Method for compensating for a contaminated calibration target used in calibrating a scanner

1. A method for compensating for a contaminated calibration target used in calibrating a scanner having a plurality of sensor pixels, said method comprising:

(a) scanning a calibration target to generate a respective plurality of calibration data samples for each sensor pixel of said plurality of sensor pixels;

(b) for said respective plurality of calibration data samples associated with a current sensor pixel of said plurality of sensor pixels, removing any calibration data sample that corresponds to a region of calibration target contamination on said calibration target, leaving filtered calibration data samples;

(c) determining a gain value for said current sensor pixel based on said filtered calibration data samples;

(d) repeating acts (b) and (c) for a next sensor pixel of said plurality of sensor pixels until a respective gain value is determined for each of said plurality of sensor pixels; and

(e) applying the determined gain values to said plurality of sensor pixels for use in subsequent image scanning by said scanner.

2. The method of claim 1 , wherein said calibration target without any contamination in a uniform neutral tone, and wherein said region of calibration target contamination includes at least one imperfection in at least one of uniformity and neutrality of said calibration target.

3. The method of claim 2 , said uniform neutral tone of said calibration target being any single tone adhering to the equations luminance L*>TL and chrominance a* & b*<Tab as defined by CIELAB color space, where TL is a predetermined luminance threshold and Tab is a predetermined chrominance threshold.

4. The method of claim 1 , wherein prior to said removing of act (b), the method further comprising:

determining a maximum calibration value of said respective plurality of calibration data samples;

determining a minimum calibration value of said respective plurality of calibration data samples;

determining an average calibration value of said plurality of calibration data samples;

determining a threshold; and

determining an existence of said region of calibration target contamination of said calibration target based on mathematical relationship among said maximum calibration value, said minimum calibration value, said average calibration value, and said threshold.

5. The method of claim 4 , wherein said predetermined Threshold is a constant empirically derived threshold.

6. The method of claim 1 , wherein said removing of act (b) includes:

(b1) identifying a minimum calibration value of said respective plurality of calibration data samples;

(b2) identifying an average calibration value of said respective plurality of calibration data samples;

(b3) determining a first difference between a current calibration value of a current calibration sample of said respective plurality of calibration data samples and said minimum calibration value;

(b4) determining a second difference between said average calibration value and said minimum calibration value;

(b5) forming a ratio of said first difference and said second difference;

(b6) if said ratio is less than a predetermined threshold, then designating said current calibration value as corresponding to said region of calibration target contamination;

(b7) repeating acts hi through b6 for each calibration data sample of said respective plurality of calibration data samples; and

(b8) removing any calibration data sample corresponding to said region of calibration target contamination, leaving said filtered calibration data samples.

7. The method of claim 6 , wherein said predetermined threshold is a constant empirically derived threshold.

8. The method of claim 1 , wherein said scanner is incorporated into an imaging apparatus.

9. A method for compensating for a contaminated calibration target used in calibrating a scanner having a plurality of sensor pixels, said method comprising:

(a) scanning a calibration target to generate a respective plurality of calibration data samples for each sensor pixel of said plurality of sensor pixels;

(b) processing said respective plurality of calibration data samples associated with a current sensor pixel of said plurality of sensor pixels to determine whether there is a region of calibration target contamination associated with said current sensor pixel;

(c) filtering said respective plurality of calibration data samples to remove any calibration data sample corresponding to said region of calibration target contamination, leaving filtered calibration data samples;

(d) determining a gain value for said current sensor pixel based on said filtered calibration data samples;

(e) repeating acts (b) through (d) for a next sensor pixel of said plurality of sensor pixels until a respective gain value is determined for each of said plurality of sensor pixels; and

(f) applying the determined gain values to said plurality of sensor pixels for use in subsequent image scanning by said scanner.

10. The method of claim 9 , wherein said calibration target without any contamination in a uniform neutral tone, and wherein said region of calibration target contamination includes at least one imperfection in at least one of uniformity and neutrality of said calibration target.

11. The method of claim 10 , said uniform neutral tone of said calibration target being any single tone adhering to the equations luminance L*>TL and chrominance a* & b*<Tab as defined by CIELAB color space where TL is a predetermined luminance threshold and Tab is a predetermined chrominance threshold.

12. The method of claim 9 , wherein said processing of act (b) includes:

determining a maximum calibration value of said respective plurality of calibration data samples;

determining a minimum calibration value of said respective plurality of calibration data samples;

determining an average calibration value of said plurality of calibration data samples;

determining a first difference between said average calibration value and said minimum calibration value;

determining a second difference between said average calibration value and said maximum calibration value;

forming a ratio of said first difference and staid second difference; and if said ratio exceeds a predetermined threshold, then designating said calibration target as having said region of calibration target contamination.

13. The method of claim 12 , wherein said predetermined threshold is a constant empirically derived threshold.

14. The method of claim 9 , wherein said filtering of act (c) includes:

(c1) identifying a minimum calibration value of said respective plurality of calibration data samples;

(c2) identifying an average calibration value of said respective plurality of calibration data samples;

(c3) determining a first difference between a current calibration value of a current calibration sample of said respective plurality of calibration data samples and said minimum calibration value;

(c4) determining a second difference between said average calibration value and said minimum calibration value;

(c5) forming a ratio of said first difference and said second difference;

(c6) if said ratio is less than a predetermined threshold, then designating said current calibration value as corresponding to said region of calibration target contamination;

(c7) repeating acts c6 through c6 for each calibration data sample of said respective plurality of calibration data samples; and

(c8) removing any calibration data sample corresponding to said region of calibration target contamination, leaving said filtered calibration data samples.

15. The method of claim 14 , wherein said predetermined threshold is a constant empirically derived threshold.

16. The method of claim 9 , wherein said scanner is incorporated into an imaging apparatus.

17. A method for compensating for a contaminated calibration target used in calibrating a scanner having a plurality of sensor pixels, said method comprising:

(a) scanning a calibration target to generate a respective plurality of calibration data samples for each sensor pixel of said plurality of sensor pixels;

(b) determining a maximum calibration value of said respective plurality of calibration data samples;

(c) determining a minimum calibration value of said respective plurality of calibration data samples;

(d) determining an average calibration value of said plurality of calibration data samples;

(e) determining a first difference between said average calibration value and said minimum calibration value;

(f) determining a second difference between said average calibration value and said maximum calibration value;

(g) forming a first ratio of said first difference and said second difference, and if said first ratio exceeds a first predetermined threshold, then designating said calibration target as having a region of calibration target contamination associated with said current pixel;

(h) determining a third reference between a current calibration value of a current calibration sample of said respective plurality of calibration data samples and said minimum calibration value;

(i) forming a second ratio of said third difference and said first difference, and if said second ratio is less than a second predetermined threshold, then designating said current calibration value as corresponding to said region of calibration target contamination;

(j) repeating acts (H) and (i) for each calibration data sample of said respective plurality of calibration data samples for said current sensor pixel;

(k) removing any calibration data sample corresponding to said region of calibration target contamination, leaving filtered calibration data samples;

(l) forming a new average calibration value from said filtered calibration data samples;

(m) determining a gain value for said current sensor pixel based on said new average calibration value for said current pixel;

(n) repeating acts (b) through (m) for a next sensor pixel of said plurality of sensor pixels until a respective gain value is determined for each of said plurality of sensor pixels; and

(o) applying the determined gain values to said plurality of sensor pixels for use in subsequent image scanning by said scanner.

18. The method of claim 17 , wherein said calibration target without any contamination is a uniform neutral tone, and wherein said region of calibration target contamination includes at least one imperfection in at least one of uniformity and neutrality of said calibration target.

19. The method of claim 18 , said uniform neutral tone of said calibration target being any single tone adhering to the equations luminance L*>TL and chrominance a* & b*<Tab as defined in CIELAB color space, where TL is a predetermined luminance threshold and Tab is a predetermined chrominance threshold.

20. The method of claim 17 , wherein h of said first predetermined threshold and said second predetermined threshold is a constant empirically derived threshold.

21. A method for compensating for a contaminated calibration target used in calibrating a scanner having a plurality of sensor pixels, said method comprising:

(a) scanning a calibration target to generate a respective plurality of calibration data samples for each sensor pixel of said plurality of sensor pixels;

(b) determining a maximum calibration value of said respective plurality of calibration data samples;

(c) determining a minimum calibration value of said respective plurality of calibration data samples;

(d) determining an average calibration value of said plurality of calibration data samples;

(e) determining a first difference between said average calibration value and said minimum calibration value;

(f) determining a second difference between said average calibration value and said maximum calibration value;

(g) forming a first ratio of said first difference and said second difference, and if said first ratio exceeds a first predetermined threshold, then designating said calibration target as having a region of calibration target contamination associated with said current sensor pixel;

(h) removing any calibration data sample corresponding to said region of calibration target contamination, leaving filtered data samples; and

(i) determining a gain value for said current sensor pixel based on said filtered data samples; and

(j) applying the determined gain value to said current sensor pixel for use in subsequent image scanning by said scanner.

22. The method of claim 21 , further comprising:

repeating acts (b) through (i) for a next sensor pixel of said plurality of sensor pixels until a respective gain value is determined for each of said plurality of sensor pixels; and

applying the determined gain values to said plurality of sensor pixels for use in subsequent image scanning by said scanner.

23. A method for compensating for a contaminated calibration target used in calibrating a scanner having a plurality of sensor pixels, said method comprising:

(a) scanning a calibration target to generate a respective plurality of calibration data samples for each sensor pixel of said plurality of sensor pixels;

(b) determining a maximum calibration value of said respective plurality of calibration data samples;

(c) determining a minimum calibration value of said respective plurality of calibration data samples;

(d) determining an average calibration value of said plurality of calibration data samples;

(e) determining a first difference between said average calibration value and said minimum calibration value;

(f) determining a second difference between a current calibration value of a current calibration sample of said respective plurality of calibration data samples and said minimum calibration value

(g) forming a first ratio of said second difference and said first difference, and if said first ratio is less than a first predetermined threshold, then designating said current calibration value as corresponding to a region of calibration target contamination; and

(h) removing any calibration data sample corresponding to said region of calibration target contamination, leaving filtered data samples; and

(i) determining a gain value for said current sensor pixel based on said filtered data samples; and

(j) applying the determined gain value to said current sensor pixel for use in subsequent image scanning by said scanner.