Patent Description:
Electro-optic displays typically have a backplane provided with a plurality of pixel electrodes each of which defines one pixel of the display; conventionally, a single common electrode extending over a large number of pixels, and normally the whole display is provided on the opposed side of the electro-optic medium. The individual pixel electrodes may be driven directly (i.e., a separate conductor may be provided to each pixel electrode) or the pixel electrodes may be driven in an active matrix manner which will be familiar to those skilled in backplane technology. Since adjacent pixel electrodes will often be at different voltages, they must be separated by inter-pixel gaps of finite width in order to avoid electrical shorting between electrodes. Although at first glance it might appear that the electro-optic medium overlying these gaps would not switch when drive voltages are applied to the pixel electrodes (and indeed, this is often the case with some non-bistable electro-optic media, such as liquid crystals, where a black mask is typically provided to hide these non-switching gaps), in the case of many bistable electro-optic media the medium overlying the gap does switch because of a phenomenon known as "blooming".

Blooming refers to the tendency for 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. Although excessive blooming should be avoided (for example, in a high resolution active matrix display one does not wish application of a drive voltage to a single pixel to cause switching over an area covering several adjacent pixels, since 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 which displays numbers using a conventional seven-segment array of seven directly driven pixel electrodes for each digit. When, for example, a zero is displayed, six segments are turned black. In the absence of blooming, the six inter-pixel gaps will be visible. However, by providing a controlled amount of blooming, for example as described in the aforementioned <NUM>/<NUM>, the inter-pixel gaps can be made to turn black, resulting in a more visually pleasing digit. However, blooming can lead to a problem denoted "edge ghosting".

An area of blooming is not a uniform white or black but is typically a transition zone where, as one moves across the area of blooming, the color of the medium transitions from white through various shades of gray to black. Accordingly, an edge ghost will typically be an area of varying shades of gray rather than a uniform gray area, but can still be visible and objectionable, especially since the human eye is well equipped to detect areas of gray in monochrome images where each pixel is supposed to be pure black or pure white. ) In some cases, asymmetric blooming may contribute to edge ghosting. "Asymmetric blooming" refers to a phenomenon whereby in some electro-optic media (for example, the copper chromite/titania encapsulated electrophoretic media described in <CIT>) the blooming is "asymmetric" in the sense that more blooming occurs during a transition from one extreme optical state of a pixel to the other extreme optical state than during a transition in the reverse direction; in the media described in this patent, typically the blooming during a black-to-white transition is greater than that during a white- to-black one.

<CIT> describes a method of operating an electro-optic display, comprising: detecting a null state transition of a first pixel when transitioning from a first image to a second image; determining whether a threshold number of cardinal neighbors of the first pixel transition from a black state to a white state when transitioning from the first image to the second image; and in response to a transition to a subsequent image, applying a voltage signal to the first pixel, wherein the voltage signal has a waveform configured to generate an optical black state for the first pixel.

<CIT> describes methods and apparatus for driving an electro-optic display to display white text on a black background ("dark mode") while reducing edge artifacts, ghosting and flashy updates. Accumulation of edge artifacts is reduced by applying a special waveform transition to edge regions with methods to manage the DC imbalance introduced by the special transition. Edge artifact clearing may be achieved by identifying specific edge pixels to receive a special transition called an inverted top-off pulse ("iTop Pulse") and, since the iTop Pulse is DC imbalanced, to subsequently discharge remnant voltage from the display.

As such, driving methods that also reduces the ghosting or blooming effects are needed.

The present invention relates to methods for driving electro-optic displays, especially bistable electro-optic displays. More specifically, this invention relates to driving methods which may allow for reduced "ghosting" and edge effects, and reduced flashing in such displays. This invention is especially, 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.

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

The term "gray state" is used herein in its conventional meaning in the imaging art to refer to a state intermediate two extreme optical states of a pixel, and does not necessarily imply a black-white transition between these two extreme states. For example, several of the E Ink patents and published applications referred to below describe electrophoretic displays in which the extreme states are white and deep blue, so that an intermediate "gray state" would actually be pale blue. Indeed, as already mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of a display, and should be understood as normally including extreme optical states which are not strictly black and white, for example, the aforementioned white and dark blue states. The term "monochrome" may be used hereinafter to denote a drive scheme which only drives pixels to their two extreme optical states with no intervening gray states.

Some electro-optic materials are solid in the sense that the materials have solid external surfaces, although the materials may, and often do, have internal liquid- or gas-filled spaces. Such displays using solid electro-optic materials may hereinafter for convenience be referred to as "solid electro-optic displays". Thus, the term "solid electro-optic displays" includes rotating bichromal member displays, encapsulated electrophoretic displays, microcell electrophoretic displays and encapsulated liquid crystal displays.

The term "impulse" is used herein in its conventional meaning 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, namely the integral of current over time (which is 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.

Much of the discussion below 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 denote the entire voltage against time curve used to effect the transition from one specific initial gray level to a specific final gray level. Typically such a waveform will comprise a plurality of waveform elements; where these elements are essentially rectangular (i.e., where a given element comprises application of a constant voltage for a period of time); the elements may be called "pulses" or "drive pulses". The term "drive scheme" denotes a set of waveforms sufficient to effect all possible transitions between gray levels for a specific display. A display may make use of more than one drive scheme; for example, the aforementioned <CIT> teaches that a drive scheme may need to be modified depending upon parameters such as the temperature of the display or the time for which it has been in operation during its lifetime, and thus a display may be provided with a plurality of different drive schemes to be used at differing temperature etc. A set of drive schemes used in this manner may be referred to as "a set of related drive schemes. " It is also possible, as described in several of the aforementioned MEDEOD applications, to use more than one drive scheme simultaneously in different areas of the same display, and a set of drive schemes used in this manner may be referred to as "a set of simultaneous drive schemes.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type as described, for example, in <CIT>; <CIT>; <CIT>; <CIT><CIT>; <CIT>; <CIT>; <CIT>; and <CIT> (although this type of display is often referred to as a "rotating bichromal ball" display, the term "rotating bichromal member" is preferred as more accurate since in some of the patents mentioned above the rotating members are not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) which have two or more sections with differing optical characteristics, and an internal dipole. These bodies are suspended within liquid-filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed by applying an electric field thereto, thus rotating the bodies to various positions and varying which of the sections of the bodies is seen through a viewing surface. This type of electro-optic medium is typically bistable.

Another type of electro-optic display uses an electrochromic medium, for example an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least in part from a semi-conducting metal oxide and a plurality of dye molecules capable of reversible color change attached to the electrode; see, for example <NPL>; and<NPL>). See also <NPL>. Nanochromic films of this type are also described, for example, in <CIT>; <CIT>; and <CIT>. This type of medium is also typically bistable.

Another type of electro-optic display is an electro-wetting display developed by Philips and described in<NPL>). It is shown in <CIT> that such electro-wetting displays can be made bistable.

One type of electro-optic display, which has been the subject of intense research and development for a number of years, is the particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up electrophoretic displays tend to settle, resulting in inadequate service-life for these displays.

As noted above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using gaseous fluids; see, for example,<NPL>, and <NPL>). See also <CIT> and <CIT>. Such gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various technologies used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes. The technologies described in these patents and applications include:.

Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium could be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and that the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display may be regarded as capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet; see for example, the aforementioned <NUM>/<NUM>. Accordingly, for purposes of the present application, such polymer-dispersed electrophoretic media are regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called "microcell electrophoretic display. " In a microcell electrophoretic display, the charged particles and the suspending fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, e.g., a polymeric film. See, for example, International Application Publication No. <CIT>, and published <CIT>, both assigned to Sipix Imaging, Inc.

Many of the aforementioned E Ink and MIT patents and applications also contemplate microcell electrophoretic displays and polymer-dispersed electrophoretic displays. The term "encapsulated electrophoretic displays" can refer to all such display types, which may also be described collectively as "microcavity electrophoretic displays" to generalize across the morphology of the walls.

Another type of electro-optic display is an electro-wetting display developed by Philips and described in <NPL>). It is shown in copending application Ser. No. <CIT>, that such electro-wetting displays can be made bistable.

Other types of electro-optic materials may also be used. Of particular interest, bistable ferroelectric liquid crystal displays (FLCs) are known in the art and have exhibited remnant voltage behavior. Although electrophoretic media may be opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, some electrophoretic displays can be made to operate in a so-called "shutter mode" in which one display state is substantially opaque and one is light-transmissive. See, for example, <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>. Dielectrophoretic displays, which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see <CIT>. Other types of electro-optic displays may also be capable of operating in shutter mode.

A high-resolution display may include individual pixels which are addressable without interference from adjacent pixels. One way to obtain such pixels is to provide an array of non-linear elements, such as transistors or diodes, with at least one non-linear element associated with each pixel, to produce an "active matrix" display. An addressing or pixel electrode, which addresses one pixel, is connected to an appropriate voltage source through the associated non-linear element. When the non-linear element is a transistor, the pixel electrode may be connected to the drain of the transistor, and this arrangement will be assumed in the following description, although it is essentially arbitrary and the pixel electrode could be connected to the source of the transistor. In high-resolution arrays, the pixels may be arranged in a two-dimensional array of rows and columns, such that any specific pixel is uniquely defined by the intersection of one specified row and one specified column. The sources of all the transistors in each column may be connected to a single column electrode, while the gates of all the 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.

The display may be written in a row-by-row manner. The row electrodes are connected to a row driver, which may apply to a selected row electrode a voltage such as to ensure that all the transistors in the selected row are conductive, while applying to all other rows a voltage such as to ensure that all the transistors in these non-selected rows remain non-conductive. The column electrodes are connected to column drivers, which place upon the various column electrodes voltages selected to drive the pixels in a selected row to their desired optical states. (The aforementioned voltages are relative to a common front electrode which may be provided on the opposed side of the electro-optic medium from the non-linear array and extends across the whole display. As in known in the art, voltage is relative and a measure of a charge differential between two points. One voltage value is relative to another voltage value. For example, zero voltage ("0V") refers to having no voltage differential relative to another voltage. ) After a pre-selected interval known as the "line address time," a 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.

However, in use, certain waveforms may produce a remnant voltage to pixels of an electro-optic display, and as evident from the discussion above, this remnant voltage produces several unwanted optical effects and is in general undesirable.

As presented herein, a "shift" in the optical state associated with an addressing pulse refers to a situation in which a first 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). Remnant voltages may give rise to shifts in the optical state because the voltage applied to a pixel of the electro-optic display during application of an addressing pulse includes the sum of the remnant voltage and the voltage of the addressing pulse.

A "drift" in the optical state of a display over time refers to a situation in which the optical state of an electro-optic display changes while the display is at rest (e.g., during a period in which an addressing pulse is not applied to the display). Remnant voltages may give rise to drifts in the optical state because the optical state of a pixel may depend on the pixel's remnant voltage, and a pixel's remnant voltage may decay over time.

As discussed above, "ghosting" refers to a situation in which, after the electro-optic display has been rewritten, traces of the previous image(s) are still visible. Remnant voltages may give rise to "edge ghosting," a type of ghosting in which an outline (edge) of a portion of a previous image remains visible.

<FIG> shows a schematic of a pixel <NUM> of an electro-optic display in accordance with the subject matter submitted herein. Pixel <NUM> may include an imaging film <NUM>. In some embodiments, imaging film <NUM> may be bistable. In some embodiments, imaging film <NUM> may include, without limitation, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles.

Imaging film <NUM> may be disposed between a front electrode <NUM> and a rear electrode <NUM>. The front electrode <NUM> may be formed between the imaging film and the front of the display. In some embodiments, front electrode <NUM> may be transparent. In some embodiments, front electrode <NUM> may be formed of any suitable transparent material, including, without limitation, indium tin oxide (ITO). Rear electrode <NUM> may be formed opposite a front electrode <NUM>. In some embodiments, a parasitic capacitance (not shown) may be formed between front electrode <NUM> and rear electrode <NUM>.

Pixel <NUM> 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 specific pixel is uniquely defined by the intersection of one specified row and one specified column. In some embodiments, the matrix of pixels may be an "active matrix," in which each pixel is associated with at least one non-linear circuit element <NUM>. The non-linear circuit element <NUM> may be coupled between back-plate electrode <NUM> and an addressing electrode <NUM>. In some embodiments, non-linear element <NUM> may include a diode and/or a transistor, including, without limitation, a MOSFET. The drain (or source) of the MOSFET may be coupled to back-plate electrode <NUM>, the source (or drain) of the MOSFET may be coupled to addressing electrode <NUM>, and the gate of the MOSFET may be coupled to a driver electrode <NUM> configured to control the activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET coupled to back-plate electrode <NUM> will be referred to as the MOSFET's drain, and the terminal of the MOSFET coupled to addressing electrode <NUM> will be referred to as the MOSFET's source. However, one of ordinary skill in the art will recognize that, in some embodiments, the source and drain of the MOSFET may be interchanged.

In some embodiments of the active matrix, the addressing electrodes <NUM> of all the pixels in each column may be connected to a same column electrode, and the driver electrodes <NUM> of all the pixels in each row may be connected to a same row electrode. The row electrodes may be connected to a row driver, which may select one or more rows of pixels by applying to the selected row electrodes a voltage sufficient to activate the non-linear elements <NUM> of all the pixels <NUM> in the selected row(s). The column electrodes may be connected to column drivers, which may place upon the addressing electrode <NUM> of a selected (activated) pixel a voltage suitable for driving the pixel into a desired optical state. The voltage applied to an addressing electrode <NUM> may be relative to the voltage applied to the pixel's front-plate electrode <NUM> (e.g., a voltage of approximately zero volts). In some embodiments, the front-plate electrodes <NUM> of all the pixels in the active matrix may be coupled to a common electrode.

In some embodiments, the pixels <NUM> of the active matrix may be written in a row-by-row manner. For example, a row of pixels may be selected by the row driver, and the voltages corresponding to the desired optical states for the row of pixels may be applied to the pixels by the column drivers. After a pre-selected interval known as the "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.

<FIG> shows a circuit model of the electro-optic imaging layer <NUM> disposed between the front electrode <NUM> and the rear electrode <NUM> in accordance with the subject matter presented herein. Resistor <NUM> and capacitor <NUM> may represent the resistance and capacitance of the electro-optic imaging layer <NUM>, the front electrode <NUM> and the rear electrode <NUM>, including any adhesive layers. Resistor <NUM> and capacitor <NUM> may represent the resistance and capacitance of a lamination adhesive layer. Capacitor <NUM> may represent a capacitance that may form between the front electrode <NUM> and the back electrode <NUM>, for example, interfacial contact areas between layers, such as the interface between the imaging layer and the lamination adhesive layer and/or between the lamination adhesive layer and the backplane electrode. A voltage Vi across a pixel's imaging film <NUM> may include the pixel's remnant voltage.

In some usage applications, a display may make use of a "direct update" drive scheme ("DUDS" or "DU"). The DU may have two or more than two gray levels, typically fewer than a gray scale drive scheme ("GSDS), which can effect transitions between all possible gray levels, but the most important characteristic of a DU scheme is that transitions are handled by a simple unidirectional drive from the initial gray level to the final gray level, as opposed to the "indirect" transitions often used in a GSDS, where in at least some transitions the pixel is driven from an initial gray level to one extreme optical state, then in the reverse direction to a final gray level; in some cases, the transition may be effected by driving from the initial gray level to one extreme optical state, thence to the opposed 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 <CIT>. Thus, present electrophoretic displays may have an update time in grayscale mode of about two to three times the length of a saturation pulse (where "the length of a saturation pulse" is defined as the time period, at a specific voltage, that suffices to drive a pixel of a display from one extreme optical state to the other), or approximately <NUM>-<NUM> milliseconds, whereas a DU has a maximum update time equal to the length of the saturation pulse, or about <NUM>-<NUM> milliseconds.

It should be appreciated that the Direct Update (DU) waveform mode or driving scheme described above is used herein to explain the general working principles of the subject matter disclosed herein. It is not meant to serve as a limitation to the current subject matter. As these working principles can be easily applied to other waveform modes or schemes.

The DU waveform mode is a driving scheme that usually considers updates to white and black with empty self-transitions. The DU mode would have a short update time to bring up black and white quickly, with minimal appearance of a "flashy" transition, where the display would appear to be blinking on and off and may be visually unattractive to some viewer's eyes. The DU mode may sometimes be used to bring up menus, progress bars, keyboards etc. on a display screen. Because both the white to white and black to black transitions are null (i.e., un-driven) in the DU mode, edge artifacts may arise in the black and white backgrounds.

As described above, when an un-driven pixel lies adjacent a pixel which is being updated, a phenomenon known as "blooming" occurs, in which the driving of the driven pixel causes a change in optical state over an area slightly larger than that of the driven pixel, and this area intrudes into the area of adjacent pixels. Such blooming manifests itself as edge effects along the edges where the un-driven pixels lie adjacent driven pixels. Similar edge effects occur when using regional updates (where only a particular region of the display is updated, for example to show an image), except that with regional updates the edge effects occur at the boundary of the region being updated. Over time, such edge effects become visually distracting and must be cleared. Hitherto, such edge effects (and the effects of color drift in un-driven white pixels) have typically been removed by using a single Global Clearing or GC update at intervals. Unfortunately, use of such an occasional GC update may reintroduces the problem of a "flashy" update, and indeed the flashiness of the update may be heightened by the fact that the flashy update only occurs at long intervals.

In comparison, some of the alternative display pixel edge artifacts reduction methods may result in additional latency due to image processing designed to detect and remove edge artifacts after each image update. In addition, the use of the DC imbalance waveforms in these reduction methods would not be feasible since the small dwell time in between updates does not allow sufficient time to perform post drive discharging. And without post drive discharging, there is a potential risk to overall optical performance and module reliability.

Instead, in accordance with the present invention, pixel edge artifacts generated under a drive scheme or waveform modes are stored in a binary map, for example, each display pixel may be represented by a designator MAP (i, j), and pixels that may develop edge artifacts may be flagged and their map information (i.e., the MAP (i. j) designator) may be saved in a binary map. Illustrated below is one approach that may be used to keep track of generated edge artifacts on the map and flag such pixels:
<IMG>
<IMG>.

In this approach, when certain conditions are met, a display pixel designated MAP (i, j) may be flagged with a numerical value of <NUM>, indicating that dark edge artifacts have formed on this pixel. Some of the conditions required may include (<NUM>). this display pixel is going through a white to white transition; (<NUM>). all four cardinal neighbors (i.e., the four closest neighboring pixels) have a next graytone of white; AND (<NUM>). at least one cardinal neighbor has a current graytone that is not white; and (<NUM>). none of the neighboring pixels (i.e., the four cardinal neighbors and also the diagonal neighbors) are currently flagged for edge artifacts.

Similarly, when certain conditions are met, a display pixel MAP (i, j) may be flagged with a numerical value of <NUM>, indicating that white edges have formed on this pixel. Some of the conditions required may include (<NUM>). this pixel is going through a black to black transition; (<NUM>). at least one cardinal neighbor has a current graytone that is not black and its next graytone is black; and (<NUM>). none of the neighboring pixels (i.e., the four cardinal neighbors and also the diagonal neighbors) are currently flagged for edge artifacts.

In use, one advantage of this approach is that the above mentioned image processing (i.e., map generation and pixel flagging) can occur concurrently with the display image updating cycles, thereby avoiding the creation of extra latencies to the updating cycles, due at least in part to the reason that the generated map is only required at the completion of the update cycle.

Once an update mode has completed (e.g., the display ceases from using a particular update mode), pixel information accumulated by the generated map is later used for clearing the edge artifacts (e.g., using an out waveform mode). For example, pixels flagged for edge artifacts may be cleared with a low flash waveform with specialized waveforms.

Full clearing white to white and black to black waveforms in conjunction with special edge clearing white to white and black to black waveforms may be used to clear the edge artifacts. For example, the balanced pulse pairs described in <CIT> may be used:
<IMG>.

In this approach, a DU_OUT transition scheme (e.g., a modified DU scheme with the edge artifact reduction algorithm included) may be applied to pixels that is not going through a white to white or black to black transition, for example, these pixels may receive the normal transition updates as if they were under a normal DU drive scheme. Else, for a pixel with dark edge artifacts (i.e., MAP (i, j) = <NUM>) and going through a white to white transition, a special full white to white waveform may be applied. In some embodiments, this white to white waveform may be a waveform similar to what is illustrated in <FIG>, which may be substantially DC balanced, meaning, the sum of the voltage bias apply as a function of magnitude and time is substantially zero overall; otherwise, if a pixel is going through a white to white transition, and at least one cardinal neighbor has dark edge artifact (i.e., MAP (i, j) = <NUM>), a special edge erasing white to white waveform is applied (e.g., <FIG>); still more, if a pixel had white edge artifact (i.e., MAP (i, j) = <NUM>) and is going through a black to black transition, a special full black to black waveform, as illustrated in <FIG>, may be applied; still more, if a pixel is going through a black to black transition, AND at least one cardinal neighbor is flagged for white edge artifact (i.e., MAP (i, j) = <NUM>), apply a special edge erasing black to black waveform, as illustrated in <FIG>; otherwise, apply the black to black or white to white transition waveforms to all other pixels using waveforms from the DU-OUT waveform table.

Using the above mentioned method, full clearing white to white and black to black waveforms are used in conjunction with special edge clearing white to white and black to black waveforms to clear the edge artifacts. In some embodiments, the special edge clearing white to white waveform can take the form of a pulse pair as described in <CIT>, or a DC imbalance pulse drive to white as given in illustrated in <FIG>, in which case post drive discharge described in may be used to discharge remnant voltages and reduce device stresses. Similarly, a DC imbalanced pulse, as illustrated in <FIG>, may be used to drive a pixel to black, in which case, again, a post drive discharge may be performed. As illustrated in <FIG>, a such DC imbalanced pulse have only a drive to the positive <NUM> volts for a period of time. In this configuration, excellent edge clearing performance can be achieved at the cost of small transition appearance imperfections (e.g., flashes) due to the use of the special full clearing waveform.

In another embodiment, transition appearance imperfections (e.g., flashes) may be reduced using an alternative implementation described below.

In this approach, instead of using specialized edge clearing waveforms as described in the first method above, DC imbalanced waveforms may be used to clear the edge artifacts. In some instances, post drive discharges may be used to reduce hardware stress due to the imbalanced waveforms. In use, when a display pixel is not going through either a white to white or black to black transition, a normal DU-OUT transition is applied to the pixel. Else, if a display pixel is identified of having dark edge artifacts (i.e., MAP (i, j) = <NUM>) and is going through a white to white transition, a DC imbalanced drive pulse is used to drive the pixel to white (e.g., a pulse similar to that illustrated in <FIG>); else, if a display pixel is identified of having white edge artifacts (i.e., MAP (i, j) = <NUM>) and is going through a black to black transition, a DC imbalanced drive pulse (e.g., a pulse similar to that illustrated in <FIG>)is applied to drive the pixel to black; otherwise, invoke the black to black or white to white transitions of the DU-OUT waveform table to the display pixels.

In yet another embodiment, instead of storing edge artifact information in a designated memory location, one may bring forward the edge artifact information in an image buffer associated with the display's controller unit (e.g., using a next image buffer associated with the controller unit).

In this approach, for a pixel going through a white to white transition and all of its four cardinal neighbors having a next graytone of white, if at least one of the cardinal neighbor's current gray tone is not white, then set the pixel's next gray tone to a special white to white image state in the next image buffer; else, if a pixel's graytone transition is black to black, and at least one cardinal neighbor has a current graytone that is not black and a next graytone that is black, then the pixel's next graytone is set to a special black to black image state in the next image buffer. In use, during an update cycle the special white to white and special black to black image states can be the same as the white to white and black to black image states for both application of the waveform transition and for image processing. For the application of waveform transition, this means that:.

During the out mode, the special white state to white state received the DC imbalance pulse to white (e.g., <FIG> illustrates an exemplary such pulse) and the special black state to black state received the DC imbalance pulse to black (e.g., <FIG> illustrates an exemplary such pulse). The imaging algorithm processing occurs in the background during the DU mode updating, meaning the DU updating time can be used to process the images.

Claim 1:
A method for driving an electro-optic display having a plurality of display pixels comprising:
updating the display with a first image; and
identifying display pixels with edge artifacts after the first image update;
the method being characterized by:
creating a binary map indicating the locations of the identified display pixels with edge artifacts;
storing the identified display pixels information in a memory; and
updating the display with a second image, applying a special edge clearing waveform to each pixel flagged for edge artifacts in the binary map and undergoing a white-to-white or black-to-black transition during the updating with the second image, while other pixels undergo normal transition updates;
wherein the creating the binary map occurs concurrently with a display image update cycle.