Electro-optic display and method for driving the same

Abstract

To provide an electro-optic display and a method for driving the electro-optic display.SOLUTION: A method for driving an electro-optic display including plural display pixels is provided. The method includes detecting a transition from white / white to a gray tone at a first pixel, determining whether threshold numbers of adjacent cardinal numbers out of the first pixel undergo the transition from white / white to a gray tone or whether the first pixel is a color pixel, and applying a first wave. Also provided is an electro-optic display having a rotational two-color member and an electrochromic or electro-wetting material, and designed to implement the aforesaid method.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] (Reference to Related Application) This application is related to and claims priority to U.S. Provisional Application No. 63 / 032,721, filed May 31, 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 reducing pixel edge artifacts and / or image retention in an electro-optic display. [Background technology]

[0004] (background) Electro-optic displays typically have a backplane with a plurality of pixel electrodes, each of which defines one pixel of the display. Conventionally, a single common electrode extending across a large number of pixels, usually the entire display, is provided on the opposite side of the electro-optic medium. Individual pixel electrodes may be driven directly (i.e., a separate conductor may be provided for each pixel electrode), or the pixel electrodes may be driven in an active matrix manner, which will be familiar to those skilled in the art of backplane technology. Because adjacent pixel electrodes will often be at different voltages, they must be separated by inter-pixel gaps of finite width to avoid electrical shorts between the electrodes. At first glance, one might think that the electro-optic medium overlying these gaps would not switch when a drive voltage is applied to the pixel electrodes (indeed, this is often true for some non-bistable electro-optic media, such as liquid crystals, where a black mask is typically provided to hide these non-switching gaps), but in the case of many bistable electro-optic media, the medium overlying the gaps will switch due to a phenomenon known as "blooming."

[0005] 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 size of the pixel electrode. While excessive blooming should be avoided (e.g., in high-resolution active-matrix displays, it is undesirable for application of a drive voltage to a single pixel to cause switching over an area covering several adjacent pixels, as this would reduce the effective resolution of the display), a controlled amount of blooming is often useful. For example, consider a black-on-white electro-optic display that displays numbers using a conventional seven-segment array of seven directly driven pixel electrodes per digit. For example, when a zero is displayed, six segments are turned black. In the absence of blooming, the gaps between the six pixels would be visible. However, by providing a controlled amount of blooming, the gaps between pixels can be turned black, resulting in more visually appealing numbers, as described, for example, in U.S. Pat. No. 7,602,374, which is incorporated herein in its entirety. However, blooming can lead to a problem referred to as "edge persistence."

[0006] An area of blooming is not uniformly white or black, but is typically a transition zone where the color of the medium transitions from white to black through various shades of gray as one moves across the area of blooming. Thus, although edge afterimages will typically be areas of various shades of gray rather than uniform gray areas, they can still be visible and objectionable, particularly because the human eye has the ability to detect gray areas in monochromatic images where each pixel is assumed to be pure black or pure white. In some cases, asymmetric blooming can contribute to edge afterimages. "Asymmetric blooming" refers to the phenomenon whereby in some electro-optic media (e.g., the copper chromite / titania encapsulated electrophoretic media described in U.S. Pat. No. 7,002,728, incorporated herein in its entirety), blooming is "asymmetric" in the sense that more blooming occurs during the transition from one extreme optical state of a pixel to the other extreme optical state than during the transition in the opposite direction; in the media described in this patent, blooming during a black / white transition typically exceeds that during a white / black transition. Therefore, a driving method is needed that also reduces the afterimage or blooming effect. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 7,602,374 [Patent Document 2] U.S. Patent No. 7,002,728 Summary of the Invention [Means for solving the problem]

[0008] (Summary of the Invention) Thus, in one aspect, the subject matter presented herein provides a method for driving an electro-optic display having a plurality of display pixels, the method including detecting a white / white graytone transition on a first pixel, determining if a threshold number of adjacent ones of the first pixel have not made a white / white to graytone transition or if the first pixel is a color pixel, and applying a first waveform.

[0009] In some embodiments, the driving method may further include determining whether all four neighboring radixes of the first pixel have a next graytone of white and at least one neighboring radix of the first pixel has a current graytone that is not white, and applying the second waveform.

[0010] In another embodiment, the driving method may also include determining whether all four adjacent radixes of the first pixel have graytones next to white and at least one adjacent radix of the first pixel has a white / white graytone transition and is a color pixel, and applying the second waveform.

[0011] In yet another embodiment, the driving method may further include determining whether all four neighboring radixes of the first pixel have a next graytone of white and at least one neighboring radix of the first pixel has a current graytone that is not white and an empty previous pixel transition, and applying the second waveform.

[0012] In another embodiment, the driving method may further include determining whether all four adjacent radixes of the first pixel have gray tones next to white and at least one adjacent radix of the first pixel has a white / white gray tone transition and is a color pixel, and applying the second waveform.

[0013] In some embodiments, the first waveform may include a first component configured to drive a first pixel to an optical black state.

[0014] In some other embodiments, the first waveform may include a second component configured to drive the first pixel to an optical white state.

[0015] In some embodiments, the second waveform can include a top-off pulse.

[0016] In some other embodiments, the second waveform may include a rotation pulse.

[0017] In another aspect, the subject matter presented herein provides another method for driving an electro-optic display, the method can 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 flagging the color pixels with designators, and using the color pixel identification data as input for a waveform generation algorithm.

[0018] In some embodiments, the driving method may also include performing color filter array mapping on the color-mapped image.

[0019] In another embodiment, the driving method may further include generating a waveform for the next state image from a waveform generation algorithm.

[0020] In yet another embodiment, the driving method may also include using the generated waveform as the current state image for the next state image. The present invention 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: Detecting a white / white graytone transition on a first pixel; determining whether a threshold number of adjacent radix numbers of the first pixel do not make a white / white to graytone transition or if the first pixel is a color pixel, and applying a first waveform; A method comprising: (Item 2) Item 10. The method of item 1, further comprising: determining whether all four neighboring radixes of the first pixel have a next graytone of white and at least one neighboring radix of the first pixel has a current graytone that is not white; and applying a second waveform. (Item 3) Item 10. The method of item 1, further comprising: determining whether all four adjacent radixes of the first pixel have graytones next to white and at least one adjacent radix of the first pixel has a white / white graytone transition and is a color pixel; and applying a second waveform. (Item 4) Item 10. The method of claim 1, further comprising: determining whether all four neighboring radixes of the first pixel have a next graytone of white and at least one neighboring radix of the first pixel has a current graytone and an empty previous pixel transition that is not white; and applying a second waveform. (Item 5) Item 10. The method of item 1, further comprising: determining whether all four adjacent radixes of the first pixel have graytones next to white and at least one adjacent radix of the first pixel has a white / white graytone transition and is a color pixel; and applying a second waveform. (Item 6) Item 10. The method of item 1, wherein the first waveform includes a first component configured to drive the first pixel to an optical black state. (Item 7) Item 10. The method of item 1, wherein the first waveform has a second component configured to drive the first pixel to an optical white state. (Item 8) Item 3. The method of item 2, wherein the second waveform includes a top-off pulse. (Item 9) Item 3. The method of item 2, wherein the second waveform includes a rotation pulse. (Item 10) Item 1. An electro-optic display configured to perform the method of item 1, comprising a rotating bichromal member, electrochromic, or electrowetting material. (Item 11) Item 11. An electro-optic display according to item 10, comprising an electrophoretic material comprising a plurality of electrically charged particles disposed in a fluid and capable of moving through said fluid under the influence of an electric field. (Item 12) Item 11. An electro-optic display according to item 10, wherein the charged particles and the fluid are confined within a plurality of capsules or microcells. (Item 13) Item 11. An electro-optic display as described in item 10, wherein the charged particles and the fluid are present as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material. (Item 14) 1. A method for driving an electro-optic display, comprising: color mapping the source image into a color-mapped image for an electro-optic display; identifying color pixels from the color-mapped image and flagging the color pixels with a designator; Using the color pixel identification data as input for the waveform generation algorithm. A method comprising: (Item 15) Item 15. The method of item 14, further comprising performing color filter array mapping on the color mapped image. (Item 16) Item 15. The method of item 14, further comprising generating a waveform for a next status image from the waveform generation algorithm. (Item 17) Item 15. The method of item 14, further comprising using the generated waveform as a current state image for a next state image. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a circuit diagram illustrating an electrophoretic display.

[0022] [Figure 2] FIG. 2 shows a circuit model of the electro-optic imaging layer.

[0023] [Figure 3] FIG. 3 illustrates a cross-sectional view of an electro-optic display having a color filter array.

[0024] [Figure 4A] FIG. 4A illustrates an example cancellation waveform in accordance with the subject matter disclosed herein.

[0025] [Figure 4B] FIG. 4B illustrates an exemplary T W->W transition waveform in accordance with the subject matter disclosed herein.

[0026] [Figure 5] FIG. 5 is a flow chart illustrating a first algorithm for driving a display.

[0027] [Figure 6] FIG. 6 is a flow chart illustrating a second algorithm for driving a display.

[0028] [Figure 7] FIG. 7 illustrates a process for rendering an image on a display. DETAILED DESCRIPTION OF THE INVENTION

[0029] (Detailed explanation) The present invention relates to a method for driving electro-optic displays, particularly bistable electro-optic displays, and to an apparatus for use in such a method. More particularly, the present invention relates to a driving method that may enable reduced "afterimage" and edge effects, as well as reduced flashing, in such displays. 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 moved through the fluid under the influence of an electric field to change the appearance of the display.

[0030] The term "electro-optic," as applied to a material or display, is used in its conventional sense in the imaging arts and is used herein to refer to a material having at least one optical property with distinct first and second display states, which is changed from its first 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 may also be another optical property such as optical transmittance, reflectance, luminescence, or, in the case of displays intended for machine reading, pseudocolor in the sense of a change in reflection of electromagnetic wavelengths outside the visible range.

[0031] 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 transition between these two extreme states of black and white. For example, see E Some of the Ink patents and published applications describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. In fact, as already noted, a change in optical state may not be a change in color at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the 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 be used hereinafter to refer to a drive scheme that drives pixels to only those two extreme optical states, with no intervening gray states.

[0032] Although some electro-optic materials are solid in the sense that the material has a solid exterior surface, the material may often 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.

[0033] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to displays having display elements with first and second display states that differ in at least one optical property, such that any given element is driven with a finite-duration addressing pulse to assume either its first or second display state, and that state persists after the addressing pulse has 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 grayscale-capable particle-based electrophoretic displays are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for several other types of electro-optic displays. Displays of this type are properly referred to as "multistable" rather than bistable, although for convenience the term "bistable" may be used herein to encompass both bistable and multistable displays.

[0034] 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 with such media, an alternative definition of impulse may be used: the integral of current over time (equal to the total charge applied). The appropriate definition of impulse should be used depending on whether the medium acts as a voltage-time impulse transducer or a charge impulse transducer.

[0035] Much of the following discussion will focus 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" will be used to refer to the overall voltage versus time curve used to effect a transition from a specific initial gray level to a specific final gray level. Typically, such a waveform will comprise multiple waveform elements. That is, if these elements are approximately rectangular (i.e., if a given element comprises the application of a constant voltage over a period of time), the element may be referred to as a "pulse" or "drive pulse." The term "drive scheme" refers to a set of waveforms sufficient to effect all possible transitions between gray levels for a specific 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 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 way may be referred to as a "set of simultaneous drive schemes."

[0036] Several types of electro-optical displays are known. One type of electro-optical display is the type of rotating bicolor member as described, for example, in US 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 (displays of this type are often referred to as "rotating bicolor ball" displays, but in some of the patents described above, the term "rotating bicolor member" is preferred as more accurate, since the rotating member is not spherical). Such displays use multiple small bodies (typically spherical or cylindrical) with two or more divisions with different optical properties and an internal dipole. These bodies are suspended within a vacuole filled with liquid within the matrix, and the vacuoles are filled with liquid such that the body rotates freely. The appearance of the display is altered by applying an electric field thereto, thus rotating the body to various positions, varying the segmentation of the body seen through the viewing surface. This type of electro-optic media is typically bistable.

[0037] Another type of electro-optical display uses an electrochromic medium in the form of a nanochromic film, consisting of an electrode formed at least in part from a semiconducting metal oxide, and a plurality of dyed molecules capable of reversible color change attached to the electrodes. See, eg, O'Regan, B., et al., Nature 1991, 353, 737, and Wood, D., Information Display, 18(3), 24 (March 2002). Also, Bach, U., et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Patent Nos. 6,301,038, 6,870,657, and 6,950,220. Media of this type are also typically bistable.

[0038] 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 indicates that such electrowetting displays can be made bistable.

[0039] One type of electro-optic display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which a plurality of electrically charged particles move through a fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared to liquid crystal displays. Nevertheless, issues 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 a poor usable lifespan for these displays.

[0040] 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 also 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 due to particle settling when used in an orientation that allows such settling, such as 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 because the lower viscosity of the gaseous suspending fluid, compared to the viscosity of a liquid, allows for faster settling of electrophoretic particles.

[0041] 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 include a number of small capsules, each of which itself comprises an internal phase containing electrophoretically movable 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 the following:

[0042] (a) Electrophoretic particles, fluids, and fluid additives (see, e.g., U.S. Pat. Nos. 7,002,728 and 7,679,814)

[0043] (b) Capsules, binders, and encapsulation processes (see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719)

[0044] (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)

[0045] (d) Methods for filling and sealing microcells (see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088)

[0046] (e) Films and subassemblies containing electro-optical materials (see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564)

[0047] (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)

[0048] (g) Color formation and color control (see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564)

[0049] (h) Display Applications (see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348)

[0050] (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).

[0051] (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).

[0052] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium may be replaced with a continuous phase, thus producing so-called polymer-dispersed electrophoretic displays, in which the electrophoretic medium consists of a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and that the discrete droplets of electrophoretic fluid in such polymer-dispersed electrophoretic displays may be considered capsules or microcapsules, even though a discrete capsule membrane is not associated with each individual droplet. See, e.g., the aforementioned 2002 / 0131147. Therefore, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0053] 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 retained 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.

[0054] 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 display" can refer to any such display type, which can also be collectively described as "microcavity electrophoretic displays" to generalize across wall configurations.

[0055] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, R.A., et al., "Video-Speed Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). In co-pending application Ser. No. 10 / 711,802, filed Oct. 6, 2004, it is shown that such electrowetting displays can be made bistable.

[0056] 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 exhibit remnant voltage behavior.

[0057] Although electrophoretic media can be opaque (e.g., because in many electrophoretic media the particles substantially block the transmission of visible light through the display) and operate in a reflective mode, some electrophoretic displays can be adapted to operate in a so-called "shutter mode" in which one display state is substantially opaque and one display state is light transmissive. See, e.g., 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.

[0058] High-resolution displays may include individual pixels that are addressable without interference from neighboring pixels. One way to achieve 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, producing an "active matrix" display. The addressing or pixel electrode, which 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; although this arrangement will be assumed in the following description, it is essentially arbitrary; the pixel electrode may also be connected to the source of the transistor. 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 defined row and one defined 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.

[0059] 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 is provided opposite the nonlinear array of electro-optic medium and may extend across the entire display. As 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 on the column drivers are changed so that the next line of the display is written.

[0060] However, in use, certain waveforms can produce a residual voltage across the pixels of an electro-optic display, and as is evident from the above discussion, this residual voltage creates several unwanted optical effects and is generally undesirable.

[0061] 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 an 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). A remnant voltage can cause a shift in the optical state because the voltage applied to a pixel of the electro-optic display during application of an addressing pulse comprises the sum of the remnant voltage and the voltage of the addressing pulse.

[0062] "Drift" in the optical state of a display over time refers to the situation where the optical state of an electro-optic display changes while the display is stationary (e.g., during periods when no addressing pulses are applied to the display). Remnant voltages can cause drift in the optical state because the optical state of a pixel can depend on the remnant voltage of a pixel, and the remnant voltage of a pixel can decay over time.

[0063] As discussed above, "persistence" refers to the situation where a trace of a previous image is still visible after an electro-optic display has been rewritten. Residual voltages can give rise to "edge persistence," a type of persistence where the contours (edges) of parts of the previous image remain visible.

[0064] Exemplary EPD

[0065] 1 shows a schematic diagram of a pixel 100 of an electro-optic display in accordance with 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, for example, but not limited to, an encapsulated electrophoretic imaging film made of charged pigment particles.

[0066] The 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 surface 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 back 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 back electrode 104.

[0067] 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 defined row and one defined 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 a MOSFET may be interchanged.)

[0068] 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. 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.

[0069] 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 on the column drivers may be changed so that another line of the display is written.

[0070] 2 shows a circuit model of an electro-optic imaging layer 110 disposed between a front electrode 102 and a back 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, front electrode 102, and back electrode 104, including any adhesive layers. Resistor 212 and capacitor 214 may represent the resistance and capacitance of a laminating adhesive layer. Capacitor 216 may represent capacitance that may be formed at an interfacial contact area between layers, such as the interface between the front electrode 102 and back electrode 104, e.g., the interface between the imaging layer and the laminating adhesive layer and / or the laminating adhesive layer and the backplane electrode. The voltage Vi across the imaging film 110 of a pixel may include the residual voltage of the pixel.

[0071] In use, it is desirable for electro-optic displays such as those illustrated in Figures 1 and 2 to update subsequent images without flashing in the background of the display. However, the easy method of using a sky transition in the image to update a background color to a background color (e.g., white / white or black / black) waveform can lead to the accumulation of edge artifacts (e.g., blooming). In black and white electro-optic displays, the edge artifacts can result in the reduced top-off waveforms illustrated in Figures 4A and 4B. However, in electro-optic displays such as electrophoretic displays (EPDs) with color generated using a color filter array (CFA), maintaining color quality and contrast can sometimes be difficult.

[0072] Figure 3 illustrates a cross-sectional view of a CFA-based color EPD according to the subject matter disclosed herein. As shown in Figure 3, a color electrophoretic display (generally designated as 300) includes a backplane 302 having a plurality of pixel electrodes 304. Laminated to this backplane 302 may be an inverted front plane laminate, which may include a monochrome electrophoretic medium layer 306 having black and white extreme optical states, an adhesive layer 308, a color filter array 310 having red, green, and blue areas aligned with the pixel electrodes 304, a substantially transparent conductive layer 312 (typically formed from indium tin oxide), and a front protective layer 314.

[0073] In use, in a CFA-based color EPD, any color area in the image will result in modulation of the pixels behind each CFA element. For example, the best red color is obtained when the red CFA pixel is turned on (e.g., turned white) and the green and blue CFA pixels are turned off (e.g., black). Any blooming into the white pixel can cause a reduction in the chromaticity and brightness of the red color. Algorithms that can identify and reduce the above-mentioned edge artifacts (e.g., blooming) without sacrificing color saturation are described in further detail below.

[0074] EPD drive scheme

[0075] In some applications, the display may utilize a “direct update” drive scheme (“DUDS”). DUDS typically may have fewer, two, or more than two gray levels than grayscale drive schemes (“GSDS”), which can provide transitions between all possible gray levels, but the most important characteristic of DUDS is that, for at least some transitions, the transition is handled by a simple unidirectional drive from an initial gray level to a final gray level, 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 back to the final gray level. In some cases, a transition can be effected by driving from an initial gray level to one extreme optical state, and thus to the opposite extreme optical state, and only then to the final extreme optical state. See, for example, the drive scheme illustrated in Figures 11A and 11B of the aforementioned U.S. Pat. No. 7,012,600. Thus, the present electrophoretic display may have an update time in grayscale mode of about 2-3 times the saturation pulse length ("saturation pulse length" is defined as the time period, at a particular voltage, sufficient to drive the pixels of the display from one extreme optical state to the other), i.e., about 700-900 milliseconds, while DUDS has a maximum update time equal to the saturation pulse length, i.e., about 200-300 milliseconds.

[0076] However, variations in the drive scheme are not limited to differences in the number of gray levels used. For example, drive schemes may be divided into global drive schemes, in which a drive voltage is applied to every pixel in an area (which may be the entire display or some defined portion thereof) to which a global update drive scheme (more precisely referred to as a "global full" or "GC" drive scheme) is applied, and partial update drive schemes, 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 differ from each other), but no drive voltage is applied during zero transitions (in which the initial and final gray levels are the same). An intermediate form forms a drive scheme (designated a "global limited" or "GL" drive scheme) that is similar to the GC drive scheme, except that no drive voltage is applied to pixels undergoing a zero white / white transition. For example, in a display used as an e-book reader that displays black text on a white background, there are many white pixels, particularly within the margins and between the lines of the text, that remain unchanged from one page of text to the next. Therefore, not rewriting these white pixels substantially reduces the apparent "flashing" of display rewrites. However, certain problems remain with this type of GL drive scheme. First, as discussed in detail in some of the aforementioned MEDEOD applications, bistable electro-optic media are typically not perfectly bistable, and pixels placed in one extreme optical state will gradually drift toward intermediate gray levels over a period of minutes to hours. In particular, pixels driven to white will slowly drift toward a light gray color. Thus, in a GL drive scheme, if white pixels are allowed to remain undriven through several page turns during which other white pixels (e.g., those forming part of text characters) are driven, the newly updated white pixels will be slightly lighter than the undriven white pixels, and eventually the difference will be apparent even to an untrained user.

[0077] Second, when an undriven pixel is located adjacent to a pixel being updated, the driving of the driven pixel causes a change in optical state over an area slightly larger than the area of the driven pixel, and this area encroaches on the area of the adjacent pixel, a phenomenon known as “blooming.” Such blooming manifests as an edge effect along the edge where the undriven pixel is located adjacent to the driven pixel. A similar edge effect occurs when using area updates (where only a specific area of the display is updated, e.g., to show an image), except that with area updates, the edge effect occurs at the boundaries of the area being updated. Over time, such edge effects become visually distracting and must be eliminated. Until now, such edge effects (and the effect of color drift in undriven white pixels) have typically been eliminated by using single GC updates at intervals. Unfortunately, using such occasional GC updates can reintroduce the problem of “flashing” updates; in fact, the flashiness of the updates can be accentuated by the fact that flashing updates only occur at long intervals.

[0078] Edge artifact reduction

[0079] In practice, optical edge artifacts within pixels may be reduced using several driving methods or algorithms. For example, first, a pixel transitioning through a white / white transition is identified using adjacent radix pixels transitioning through a non-empty transition. Depending on the number of such radix pixels transitioning through such a transition, a full erase waveform, such as that illustrated in FIG. 4A , may be applied to the pixel transitioning through the white / white transition. Determining the exact number of adjacent radix pixels before the full erase waveform is applied can achieve optimal display quality depending on the specific application. As illustrated in FIG. 4A , the full erase or “F” waveform may include two full long pulses designed to drive the display pixel to black and / or white. For example, a first portion 402 with a duration of 18 frames and a magnitude of 15 volts is configured to drive the display pixel to black, followed by a second portion 404 with a duration of 18 frames and a magnitude of negative 15 volts is configured to drive the display pixel to white.

[0080] Below are some driving methods and / or algorithms that can be employed to reduce pixel edge artifacts.

[0081] Method 1 For all pixels in any order: If pixel graytone transition is not W→W, then apply standard GL transition; Else, If at least SFT adjacent cardinality is not making a white / white to graytone transition OR isColorImagePixel, Then apply FW→W transition; Else, If all four neighboring cardinals have a next graytone of white AND (at least one neighboring cardinal has a current graytone that is not white OR at least one neighboring cardinal is (graytone transition W→W AND isColorImagePixel)), Then apply TW→W transition. Else Then Use an empty (GL)W→W transition. End

[0082] In this drive method, a flag or specifier (e.g., isColorImagePixel) is used to identify display pixels that are color pixels (i.e., color display pixels) in the source image (or alternatively, in the color-mapped image). In some embodiments, the color pixels can be non-white pixels in the source image. In practice, when an EPD is transitioning from a white input image to a solid red area input image, any pixels under the red CFA will likely require a white-to-white transition. Therefore, these pixels will be applied a full clear or FW→W transition waveform, such as that illustrated 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 the number of base or neighboring pixels that have not transitioned through the white-to-white transition. The exact threshold for SFT (e.g., SFT=3 or 2, etc.) may vary and may be determined depending on the specific display conditions. All other pixels that have not transitioned through the white-to-white transition may be applied a globally limited or GL drive scheme or mode white transition (i.e., empty) waveform. Additionally, a T-to-W transition (i.e., rotated T) waveform may be applied to a pixel that is flagged or designated as being a color pixel. For example, if all four neighbors of the pixel have a next graytone of white, and at least one neighbor has a current graytone that is not white, or at least one neighbor has a white / white graytone transition, and the pixel is a color pixel under a CFA, a T white / white transition is applied. It should be understood that the present driving method does not require knowledge of the current waveform state of the current image, but instead requires only the graytone state of the current input image.

[0083] 4B illustrates an exemplary TW→W transition waveform 406. This TW→W transition waveform 406 can include a variable number of rotation pulses 410 with variable locations within the waveform 406 and a variable number of top-off pulses 408 with variable locations within the waveform 406 relative to the rotation pulses 410. In some embodiments, a single top-off pulse 408 corresponds to one frame of driving white with an amplitude of negative 15 volts, and the rotation pulse 410 can include one frame of driving to black at 15 volts followed by one frame of driving to white at negative 15 volts. The rotation pulse 410 can be repeated as illustrated in FIG. 4B for multiple repetitions, and the top-off pulse 408 can be located before, after, and / or between the rotation pulses 410.

[0084] 5, in practice, for all pixels of an electro-optic display, if the graytone transition for a display pixel of the display is not W→W (i.e., white / white), as shown in step 502, then a waveform from a standard GL drive scheme or drive mode is applied, as shown in step 504. Otherwise, in step 506, if at least a SFT number of neighboring cardinal points of this display pixel are not making a graytone transition from white / white or are flagged with the isColorImagePixel specifier (i.e., this particular display pixel is a color pixel in the source image (or alternatively, in a color-mapped image)), then a FW→W transition waveform (e.g., FIG. 4A) is applied (see step 508). Otherwise, in step 510, if all four neighbors of the display pixel have a next graytone of white and at least one neighbor has a current graytone that is not white, or at least one neighbor has a graytone transition white / white and is flagged as an isColorImagePixel pixel (i.e., is a color pixel), then apply the T W->W transition waveform (e.g., see FIG. 4B) (see step 512). Otherwise, in step 514, apply an empty GL W->W transition waveform.

[0085] In some embodiments, the previous image state or pixel state from the previous pixel transition may be added to the algorithm to determine the transition waveform to be applied, as in the drive method or algorithm below and illustrated in Figure 6. This algorithm may be used to filter out pixels that underwent a non-empty transition in the previous image update, and instead do not have the rotation waveform applied.

[0086] Method 2 For all pixels in any order: If pixel graytone transition is not W→W, then apply standard GL transition. Else If at least the SFT adjacent cardinality is not making a white / white to graytone transition OR isColorImagePixel, then apply a FW→W transition. Else If all four neighboring cardinals have a next graytone of white AND (at least one neighboring cardinal has a current graytone that is not white AND the previous pixel transition was empty) OR at least one neighboring cardinal is (graytone transition W→W AND isColorImagePixel), Then apply T W->W transition. Else Then Use an empty (GL)W→W transition. End

[0087] This second method is similar to Method 1 described above, but takes into account the image graytone state from the currently displayed image. For pixels that have undergone a non-empty transition in the currently displayed image, the rotation waveform will not be applied for subsequent images. This method may result in less power consumption for the EPD.

[0088] 6, in practice, for all pixels of an electro-optic display, if the graytone transition for a display pixel of the display is not W→W (i.e., white / white), as shown in step 602, then a waveform from a standard GL drive scheme or drive mode is applied, as shown in step 604. Otherwise, in step 606, if at least an SFT number of neighboring cardinal points of this display pixel are not making a graytone transition from white / white or are flagged with the isColorImagePixel specifier (i.e., this particular display pixel is a color pixel in the source image (or alternatively, in a color-mapped image)), then a FW→W transition waveform (e.g., FIG. 4A) is applied (see step 608). Otherwise, in step 610, if all four neighboring radixes of the display pixel have a next graytone of white, and at least one neighboring radix has a current graytone that is not white, and its previous pixel transition was empty, or at least one neighboring radix has a white / white graytone transition and is flagged as an isColorImagePixel pixel, apply the T W->W transition waveform (e.g., see FIG. 4B) (see step 612). Otherwise, in step 614, apply the empty GL W->W transition waveform.

[0089] In some embodiments, identifying display pixels as color pixels and flagging them with the designator isColorImagePixel preferably occurs before the image is rendered on the display. Referring now to FIG. 7 , identifying color pixels and flagging them with the designator “isColorImagePixel” 704 may occur before the quantization step 708 in a display controller capable of controlling the operation of a bi-stable electro-optic display. In operation, an image or source image 700 may first be processed by a color mapping algorithm 702 associated with the controller. The color mapping algorithm 702 may be configured to process the source image 700 into a color-mapped image 720 to match the colors available on a particular display and achieve an optimal color visual effect on the particular display. Subsequently, color pixels in the color-mapped image 720 may be identified and flagged as isColorImagePixel 704 and fed to the algorithm 710. It should be understood that this identification and flagging occurs before the CFA mapping 706 step and the image dither and quantization 708 step. The algorithm 710 waveforms can then be used and assigned to display pixels to display an image. Waveforms for displaying image 720 can then be sent to EPD 716 in a waveform step 712. In some embodiments, these waveforms 712 can be recycled back to the algorithm 710 to be used as inputs (i.e., waveforms for the current state image 714) to generate waveforms for the next image state.

[0090] It will be apparent to those skilled in the art that numerous 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 whole of the foregoing description is to be interpreted in an illustrative rather than a restrictive sense.

Claims

1. A method for driving an electro-optic display, said method comprising: color mapping a source image to a color-mapped image for said electro-optic display; identifying color pixels from the color-mapped image and flagging the color pixels with a designator; Using color pixel identification data as input for a waveform generation algorithm. A method comprising:

2. The method described in claim 1, further comprising performing color filter array mapping on the color-mapped image.

3. The method described in claim 1, further comprising generating a waveform for a next state image from the waveform generation algorithm.

4. The method of claim 1, further comprising using the generated waveform as a current state image for a next state image.

5. The method of claim 1, wherein one or more rotation pulses are applied to display a plurality of pixels having all four basic adjacent pixels having a gray tone next to white and at least one basic adjacent pixel that is a color display pixel flagged with the designator.

6. The method described in claim 5, wherein each rotation pulse includes multiple repeating sets of one frame of a positive 15 volt pulse and one frame of a negative 15 volt pulse.

7. The method of claim 1, wherein at least one top-off pulse is applied to display a plurality of pixels having all four basic adjacent pixels having the next gray tone of white and at least one basic adjacent pixel that is a color display pixel flagged with the designator.

8. The method described in claim 7, wherein each top-off pulse includes one frame of a negative 15 volt pulse.

9. A method for driving a color electrophoretic display including a color filter array between a viewer and an electrophoretic medium including black particles and white particles, the color electrophoretic display having a plurality of display pixels, the method comprising: color mapping a source image to a color-mapped image for said color electrophoretic display; identifying color display pixels from the source image and flagging the color display pixels with a designator; using said specifier as an input for a waveform generation algorithm to determine whether to apply a blanking waveform when transitioning a color display pixel; A method comprising:

10. The method of claim 9, further comprising performing color filter array mapping on the color-mapped image.

11. The method described in claim 9, further comprising generating a waveform for a next state image from the waveform generation algorithm.

12. The method of claim 9, further comprising using the generated waveform as a current state image for a next state image.

13. The method of claim 9, wherein the full erase white / white waveform includes a first component configured to drive the electrophoretic medium of a color display pixel flagged with the designator to an optical black state, and a second component configured to drive the electrophoretic medium of the color display pixel flagged with the designator to an optical white state.

14. The method of claim 9, wherein one or more rotation pulses are applied to display a plurality of pixels having all four basic adjacent pixels having a gray tone next to white and at least one basic adjacent pixel that is a color display pixel flagged with the designator.

15. The method of claim 14, wherein each rotation pulse includes multiple repeating sets of one frame of a positive 15 volt pulse and one frame of a negative 15 volt pulse.

16. The method of claim 9, wherein at least one top-off pulse is applied to display a plurality of pixels having all four basic adjacent pixels having a gray tone next to white and at least one basic adjacent pixel that is a color display pixel flagged with the designator.

17. The method of claim 16, wherein each top-off pulse comprises one frame of a negative 15 volt pulse.

Images