Image processing method and image processing device for reducing color shift

• US 10,621,930 B2
• Filed: 02/13/2018
• Issued: 04/14/2020
• Est. Priority Date: 02/13/2018
• Status: Active Grant

• Current Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Original Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Inventors: Wu, Tung-Ying
• Primary Examiner(s): Snyder, Adam J
• Application Number:
  US15/895,993
• Publication Number:
  US 20190251916A1
• Time in Patent Office: 791 Days
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2340/0457 Improvement of perceived resolution by subpixel rendering
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127

Abstract

A method for processing an image includes the following steps. A data of the image including a first pixel and a second pixel adjacent to each other is provided. A first subpixel of the first pixel and a second subpixel of the second pixel are set as a higher subpixel and a lower subpixel. A lookup process is performed to determine a shifted gray level of the higher subpixel and a shifted gray level of the lower subpixel in accordance with the gray level of the higher subpixel and the gray level of the lower subpixel respectively. A gray level of the higher subpixel and a gray level of the lower subpixel are updated in accordance with the shifted gray level of the higher subpixel and the shifted gray level of the lower subpixel.

Claims

1. A method for processing an image, comprising:

providing a data of the image, wherein the image comprises a first pixel and a second pixel adjacent to each other, wherein each of the first pixel and the second pixel has a plurality of subpixels, wherein the data comprises a gray level of each of the subpixels;

setting a first subpixel of the subpixels of the first pixel and a second subpixel of the subpixels of the second pixel as a higher subpixel and a lower subpixel, wherein the color of the first subpixel is the same as the color of the second subpixel;

performing a lookup process to determine a shifted gray level of the higher subpixel and a shifted gray level of the lower subpixel in accordance with the gray level of the higher subpixel and the gray level of the lower subpixel respectively, wherein the shifted gray level of the higher subpixel is greater than the shifted gray level of the lower subpixel; and

updating the gray level of the first subpixel and the gray level of the second subpixel in accordance with the shifted gray level of the higher subpixel and the shifted gray level of the lower subpixel;

wherein setting the first subpixel and the second subpixel as the higher subpixel and the lower subpixel comprises,

calculating a gray-level difference which is a difference between the gray level of the first subpixel and the gray level of the second subpixel;

determining the first subpixel and the second subpixel as the higher subpixel and the lower subpixel if the gray-level difference is less than a difference threshold; and

determining the first subpixel and the second subpixel as the lower subpixel and the higher subpixel if the gray-level difference is greater than or equal to the difference threshold.

2. The method of claim 1, further comprising:

performing an edge detection on the first subpixel and on the second subpixel respectively to determine whether an edge is presented;

decreasing the shifted gray level of the higher subpixel to obtain a decreased shifted gray level, and increasing the shifted gray level of the lower subpixel to obtain an increased shifted gray level, if the edge is presented; and

replacing the shifted gray level of the higher subpixel and the shifted gray level of the lower subpixel with the decreased shifted gray level and the increased shifted gray level, respectively, before updating the gray level of the first subpixel and the gray level of the second subpixel, if the edge is presented.

3. The method of claim 2, wherein each of the first pixel and the second pixel has a plurality of neighboring pixels, wherein each of the neighboring pixels has a plurality of subpixels, and the neighboring pixels of the first pixel do not comprise the other pixels positioned in a next row of the first pixel, and the neighboring pixels of the second pixel do not comprise the other pixels positioned in a next row of the second pixel,

wherein performing the edge detection on the first subpixel and on the second subpixel respectively to determine whether the edge is presented comprises:

calculating a gray level difference of the first subpixel which is a difference between the gray level of the first subpixel and a gray level of a third subpixel of the subpixels of the neighboring pixels of the first pixel, wherein the color of the third subpixel is the same as the color of the first subpixel;

calculating a gray level difference of the second subpixel which is the difference between the gray level of the second subpixel and a gray level of a fourth subpixel of the subpixels of the neighboring pixels of the second pixel, wherein the color of the fourth subpixel is the same as the color of the second subpixel; and

determining the edge is presented if either a greatest value of the gray level differences of the first subpixel is larger than or equal to an edge threshold or a greatest value of the gray level differences of the second subpixel is larger than or equal to the edge threshold.

4. The method of claim 2,

wherein a formula of decreasing the shifted gray level of the higher subpixel to obtain the decreased shifted gray level is as follows:

5. The method of claim 2,

wherein a formula of increasing the shifted gray level of the lower subpixel to obtain the increased shifted gray level is as follows:

6. The method of claim 1, further comprising:

performing a color conversion to obtain a plurality of color values of the first pixel and a plurality of color values of the second pixel in accordance with the gray levels of the subpixels of the first pixel and the gray levels of the subpixels of the second pixel respectively;

performing a color lookup process to determine a corrected gain of the first subpixel and a corrected gain of the second subpixel in accordance with the color values of the first pixel and the color values of the second pixel respectively; and

multiplying the gray level of the first subpixel by the corrected gain of the first subpixel, and multiplying the gray level of the second subpixel by the corrected gain of the second subpixel, before performing the lookup process.

7. The method of claim 6, wherein the color conversion is an RGB-to-HSV conversion or an RGB-to-HSL conversion.

8. The method of claim 1, wherein each of the first subpixel and the second subpixel is one of a red subpixel, a green subpixel, and a blue subpixel.

9. The method of claim 1, wherein each of the first subpixel and the second subpixel is one of a red subpixel, a green subpixel, a blue subpixel, and a white subpixel.

10. The method of claim 9, further comprising:

performing an RGB-to-RGBW conversion before setting the first subpixel and the second subpixel.

11. A device for processing an image, comprising:

a receiving circuit configured to receive a data of the image, wherein the image comprises a first pixel and a second pixel adjacent to each other, wherein each of the first pixel and the second pixel has a plurality of subpixels, wherein the data comprises a gray level of each of the subpixels;

a setting circuit configured to set a first subpixel of the subpixels of the first pixel and a second subpixel of the subpixels of the second pixel as a higher subpixel and a lower subpixel, wherein the color of the first subpixel is the same as the color of the second subpixel;

a lookup circuit configured to perform a lookup process to determine a shifted gray level of the higher subpixel and a shifted gray level of the lower subpixel in accordance with the gray level of the higher subpixel and the gray level of the lower subpixel respectively, wherein the shifted gray level of the higher subpixel is greater than the shifted gray level of the lower subpixel; and

an updating circuit configured to update the gray level of the first subpixel and the gray level of the second subpixel in accordance with the shifted gray level of the higher subpixel and the shifted gray level of the lower subpixel;

wherein the setting circuit is configured to perform the following steps;

calculating a gray-level difference which is a difference between the gray level of the first subpixel and the gray level of the second subpixel;

determining the first subpixel and the second subpixel as the higher subpixel and the lower subpixel if either the gray-level difference is less than a difference threshold or the gray level of the first subpixel is greater than or equal to the gray level of the second subpixel; and

determining the first subpixel and the second subpixel as the lower subpixel and the higher subpixel if the gray-level difference is greater than or equal to the difference threshold and the gray level of the first subpixel is less than the gray level of the second subpixel.

12. The device of claim 11, further comprising:

an edge detection circuit configured to perform an edge detection on the first subpixel and on the second subpixel respectively to determine whether an edge is presented;

an edge correction circuit configured to decrease the shifted gray level of the higher subpixel to obtain a decreased shifted gray level and to increase the shifted gray level of the lower subpixel to obtain an increased shifted gray level, and to replace the shifted gray level of the higher subpixel and the shifted gray level of the lower subpixel with the decreased shifted gray level and the increased shifted gray level before updating the gray level of the first subpixel and the gray level of the second subpixel, respectively, if the edge is presented.

13. The device of claim 12, wherein each of the first pixel and the second pixel has a plurality of neighboring pixels, wherein each of the neighboring pixels has a plurality of subpixels, and the neighboring pixels of the first pixel do not comprise the other pixels positioned in a next row of the first pixel, and the neighboring pixels of the second pixel do not comprise the other pixels positioned in the next row of the second pixel,

wherein the edge detection circuit is configured to perform the following steps:

calculating a gray level difference of the first subpixel which is a difference between the gray level of the first subpixel and a gray level of a third subpixel of the subpixels of the neighboring pixels of the first pixel, wherein the color of the third subpixel is the same as the color of the first subpixel;

calculating a gray level difference of the second subpixel which is the difference between the gray level of the second subpixel and a gray level of a fourth subpixel of the subpixels of the neighboring pixels of the second pixel, wherein the color of the fourth subpixel is the same as the color of the second subpixel; and

determining the edge is presented if either a greatest value of the gray level differences of the first subpixel is larger than or equal to an edge threshold or a greatest value of the gray level differences of the second subpixel is larger than or equal to the edge threshold.

14. The device of claim 12,

wherein a formula of decreasing the shifted gray level of the higher subpixel to obtain the decreased shifted gray level is as follows:

15. The device of claim 14,

wherein a formula of increasing the shifted gray level of the lower subpixel to obtain the increased shifted gray level is as follows:

16. The device of claim 11, further comprising:

a color conversion circuit configured to perform a color conversion to obtain a plurality of color values of the first pixel and a plurality of color values of the second pixel in accordance with the gray levels of the subpixels of the first pixel and the gray levels of the subpixels of the second pixel respectively;

a color lookup circuit configured to perform a color lookup process to determine a corrected gain of the first subpixel and a corrected gain of the second subpixel in accordance with the color values of the first pixel and the color values of the second pixel respectively; and

wherein the updating circuit is further configured to multiply the gray level of the first subpixel by the corrected gain of the first subpixel and to multiply the gray level of the second subpixel by the corrected gain of the second subpixel, before performing the lookup process.

17. The device of claim 16, wherein the color conversion is an RGB-to-HSV conversion or an RGB-to-HSL conversion.

18. The device of claim 11, wherein each of the first subpixel and the second subpixel is one of a red subpixel, a green subpixel, and a blue subpixel.

19. The device of claim 11, wherein each of the first subpixel and the second subpixel is one of a red subpixel, a green subpixel, a blue subpixel, and a white subpixel.

20. The device of claim 19, further comprising:

an RGB-to-RGBW conversion circuit configured to perform an RGB-to-RGBW conversion before setting the first subpixel and the second subpixel.

21. A method for processing an image, comprising:

providing a data of the image, wherein the image comprises a plurality of pixels, wherein each of the pixels has a plurality of subpixels, the data comprises a gray level of each of the subpixels, wherein the pixels comprise a first pixel and a second pixel positioned at a first column in sequence, wherein the pixels further comprise a third pixel and a fourth pixel positioned at a second column in sequence, wherein the first column is adjacent to the second column, wherein the first pixel is adjacent to the third pixel;

setting a first subpixel of the subpixels of the first pixel, a second subpixel of the subpixels of the second pixel, a third subpixel of the subpixels of the third pixel, and a fourth subpixel of the subpixels of the fourth pixel as a first higher subpixel, a first lower subpixel, a second higher subpixel, and a second lower subpixel, wherein the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel have the same color;

performing a lookup process to determine a shifted gray level of the first higher subpixel and a shifted gray level of the first lower subpixel in accordance with the gray level of the first higher subpixel and the gray level of the first lower subpixel, respectively;

performing a recovery process to determine a shifted gray level of the second higher subpixel and a shifted gray level of the second lower subpixel in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively; and

updating the gray level of the first subpixel, the gray level of the second subpixel, the gray level of the third subpixel, and the gray level of the fourth subpixel in accordance with the shifted gray level of the first subpixel, the shifted gray level of the second subpixel, the shifted gray level of the third subpixel, and the shifted gray level of the fourth subpixel, respectively.

22. The method of claim 21, wherein performing the recovery process comprises:

performing a recovery lookup process to determine a second higher gain value and a second lower gain value in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively;

multiplying the shifted gray level of the first higher subpixel by the second higher gain value to determine the shifted gray level of the second higher subpixel; and

multiplying the shifted gray level of the first lower subpixel by the second lower gain value to determine the shifted gray level of the second lower subpixel.

23. The method of claim 21, wherein performing the recovery process comprises:

performing a recovery lookup process to determine a second higher difference value and a second lower difference value in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively;

adding the second higher difference value to the shifted gray level of the first higher subpixel to determine the shifted gray level of the second higher subpixel; and

adding second lower difference value to the shifted gray level of the first lower subpixel to determine the shifted gray level of the second lower subpixel.

24. The method of claim 21, wherein setting the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel as the first higher subpixel, the first lower subpixel, the second higher subpixel, and the second lower subpixel comprises:

setting the first subpixel as the first higher subpixel;

setting the second subpixel as the first lower subpixel;

setting the third subpixel as the second lower subpixel; and

setting the fourth subpixel as the second higher subpixel.

25. The method of claim 21, wherein setting the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel as the first higher subpixel, the first lower subpixel, the second higher subpixel, and the second lower subpixel comprises:

setting the first subpixel as the first lower subpixel;

setting the second subpixel as the first higher subpixel;

setting the third subpixel as the second higher subpixel; and

setting the fourth subpixel as the second lower subpixel.

26. The method of claim 21, wherein each of the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel is one of a red subpixel, a green subpixel, and a blue subpixel.

27. A device for processing an image, comprising:

a receiving circuit configured to receive a data of the image, wherein the image comprises a plurality of pixels, wherein each of the pixels has a plurality of subpixels, the data comprises a gray level of each of the subpixels, wherein the pixels comprise a first pixel and a second pixel positioned at a first column in sequence, wherein the pixels further comprise a third pixel and a fourth pixel positioned at a second column in sequence, wherein the first column is adjacent to the second column, wherein the first pixel is adjacent to the third pixel;

a setting circuit configured to set a first subpixel of the subpixels of the first pixel, a second subpixel of the subpixels of the second pixel, a third subpixel of the subpixels of the third pixel, and a fourth subpixel of the subpixels of the fourth pixel as a first higher subpixel, a first lower subpixel, a second higher subpixel, and a second lower subpixel, wherein the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel have the same color;

a lookup circuit configured to perform a lookup process to determine a shifted gray level of the first higher subpixel and a shifted gray level of the first lower subpixel in accordance with the gray level of the first higher subpixel and the gray level of the first lower subpixel, respectively;

a recovery lookup circuit configured to perform a recovery process to determine a shifted gray level of the second higher subpixel and a shifted gray level of the second lower subpixel in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively; and

an updating circuit configured to update the gray level of the first subpixel, the gray level of the second subpixel, the gray level of the third subpixel, and the gray level of the fourth subpixel in accordance with the shifted gray level of the first subpixel, the shifted gray level of the second subpixel, the shifted gray level of the third subpixel, and the shifted gray level of the fourth subpixel, respectively.

28. The device of claim 27, performing the recovery process comprises:

performing a recovery lookup process to determine a second higher gain value and a second lower gain value in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively;

multiplying the shifted gray level of the first higher subpixel by the second higher gain value to determine the shifted gray level of the second higher subpixel; and

multiplying the shifted gray level of the first lower subpixel by the second lower gain value to determine the shifted gray level of the second lower subpixel.

29. The device of claim 27, performing the recovery process comprises:

performing a recovery lookup process to determine a second higher difference value and a second lower difference value in accordance with the shifted gray level of the first higher subpixel and the shifted gray level of the first lower subpixel, respectively;

adding the second higher difference value to the shifted gray level of the first higher subpixel to determine the shifted gray level of the second higher subpixel; and

adding the second lower difference value to the shifted gray level of the first lower subpixel to determine the shifted gray level of the second lower subpixel.

30. The device of claim 27, wherein the setting circuit is configured to perform the following steps:

setting the first subpixel as the first higher subpixel;

setting the second subpixel as the first lower subpixel;

setting the third subpixel as the second lower subpixel; and

setting the fourth subpixel as the second higher subpixel.

31. The device of claim 27, wherein the setting circuit is configured to perform the following steps:

setting the first subpixel as the first lower subpixel;

setting the second subpixel as the first higher subpixel;

setting the third subpixel as the second higher subpixel; and

setting the fourth subpixel as the second lower subpixel.

32. The device of claim 27, wherein each of the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel is one of a red subpixel, a green subpixel, and a blue subpixel.