Techniques for Modifying Image Field Data Obtained Using Illumination Sources

• US 20070262236A1
• Filed: 05/15/2006
• Published: 11/15/2007
• Est. Priority Date: 05/15/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Zoran Corporation (Qualcomm, Inc.)
• Inventors: Pertsel, Shimon
• Granted Patent: US 7,755,672 B2
• Time in Patent Office: Days
• US Class Current: 250/208.100
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 23/76 by influencing the image signals

Abstract

Techniques for modifying data of an image that can be implemented in a digital camera, video image capturing device and other optical systems are provided to correct for non-uniform illumination and/or effects of saturation appearing in data obtained using one or more artificial illumination sources. In an implementation, correction factors are derived using data from at least two images that have been captured with different illumination levels of the object scene and close in time to the capture of the image of interest. Typically, the image of interest is of higher resolution than at least one of the at least two images.

Claims

1. A method of modifying data of an image of an object field being electronically captured, comprising:

capturing two or more image data sets of the object field with different levels of artificial illumination;

generating, from the captured image data sets, data that corrects for the artificial illumination being non-uniform across the object field;

acquiring an image data set of interest of the object field, where the resolution of the data set of interest is greater than the resolution of at least one of the other two or more image data sets; and

applying the illumination correction data set to the image data set of interest to obtain an illumination-corrected image data set of interest, thereby compensating for variations in the intensity across the image field that are attributable to the artificial illumination of the object field.

2. The method of claim 1, additionally comprising:

revising the illumination correction data set according to said at least one of the other two or more image data sets in order to compensate for saturation of one or more portions of the image data set of interest, wherein said revising is carried out following generating illumination correction data and before applying the illumination correction data.

3. The method of claim 1, wherein the acquired image data set of interest is one of the captured two or more image data sets.

4. The method of claim 1, wherein the acquired image data set of interest is separate from the other two or more image data sets.

5. The method of claim 1, wherein one of the different levels of artificial illumination is zero.

6. The method of claim 5, wherein generating the illumination correction data includes making a calculation according to the formula:

IC[x,y]=(b[x,y]−

a[x,y]),

where IC[x,y] is the illumination correction as a function of the position (x,y) of an image data point of interest, b[x,y] is the intensity as a function of the position (x,y) of the data point in the image data set captured with zero artificial illumination, and a[x,y] is the intensity as a function of the position (x,y) of the data point in the image data set captured at non-zero artificial illumination.

7. The method of claim 1, wherein none of the different levels of artificial illumination is zero.

8. The method of claim 7, wherein the image data set of interest is the image data set captured at a higher of the different illumination levels.

9. The method of claim 7, wherein generating the illumination correction data includes making a calculation according to the formula:

IC[x,y]=Y/X(b[x,y]−

a[x,y]),

where IC[x,y] is the illumination correction as a function of the position (x,y) of an image data point of interest captured at illumination level X, b[x,y] is the intensity as a function of the position (x,y) of the data point in the image data set, a[x,y] is the intensity as a function of the position (x,y) of the data point in the image data set of interest captured at illumination level Y, and wherein Y is greater than X.

10. The method of claim 2, wherein revising the illumination correction data set includes normalizing the acquired image data set of interest to identify any portions of the image data set of interest that are saturated.

11. The method of claim 10, wherein normalizing the acquired image data set of interest comprises:

defining at least one of an upper normalization threshold level I_U and a lower normalization threshold I_L, wherein I_U and I_L each are no less than zero and no greater than a set maximum number;

if U has been obtained, determining an upper normalization level I_U, such that U % of data points in the image of interest are less than I_U; and

if L has been obtained, determining a lower normalization level I_L, such that L % of data points in the image of interest are greater than I_L.

12. The method of claim 2, wherein acquiring the image data set of interest includes receiving at least one normalization threshold level selection from a user.

13. The method of claim 2, wherein acquiring the image data set of interest includes retrieving at least one stored normalization threshold selection.

14. The method of claim 1, wherein the capturing, generating, and applying functions are all accomplished on a single integrated circuit chip.

15. The method of claim 1, wherein the capturing, generating, and applying functions are all performed by electronic circuits dedicated to carrying out these functions.

16. The method of claim 1, wherein a data point of the captured two or more image data sets is either one or more individual pixels or one or more groups of neighboring pixels.

17. A method of modifying an image field being electronically captured using artificial illumination, comprising:

directing the capture of a first image data set of the image field corresponding to a first illumination level;

directing the capture of a second image data set of the image field corresponding to a second illumination level different from the first illumination level;

designating an image data set of interest of the image field, where the resolution of the data set of interest is greater than the resolution of at least one of the other two image data sets;

calculating a relationship between the first and second illumination levels;

generating an illumination correction data set from the first and second image data sets; and

applying the illumination correction data set and the illumination level relationship to the image data set of interest to obtain an illumination-corrected image data set of interest, thereby compensating for uneven distribution of light across the image field.

18. The method of claim 17, wherein designating an image data set of interest includes selecting an image data set of interest from the first image data set or the second image data set.

19. The method of claim 17, wherein designating an image data set of interest includes acquiring an image data set of interest other than the first or second captured image data sets.

20. A method of modifying an image field being electronically captured, comprising:

capturing a first image data set of the image field corresponding to a first artificial illumination level;

capturing a second image data set of the image field corresponding to a second artificial illumination level different from said first illumination level;

generating, from the captured first and second image data sets, illumination correction data as a function of position to compensate for uneven distribution of light from the illumination source;

obtaining an image data set of interest of the image field, where the resolution of the data set of interest is greater than the resolution of the other one or more image data sets; and

applying the illumination correction data set to the image data set of interest to obtain an illumination-corrected image data set of interest, thereby compensating for variations in the intensity across the artificial illumination.

21. The method of claim 20, wherein one of the first or second artificial illumination levels is zero.

22. The method of claim 20, wherein neither of the first nor second artificial illumination levels is zero.

23. A method of modifying an image field being electronically captured, comprising:

capturing two or more image data sets of the image field;

generating, from the captured image data sets, data that corrects for (1) any variations of intensity of artificial illumination of the image field as a function of position across the image field, and (2) any areas of saturation of the image field;

acquiring an image data set of interest of the image field; and

applying the illumination correction data set to the image data set of interest to obtain a corrected image data set of interest.

24. A method of correcting a set of data of an image of interest obtained by use of a photosensor, comprising:

capturing first and second sets of data of respective first and second images on the photosensor of an object scene illuminated with first and second levels of artificial illumination that are different from each other,

acquiring the set of data of the image of interest with the photosensor when the object scene is illuminated with a third level of artificial illumination that is between and different from the first and second levels, and

utilizing data from the first and second sets of data to correct the set of data of the image of interest for any areas of negative or positive saturation of the photosensor by the image of interest.

25. The method of claim 24, wherein the first and second sets of data are captured with an image resolution that is less than that with with the set of data of the image of interest are acquired.

26. The method of claim 24, wherein the first level of artificial illumination is zero.

27. An integrated circuit chip containing circuits capable of receiving and processing data obtained from a two-dimensional optical image detector, comprising:

said circuits functioning to capture two or more image data sets of an image field as illuminated by an illumination source, and that acquires an image data set of interest of the image field, where the resolution of the data set of interest is greater than the resolution of at least one of the other two or more image data sets; and

said circuits further functioning to generate, from the captured image data sets, a set of data that corrects for artificial illumination of the image field as a function of position across the image field, and that applies the illumination correction data set to the image data set of interest to obtain an illumination-corrected image data set of interest, thereby compensating for variations in the intensity across the image field that are attributable to the artificial illumination.

28. The integrated circuit chip of claim 27, said circuits further functioning to generate, from the captured image data sets, a set of data that corrects for at least one of negative or positive saturation of one or more regions of the image detector, and that applies the saturation correction data set to the image data set of interest to obtain a saturation corrected image data set of interest.

29. An integrated circuit chip containing circuits capable of receiving and processing data obtained from a two-dimensional optical image detector, comprising:

said circuits functioning to capture two or more image data sets of an image field as illuminated by an illumination source, and that acquires an image data set of interest of the image field, where the resolution of the data set of interest is greater than the resolution of at least one of the other two or more image data sets; and

said circuits further functioning to generate, from the captured image data sets, a set of data that corrects for at least one of negative or positive saturation of one or more regions of the image detector, and that applies the saturation correction data set to the image data set of interest to obtain a saturation corrected image data set of interest.

30. A digital camera, comprising within a single unit:

a photodetector system that captures data of an image cast thereon,

an optical system capable of casting an image of an object scene onto the photodetector,

a flash illumination device capable of illuminating the object scene with at least first and second levels of illumination,

a controller that causes at least first and second sets of image data of the object scene to be captured with respective first and second levels of illumination, and

a signal processor capable of;

determining, from the captured first and second sets of data, variations in intensity in an image cast on the photodetector system,

calculating therefrom data that corrects for uneven intensity distribution across the illumination of the object scene by the flash illumination device,

storing the correction data, and

thereafter combining the stored correction data with data of at least one other image captured by the photodetector system in order to correct for variations in the intensity across said at least one other image that are attributable to the flash illumination, wherein said at least one other image is captured by the photodetector system with a resolution that is higher than the resolution of the first or second sets of data.

31. A digital camera, comprising within a single unit:

a photodetector system that captures data of an image cast thereon,

an optical system capable of casting an image of an object scene onto the photodetector,

a flash illumination device capable of illuminating the object scene with at least first, second and third levels of illumination, wherein the second level is greater than the first level and the third level is greater than the second level,

a controller that causes at first, second and third sets of image data of the object scene to be captured with respective first, second and third levels of illumination, and

a signal processor that operates to;

calculate, from the captured first and third sets of data, data that corrects for any negative or positive saturation of the photodetector system in the second set of data,

at least temporarily store the saturation correction data, and

thereafter combine the stored saturation correction data with the second set of data in order to correct for effects of any negative or positive saturation therein.

32. The digital camera of claim 31, wherein the signal processor further operates to process the second set of data with a resolution that is higher than the resolution of the first and third sets of data.

33. The digital camera of claim 31, wherein the signal processor further operates to:

determine, from the captured first and third sets of data, variations in intensity in an image cast on the photodetector system,

calculate therefrom data that corrects for uneven intensity distribution across the illumination of the object scene by the flash illumination device,

at least temporarily store the intensity correction data, and

thereafter combine the stored correction data with second set of data in order to correct for variations in the intensity across the image of the second set of data that are attributable to non-uniformity of the flash illumination.

34. The digital camera of claim 33, wherein the signal processor further operates to process the second set of data with a higher resolution than the first and third sets of data.