EP0468474A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
A method of compensating scattered characteristics of infrared detector elements
Assignee: Fujitsu Ltd
•
Filing: 1991-07-24
•
Granted: —
•
Expires: 2011-07-24
Abstract
Abstract A method of compensating scattered characteristics of infrared detector elements, in which a thermal image of a scene is input via a focusing lens (5) onto the detector elements (9). The image on the detector elements is defocused by adjusting the focusing lens; and a first signal level output from each detector element is measured. Then, the image is focused, and a second signal level output from each detector element is compensated using the first signal level. In the case where the image is optically scanned over the linearly arranged detector elements, the first signal level may be averaged over a number of scans to obtain an average level of each detector element, and may be further averaged over a number of different scan directions. The scan direction is rotated by rotating a prism (4) around the light path (P), to predetermined angular positions between 0 to 90 degrees. This enables the defocused light incident on the detector elements to be more properly averaged, to provide an improved average level. Thermal image data of a central portion of the scene may be excluded from the averaging operation, because it includes noise due to a narcissus effect, and because even if scan directions are varied by prism rotation the central image portion stays the same, both effects deteriorating the averaging.
Inventors
- 👤 Tsutomu c/o Fujitsu Limited Hanafusa
- 👤 Kikuo c/o Fujitsu Limited Shiraishi
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 18:06
CPC Classifications
G; G01; G01J; G01J5/00; G01J5/10; G01J5/48; G01J5/80; H; H04; H04N; H04N25/00; H04N25/20; H04N25/21; H04N25/60; H04N25/67; H04N25/671; H04N25/673; H04N25/674; G01J2005/0077
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
106 words
A method of compensating scattered characteristics of infrared detector elements, comprising the steps of:- (a) forming an image of a scene to be monitored on the detector elements; (b) defocusing the image on the detector elements, so that a substantially even light distribution is incident on substantially all of the detector elements; (c) measuring a first signal level output from each of the detector elements; (d) focusing the image onto the detector elements; (e) measuring a second signal level output from each of the detector elements; and (f) for each of the detector elements, compensating said second signal level by employing said first signal level, respectively.
Claim 2
Independent Claim
106 words
A method of compensating scattered characteristics of infrared detector elements, comprising the steps of:- (a) forming an image of a scene to be monitored on the detector elements; (b) defocusing the image on the detector elements, so that a substantially even light distribution is incident on substantially all of the detector elements; (c) measuring a first signal level output from each of the detector elements; (d) focusing the image onto the detector elements; (e) measuring a second signal level output from each of the detector elements; and (f) for each of the detector elements, compensating said second signal level by employing said first signal level, respectively.
Claim 3
Dependent Claim
68 words
A method as claimed in claim 1, wherein the detector elements are arranged in a line, and the method further comprises after step (c) the step of:- averaging said measured signal levels of each detector element over a predetermined number of scans so as to provide a respective first averaged level, and wherein step (f) is carried out by employing said first averaged level for each detector element.
Claim 4
Dependent Claim
18 words
A method as claimed in claim 1 or 2, wherein the detector elements comprise a charge- coupled device.
Claim 5
Dependent Claim
23 words
A method as claimed in claim 1, 2, or 3, wherein the scattered characteristic to be compensated is a DC (direct current) offset.
Claim 6
Dependent Claim
28 words
A method as claimed in claim 2, wherein step (f) comprises the step of:- subtracting said first averaged level from said second signal level, for each detector element.
Claim 7
Independent Claim
246 words
A method of compensating scattered characteristics of infrared detector elements arranged in a line and provided in an infrared thermal imaging apparatus, an image of a scene to be monitored being scanned across the line, comprising the steps of:- (a) inputting the image via an image rotating means and a focusing means, each placed in a light path of said scene, onto the detector elements; (b) defocusing the image on said detector elements; (c) measuring a first signal level output from each of the detector elements; (d) averaging said measured first signal levels of each detector element for a predetermined number of scans so as to provide a respective first averaged level; (e) rotating said image rotating means around said light path by a predetermined angle so as to rotate a direction of scanning of the image; (f) repeating said steps (c) to (e), at a plurality of predetermined angular positions of said image rotating means; (g) averaging said first averaged levels measured at all of said angular positions for each detector element, so as to provide a second averaged level of each detector element; (h) fixing said angular position at an angle where the image is properly oriented with respect to the detector elements; (i) focusing the image onto the detector elements; (j) measuring a second signal level output from each of the detector elements; and (k) for each of the detector elements, compensating said second signal level by employing the respective second averaged level.
Claim 8
Independent Claim
246 words
A method of compensating scattered characteristics of infrared detector elements arranged in a line and provided in an infrared thermal imaging apparatus, an image of a scene to be monitored being scanned across the line, comprising the steps of:- (a) inputting the image via an image rotating means and a focusing means, each placed in a light path of said scene, onto the detector elements; (b) defocusing the image on said detector elements; (c) measuring a first signal level output from each of the detector elements; (d) averaging said measured first signal levels of each detector element for a predetermined number of scans so as to provide a respective first averaged level; (e) rotating said image rotating means around said light path by a predetermined angle so as to rotate a direction of scanning of the image; (f) repeating said steps (c) to (e), at a plurality of predetermined angular positions of said image rotating means; (g) averaging said first averaged levels measured at all of said angular positions for each detector element, so as to provide a second averaged level of each detector element; (h) fixing said angular position at an angle where the image is properly oriented with respect to the detector elements; (i) focusing the image onto the detector elements; (j) measuring a second signal level output from each of the detector elements; and (k) for each of the detector elements, compensating said second signal level by employing the respective second averaged level.
Claim 9
Dependent Claim
16 words
A method as claimed in claim 6, wherein said image rotating means is a derotation prism.
Claim 10
Dependent Claim
20 words
A method as claimed in claim 7, wherein said prism is rotated in a range of 0 to 90 degrees.
Claim 11
Independent Claim
27 words
A method as claimed in any of claims 1 to 5, wherein step (e) is carried out for an area excluding a central portion of the image.
Claim 12
Dependent Claim
26 words
A method as claimed in claim 6, 7 or 8, wherein step (d) is carried out for an area excluding a central portion of the image.
Claim 13
Independent Claim
50 words
A method as claimed in claims 1, 2 and 9 in combination, wherein said central portion of the image is a portion in which a measured temperature is below a predetermined threshold level which is lower than said first averaged level by a noise equivalent temperature difference of the apparatus.
Claim 14
Dependent Claim
45 words
A method as claimed in claim 10, wherein said central portion of the image is a portion in which a measured temperature is below a predetermined threshold level which is lower than said second averaged level by a noise equivalent temperature difference of the apparatus.
Claim 15
Independent Claim
199 words
A method of compensating scattered characteristics of two-dimensionally arranged infrared detector elements provided in an infrared temperature detecting apparatus, comprising the steps of:- (a) inputting an image of a scene through an image-rotating means and a focusing means, each placed in a light path of said scene, onto the detector elements; (b) defocusing the image on said detector elements; (c) measuring first signal levels output from each of detector elements; (d) rotating said image rotating means around said light path by a predetermined angle so as to rotate an orientation of the image; (e) repeating said steps (c) to (d), at a plurality of predetermined angular positions of said image rotating means; (f) averaging said first signal levels measured at all of said angular positions for each detector element so as to provide an averaged level of each detector element; (g) fixing said angular position at an angle where the image is properly oriented with respect to the detector elements; (h) focusing the image onto the detector elements; (i) measuring second signal levels output from each of the detector elements; and (j) for each of the detector elements, compensating said second signal level by employing the respective averaged level.
Claim 16
Independent Claim
199 words
A method of compensating scattered characteristics of two-dimensionally arranged infrared detector elements provided in an infrared temperature detecting apparatus, comprising the steps of:- (a) inputting an image of a scene through an image-rotating means and a focusing means, each placed in a light path of said scene, onto the detector elements; (b) defocusing the image on said detector elements; (c) measuring first signal levels output from each of detector elements; (d) rotating said image rotating means around said light path by a predetermined angle so as to rotate an orientation of the image; (e) repeating said steps (c) to (d), at a plurality of predetermined angular positions of said image rotating means; (f) averaging said first signal levels measured at all of said angular positions for each detector element so as to provide an averaged level of each detector element; (g) fixing said angular position at an angle where the image is properly oriented with respect to the detector elements; (h) focusing the image onto the detector elements; (i) measuring second signal levels output from each of the detector elements; and (j) for each of the detector elements, compensating said second signal level by employing the respective averaged level.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.