US4302673A
Expired / Lapsed
US
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Technique for optical non-uniformity correction of an imaging system
Assignee: United States Department of the Army
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Filing: 1980-07-15
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Granted: 1981-11-24
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Expires: 2000-07-15
Abstract
Abstract A technique for optical non-uniformity correction of a focal plane imagingystem wherein incoming objective scene light rays impinging on each detector in a focal plane array is corrected on a pixel-by-pixel basis by optical correction means from a separate optical source. The optical correction means is comprised of a multiplicative correction means and an additive correction means. The multiplicative correction means is comprised of a responsivity mask positioned on or near the focal plane that provides a multiplicative factor of unity or less to each detector to cause more uniform sensitivity of the detectors. The additive correction means is comprised of the separate optical source that is positioned in a separate optical train and is comprised of an additive optical correction mask aligned with a light source and focusing screen means and image relay that relay the additive optical correction sensitizing illumination onto the focal plane array or the pixel-by-pixel basis. The additive correction may be used alone.
Inventors
- 👤 Vincent T. Bly
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 18:27
CPC Classifications
H; H10; H10F; H10F39/00; H10F39/10; H10F39/107; H04; H04N; H04N25/00; H04N25/60; H04N25/67; H04N25/671
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
84 words
In a focal plane array infrared imaging system, means of optical non-uniformity correction of fixed pattern noise, said means comprising: a multiplicative correction means for selectively limiting the sensitivity of each detector to the least sensitive detector of a plurality of detectors in said focal plane array; and an additive optical correction means for selectively adding sensitizing illumination to each of said plurality of detectors on a pixel-by-pixel basis to provide uniform output from said focal plane array at a desired operating flux level.
Claim 2
Dependent Claim
84 words
In a focal plane array infrared imaging system, means of optical non-uniformity correction of fixed pattern noise, said means comprising: a multiplicative correction means for selectively limiting the sensitivity of each detector to the least sensitive detector of a plurality of detectors in said focal plane array; and an additive optical correction means for selectively adding sensitizing illumination to each of said plurality of detectors on a pixel-by-pixel basis to provide uniform output from said focal plane array at a desired operating flux level.
Claim 3
Dependent Claim
57 words
A means of optical non-uniformity correction as set forth in claim 1 wherein said multiplicative correction means is comprised of a responsivity correction mask overlaying said focal plane array which spatially modulates as a multiple of unity or less the sum of the flux from the additive optical correction means sensitizing illumination and the input scene flux.
Claim 4
Dependent Claim
149 words
A means of optical non-uniformity correction as set forth in claim 2 wherein said additive correction means is comprised of: a light source that emits an even flood of light therefrom; a focusing screen means for bending and focusing said light rays; an additive optical correction mask in optical alignment with said focusing screen means wherein said additive optical correction mask is a photographic film that has a two-dimensional array of neutral density elements with each element aligned with a corresponding detector in said focal plane array; and image relay optics for relaying said sensitizing illumination on a pixel-by-pixel basis from said additive optical correction mask onto said focal plane array wherein an extra flood of photons is added to the incident scene photons from the input scene on each detector in which the extra flood of photons is proportional to the transmittance of the corresponding neutral density element.
Claim 5
Dependent Claim
22 words
A means of optical non-uniformity as set forth in claim 3 wherein said focusing screen means is a Fresnel lens and diffuser.
Claim 6
Dependent Claim
52 words
A means of optical non-uniformity correction as set forth in claim 1 wherein said additive optical correction mask is a photographic film having a stable photographic transparency in accordance with a digitization of the focal plane output from each detector with application of at least two different levels of uniform input flux.
Claim 7
Dependent Claim
30 words
A means of optical non-uniformity correction as set forth in claim 5 wherein said image relay means is comprised of a relay lens and an uncoated cellulose nitrate pellicle beam-splitter.
Claim 8
Dependent Claim
37 words
A means of optical non-uniformity correction as set forth in claim 6 wherein said image relay means further comprises at least one folding mirror between said additive optical correction mask and said uncoated cellulose nitrate pellicle beam-splitter.
Claim 9
Dependent Claim
40 words
A means of optical non-uniformity correction as set forth in claim 6 wherein the wavelength of said light source is compatible with the wavelength of the focal plane array materials and the materials of said uncoated cellulose nitrate pellicle beam-splitter.
Claim 10
Dependent Claim
51 words
A means as set forth in claim 8 wherein said light source is in the visible to near infrared spectral regions, said relay lens is clear glass, and said focal plane array material are semiconducting materials with bandgaps suitable for infrared spectral region detection and absorb visible and near infrared photons.
Claim 11
Dependent Claim
17 words
A means as set forth in claim 8 wherein said light source is a light emitting diode.
Claim 12
Dependent Claim
28 words
A means as set forth in claim 10 wherein said uncoated cellulose nitrate pellicle beam-splitter has a ratio of 1% to 5% reflection and 99% to 95% transmission.
Claim 13
Dependent Claim
17 words
A means as set forth in claim 8 wherein said light source is a grain-of-wheat incandescent bulb.
Claim 14
Dependent Claim
16 words
A means as set forth in claim 9 wherein said focal plane array materials are Indium-Antimonide.
Claim 15
Dependent Claim
16 words
A means as set forth in claim 9 wherein said focal plane array materials are Mercury-Cadmium-Telluride.
Claim 16
Dependent Claim
16 words
A means as set forth in claim 9 wherein said focal plane array materials are Lead-Tin-Telluride.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-11-23 | 1985-05-25 | 1985-11-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-11-23 | 1989-05-25 | 1989-11-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-11-23 | 1993-05-25 | 1993-11-24 | $7700.00 | Window Closed / Lapsed |