Electro-optic display and method for driving the same

Abstract

To provide a suitable electro-optic display and a method for driving the same.SOLUTION: A method for driving an electro-optic display, the electro-optic display having a plurality of display pixels, the method comprising: dithering a grayscale image to a black and white image; updating the plurality of display pixels to display the black and white image; and converting the black and white image back to the grayscale image.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] (Reference to Related Application) This application is related to and claims priority to U.S. Provisional Application No. 63 / 086,118, filed October 1, 2020.

[0002] The entire disclosure of the aforementioned application is incorporated herein by reference.

[0003] (Subject of the invention) The present invention relates to a method for driving an electro-optic display, and more particularly to a driving method for displaying an image. [Background technology]

[0004] (background) Particle-based electrophoretic displays have been the subject of intense research and development for many years. In such displays, a plurality of charged particles (sometimes referred to as pigment particles) move through a fluid under the influence of an electric field. The electric field is typically provided by a conductive film or a transistor such as a field-effect transistor. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption compared to liquid crystal displays. Such electrophoretic displays have slower switching speeds than LCD displays. In addition, electrophoretic displays can be sluggish at low temperatures because the viscosity of the fluid limits the movement of the electrophoretic particles. Despite these drawbacks, electrophoretic displays can be found in everyday items such as e-books (e-readers), mobile phones and mobile phone covers, smart cards, signs, watches, shelf labels, and flash drives.

[0005] Many commercially available electrophoretic media essentially display only two colors, with gradations between extreme black and extreme white, known as "gray scale." Such electrophoretic media either use a single type of electrophoretic particles having a first color in a colored fluid having a second, different color (in which case the first color is displayed when the particles are placed adjacent to the display's viewing surface and the second color is displayed when the particles are moved away from the viewing surface), or they use first and second types of electrophoretic particles having different first and second colors in a non-colored fluid. In the latter case, the first color is displayed when the first type of particles is placed adjacent to the display's viewing surface, and the second color is displayed when the second type of particles is placed adjacent to the viewing surface. Typically, the two colors are black and white.

[0006] Although seemingly simple, electrophoretic media and devices exhibit complex behavior. For example, it has been found that good image display requires non-simple "on / off" voltage pulses. Rather, complex "waveforms" are required to drive the particles between states and to ensure that the produced image is of sufficiently good quality. Therefore, a need exists for driving methods for implementing image display in electrophoretic displays. Summary of the Invention [Means for solving the problem]

[0007] (Summary of the Invention) The present invention provides a method for driving an electro-optic display having a plurality of display pixels, the method including dithering a grayscale image into a black and white image, updating the plurality of display pixels to display the black and white image, and converting the black and white image back to the grayscale image.

[0008] In some embodiments, the method may further include applying a waveform configured to remove artifacts from the plurality of display pixels. In some other embodiments, dithering the grayscale image to a black and white image includes using a halftoning algorithm. In yet another embodiment, the halftoning algorithm is a green-noise halftoning algorithm. The present specification also provides, for example, the following items: (Item 1) 1. A method for driving an electro-optic display having a plurality of display pixels, the method comprising: dithering a grayscale image to a black and white image; updating the plurality of display pixels to display the monochrome image; converting said black and white image back to said grayscale image; A method comprising: (Item 2) Item 10. The method of item 1, further comprising applying a waveform configured to remove artifacts from the plurality of display pixels. (Item 3) Item 10. The method of item 1, wherein the step of dithering the grayscale image to a black and white image includes using a halftoning algorithm. (Item 4) Item 4. The method according to item 3, wherein the halftoning algorithm is a green noise halftoning algorithm. (Item 5) Item 10. The method of item 1, wherein the step of dithering the grayscale image to a black and white image includes using clustered halftoning maps. (Item 6) Item 10. The method of item 1, wherein the step of updating the plurality of display pixels includes applying a single frame of negative polarity voltage to the display pixels when the display pixels switch from a black optical state to a white optical state. (Item 7) Item 10. The method of item 1, wherein the step of updating the plurality of display pixels includes applying a single frame of positive polarity voltage to the display pixels when the display pixels switch from a white optical state to a black optical state. (Item 8) Item 10. The method of item 1, wherein the step of updating the plurality of display pixels includes using a waveform with n frames, where n is an integer. (Item 9) Item 9. The method according to item 8, wherein n=3. (Item 10) The step of updating the plurality of display pixels comprises: n 9. The method of claim 8, comprising using a waveform. (Item 11) Item 9. The method of item 8, wherein the step of updating the plurality of display pixels includes using 27 waveforms. (Item 12) Item 10. The method of item 1, wherein the step of updating the plurality of display pixels is substantially DC balanced. (Item 13) Item 10. The method of item 1, wherein the electro-optic display is an electrophoretic display having an electro-optic medium. (Item 14) Item 14. An electro-optic display according to item 13, wherein the electro-optic medium is a rotating dichroic member or an electrochromic medium. (Item 15) Item 14. An electro-optic display as described in item 13, wherein the electro-optic medium is an electrophoretic medium comprising a plurality of charged particles in a fluid, capable of moving through the fluid upon application of an electric field to the electro-optic medium. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram illustrating an electrophoretic display.

[0010] [Figure 2] Figure 2 shows a circuit model of the electro-optical imaging layer.

[0011] [Figure 3] FIG. 3 illustrates an exemplary process for enabling smooth animation updates.

[0012] [Figure 4] 4a-4c illustrate the halftoning process for converting a grayscale image to a black and white image.

[0013] [Figure 5] FIG. 5 illustrates an exemplary process for generating smooth animation.

[0014] [Figure 6] FIG. 6 illustrates an exemplary look-up table (LUT).

[0015] [Figure 7] FIG. 7 illustrates an example image state assignment after the image processing algorithm has assigned appropriate waveforms to enable smooth scrolling animation.

[0016] [Figure 8] FIG. 8 illustrates an exemplary sequential image update process. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Detailed explanation) The present invention relates to electro-optic displays, and in particular to a method for driving a bistable electro-optic display and an apparatus for use in such a method. More particularly, the present invention relates to a driving method for displaying images. The present invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays in which one or more types of electrically charged particles are present in a fluid and are caused to move through the fluid under the influence of an electric field so as to change the appearance of the display.

[0018] The term "electro-optic," as applied to a material or display, is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states that differ in at least one optical property, where the material is changed from its first display state to its second display state by application of an electric field to the material. The optical property is typically color perceptible to the human eye, but it may also be optical transmittance, reflectance, luminescence, or, in the case of displays intended to be machine-readable, another optical property such as pseudocolor in the sense of a change in reflection of electromagnetic wavelengths outside the visible range.

[0019] The term “gray state” is used herein in its conventional sense in the imaging arts to refer to a state intermediate between two extreme pixel optical states, and does not necessarily imply a black-to-white transition between these two extreme states. For example, several of the E Ink patents and published applications referenced below describe electrophoretic displays in which the extreme states are white and dark blue, whereby the intermediate “gray state” is actually light blue. In fact, as already noted, a change in optical state may not be a change in color at all. The terms “black” and “white” may hereinafter be used to refer to the two extreme optical states of a display and should generally be understood to include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term “monochrome” may hereinafter be used to refer to a drive scheme that drives pixels to only those two extreme optical states, without any intervening gray states.

[0020] Some electro-optic materials are solid in the sense that the material has a solid exterior surface, but the material can, and often does, have an interior liquid- or gas-filled space. Such displays using solid electro-optic materials may hereinafter be referred to for convenience as "solid electro-optic displays." Thus, the term "solid electro-optic display" includes rotating dichroic member displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

[0021] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to a display comprising display elements having first and second display states that differ in at least one optical property, such that after any given element is driven with an addressing pulse of finite duration to assume either its first or second display state, that state persists after the addressing pulse is terminated for at least several times, e.g., at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Pat. No. 7,170,670 shows that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for some other types of electro-optic displays. Displays of this type are properly referred to as "bistable" rather than bistable, although for convenience the term "bistable" may be used herein to encompass both bistable and bistable displays.

[0022] The term "impulse" is used herein in its conventional sense of the integral of voltage with respect to time. However, some bistable electro-optic media act as charge transducers, and in such media, an alternative definition of impulse may be used: the integral of current over time (equal to the total charge applied). Depending on whether the medium is acting as a voltage-time impulse transducer or a charge impulse transducer, the appropriate definition of impulse should be used.

[0023] Much of the discussion below 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 or may not be different from the initial gray level). The term "waveform" is used to refer to the overall voltage versus time curve used to effect a transition from a particular initial gray level to a particular final gray level. Typically, such waveforms comprise multiple waveform elements, and when these elements are approximately rectangular (i.e., when a given element comprises the application of a constant voltage over a period of time), the elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to effect all possible transitions between gray levels for a particular display. A display may utilize more than one drive scheme. For example, the aforementioned U.S. Patent No. 7,012,600 teaches that a drive scheme may need to be modified depending on parameters such as the temperature of the display or the amount of time it has been in operation during its lifetime, and thus a display may be provided with multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this manner may be referred to as a "set of related drive schemes." Also, as described in some of the aforementioned MEDEOD applications, it is possible to use more than one drive scheme simultaneously in different areas of the same display, and a set of drive schemes used in this manner may be referred to as a "set of simultaneous drive schemes."

[0024] Several types of electro-optic displays are known. One type of electro-optic display is the rotating dichroic member type, as described, for example, in U.S. Patent Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071, 6,055,091, 6,097,531, 6,128,124, 6,137,467, and 6,147,791. (This type of display is often referred to as a "rotating dichroic ball" display, but in some of the above-mentioned patents, the rotating member is not spherical, so the term "rotating dichroic member" is preferred as it is more accurate.) Such displays use a large number of small objects (typically spherical or cylindrical) having two or more portions with different optical properties and an internal dipole. These objects are suspended within liquid-filled vacuoles in a matrix, and the vacuoles are filled with liquid so that the objects are free to rotate. The appearance of the display is changed by applying an electric field to it, thereby rotating the objects into various positions and changing the portion of the object that is seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0025] Another type of electro-optic display uses an electrochromic medium (e.g., in the form of a nanochromic film comprising electrodes formed at least in part from a semiconducting metal oxide and a plurality of dye molecules attached to the electrodes capable of reversible color change). See, for example, O'Regan, B., et al., Nature 1991, 353, 737, and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Pat. Nos. 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0026] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, RA, et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such electrowetting displays can be made bistable.

[0027] One type of electro-optic display that has been the subject of intense research and development for many years is the particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption. Nevertheless, 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 an inadequate usable lifespan for these displays.

[0028] As noted above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using gaseous fluids (see, e.g., Kitamura, T., et al., "Electrical toner movement for electronic paper-like display," IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically," IDW Japan, 2001, Paper AMD4-4). See also U.S. Patent Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media are believed to be susceptible to the same types of problems as liquid-based electrophoretic media, resulting from particle settling, when the media is used in an orientation that allows such settling, for example, in a sign where the media is positioned in a vertical plane. In fact, particle settling is believed to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media due to the lower viscosity of the gas-suspending fluid compared to the viscosity of the fluid, which allows for faster settling of the electrophoretic particles.

[0029] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise a multitude of small capsules, 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 capsules themselves are held within a polymer binder, forming a coherent layer positioned between two electrodes. Techniques described in these patents and applications include:

[0030] (a) Electrophoretic particles, fluids, and fluid additives (see, e.g., U.S. Pat. Nos. 7,002,728 and 7,679,814)

[0031] (b) Capsules, binders, and encapsulation processes (see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719)

[0032] (c) Microcell structures, wall materials, and methods of forming the microcells (see, e.g., U.S. Patent Nos. 7,072,095 and 9,279,906)

[0033] (d) Methods for filling and sealing microcells (see, e.g., U.S. Pat. Nos. 7,144,942 and 7,715,088)

[0034] (e) Films and subassemblies containing electro-optical materials (see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564)

[0035] (f) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays (see, e.g., U.S. Pat. Nos. 7,116,318 and 7,535,624)

[0036] (g) Color formation and color control (see, e.g., U.S. Pat. Nos. 7,075,502 and 7,839,564)

[0037] (h) Display Applications (see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348)

[0038] (i) Non-electrophoretic displays, such as those described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160, as well as non-display applications of encapsulation and microcell technology (see, e.g., U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710).

[0039] (j) Methods for driving displays (e.g., U.S. Patent Nos. 5,930,026, 6,445,489, 6,504,524, 6,512,354, 6,531,997, 6,753,999, 6,825,970, 6,900,851, 6,995,550, 7,012,600, 7,023,420, 7,034,783, 7,061,166, 7,061,662, 7,116,466, 7,119,772, 7,177,066, 7,193,625, 7,222,224, 7,222,226, 7,222,228 ... No. 02,847, No. 7,242,514, No. 7,259,744, No. 7,304,787, No. 7,312,794, No. 7,327 ,511, No. 7,408,699, No. 7,453,445, No. 7,492,339, No. 7,528,822, No. 7,545,3 No. 58, No. 7,583,251, No. 7,602,374, No. 7,612,760, No. 7,679,599, No. 7,679,813 No. 7,683,606, No. 7,688,297, No. 7,729,039, No. 7,733,311, No. 7,733,335, No. No. 7,787,169, No. 7,859,742, No. 7,952,557, No. 7,956,841, No. 7,982,479, No. 7, No. 999,787, No. 8,077,141, No. 8,125,501, No. 8,139,050, No. 8,174,490, No. 8,24 No. 3,013, No. 8,274,472, No. 8,289,250, No. 8,300,006, No. 8,305,341, No. 8,314, No. 784, No. 8,373,649, No. 8,384,658, No. 8,456,414, No. 8,462,102, No. 8,537,105 No. 8,558,783, No. 8,558,785, No. 8,558,786, No. 8,558,855, No. 8,576,164, No. 8,576,259, No. 8,593,396, No. 8,605,032, No. 8,643,595, No. 8,665,206, No. 8 ,681,191, No.8,730,153, No.8,810,525, No.8,928,562, No.8,928,641, No.8,9 No. 76,444, No. 9,013,394, No. 9,019,197, No. 9,019,198, No. 9,019,318, No. 9,082,Nos. 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 Nos. 2003 / 0102858, 2004 / 0246562, 2005 / 0253777, 2007 / 0070032, 2007 / 0076289, 2007 / 0091418, 2007 / 0103427, 2007 / 0176912, 2007 / 0296452, 2008 / 0024429, 2008 / 0024482, 2008 / 0136774, 2008 / 0169821, 2008 / 0218471, No. 2008 / 0291129, No. 2008 / 0303780, No. 2009 / 0174651, No. 2009 / 0195568, No. 2009 / 0322721, No. 2010 / 0194733, No. 2010 / 0194789, No. 2010 / 02 20121, 2010 / 0265561, 2010 / 0283804, 2011 / 0063314, 2011 / 0175875, 2011 / 0193840, 2011 / 0193841, 2011 / 0199671, 2 No. 011 / 0221740, No. 2012 / 0001957, No. 2012 / 0098740, No. 2013 / 0063333, No. 2013 / 0194250, No. 2013 / 0249782, No. 2013 / 0321278, No. 2014 / 0009 No. 817, No. 2014 / 0085355, No. 2014 / 0204012, No. 2014 / 0218277, No. 2014 / 0240210, No. 2014 / 0240373, No. 2014 / 0253425, No. 2014 / 0292830, No. 201 (See Nos. 4 / 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).

[0040] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called "polymer-dispersed electrophoretic display" in which the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymer material, and that the discrete droplets of electrophoretic fluid in such a polymer-dispersed electrophoretic display can be considered capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet. See, for example, the aforementioned U.S. Patent No. 2002 / 0131147. Therefore, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0041] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, the charged particles and suspending fluid are not encapsulated in microcapsules, but instead are confined within a plurality of cavities formed in a carrier medium, e.g., a polymer film. See, e.g., International Application Publication No. WO 02 / 01281 and Published U.S. Application No. 2002 / 0075556 (both assigned to Sipix Imaging, Inc.).

[0042] Many of the aforementioned E Ink and MIT patents and applications also discuss microcell electrophoretic displays and polymer-dispersed electrophoretic displays. The term "encapsulated electrophoretic displays" can refer to any such display type, which may also be collectively described as "microcavity electrophoretic displays" to generalize across wall configurations.

[0043] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, RA, et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). Co-pending application Ser. No. 10 / 711,802, filed Oct. 6, 2004, shows that such electrowetting displays can be made bistable.

[0044] Other types of electro-optic materials may also be used, most notably bistable ferroelectric liquid crystal displays (FLCs) which are known in the art and have exhibited remnant voltage behavior.

[0045] Although electrophoretic media are opaque (e.g., in many electrophoretic media, because the particles substantially block the transmission of visible light through the display) and can operate in a reflective mode, some electrophoretic displays can be made to operate in a so-called "shutter mode," in which one display state is substantially opaque and one is light-transmitting. See, for example, U.S. Patent Nos. 6,130,774 and 6,172,798, as well as U.S. Patent Nos. 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on variations in electric field strength, can operate in a similar mode. See U.S. Patent No. 4,418,346. Other types of electro-optic displays may also be capable of operating in a shutter mode.

[0046] High-resolution displays may include individual pixels that are addressable without interference from neighboring pixels. One approach to achieving such pixels is to provide an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel to create an "active matrix" display. The addressing or pixel electrode that addresses a pixel is connected to an appropriate voltage source through the associated nonlinear element. When the nonlinear element is a transistor, the pixel electrode may be connected to the drain of the transistor, which is essentially arbitrary, and the pixel electrode may be connected to the source of the transistor, although this arrangement will be assumed in the following description. In high-resolution arrays, 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 designated row and one designated column. The sources of all transistors in each column may be connected to a single column electrode, while the gates of all transistors in each row may be connected to a single row electrode. Again, the assignment of sources to rows and gates to columns may be reversed as desired.

[0047] The display may be written in a row-by-row manner. The row electrodes are connected to a row driver, which may apply a voltage to a selected row electrode to ensure that all transistors in the selected row are conductive, while applying a voltage to all other rows to ensure that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to a column driver, which applies voltages to the various column electrodes selected to drive the pixels in a selected row to their desired optical states. (These voltages are relative to a common front electrode, which may extend across the entire display and is provided opposite the nonlinear array of electro-optic medium. As is known in the art, voltages are relative and are a measure of the charge difference between two points. One voltage value is relative to another voltage value. For example, zero voltage (“0V”) refers to having no voltage difference relative to another voltage.) After a preselected interval known as the “line address time,” the selected row is deselected, another row is selected, and the voltages to the column drivers are changed so that the next line of the display is written.

[0048] However, in use, certain waveforms can create a remnant voltage across the pixels of an electro-optic display, which, as is clear from the above discussion, creates several unwanted optical effects and is generally undesirable.

[0049] As presented herein, a "shift" in the optical state associated with an addressing pulse refers to the situation where the initial application of a particular addressing pulse to the electro-optic display results in a first optical state (e.g., a first gray tone), and a subsequent application of the same addressing pulse to the electro-optic display results in a second optical state (e.g., a second gray tone). Because the voltage applied to a pixel of the electro-optic display during application of an addressing pulse includes the total of the remnant voltage and the voltage of the addressing pulse, the remnant voltage can cause a shift in the optical state.

[0050] "Drift" in the optical state of a display over time refers to a situation in which the optical state of an electro-optic display changes while the display is at rest (e.g., during periods when no addressing pulses are applied to the display). Because the optical state of a pixel may depend on the pixel's remnant voltage, and the pixel's remnant voltage may decay over time, the remnant voltage may cause drift in the optical state.

[0051] "Persistence" refers to the situation where a trace of a previous image is still visible after an electro-optic display has been rewritten. Residual voltage can give rise to "edge persistence," a type of persistence in which the outline (edge) of part of the previous image(s) remains visible.

[0052] Exemplary EPD

[0053] 1 shows a schematic diagram of a pixel 100 of an electro-optic display in accordance with the presently presented subject matter. 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, for example, but not limited to, an encapsulated electrophoretic imaging film that may include charged pigment particles.

[0054] The imaging film 110 may be disposed between the front electrode 102 and the rear electrode 104. The front electrode 102 may be formed between the imaging film and the front of the display. In some embodiments, the front electrode 102 may be transparent. In some embodiments, the front electrode 102 may be formed from any suitable transparent material, including, but not limited to, indium tin oxide (ITO). The rear electrode 104 may be formed opposite the front electrode 102. In some embodiments, a parasitic capacitance (not shown) may form between the front electrode 102 and the rear electrode 104.

[0055] 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 designated row and one designated column. In some embodiments, the matrix of pixels may be an "active matrix" in which each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 may be coupled between the backplate electrode 104 and the addressing electrode 108. In some embodiments, the nonlinear element 120 may include a diode and / or a transistor (including, but not limited to, a MOSFET). The drain (or source) of the MOSFET may be coupled to the backplate electrode 104, the source (or drain) of the MOSFET may be coupled to the addressing electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106 configured to control activation and deactivation of the MOSFET (for convenience, the terminal of the MOSFET that is coupled to the backplate electrode 104 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET that is coupled to the addressing electrode 108 will be referred to as the source of the MOSFET; however, those skilled in the art will recognize that in some embodiments, the source and drain of the MOSFET may be swapped).

[0056] In some active matrix embodiments, the addressing electrodes 108 of all pixels in each column may be connected to the same column electrode, and the driver electrodes 106 of all pixels in each row may be connected to the same row electrode. The row electrodes may be connected to a row driver, which may select one or more rows of pixels by applying a voltage to the selected row electrode sufficient to activate the nonlinear elements 120 of all pixels 100 in the selected row(s). The column electrodes may be connected to a column driver, which may apply a suitable voltage to the addressing electrodes 106 of the selected (activated) pixels to drive the pixels to a desired optical state. The voltage applied to the addressing electrodes 108 may be relative to the voltage applied to the pixel's front plate electrode 102 (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.

[0057] In some embodiments, the active matrix pixels 100 may be written in a row-by-row manner. For example, a row of pixels may be selected by a row driver, and voltages corresponding to the desired optical state for the row of pixels may be applied to the pixels by a column driver. After a preselected interval known as a "line address time," the selected row may be deselected, another row may be selected, and the voltages to the column drivers may be changed so that another line of the display is written.

[0058] 2 shows a circuit model of the electro-optic imaging layer 110 disposed between the front electrode 102 and the rear electrode 104 in accordance with the subject matter presented herein. Resistor 202 and capacitor 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, the front electrode 102, and the rear electrode 104, including any adhesive layers. Resistor 212 and capacitor 214 may represent the resistance and capacitance of a lamination adhesive layer. Capacitor 216 may represent capacitance that may form at an interface contact area between layers, such as the interface between the front electrode 102 and the rear electrode 104, e.g., between the imaging layer and a lamination adhesive layer and / or between a lamination adhesive layer and a backplane electrode. The voltage Vi across the imaging film 110 of a pixel may include the residual voltage of the pixel.

[0059] In practice, conventional video rate displays using non-bistable media, such as phosphor screens on cathode ray tubes and conventional liquid crystal displays, require frame rates in excess of about 25 frames per second (fps) to provide acceptable video quality (video displays at 15 fps are common on the Internet, resulting in a significant lack of video quality). However, bi-stable and certain other electro-optic displays have been found to be capable of producing good quality images at frame rates significantly below 25 fps, and within the range of about 10 to about 20 fps, preferably about 13 to about 20 fps. Experienced observers have determined that encapsulated electrophoretic displays operating at 15 fps can produce video quality that appears substantially equivalent to that produced by non-bistable displays operating at about 30 fps.

[0060] There are many possible reasons for this unexpectedly high image quality at low frame rates, one explanation being that part of the explanation is thought to be the way in which continuous images on a bi-stable display assist the eye in "blending" successive images to create the illusion of motion. All image displays rely on the eye's ability to blend a series of still images to create the illusion of motion. However, many types of image displays actually introduce temporary intervening "images" that disrupt the blending process. For example, a motion film display using a mechanical film projector actually places a first still image on the screen, then displays a blank screen for a very brief period as the projector advances the film to the next frame, after which it displays a second still image.

[0061] The subject matter presented herein includes drive methods that utilize interruptible waveform updates while maintaining substantial DC balance, meaning that the net resulting impulse from the updates is substantially zero, thereby enabling smooth pipelined animation updates. In some embodiments, the drive methods presented herein further provide strategies for addressing the persistence effect. In cases such as those described above, "persistence" refers to a situation in which a trace of the previous image(s) is still visible after the electro-optic display has been rewritten. Residual voltages can cause "edge persistence," a type of persistence in which the contours (edges) of parts of the previous image remain visible.

[0062] Referring now to FIG. 3, a flowchart of a driving process 300 for enabling smooth animated updates in accordance with the subject matter disclosed herein is illustrated therein. This process 300 may include a first step 302 in which a grayscale image is dithered to a black and white image. The dithered image is then processed in an image processing step 304, which may include animating the dithered image using the pipeline / parallel update capabilities of a controller associated with the electro-optic display. In some embodiments, a 5-bit waveform lookup table (LUT) (e.g., step 306) may be used to implement an interruptible direct update strategy (e.g., step 308) while maintaining DC balance to enable smooth updates. Additionally, in some embodiments, a special waveform may be used to erase any persistence artifacts in the erase update data 310.

[0063] In practice, the dithering step 302 of Figure 3 may process a grayscale image (e.g., Figure 4a) into a black and white only image that is an exact replica of the original image by using halftoning algorithms commonly used in the art, such as a green noise halftone algorithm (e.g., Figure 4b) and / or a clustered halftoning map (e.g., Figure 4c). In some embodiments, for animated applications where the direction of the animation is captured, such as scrolling a page up and down or left and right, it may be preferable to rotate the clustered dot screen in a preferred direction relative to the direction of the animated scrolling.

[0064] In some embodiments, with the halftoning process of step 302 producing only a black and white image for the display pixels, only the following transitions need be considered: White → Black white → white Black → White white → white

[0065] In practice, as with driving methods that utilize relatively short pulses to change the grayscale of a pixel (the direct update or DU method, described below), the white-to-white and black-to-black transitions may be left empty, which maintains DC balance and also reduces the appearance of the transitions.

[0066] As explained above, for some display applications, the display may utilize a “direct update” drive scheme (“DU” drive scheme). A DU drive scheme may typically have fewer than two or more than two gray levels than a grayscale drive scheme (“GSDS”), which can result in transitions between all possible gray levels. However, the most important characteristic of a DU drive scheme is that, for at least some transitions, the transition is driven from an initial gray level to a final gray level by a simple unidirectional drive, as opposed to the “indirect” transitions often used in GSDS, where a pixel is driven from an initial gray level to one extreme optical state and then driven in the opposite direction to the final gray level. In some cases, a transition may be brought about by driving from an initial gray level to one extreme optical state and then to the opposite extreme optical state, and only then can it be driven to the final extreme optical state. See, for example, the drive scheme illustrated in FIGS. 11A and 11B of the aforementioned U.S. Pat. No. 7,012,600. Thus, the present electrophoretic displays may have update times in grayscale mode that are about 2-3 times the saturation pulse length ("saturation pulse length" is defined as the period at a particular voltage that is sufficient to drive a pixel of the display from one extreme optical state to the other), i.e., about 700-900 milliseconds, while DUDS have a maximum update time equal to the saturation pulse length, i.e., about 200-300 milliseconds.

[0067] In some embodiments, the white-to-black transition described above can include a pulse driven with a positive voltage relative to the pulse length frame, and the black-to-white transition can include a pulse driven with a negative voltage, in which case the pulse length can be between 15 and 21 frames at a temperature of approximately 25°C.

[0068] However, for smooth video transitions, the white-to-black and black-to-white transitions are configured to be interruptible, preferably with every frame update, since in animation mode a given pixel may require a change of optical state to black or white every frame.

[0069] 5 illustrates an example of a waveform that may be applied for a series of pixel state changes in each frame. To maintain DC balance, the following rules may be applied in each frame:

[0070] Rule #1: When a pixel switches from black to white, apply a single frame of negative polarity voltage, and when a pixel switches from white to black, apply a single frame of positive polarity voltage.

[0071] Rule #2: For an unchanged state, a single frame voltage is applied continuously until a pulse length is reached where subsequent updates to the same state are driven at zero volts.

[0072] Rule #3: At the end of the animation sequence, apply extra impulse potentials to reach the desired black and white states and complete the DC balance cycle.

[0073] In practice, a waveform of n frames in duration may be used to permute all possible voltage combinations of -15 volts, 0 volts, and +15 volts required to drive a pixel. This allows for n possible voltage combinations. n Give the total number of items, or in this case n 3Gives the total number of such lists of voltage combinations (e.g., n 3 n) can be implemented using a 5-bit waveform look-up table (LUT) that provides 32 waveform slots. In some other embodiments, n are implemented using a 4-bit waveform LUT that provides 16 waveform slots. 2 A combination of voltages can be achieved.

[0074] Referring now to FIG. 6, FIG. 6 shows the 3 FIG. 1 illustrates a LUT with voltage combinations, in which case 27 waveforms can be generated. In some embodiments, an image processing algorithm can assign appropriate LUT states to a sequence of images to give the illusion of smooth animation. An example of image states assigned to an appropriate waveform LUT to generate a smooth scrolling animation is shown in FIG. 7. In some cases, if the waveform is more than one frame in duration (e.g., n>1), sequential images can be concatenated, as shown in FIG. 8. In such cases, the EPD controller may use its pipeline update capability to continuously queue these images in a pipeline image buffer.

[0075] Additionally, special waveforms may be utilized to eliminate artifacts such as blooming and / or ghosting at the end or during image updates. In some embodiments, this artifact elimination may be performed when the display process results from a black and white dithering pattern relative to the original final grayscale image. For example, a unipolar waveform may be used to eliminate artifacts on the white or black state with the use of a post-drive discharge.

[0076] It will be apparent to those skilled in the art that numerous changes and modifications may be made to the specific embodiments of the invention described above without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be interpreted in an illustrative sense, rather than a restrictive sense.

Claims

1. A method for driving an electro-optic display having a plurality of display pixels, the electro-optic display being an electrophoretic display having an electro-optic medium, the method comprising: dithering one or more grayscale images into a black and white image; updating the plurality of display pixels to display the monochrome image as a series of images to give the illusion of smooth animation, wherein updating the plurality of display pixels to display the monochrome image includes using 3 n waveforms, each waveform having n frames, where n is an integer greater than or equal to 1; updating the plurality of display pixels to display a final grayscale image at the end of the series of images; A method comprising:

2. The method of claim 1, further comprising applying a waveform configured to remove artifacts from the plurality of display pixels.

3. The method of claim 1, wherein dithering one or more grayscale images into a black and white image includes using a halftoning algorithm.

4. The method described in claim 3, wherein the halftoning algorithm is a green noise halftoning algorithm.

5. The method of claim 1, wherein dithering one or more grayscale images into a black and white image includes using clustered halftoning maps.

6. The method of claim 1, wherein updating the plurality of display pixels to display the black and white image includes applying a single frame of negative polarity voltage to the display pixels when the display pixels switch from a black optical state to a white optical state.

7. The method of claim 1, wherein updating the plurality of display pixels to display the black and white image includes applying a single frame of positive polarity voltage to the display pixels when the display pixels switch from a white optical state to a black optical state.

8. The method of claim 1, wherein n=3.

9. The method of claim 1, wherein updating the plurality of display pixels to display the black and white image includes using 27 waveforms.

10. The method of claim 1, wherein updating the plurality of display pixels to display the black and white image includes using a waveform that substantially maintains DC balance of the electro-optical display.

11. The method of claim 1, wherein the electro-optical medium is a rotating bichromatic member or an electrochromic medium.

12. The method of claim 1, wherein the electro-optic medium is an electrophoretic medium comprising a plurality of charged particles in a fluid that are capable of moving through the fluid upon application of an electric field to the electro-optic medium.

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