Method, program and apparatus for efficiently removing stray-flux effects by selected-ordinate image processing

• US 20030053712A1
• Filed: 09/20/2001
• Published: 03/20/2003
• Est. Priority Date: 09/20/2001
• Status: Active Grant

• Current Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: Jansson, Peter Allan
• Granted Patent: US 6,829,393 B2
• Time in Patent Office: Days
• US Class Current: 382/275
• CPC Class Codes: G06T 2207/10008 from scanner, fax or copier
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20016 Hierarchical, coarse-to-fine, multiscale or multiresolution image processing; Pyramid transform
• CPC Class Codes: G06T 2207/20021 Dividing image into blocks, subimages or windows
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: G06V 10/30 Noise filtering

Abstract

The present invention is directed toward correcting a corrupted image of an object to remove the effects of smearing or misdirected flux in the image, wherein the image comprises one or more dimensions and has a plurality of image elements. The method of the present invention comprises the steps of:

a) sampling portions of the image of the object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with each of the plurality of image elements thereby to obtain a correction to the image.

The present invention is also implemented as a computer readable medium for controlling a computer to implement the steps of the method and in apparatus form.

Claims

1. A method of correcting an image of an object, the image comprising one or more dimensions and having a plurality of image elements and the image being corrupted by smearing, to remove the effect of the smearing on the image, the method comprising the steps of:

a) sampling portions of the image of the object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with each of the plurality of image elements thereby to obtain a correction to the image.

2. The method of claim 1 further comprising, before step a), the step of determining a weighting function that characterizes the smearing.

3. The method of claim 1 further comprising:

d) applying the correction to the image to remove therefrom the smearing corruption to create a corrected image.

4. The method of claim 3 further comprising the steps of:

e) applying an additional correction term containing a sum of implicitly weighted samples to each element of the corrected image to update the corrected image;

f) repeating step e) until a predetermined stopping criterion has been satisfied.

5. The method of claim 4, where the image is used as a first approximation to the corrected image.

6. The method of claim 4, wherein the number of dimensions of the image differs from the number of dimensions of the object.

7. A method of obtaining values of image elements, the image having a plurality of dimensions, in an flux imaging system characterized by a portion of the image flux being misdirected, the method comprising the steps of:

a) sampling portions of an object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with a plurality of image elements thereby to obtain the values of the image elements.

8. The method of claim 7 further comprising, before step a), determining a weighting function that characterizes the misdirection.

9. The method of claim 7, wherein the number of dimensions of the image differs from the number of dimensions of the object.

10. A method of correcting an image of an object, the image having a plurality of image elements and the image being corrupted by stray flux, to remove the effect of stray flux on the image, the method comprising the steps of:

a) sampling portions of the image of the object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with each of the plurality of image elements thereby to obtain a correction to the image.

11. The method of claim 10 wherein the image comprises a plurality of uniform regions, wherein the weighting function within a uniform region does not vary by more than a predetermined amount.

12. The method of claim 11 wherein each uniform region of the object or its corresponding image is associated with a different sampling pattern.

13. The method of claim 10 further comprising:

d) applying the correction to the image to remove therefrom the stray-flux corruption.

14. A method of filtering an image, the method comprising the steps of:

a) sampling portions of the image at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with a plurality of image elements thereby to compute a filtered image.

15. The method of claim 14 wherein the image comprises a plurality of uniform regions, wherein the weighting function within a uniform region does not vary by more than a predetermined amount.

16. The method of claim 15 wherein each uniform region of the object or its corresponding image is associated with a different sampling pattern.

17. A method of obtaining values of image elements, the method comprising the steps of:

a) sampling portions of an object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with a plurality of image elements thereby to obtain the values of the image elements.

18. The method of claim 17, wherein the number of dimensions of the image differs from the number of dimensions of the object.

19. The method of claim 17 wherein the image comprises a plurality of uniform regions, wherein the weighting function within a uniform region does not vary by more than a predetermined amount.

20. The method of claim 19 wherein each uniform region of the object or its corresponding image is associated with a different sampling pattern.

21. A method for imaging an object having a predetermined number of discrete portions thereon, the object having flux emanating therefrom, by generating a signal representative of the total incident flux on each area element of a target plane, each area element corresponding to a portion of the object, the signal being representative of the sum of flux emanating from the corresponding portion of the object plus flux scattered from scattering volumes external to the object, the method comprising the steps of:

a) characterizing the flux scattered by the scattering volumes from each portion of the object to create a weighting function representing the total flux incident on a particular target-plane area element;

b) sampling the portions of the object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to the weighting function created in step a);

c) summing the implicitly weighted samples to create an approximation to a weighted integral;

d) repeating steps a)-c) for each target-plane element to compute weighted integrals associated with a plurality of target-plane elements thereby to compute an image correction;

e) employing the image correction thus obtained to remove from target-plane flux signals the contribution to such signals caused by scattered flux.

22. The method of claim 21, wherein the target plane comprises a plurality of smaller isoplanatic patches, and wherein such patches may be associated with different weighting functions.

23. The method of claim 22 wherein each isoplanatic patch has a sample pattern associated therewith.

24. The method of claim 22 wherein the size of each isoplanatic patch is associated with the spatial rate of change of the weighting function.

25. The method of claim 21 wherein the weighting function within each isoplanatic patch does not vary by more than a predetermined amount.

26. The method of claim 21, wherein the sample intervals of step b) for sampling the portions of the object at unequal intervals are obtained from an image pyramid.

27. An apparatus for correcting an image of an object, the image having a plurality of image elements and the image being corrupted by stray flux, to remove the effect of stray flux on the image, the apparatus comprising:

a) an image memory having one or more partitions for storing an input image and a corrected image;

b) an arithmetic logic unit for performing arithmetic computations;

c) a plurality of look up tables for storing selected-ordinate image coordinate values;

d) a controller for addressing the image memory and selecting lookup tables;

where, in operation

1) an image of the object is stored in the image memory;

2) the controller selects an element of the image;

3) the controller selects a lookup table, and a corresponding scale factor, appropriate to that image element, each lookup table containing information to generate a pattern of sample coordinates of the image of the object, the samples being at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

4) the controller steps through the lookup table and the arithmetic logic unit sums the implicitly weighted samples and multiplies them by the scaling factor to create an approximation to a weighted integral for that image element;

5) the weighted integral is stored in the image memory;

6) the controller selects a next element and steps

     3) -5) are repeated to compute weighted integrals associated with each of the plurality of image elements, thereby to obtain a corrected image.

28. The apparatus of claim 27 wherein

the weighted integral created in step 5) is subtracted from the image value and the resulting value is stored in the image memory.

29. A computer-readable medium containing instructions for providing program control for a computer controller to remove the effects of the spatial smearing on an image of an object, the image comprising one or more dimensions and having a plurality of image elements, by implementing the steps of:

a) sampling portions of the image of the object at unequal intervals, the intervals being selected to effect an implicit weighting of the samples corresponding to a predetermined weighting function;

b) summing the implicitly weighted samples to create an approximation to a weighted integral;

c) repeating steps a)-b) to compute weighted integrals associated with each of the plurality of image elements thereby to obtain a correction to the image.