Method for detecting and correcting defective pixels in a digital image sensor

• US 20040051798A1
• Filed: 09/18/2002
• Published: 03/18/2004
• Est. Priority Date: 09/18/2002
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Zhang, Xuemei, Ying, Bond Yu-Pong, Kakarala, Ramakrishna, Stanback, John H.
• Granted Patent: US 7,283,164 B2
• Time in Patent Office: Days
• US Class Current: 348/246
• CPC Class Codes: H04N 2209/045 using mosaic colour filter
• CPC Class Codes: H04N 25/68 applied to defects

Abstract

A bad pixel correction (BPC) algorithm that can be implemented on the image sensor chip is provided for detecting and correcting defective pixels in a digital color image sensor. Gradients of neighboring pixels in at least one other color plane than the color plane of a current pixel and a range of sensor values from neighboring pixels in the same color plane as the current pixel are determined. If the sensor value of the current pixel is outside of the range by a threshold amount that is calculated using one or more of the gradients, the current pixel is determined to be a defective pixel, and replaced using the sensor values of the neighboring pixels in the same color plane.

Claims

1. A digital image sensor for detecting and correcting sensor values from defective pixels in an image, comprising:

an array of pixels arranged in rows and columns, each of said pixels in said array of pixels producing a respective sensor value for an image;

a buffer for storing at least part of said sensor values produced by at least one of said rows of said pixels for said image, one of said sensor values being a current sensor value in a first color plane produced by a current one of said pixels; and

a processor connected to receive said sensor values stored in said buffer, compute one or more gradients from said sensor values in at least a second color plane and determine whether said current pixel is defective using said one or more gradients.

2. The sensor of claim 1, wherein said processor further calculates a threshold amount using said one or more gradients and a range of values for said current pixel based on said sensor values produced by neighboring ones of said pixels in said first color plane stored within said buffer, said current pixel being defective when said current sensor value is outside of said range of values by more than said threshold amount.

3. The sensor of claim 2, wherein said processor further replaces said current sensor value with a replacement value calculated using said sensor values produced by said neighboring pixels.

4. The sensor of claim 3, wherein said range of values includes a maximum value and a minimum value from said sensor values produced by said neighboring pixels, said current pixel being defective when a difference value between said current sensor value and either said maximum value or said minimum value exceeds said threshold amount.

5. The sensor of claim 4, wherein said replacement value is a median value of said sensor values produced by said neighboring pixels.

6. The sensor of claim 4, wherein said maximum value can be increased by the maximum of one or more same color gradients computed from said neighboring pixels and said minimum value can be decreased by the minimum of said one or more same color gradients when said current sensor value is consistent with said one or more same color gradients.

7. The sensor of claim 6, wherein said one or more same color gradients includes one or more current row same color gradients computed from said neighboring pixels in a current one of said rows including said current pixel.

8. The sensor of claim 7, wherein said one or more same color gradients further includes one or more vertical same color gradients computed from said neighboring pixels in said current row and one or more additional ones of said rows above or below said current row, said maximum value being increased by the maximum of said current row same color gradients and said minimum value being decreased by the minimum of said current row same color gradients.

9. The sensor of claim 4, wherein said maximum value can be increased by the maximum of said one or more gradients computed from additional neighboring ones of said pixels in said second color plane within a current one of said rows including said current pixel and said minimum value can be decreased by the minimum of said one or more gradients computed from said additional neighboring pixels when said current sensor value is consistent with said one or more gradients.

10. The sensor of claim 4, wherein said processor further calculates a minimum average gradient using said one or more gradients, said threshold amount being calculated using said minimum average gradient and one or more threshold parameters.

11. The sensor of claim 10, wherein said minimum average gradient is the minimum of the absolute value of the average of said one or more gradients in said first color plane and said second plane on a first side of said current pixel and the absolute value of the average of said one or more gradients in said first color plane and said second color plane on a second side of said current pixel.

12. The sensor of claim 10, wherein said threshold parameters include a scale factor multiplied by said minimum average gradient and a pedestal added to the product of said minimum average gradient and said scale factor.

13. The sensor of claim 10, wherein said processor further calculates a minimum vertical gradient from one or more vertical gradients computed from neighboring ones of said pixels to said current pixel in said first color plane in different ones of said rows than said current pixel.

14. The sensor of claim 13, wherein said processor determines that said current pixel is defective when said difference value exceeds said threshold amount and said minimum vertical gradient exceeds said threshold amount.

15. The sensor of claim 4, wherein said processor further determines that said current pixel is defective when said current sensor value exceeds said maximum value by more than a threshold parameter.

16. The sensor of claim 3, wherein said range of values includes a maximum estimate, a minimum estimate and a mean estimate calculated using said one or more gradients, said threshold amount being calculated using said mean estimate and one or more threshold parameters, said current pixel being defective when said current sensor value is greater than said maximum estimate or less than said minimum estimate by more than said threshold amount.

17. The sensor of claim 16, wherein said replacement value is said mean estimate.

18. The sensor of claim 16, wherein said range of values includes eight estimates, said maximum estimate being the maximum of said eight estimates, said minimum estimate being the minimum of said eight estimates and said mean estimate being the mean of said eight estimates, each of said eight estimates being calculated by adding said sensor value from a surrounding one of said pixels in said first color plane to said one or more gradients in at least said second color plane in the direction of said added sensor value.

19. A method for detecting defective pixels, comprising:

storing sensor values produced by at least part of one row of pixels in a sensor for an image, one of said sensor values being a current sensor value in a first color plane produced by a current one of said pixels;

computing one or more gradients from said sensor values in at least a second color plane; and

determining whether said current pixel is defective using said one or more gradients.

20. The method of claim 19, wherein said step of determining further comprises:

calculating a threshold amount using said one or more gradients;

calculating a range of values for said current pixel based on said sensor values produced by neighboring ones of said pixels in said first color plane; and

determining that said current pixel is defective when said current sensor value is outside of said range of values by more than said threshold amount.

21. The method of claim 20, further comprising:

replacing said current sensor value with a replacement value calculated using said sensor values produced by said neighboring pixels.

22. The method of claim 21, wherein said range of values includes a maximum value and a minimum value from said sensor values produced by said neighboring pixels, said step of determining further comprising:

determining that said current pixel is defective when a difference value between said current sensor value and either said maximum value or said minimum value exceeds said threshold amount.

23. The method of claim 22, wherein said step of replacing further comprises:

calculating a median value of said sensor values produced by said neighboring pixels; and

using said median value as said replacement value.

24. The method of claim 22, wherein said step of calculating said range of values further comprises:

increasing said maximum value by the maximum of one or more same color gradients computed from said neighboring pixels when said current sensor value is consistent with said one or more same color gradients; and

decreasing said minimum value by the minimum of said one or more same color gradients when said current sensor value is consistent with said one or more same color gradients.

25. The method of claim 24, wherein said step of calculating said range of values further comprises:

computing said one or more same color gradients from said neighboring pixels in a current one of said rows including said current pixel.

26. The method of claim 25, wherein said step of calculating said range of values further comprises:

computing said one or more same color gradients from said neighboring pixels in said current row and one or more additional ones of said rows above or below said current row.

27. The method of claim 22, wherein said step of calculating said range of values further comprises:

increasing said maximum value by the maximum of said one or more gradients computed from additional neighboring ones of said pixels in said second color plane within a current one of said rows including said current pixel when said current sensor value is consistent with said one or more gradients; and

decreasing said minimum value by the minimum of said one or more gradients computed from said additional neighboring pixels when said current sensor value is consistent with said one or more gradients.

28. The method of claim 22, wherein said step of calculating said threshold amount further comprises:

calculating a minimum average gradient using said one or more gradients; and

calculating said threshold amount using said minimum average gradient and one or more threshold parameters.

29. The method of claim 28, wherein said step of calculating said minimum average gradient further comprises:

determining the minimum of the absolute value of the average of said one or more gradients in said first color plane and said second plane on a first side of said current pixel and the absolute value of the average of said one or more gradients in said first color plane and said second color plane on a second side of said current pixel.

30. The method of claim 28, wherein threshold parameters include a scale factor and a pedestal, and wherein said step of calculating said threshold amount further comprises:

multiplying said scale factor by said minimum average gradient; and

adding said pedestal to the product of said minimum average gradient and said scale factor.

31. The method of claim 28, wherein said step of determining that said current pixel is defective further comprises:

calculating a minimum vertical gradient from one or more vertical gradients computed from neighboring ones of said pixels to said current pixel in said first color plane in different ones of said rows than said current pixel; and

determining that said current pixel is defective when said difference value exceeds said threshold amount and said minimum vertical gradient exceeds said threshold amount.

32. The method of claim 22, wherein said step of determining that said current pixel is defective further comprises:

determining that said current pixel is defective when said current sensor value exceeds said maximum value by more than a threshold parameter.

33. The method of claim 21, wherein said range of values includes a maximum estimate, a minimum estimate and a mean estimate calculated using said one or more gradients, said threshold amount being calculated using said mean estimate and one or more threshold parameters, said step of determining further comprising:

determining that said current pixel is defective when said current sensor value is greater than said maximum estimate or less than said minimum estimate by more than said threshold amount.

34. The method of claim 33, wherein said step of replacing further comprises:

replacing said current sensor value with said mean estimate.

35. The method of claim 33, wherein said range of values includes eight estimates, said maximum estimate being the maximum of said eight estimates, said minimum estimate being the minimum of said eight estimates and said mean estimate being the mean of said eight estimates, said step of calculating said range of values further comprising:

calculating each of said eight estimates by adding said sensor value from a surrounding one of said pixels in said first color plane to said one or more gradients in said second color plane in the direction of said added sensor value.