Controller and methods for quantization and error diffusion in an electrowetting display device

1. A method of driving an electrowetting display device including a plurality of sub-pixels, the method comprising:

determining a first sub-pixel of the plurality of sub-pixels is in an open state and a first target reflectance level of the first sub-pixel is less than a threshold reflectance level;

setting a first reflectance level of the first sub-pixel in the plurality of sub-pixels to a threshold reflectance level;

determining the first sub-pixel of the plurality of sub-pixels is in a closed state and the first target reflectance level of the first sub-pixel is less than the threshold reflectance level;

setting the first reflectance level of the first sub-pixel to a minimum reflectance level;

determining a reflectance quantization error by comparing the first reflectance level of the first sub-pixel to the first target reflectance level of the first sub-pixel, the first target reflectance level of the first sub-pixel based at least in part on image data for a first source image pixel of a plurality of source image pixels;

setting a second reflectance level of a second sub-pixel in the plurality of sub-pixels to a second target reflectance level of the second sub-pixel based at least in part on image data for a second source image pixel of the plurality of source image pixels plus a first fraction of the reflectance quantization error;

setting a third reflectance level of a third sub-pixel in the plurality of sub-pixels to a third target reflectance level of the third sub-pixel based at least in part on image data for a third source image pixel of the plurality of source image pixels plus a second fraction of the reflectance quantization error; and

setting a fourth reflectance level of a fourth sub-pixel in the plurality of sub-pixels to a fourth target reflectance level of the fourth sub-pixel based at least in part on image data for a fourth source image pixel of the plurality of source image pixels plus a third fraction of the reflectance quantization error.

2. The method of claim 1 , wherein the first sub-pixel is in a first pixel of the electrowetting display device and the second sub-pixel is in a second pixel of the electrowetting display device, the method further comprising determining the first fraction is ½.

3. The method of claim 2 , further comprising determining the first pixel and the second pixel are in a same row of pixels in the electrowetting display device.

4. The method of claim 2 , wherein the third sub-pixel is associated with a third pixel of the electrowetting display device and the fourth sub-pixel is associated with a fourth pixel of the electrowetting display device, the method further comprising:

determining the second fraction is ¼; and

determining the third fraction is ¼.

5. The method of claim 4 , further comprising determining the third pixel and the fourth pixel are in a same row of pixels in the electrowetting display device.

6. The method of claim 1 , further comprising, before setting a reflectance level of a first sub-pixel in the plurality of sub-pixels to a minimum reflectance level or a threshold reflectance level:

identifying a white sub-pixel adjacent to the first sub-pixel;

determining a fifth target reflectance level of the white sub-pixel;

comparing the fifth target reflectance level of the white sub-pixel to the threshold reflectance level;

determining that the fifth target reflectance level of the white sub-pixel is less than the threshold reflectance level;

determining a metamer transfer value based at least in part on the fifth target reflectance;

setting a reflectance level of the white sub-pixel based on the determination of the metamer transfer value; and

distributing the metamer transfer value to each sub-pixel of a set of sub-pixels neighboring the white sub-pixel.

7. The method of claim 6 , wherein determining a metamer transfer value further comprises:

identifying, in the plurality of sub-pixels, the set of sub-pixels neighboring the white sub-pixel;

determining a first sub-pixel of the set of sub-pixels neighboring the white sub-pixel having a greatest target reflectance level, wherein the first sub-pixel has a first target reflectance level greater than or equal to a second target reflectance level of a second sub-pixel of the set of sub-pixels neighboring the white sub-pixel and the first target reflectance level is greater than or equal to a third target reflectance level of a third sub-pixel of the set of sub-pixels neighboring the white sub-pixel; and

setting a maximum metamer transfer value equal to (1—the first target reflectance level).

8. The method of claim 7 , further comprising:

determining a target reflectance level of the first sub-pixel, the target reflectance level of the first sub-pixel based at least in part on image data for a first source image pixel of a plurality of source image pixels;

setting a reflectance level of the first sub-pixel to the target reflectance level of the first sub-pixel plus the metamer transfer value; and

setting the reflectance level of the white sub-pixel to a target reflectance level of the white sub-pixel minus the metamer transfer value.

9. The method of claim 8 , further comprising determining each sub-pixel in the set of sub-pixels is associated with a first pixel containing the white sub-pixel or a second pixel adjacent to the first pixel.

10. A method of driving an electrowetting display device including a plurality of sub-pixels, the method comprising:

determining a first sub-pixel of the plurality of sub-pixels is in an open state and a first target reflectance level of the first sub-pixel is less than a threshold reflectance level;

setting a first reflectance level of the first sub-pixel in the plurality of sub-pixels to a threshold reflectance level;

determining the first sub-pixel of the plurality of sub-pixels is in a closed state and the first target reflectance level of the first sub-pixel is less than the threshold reflectance level;

setting the first reflectance level of the first sub-pixel to a minimum reflectance level;

determining a reflectance quantization error by comparing the first reflectance level of the first sub-pixel to a first target reflectance level of the first sub-pixel, the first target reflectance level of the first sub-pixel based at least in part on image data for a first source image pixel of a plurality of source image pixels; and

setting a second reflectance level of a second sub-pixel in the plurality of sub-pixels to a second target reflectance level of the second sub-pixel based at least in part on image data for a second source image pixel of the plurality of source image pixels plus a first fraction of the reflectance quantization error.

11. The method of claim 10 , wherein the first sub-pixel is in a first pixel of the electrowetting display device and the second sub-pixel is in a second pixel of the electrowetting display device, the method further comprising determining the first fraction is ½.

12. The method of claim 10 , further comprising determining the first pixel and the second pixel are in a same row of pixels in the electrowetting display device.

13. The method of claim 10 , further comprising:

setting a third reflectance level of a third sub-pixel in the plurality of sub-pixels to a third target reflectance level of the third sub-pixel based at least in part on image data for a third source image pixel of the plurality of source image pixels plus a second fraction of the reflectance quantization error; and

setting a fourth reflectance level of a fourth sub-pixel in the plurality of sub-pixels to a fourth target reflectance level of the fourth sub-pixel based at least in part on image data for a fourth source image pixel of the plurality of source image pixels plus a third fraction of the reflectance quantization error.

14. The method of claim 13 , wherein the third sub-pixel is associated with a third pixel of the electrowetting display device and the fourth sub-pixel is associated with a fourth pixel of the electrowetting display device, the method further comprising:

determining the second fraction is ¼; and

determining the third fraction is ¼.

15. An electrowetting display device, comprising:

a first support plate and a second support plate opposite the first support plate;

a pixel region between the first support plate and the second support plate, the pixel region including a data line and a gate line for controlling a state of a first sub-pixel of a plurality of sub-pixels of the electrowetting display device; and

a display controller configured to:

determine the first sub-pixel of the plurality of sub-pixels is in an open state and a first target reflectance level of the first sub-pixel is less than a threshold reflectance level;

set a first reflectance level of the first sub-pixel in the plurality of sub-pixels to a threshold reflectance level;

determine the first sub-pixel of the plurality of sub-pixels is in a closed state and the first target reflectance level of the first sub-pixel is less than the threshold reflectance level;

set the first reflectance level of the first sub-pixel to a minimum reflectance level;

determine a reflectance quantization error by comparing the first reflectance level of the first sub-pixel to the first target reflectance level of the first sub-pixel, the first target reflectance level of the first sub-pixel based at least in part on image data for a first source image pixel of a plurality of source image pixels;

set a second reflectance level of a second sub-pixel in the plurality of sub-pixels to a second target reflectance level of the second sub-pixel based at least in part on image data for a second source image pixel of the plurality of source image pixels plus a first fraction of the reflectance quantization error;

set a third reflectance level of a third sub-pixel in the plurality of sub-pixels to a third target reflectance level of the third sub-pixel based at least in part on image data for a third source image pixel of the plurality of source image pixels plus a second fraction of the reflectance quantization error; and

set a fourth reflectance level of a fourth sub-pixel in the plurality of sub-pixels to a fourth target reflectance level of the fourth sub-pixel based at least in part on image data for a fourth source image pixel of the plurality of source image pixels plus a third fraction of the reflectance quantization error.

16. The electrowetting display device of claim 15 , wherein the first sub-pixel is in a first pixel of the electrowetting display device and the second sub-pixel is in a second pixel of the electrowetting display device, and the first fraction is ½.

17. The electrowetting display device of claim 16 , wherein the display controller is further configured to:

determine the first pixel and the second pixel are in a same row of pixels in the electrowetting display device.

18. The electrowetting display device of claim 16 , wherein the third sub-pixel is associated with a third pixel of the electrowetting display device and the fourth sub-pixel is associated with a fourth pixel of the electrowetting display device; and

wherein the display controller is further configured to:

determine the second fraction is ¼; and

determine the third fraction is ¼.