System and method for scanner calibration

• US 6,571,189 B2
• Filed: 05/14/2001
• Issued: 05/27/2003
• Est. Priority Date: 05/14/2001
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Bohan, David G., Capps, Virginia K., Keithley, Douglas G., Jensen, Nanette C.
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): DOUGHERTY, ANTHONY T
• Application Number:
  US09/855,211
• Publication Number:
  US 20020169574A1
• Time in Patent Office: 743 Days
• Field of Search: 702/90, 702/91, 702/104, 399/32, 399/47, 399/51, 399/59, 399/31, 399/74, 358/3, 358/23, 358/3.22, 358/406, 358/461, 358/448, 358/462, 358/464, 358/465, 358/471-498, 250/559.1, 250/208.1, 250/235
• US Class Current: 702/104
• CPC Class Codes: H04N 1/407 Control or modification of tonal gradation or of extreme levels, e.g. background level

Abstract

A system and method are provided for calibrating an output from a sensor array in a scanner. The system comprises a processor circuit having a processor and a memory. Stored on the memory and executable by the processor is the scanner calibration logic. The scanner calibration logic comprises logic for determining a minimum dark value for the sensor array, and logic for determining an optimum exposure time of a number of light sources associated with the sensor array. The scanner calibration logic also includes logic for determining a maximum white value for the sensor array at the exposure time, and logic for setting an analog offset based upon the minimum dark value. The scanner calibration logic further comprises logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.

Claims

1. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value; and

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.

2. The method of claim 1, wherein the step of determining the minimum dark value for the sensor array further comprises:

setting the exposure time to zero;

scanning the sensors in the sensor array with an exposure time of zero to obtain a dark value from each one of the sensors; and

identifying a minimum one of the dark values as the minimum dark value.

3. The method of claim 1, further comprising verifying the analog offset and the analog gain.

4. The method of claim 3, wherein the verifying of the analog offset and the analog gain further comprises:

setting the exposure time to zero;

scanning a number of sensors in the sensor array to obtain a number of sensor values;

determining whether any one of the sensor values is clipped high by a circuit component to which the sensor values are applied; and

disqualifying a sensor in the sensor array that generated the ones of the sensor values that are clipped high.

5. The method of claim 3 wherein the verifying of the analog offset and the analog gain further comprises:

setting the exposure time to the optimum exposure time;

scanning a number of sensors in the sensor array to obtain a number of sensor values;

determining whether any one of the sensor values is clipped low by a circuit component to which the sensor values are applied; and

adjusting the analog offset and the analog gain if any one of the sensor values is clipped low.

6. The system of claim 3, wherein the logic for verifying the analog offset and the analog gain further comprises:

logic for setting the exposure time to zero;

logic for executing a scanning of a number of sensors in the sensor array to obtain a number of sensor values;

logic for determining whether any one of the sensor values is clipped high by a circuit component to which the sensor values are applied; and

logic for disqualifying a sensor in the sensor array that generated the ones of the sensor values that are clipped high.

7. The system of claim 3, wherein the logic for verifying of the analog offset and the analog gain further comprises:

logic for setting the exposure time to the optimum exposure time;

logic for scanning a number of sensors in the sensor array to obtain a number of sensor values;

logic for determining whether any one of the sensor values is clipped low by a circuit component to which the sensor values are applied; and

logic for adjusting the analog offset and the analog gain if any one of the sensor values is clipped low.

8. The method of claim 1, wherein the step of determining the optimum exposure time of the number of light sources associated with the sensor array further comprises determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time.

9. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value;

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the determining the minimum dark value for the sensor array further comprises;

setting the exposure time to zero;

scanning the sensors in the sensor array with an exposure time of zero to obtain a dark value from each one of the sensors; and

identifying a minimum one of the dark values as the minimum dark value; and

wherein the step of scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises;

applying an analog offset equal to a midrange value of a predetermined sensor output range to an output of the sensor array;

applying a unity analog gain to the output of the sensor array; and

scanning the sensors in the sensor array.

10. The method of claim 9, wherein the step of scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises disqualifying any one of the sensors generating a corresponding one of the dark values below a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

11. The method of claim 9, wherein the step of scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises disqualifying any one of the sensors that generates the dark value above a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

12. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value;

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the step of setting an analog offset based upon the minimum dark value further comprises generating an analog offset that places the minimum dark value at a predefined threshold greater than the bottom of an operating sensor signal range.

13. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value;

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the determining of the optimum exposure time of the number of light sources associated with the sensor array further comprises determining a saturation exposure time of each one of a number sensors in the sensor array,

wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the step of determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

maximizing the exposure time;

performing a scan with the sensor array; and

disqualifying any of the sensors in the sensor array generating a sensor value below a predetermined minimum threshold.

14. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value;

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value;

wherein the determining of the optimum exposure time of the number of light sources associated with the sensor array further comprises determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the step of determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

setting the exposure time to a maximum exposure time and scanning the sensor array to obtain a first sensor value for each of the sensors;

repeatedly decrementing the exposure time by a predefined value and rescanning the sensor array to obtain a number of subsequent sensor values for each of the sensors; and

maintaining a highest one of the first sensor value and the subsequent sensor values as the saturation exposure time for each one of the sensors.

15. A method for calibrating an output from a sensor array in a scanner, comprising:

determining a minimum dark value for the sensor array;

determining an optimum exposure time of a number of light sources associated with the sensor array;

determining a maximum white value for the sensor array at the exposure time;

setting an analog offset based upon the minimum dark value;

setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the determining of the optimum exposure time of the number of light sources associated with the sensor array further comprises determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the step of determining the optimum exposure time of the number of light sources associated with the sensor array further comprises;

determining a second exposure time at which the sensors generate a number of corresponding sensor values that are less than the saturation sensor values, respectively, by a predetermined threshold amount; and

calculating a third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time.

16. The method of claim 15, wherein the step of calculating the third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time further comprises interpolating the third sensor exposure time for each of the sensors between the saturation exposure time and the second exposure time.

17. The method of claim 15, wherein the step of determining the optimum exposure time of the number of light sources associated with the sensor array further comprises determining a minimum one of the third sensor exposure times.

18. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory;

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value; and

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.

19. The system of claim 18, wherein the logic for determining the minimum dark value for the sensor array further comprises:

logic for setting the exposure time to zero;

logic for scanning the sensors in the sensor array with the exposure time of zero to obtain a dark value from each one of the sensors; and

logic for identifying a minimum one of the dark values as the minimum dark value.

20. The system of claim 18, wherein the logic for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises logic for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time.

21. The system of claim 18, further comprising logic for verifying the analog offset and the analog gain.

22. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory;

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value; and

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the logic for determining the minimum dark value for the sensor array further comprises;

logic for setting the exposure time to zero;

logic for scanning the sensors in the sensor array with the exposure time of zero to obtain a dark value from each one of the sensors; and

logic for identifying a minimum one of the dark values as the minimum dark value; and

wherein the logic for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises;

logic for applying an analog offset equal to a midrange value of a predetermined sensor output range to an output of the sensor array;

logic for applying a unity analog gain to the output of the sensor array; and

logic for scanning the sensors in the sensor array.

23. The system of claim 22, wherein the logic for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises logic for disqualifying any one of the sensors generating a corresponding one of the dark values below a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

24. The system of claim 22, wherein the logic for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises logic for disqualifying any one of the sensors that generates the dark value above a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

25. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory; and

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value;

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the logic for setting an analog offset based upon the minimum dark value further comprises logic for generating an analog offset that places the minimum dark value at a predefined threshold greater than the bottom of an operating sensor signal range.

26. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory;

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value;

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the logic for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises logic for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the logic for determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

logic for setting the exposure time to a maximum;

logic for performing a scan with the sensor array; and

logic for disqualifying any of the sensors in the sensor array generating a sensor value below a predetermined minimum threshold.

27. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory;

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value;

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the logic for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises logic for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the logic for determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

logic for setting the exposure time to a maximum exposure time and scanning the sensor array to obtain a first sensor value for each of the sensors;

logic for repeatedly decrementing the exposure time by a predefined value and rescanning the sensor array to obtain a number of subsequent sensor values for each of the sensors; and

logic for maintaining a highest one of the first sensor value and the subsequent sensor values as the saturation exposure time for each one of the sensors.

28. A system for calibrating an output from a sensor array in a scanner, comprising:

a processor circuit having a processor and a memory;

scanner calibration logic stored in the memory and executable by the processor, the scanner calibration logic comprising;

logic for determining a minimum dark value for the sensor array;

logic for determining an optimum exposure time of a number of light sources associated with the sensor array;

logic for determining a maximum white value for the sensor array at the exposure time;

logic for setting an analog offset based upon the minimum dark value;

logic for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the logic for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises;

logic for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

logic for determining a second exposure time at which the sensors generate a number of corresponding sensor values that are less than the saturation sensor values, respectively, by a predetermined threshold amount; and

logic for calculating a third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time.

29. The system of claim 28, wherein the logic for calculating the third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time further comprises logic for interpolating the third sensor exposure time for each of the sensors between the saturation exposure time and the second exposure time.

30. The system of claim 28, wherein the logic for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises logic for determining a minimum one of the third sensor exposure times.

31. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value; and

means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to a maximum white value.

32. The system of claim 31, wherein the means for determining the minimum dark value for the sensor array further comprises:

means for setting the exposure time to zero;

means for scanning the sensors in the sensor array with the exposure time of zero to obtain a dark value from each one of the sensors; and

means for identifying a minimum one of the dark values as the minimum dark value.

33. The system of claim 31, wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises means for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time.

34. The system of claim 31, further comprising means for verifying the analog offset and the analog gain.

35. The system of claim 34, wherein the means for verifying the analog offset and the analog gain further comprises:

means for setting the exposure time to zero;

means for executing a scanning of a number of sensors in the sensor array to obtain a number of sensor values;

means for determining whether any one of the sensor values is clipped high by a circuit component to which the sensor values are applied; and

means for disqualifying a sensor in the sensor array that generated the ones of the sensor values that are clipped high.

36. The system of claim 34, wherein the means for verifying of the analog offset and the analog gain further comprises:

means for setting the exposure time to the optimum exposure time;

means for scanning a number of sensors in the sensor array to obtain a number of sensor values;

means for determining whether any one of the sensor values is clipped low by a circuit component to which the sensor values are applied; and

means for adjusting the analog offset and the analog gain if any one of the sensor values is clipped low.

37. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value; and

means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the means for determining the minimum dark value for the sensor array further comprises;

means for setting the exposure time to zero;

means for scanning the sensors in the sensor array with the exposure time of zero to obtain a dark value from each one of the sensors; and

means for identifying a minimum one of the dark values as the minimum dark value; and

wherein the means for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises;

means for applying an analog offset equal to a midrange value of a predetermined sensor output range to an output of the sensor array;

means for applying a unity analog gain to the output of the sensor array; and

means for scanning the sensors in the sensor array.

38. The system of claim 37, wherein the means for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises means for disqualifying any one of the sensors generating a corresponding one of the dark values below a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

39. The system of claim 37, wherein the means for scanning the sensors in the sensor array with the exposure time of zero to obtain the dark value from each one of the sensors further comprises means for disqualifying any one of the sensors that generates the dark value above a predetermined threshold with the application of the analog offset equal to the midrange value of a predetermined sensor output range.

40. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value; and

wherein the means for setting an analog offset based upon the minimum dark value further comprises means for generating an analog offset that places the minimum dark value at a predefined threshold greater than the bottom of an operating sensor signal range.

41. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value;

means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises means for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the means for determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

means for setting the exposure time to a maximum;

means for performing a scan with the sensor array; and

means for disqualifying any of the sensors in the sensor array generating a sensor value below a predetermined minimum threshold.

42. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value;

means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises means for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the means for determining the saturation exposure time of each one of the number sensors in the sensor array further comprises;

means for setting the exposure time to a maximum exposure time and scanning the sensor array to obtain a first sensor value for each of the sensors;

means for repeatedly decrementing the exposure time by a predefined value and rescanning the sensor array to obtain a number of subsequent sensor values for each of the sensors; and

means for maintaining a highest one of the first sensor value and the subsequent sensor values as the saturation exposure time for each one of the sensors.

43. A system for calibrating an output from a sensor array in a scanner, comprising:

means for determining a minimum dark value for the sensor array;

means for determining an optimum exposure time of a number of light sources associated with the sensor array;

means for determining a maximum white value for the sensor array at the exposure time;

means for setting an analog offset based upon the minimum dark value;

means for setting an analog gain associated with the sensor array based on a sensor output range from the minimum dark value to the maximum white value;

wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises means for determining a saturation exposure time of each one of a number sensors in the sensor array, wherein the sensors generate a corresponding number of saturation sensor values when scanned at the saturation exposure time; and

wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises;

means for determining a second exposure time at which the sensors generate a number of corresponding sensor values that are less than the saturation sensor values, respectively, by a predetermined threshold amount; and

means for calculating a third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time.

44. The system of claim 43, wherein the means for calculating the third sensor exposure time for each of the sensors between the second exposure time and the saturation exposure time further comprises means for interpolating the third sensor exposure time for each of the sensors between the saturation exposure time and the second exposure time.

45. The system of claim 43, wherein the means for determining the optimum exposure time of the number of light sources associated with the sensor array further comprises means for determining a minimum one of the third sensor exposure times.