Method for shading an optical sensing element such as in a scanner

1. A method for shading an optical sensing element of a scan bar of an optical scanner having a shading calibration strip comprising the steps of:

a) sequentially obtaining reference values of the output signal of the optical sensing element while relatively moving the scan bar including the optical sensing element over the shading calibration strip;

b) applying an edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading calibration strip;

c) calculating an average of the reference values obtained in step a) while excluding each of the reference values determined to be from an optical defect in step b) in calculating the average; and

d) calibrating the output signal of the optical sensing element to the shading calibration strip using at least the average calculated in step c).

2. The method of claim 1 , wherein the shading calibration strip includes a first area of a first color, wherein each optical defect consists essentially of a color optical defect disposed on the first area, and wherein step a) moves the scan bar including the optical sensing element over the first area.

3. The method of claim 2 , wherein the first color is a white color.

4. The method of claim 3 , wherein step a) moves the scan bar including the optical sensing element in a substantially straight line over the first area.

5. The method of claim 1 , wherein the sequential reference values of step a) include sequential (N−1), N and (N+1) reference values, wherein step b) includes using a [−1, 0, +1] edge detection filter which, when applied to the N reference value, has a filter output equal to a sum of: (−1) times the (N−1) reference value; (0) times the N reference value; and (+1) times the (N+1) reference value, wherein the filter output from applying the edge detection filter to the N reference value is added to a sum of filter outputs for previous reference values yielding an N updated sum, and wherein step b) determines that the N reference value is from an optical defect on the shading calibration strip when the absolute value of the N updated sum exceeds a previously determined noise threshold of the optical sensing element.

6. The method of claim 1 , wherein step b) applies at least a three-measurement edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading calibration strip.

7. The method of claim 1 , wherein step a) moves the scan bar including the optical sensing element in a substantially straight line over the first area.

8. A method for shading an optical sensing element of a scan bar of an optical scanner having a shading calibration strip comprising the steps of:

a) seciuentially obtaining reference values of the output signal of the optical sensing element while relatively moving the scan bar including the optical sensing element over the shading calibration strip;

b) applying an edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading calibration strip;

c) calculating an average of the reference values obtained in step a) while excluding each of the reference values determined to be from an optical defect in step b) in calculating the average; and

d) calibrating the output signal of the optical sensing element to the shading calibration strip using at least the average calculated in step c); and also including the step of determining if the first reference value determined by step b) to be from an optical defect is actually of a trailing edge of an optical defect and including the step of restarting steps b) and c) at a reference value at or past the trailing edge of the optical defect.

9. The method of claim 8 , wherein step c) includes adding a reference value, determined in step b) not to be from an optical defect, to a reference-value sum of previous reference values, determined in step b) not to be from an optical defect, before step b) determines if the next reference value is or is not from an optical defect on the shading calibration strip.

10. The method of claim 9 , wherein step c) increments a counter by one each time a reference value is added to the reference-value sum, and wherein step c) calculates the average by dividing the final reference-value sum by the final value of the counter.

11. A method for shading an optical sensing element of an optical sensor comprising the steps of:

a) sequentially obtaining reference values of the output signal of the optical sensing element while relatively moving the optical sensor including the optical sensing element over a shading reference target;

b) applying an edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading reference target;

c) calculating an average of the reference values obtained in step a) while excluding each of the reference values determined to be from an optical defect in step b) in calculating the average; and

d) calibrating the output signal of the optical sensing element to the shading reference target using at least the average calculated in step c).

12. The method of claim 11 , wherein the shading calibration strip includes a first area of a first color, wherein each optical defect consists essentially of a color optical defect disposed on the first area, and wherein step a) moves the optical sensor including the optical sensing element over the first area.

13. The method of claim 12 , wherein the first color is a white color.

14. The method of claim 13 , wherein step a) moves the optical sensor including the optical sensing element in a substantially straight line over the first area.

15. The method of claim 11 , wherein the sequential reference values of step a) include sequential (N−1), N and (N+1) reference values, wherein step b) includes using a [−1, 0, +1] edge detection filter which, when applied to the N reference value, has a filter output equal to a sum of: (−1) times the (N−1) reference value; (0) times the N reference value; and (+1) times the (N+1) reference value, wherein the filter output from applying the edge detection filter to the N reference value is added to a sum of filter outputs for previous reference values yielding an N updated sum, and wherein step b) determines that the N reference value is from an optical defect on the shading reference target when the absolute value of the N updated sum exceeds a previously determined noise threshold of the optical sensing element.

16. The method of claim 11 , wherein step b) applies at least a three-measurement edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading reference target.

17. The method of claim 11 , wherein step a) moves the optical sensor including the optical sensing element in a substantially straight line over the first area.

18. A method for shading an optical sensing element of an optical sensor comprising the steps of:

a) sequentially obtaining reference values of the output signal of the optical sensing element while relatively moving the optical sensor including the optical sensing element over a shading reference target;

b) applying an edge detection filter to each of the reference values obtained in step a) in determining if each of the reference values is or is not from an optical defect on the shading reference target;

c) calculating an average of the reference values obtained in step a) while excluding each of the reference values determined to be from an optical defect in step b) in calculating the average; and

d) calibrating the output signal of the optical sensing element to the shading reference target using at least the average calculated in step c); and also including the step of determining if the first reference value determined by step b) to be from an optical defect is actually of a trailing edge of an optical defect and including the step of restarting steps b) and c) at a reference value at or past the trailing edge of the previous optical defect.

19. The method of claim 18 , wherein step c) includes adding a reference value, determined in step b) not to be from an optical defect, to a reference-value sum of previous reference values, determined in step b) not to be from an optical defect, before step b) determines if the next reference value is or is not from an optical defect on the shading reference target.

20. The method of claim 19 , wherein step c) increments a counter by one each time a reference value is added to the reference-value sum, and wherein step c) calculates the average by dividing the final reference-value sum by the final value of the counter.