Such electrowetting displays can be made bistable as shown in us patent No.7,420,549.

One type of electro-optic display that has been the subject of intensive research and development for many years is a particle-based electrophoretic display in which a plurality of charged particles move through a fluid under the influence of an electric field. Electrophoretic displays may have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. However, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in insufficient lifetime of 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 the electrophoretic medium can be produced using a gaseous fluid; see, e.g., 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 organic substrates charged semiconductor, IDW Japan,2001, Paper AMD 4-4). 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 the particles to settle, such as in signs where the media are arranged in a vertical plane, such gas-based electrophoretic media are susceptible to the same type of problems due to the same settling of particles as liquid-based electrophoretic media. In fact, the problem of particle settling in gas-based electrophoretic media is more severe than in liquid-based electrophoretic media, because the lower viscosity of gaseous suspending fluids allows faster settling of the electrophoretic particles compared to liquids.

A number of patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and yingke corporation describe various techniques for encapsulating electrophoretic and other electro-optic media. These encapsulated media comprise a plurality of microcapsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsule itself is held in a polymeric binder to form a coherent layer between the two electrodes. The techniques described in these patents and applications include:

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

(b) capsule, adhesive and packaging process; see, e.g., U.S. patent nos. 6,922,276 and 7,411,719;

(c) microcell structures, wall materials, and methods of forming microcells; see, e.g., U.S. patent nos. 7,072,095 and 9,279,906;

(d) a method for filling and sealing a microcell; see, e.g., U.S. patent nos. 7,144,942 and 7,715,088;

(e) films and sub-assemblies comprising electro-optic material; see, e.g., U.S. Pat. Nos. 6,982,178 and 7,839,564;

(f) backsheets, 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;

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

(h) An application for a display; see, e.g., U.S. patent nos. 7,312,784; 8,009,348, respectively;

(i) non-electrophoretic displays, as described in U.S. patent No.6,241,921 and U.S. patent application publication No. 2015/0277160; and the use of packaging and microcell technology in addition to displays; see, e.g., U.S. patent application publication nos. 2015/0005720 and 2016/0012710; and (j) a method for driving a display; see, e.g., U.S. Pat. Nos. 5,930,026; 6,445,489, respectively; 6,504,524; 6,512,354, respectively; 6,531,997, respectively; 6,753,999, respectively; 6,825,970, respectively; 6,900,851, respectively; 6,995,550, respectively; 7,012,600; 7,023,420, respectively; 7,034,783, respectively; 7,061,166, respectively; 7,061,662, respectively; 7,116,466, respectively; 7,119,772; 7,177,066, respectively; 7,193,625, respectively; 7,202,847, respectively; 7,242,514, respectively; 7,259,744; 7,304,787, respectively; 7,312,794, respectively; 7,327,511, respectively; 7,408,699, respectively; 7,453,445, respectively; 7,492,339, respectively; 7,528,822, respectively; 7,545,358, respectively; 7,583,251, respectively; 7,602,374, respectively; 7,612,760, respectively; 7,679,599, respectively; 7,679,813, respectively; 7,683,606, respectively; 7,688,297, respectively; 7,729,039, respectively; 7,733,311, respectively; 7,733,335, respectively; 7,787,169, respectively; 7,859,742, respectively; 7,952,557, respectively; 7,956,841, respectively; 7,982,479, respectively; 7,999,787, respectively; 8,077,141, respectively; 8,125,501, respectively; 8,139,050, respectively; 8,174,490, respectively; 8,243,013, respectively; 8,274,472, respectively; 8,289,250, respectively; 8,300,006, respectively; 8,305,341, respectively; 8,314,784, respectively; 8,373,649, respectively; 8,384,658, respectively; 8,456,414, respectively; 8,462,102, respectively; 8,537,105, respectively; 8,558,783, respectively; 8,558,785, respectively; 8,558,786, respectively; 8,558,855, respectively; 8,576,164, respectively; 8,576,259, respectively; 8,593,396, respectively; 8,605,032, respectively; 8,643,595, respectively; 8,665,206, respectively; 8,681,191, respectively; 8,730,153, respectively; 8,810,525, respectively; 8,928,562, respectively; 8,928,641, respectively; 8,976,444, respectively; 9,013,394, respectively; 9,019,197, respectively; 9,019,198, respectively; 9,019,318, respectively; 9,082,352, respectively; 9,171,508, respectively; 9,218,773, respectively; 9,224,338, respectively; 9,224,342, respectively; 9,224,344, respectively; 9,230,492, respectively; 9,251,736, respectively; 9,262,973, respectively; 9,269,311, respectively; 9,299,294, respectively; 9,373,289, respectively; 9,390,066, respectively; 9,390,661, respectively; and 9,412,314; and U.S. patent application publication No. 2003/0102858; 2004/0246562, respectively; 2005/0253777, respectively; 2007/0070032, respectively; 2007/0076289, respectively; 2007/0091418, respectively; 2007/0103427, respectively; 2007/0176912, respectively; 2007/0296452, respectively; 2008/0024429, respectively; 2008/0024482, respectively; 2008/0136774, respectively; 2008/0169821, respectively; 2008/0218471, respectively; 2008/0291129, respectively; 2008/0303780, respectively; 2009/0174651, respectively; 2009/0195568, respectively; 2009/0322721, respectively; 2010/0194733, respectively; 2010/0194789, respectively; 2010/0220121, respectively; 2010/0265561, respectively; 2010/0283804, respectively; 2011/0063314, respectively; 2011/0175875, respectively; 2011/0193840, respectively; 2011/0193841, respectively; 2011/0199671, respectively; 2011/0221740, respectively; 2012/0001957, respectively; 2012/0098740, respectively; 2013/0063333, respectively; 2013/0194250, respectively; 2013/0249782, respectively; 2013/0321278, respectively; 2014/0009817, respectively; 2014/0085355, respectively; 2014/0204012, respectively; 2014/0218277, respectively; 2014/0240210, respectively; 2014/0240373, respectively; 2014/0253425, respectively; 2014/0292830, respectively; 2014/0293398, respectively; 2014/0333685, respectively; 2014/0340734, respectively; 2015/0070744, respectively; 2015/0097877, respectively; 2015/0109283, respectively; 2015/0213749, respectively; 2015/0213765, respectively; 2015/0221257, respectively; 2015/0262255, respectively; 2016/0071465, respectively; 2016/0078820, respectively; 2016/0093253, respectively; 2016/0140910, respectively; 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 creating 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 polymer-dispersed electrophoretic display can be considered capsules or microcapsules, even if no discrete capsule film is associated with each individual droplet; see, for example, U.S. publication No. 2002/0131147. Accordingly, 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 microcell electrophoretic displays, the charged particles and suspending fluid are not encapsulated within microcapsules, but rather are held in a plurality of cavities formed within a carrier medium (e.g., a polymer film). See, for example, international application publication No. wo 02/01281 and published U.S. application No.2002/0075556, both assigned to Sipix Imaging, inc.

Many of the aforementioned yingk and MIT patents and applications also contemplate microcell electrophoretic displays and polymer dispersed electrophoretic displays. The term "encapsulated electrophoretic display" may refer to all such display types, which may also be collectively referred to as "microcavity electrophoretic displays" to generalize the morphology of the entire wall.

Another type of electro-optic display is the electro-wetting display developed by Philips, described in Hayes, R.A. et al, "Video-Speed Electronic Paper Based on electric wetting," Nature,425,383-385 (2003). As shown in co-pending application serial No.10/711,802 filed on 6.10.2004, such electrowetting displays can be made bistable.

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

Although electrophoretic media may be opaque (because, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, some electrophoretic displays may 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. Pat. Nos. 6,130,774 and 6,172,798 and U.S. Pat. Nos. 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. A dielectrophoretic display similar to an electrophoretic display but relying on a change in electric field strength may operate in a similar mode; see U.S. patent No.4,418,346. Other types of electro-optic displays can also operate in a shutter mode.

A high resolution display may include individual pixels that are addressable and not disturbed by adjacent pixels. One way of obtaining such pixels is to provide an array of non-linear elements (e.g. transistors or diodes) with at least one non-linear element associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode used to address a pixel is connected to a suitable voltage source via an associated non-linear element. When the non-linear element is a transistor, the pixel electrode may be connected to a drain of the transistor, and this arrangement will be adopted in the following description, although it is arbitrary in nature and the pixel electrode may be connected to a source of the transistor. In a high resolution array, pixels may 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 may be connected to a single column electrode and the gates of all transistors in each row may be connected to a single row electrode; again, the arrangement of source to row and gate to column may be reversed as desired.

The display can be written in a row-by-row fashion. The row electrodes are connected to a row driver which can apply a voltage to the selected row electrode, for example to ensure that all transistors in the selected row are conductive, while applying a voltage to all other rows, for example to ensure that all transistors in these non-selected rows remain non-conductive. The column electrodes are connected to a column driver which applies voltages to the various column electrodes which are selected to drive the pixels in the selected row to their desired optical states. (the foregoing voltages are relative to a common front electrode that may be disposed on the opposite side of the electro-optic medium from the non-linear array and extend across the entire display. As is known in the art, voltages are relative and are a measure of the difference in charge between two points.

However, in use, certain waveforms may produce residual voltages to the pixels of the electro-optic display, and as is apparent from the above discussion, such residual voltages produce several undesirable optical effects and are generally undesirable.

As described herein, a "shift" in an optical state associated with an addressing pulse refers to a situation in which a particular addressing pulse is first applied to an electro-optic display resulting in a first optical state (e.g., a first gray scale) and the same addressing pulse is subsequently applied to the electro-optic display resulting in a second optical state (e.g., a second gray scale). 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.

"drift" of the optical state of the display over time refers to the situation in which the optical state of the electro-optic display changes when the display is at rest (e.g., during a period of time in which an addressing pulse is not applied to the display). Since the optical state of a pixel may depend on the residual voltage of the pixel, and the residual voltage of the pixel may decay over time, the residual voltage may cause a drift of the optical state.

As mentioned above, "ghosting" refers to the situation where after rewriting an electro-optic display, traces of the previous image are still visible. The residual voltage may cause "edge ghosting", a type of ghosting in which the contours (edges) of a portion of the previous image remain visible.

Exemplary EPD

Fig. 1 shows 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, imaging film 110 may be bistable. In some embodiments, 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 back 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 back electrode 104.

The pixel 100 may be one of a plurality of pixels. The plurality of 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 non-linear circuit element 120. A non-linear circuit element 120 may be coupled between the backplane electrode 104 and the address electrode 108. In some embodiments, the non-linear element 120 may include a diode and/or a transistor, including but not limited to a Metal Oxide Semiconductor Field Effect Transistor (MOSFET). The drain (or source) of the MOSFET may be coupled to the backplane electrode 104, the source (or drain) of the MOSFET may be coupled to the address electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106, the driver electrode 106 being configured to control activation and deactivation of the MOSFET. (for simplicity, the terminal of the MOSFET coupled to the backplane 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.

In some embodiments of the active matrix, the address 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 which may select one or more rows of pixels by applying a voltage to the selected row electrodes, the voltage being sufficient to activate the non-linear elements 120 of all pixels 100 in the selected row. The column electrodes may be connected to a column driver which may apply voltages on the address electrodes 106 of selected (activated) pixels suitable for driving the pixels to a desired optical state. The voltage applied to the address electrode 108 can be relative to the voltage applied to the front plate electrode 102 of the pixel (e.g., a voltage of about zero volts). In some embodiments, the front plate 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 may be written in a row-by-row manner. For example, a row driver may select a row of pixels, and a column driver may apply voltages to the pixels corresponding to the desired optical states of the row of pixels. After a pre-selection interval called "row address time", the selected row may be deselected, another row may be selected, and the voltage on the column driver may be changed to cause another row of the display to be written.

Fig. 2 illustrates a circuit model of an electro-optic imaging layer 110, the electro-optic imaging layer 100 disposed between a front electrode 102 and a back electrode 104, according to the subject matter presented herein. Resistor 202 and capacitor 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, front electrode 102, and back electrode 104, including any adhesive layers. Resistor 212 and capacitor 214 may represent the resistance and capacitance of the laminating adhesive layer. The capacitor 216 may represent a capacitance that may be formed between the front electrode 102 and the back electrode 104, for example, an interfacial contact area between layers, such as an interface between an imaging layer and a lamination adhesive layer and/or an interface between a lamination adhesive layer and a backplane electrode. The voltage Vi across the imaging film 110 of a pixel may comprise the residual voltage of the pixel.

Detecting and reducing or removing edge artifacts and ghosting in electro-optic displays as described above, which would likely require additional image data processing, the detect and clear methods described in U.S. patent publication No.2013/0194250a1 to Amundson et al ("Amundson") and U.S. patent publication No.2016/0225322a1 to Sim et al ("Sim") are some of the image data processing methods that may be employed, all of which are incorporated herein in their entirety. However, such image data processing methods and the removal of edge artifacts and pixel ghosting may itself require processing time, which may not always be available. As such, in a fast Update waveform mode (rapid _ pulse _ Update _ waveform mode), such as the Direct Update waveform mode (Direct Update waveform mode) described below, it may be desirable to perform image data processing concurrently with the image data Update process. In addition, edge artifact and pixel ghosting clean-up can be triggered and performed only when needed.

Direct update or DUDS

In some applications, the display may utilize a fast update waveform mode, such as a "direct update" waveform mode (DUDS). The DUDS may have two or more grey levels, typically less than a Grey Scale Drive Scheme (GSDS) which can effect transitions between all possible grey levels, but the most important feature of the DUDS is that its transition is handled by a simple unidirectional drive from an initial grey level to a final grey level, unlike the "indirect" transition commonly used in GSDS in which, at least in some transitions, a pixel is driven from an initial grey level to one extreme optical state and then in the opposite direction to the final grey level; in some cases, the transition may be achieved by driving from an initial gray level to one extreme optical state, then to the opposite extreme optical state, and then to the final extreme optical state-see, for example, the driving schemes shown in fig. 11A and 11B of the aforementioned U.S. patent No.7,012,600. Thus, the update time of current electrophoretic displays in grayscale mode may be about two to three times the saturation pulse length (where "saturation pulse length" is defined as the period of time at a certain voltage sufficient to drive the pixels of the display from one extreme optical state to the other extreme optical state), or about 700-.

It should be appreciated that the Direct Update (DU) waveform patterns or drive schemes described above are used herein to explain the general principles of operation of the subject matter disclosed herein. This is not meant to limit the present subject matter. As these principles of operation can be readily applied to other waveform patterns or schemes.

The DU waveform mode is a driving scheme that generally considers the use of blank self-transition updates to white and black. The DU mode has a short update time to bring black and white quickly, presenting the appearance of a minimal "flicker" transition where the display will appear to be dim and may not be visually appealing to the eyes of some viewers. The DU mode is sometimes available to bring up menus, progress bars, keyboards, etc. on the display screen. Since both the white-to-white and black-to-black transitions are empty (i.e., not driven) in the DU mode, edge artifacts may occur in the black and white backgrounds.

As described above, when an undriven pixel is adjacent to a pixel being updated, a phenomenon known as "blooming" occurs in which the driving of a driven pixel causes a change in optical state over an area slightly larger than the driven pixel, and the area invades into the area of an adjacent pixel. This dispersion manifests itself as edge effects along the edges of the undriven pixels that abut the driven pixels. Similar edge effects occur when using region updates (where only certain regions of the display, e.g. the regions used to display an image, are updated), except that the edge effect of the region update occurs at the boundary of the updated region. Over time, such edge effects become visually distracting and must be removed. Heretofore, such edge effects (and the effects of color drift in undriven white pixels) have typically been removed by using a single Global clean-up (single Global cleaning) or GC update at intervals. Unfortunately, using such random GC updates may reintroduce the problem of "flickering" updates, and in fact, the flickering of the updates may be enhanced by the fact that the flickering updates occur only at long intervals.

Simultaneous image update and edge artifact data processing

In comparison, some display pixel edge artifact reduction methods may result in additional delay, as image processing is designed to detect and remove edge artifacts after each image update. In addition, using a DC imbalance waveform in these reduction methods would not be feasible because the small dwell time between updates (such as the DU mode described above) does not allow enough time to perform the post-drive discharge. And would pose a potential risk to overall optical performance and module reliability if not discharged after driving.

Alternatively, in some embodiments, image data processing such as described in Amundson and Sim may be performed simultaneously with the image update processing. For example, as the display 100 updates a first image, the image data of the first and subsequent second images may be processed to identify pixels that may develop edge artifacts or other undesirable optical defects. This data may then be saved in a buffer memory for later time to perform an edge artifact clean-up process. In some embodiments, data processing of subsequent images may occur as the images are fed to the EPDC. In some other embodiments, where it is known which images are to be updated to the display, data processing of the images may occur before subsequent images are updated.

One way to record or generate and preserve this edge artifact information as an electro-optic display undergoes optical changes is to generate a map (map), which may include information such as which pixels within the display will likely develop edge artifacts. One such method is described in U.S. patent application No. us2016/128,996 to Sim et al, which is hereby incorporated by reference in its entirety.

For example, in some embodiments, pixel edge artifacts generated under a drive scheme or waveform pattern may be stored in memory (e.g., a binary MAP), e.g., each display pixel may be represented by the indicator MAP (i, j), and pixels that may develop edge artifacts may be marked and their MAP information (i.e., MAP (i, j) indicators) saved in the binary MAP. One method that may be used to record edge artifacts generated on the map and mark such pixels is shown below:

MAP (i, j) is 0, j for all i, j

For all DU updates in order

For all pixels (i, j) in any order

MAP (i, j) is 1 if the pixel gray transition is white → white and the next gray of all four primary neighbors is white, and the current gray of at least one primary neighbor is not white, and all neighbors of MAP (i, j) are 0.

Otherwise, if the pixel gray transition is black → black and the current gray of at least one primary neighbor is not black and the next gray is black and all neighbors of MAP (i, j) are 0, MAP (i, j) ═ 2.

End up

End up

End up

In this approach, a display pixel denoted as MAP (i, j) may be labeled with a value of 1 when certain conditions are met, indicating that a dark-edge artifact has formed on that pixel. Some conditions that may be desired may include (1) the display pixel is undergoing a white-to-white transition; (2) the next gray level of all four major neighbors (i.e., the four nearest neighbors) is white; and (3) the current gray level of at least one primary neighbor is not white; and (4) none of the neighboring pixels (i.e., the four primary neighbors and the diagonal neighbors) are currently marked as edge artifacts.

Similarly, when certain conditions are met, display pixel MAP (i, j) may be labeled with a value of 2, indicating that a white edge has formed on the pixel. Some conditions that may be required may include (1) the pixel is undergoing a black-to-black transition; (2) the current gray level of at least one primary neighbor is not black and its next gray level is black; and (3) none of the neighboring pixels (i.e., the four primary neighbors and the diagonal neighbors) are currently marked as edge artifacts.

In use, one advantage of this approach is that the image processing described above (i.e. map generation and pixel labeling) can occur simultaneously with the display image update period, thus avoiding the additional delay to the update period due, at least in part, to the generated map being only needed when the update period is complete.

Once the update mode has been completed (e.g., the display ceases to use a particular update mode), the pixel information accumulated by the generated map may be used later to clear edge artifacts (e.g., using an output waveform mode). For example, pixels marked with edge artifacts may be cleared with a low flicker waveform having a specialized waveform.

In some embodiments, completely clearing white-to-white and black-to-black waveforms and specific edge clearing white-to-white and black-to-black waveforms may be used together to clear edge artifacts. Balanced pulse pairs such as those described in U.S. patent application No.2013/0194250, which is incorporated herein in its entirety, describe:

for all pixels (i, j) in any order

If the pixel grayscale transition is not white → white and not black → black, then the normal DU _ OUT transition is invoked

Otherwise, if MAP (i, j) is 1 and the pixel grayscale transition is white → white, then a particular full white to white waveform is applied

Otherwise, if the pixel gray transition is white → white and the MAP (i, j) of at least one primary neighbor is 1, then a specific edge erase white to white waveform is applied.

Otherwise, if MAP (i, j) ═ 2 and the pixel grayscale transition is black → black, then a particular full black-to-black waveform is applied.

Otherwise, if the pixel gray transition is black → black and the MAP (i, j) of at least one primary neighbor is 2, then a specific edge erase black-to-black waveform is applied.

Otherwise, call the black → black/white → white transition of the DU _ OUT waveform table

End up

End up

In this approach, a DU OUT transition scheme (e.g., a modified DU scheme including an edge artifact reduction algorithm) may be applied to pixels that are not undergoing a white-to-white or black-to-black transition, e.g., these pixels may receive a general transition update as if they were under a general DU drive scheme. Otherwise, for pixels that have dark edge artifacts (i.e., MAP (i, j) ═ 1) and are undergoing a white-to-white transition, a particular all-white-to-white waveform may be applied. In some embodiments, the white-to-white waveform may be a waveform similar to that shown in fig. 3c, which may be substantially DC balanced, meaning that the sum of the applied voltage biases as a function of amplitude and time is generally approximately zero; otherwise, if the pixel is undergoing a white-to-white transition and at least one primary neighbor has a dark-edge artifact (i.e., MAP (i, j) ═ 1), then a special edge-erasure white-to-white waveform is applied (e.g., fig. 3 a); again, if a pixel had a white edge artifact (i.e., MAP (i, j) ═ 2) and is undergoing a black-to-black transition, then a particular full black-to-black waveform as shown in fig. 4b may be applied; again, if a pixel is undergoing a black-to-black transition and at least one primary neighbor is marked as a white edge artifact (i.e., MAP (i, j) ═ 2), then a specific edge erase black-to-black waveform as shown in fig. 4a is applied; otherwise, the black-to-black or white-to-white transition waveforms are applied to all other pixels using the waveforms in the DU-OUT waveform table.

Using the above method, the full clean white to white and black to black waveforms are used with specific edge clean white to white and black to black waveforms to clean up edge artifacts. In some embodiments, the specific edge-clearing white-to-white waveform may take the form of a pulse pair as described in U.S. patent publication No.2013/0194250 to Amundson et al, which is incorporated herein in its entirety, or a DC unbalanced pulse drive to white as shown in fig. 3b, in which case the post-drive discharge may be used to relieve residual voltage and reduce device stress. Similarly, a DC-unbalanced pulse as shown in fig. 4a may be used to drive the pixel to black, in which case a post-drive discharge may also be performed. Such a DC imbalance pulse is driven to only positive 15 volts for a period of time, as shown in fig. 4. In this configuration, since a specific full clean waveform (special full clean waveform) is used, excellent edge clean performance can be achieved at the expense of small transition appearance defects (e.g., flicker).

In another embodiment, the following alternative embodiments may be used to reduce transitional appearance defects (e.g., flicker).

For all pixels (i, j) in any order

If the pixel grayscale transition is not white → white and not black → black, then the generic DU _ OUT transition is invoked

Otherwise, if MAP (i, j) is 1 and the pixel gray transition is white → white, then a DC unbalanced drive pulse is applied to white.

Otherwise, if MAP (i, j) ═ 2 and the pixel gradation transition is black → black, DC balance driving is applied to black.

Otherwise, call the black → black/white → white transition of the DU _ OUT waveform table

End up

End up

In this method, instead of using a special edge clearing waveform (specializeded clearing waveform) as described in the first method above, a DC imbalance waveform may be used to clear the edge artifact. In some cases, post-drive discharge may be used to reduce hardware stress due to unbalanced waveforms. In use, when a display pixel is not undergoing a white-to-white or black-to-black transition, a general DU-OUT transition is applied to the pixel. Otherwise, if the display pixel is identified as having a dark edge artifact (i.e. MAP (i, j) ═ 1) and is undergoing a white to white transition, then a DC unbalanced drive pulse is used to drive the pixel to white (e.g. a pulse similar to that shown in fig. 3 b); otherwise, if the display pixel is identified as having a white edge artifact (i.e. MAP (i, j) ═ 2) and is undergoing a black-to-black transition, a DC unbalanced drive pulse (e.g. a pulse similar to that shown in fig. 4 a) is applied to drive the pixel to black; otherwise, a black-to-black or white-to-white transition of the DU-OUT waveform table is invoked to the display pixel.

In yet another embodiment, instead of storing the edge artifact information to a specified memory location, the edge artifact information may be brought ahead of time into an image buffer associated with a controller unit (EPDC) of the display (e.g., using a next image buffer associated with the controller unit).

For all DU updates in order

For all pixels (i, j) in any order:

if the pixel gray transition is white → white, and the next gray of all four primary neighbors is white, and the current gray of at least one primary neighbor is not white, then the next gray is set to a particular white-to-white image state.

Otherwise, if the pixel gray transition is black → black, and the current gray of the at least one primary neighbor is not black and the next gray is black, then the next gray is set to the particular black-to-black image state.

End up

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End up

In the method, for a pixel undergoing a white-to-white transition and the next gray level of all four primary neighbors being white, if the current gray level of at least one primary neighbor is not white, then setting the next gray level of the pixel to a particular white-to-white image state in the next image buffer; otherwise, if the gray scale transition of the pixel is black to black, and the current gray scale of the at least one primary neighbor is not black and the next gray scale is black, then the next gray scale of the pixel is set to the particular black to black image state in the next image buffer. In use, during the update period, the particular white-to-white and particular black-to-black image states may be the same as the white-to-white and black-to-black image states for applying both the waveform transition and the image processing. For the application of a waveform transition, this means:

the specific white state → white state (i.e., white state to white state) is equivalent to the white state of the waveform lookup table → white state (i.e., white state to white state)

The specific white state → any gray state (i.e., white state to any gray state) is equivalent to the white state of the waveform lookup table → any gray state (i.e., white state to any gray state), and so on

The specific black state → black state (i.e., black state to black state) is equivalent to the black state of the waveform lookup table → black state (i.e., black state to black state)

The particular black state → any gray state (i.e., black state to any gray state) is equivalent to the black state of the waveform lookup table → any gray state (i.e., black state to any gray state), and so on.

During this output mode, the specific white state to white state receives a DC imbalance pulse to white (e.g., fig. 3b shows an exemplary such pulse), and the specific black state to black state receives a DC imbalance pulse to black (e.g., fig. 4a shows an exemplary such pulse). During the DU mode update, imaging algorithm processing occurs in the background, which means that DU update time is available to process the image.

Fig. 5a and 5b show displays with no and with an applied edge artifact reduction. In fact, without applying edge artifact reduction, the white edges on the black background are clearly visible, as shown in fig. 5 a. In contrast, fig. 5b shows that the white edge is cleared using one of the proposed methods presented herein.

In some embodiments, pixels having or potentially developing edge artifacts may be marked as described above and stored in a different memory location than the memory buffer used for image updates. For example in a memory physically separate from the buffer memory for image updates. In some cases, however, it may be desirable to reduce the amount of memory used. As such, in some embodiments, the memory used for image updates (e.g., the image update buffer memory) may also be used to store accumulated edge artifact information. For example, when an electro-optic display is undergoing an optical change (e.g., an image update), instead of generating a map with all pixels, individual pixels may be associated with indicators designed to indicate whether a particular pixel has edge artifacts. The indicator may be used to indicate whether a particular pixel is marked as an edge artifact. As the display undergoes more image updates (e.g., more optical changes), presumably more pixels may be marked as edge artifacts (e.g., marking or turning on edge artifact indicators associated with these pixels). At a later time, these pixels marked as edge artifacts may all be cleared or reset together by the reset waveform.

Edge artifact removal

The edge artifact data that has been processed can be used at a convenient time to clean up the edge artifact. The purge process may be triggered or initiated by various conditions.

In some embodiments, the purge request may be initiated by the host (e.g., processor), similar to other requests sent by the host to the EPDC, and may be sent simultaneously with other image update requests. For example, after an interactive session in which the display is updated using the DUDS waveform pattern, to clear edge artifacts accumulated due to the DUDS waveform pattern, the host may request the EPDC to set a specific time frame (time frame) for clearing the edge artifacts.

In some other embodiments, the clearing process may be initiated at the convenience of the display. For example, when the EPDC has been idle for a certain time, the EPDC may choose to initiate a clean-up process to clean up edge artifacts using the accumulated edge artifact data.

In yet another embodiment, the processed image data, including identifying data for pixels having edge artifacts, may be used by a drive scheme or update waveform pattern that includes waveforms for clearing edge artifacts. For example, in an application using pen input, where the DUDS waveform pattern is used for its fast response time, the subsequent waveform pattern used for antialiasing may include an edge artifact removal waveform, and the subsequent waveform pattern may utilize the processed image data with edge artifact information to remove edge artifacts.

In some embodiments, a Global Edge Cleaning (GEC) waveform pattern may be used to clean up Edge artifacts. FIG. 6 shows sample GEC waveforms, where such waveforms include top-off pulses configured to drive the display pixels to extreme optical states. Such a waveform may consist of a duration of 6 frames (frames) or 66ms at a temperature of 25 degrees celsius. The GEC may be shorter in duration compared to a waveform pattern with a built-in edge cleanup section. In this way, GEC can be conveniently employed in conjunction with various existing drive waveform modes to clear edges without introducing excessive delay. For example, when GEC is used with the DUDS waveform mode described above, since GEC takes only a short duration, the post-drive discharge may be performed immediately after GEC before updating the subsequent image on the display. In some embodiments, the EPDC may choose and choose which waveform to use depending on the amount of edge artifacts present. For example, if the amount of edge artifacts exceeds a threshold, the EPDC may select a global clear waveform (mode) to clear the entire display.

In another embodiment, the EPDC may initiate a clear waveform if the pixels with edge artifacts become too large. For example, the EPDC may have an algorithm configured to record the total number of pixels with edge artifacts and compare to the total number of pixels in the display. The comparison may be stored as a percentage value in a buffer memory. The stored value may be periodically compared to a predetermined threshold value and if the stored value exceeds the threshold value, the EPDC may select to initiate a global clear waveform mode, wherein the global clear waveform may reset each pixel within the display (e.g., drive each pixel to an extreme gray or color 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. The foregoing description, therefore, is to be considered in all respects as illustrative and not restrictive.

Claims (8)

1. A method for driving an electro-optic display having a plurality of display pixels and controlled by a display controller associated with a host for providing operating instructions to the display controller, the method comprising:

updating the display with a first image;

updating the display with a second image subsequent to the first image;

processing image data associated with the first and second images to identify display pixels having edge artifacts and generate image data associated with the identified pixels;

storing image data associated with pixels having edge artifacts at a memory location; and

a waveform is initiated to clear the edge artifact.

2. The method of claim 1, wherein generating image data associated with the identified pixel comprises marking the identified pixel with an indicator.

3. The method of claim 2, wherein the step of identifying display pixels having edge artifacts comprises determining display pixels having a different gray scale than at least one of their primary neighbors.

4. The method of claim 2, wherein the step of identifying display pixels having edge artifacts comprises marking the identified pixels in a buffer memory associated with a controller of the display.

5. The method of claim 1, wherein the step of initiating a series of waveforms comprises receiving a clear command from the host.

6. The method of claim 1, wherein the step of initiating a series of waveforms comprises the display controller initiating a clear waveform after being idle for a predetermined duration.

7. The method of claim 1, wherein the step of initiating a series of waveforms comprises applying a waveform pattern having a waveform for clearing edge artifacts.

8. The method of claim 1, wherein the step of initiating a series of waveforms comprises applying a DC imbalance waveform.

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