TECHNIQUES FOR MODIFYING IMAGE FIELD DATA OBTAINED USING ILLUMINATION SOURCES

• US 20100225797A1
• Filed: 05/18/2010
• Published: 09/09/2010
• 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 8,203,622 B2
• Time in Patent Office: Days
• US Class Current: 348/311
• 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 for correcting image data of a scene by a digital camera, the method comprising the acts of:

capturing a first image of the scene corresponding to a first illumination level;

capturing a second image of the scene corresponding to a second illumination level, wherein the second illumination level is different from the first illumination level;

determining correction factors for a non-uniform illumination area of the first image based on image data of the first and second images, wherein correction factors are determined for one or more representative pixels; and

applying the correction factors to the non-uniform illumination area of the first image to obtain an illumination corrected image, wherein the correction factors are applied to one or more pixels associated with the non-uniform illumination area of the first image based on position of a pixel relative to at least one of the representative pixels.

2. The method of claim 1, wherein the first illumination level corresponds to natural lighting, and the second illumination level corresponds to an artificial illumination level generated by the digital camera.

3. The method of claim 1, wherein the first illumination level corresponds to an artificial illumination level generated by the digital camera, and the second illumination level corresponds to a second artificial illumination level generated by the digital camera, wherein the second artificial illumination level is greater than the first.

4. The method of claim 1, wherein correction factors for the one or more pixels associated with the non-uniform illumination area of the first image are predicted based on distance to a representative pixel.

5. The method of claim 1, wherein correction factors are determined for one or more representative pixels of each grid block of the image sensor.

6. The method of claim 1, wherein the correction factors are determined based on an illumination difference between pixels associated with the first and second illumination levels.

7. The method of claim 1, wherein applying the correction factors includes multiplying each pixel of the first image by a non-uniform image correction factor.

8. The method of claim 1, wherein applying the correction factors includes applying the correction factors to one of a portion of the image, and the entire image.

9. The method of claim 1, wherein the correction factors are determined to correct for saturation of one or more pixels associated with the non-uniform illumination area of the first image.

10. The method of claim 1, wherein determining correction factors is further based on detection of a third image corresponding to a third illumination level.

11. The method of claim 1, wherein the correction factors are determined according to the formula:

IC[x,y]=(a[x,y]−

b[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.

12. The method of claim 1, wherein the correction factors are determined according to the formula:

IC[x,y]=Y/X(a[x,y]−

b[x,y]),

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

13. The method of claim 1, further comprising acquiring an image data set of interest to determine the non-uniform illumination area, and receiving at least one normalization threshold level from a user.

14. The method of claim 13, further comprising normalizing the acquired image data set of interest, wherein normalizing 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.

15. A digital camera comprising:

a sensor configured to capture image data;

a flash illumination device configured to illuminate a scene with at least one level of illumination; and

a processor coupled to the sensor and the flash illumination device, the processor configured to

receive a first image of the scene corresponding to a first illumination level;

receive a second image of the scene corresponding to a second illumination level, wherein the second illumination level is different from the first illumination level;

determine correction factors for a non-uniform illumination area of the first image based on image data of the first and second images, wherein correction factors are determined for one or more representative pixels; and

apply the correction factors to the non-uniform illumination area of the first image to obtain an illumination corrected image, wherein the correction factors are applied to one or more pixels associated with the non-uniform illumination area of the first image based on position of a pixel relative to at least one of the representative pixels.

16. The digital camera of claim 15, wherein the first illumination level corresponds to natural lighting, and the second illumination level corresponds to an artificial illumination level generated by the flash illumination device.

17. The digital camera of claim 15, wherein the first illumination level corresponds to an artificial illumination level generated by the flash illumination device, and the second illumination level corresponds to a second artificial illumination level generated by the flash illumination device, wherein the second artificial illumination level is greater than the first.

18. The digital camera of claim 15, wherein correction factors for the one or more pixels associated with the non-uniform illumination area of the first image are predicted based on distance to a representative pixel.

19. The digital camera of claim 15, wherein correction factors are determined for one or more representative pixels of each grid block of the image sensor.

20. The digital camera of claim 15, wherein the correction factors are determined based on an illumination difference between pixels associated with the first and second illumination levels.

21. The digital camera of claim 15, wherein applying the correction factors by the processor includes multiplying each pixel of the first image by a non-uniform image correction factor.

22. The digital camera of claim 15, wherein applying the correction factors by the processor includes applying the correction factors to one of a portion of the image, and the entire image.

23. The digital camera of claim 15, wherein the processor determines correction factors to correct for saturation of one or more pixels associated with the non-uniform illumination area of the first image.

24. The digital camera of claim 15, wherein the processor determines the correction factors based on detection of a third image corresponding to a third illumination level.

25. The digital camera of claim 15, wherein the correction factors are determined by the processor according to the formula:

IC[x,y]=(a[x,y]−

b[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.

26. The digital camera of claim 15, wherein the correction factors are determined by the processor according to the formula:

IC[x,y]=Y/X(a[x,y]−

b[x,y]),

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

27. The digital camera of claim 15, wherein the processor is further configured to acquire an image data set of interest to determine the non-uniform illumination area, and receive at least one normalization threshold level from a user.

28. The digital camera of claim 27, wherein the processor is further configured to normalize the acquired image data set of interest by:

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.

29. A method for correcting image data of a scene by a digital camera, the method comprising the acts of:

capturing a first image of the scene corresponding to a first illumination level;

capturing a second image of the scene corresponding to a second illumination level, wherein the second illumination level is different from the first illumination level;

acquiring an image data set of interest based on the first and second illumination levels, the image data set of interest associated with a non-uniform illumination area of the first image;

determining correction factors for the image data set of interest based on image data of the first and second images, wherein correction factors are determined for one or more representative pixels; and

applying the correction factors to the image data set of interest to obtain an illumination corrected image, wherein the correction factors are applied to one or more pixels associated with the non-uniform illumination area of the first image based on the position of a pixel relative to at least one of the representative pixels.