HK1237113B - Font control for electro-optic displays and related apparatus and methods - Google Patents

Description

Font control for electro-optical displays and related devices and methods

Citation of Related Applications

This application claims the benefit of U.S. Provisional Application Serial No. 62/109,769, filed January 30, 2015, which and all other U.S. patents and published and co-pending applications referenced below are incorporated herein by reference in their entirety.

Technical Field

The present application relates to electro-optical displays and, more particularly, aspects thereof relate to controlling such displays when using glyphs to display text, characters, symbols, and the like.

Summary of the Invention

Aspects of the present application provide methods for displaying text, characters, symbols, etc. on an electro-optical display at two or more bit depths with little or no change between hintings. In some embodiments, the same hinting is used to sequentially display the same text at two different bit depths.

According to aspects of the present application, a method for driving a display is provided, the method comprising displaying text information, characters, or symbols in a font on the display at a first bit depth using at least one font hinting, and after displaying the text information at the first bit depth, displaying the text information in the font on the display at a second bit depth using at least one font hinting.

According to another aspect of the present application, a method is provided for updating an electro-optic display in a manner that reduces artifacts without increasing flicker in the display. In some embodiments, a pixel mask is used that defines a greater number of pixels to be updated than are included in the glyph being updated.

According to aspects of the present application, a method for driving a display is provided, the method comprising: displaying a glyph on the display, the glyph occupying a first number of pixels of the display, and flashing a second number of pixels of the display including the glyph, wherein the second number of pixels is greater than the first number of pixels. In some embodiments, a subset of the pixels of the display is smaller than or equal to a convex hull including the glyph.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and embodiments of the present application will be described with reference to the following figures. It should be understood that the figures are not necessarily drawn to scale. Items appearing in multiple figures are represented by the same reference numerals in all figures in which they appear.

FIG1 is a schematic representation of a device with an associated display according to a non-limiting embodiment of the present application.

FIG. 2 is a cross-sectional view of an example of an electrophoretic display.

FIG. 3 is a schematic block diagram illustrating the manner in which the controller unit shown in FIG. 1 may generate certain output signals.

FIG4 is a schematic diagram illustrating how the previous state of a display pixel affects the current pixel value.

FIG5 shows example glyphs for a serif font for multi-bit and 1-bit font depths.

FIG. 6 shows example glyphs for a sans-serif font for multi-bit and 1-bit font depths.

FIG. 7A is an example pixelated glyph.

FIG. 7B is an outline of the glyph in FIG. 7A .

8A-G are example masks that may be applied to the example glyph of FIG. 7A when updating a display, according to non-limiting embodiments of the present application.

DETAILED DESCRIPTION

Aspects of the present application provide methods for displaying text, characters, symbols, or the like on an electro-optical display at two or more bit depths with little or no change between adjustments. Another aspect of the present application provides methods for displaying a glyph having a first number of pixels and thereafter removing the glyph by flashing a second number of pixels of the display containing the glyph, wherein the second number of pixels is greater than the first number of pixels.

The term "electro-optical," as applied to a material or display, is used herein in its conventional sense in the field of imaging to refer to a material having first and second display states that differ in at least one optical property, the material being caused to change from its first display state to its second display state by application of an electric field to the material. While the optical property is typically color perceptible to the human eye, it may be other optical properties such as light transmission, reflection, luminescence, or, in the case of displays intended for machine reading, false color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

The term "grey state" is used here in its conventional sense in the field of imaging to refer to a state between the two extreme optical states of a pixel, but does not necessarily mean a black and white transition between the two extreme states. For example, an electrophoretic display may have extreme states, which are white and dark blue, so that the intermediate "grey state" is actually light blue. In fact, as already mentioned, the change of optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochromatic" may be used hereinafter to refer to a drive scheme in which a pixel is driven only to its two extreme optical states, without an intermediate grey state.

Some electro-optic materials are solid in the sense that they have a solid outer surface, but the materials can, and often do, have internal liquid- or gas-filled spaces. For convenience, such displays using solid-state electro-optic materials may be referred to as "solid-state electro-optic displays." Thus, the term "solid-state electro-optic display" includes rotating two-color component displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

The terms "bistable" and "bistability" are used herein in their conventional sense in the art to refer to a display comprising display elements having first and second display states, said first and second display states differing in at least one optical property such that, after any given element is driven to assume its first or second display state by an addressing pulse of finite duration, that state persists after termination of the addressing pulse for a time that is 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 supporting grayscale are stable not only in their extreme black and white states but also in intermediate gray states, as are some other types of electro-optical displays. Such displays are properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" will be used herein to cover both bistable and multistable displays.

Several types of electro-optic displays are known. One type of electro-optic display is a rotating dichromatic element type, as described, for example, in U.S. Patent Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071; 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791 (although this type of display is often referred to as a "rotating dichromatic sphere" display, the term "rotating dichromatic element" is preferably more accurate because the rotating elements in some of the aforementioned patents are not spherical). This display uses many small bodies (usually spherical or cylindrical) and internal dipoles. The bodies consist of two or more parts with different optical properties. These bodies are suspended within a matrix of liquid-filled cavities, which are filled with liquid to allow the bodies to rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the body to various positions and changing the part of the body that is seen through the viewing surface.This type of electro-optical medium is generally bistable.

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

Another type of electro-optical display is the electrowetting display developed by Philips and described in Hayes, R.A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). It is shown in U.S. Patent No. 7,420,549 that such an electrowetting display can be made bi-stable.

One type of electro-optical display that has been the subject of extensive research and development for many years is the particle-based electrophoretic display (EPD), in which a plurality of charged particles are moved through a fluid under the influence of an electric field. Electrophoretic displays can offer the following attributes compared to liquid crystal displays: good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues with the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up EPDs tend to settle, resulting in a limited useful life for these displays.

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

(a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

(b) capsules, adhesives, and encapsulation processes; see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719;

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

(d) Backplanes, adhesive layers and other auxiliary layers and methods for use in displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

(e) color formation and color adjustment; see, e.g., U.S. Patent No. 7,075,502 and U.S. Patent Application Publication No. 2007/0109219;

(f) Methods for driving displays; see, 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; 7,116,466; 7,119,772; 7,193,625; 7,202,847; 7,259,7 44; 7,304,787; 7,312,794; 7,327,511; 7,453,445; 7,492,339; 7,528,822; 7,545,358; 7,583,251; 7,602,374; 7,612,760; 7,679,599; 7,688,297; 7,729,039; 7,733,311; 7,733,335; 7,787,169; 7,952,557; 7,956,841; 7,999,787; 8,077,141; 8,125,501; 8,139,050; 8,174,490; 8,289,250; 8,300,006; 8,305,341; 8,314,784; 8,384,658; 8,558,783; and 8,558,785; and U.S. Patent Application Publication Nos. 2003/0102858; 2005/0122284; 2005/0253777; 2007/0091418; 2007/0103427; 200 8/0024429; 2008/0024482; 2008/0136774; 2008/0291129; 2009/0174651; 2009/0179923; 2009/0195568; 2009/0322721; 2010/0220121; 2010/0265561; 2011/0193840; 2011/0193841; 2011/0199671; 2011/0285754; and 2013/0194250;

(g) Display applications; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and

(h) Non-electrophoretic displays, such as those described in U.S. Patent Nos. 6,241,921; 6,950,220; 7,420,549; and 8,319,759; and U.S. Patent Application Publication No. 2012/0293858.

Another type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged particles and fluids are not encapsulated in microcapsules, but rather are held within cavities formed within a carrier medium (usually a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both issued to Sipix Imaging.

Other types of electro-optical materials may also be used in aspects of the present application.Of particular interest, bistable ferroelectric liquid crystal displays (FLCs) are known in the art.

Electro-optical displays typically comprise a layer of electro-optical material and at least two other layers arranged on opposite sides of the electro-optical material, one of the two layers being an electrode layer. In most such displays, the two layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned into elongated row electrodes, and the other electrode layer patterned into elongated column electrodes extending at right angles to the row electrodes, the pixels being defined by the intersections of the row and column electrodes. Alternatively, and more typically, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines a pixel of the display. In another type of electro-optical display, which is intended for use with a stylus, print head or similar movable electrode that is separate from the display, only one layer adjacent to the electro-optical layer comprises electrodes, and the layer on the opposite side of the electro-optical layer is typically a protective layer that is intended to prevent the movable electrode from damaging the electro-optical layer.

The term L* may be used herein and may be denoted “L*.” L* has the usual CIE definition: L*=116(R/R0)1/3−16, where R is the reflectance and R0 is the standard reflectance value.

The term "impulse" is used here in its conventional sense, namely, the integral of voltage with respect to time. However, some bistable electro-optical media are used as charge converters, and for such media, an alternative definition of impulse may be used, namely, the integral of current with respect to time (which is equal to the total applied charge). Depending on whether the medium is used as a voltage-to-time impulse converter or as a charge-to-impulse converter, the appropriate definition of impulse should be used.

A complicating issue in driving electrophoretic displays is the need for so-called "DC balancing." As described in U.S. Patent Nos. 6,531,997 and 6,504,524, problems can be encountered and the operating life of the display reduced if the method used to drive the display does not produce a zero, or near-zero, net time-averaged applied electric field across the electro-optic medium. Driving methods that produce a zero net time-averaged applied electric field across the electro-optic medium are conveniently referred to as "direct current balancing" or "DC balancing."

As already noted, encapsulated electrophoretic media typically comprise electrophoretic capsules disposed in a polymeric binder that serves to form the discrete capsules into a coherent layer. The continuous phase in polymer-dispersed electrophoretic media, and the cell walls of microcellular media, serve similar functions. It has been discovered by Iink researchers that the specific material used as the binder in an electrophoretic medium can influence the electro-optical properties of the medium. Among the electro-optical properties of electrophoretic media that are influenced by the choice of binder is the so-called "dwell time dependence," which is discussed in U.S. Patent No. 7,119,772 (see, in particular, FIG. 34 and the associated description). It has been found that, at least in some cases, the impulse required to switch between two specific optical states of a bistable electrophoretic display varies with the dwell time of a pixel in its initial optical state, and this phenomenon is referred to as "dwell time dependence" or "DTD." Obviously, it is desirable to keep the DTD as small as possible because the DTD affects the difficulty of driving the display and can affect the quality of the image produced; for example, the DTD can cause pixels in an area that is expected to form a uniform gray to differ slightly in grayscale from one another, and the human eye is very sensitive to such variations. Although it is known that the choice of binder affects the DTD, the selection of an appropriate binder for any particular electrophoretic medium has heretofore been based on trial and error, with no inherent understanding of the relationship between the DTD and the chemical properties of the binder.

Some of the following discussion focuses on methods for driving one or more pixels of an electro-optical display through a transition from an initial grayscale to a final grayscale (which may be different from or the same as the initial grayscale). The term "waveform" will be used to refer to the overall voltage versus time curve used to achieve the transition from a particular initial grayscale to a particular final grayscale. Typically, such a waveform will include multiple waveform elements; where these elements are substantially rectangular (i.e., a given element includes applying a constant voltage for a period of time); the elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to achieve all possible transitions between grayscales for a particular display. A display may utilize more than one drive scheme; for example, U.S. Patent No. 7,012,600 teaches that the drive scheme may need to be modified based on parameters such as the temperature of the display or the amount of time it has been in operation during its lifetime, and thus a display may be provided with multiple different drive schemes for use at different temperatures, etc. A set of drive schemes used in this manner may be referred to as a "set of related drive schemes." It is also possible to use more than one drive scheme simultaneously in different areas of the same display, and a set of drive schemes used in this manner may be referred to as a "set of simultaneous drive schemes."

The inventor has understood that when displaying text on an electro-optical display, there is sometimes a compromise between the time it takes to display the text and the quality of the text displayed, both of which can depend on the bit depth used for the text. Text displayed using a lower bit depth can appear more pixelated than the same text displayed using a higher bit depth. However, when using a higher bit depth, more time may be required to drive the display. The bit depth selected for displaying text can depend on the preference for the overall user experience. For example, when displaying text quickly, such as when turning pages between pages on an electronic display, such as when using an e-reader, text can be displayed with a 1-bit (black and white) depth. When text is displayed with better quality, more time is required to display the text to a higher bit depth, such as a 4-bit grayscale. Thus, a method for displaying text in a scene where a user expects high speed and high quality is to initially display text with a low bit depth (e.g., 1-bit depth) and then update the same text to a higher quality bit depth (e.g., 4-bit depth) to provide a better view of the text.

However, the inventors have recognized that standard font rendering algorithms produce inconsistencies between high bit depth text and low bit depth text displayed in the same font. For example, the size of text characters or glyphs may change between two different bit depths. Therefore, if a page of text displayed at one bit depth is changed to a different bit depth, the positions of the glyphs that make up the text may change to accommodate the size change caused by the different bit depths. Additional font elements, such as stems and serifs, may be commanded or even canceled or reduced by font instructions or font hinting. Because the font hinting for displaying glyphs is different between the lower and higher bit depths, inconsistencies may arise.

Thus, aspects of the present application disclose techniques for rendering fonts at different bit depths, wherein inconsistencies between characteristics (such as font hinting) at different bit depths are reduced or eliminated entirely. In some embodiments, the same font hinting is used for more than one bit depth. By using this technique, text displayed on a display (e.g., an electrophoretic display) can be quickly displayed at a low bit depth and changed to a higher bit depth without noticeable changes in the text, which can improve the user experience.

In addition, the inventors have recognized that changing the text displayed on some electronic displays, such as electro-optical displays, may produce artifacts as pixels change from one pixel color or value to another. The text on a display is a series of characters or glyphs. A portion of the pixels on the display are driven to non-white pixel values to display each glyph, typically gray or black, but other colors are possible. When changing text on a display, such as changing to another page (e.g., on an e-reader), some of the pixels displaying the glyphs may change values to display the new text. White pixels adjacent to non-white pixels (e.g., black and/or gray pixels) may produce artifacts when the new text is displayed. Such artifacts may include edge ghosting, where the edges of previous text glyphs remain on the display. Such artifacts may accumulate over time as the display undergoes repeated text updates.

Previous techniques for reducing the presence of edge ghosting include a global update of all pixels on the display to the same pixel value, such as white, before displaying new text. In some cases, multiple global updates are performed to ensure elimination of artifacts. However, such global update techniques produce a flickering display, which is undesirable for the reader. Flicker may result from actively driving all pixels or a subset of pixels to the same pixel value or from actively driving all pixels or a subset of pixels to the next image. As used herein, the term actively driving pixels to a value (i.e., grayscale) does not include null transitions or zero voltage transitions.

Aspects of the present application provide techniques for reducing the presence of edge ghosting and reducing flicker in displays. This technique involves defining an area of pixels, including pixels in a glyph and some pixels adjacent to the glyph, that are to be changed to white before the entire display is updated to the new text. The area of pixels in the glyph and pixels adjacent to the glyph can be referred to as a mask. By using this mask, the number of white-black and/or white-gray boundaries is reduced and updating the pixels within the mask can reduce the presence of edge ghosting. Using this mask can reduce the appearance of flicker because only a portion of the pixels are restored to white, while still maintaining a level of accuracy in the displayed text.

The above aspects and embodiments and further aspects and embodiments are further described below. These aspects and/or embodiments may be used individually, all together or in any combination of two or more, as the application is not limited in this respect.

Aspects of the present application relate to methods and apparatus for driving a display having an electro-optic medium that is sensitive to the polarity of an applied electric field. Such a display may include any suitable electro-optic display, including an electrophoretic display, a rotating two-color component display, and a device having such an electro-optic display, such as an e-reader and an electronic paper. An exemplary device in which aspects of the present application may be used is shown in FIG1 . An overall example device 10 may include an image source, shown as a personal computer 12, which may output data representing an image on a data line 14. The data lines may extend to a controller unit 16. The controller unit 16 may generate a set of output signals on a data bus 18 and a second set of signals on a different data line 20. The data bus 18 may be connected to a row (or gate) driver 22, and the data bus 20 may be connected to a plurality of column (or source) drivers 24. The row and column drivers control the operation of a bistable electro-optic display 26.

Fig. 2 illustrates the cross-sectional view of exemplary display architecture (for example, electro-optical display 26).Display architecture can comprise single common transparent electrode 202 on a side of electro-optic layer 210, and this common electrode 202 extends across all pixels on display.This common electrode 202 is between electro-optic layer 210 and observer, and forms the observation surface 216 that observer observes display.On the opposite side of electro-optic layer, the matrix of pixel electrode is provided, and it is configured so that each pixel electrode is uniquely limited by the intersection of single row and single column with row and column.Although only three pixels 204,206 and 208 are shown in Fig. 2, the pixel of any suitable number can be used for this electro-optical display.In addition or alternatively, the arrangement of common electrode and pixel can be reversed.The electric field experienced by each pixel of electro-optic layer is controlled by changing the voltage being applied to the associated pixel electrode relative to the voltage being applied to the common electrode.

The electro-optic layer may comprise any suitable electro-optic medium. In the example shown in FIG2 , the electro-optic medium comprises positively charged white particles 212 and negatively charged black particles 214. The electric field applied on the pixel can change the pixel value of a particular pixel by positioning particles 212 and 214 in the space between the common electrode and the pixel electrode so that the particles closer to the viewing surface 216 determine the pixel value. The pixels in the exemplary display shown in FIG2 are in a black state (pixels 204 and 208) or a white state (pixel 206), and the information on such a display may be referred to as 1-bit depth. A gray state or pixel value can be formed by applying a voltage signal to create a mixture of black and white particles visible to an observer via the viewing surface.

Any suitable method and apparatus for driving the voltage signals applied to the pixel electrodes and the common electrode can be used. FIG3 illustrates how the exemplary controller 16 of FIG1 generates the voltage signals. The voltage signals can include bit voltage values for the pixels, such as D0:D5 for a six-bit voltage signal, and a polarity signal POL for the common electrode 202. Although a six-bit voltage signal is shown for the exemplary controller in FIG3 , any suitable number of bit voltage signals can be used to form the bit depth. The controller stores data representing a final image 120 (the image desired to be written to the display), an initial image 122 previously written to the display, and optionally one or more previous images 123 written to the display before the initial image. The controller uses the data for a particular pixel in the initial, final, and previous images 120, 122, and 123 as a pointer to a lookup table 124, which provides the value of the impulse that must be applied to the particular pixel to change the pixel's state to the desired grayscale in the final image. The resulting output from the lookup table 124, along with the output from the frame counter 126, is supplied to a voltage-to-frame array 128, which generates a control voltage signal. The driving of a bi-stable electro-optic display using a look-up table is described in more detail in the aforementioned US Patent No. 7,012,600.

As previously described, when the pixel value of a pixel is changed to a different value, the previously applied voltage or pixel value of the pixel may affect the current pixel value. Figure 4 shows an example of a black "E" on a white background on an example display in image 402, where the pixels in the "E" are black and have a value of "1", and the pixels outside the "E" are white and have a value of "4". However, when the display is subsequently driven to form a uniform gray background (image 404), the previously black pixels forming the letter "E" have different pixel values than the previously white pixels of the background. This difference in pixel values can be referred to as gray tone error and can produce artifacts in the information or text displayed on the display, such as ghosting and edge artifacts, where part of the previous image is still apparent in the current image. Previous techniques for reducing such artifacts may include applying a voltage waveform over a longer period of time and flashing it to eliminate ghosting effects. The present application includes techniques for improving the time it takes to render text and reducing artifacts in the text that is ultimately displayed.

Techniques for improving (e.g., increasing) the time it takes to display text can include quickly displaying text at a low bit depth and changing to a higher bit depth without noticeable changes in the text. Computer fonts include font data files with outlines and fine-tuning to be used when displaying glyphs on a display. Specific instructions or fine-tuning can be consistent between different bit depths, allowing text to be displayed in a consistent manner between different bit depths. These fine-tuning can include size, kerning, bold thickness, arm thickness, glyph spacing, glyph width, glyph height, ascender length, descender length, and serif thickness. According to aspects of the present application, these fine-tuning can be consistent between text displayed at low and high bit depths so as to reduce inconsistencies between different bit depths.

Figures 5 and 6 show examples of consistent font hinting being applied to glyphs of 1-bit (e.g., A2) and multiple bit depths (e.g., GC16). The consistent nature of fonts between different bit depths improves overall text quality and can be used to improve the user experience. 1-bit depth can be used to quickly display glyphs (e.g., for fast updates), while multiple bit depths can be used to utilize standard update displays. In some embodiments, text at 1-bit depth can be displayed first before text is updated to multiple bit depths. As previously described, it is desirable to minimize or eliminate differences in hinting between different depths to improve the user viewing experience.

5 shows an exemplary sans serif font for multi-bit font depth text 502 and 1-bit font depth text 504. The glyphs in 1-bit depth text 504 have the same width in multi-bit 502, as shown by width 506 for the letter "x" and 508 for the letter "l." Additionally, the boldface and arms of the glyphs 502 and 504 have the same thickness.

FIG6 shows an exemplary serif font (Times New Roman) for a multi-bit font depth 602 and a single-bit font depth 604. The exemplary serif in the letter "R" is indicated by 616. To define features in a font, an x-line 610 is used as a reference for comparison with other feature lines of the font. The baseline 612 refers to the line on which the letters rest, marking the bottom of most letters. The x-height refers to the height of lowercase letters above the baseline. The top line 608 specifies the height of uppercase letters from the baseline 612, with the height of uppercase letters being 617. The descender 614 refers to the distance below the baseline for some glyphs (e.g., p, g, j). The ascender 606 refers to the top of the ascender, and the distance the ascender extends above the x-height is set by the ascender. The position of the descender and ascender can vary from font to font. The font height 618 refers to the height of the font from the descender 614 to the ascender 606. 6 , glyph height 618, ascenders 606, descenders 614, and serifs 616 can be the same for 1-bit depth text 604 and multi-bit depth text 602. Additionally, kerning, or the spacing between glyphs, can be the same for the different bit depths. In some embodiments, features of specific glyphs, including disconnected pixels such as region 620 of the letter "E," can be eliminated to improve the overall quality of the rendered text.

In some embodiments, a technique for achieving a font pair rendered as shown in Figures 5 and 6 above without differences in hinting between different bit depths can include rendering a font at 1-bit depth using hints from different bit depths. A font renderer can read a font file and use the embedded hints or instructions in the font file for 1-bit depth to display text, and if the text is updated to different bit depths, the same hints or instructions are used to display the text at different bit depths, as opposed to using unique hints for each bit depth. As an example, the renderer can use embedded hints for 1-bit depth to display text at 1-bit depth, and when the text is converted to multiple bit depths, use the same hints from the 1-bit version.

In some embodiments, font hinting can be specifically designed and/or selected for more than one bit depth to reduce inconsistencies between different bit depths. Such designed hinting can be selected from pre-existing hinting used in font files for a particular font or bit depth and/or can be uniquely designed. The designed font hinting can be used to render text in a font at different bit depths.

In some embodiments, a threshold algorithm can be applied to render fonts for multiple bit depths. Displaying text in a 1-bit depth font can include rendering the text in multiple bit depths and applying a threshold algorithm to convert the multiple bit depth text into 1-bit depth text. Such a threshold algorithm can include applying a threshold to the multiple bit depth text and converting the pixels forming the text into 1-bit values based on the threshold. For example, pixel values above the threshold are converted into white pixels, while pixels below the threshold are converted into black pixels to render the text in 1-bit depth.

In some embodiments, different waveforms or voltage signals can be used to render text at multiple bit depths. The waveforms can be designed for the speed at which text is displayed on a display and/or the quality of the rendered text. As an example, one waveform can render text quickly, but the text may have poor quality, while another waveform can render text at higher quality for a longer period of time. Thus, various techniques can be used to render text at different bit depths while reducing differences in appearance.

The present application also includes a technique for reducing artifacts when updating text to new information while reducing flicker on a display. An update mask can be applied to each rendered glyph for a particular font. The mask can include pixels other than the pixels in the rendered glyph. The additional pixels can be pixels adjacent to the pixels in the glyph. When updating text information on a display, the pixels within the mask can be updated to pixel values, such as white, before or during the display of the new text. Areas outside the update mask (i.e., background pixels) will likely be converted from white to white so that they do not flicker, and since they are converted from white to white, they may not be updated. The update mask can be created in any suitable manner, such as by an algorithm or a user. The update mask can be created while the font is being rendered, as part of the rendering process, and/or after the font is rendered on the display.

Based on reducing overall flicker and/or improving the quality of displayed text, masks can be formed for specific glyphs. The mask can reduce the number of edges in the updated area to reduce overall edge artifacts. The mask can also fill in closed areas within the glyph and/or fill in areas outside the glyph but, for example, within the convex hull. The convex hull of a set X of points in Euclidean space or a plane is the smallest convex set that contains X. When X is a bounded subset of the plane, the convex hull can be visualized as a shape formed by a rubber band stretched around X. This can be called a convex envelope. More formally, the convex hull can be defined as the intersection of all convex sets that contain X or the set of all convex combinations of points in X. In some cases, the length of the edge can be considered, and the mask can be designed to reduce continuous straight edges to minimize the visibility of edge artifacts. Since there is an increase in flicker across the screen by including pixels outside the boundaries of the glyph that are pixelated in the update, the mask can be optimized to consider the balance between flicker and edge reduction levels. The update mask can be formed based on an edge reduction level, where the edge reduction level can be determined based on the total edges in the mask and the number of pixels in the mask being updated. This edge reduction level for a particular mask can be determined based on the ratio of the difference between the number of edges in the pixelated glyph and the mask to the difference between the number of pixels in the mask and the pixelated glyph. Additionally or alternatively, corners where two edges meet can show stronger ghosting than other areas, and the mask can be selected to minimize the amount of corners for the updated area. In some embodiments, the mask can include areas of consecutive characters and can be defined by how particular glyphs are connected to each other.

Figure 7A shows an exemplary pixelated text element 702 that can be displayed on an electro-optical display. The outline of text element 702 is shown by 704 in Figure 7B. In order to change the letter "a" to another glyph, some pixels within area 704 may need to be changed to another pixel value. A mask can be used to update area 704 and some adjacent pixels. Figures 8A-G are exemplary masks that may be applied when updating text element 702 to another glyph. The mask includes pixels of text element 702 and additional pixels that fall within the convex hull of the pixels of text element 702. The mask can include additional pixels to reduce the number of edges and/or the length of all edges to reduce the rate of edge accumulation.

As an example, mask 802 in FIG8A includes pixels in glyph 702 and region 804, forming a closed glyph for a pixelated letter, wherein the glyph has no holes. In another example, mask 806 in FIG8B includes additional pixel regions 808 and 810. Region 810 in FIG8B is an example of how the number of edges can be reduced by updating additional pixels in region 810, and how edge artifacts due to ghosting can be reduced by including region 810 in the mask. Another example of a mask for updating pixelated glyph 702 can include 811 in FIG8C , which includes pixels from 704 as well as regions 810 and 812, and similarly reduces edge length. Another example is mask 814 in FIG8D , which includes pixels from 704 as well as regions 810, 812, 816, and 818. The inclusion of regions 816 and 818 can reduce artifacts due to corners. FIG8E is an example of a convex hull where all points are contained within envelope 820. FIG8F is an example of a checkerboard pattern 832 within the convex hull 822, which includes regions 826 and 830, identifying the selected update region and switching between the updated regions every other update, i.e., black region 824 for the first update and white region 828 for the next update. Similar to FIG8F, FIG8G is an example of a checkerboard pattern 830 that overlays glyphs 828 to identify the regions updated when eliminated, i.e., white 832 for the first update and black 834 for the next update, then white, then black, etc. The updates can be sequential, or they can be ordered, such as black, black, white, white, or any order in which the regions are regularly updated to prevent edge ghosting. The white checkerboard represents the region updated during the first update, while the black checkerboard represents the region updated during the second update. The black and white squares in the checkerboard can be assigned to display a complete panel or a partial panel, or can be assigned randomly.

Thus, it should be understood that the particular mask selected for a given update can be selected based on the number of edges and/or corners in the mask and the total number of pixels updated by applying the mask. In this way, artifacts (e.g., edge artifacts) can be minimized without an unacceptable increase in flicker.

Having thus described several aspects and embodiments of the technology of the present application, it will be understood that various changes, modifications and improvements will readily occur to those of ordinary skill in the art. Such changes, modifications and improvements are intended to be within the spirit and scope of the technology described in this application. For example, one of ordinary skill in the art will readily envision various other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is indeed within the scope of the embodiments described herein. Those skilled in the art will understand, or will be able to confirm by using only routine experimentation, many equivalents to the specific embodiments described herein. Therefore, it will be understood that the above embodiments are presented by way of example only, and within the scope of the appended claims and their equivalents, embodiments of the present invention may be practiced other than as specifically described. In addition, any combination of two or more features, systems, products, materials, kits and/or methods described herein is included within the scope of this disclosure where such features, systems, products, materials, kits and/or methods are not inconsistent with each other.

Claims (4)

1. A method for driving an electro-optic display, the method comprising: The glyphs are first displayed on the monitor, wherein font fine-tuning is used to display the glyphs in the font, wherein the glyphs are first displayed with a first-order depth; and The same glyphs are displayed a second time on the display at a second bit depth, wherein the same font is used to fine-tune the second display of the glyphs in the font; Wherein, the first bit depth has fewer bits than the second bit depth, and wherein the time required to display the glyph at the first bit depth is shorter than the time required to display the glyph at the second bit depth. 2. The method according to claim 1, wherein the first bit depth is 1 bit. 3. The method of claim 1, wherein the font fine-tuning is specific to the second bit depth. 4. The method of claim 1, wherein the font fine-tuning is configured to optimize the characteristics of the font for the first bit depth and the second bit depth.