HK40081977A - Electro-optic displays, and methods for driving same - Google Patents

Description

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

Reference to related applications

This application is related to and claims priority from U.S. provisional application 63/032,721, filed on 31/5/2020.

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

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 these 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 typically provided to hide these 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 U.S. Pat. No.7,602,374, which is incorporated herein in its entirety, the inter-pixel gaps can be made black, making the numbers more aesthetically pleasing. However, diffusion causes a problem called "edge ghosting".

The dispersed regions are not uniformly white or black but are generally transition regions where the color of the medium transitions from white to black through various gray levels as one moves across the dispersed regions. Thus, edge ghosting will typically be areas of varying gray shade, rather than uniform gray areas, but still visible and objectionable, particularly because 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 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, which is incorporated herein in its entirety) 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, generally, the dispersion is greater during the black-to-white transition than during the white-to-black transition.

Thus, a driving method that also reduces the ghost or dispersion effects is needed.

Disclosure of Invention

Thus, in one aspect, the subject matter disclosed herein provides a method of driving an electro-optic display having a plurality of display pixels, which may include detecting a white-to-white gray scale transition on a first pixel, and determining whether a threshold number of primary neighbors of the first pixel have not made a gray scale transition from white to white, 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 gray levels of all four primary neighbors of the first pixel are all white and the current gray level of at least one primary neighbor of the first pixel is not white, and applying the second waveform.

In another embodiment, the driving method may also include determining whether the next gray levels of all four primary neighbors of the first pixel are all white and at least one primary neighbor of the first pixel has a white-to-white gray level transition and is a color pixel, and applying the second waveform.

In yet another embodiment, the driving method may include determining whether the next gray levels of all four primary neighbors of the first pixel are all white and at least one primary neighbor of the first pixel has a current gray level that is not white and an empty previous pixel transition, and applying the second waveform.

In another embodiment, the driving method may include determining whether the next gray levels of all four main neighbors of the first pixel are all white and at least one main neighbor of the first pixel has a white to white gray level transition and is a color pixel, and applying the 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-off pulse.

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

In another aspect, the subject matter presented herein provides another method of driving an electro-optic display that may include color mapping a source image into 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 the color mapped image.

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

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

Drawings

Fig. 1 is a circuit diagram showing an electrophoretic display;

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

FIG. 3 shows a cross-sectional view of an electro-optic display having a color filter array;

FIG. 4A illustrates an exemplary clear waveform according to the subject matter disclosed herein;

fig. 4B illustrates an exemplary T W → W transition waveform in accordance with the subject matter disclosed herein;

FIG. 5 is a flow chart showing a first algorithm for driving a display;

FIG. 6 is a flow chart showing a second algorithm for driving a display; and

FIG. 7 illustrates a process of rendering an image on a display.

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 meaning 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 either its first or second display state by an addressing pulse of finite duration, that state will, after the addressing pulse has terminated, last 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. 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 that follows focuses on methods for driving one or more pixels of an electro-optic display through a transition from an initial gray level to a final gray level (which may be different than 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. Pat. 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 sphere" 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. This type of nano-electrochromic film is described, for example, in U.S. Pat. nos. 6,301,038;6,870,657; 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 U.S. 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 insulating substrates charged triangular display", IDW Japan,2001, paper AMD4-4). See also U.S. Pat. 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 body, adhesive and packaging process; see, e.g., U.S. Pat. Nos. 6,922,276 and 7,411,719;

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

(d) A method for filling and sealing a microcell; see, e.g., U.S. Pat. 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. Pat. Nos. 7,116,318 and 7,535,624;

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

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

(i) Non-electrophoretic displays, as described in U.S. Pat. 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;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;7,859,742;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;9,224,338;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 No.2003/0102858;2004/0246562;2005/0253777;2007/0070032;2007/0076289;2007/0091418;2007/0103427;2007/0176912;2007/0296452;2008/0024429;2008/0024482;2008/0136774; 2008/0169818; 2008/0218471;2008/0291129;2008/0303780;2009/0174651;2009/0195568;2009/0322721;2010/0194733;2010/0194789;2010/0220121;2010/0265561;2010/0283804;2011/0063314;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;2014/0240373;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 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, e.g., 2002/0131147, supra. Accordingly, for 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). Such electrowetting displays can be made bistable as shown in co-pending application serial No.10/711,802 filed on 6.10.2004.

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. Pat. 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, the 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 one particular row and one 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 the optical state associated with an addressing pulse refers to the situation where a particular addressing pulse is first applied to the electro-optic display resulting in a first optical state (e.g. a first grey scale) and the same addressing pulse is subsequently applied to the electro-optic display resulting in a second optical state (e.g. a second grey scale). Since the voltage applied to a pixel of the electro-optic display during 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 one particular row and one 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 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 an 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 according to the subject matter presented herein, the electro-optic imaging layer 100 being disposed between a front electrode 102 and a back electrode 104. Resistor 202 and capacitor 204 may represent the resistance and capacitance of 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 lamination adhesive layers. The capacitor 216 may represent a capacitance that may be formed between the front electrode 102 and the back electrode 104, e.g., 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.

In use, it is desirable for an electro-optic display as shown in figures 1 and 2 to be updated to a subsequent image without flicker in the background of the display. However, the direct approach of using null transitions in image updates for background-color to background-color (e.g., white to white or black to black) waveforms may lead to the establishment of edge artifacts (e.g., blooming). In black and white electro-optic displays, the edge artifact may be a simplified top-off (top-off) waveform as shown in fig. 4A and 4B. However, in electro-optic displays, such as electrophoretic displays (EPDs), having colors generated using Color Filter Arrays (CFAs), maintaining color quality and contrast can sometimes be challenging.

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

In use, in CFA-based color EPD, any colored region in the image will result in modulation of the pixel behind each CFA element. For example, when a red CFA pixel is on (e.g., turned white) and green and blue CFA pixels are off (e.g., black), an optimal red color may be obtained. Any diffusion into a white pixel may result in a reduction in the chromaticity and brightness of the red. Some algorithms are explained in more detail below in which the above-described edge artifacts (e.g., blooming) can be identified and reduced without sacrificing color saturation.

EPD drive scheme

In some applications, the display may use a "direct update" drive scheme ("DUDS"). DUDS may have two or more gray levels, typically less than a gray scale drive scheme ("GSDS"), which can effect transitions between all possible gray levels, but the most important feature of DUDS is that its transitions are handled by a simple one-way drive from an initial gray level to a final gray level, as opposed to the "indirect" transitions commonly used in GSDS, in which, at least in some transitions, a pixel is driven from an initial gray level to one extreme optical state and then in the opposite direction to the final gray 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 FIGS. 11A and 11B of the aforementioned U.S. Pat. No.7,012,600. Thus, the update time of current electrophoretic displays in grayscale mode may be about two to three times, or about 700-900 milliseconds, of the saturation pulse length (where "saturation pulse length" is defined as the period of time sufficient to drive a pixel of the display from one extreme optical state to the other at a particular voltage), while the maximum update time of DUDS is equal to the saturation pulse length, or about 200-300 milliseconds.

However, the variation of the driving scheme is not limited to the number difference of the gray scales used. For example, the drive schemes may be divided into a global drive scheme in which a drive voltage is applied to each pixel in a region (possibly the entire display or some defined portion thereof) to which a global update drive scheme (more accurately referred to as a "global full" or "GC" drive scheme) is being applied, and a partial update drive scheme in which a drive voltage is applied only to pixels undergoing non-zero transitions (i.e., transitions in which the initial and final gray levels are different from one another), but no drive voltage is applied during zero transitions (in which the initial and final gray levels are the same). An intermediate form of drive scheme (named "globally limited" or "GL" drive scheme or drive mode) is similar to the GC drive scheme, except that no drive voltage is applied to the pixels undergoing a white-to-white zero transition. In displays used, for example, as electronic book readers, black text is displayed on a white background, particularly with many white pixels between the margin and the line of text that remains constant from one page of text to the next; therefore, not rewriting these white pixels will greatly reduce the apparent "flicker" of the display rewriting. However, there are still some problems in this type of GL driving scheme. First, as discussed in detail in some of the above mentioned MEDEOD applications, bistable electro-optic media are not generally fully bistable, and pixels in one extreme optical state may gradually drift toward intermediate gray levels in a matter of minutes to hours. In particular, pixels driven to white will slowly drift to light gray. Thus, if a white pixel is allowed to remain undriven after a number of page turns in a GL drive scheme, during which other white pixels (e.g., those that make up a portion of a text character) are driven, the newly updated white pixel will be slightly lighter than the undriven white pixel, and eventually the difference will become apparent even to an untrained user.

Secondly, 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 GC update at intervals. Unfortunately, using such random GC updates re-introduces 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.

Edge artifact reduction

In practice, several driving methods or algorithms can be used to reduce optical edge artifacts in the pixels. For example, a pixel undergoing a white-to-white transition and a primary neighboring pixel undergoing a non-empty transition may be identified first, and depending on how many such primary pixels undergo such a transition, a full clearing waveform (a full clearing waveform), such as that shown in fig. 4A, may be applied to the pixel undergoing a white-to-white transition. Where determining the exact number of adjacent primary pixels before the full erase waveform is to be applied can be designed to achieve the best display quality depending on the particular application. As shown in fig. 4A, the full clear or "F" waveform may include two full long pulses intended to drive a display pixel to black and/or white. For example, a first portion 402 of duration 18 frames and magnitude 15 volts configured to drive the display pixels to black is followed by a second portion 404 of duration 18 frames and magnitude 15 volts configured to drive the display pixels to white.

The following are some driving methods and/or algorithms that may be employed 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;

if not, then the mobile terminal can be switched to the normal mode,

if at least the SFT primary neighbors do not make a grayscale transition from white to white or are color image pixels (iscoloromemagepixel), the F W → W transition is applied;

if not, then the mobile terminal can be switched to the normal mode,

if the next gray levels of all four primary neighbors are white, and (the current gray level of at least one primary neighbor is not white or at least one primary neighbor is (W → W gray level transition and is a color image pixel)), the T W → W transition is applied.

Otherwise, the null (GL) W → W transition is used.

End up

In this driving method, a flag or indicator (e.g., "is a color image pixel") is used to identify a display pixel (i.e., a color display pixel) that is a color pixel in the source image (or alternatively in the color mapped image). In some embodiments, the colored pixels may be pixels in the source image that are not white. In fact, each pixel under a red CFA may require a white-to-white transition when the EPD changes from a white input image to a pure red area input image. Thus, these pixels will be applied with a full clear or fw → W transition waveform, such as the waveform shown in fig. 4A. In another embodiment, another indicator (e.g., SFT) may be used to determine whether to apply a full clear or fw → W transition waveform, depending on how many primary or neighboring pixels do not experience a white-to-white transition. The exact threshold for SFT (e.g., SFT =3 or 2, etc.) may vary and may be determined according to the particular display conditions. All other pixels that do not undergo a white-to-white transition may apply a globally limited or GL drive scheme or a pattern white transition (i.e., null) waveform. Further, the T W → W transition (i.e., rotating T) waveform may be applied to pixels marked or indicated as color pixels. For example, if the next gray level of all four primary neighbors of a pixel is white and the current gray level of at least one primary neighbor is not white, or at least one primary neighbor has a white-to-white gray level transition and is a color pixel under CFA, then the T white-to-white transition is applied. It will be appreciated that this driving method does not require knowledge of the current waveform state of the current image, but only the grey state of the current input image.

FIG. 4B illustrates an exemplary TW → W transition waveform 406. The T W → W transition waveform 406 may include a variable number of rotation pulses 410 having variable positions in the waveform 406, and a variable number of top-off pulses 408 having variable positions within the waveform 406 relative to the rotation pulses 410. In some embodiments, the single top-off pulse 408 corresponds to a frame that is driven white at a magnitude of minus 15 volts, while the rotation pulse 410 may include a frame that is driven to black at 15 volts and a frame that is driven to white at minus 15 volts. The rotation pulse 410 itself may be repeated multiple times, as shown in fig. 4B, while the top-off pulse 408 may precede the rotation pulse 410, follow the rotation pulse 410, and/or be in between the rotation pulses 410.

Referring now to FIG. 5, in practice, for all pixels of an electro-optic display, if the gray scale transition of a display pixel of the display is not W → W (i.e., white to white), as shown at step 502, then the waveform from the standard GL drive scheme or drive mode is applied, as shown at step 504; otherwise, in step 506, if at least the SFT number of the major neighbors of this display pixel have not made a white to white gray scale transition, or are marked by a "is color image pixel" indicator (i.e., this particular display pixel is a color pixel in the source image (or alternatively in a color mapped image)), then the FW → W transition waveform (e.g., fig. 4A) is applied, see step 508; otherwise, in step 510, if the next gray levels of all four primary neighbors of the display pixel are white and the current gray level of at least one primary neighbor is not white or at least one primary neighbor has a white-to-white gray level transition and is marked as a "color image pixel" pixel (i.e., is a color pixel), then the T W → W transition waveform (e.g., fig. 4B) is applied, see step 512; otherwise, an empty GL W → W transition waveform is applied in step 514.

In some embodiments, the previous image state or pixel state from a previous pixel transition may be added to the algorithm to determine which transition waveform to apply, as shown in the following driving method or algorithm and in fig. 6. Instead of applying a rotating waveform, the algorithm may be used to screen out pixels that have undergone a non-null transition in a previous image update.

Method 2

For all pixels in any order:

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

if not, then the mobile terminal can be switched to the normal mode,

if at least the SFT primary neighbor does not make a white to white grayscale transition or is a color image pixel, then the fw → W transition is applied;

if not, then,

the T W → W transition is applied if the next gray levels of all four primary neighbors are white and (the current gray level of at least one primary neighbor is not white and the previous pixel transition is empty) or at least one primary neighbor is (the W → W gray level transition and is a color image pixel).

Otherwise, the null (GL) W → W transition is used.

End up

This second method is similar to method 1 above, but takes into account the image grey state from the currently displayed image. For pixels that have undergone a non-idle transition in the currently displayed image, no rotation waveform will be applied to subsequent images. This approach may result in less power consumption for the EPD.

Referring now to FIG. 6, in practice, for all pixels of an electro-optic display, if the gray scale transition of a display pixel of the display is not W → W (i.e., white to white), as shown in step 602, then the waveform from the standard GL drive scheme or drive mode is applied, as shown in step 604; otherwise, in step 606, if at least the SFT number of the primary neighbors of the display pixel have not made a white to white gray scale transition, or are marked by a "is color image pixel" indicator (i.e., the particular display pixel is a color pixel in the source image (or alternatively in a color mapped image)), then the FW → W transition waveform (e.g., fig. 4A) is applied, see step 608; otherwise, in step 610, if the next gray levels of all four primary neighbors of the display pixel are white, and the current gray level 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 gray level transition and is marked as "being a color image pixel", then the TW → W transition waveform (e.g., fig. 4B) is applied, see step 612; otherwise, an empty GL W → W transition waveform is applied in step 614.

In some embodiments, it is preferred that before rendering the image on the display, the display pixels are identified as color pixels and they are marked with the indicator "are color image pixels". Referring now to fig. 7, prior to quantization step 708, at a display controller capable of controlling the operation of the bistable electro-optic display, color pixels may be identified and marked 704 with an indicator "are color image pixels". In operation, an image or source image 700 may first be processed by a color mapping algorithm 702 associated with a controller. The color mapping algorithm 702 may be configured to process the source image 700 into a color mapped image 720 to fit the colors available for a particular display to achieve the best color visual effect on that particular display. The color pixels in color mapped image 720 may then be identified and labeled as "are color image pixels" 704 and input to algorithm 710. It should be appreciated that this identification and marking occurs prior to the CFA mapping 706 step and the image dithering and quantization 708 step. The waveforms are then used to display an image using an algorithm 710 that can be assigned to the display pixels. The waveforms of display image 720 may then be sent to EPD 716 at waveform step 712. In some embodiments, these waveforms 712 may be recycled to the algorithm 710 for use as input (i.e., the waveform for the current state image 714) to generate the waveform 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. Accordingly, the foregoing description is to be considered in all respects as illustrative and not restrictive.

Claims (17)

1. A method for driving an electro-optic display having a plurality of display pixels, the method comprising:

detecting a white-to-white gray scale transition on the first pixel; and

it is determined whether a threshold number of primary neighbors of the first pixel have not made a gray scale transition from white to white or whether the first pixel is a color pixel and a first waveform is applied.

2. The method of claim 1, further comprising determining whether the next gray levels of all four primary neighbors of the first pixel are all white and the current gray level of at least one primary neighbor of the first pixel is not white, and applying a second waveform.

3. The method of claim 1, further comprising determining whether the next gray levels of all four primary neighbors of the first pixel are all white and at least one primary neighbor of the first pixel has a white to white gray level transition and is a color pixel, and applying a second waveform.

4. The method of claim 1, further comprising determining whether the next gray levels of all four primary neighbors of the first pixel are all white and at least one primary neighbor of the first pixel has a current gray level that is not white and an empty previous pixel transition, and applying a second waveform.

5. The method of claim 1, further comprising determining whether the next gray levels of all four main neighbors of the first pixel are all white and at least one main neighbor of the first pixel has a white-to-white gray level transition and is a color pixel, and applying a second waveform.

6. The method of claim 1, wherein the first waveform includes a first component configured to drive the first pixel to an optically black state.

7. The method of claim 1, wherein the first waveform includes a second component configured to drive the first pixel to an optical white state.

8. The method of claim 2, wherein the second waveform comprises a top-off pulse.

9. The method of claim 2, wherein the second waveform comprises a rotation pulse.

10. An electro-optic display configured to perform the method of claim 1, comprising a rotating bichromal member, electrochromic or electrowetting material.

11. An electro-optic display according to claim 10 comprising an electrophoretic material comprising a plurality of electrically charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field.

12. An electro-optic display according to claim 10 wherein the electrically charged particles and the fluid are confined in a plurality of capsules or microcells.

13. An electro-optic display according to claim 10 wherein the electrically charged particles and the fluid are present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material.

14. A method for driving an electro-optic display, comprising:

color mapping a source image into a color mapped image for an electro-optic display;

identifying color pixels from the color mapped image and marking the color pixels with an indicator; and

using the identification data of the color pixels as input to a waveform generation algorithm.

15. The method of claim 14, further comprising performing color filter array mapping on the color mapped image.

16. The method of claim 14, further comprising generating a waveform for a next state image from the waveform generation algorithm.

17. The method of claim 14, further comprising using the generated waveform as a current state image for a next state image.