System and method of intensity correction

• US 20060115182A1
• Filed: 11/30/2004
• Published: 06/01/2006
• Est. Priority Date: 11/30/2004
• Status: Abandoned Application

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Silverstein, D. Amnon, Deng, Yining
• Application Number:
  US11/001,228
• Publication Number:
  US 20060115182A1
• Time in Patent Office: Days
• US Class Current: 382/284
• CPC Class Codes: G06T 2200/32 involving image mosaicing
• CPC Class Codes: G06T 5/009 Global, i.e. based on properties of the image as a whole applied in cameras using an electronic image sensor H04N23/80, H04N23/70
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

A method of intensity correction of at least two frames, each frame comprising a sequence of at least two images, each image at a different image position in the sequence and each pair of adjacent images having an overlap region. The method includes selecting an image at a same image position in each frame as a reference image. A set of global intensity transformations is determined, one global intensity transformation for all pairs of adjacent images at corresponding pairs of adjacent images positions of all frames, wherein the global intensity transformations are relative to the reference images. Each global intensity transformation is applied to each pixel of one image at each corresponding pair of adjacent image positions.

Claims

1. A method of intensity correction of at least two frames, each frame comprising a sequence of at least two images, each image at a different image position in the sequence and each pair of adjacent images having an overlap region, the method comprising:

selecting an image at a same image position in each frame as a reference image;

determining a set of global intensity transformations, one global intensity transformation for all pairs of adjacent images at corresponding pairs of adjacent images positions of all frames, wherein the global intensity transformations are relative to the reference images; and

applying each global intensity transformation to each pixel of one image at each corresponding pair of adjacent image positions.

2. The method of claim 1 further comprising:

determining a mapping between corresponding pixels in the overlap region of each pair of adjacent images;

wherein determining the set of global intensity transformations further comprises optimizing a value of a function representative of the relative intensity levels between corresponding pixels in the overlap region of pairs of adjacent images at corresponding pairs of adjacent image positions of selected frames.

3. The method of claim 1, wherein selecting a reference image comprises selecting an image at an image position approximately at a center of the sequence of images.

4. The method of claim 1, wherein the selected frames comprise all frames of the set of frames.

5. The method of claim 1, further comprising:

determining a local intensity transformation for the images of each pair of adjacent image positions of the selected frames, wherein each local intensity transformation is based on optimizing a value of a function representative of the relative intensity levels between corresponding pixels in the overlap region of pairs of adjacent images at corresponding pairs of adjacent image positions of selected frames, and wherein the global intensity transformations are based on the local intensity transformations for the images at the corresponding pair of adjacent image positions of the selected frames.

6. The method of claim 1, further comprising:

aligning each pair of adjacent images of each frame.

7. The method of claim 1, wherein the global intensity transformations comprise linear transformations.

8. The method of claim 7, wherein each global intensity transformation comprises a matrix.

9. The method of claim 7, wherein the global intensity transformations are determined using linear regression techniques.

10. The method of claim 9, wherein a mean square error of a linear regression of intensity values of at least one color channel between the pixels in the overlap region of pairs of adjacent images at corresponding pairs of adjacent image positions of the selected frames is optimized.

11. The method of claim 1, wherein the global intensity transformations comprise non-linear transformations.

12. The method of claim 11, wherein each global intensity transformation comprises an exponential function.

13. The method of claim 11, wherein the global intensity transformations are determined using non-linear regression techniques.

14. The method of claim 12, wherein the exponential function is based on optimizing a match between average intensity levels of pixels in the overlap region of pairs of adjacent images at corresponding pairs of adjacent image positions of the selected frames.

15. The method of claim 12, wherein determining an intensity transformation for correcting an average intensity of a first image of a pair of overlapping adjacent images to substantially match an average intensity of a second image of the pair of images comprises:

determining a first average intensity of pixels in the overlap of the first image and a second average intensity of pixels in the overlap region of the second image;

determining a gain value based on a ratio of the second average intensity to the first average intensity;

estimating an intensity correction exponent based on the gain value;

determining an adjusted first average intensity based on the intensity correction exponent;

determining an adjusted gain value based on a ratio of the adjusted first average intensity to the second average intensity; and

adjusting the intensity correction exponent based on the adjusted gain value until the adjusted gain value is within a desired range.

16. The method of claim 15, wherein determining an adjusted first average intensity includes raising an intensity level of each pixel in the overlap region of the first to the power of the intensity correction exponent.

17. The method of claim 15, wherein the intensity correction exponent is adjusted until the adjusted gain value is substantially equal to one.

18. A system for processing at least two frames, each frame comprising a sequence of at least two mages, each image at a different image position in the sequence and each pair of adjacent images having an overlap region, the system comprising:

a reference select module to select an image at a same image position in each frame as a reference image;

a global transformation module to determine a set of global intensity transformations, one global intensity transformation for all pairs of adjacent images at corresponding pairs of adjacent images positions of all frames, wherein the global intensity transformations are relative to the reference images; and

a correction module to apply each global intensity transformation to each pixel of one image at each corresponding pair of adjacent image positions.

19. The system of claim 18, further comprising an overlap detection module to determine a mapping between corresponding pixels in the overlap region of each pair of adjacent images and wherein the global transformation module determines each global intensity transformation based on optimizing a value of a function representative of the relative intensity levels between corresponding pixels in the overlap region of pairs of adjacent at corresponding pairs of adjacent image positions of selected frames.

20. The system of claim 18, further comprising an aligning module for aligning each pair of adjacent images of each frame prior to selecting an image at a same image position in each frame as a reference image.

21. The system of claim 18, further comprising a combining module for stitching together the sequence of images of each frame such that each frame forms a composite image, subsequent to applying each global intensity transformation to each pixel of one image at each corresponding pair of adjacent image positions.

22. A system comprising:

means for receiving a set of at least two frames, each frame comprising a sequence of at least two images, each image at a different image position in the sequence and each pair of adjacent images having an overlap region;

means for selecting an image at a same image position in each frame as a reference image;

means for determining a set of global intensity transformations, one global intensity transformation for all pairs of adjacent images at corresponding pairs of adjacent images positions of all frames, wherein each global intensity transformation is based on optimizing a value of a function representative of the relative intensity levels between corresponding pixels in the overlap region of pairs of adjacent at corresponding pairs of adjacent image positions of selected frames, and wherein the global intensity transformations are relative to the reference images; and

means for applying each global intensity transformation to each pixel of one image at each corresponding pair of adjacent image positions.

23. The system of claim 22, further comprising:

means for mapping between corresponding pixels in the overlap region of each pair of adjacent images.

24. The system of claim 22, further comprising:

means for aligning each pair of adjacent images of each frame.

25. The system of claim 22, further comprising:

means for determining a local intensity transformation for the images of each pair of adjacent image positions of the selected frames, wherein each local intensity transformation is based on optimizing a value of a function representative of the relative intensity levels between corresponding pixels in the overlap region of pairs of adjacent at corresponding pairs of adjacent image positions of selected frames, and wherein the global intensity transformations are based on the local intensity transformations for the images at the corresponding pair of adjacent image positions of the selected frames.

26. A computer-readable medium including instructions executable by a processing system for performing a process on a sequence of frames, each frame comprising a sequence of at least two images, each image at a different image position in the sequence and each pair of adjacent images having an overlap region comprising:

selecting an image at a same image position in each frame as a reference image;

determining a set of global intensity transformations, one global intensity transformation for all pairs of adjacent images at corresponding pairs of adjacent image positions of all frames, wherein the global intensity transformations are relative to the reference images; and

applying each global intensity transformation to each pixel of one image at each corresponding pair of adjacent image positions.

27. A method of intensity correction for a sequence of at least two images, the sequence including at least a first pair of adjacent images having an overlap region, the first pair of adjacent images including a first image and a second mage, the method comprising:

determining a first average intensity of pixels of the first image in the overlap region and a second average intensity of pixels of the second image in the overlap region;

determining a gain value based a ratio of the second average intensity to the first average intensity;

estimating an intensity correction exponent based on the gain value;

determining an adjusted first average intensity based on the intensity correction exponent;

determining an adjusted gain value based on a ratio of the adjusted first average intensity to the second average intensity; and

adjusting the intensity correction exponent based on the adjusted gain value until the adjusted gain value is within a desired range.

28. The method of claim 27, wherein determining an adjusted first average intensity includes raising an intensity level of each pixel in the overlap region of the first to the power of the intensity correction exponent.

29. The method of claim 27, wherein the intensity correction exponent is adjusted until the adjusted gain value is substantially equal to one.