Method for rendering color images

• US 10,270,939 B2
• Filed: 05/11/2017
• Issued: 04/23/2019
• Est. Priority Date: 05/24/2016
• Status: Active Grant

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: E Ink Holdings Incorporated
• Inventors: Crounse, Kenneth R.
• Primary Examiner(s): Nguyen, Anh-Vinh T
• Application Number:
  US15/592,515
• Publication Number:
  US 20170346989A1
• Time in Patent Office: 712 Days
• Field of Search: None
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/2059 using error diffusion
• CPC Class Codes: G09G 3/344 based on particles moving in a fluid or in a gas, e.g. electrophoretic devices electrophoretic devices per se G02F1/167
• CPC Class Codes: H04N 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence

Abstract

An image is rendered on a display having a limited number of primary colors by (104) combining input data representing the color of a pixel to be rendered with error data to form modified input data, determining in a color space the simplex (208—typically a tetrahedron) enclosing the modified input data and the primary colors associated with the simplex, converting (210) the modified image data to barycentric coordinates based upon the primary colors associated with the simplex and (212) setting output data to the primary having the largest barycentric coordinate, calculating (214) the difference between the modified input data and the output data for the pixel, thus generating error data, applying (106) this error data to at least one later-rendered pixel, and applying the output data to the display and thus rendering the image on the display. Apparatus and computer-storage media for carrying out this process are also provided.

Claims

1. A method of rendering an image on a plurality of pixels of a display, wherein each of the plurality of pixels can display any one of a set of primary colors, the method comprising:

receiving input data representing the colors of the plurality of pixels to be rendered;

for each of said plurality of pixels in sequence;

combining the input data with error data-to form modified input data;

determining in a color space the simplex enclosing the modified input data, and the display primary colors associated with the simplex;

converting the modified input data to barycentric coordinates based upon the simplex and setting output data for the pixel to the primary color having the largest barycentric coordinate; and

calculating the difference between the modified input data and the output data for the pixel and thereby generating error data for the pixel;

the error data thus generated being used in the processing of input data of at least one pixel later in the sequence of pixels; and

supplying the output data for the plurality of pixels to the display and thereby rendering the image on the plurality of pixels of the display.

2. The method of claim 1 further comprising testing the modified input data to determine whether it is within the color gamut of the display and, if the modified input data is outside this color gamut, further modifying the modified input data by projecting the modified input data on to the color gamut to produce projected input data which are used in place of the modified input data in the later stages of the method.

3. The method of claim 2 wherein the projection of the modified input data is effected towards the neutral axis of the color space along a line of constant lightness and hue.

4. The method of claim 2 wherein the projection of the modified input data is effected towards the color represented by the input data for the pixel until the boundary of the color gamut is reached.

5. The method of claim 2 wherein the projected input data is used for both the conversion to barycentric coordinates and for the generation of the error data.

6. The method of claim 2 wherein the projected input data is used for the conversion to barycentric coordinates but the modified image data prior to the projection is used for the generation of the error data.

7. The method of claim 1 wherein the color space is three-dimensional so that the simplex is a tetrahedron.

8. The method of claim 1 wherein the error data is used in the processing of input data of more than one pixel later in the sequence of pixels.

9. The method of claim 1 wherein the error data is used in the processing of input data of at least four pixels later in the sequence of pixels.

10. The method of claim 9 wherein the at least four pixels receive differing amounts of the error data.

11. The method of claim 1 wherein the display is an electrophoretic display.

12. An apparatus comprising a display device having a plurality of pixels, each of which is arranged to display any one of a plurality of primary colors, and a computing device capable of carrying out the method of claim 1 and supplying its output data for the plurality of pixels to the display device, thereby causing the display device to display an image.

13. A non-transitory computer storage medium comprising instructions that when executed by a processor cause the processor to carry out the method of claim 1.