Dithered image reconstruction

• US 5,838,813 A
• Filed: 12/20/1996
• Issued: 11/17/1998
• Est. Priority Date: 12/20/1996
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Kancler, Henry C., Roberts, James D.
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US08/770,493
• Time in Patent Office: 697 Days
• Field of Search: 382/270, 382/312, 382/103, 382/275, 382/274, 358/406, 358/471, 358/474, 358/494, 358/504, 358/505, 358/446, 358/461, 358/463, 348/169, 250/208.1, 250/214 AG
• US Class Current: 382/103
• CPC Class Codes: H04N 1/401 Compensating positionally unequal response of the pick-up or reproducing head H04N1/403 takes precedence
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• CPC Class Codes: H04N 25/674 based on the scene itself, e.g. defocusing
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A dithered image reconstruction system and method that compensates for inter-detector errors in a manner that does not adversely affect detection of small-amplitude images in the presence of a very bright large-amplitude background. An overlapping dither pattern is employed in a detector array (103), and outputs generated by individual detectors (302) are adjusted in an iterative fashion to hold all outputs for a particular detector substantially constant, while allowing each set of outputs for each image section to converge on a solution. The system and method do not substantially distort the received signal, nor do they fail when the image characteristics have little spatial variation, such as when a large target area is being detected.

Claims

1. A method for reconstructing a dithered image, comprising:

(a) applying a detector array to an image, the image comprising a plurality of image sections, the detector array comprising a plurality of detectors, each detector having a plurality of dither positions, each dither position associating the detector with one of the image sections;

(b) adjusting each detector to a first dither position;

(c) for each detector, obtaining a first signal corresponding to an associated image section for the first dither position;

(d) adjusting each detector to a subsequent dither position;

(e) for each detector, obtaining a subsequent signal corresponding to an associated image section for the subsequent dither position;

(f) for each image section, determining an estimated output signal by comparing the signals obtained in steps (c) and (e) corresponding to the image section and further comparing the signals obtained in steps (c) and (e) for each detector having a dither position associating the detector with the image section; and

(g) generating an output comprising the estimated output signals for the image sections.

2. The method of claim 1, wherein a first dither position of a first one of the detectors corresponds to a subsequent dither position of a second one of the detectors.

3. The method of claim 1, further comprising:

(e.1) repeating steps (d) and (e) until each detector has been positioned in each of the dither positions for the detector.

4. The method of claim 1, wherein step (f) comprises:

(f.1) for each detector, determining an adjustment value for adjusting all obtained signals for the detector; and

(f.2) applying the determined adjustment value to all obtained signals for the detector.

5. The method of claim 1, wherein step (f) comprises:

(f.1) for each image section;

(f.1.1) determining an average signal value; and

(f.1.2) for each detector associated with the image section, determining an adjustment value for the image section;

(f.2) for each detector, performing the steps of;

(f.2.1) determining an average of the adjustment values determined in step (f.1.2); and

(f.2.2) for each image section associated with the detector, determining an adjusted signal by applying the average adjustment value to the obtained signal for the image section; and

(f.3) for each image section, determining an estimated output signal by averaging the adjusted signals for each detector at the dither position corresponding to the image section.

6. The method of claim 5, further comprising:

(f.3.1) selectively repeating steps (f.1) through (f.3) until a predetermined condition is reached.

7. The method of claim 5, further comprising:

(f.3.1) for each image section, comparing the adjusted signals for each detector at the dither position corresponding to the image section; and

(f.3.2) responsive to the comparison of step (f.3.1) indicating that the adjusted signals differ by at least a predetermined threshold amount, repeating steps (f.1) through (f.3.1).

8. The method of claim 5, wherein step (f.2.2) comprises:

(f.2.2.1) multiplying the average of the adjustment values by a tuning coefficient to obtain a tuned average adjustment value; and

(f.2.2.2) determining an adjusted signal for each image section associated with the detector by applying the tuned average adjustment value to the obtained signal for the image section.

9. The method of claim 5, further comprising:

(h) applying the detector array to a second image;

(i) adjusting each detector to the first dither position;

(j) for each detector, obtaining a first signal corresponding to the associated image section for the first dither position;

(k) adjusting each detector to a subsequent dither position;

(l) for each detector, obtaining a subsequent signal corresponding to the associated image section for the subsequent dither position;

(m) adjusting the signals obtained in steps (j) and (l) by the average adjustment value determined in step (f.2.1); and

(n) repeating steps (f.1) through (f.3) for the second image.

10. The method of claim 1, wherein step (f) comprises:

(f.1) for each detector;

(f.1.1) obtaining a set of adjustment values, each adjustment value corresponding to one of the image sections;

(f.1.2) determining an average adjustment value from the set of adjustment values; and

(f.1.3) applying the average adjustment value to output signals of the detector to obtain adjusted output signals;

(f.2) selectively repeating step (f.1) until a predetermined condition is reached; and

(f.3) for each image section, determining an average adjusted output signal from the adjusted output signals.

11. The method of claim 10, wherein step (f.1.2) further comprises:

(f.1.2.1) multiplying the average adjustment value by a tuning coefficient.

12. The method of claim 11, further comprising:

(f.1.4) applying an intra-detector adjustment factor to each adjusted output signal;

wherein the intra-detector adjustment factor comprises a tuned adjustment value for the adjusted output signal.

13. The method of claim 10,

wherein step (e) further comprises (e.1) for each image section, determining an average signal measurement;

and wherein step (f.1.1) comprises, for each image section covered by the detector, determining a difference between the average signal measurement and the detector output signal.

14. A system for reconstructing a dithered image comprising:

a detector array, the detector array adapted to receive an image, the image comprising a plurality of image sections, the detector array comprising a plurality of detectors, each detector having a plurality of dither positions, each dither position associating the detector with one of the image sections, each detector for obtaining a first signal corresponding to an associated image section for a first dither position and a subsequent signal corresponding to an associated image section for a subsequent dither position;

a detector array controller coupled to the detector array, for adjusting each detector to a first dither position and to at least one subsequent dither position;

a signal processor coupled to the detector array, for determining for each image section an estimated output signal by comparing the obtained signals corresponding to the image section and further comparing the obtained signals for each detector with other obtained signals for the detector; and

an output device coupled to the signal processor for generating an output comprising the estimated output signals of the signal processor.

15. The system of claim 14, wherein a first dither position of a first one of the detectors corresponds to a subsequent dither position of a second one of the detectors.

16. The system of claim 14, wherein the signal processor determines, for each detector, an adjustment value for adjusting all obtained signals for the detector, and applies the determined adjustment value to all obtained signals for the detector.

17. The system of claim 14, wherein the signal processor comprises:

a signal averaging module for determining an average signal value for each image section;

an adjustment value determining module coupled to the signal averaging module for determining an adjustment value for each image section for each detector associated with the image section;

an adjustment value averaging module coupled to the adjustment value determining module for determining an average of the adjustment values for each detector;

an adjusted signal generator coupled to the adjustment value averaging module for determining for each detector, a plurality of adjusted signals, each adjusted signal corresponding to an image section, by applying the average adjustment value to the obtained signal for the image section; and

an estimated output signal generator coupled to the adjusted signal generator, for determining for each image section an estimated output signal by averaging the adjusted signals for each detector at the dither position corresponding to the image section.

18. The system of claim 17, further comprising:

an adjustment value tuner coupled to the adjustment value averaging module, for multiplying the average of the adjustment values by a tuning coefficient to obtain a tuned average adjustment value;

and wherein the adjusted signal generator applies the tuned average adjustment value to the obtained signal for the image section.