Method and apparatus for setting black level in an imager using both optically black and tied pixels

• US 7,427,735 B2
• Filed: 12/14/2005
• Issued: 09/23/2008
• Est. Priority Date: 12/14/2005
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Eskerud, Erik
• Primary Examiner(s): Luu; Thanh X
• Application Number:
  US11/302,124
• Publication Number:
  US 20070131846A1
• Time in Patent Office: 1,014 Days
• Field of Search: 250/208.1, 348/241, 348/243, 348/245
• US Class Current: 250/208.1
• CPC Class Codes: H04N 25/621 for the control of blooming
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/677 for reducing the column or line fixed pattern noise
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors

Abstract

An imaging pixel array includes an active area of pixels, organized into rows and columns of pixels. The array also includes a plurality of dark pixel columns adjacent to the active area of pixels such that rows of pixels in the active area of pixels extend across the plurality of dark pixel columns. The plurality of dark pixel columns are composed of tied pixels. The array also includes a plurality of dark pixel rows adjacent to the active area of pixels and the plurality of dark pixel columns such that columns of pixels in the active area of pixels extend across the plurality of dark pixel rows. The plurality of dark pixel rows are composed of both optically black pixels and tied pixels on the same row.

Claims

1. An imaging pixel array, comprising:

an active area of pixels, organized as a plurality of rows and columns of pixels; and

a plurality of dark pixels arranged in at least one of pixel rows and pixel columns which are adjacent said active area of pixels, said plurality of dark pixels comprising optically black pixels and tied pixels, wherein each row of the plurality of dark pixels comprises equal numbers of optically black pixels and tied pixels arranged in a portion of the dark pixel rows that corresponds in width with the active area of pixels.

2. The imaging pixel array of claim 1, wherein the optically black pixels and tied pixels in the plurality of dark pixel rows are organized in a checkerboard pattern.

3. The imaging pixel array of claim 1, wherein each portion of dark pixel rows includes a first half of only optically black pixels and a second half of only tied pixels, the first and the second halves of adjacent dark pixel rows being located on alternating sides of a vertical axis marking the midpoint of the dark rows.

4. The imaging pixel array of claim 1, wherein the optically black pixels and the tied pixels in the plurality of dark pixel rows are organized in a symmetrical pattern.

5. An apparatus for providing pixel correction values for an imager, said apparatus comprising:

a black level correction module that calculates a black level correction value based on output values of optically black pixels and tied pixels from a same row of a plurality of dark pixel rows of a pixel array;

an averaging module to calculate an average optically black pixel output and an average tied pixel output for each row in the plurality of dark pixel rows;

a determining module to determine a difference between the average optically black pixel output and the average tied pixel output for each row in the plurality of dark pixel rows; and

a calculating module to calculate the black level correction value as an average of the determined differences.

6. The apparatus of claim 5, wherein the optically black pixels and tied pixels in the plurality of dark pixel rows are organized in a checkerboard pattern.

7. The apparatus of claim 5, wherein each row of the plurality of dark pixel rows is organized into a first half and a second half, the first half comprising optically black pixels, and the second half comprising tied pixels.

8. The apparatus of claim 7, wherein the first and the second halves of pixels are located on alternating sides of adjacent dark pixel rows.

9. The apparatus of claim 5, wherein the optically black pixels and the tied pixels in the plurality of dark pixel rows are organized in a symmetrical pattern.

10. A method of correcting pixel signals of an imager, said method comprising:

calculating an average optically black pixel output and an average tied pixel output for each row in a plurality of dark pixel rows in a pixel array of the imager;

determining a difference between the average optically black pixel output and the average tied pixel output for each row;

averaging the determined differences to generate a black level correction value; and

using the black level correction value to correct the pixel outputs of each pixel in the imager pixel array that is not located in the plurality of dark pixel rows.

11. The method of claim 10, wherein the average optically black pixel output and the average tied pixel output for each row are calculated from a plurality of optically black and tied pixels arranged in a checkerboard pattern within the plurality of dark pixel rows.

12. The method of claim 10, wherein the average optically black pixel output and the average tied pixel output for each row are calculated from a plurality of optically black and tied pixels arranged in a symmetrical pattern within the plurality of dark pixel rows.

13. An imager, comprising:

a pixel array, comprising;

an active area of pixels, composed of rows and columns of pixels; and

a plurality of dark pixels arranged in at least one of pixel rows and pixel columns which are adjacent said active area of pixels, said plurality of pixels comprising optically black pixels and tied pixels; and

a black level calculating module that calculates a black level correction value based on the outputs of the optically black pixels and the tied pixels in a same row of the plurality of dark pixel rows;

an averaging module to calculate an average optically black pixel output and an average tied pixel output for each row in the plurality of dark pixel rows;

a comparing module to determine a difference between the average optically black pixel output and the average tied pixel output for each row; and

a calculating module to calculate the black level correction value as an average of the determined differences.

14. The imager of claim 13, wherein the optically black pixels and tied pixels in the plurality of dark pixel rows are organized in a checkerboard pattern.

15. The imager of claim 13, wherein each row of the plurality of dark pixel rows is organized into a first half and a second half, the first half comprising optically black pixels, and the second half comprising tied pixels.

16. The imager of claim 15, wherein the first and the second halves of pixels are located on alternating sides of adjacent dark pixel rows.

17. The imager of claim 13, wherein the optically black pixels and the tied pixels in the plurality of dark pixel rows are organized in a symmetrical pattern.

18. An imaging system, comprising:

an imager, comprised of;

a pixel array, comprising;

an active area of pixels, composed of rows and columns of pixels; and

a plurality of dark pixels arranged in at least one of pixel rows and pixel columns which are adjacent said active area of pixels, said plurality of pixels comprising optically black pixels and tied pixels, wherein each row of the plurality of dark pixels comprises equal numbers of optically black pixels and tied pixels arranged in a portion of the dark pixel rows that correspond in width with the active area of pixels; and

a black level calculating module that calculates a black level correction value based on the outputs of the equal number of the optically black pixels and the tied pixels.

19. The system of claim 18, wherein the black level calculating module further comprises:

averaging module to calculate an average optically black pixel output and an average tied pixel output for each row in the plurality of dark pixel rows;

comparing module to determine a difference between the average optically black pixel output and the average tied pixel output for each row; and

calculating module to calculate the black level correction value as an average of the determined differences.

20. The system of claim 18, wherein the optically black pixels and tied pixels in the plurality of dark pixel rows are organized in a checkerboard pattern.

21. The system of claim 18, wherein each row of the plurality of dark pixel rows is organized into a first half and a second half, the first half comprising optically black pixels, and the second half comprising tied pixels.

22. The system of claim 21, wherein the first and the second halves of pixels are located on alternating sides of adjacent dark pixel rows.

23. The system of claim 18, wherein the optically black pixels and the tied pixels in the plurality of dark pixel rows are organized in a symmetrical pattern.

24. A carrier medium for carrying a program for operating a processor to perform the acts of:

calculating an average optically black pixel output and an average tied pixel output for each row in a plurality of dark pixel rows in a pixel array;

determining a difference between the average optically black pixel output and the average tied pixel output for each row;

averaging the determined differences to generate a black level correction value; and

using the black level correction value to correct the pixel outputs of each pixel in the pixel array that is not located in the plurality of dark rows.

25. The carrier medium of claim 24, wherein the average optically black pixel output and the average tied pixel output for each row are calculated from a plurality of optically black and tied pixels arranged in a checkerboard pattern within the plurality of dark pixel rows.

26. The carrier medium of claim 24, wherein the average optically black pixel output and the average tied pixel output for each row are calculated from a plurality of optically black and tied pixels arranged in a symmetrical pattern within the plurality of dark pixel rows.

27. An imaging pixel array, comprising:

an active area of pixels, organized as a plurality of rows and columns of pixels; and

a plurality of dark pixels arranged in at least one of pixel rows and pixel columns which are adjacent said active area of pixels, said plurality of dark pixels comprising optically black pixels and tied pixels, wherein each row of the plurality of dark pixels comprises equal numbers of optically black pixels and tied pixels arranged in a portion of the dark pixel rows that corresponds in width with the active area of pixels and the optically black pixels and tied pixels are organized in a checkerboard pattern.