Driving scheme for improved color gamut in color electrophoretic displays

Abstract

The present invention relates to a method for driving an electro-optical display. More specifically, the present invention relates to a driving method for reducing pixel edge artifacts and / or image residue in an electro-optical display. The present invention provides a waveform for driving an electrophoretic display which includes a color filter between the viewer and the electrophoretic medium. Because the waveform results in each image update passing through a white state before the final state, the overall color gamut is wider and more predictable overall than simply driving an electrophoretic display which includes a color filter with a waveform used for a black and white grayscale display.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 448,870, filed Feb. 28, 2023. The content of all applications, patents, and publications are incorporated by reference in their entirety.

[0002] (Subject matter of the invention) The present invention relates to a method for driving an electro - optical display. More specifically, the present invention relates to a driving method for reducing pixel edge artifacts and / or image retention in an electro - optical display.

Background Art

[0003] An electro - optical display typically has a backplane that provides a plurality of pixel electrodes, each defining one pixel of the display. Conventionally, a large number of pixels, usually a single common electrode extending across the entire display, are provided on the opposite side of the electro - optical medium. Individual pixel electrodes can be driven directly (i.e., a separate conductor can be provided for each pixel electrode) or the pixel electrodes can be driven in an active - matrix - like fashion well - known to those skilled in the backplane art. Since adjacent pixel electrodes are often at different voltages, they must be separated by a gap of finite width between pixels to avoid electrical short - circuits between the electrodes. At first glance, the electro - optical medium overlapping these gaps may appear not to switch when a driving voltage is applied to the pixel electrodes (in fact, this is often true for some non - bistable electro - optical media such as liquid crystals, in which case a black mask is usually provided to hide these non - switching gaps), but in the case of many bistable electro - optical media, the medium overlapping the gaps switches due to a phenomenon known as “blooming”.

[0004] Blooming refers to the tendency for the 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. Excessive blooming should be avoided (for example, in high-resolution active-matrix displays, it is undesirable for the 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), but a controlled amount of blooming is often useful. For example, consider a black-on-white electro-optic display that displays digits using a conventional 7-segment array with 7 directly driven pixel electrodes for each digit. For example, when zero is displayed, 6 segments are turned black. If blooming were absent, the gaps between the 6 pixels would be visible. However, by providing a controlled amount of blooming, as described, for example, in U.S. Patent No. 7,602,374, which is incorporated herein in its entirety, the gaps between pixels can be turned black, resulting in a more visually pleasing digit. However, blooming can lead to a problem called "edge ghosting."

[0005] In monochrome electrophoretic displays, such as those found in many electronic readers, the blooming area is not uniformly white or black, but is typically a transition zone, and as one moves across the blooming area, the color of the medium transitions from white to black through various shades of gray. Thus, edge ghosting is usually not a uniform gray area, but rather an area of ​​changing gray shades, yet it can still be visible and unpleasant, especially since the human eye has the ability to detect gray areas in a monochrome image where each pixel is assumed to be either pure black or pure white. In some cases, asymmetric blooming can contribute to edge ghosting. "Asymmetric blooming" refers to a phenomenon in which blooming is "asymmetric" in some electro-optical media (for example, the copper chromite / titania encapsulated electrophoretic media described in U.S. Patent No. 7,002,728, which is incorporated herein by whole) in that more blooming occurs during the transition from one extreme optical state to the other of a pixel than during the transition in the reverse direction, and in the media described herein, blooming during the transition from black to white is usually greater than that during the transition from white to black.

[0006] Image defects caused by edge ghosting are exacerbated when a color filter array is added on top of a layer of monochrome electrophoretic media, as is done in Kaleido® displays manufactured by E Ink Holdings (Hsin Chu, Taiwan) (Kaleido® displays are formed by directly applying color filters to an electrophoretic media layer formed from microcapsules containing monochrome electrophoretic particles dispersed in a nonpolar solvent; see, for example, U.S. Patent No. 9,170,467 incorporated by reference throughout). In such CFA-EPD displays, edge ghosting can result in different shades of red, green, or blue when a particular pixel is associated with a color filter. Such edge ghosting can result in not only slightly "shifted" red, green, or blue colors, but overall, the edge ghosting phenomenon can result in dithered colors that are different shades from the desired dithered color. Also, for example, when a display switches from a field of monochrome text to a color photograph, edge ghosting can result in a corduroy pattern appearing within a monochrome area. Both of these color edge ghosting phenomena are detrimental to the final product. Therefore, a driving method is needed that also reduces ghosting or blooming effects for both black and white and color images. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 7,602,374 [Overview of the project] [Means for solving the problem]

[0008] (Detailed explanation) The present invention relates to a method for driving an electro-optical display, particularly a bistable electro-optical display, and an apparatus for use in such a method. More specifically, the present invention relates to a driving method that can enable the reduction of "ghosting" and edge effects, as well as the reduction of flashing, in such a display. The present invention is not exclusive, but is particularly intended for use in conjunction with particle-based electrophoretic displays, in which one or more types of charged particles are present in a fluid and moved through the fluid under the influence of an electric field to change the appearance of the display. [Brief explanation of the drawing]

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

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

[0011] [Figure 3] Figure 3 illustrates an encapsulated electrophoretic display that includes a color filter array above capsules containing black and white charged pigment particles.

[0012] [Figure 4] Figure 4 shows a cross-sectional view of an electro-optical display having a color filter array.

[0013] [Figure 5] Figure 5 illustrates the image file processing from RGB image data for display on an encapsulated electrophoretic display with a color filter.

[0014] [Figure 6] Figure 6 illustrates an exemplary waveform configured to reduce blooming and / or ghosting effects within a display pixel.

[0015] [Figure 7] Figure 7 illustrates a tuning method for reducing blooming and / or ghosting phenomena in the EPD.

[0016] [Figure 8] Figure 8 illustrates the differences between GC16, GCC16, and the GCC16 - New driving mode.

[0017] [Figure 9A] Figures 9A - 9C illustrate the reduction of planar ghosting phenomena by using the GCC16 - New mode. [Figure 9B] Figures 9A - 9C illustrate the reduction of planar ghosting phenomena by using the GCC16 - New mode. [Figure 9C] Figures 9A - 9C illustrate the reduction of planar ghosting phenomena by using the GCC16 - New mode.

[0018] [Figure 10] Figure 10 illustrates a significant improvement in differential ghost reduction by using the GCC16 - New mode.

[0019] [Figure 11] Figure 11 illustrates a color gamut improved using the GCC16 - New driving scheme.

[0020] [Figure 12] Figure 12 illustrates the consistency of the color gamut using the GCC16 - New driving scheme regardless of whether the previous state was black or white.

Embodiments for Carrying Out the Invention

[0021] The term “electro-optics” is used herein in its conventional sense in the field of imaging technology, as applied to materials or displays, and refers to a material having a first and second display state in which at least one optical property differs, wherein the material is changed from its first display state to its second display state by the application of an electric field to the material. The optical property is usually color perceptible to the human eye, but may be other optical properties such as optical transmittance, reflectance, luminescence, or, in the case of a display intended for machine reading, pseudocolor in the sense of a change in reflectance at electromagnetic wavelengths outside the visible range.

[0022] The term “gray state” is used herein in its conventional sense in the field of imaging technology, referring to an intermediate state between the two extreme optical states of a pixel, and not necessarily signifying a transition between black and white between these two extreme states. For example, some of E INK’s patents and published applications referenced below describe electrophoretic displays where the extreme states are white and dark blue, with the intermediate “gray state” actually being light blue. In fact, as already described, the change in optical state may not be a change in color at all. The terms “black” and “white” may hereafter 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, e.g., the aforementioned white and dark blue states. The term “monochrome” may hereafter be used to refer to a driving scheme that drives pixels only to the two extreme optical states that do not have an intervening gray state.

[0023] Some electro-optic materials are solid in the sense that they have a solid external surface, but the materials may, and often do, have an internal liquid or gas-filled space. Such displays using solid electro-optic materials may, for convenience, hereafter be referred to as “solid electro-optic displays.” Therefore, the term “solid electro-optic displays” includes rotating two-color member displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

[0024] The terms “bistable” and “bistable” are used herein in their conventional sense in the art and refer to a display having a display element having a first and second display state having at least one different optical property, such that after any given element is driven by a finite-duration addressing pulse, it takes on either the first or second display state, and after the addressing pulse has ended, the state continues 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. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of grayscale 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. This type of display is properly called “multistable” rather than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0025] The term “impulse” is used herein in its conventional sense as the integral of voltage over time. However, some bistable electro-optic media act as charge transducers, and in the case of such media, an alternative definition of impulse, namely the integral of current over time (equal to the total charge applied), may be used. 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.

[0026] Much of the following discussion will focus on methods for driving one or more pixels of an electro-optical display through transitions 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 describe the entire curve of voltage over time used to influence a transition from one particular initial gray level to a particular final gray level. Typically, such a waveform will consist of multiple waveform elements. If these elements are essentially rectangular (i.e., a given element consists of the application of a constant voltage over a period of time), the element may be called a “pulse” or “driving pulse.” The term “driving scheme” refers to a set of waveforms sufficient to influence all possible transitions between gray levels for a particular display. A display may utilize more than one driving scheme. For example, U.S. Patent No. 7,012,600, mentioned above, teaches that a driving scheme may need to be modified depending on parameters such as the temperature of the display or the time it has been operating during its lifetime, and therefore a display may be provided with multiple different driving schemes for use at different temperatures, etc. The set of driving schemes used in this manner may be referred to as the “associated driving scheme set.” Furthermore, as described in some of the aforementioned MEDEOD applications, it is also possible to use more than one drive scheme simultaneously within different areas of the same display, and the set of drive schemes used in this form may be referred to as a “set of simultaneous drive schemes.”

[0027] Several types of electro-optical displays are known. One type of electro-optical display is the rotating dicolor member type, as described, for example, in U.S. Patents 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 dicolor ball” display, but in some of the patents mentioned above, the rotating member is not spherical, so the term “rotating dicolor member” is preferred as it is more accurate). Such displays use a number of small bodies (usually spherical or cylindrical) having two or more segments with different optical properties and an internal dipole. These bodies are suspended within vacuoles filled with liquid in a matrix, and the vacuoles are filled with liquid so that the bodies can rotate freely. The appearance of the display is changed by applying an electric field to them, thereby rotating the bodies to various positions and varying which parts of the bodies are visible through the viewing surface. This type of electro-optical medium is usually bistable.

[0028] Another type of electro-optical display uses an electrochromic medium in the form of a nanochromic film, which consists of an electrode at least partially formed from a semiconductor metal oxide and a plurality of color-reversibly changing dye molecules attached to the electrode. See, for example, O'Regan, B., et al., Nature 1991, 353, 737 and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0029] Another type of electro-optical 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 an electrowetting display can be made bistable.

[0030] One type of electro-optical display that has been the subject of intense research and development for many years is the particle-based electrophoretic display, in which multiple charged particles move through a fluid under the influence of an electric field. When compared to liquid crystal displays, electrophoretic displays can possess attributes such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. Nevertheless, problems associated with the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in an unsatisfactory usable lifespan for these displays.

[0031] 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 a gaseous fluid (see, for example, 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). Similarly, see U.S. Patents 7,321,459 and 7,236,291. Such gas-based electrophoretic media are considered susceptible to the same types of problems as liquid-based electrophoretic media due to particle sedimentation when used in orientations that allow such sedimentation, for example, in signs where the media is positioned in a vertical plane. In fact, particle sedimentation is considered a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media due to the lower viscosity of gaseous suspension fluids compared to the viscosity of liquids, which allows for faster sedimentation of electrophoretic particles.

[0032] Numerous patents and applications, assigned to or filed in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, describe various techniques used in encapsulated electrophoretic media and other electro-optical media. Such encapsulated media comprise numerous small capsules, each comprising an inner phase containing electrophoretically mobile particles in a fluid medium, and a capsule wall surrounding the inner phase. Typically, the capsules are held within a polymer binder, forming a tightly packed layer positioned between two electrodes. The techniques described in these patents and applications include:

[0033] (a) Electrophoretic particles, fluids, and fluid additives (see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814)

[0034] (b) Capsules, binders, and encapsulation processes (see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719)

[0035] (c) Microcell structures, wall materials, and methods for forming microcells (see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906)

[0036] (d) Methods for filling and sealing microcells (see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088)

[0037] (e) Films and subassemblies containing electro-optical materials (see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564)

[0038] (f) Backplanes, adhesive layers, and other auxiliary layers, and methods used in displays (see, for example, U.S. Patents No. 7,116,318 and 7,535,624)

[0039] (g) Color formation and color adjustment (see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564)

[0040] (h) Application of the display (see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348)

[0041] (i) Non-electrophoretic displays as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160, as well as applications of non-display encapsulation and microcell technologies (see, for example, U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710).

[0042] (j) Methods for driving a display (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, 7,2 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,No. 314, and U.S. Patent Application Publications No. 2003 / 0102858, 2004 / 0246562, 2005 / 0253777, 2007 / 0070032, 2007 / 0076289, 2007 / 0091418, 2007 / 0103427, 2007 / 0176912, 2007 / 0296452, 2008 / 0024429, 2008 / 0024482, 2008 / 0136774, 2008 / 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 issues 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).

[0043] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules within an encapsulated electrophoretic medium are replaced with a continuous phase, thus 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 within such a polymer-dispersed electrophoretic display can be considered capsules or microcapsules even if the discrete capsule membrane is not associated with each individual droplet. See, for example, Patent No. 2002 / 0131147 mentioned above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a variant of encapsulated electrophoretic media.

[0044] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged particles and suspension fluids are not encapsulated within microcapsules, but instead are held within a carrier medium, such as a polymer film, containing multiple cavities. See, for example, International Patent Application Publication WO02 / 01281 and Published U.S. Patent Application 2002 / 0075556 (both assigned to SiPix Imaging, Inc.).

[0045] Many of the aforementioned E INK and MIT patents and applications also consider microcell electrophoretic displays and polymer-dispersed electrophoretic displays. The term “encapsulated electrophoretic display” can refer to all such display types, and this can also be described collectively as “microcavity electrophoretic displays” to generalize across wall configurations.

[0046] Another type of electro-optical 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.

[0047] Other types of electro-optical materials can also be used. Of particular note is the bistable ferroelectric liquid crystal display (FLC), which is known in the art and exhibits residual voltage behavior.

[0048] Electrophoretic media are opaque (for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and can operate in reflective mode. However, some electrophoretic displays can be configured to operate in a so-called "shielding mode," where one display state is substantially opaque and the other is light-transmitting. See, for example, U.S. Patents 6,130,774 and 6,172,798, and U.S. Patents 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectric displays, which are similar to electrophoretic displays but rely on variations in electric field intensity, can operate in a similar mode. See, for example, U.S. Patent 4,418,346. Other types of electro-optical displays may also be capable of operating in shielding mode.

[0049] High-resolution displays may include individual pixels that are addressable without interference from adjacent pixels. One way to obtain such pixels is to provide an array of nonlinear elements, such as transistors or diodes, and produce an "active matrix" display with at least one nonlinear element associated with each pixel. An addressing electrode or pixel electrode that addresses a single pixel is connected to a suitable 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, and although this arrangement will be assumed in the following description, it is essentially arbitrary, and the pixel electrode may also be connected to the source of the transistor. In a high-resolution array, pixels may be arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of 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 if desired.

[0050] The display can be written in a row-by-row manner. Row electrodes are connected to row drivers, which can apply a voltage to the selected row electrodes such that all transistors in the selected row are conductive, while voltages can apply to all other rows such that all transistors in those unselected rows remain nonconductive. Column electrodes are connected to column drivers, which can apply voltages to various column electrodes such that voltages are selected to drive the pixels in the selected rows to their desired optical states (the aforementioned voltages are provided on the opposite side of the nonlinear array of the electro-optic medium and on a common front electrode that may extend throughout the entire display. 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") means there is no voltage difference to another voltage). After a pre-selected 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.

[0051] However, during use, certain waveforms can generate residual voltages in the pixels of an electro-optical display, and as is evident from the above discussion, these residual voltages produce several unwanted optical effects and are generally undesirable.

[0052] As presented herein, “shift” in an optical state associated with an addressing pulse refers to a situation where the initial application of a particular addressing pulse to an electro-optical display results in a first optical state (e.g., a first gray tone), and subsequent application of the same addressing pulse to the electro-optical display results in a second optical state (e.g., a second gray tone). Since the voltage applied to the pixels of the electro-optical display during the application of the addressing pulse includes the sum of the residual voltage and the voltage of the addressing pulse, the residual voltage can cause a shift in the optical state.

[0053] "Drift" in the optical state of a display over time refers to a situation where the optical state of an electro-optical display changes while the display is stationary (for example, during periods when no addressing pulses are applied to the display). Since the optical state of a pixel can depend on the residual voltage of the pixel, and the residual voltage of a pixel can decay over time, residual voltage can cause drift in the optical state.

[0054] As discussed above, “ghosting” refers to a situation where, after an electro-optical display has been rewritten, traces of the previous (one or more) image remain visible. Residual voltage can cause “edge ghosting,” a type of ghosting where some of the contours (edges) of the previous image remain visible.

[0055] Exemplary CFA-EPD

[0056] Figure 1 shows a schematic diagram of a pixel 100 of an electro-optical display according to the subject matter presented herein. The pixel 100 may include an imaging film 110. In some embodiments, the imaging film 110 may be bistable. In some embodiments, the imaging film 110 may include an encapsulated electrophoretic imaging film, which may, for example, include charged dye particles. For the most part of the following description, the imaging film 110 includes microcapsules dispersed in a polymer binder (i.e., a solid imaging layer), and the microcapsules include black and white charged pigments dispersed in a nonpolar solvent.

[0057] The imaging film 110 may be positioned 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 be formed between the front electrode 102 and the back electrode 104.

[0058] Pixel 100 may be one of several pixels. Multiple pixels may be arranged in a two-dimensional array of rows and columns, forming 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 pixel matrix may be an "active matrix" in which each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 may be coupled between a back-board electrode 104 and an addressing electrode 108. In some embodiments, the nonlinear element 120 may include a diode and / or a transistor, including a MOSFET. The drain (or source) of the MOSFET may be coupled to the back-board electrode 104, the source (or drain) of the MOSFET may be coupled to the addressing electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106 configured to control the activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET coupled to the back substrate electrode 104 will be referred to as the MOSFET drain, and the terminal of the MOSFET coupled to the addressing electrode 108 will be referred to as the MOSFET source. However, those skilled in the art will recognize that in some embodiments, the source and drain of the MOSFET may be interchangeable.)

[0059] In some embodiments of the active matrix, the addressing electrodes 108 of all pixels in each column may be connected to the same column electrode, and the driver electrodes 106 of all pixels in each row may be connected to the same row electrode. The row electrode may be connected to a row driver, which can select one or more rows of pixels by applying a voltage to the selected row electrode sufficient to activate the nonlinear element 120 of all pixels 100 in the selected (one or more) rows. The column electrode may be connected to a column driver, which can apply a voltage suitable for driving the pixels to a desired optical state to the addressing electrode 106 of the selected (activated) pixels. The voltage applied to the addressing electrode 108 may be relative to the voltage applied to the front substrate electrode 102 of the pixel (e.g., a voltage of about 0 volts). In some embodiments, the front substrate electrodes 102 of all pixels in the active matrix may be coupled to a common electrode.

[0060] In some embodiments, the pixels 100 of the active matrix can be written in a row-by-row manner. For example, a row of pixels may be selected by a row driver, and a voltage corresponding to a desired optical state for the row of pixels may be applied to the pixel by a column driver. After a pre-selected interval known as the "line address time," the selected row may be deselected, another row may be selected, and the voltage on the column driver may be changed so that another row of the display is written. In some embodiments, row-by-row addressing is controlled by a controller, which may be a commercially produced microchip that is electrically coupled to the column driver and row selector (known as a gate driver) and adjusts the application of the correct electrical voltage to the pixels 100.

[0061] Figure 2 shows a circuit model of an electro-optic imaging layer 110 positioned between the front electrode 102 and the back electrode 104, according to the subject matter presented herein. Resistors 202 and capacitors 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, the front electrode 102 and the back electrode 104, including any adhesive layer. Resistors 212 and capacitors 214 may represent the resistance and capacitance of the laminated adhesive layer. Capacitor 216 may represent capacitance that can be formed at interlayer interface contact areas between the front electrode 102 and the back electrode 104, for example, at the interface between the imaging layer and the laminated adhesive layer and / or between the laminated adhesive layer and the back substrate electrode. The voltage Vi across the pixel imaging film 110 may include the residual voltage of the pixel.

[0062] When in use, it is desirable that electro-optic displays, such as those illustrated in Figures 1 and 2, update subsequent images without flashing the display background. However, a simple method using empty transitions in the image to update a background color (e.g., white to white or black to black) waveform can lead to the accumulation of edge artifacts (e.g., blooming). In black and white electro-optic displays, edge artifacts can be reduced by top-off waveforms. However, in electro-optic displays such as electrophoretic displays (EPDs) with colors produced using color filter arrays (CFAs), maintaining color quality and contrast can sometimes be difficult.

[0063] Display devices can be constructed using the electrophoretic fluid of the present invention in several ways known in the prior art. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into a microcell structure and then sealed with a polymer layer. The microcapsules or microcell layers can be coated or embossed onto a plastic substrate or film that will bear a transparent coating of conductive material. This assembly can be laminated to a back substrate that will bear the pixel electrodes using a conductive adhesive. Alternatively, the electrophoretic fluid can be directly distributed onto a thin open-cell grid arranged on a back substrate containing the active matrix of the pixel electrodes. The filled grid can then be top-sealed with an integrated protective sheet / light-transmitting electrode.

[0064] With respect to Figure 3, the electrophoretic display 301 typically includes an upper transparent electrode 310, an electrophoretic medium 320, and a bottom electrode 330, the bottom electrode 330 being a pixel electrode of an active matrix of pixels controlled by thin-film transistors (TFTs), which are often discussed in more detail above. The electrophoretic medium 320 contains at least one electrophoretic particle 321, however, a second electrophoretic particle 322, or a third electrophoretic particle 323, a fourth electrophoretic particle 324, or more particles are feasible. The electrophoretic medium 320 typically contains a solvent such as isoparaffin and may also contain dispersed polymers and charge control agents to promote state stability, e.g., bistability, i.e., the ability to maintain an electro-optical state without inputting any additional energy.

[0065] The electrophoretic medium 320 is typically compartmentalized by microcapsules 326, but alternative structures such as microcells (not shown) may be used. The entire display stack is typically placed on a substrate 350, which can be rigid or flexible. The electrophoretic display 301 also typically includes a protective layer 360, which may simply protect the upper electrode 310 from damage or enclose the entire electrophoretic display 301 to prevent the ingress of water, etc. The electrophoretic display 301 may also include one or more adhesive layers 340 and 370, as needed. In some cases, a color filter layer 375 may be applied to the adhesive layer 370, as described below with respect to Figure 4. The structure and components of electrophoretic displays, dyes, adhesives, electrode materials, etc., are described in numerous patents and patent applications published by E Ink Corporation, including U.S. Patent Nos. 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564, all of which are incorporated herein by reference in their entirety.

[0066] Figure 4 illustrates a cross-sectional view of a CFA-based color electrophoretic display (EPD) according to the subject matter disclosed herein. As shown in Figure 4, the color electrophoretic display (generally designated as 400) comprises a back substrate 402 carrying a plurality of pixel electrodes 404. A double-peel front substrate laminate may be laminated to this back substrate 402, and this double-peel front substrate laminate may comprise an electrophoretic medium layer 406 having black and white extreme optical states and an adhesive layer 408 to be exposed after removal of a release sheet (not shown). A color filter array 410 having red, green, and blue areas matched to the pixel electrodes 404 can be applied directly to the adhesive layer 408, for example, using an inkjet printer. After the color filter array 410 is applied to the adhesive layer 408, a substantially transparent conductive layer 412 (typically formed from indium tin oxide sputtered onto a thin film of PET) and a front protective layer 414 protect the substantially transparent conductive layer 412 and provide a moisture barrier.

[0067] A CFA-based color EPD400 will produce all colors by modulating the pixels behind each CFA element. For example, the best red is obtained when the red CFA pixel is turned on (e.g., changed to white) and the green and blue CFA pixels are turned off (e.g., black). It is understood that the color subpixel pattern may include a certain amount of white, i.e., uncolored area, in order to enhance the white state of the CFA-based color EPD400. For example, each pixel area may contain red, green, blue, and white subpixels. (Typically, each colored subpixel is approximately the size of the pixel electrode on the back substrate, however, a color filter element spanning more than one pixel electrode may be selected.) By using front light guides and the addition of low-power LED lighting, the resulting display brightness can be increased sufficiently to achieve a good color gamut using normal indoor lighting.

[0068] A method for converting a standard RGB image, such as one used for display on an LCD monitor, to a CFA-EPD image is described here with reference to Figure 5. The system includes a storage medium capable of storing image data for a certain length of time, e.g., non-transient memory, e.g., a recordable magnetic medium or random-access memory. Image data typically includes a two-dimensional image in which colors are assigned to specific locations in the xy plane, i.e., pixels. Often, image data is in a raster format that identifies each pixel by row and column location. In practice, RGB image data can be in one of several compressed image formats, such as jpeg, TIFF, png, pdf, or some other formats. It is understood that compressed files can be decompressed during conversion. When RGB image data is described as containing 4 bits or more of RGB color, the colors correspond to a color gamut of at least 4096 colors, i.e., each red, green, or blue pixel has 16 or more gray levels (2 4=16), which is understood to mean that there are 4 bits per channel. In some technical literature, this is assumed to be 12-bit color (2 12 This can be referred to as =4096 (16×16×16=4096). A suitable lookup table can be constructed for higher color levels, such as 5, 6, or 8 bits per channel color.

[0069] The RGB image data begins in a first storage medium 510 which is operably coupled to the processor 530 so that the processor 530 can access the RGB image data. The processor 530 may be a specialized processor such as the i.MX6 series image processor from NXP Semiconductors (Eindhoven, The Netherlands), or the processor 530 may be a personal computer or other computing platform configured to resize, modify, and reassign pixel colors to the RGB image data. As part of the reassignment calculation, the processor 530 will access a lookup table (LUT) 520 which correlates 4 bits or more of RGB color to a specific combination of at least three non-white subpixels and white subpixels (subpixels have only "on" and "off" states). If necessary, upon receiving RGB image data from the first storage medium 510, the processor resizes the image data based on the size of the display pixels, which include at least three non-white subpixels and white subpixels, each of which has a different color, and each subpixel has only an "on" state and an "off" state (for example, if at least three non-white subpixels and white subpixels have a larger area than the underlying pixel electrodes driving the transition, these pixels may be referred to as "super pixels." For example, the display medium directly beneath a color filter array may have 300 pixel electrodes per inch, however each colored subpixel in the color filter array may actually provide only 40 super pixels per inch. Therefore, "super pixels" should be interpreted as a subset of "pixels").

[0070] In many cases, RGB image data will contain much more information about pixels than can be displayed on a screen. This also occurs, for example, when converting image data from a high-resolution digital camera where much more information exists across the image than can be displayed. Therefore, the first step would be to resize the RGB image to fit the number of available pixels / superpixels. Typically, this step involves binning a portion of the RGB data to correspond to the number and location of superpixels. In some embodiments, the RGB colors of the binned data would be averaged and assigned RGB colors to the binned data, or the median color could be identified among the resized RGB image data. The palette can be corrected for white and black points as desired, or distorted to address color bias or shift. After resizing, the resized RGB data can be gamma corrected and / or sharpened using known techniques. For example, the resized data can be sharpened using algorithms with the Laplacian operator. Once these steps are complete, the processor 530 will match the resized data colors to the measured superpixel colors by comparing the colors of the resized data with the lookup table 520. Using the lookup table, the processor 530 assigns a color to each unit of the resized RGB data that corresponds to a specific combination of colored subpixels. In other embodiments, the measured specific combinations are converted to L*a*b* data, which is then mapped into the sRGB space using a known algorithm.

[0071] Once the processor 530 assigns a specific combination to the resized data, the data is written to a third storage medium 540, where it is held until it is finally sent to an image driver 550, which coordinates the activation of various scan and data lines responsible for switching the electro-optical pixels of the active matrix 580 from an "off" state to an "on" state and producing an image. Figure 5 shows the active matrix 580, but it is understood that the principle of the present invention can be used to convert colors for display on an electro-optical medium driven by a partitioned display, such as an indirectly driven display.

[0072] Simultaneously, the processor 530 assigns new colors to the resized data, and the processor 530 may also dither the resized data to improve the perception of the final image. Such dithering is well known in printing technology. When a dithered image is viewed at a sufficient distance, the individual colored pixels merge into a perceived uniform color by the human visual system. Due to the trade-off between color depth and spatial resolution, a dithered image has a characteristic graininess when viewed at close range, compared to an image where the available color palette at each pixel location has the same depth as required to render the image as a whole on the display. However, dithering often reduces the presence of color banding, which is more undesirable than graininess, especially when viewed at a distance.

[0073] Algorithms for assigning specific colors to specific pixels have been developed to avoid undesirable patterns and textures in images rendered by dithering. Such algorithms may involve error diffusion, a technique in which errors (i.e., quantization residuals) arising from the difference between the color requested at a given pixel and the nearest color in the palette per pixel are dispersed to neighboring pixels that have not yet been processed. European Patent No. 0677950 describes such a technique in detail, while U.S. Patent No. 5,880,857 describes metrics for comparing dithering techniques. U.S. Patent No. 5,880,857 is incorporated herein by reference in its entirety. This set of points can be transformed arbitrarily to facilitate dithering used to render colored images. For example, the measured sRGB values ​​of primary colors can be moved closer to the target point in source space. The target image in source space can also be transformed, for example, by being linearly scaled to correspond to the measured black and white states of the display (i.e., each point in the image can be normalized to the measured dynamic range of the display). Following such a transformation, three-dimensional color image dithering may be performed using algorithms known in the art, such as Floyd-Steinberg dithering. Other dithering techniques, such as blue noise mask dithering, may also be used.

[0074] It has been observed that the measured color of a particular combination of subpixels can vary with temperature. In the case of electro-optic displays including electrophoretic media, temperature variations can arise from changes in white state reflectance with temperature. This deviation may require the lookup table to associate different sets of RGB colors with specific combinations of subpixel colors. Therefore, in some embodiments, the CFA-EPD400 includes a temperature sensor 590. Temperature readings from the temperature sensor 590 may be the basis for selecting a temperature-dependent lookup table. In alternative embodiments, the electro-optic medium may be limited to 1-bit subpixel colors at some temperature ranges, but may allow for higher color levels at other temperatures. In these embodiments, the lookup table may be expanded based on temperature. For example, if an electrophoretic display has 2-bit subpixels at room temperature but only 1-bit subpixels at high temperatures, the temperature data can cause the processor to switch from a lookup table that maps 256 specific combinations of subpixel colors onto an RGB palette to the lookup table described above, i.e., a lookup table that maps 166 specific combinations of subpixel colors onto an RGB palette.

[0075] Naturally, blooming and pixel merging still affect the final image of the CFA-EPD400. Importantly, any blooming to white pixels (if present) can cause a reduction in red chromaticity and brightness. Furthermore, the rendered image may be sensitive to differential blooming ghosting. Also, the fringe field of switching pixels can affect the optical state of neighboring pixels. For example, in a dithered image, there is a pixel-level size pattern, and pixels transition to entirely different optical states. Alternatively, pixels can transition from different initial optical states to the same optical state using different waveforms, resulting in pixels suffering different blooming artifacts, and they can transition to slightly different final brightness (e.g., ghosting effect). All of these blooming artifacts can cause differential blooming ghosting. Algorithms that can identify and reduce the edge artifacts (e.g., ghosting and / or blooming) described above are explained in more detail below.

[0076] EPD drive scheme

[0077] In many cases, basic color control is a matter of delivering the correct voltage to achieve the desired grayscale in a given color subpixel. Nevertheless, the driving scheme must consider not only the final gray level, but also the grayscale state of the pixel immediately before (or earlier than) the update, the length of the update time, and the "flashing effect" of the update. With regard to grayscale (black / white) driving, the driving scheme can be divided into a global driving scheme (more precisely, referred to as a "globally complete" or "GC" driving scheme) where the driving voltage is applied to all pixels within the area to which a global update driving scheme is applied (which may be the entire display or several defined parts thereof), and a partial update / direct update driving scheme ("DU" driving scheme) where the driving voltage is applied only to pixels undergoing non-zero transitions (i.e., transitions where the initial gray level and the final gray level are different from each other), but no driving voltage is applied to any pixels within the area undergoing zero transitions (where the initial gray level and the final gray level are the same). For administrative purposes, drive schemes may also be labeled using the number of gray levels available, which depends on the memory and processing capacity of the drive electronics, such as the controller. Thus, a GC scheme for 3-bit drive is GC-8, and a GC scheme for 4-bit drive is GC-16. In some cases, a lower bit level controller is used, even though all other components (electrophoretic medium, front electrode, back substrate) are the same, due to cost or power requirements.

[0078] Furthermore, there exists an intermediate drive scheme (designated as a "global limit" or "GL" drive scheme) which is similar to a GC drive scheme except that no drive voltage is applied to pixels undergoing zero transitions, such as white-to-white or black-to-black transitions, but all other pixels in the area undergo a full GC update. For example, in a display used as an e-book reader, i.e., displaying black text on a white background, there are many white pixels, particularly in the margins and between lines of text that remain unchanged from page one to the next. Therefore, not rewriting these white pixels substantially reduces the apparent "flashing effect" of display rewriting. However, some problems remain in this type of GL drive scheme. Firstly, as discussed in detail in some of the aforementioned MEDEOD applications, bistable electro-optical media are not usually perfectly bistable, and pixels placed in one extreme optical state gradually drift towards an intermediate gray level over a period of several minutes to several hours. In particular, the white pixels being driven slowly drift towards a lighter gray color. Therefore, if a GL driving scheme allows white pixels to remain undriven through several page turns, other white pixels (e.g., pixels forming parts of text characters) will be driven during that time, and the newly updated white pixels will be slightly brighter than the undriven white pixels, and eventually, the difference will be obvious even to an untrained user. Secondly, when an undriven pixel is located adjacent to an updated pixel, the driving of the driven pixel causes a change in the 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 appears as an edge effect along the edge where the undriven pixel is located adjacent to the driven pixel.Similar edge effects occur when using region updates (where only a specific area of ​​the display is updated to show an image), except that in the case of region updates, the edge effect occurs at the boundary of the area being updated. Over time, such edge effects can become visually distracting and must be eliminated, for example, using appropriate GC updates. Historically, such edge effects (and the effect of color drift in undriven white pixels) have typically been eliminated by using a single GC update at intervals, for example, after 4 updates, 6 updates, 8 updates, 12 updates, or 20 updates. Unfortunately, using GC updates at intervals reintroduces the "flushing" update problem, and in fact, the flashing effect of updates can be amplified by the fact that only flashing updates occur at long intervals, which can be distracting for some users.

[0079] When electrophoretic displays control color through color filters, as described above, color drift becomes even more pronounced, prompting CFA-EPDs to perform GC updates more frequently than "typical" EPDs that are grayscale only. In addition, in electronic readers with color photographs, when switching between black and white and CFA-color images, blooming due to the previous grayscale state will appear as a very noticeable ghosting phenomenon. Indeed, many CFA-EPDs have a separate button on the screen specifically for performing a GC update to remove ghosting and improve dithered colors. In many cases, the increased sensitivity to ghosting / blooming / edge effects necessitates further modifications to existing black and white driving schemes. In such cases, the driving scheme is often labeled with an additional "C" for Color. Thus, the GC16 waveform becomes GCC16 when modified for use with CFA-EPDs.

[0080] Ghosting and / or Blooming Reduction Waveform for CFA EPD

[0081] Shown in Figure 6 is an exemplary waveform 600 tuned for minimal planar ghosting by adjusting the leading pulse portion using the p1 parameter (the waveform is a series of voltages applied to a given display pixel over several active matrix update counts, i.e., "frames." The voltages are relative, but it is understood that a typical waveform voltage is ±15V, corresponding to the voltage difference between the top-light transparent electrode and the pixel electrode). The waveform in Figure 6 could be, for example, part of a 4-bit driving scheme, i.e., 16 different gray levels would be available. As shown in Figure 6, the solid gray bars represent the start (or end) time of the voltage pulse applied to the display pixel, while the dotted area represents the potential time width of the pulse, and the dotted area can vary from zero to multiple frames. The waveform 600 may have, for example, a first leading pulse portion that drives the display pixel to a first extreme optical state using a negative magnitude top-off pulse. Next, an intermediate pulse may be applied, consisting of two positive top-off pulses, which drives the display pixel to an optical limit opposite to the optical limit of the preceding pulse portion. The two pulses of the intermediate pulse portion may be separated by a gap (V=0V) of duration gm2, where gm2 can be variably defined depending on the application requirements. Furthermore, a set pulse portion may follow the intermediate pulse portion. The set pulse portion may include two negative top-off pulses opposite to the top-off pulses of the intermediate pulse portion. The set pulse portion can be designed to drive the display pixel to an optical limit opposite to the optical limit of the intermediate pulse portion. The two negative top-off pulses of the set pulse portion may be separated by a gap gm3, where gm3 can be variably defined depending on the application requirements.

[0082] An embodiment of a tuning method 700 for minimizing differential blooming using the waveform 600 of Figure 6 is shown in Figure 7. Starting with a set of GC16 waveforms for driving black and white gray levels, the tuning is performed to compensate for the CFA interaction as described above, thereby producing GCC16. However, with respect to the new waveform set, all parameters defining the set pulse for gray-tone transitions (i.e., the last part of the waveform) are replaced with a tuning step from white to gray tone (e.g., gray tone setting known as GTP tuning), which is suitable for driving from white pixels to the desired gray level. Ghosting tuning is then performed by tuning the width of the preceding pulse while leaving the set pulse defined by the white / gray tone waveform. Next, by varying p1 and ga1 (i.e., as shown in Figure 6), "flushing" of transitions (where the pixel is required to transition through the white state) can be reduced. Thus, p1 and ga1 are simplified to improve overall performance (see Figure 8). Naturally, the central pulse remains important for DC balance, and to minimize differential blooming, the ink needs to compensate for the transition to the white state by, for example, temporarily driving to black during the intermediate pulse (the DC-balanced waveform has zero total impulses (voltage × time)). Nevertheless, the p1 parameter is fixed so as not to remove more than two-thirds of the intermediate pulse. The resulting driving scheme is known as GCC16-New. Essentially, by setting all set pulses from white to gray tones in the GCC16, each pixel "passes through" the white state on its way to the final display state, even when the actual transition is gray tone 1 -> gray tone 2.

[0083] Of particular note is that the simplified GCC16-New waveform, resulting from modifying the GCC16 waveform by shifting the set pulse from GCC16 and allowing p1 and ga1 to occupy some portion of the central pulse, is faster and flashes less. While the exact reason is not entirely clear, it is theorized that CFA in combination with excess illumination from front light "washes away" some of the visual "sharpness" that would otherwise be covered only by high-contrast black and white pigments, making the difference between the GCC16 drive configuration and the GCC16-New waveform less visually pronounced, but enabling shorter waveforms and faster updates. In addition, as will be explained below, the GCC16-New waveform may also have a more reliable color gamut that is substantially independent of the pixel's previous state.

[0084] Figure 8 illustrates different drive modes GC16, GCC16, and GCC16-New for comparison. For each drive mode, 16 drive schemes for the corresponding 7th gray level are illustrated, with the leftmost being the darkest state and the rightmost being the brightest (i.e., most colored) state. The GCC16-New mode is simpler and faster to implement to achieve minimal differential blooming and planar ghosting without introducing major changes to the current software and / or color rendering algorithm (described above). The GCC16-New drive scheme also improves gray-tone-to-gray-tone transition appearance and minimizes differential blooming and ghosting compared to GC16 and GCC16. Furthermore, the tuning method 700 presented in Figure 7 also reduces the short-circuit time in the center of the waveform required in the GCC16 waveform (allowing the pixel electrode and upper electrode to balance). Method 700 also minimizes the white state difference between GCC16 mode and GC16 / GL16 mode, further reducing ghosting caused by the white-to-white transition in ingL16 mode when switching between GCC16 mode and GL16 mode. Such GC16 / GL16 to GCC16 and vice versa is particularly common when displaying timetables on outdoor signs, which may typically involve providing a black and white text table, then a full-color image (i.e., an advertisement), and back again.

[0085] Figures 9A and 9B illustrate that the GCC16-New mode, when used in a grayscale electrophoretic display (i.e., without a color filter), successfully reduces planar ghosting compared to the GC16 and GCC16 modes. When coupled with CFA, as shown in Figure 9C, planar ghosting is not as pronounced, but when the color is dithered, edge ghosting can cause color shifts, particularly in skin tones, where the human eye is very sensitive to shading.

[0086] The mechanism for this color shift is more clearly visible under a microscope, as shown in Figure 10. Comparing the filling patterns for a dark green field (i.e., filled with red, blue, and white subpixels) arising from a white field (WS) and a black field (DS) using GCC16, it can be confirmed that a color shift exists depending on whether the new state started from WS or DS, and this is carried over from the GC16 waveform into the set pulse (see left panel of Figure 10). In contrast, the GCC16-New waveform incorporates a set pulse from white to gray tones, which essentially leads to the final transition through the white state, even for gray-tone updates. As shown in the upper right of Figure 9, the green filling coefficient is much more stable whether starting from WS and DS, and therefore the final color is more stable.

[0087] The improved color consistency resulting from the GCC16-New waveform was confirmed across all colors by activating the CFA-EPD device through a series of color pattern image updates under a calibrated optical bench. The resulting measurements can be used to construct a gamut plot, as shown in Figure 11. As shown in Figure 11, when the GCC16 waveform is used, the resulting gamut when starting from a white state (i.e., all pixels are driven to white before updating) is significantly larger than the gamut when starting from a dark state. This result is not surprising when viewed in light of the microscopic image in Figure 10. However, when implementing the GCC16-New driving scheme, the two gamuts (i.e., from WS and from DS) are virtually indistinguishable. However, as shown in Figure 12, this is not simply a matter of averaging the two gamuts (i.e., GCC16 from WS and GCC16 from DS). Implementing the GCC16-New waveform brings the gamut from DS to gray tones into the gamut from WS to gray tones, with respect to the most part. The result is better and more true color performance for electrophoretic displays that include a color filter above the monochrome capsule layer.

[0088] It will be apparent to those skilled in the art that numerous modifications and alterations can be made to the specific embodiments of the invention described above without departing from the scope of the present invention. Accordingly, the entire preceding description should be interpreted in an illustrative rather than restrictive sense.

Claims

1. A method for driving an electrophoretic display comprising a color filter layer between a viewer and a layer of electrophoretic medium, wherein the electrophoretic medium comprises black and white charged particles and is addressed by a plurality of display pixels, and the method is Updating the display using the first image, Updating the display using a second image, wherein at least some of the plurality of display pixels are updated with the second image using a waveform comprising a lead pulse, an intermediate pulse, and a set pulse, the intermediate pulse and the set pulse driving the white particles to be adjacent to the color filter layer before a desired color state of the second image is achieved. Methods that include...

2. The method according to claim 1, wherein the desired color state of the second image is not a color state in which the white particles are adjacent to the color filter layer.

3. The method according to claim 1, wherein the intermediate pulse drives the black particles to be adjacent to the color filter layer before the white particles are driven to be adjacent to the color filter layer.

4. The method according to claim 1, wherein the waveform is substantially DC balanced.

5. The method according to claim 1, wherein a plurality of waveforms for updating the electrophoretic display, which includes a color filter layer, are stored in a memory that will be accessed by a controller for the display.

6. The method according to claim 5, wherein 16 different waveforms are stored in memory to achieve the desired color state of the second image.

7. The method according to claim 1, wherein the black and white charged particles are enclosed within a plurality of microcapsules or microcells.

8. A display controller capable of controlling the operation of multiple pixel electrodes for an electrophoretic display, the electrophoretic medium comprising a color filter layer between the viewer and a layer of electrophoretic medium, wherein the electrophoretic medium comprises black and white charged particles, and the controller is configured to perform a driving method, the driving method is The method involves providing a series of voltages to the plurality of pixel electrodes over the refresh cycle, the series of voltages including a lead pulse, an intermediate pulse, and a set pulse, the intermediate pulse and the set pulse driving the white particles in the plurality of pixels to be adjacent to the color filter layer before achieving a final color state in which the white particles are not adjacent to the color filter layer. A display controller, including one.

9. The display controller according to claim 8, further comprising the controller driving the black particles to be adjacent to the color filter layer before the white particles are driven to be adjacent to the color filter layer.

10. The display controller according to claim 8, wherein the display controller is operably coupled to column drivers and row drivers of the active matrix of pixel electrodes.

11. The display controller according to claim 8, wherein the display controller is operably coupled to a memory, the memory storing instructions for the set of voltages to be provided to the plurality of pixel electrodes in order to achieve the final color state.

12. The display controller according to claim 11, wherein the memory stores a set of 16 different instructions for the series of voltages that will be provided to the plurality of pixel electrodes in order to achieve the final color state.

Images