Method for compensating the non-uniformity of imaging devices

• US 6,392,216 B1
• Filed: 07/30/1999
• Issued: 05/21/2002
• Est. Priority Date: 07/30/1999
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Peng-Tan, Yap
• Primary Examiner(s): ALLEN, STEPHONE B
• Application Number:
  US09/364,368
• Time in Patent Office: 1,026 Days
• Field of Search: 250/208.1, 348/231, 348/294, 348/308, 348/362, 348/364, 348/366, 358/513, 358/519, 358/520, 358/523, 358/525
• US Class Current: 250/208.1
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: H04N 25/63 applied to dark current

Abstract

A method and apparatus for compensating non-uniformity of imaging response is described. A plurality of locations on the imaging device is selected. The light intensity for each of the selected location is measured. The measured light intensities are normalized using a reference light intensity and the normalized light intensities are stored in a memory.

Claims

1. A method comprising:

selecting a plurality of locations on an imaging device;

measuring a light intensity for each of the selected locations;

normalizing each measured light intensity using a reference light intensity; and

storing the normalized plurality of light intensities in a memory;

determining a compensation factor for the selected location on the imaging device using the stored normalized light intensity;

interpolating the compensation factor to a group of pixels in the vicinity of the selected location; and

correcting the non-uniformity of the group of pixels using the interpolated compensation factors.

2. The method as in claim 1, wherein measuring the light intensity for each of the selected locations further comprises:

selecting a plurality of pixels at the selected location;

measuring light intensities of the plurality of pixels

determining a median value from the measured light intensities; and

using the median value as the light intensity for the selected location.

3. The method as in claim 1, wherein using a reference light intensity includes using a maximum measured light intensity from the measured plurality o f light intensities.

4. The method as in claim 1, wherein the method is performed for a plurality of color plans associated with the imaging device.

5. A method comprising:

retrieving previously stored indices from a memory wherein each index corresponds to a selected location on an imaging device;

determining a compensation factor for the selected location on the imaging device using the stored index;

interpolating the compensation factor to a group of pixels in the vicinity of the selected location; and

correcting the non-uniformity of the group of pixels using the interpolated compensation factors.

6. The method as in claim 5, further comprising:

multiplying the compensation factor by a weighting factor to adjust a non-uniformity compensation of a pixel.

7. The method as in claim 5, wherein the step of interpolating is performed using bi-cubic interpolation.

8. A processor readable medium which when executed by a processor causes the processor to perform a method comprising:

selecting a plurality of locations on an imaging device;

measuring a light intensity for each of the selected locations;

normalizing each measured plurality of light intensity using a reference light intensity; and

storing the normalized plurality of light intensities in a memory;

determining a compensation factor for the selected location on the imaging device using the stored normalized light intensity;

interpolating the compensation factor to a group of pixels in the vicinity of the selected location; and

correcting the non-uniformity of the group of pixels using the interpolated compensation factors.

9. The processor readable medium as in claim 8, wherein measuring the light intensity for each of the selected locations further comprises:

selecting a plurality of pixels at the selected location;

measuring light intensities of the plurality of pixels

determining a median value from the measured light intensities; and

using the median value as the light intensity for the selected location.

10. The processor readable medium as in claim 8, wherein using a reference light intensity includes using a maximum measured light intensity from the measured plurality of light intensities.

11. The processor readable medium as in claim 8, wherein the method is performed for a plurality of color planes associated with the imaging device.

12. A processor readable medium which when executed by a processor causes the processor to execute a method comprising:

retrieving previously stored indices from a memory wherein each index corresponds to a selected location on an imaging device;

determining a compensation factor for the selected location on the imaging device using the stored index;

interpolating the compensation factor to a group of pixels in the vicinity of the selected location; and

correcting the non-uniformity of the group of pixels using the interpolated compensation factors.

13. The processor readable medium as in claim 12, further comprising:

multiplying the compensation factor by a weighting factor to adjust a compensation of a pixel.

14. The processor readable medium as in claim 12, wherein the step of interpolating is performed using bi-cubic interpolation.

15. An apparatus comprising:

a first circuit to select a plurality of locations on an imaging device;

a second circuit to measure a light intensity for each of the selected locations;

a third circuit to normalize each measured light intensity using a reference light intensity; and

a memory to store the normalized plurality of light intensities; and

additional circuits to determine a compensation factor for the selected location on the imaging device using the stored normalized light intensity, interpolate the compensation factor to a group of pixels in the vicinity of the selected location, and correct the non-uniformity of the group of pixels using the interpolated compensation factors.

16. The apparatus as in claim 15, wherein the second circuit to measure the light intensity for each of the selected locations further comprises:

a fourth circuit to select a plurality of pixels at the selected location;

a fifth circuit to measure light intensities of the plurality of pixels

a sixth circuit to determine a median value from the measured light intensities; and

a seventh circuit to use the median value as the light intensity for the selected location.

17. The apparatus as in claim 15 wherein the third circuit uses a maximum measured light intensity from the measured plurality of light intensities to normalize the plurality of light intensities.

18. The apparatus of claim 15 wherein the apparatus is included in a computer system.

19. An apparatus comprising:

a first circuit to retrieve previously stored indices from a memory wherein each index corresponds to a selected location on an imaging device;

a second circuit to determine a compensation factor for the selected location on the imaging device using the stored index;

a third circuit to interpolate the compensation factor to a group of pixels in the vicinity of the selected location; and

a fourth circuit to correct the non-uniformity of the group of pixels using the interpolated compensation factors.

20. The apparatus as in claim 19, further comprising:

a fifth circuit to multiply the compensation factor by a weighting factor to adjust a compensation of a pixel.

21. The apparatus as in claim 19, wherein the third circuit performs interpolation using bi-cubic interpolation.

22. The apparatus as in claim 19, wherein the apparatus in included in a computer system.

23. A method for reducing apparent non-uniformity of an electronic imaging system response, comprising:

retrieving a plurality of responsivity values for an image sensor of said system, each value represents intensity of incident light at a different, selected location of the image sensor during a capture of a first digital image of a uniform scene using the sensor, the plurality being a fraction of a total number of pixels that constitute the first digital image;

using each of the plurality of responsivity values, interpolating a plurality of compensation factors that are to be applied to compensate a plurality of pixels, respectively, in a second digital image captured using the system, the plurality of pixels are produced by a vicinity of the selected location of the image sensor; and

applying the plurality of compensation factors to the second digital image.

24. The method of claim 23 wherein the plurality of responsivity values and the plurality of compensation factors are for the same color plane, the method further comprising:

retrieving a plurality of responsivity values for each additional color plane of the image sensor;

interpolating a plurality of compensation factors that are to be applied to compensate a plurality of pixels for each additional color plane of the image sensor; and

applying the plurality of compensation factors to pixel values in each additional color plane to completely compensate the second digital image.

25. The method of claim 23 wherein the plurality of responsivity values represent a plurality of equispaced locations of the sensor.

26. The method of claim 25 wherein each of the plurality of responsivity values is an average of a plurality of pixel values taken from a vicinity of the selected location.

27. The method of claim 26 wherein the plurality of responsivity values have been normalized, prior to being retrieved, to a reference value.

28. The method of claim 27 wherein the reference value is a maximum of the plurality of pixel values that are used to compute the average.