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US-12626671-B2 - Methods for producing full-color e-paper images with low grain

US12626671B2US 12626671 B2US12626671 B2US 12626671B2US-12626671-B2

Abstract

Improved methods for driving color electro-optic displays, such as electrophoretic displays with multi-particle electrophoretic media. When driving between a first image having a high color depth (i.e., greater than 64 distinct colors) and a second image having a high color depth, the data processing load can be reduced by mapping the set of colors in the first image to a reduced color set. In a preferred embodiment, the electro-optic medium is an electrophoretic medium that includes a white particle and cyan, yellow, and magenta subtractive primary-colored particles. Images with high color depth look less grainy and are more appealing to consumers.

Inventors

  • Kenneth R Crounse
  • Amit Deliwala
  • Hjalmar Edzer Ayco Huitema
  • Stephen J. Telfer

Assignees

  • E INK CORPORATION

Dates

Publication Date
20260512
Application Date
20250123

Claims (13)

  1. 1 . A method for driving an electro-optic medium between a first optical state and a second optical state, wherein the electro-optic medium is disposed between first and second electrodes and the electro-optic medium changes optical states in response to voltage sequences applied between the first and second electrodes, wherein the electro-optic medium is capable of producing at least 64 distinct optical states, the method comprising: mapping the first optical state to a reduced color state, wherein the first optical state comprises one of the at least 64 distinct optical states and the reduced color state is one of no more than 16 distinct colors; identifying a voltage sequence that will cause the electro-optic medium to transition from the reduced color state mapped from the first optical state to the second optical state, wherein the second optical state comprises another one of the at least 64 distinct optical states; and providing the voltage sequence between the first and second electrodes.
  2. 2 . The method of claim 1 , wherein the electro-optic medium is capable of producing 128 distinct optical states.
  3. 3 . The method of claim 1 , wherein the reduced color state is one of eight distinct colors.
  4. 4 . The method of claim 3 , wherein the eight distinct colors are red, green, blue, cyan, yellow, magenta, white, and black.
  5. 5 . The method of claim 1 , wherein the mapping comprises matching the first optical state and the reduced color state on a look-up-table.
  6. 6 . The method of claim 1 , wherein the providing step is done by a controller.
  7. 7 . The method of claim 1 , wherein the electro-optic medium is an electrophoretic medium.
  8. 8 . The method of claim 7 , wherein the electrophoretic medium includes a reflective white particle and at least one subtractive color particle or a reflective white particle and at least one reflective (non-white) color particle.
  9. 9 . The method of claim 8 , wherein the electrophoretic medium includes a fourth type of electrophoretic particle.
  10. 10 . The method of claim 9 , wherein two of the types of particles are negatively charged and two of the types of particles are positively charged, or wherein one of the types of particles is negatively charged and three of the types of particles are positively charged, or wherein three of the types of particles are negatively charged and one of the types of particles is positively charged.
  11. 11 . The method of any of claim 10 , wherein the electrophoretic medium is encapsulated in microcapsules or microcells.
  12. 12 . The method of claim 1 , wherein the first electrode is a light-transmissive electrode and the second electrode is a pixel electrode of an active matrix of pixel electrodes.
  13. 13 . The method of claim 1 , wherein the voltage sequence is DC balanced.

Description

RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63/624,778, filed Jan. 24, 2024. All patents and publications disclosed herein are incorporated by reference in their entireties. BACKGROUND An electrophoretic display (EPD) changes color by modifying the position of one or more charged colored particles with respect to a light-transmissive viewing surface. Such electrophoretic displays are typically referred to as “electronic paper” or “ePaper” because the resulting display has high contrast and is sunlight-readable, much like ink on paper. Electrophoretic displays have enjoyed widespread adoption in eReaders because the electrophoretic displays provide a book-like reading experience, use little power, and allow a user to carry a library of hundreds of books in a lightweight handheld device. Such devices are increasingly being adapted to display of out-of-home (OOH) digital content, such as shelf labels, outdoor advertisement and transportation signage. For many years, electrophoretic displays included only two types of charged color particles, black and white. (To be sure, “color” as used herein includes black and white.) The white particles are often of the light scattering type, and comprise, e.g., titanium dioxide, while the black particles are absorptive across the visible spectrum, and may comprise carbon black, or an absorptive metal oxide, such as copper chromite. In the simplest sense, a black and white electrophoretic display only requires a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels)—either segmented electrodes or an active matrix of pixel electrodes controlled by transistors—a pattern can be made to appear electronically at the viewing surface. The pattern can be, for example, the text to a book. More recently, a variety of color option have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black, white, yellow), and four color displays (black, white, red, yellow). Similar to the operation of black and white electrophoretic displays, electrophoretic displays with three or four reflective pigments operate similar to the simple black and white displays because the desired color particle is driven to the viewing surface. The driving schemes are far more complicated than only black and white, but in the end, the optical function of the particles is the same. Advanced Color electronic Paper (ACeP™) also includes four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thereby allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and ink-jet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the instance of ACeP, the relative positions of the cyan, yellow, magenta and white particles with respect to the viewing surface will determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometer-sized) pigments within a working space of about 10 to 20 micrometers in thickness. Obviously, variations in the position of the pigments will result in incorrect colors being displayed at a given pixel. Accordingly, exquisite voltage control is required for such a system. More details of this system are available in the following U.S. Patents, all of which are incorporated by reference in their entireties: U.S. Pat. Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, 10,593,272, and 10,657,869. Unsurprisingly, having more colors available for displaying an image results in better-looking images, especially when the subject is a human or a landscape. Additionally, it has been found that images with the same pixel resolution, but smaller color sets tend to looking “grainy” because of the notable color differences between adjacent pixels that vary by only one shade. See also FIG. 7. Having more color depth comes with a price, however. Achieving hundreds of distinct color states with an ACeP-like system requires longer waveforms (voltage impulse sequences) so that all of the color particles are arranged in the correct order and with the correct spacing vis-à-vis the white pigment and the top light-transmissive electrode (viewing surface). [A distinct color state has a set of coordinates in the CIELAB color space (i.e., L*, a, b values) different from another distinct co