GB1564999A – Line-scanning systems
– Google Patents
GB1564999A – Line-scanning systems
– Google Patents
Line-scanning systems
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Publication number
GB1564999A
GB1564999A
GB49513/77A
GB4951377A
GB1564999A
GB 1564999 A
GB1564999 A
GB 1564999A
GB 49513/77 A
GB49513/77 A
GB 49513/77A
GB 4951377 A
GB4951377 A
GB 4951377A
GB 1564999 A
GB1564999 A
GB 1564999A
Authority
GB
United Kingdom
Prior art keywords
scanning
rotation
axis
detector elements
delay
Prior art date
1976-12-03
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB49513/77A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Optische Industrie de Oude Delft NV
Original Assignee
Optische Industrie de Oude Delft NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1976-12-03
Filing date
1977-11-29
Publication date
1980-04-16
1977-11-29
Application filed by Optische Industrie de Oude Delft NV
filed
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Optische Industrie de Oude Delft NV
1980-04-16
Publication of GB1564999A
publication
Critical
patent/GB1564999A/en
Status
Expired
legal-status
Critical
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Classifications
H—ELECTRICITY
H04—ELECTRIC COMMUNICATION TECHNIQUE
H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
H04N3/02—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only
H04N3/08—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only having a moving reflector
H04N3/09—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only having a moving reflector for electromagnetic radiation in the invisible region, e.g. infra-red
C—CHEMISTRY; METALLURGY
C07—ORGANIC CHEMISTRY
C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
C07C45/56—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds from heterocyclic compounds
C—CHEMISTRY; METALLURGY
C07—ORGANIC CHEMISTRY
C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
C07C47/00—Compounds having —CHO groups
C07C47/52—Compounds having —CHO groups bound to carbon atoms of six—membered aromatic rings
C07C47/56—Compounds having —CHO groups bound to carbon atoms of six—membered aromatic rings containing hydroxy groups
C07C47/565—Compounds having —CHO groups bound to carbon atoms of six—membered aromatic rings containing hydroxy groups all hydroxy groups bound to the ring
G—PHYSICS
G01—MEASURING; TESTING
G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
G01C11/02—Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures
G01C11/025—Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures by scanning the object
Description
PATENT SPECIFICATION
Application No 49513/77 ( 22) Filed 29 Nov 1977 Convention Application No ( 19) 7613491 Filed 3 Dec 1976 in Netherlands (NL) Complete Specification Published 16 Apr 1980
INT CL 3 H 04 N 7/00 Index at Acceptance H 4 F D 24 D 27 A 1 D 27 R 9 D 275 D 3 OT 1 D 42 V D 53 M D 61 D 83 B DX ( 54) IMPROVEMENTS IN OR RELATING TO LINE-SCANNING SYSTEMS.
( 71) We, N V OPTISCHE INDUSTRIE «De Oude Delft», a Dutch body corporate of Van Miereveltlaan 9, Delft, The Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: –
This invention relates to apparatus for scanning an area emitting a given kind of radiation, and for processing the radiation thus collected into a form suitable for reproduction or recording.
Apparatus of the kind to which this invention relates is described, for example, in United States Patent 3,632,870 and comprises one or more surfaces reflecting the radiation, and which surfaces are rotatable about an axis of rotation; a configuration of detector elements with an array of N elements for simultaneously scanning N field lines transversely to said axis of rotation: and N light modulator units each responsive to an output signal derived from an associated one of said N detector elements.
Such apparatus is generally used on board of aircraft for reconnaissance purposes.
In apparatus arranged in accordance with this prior art, the rotatable reflective surfaces, or mirrors, are parallel to the axis of rotation, a scanning beam and the beam to be deflected to an associated detector element being coplanar in a plane normal to the axis of rotation.
A scanning beam moves along the radiant area at an angular velocity twice that of the axis of rotation With an array of detector elements located so that its longitudinal direction is parallel to the direction of advance of the apparatus (the flight direction of the aircraft), the apparatus will scan the ground along a plurality of separate lines, the length of the strip being instantaneously viewed by the detector device increasing proportionally to the length of the scanning line, and hence proportionally to 1/cos so,< being the instantaneous scanning angle, herein defined 45 as the angle through which a scanning surface has been rotated relative to said axis of rotation from a reference position at which any line of said scanning surface extending in a direction perpendicular to said axis of rotation, 50 is parallel to said area to be scanned This means that when the scanning angle is increased the field lines being scanned become spaced an increasingly large distance apart, as a consequence of which the strip traversed 55 during one sweep may begin to overlap the strip traversed during a next sweep In order to avoid the consequential drawback of possible image blurring, in this prior technique, during the reproduction or recording of the collected 60 image information, use is made of a system in which the lines traversed for reproduction or recording are matched in form to those along which the field is actually scanned However, in this technique, only a relatively narrow strip of 65 constant width of the line pattern is used for reproduction or recording This means that as the scanning angle is increased the signals derived from the detector elements at the front and rear ends of an array will contribute to the 70 reproduction to an increasingly lesser extent.
When the scanning angle is 60 only half of the detector elements of such an array will contribute effectively This accordingly degrades the quality of the reproduced or recorded image 75 The problems inherent in this prior technique are not encountered, if the reflective surfaces of the scanner are at an angle, of preferably 450, to the axis of rotation For in that case the scanning beam is rotated by the scanning 80 ( 21) ( 31) I" If) ( 11) 1 564 999 ( 32) ( 33) ( 44) ( 51) ( 52) 1 564 999 mirror, whereby the scan lines traversed by an array of detector elements are caused to remain parallel to each other Such a rotated scanning beam, however, results in the scan lines being different in length, which detracts from this important advantage.
If, for example, the array of detector elements is arranged to extend vertically in its longitudinal direction, the detector elements, after reflection at the scanning mirror, will be projected vertically under the aircraft as a row of image elements parallel to the axis of rotation and hence, assuming the axis of rotation and hence, assuming the axis of rotation extends in the flight direction, parallel to this flight direction Where, however, the scanning beam is rotated it is found that the projection of the row of image elements is distorted, while they also increase in size As a result of such distortion, the area over which the aircraft flies will be scanned during each scan according to a plurality of parallel lines, corresponding to the number of detector elements making up the array, but the length of these scan lines will vary in dependence upon the scanning angle (p This means that an area covered during one scan by the array of detector elements has the form of a trapezium, which may cause image distortion during image reproduction or recording.
A possible solution for this problem is proposed in Dutch patent application 6812267, which was laid open to public inspection on March 3,1970 This proposal utilizes an optical method, and contemplates simulating the geometry of the projected field on the terrain.
This prior technique has the drawback, however, that it is impossible to use large-aperture optics for the reproduction, which makes it necessary to use light sources of very high intensity.
The present invention provides a different solution, in which, on the one hand, the image distorting effect resulting from the inequality of the scan lines traversed is eliminated by an electrical means, and on the other hand, the isochronous image signals obtained from such elimination process are converted by optical means into a rotation-symmetrical beam configuration that can be combined with known per se large-aperture optics for reproduction or recording.
According to the present invention, there is provided apparatus for scanning with a scanning beam an area emitting a given kind of radiation, and for processing the radiation thus collected into a form suitable for reproduction and recording, which comprises one or more surfaces reflecting the radiation, which surfaces are rotatable about an axis of rotation; a configuration of detector elements with an array of N elements for simultaneously reading n field lines of field elements transversely to said axis of rotation; and N light modulator units each responsive to an output signal derived from an associated one of said n detector elements, characterized in that each of said reflectingsurfaces is at a fixed angle, of preferably 45, to said axis of rotation; each of a plurality of the detector elements is coupled 70 to a separate delay device serving to delay the signal from the associated detector element by a time interval varying with the scanning angle p (as hereinbefore defined) according to a pre-determined function, the arrangement 75 being such that field elements located in a row parallel to said axis of rotation, are effective to produce isochronous signals at the respective outputs of the delay devices; and in that said light modulator units are optically 80 coupled at their output end to prism means for combining the N separate beams of radiation generated by the N light modulator units, each of which light beams has been modulated with the appropriately delayed output signal from an 85 associated one of said detector elements, to form a beam comprising N rotation-symmetrical component beams co-axially shifted together.
One embodiment of the invention will now be described, by way of example, with 90 reference to the accompanying drawings In said drawings, Figure 1 is a diagram illustrating the image distortion arising in a scanner used in apparatus according to the present invention; 95 Figure 2 is a diagram showing an embodiment of the present invention; and Figure 3 is a diagram showing the configuration of the frequency of a control signal as a function of the scanning angle 100 In the diagram of Figure 1, the flight direction and the scanning direction are respectively designated by v and a Designated by 1, 2, 3 and 4 are four image frames, or the projections of four detector elements arranged 105 in a vertical array in opposition to a rotary scanning mirror disposed at an angle of 450 to its axis of rotation, which axis extends in the direction of flight Frames 1, 2, 3 and 4 are formed when the scanning beam, or the 110 scanning mirror, encloses a scanning angle sp of 0 with the vertical When, using such a mirror, angle so is increased the axes of the image frames will traverse mutually parallel lines over the field to be scanned As angle <' 115 increases, however, the scanning beams will also rotate about their own optical axis; it can be shown that such rotation corresponds to the rotation of the mirror The row of image frames projected on the field to be scanned 120 will be rotated, too, so that when angle p has a given value a set of image frames will be projected on the field to be scanned as shown at 1 ', 2 ', 3 ' and 4 ' The solution according to the present invention, whereby the image 125 distorting effect resulting from such a rotation of the detector image is eliminated, will be best understood from a consideration of a line located in the field to be scanned, parallel to the flight direction Each detector element of 130 1 564999 the array being considered will generate a signal at the moment when its image frame, such as 1, projected on the field being scanned will sweep across this line This moment is different for each one of the array of detector elements under consideration When the angular distance between two successive detector elements of the array is y, it will be seen that the image frame projection of the first detector element will be advanced in the scanning direction relatively to the next element of the array under consideration by an angle Ap = sin sp.
At a constant angular velocity W of the axis of rotation, and hence of the scanning beam, we have the equation A = w At, in which At is the time difference between the electrical signals derived from adjacent detector elements, generated when the projections of these detector elements reach the line under consideration It is seen, therefore, that this time difference At is proportional to sin tp The effect resulting from the rotation of the scanning beam can thus be eliminated according to the present invention by delaying the leading signal by a time interval varying proportionally to a given function, i e sin qo In a practical case, in which y = 1 mrad and co = 600 rad sec 1, the signal from a detector element will have to be delayed relatively to the adjacent one in the array under consideration by an interval of up to approximately 0 83 jisec When, for example, four detectors are used in an array, the maximum delay to be introduced will be given by 3 0 83 = 2 5 psec, introducing a lead on one scanning side, and a lag between the signals on the other When, however, a fixed delay is added to the delayed signals in all instances, it is possible to operate with lagging signals throughout the full scan area These delay periods are small relatively to the time required for one scan, which for example is of the order of 3 3 milliseconds.
Figure 1 also shows, in dotted lines, that the strip of terrain covered by the detector elements during a scan is in principle trapezoidal in shape, so that during successive sweeps a pattern of trapezoidal strips is scanned This means that, without the employment of distortion-eliminating means, a line parallel to the direction of flight will be depicted as a serrated line.
Figure 2 shows a diagram of one embodiment of the present invention As shown, there are four detector elements 1-4, disposed according to a vertical array and opposite a scanner (not shown) rotatable about an axis and comprising, for example, three mirrors each enclosing a fixed angle of 450 with the axis of rotation According to the invention, each of these detector elements, except for the last, is coupled to a separate delay device V 1 to V 3 Each of these delay devices is arranged to delay the electrical signal received from the associated detector element by a time interval varying during a scan according to a pre-determined function of the scanning angle po If the time difference At between the signals from adjacent detector elements, such as 1 and 2, is given by p/w sin ep, the delay device V,, associated with the first detector 70 element 1 must always introduce a delay of 3 At = 3 y/w sin,o, while the next delay devices have to introduce a delay of 2 At and At respectively With such an organization, only those signals which correspond to a central, 75 rectangular portion, determined by a given maximum angle p A of a trapezoidal field strip, as obtained each time when during a scan the projections of the detector elements are swept over the terrain, will be processed further and 80 effectively used in the reproduction or recording.
When the electrical signals from the detector elements have been delayed in the manner described above there are in effect formed isochronous signals representative of an image 85 geometry corresponding to the geometry on the area scanned, in other words, a given distance ratio in this area is also represented by the electrical signals thus delayed That is to say, the thus delayed signals can be regarded as 90 signals obtained when the scanner has scanned a number of parallel and equally long lines of the area covered.
The signals can be delayed in the desired manner using analogue shift registers, preferably 95 in the form of charge coupled devices, in which a signal presented at the input is stored in the form of a proportional amount of electrical charge in a respective semi-conductive region.
In response to a control signal applied to such a 100 shift register, the charge thus stored can be shifted to an adjacent region of the shift register It is accordingly possible to form an analogue shift register with N stages, each stage being capable of introducing an 105 incremental delay of At If the control signal for shifting the stored information has a frequency f, i e the period T of the control signal equals 1/f, then after completion of n cycles or excursions of the control signal, a 110 signal presented to a delay device will have been shifted through N stages, whereby it has been delayed by a time interval of n At If the period T is selected to equal the incremental delay interval At, the delay introduced by a 115 delay device will be given by n/f It is thus possible to achieve the desired scan angledependent delay for the signals by causing the frequency f to vary in the desired manner according to a sinusoidal function in dependence 120 on the scanning angle po.
Figure 3 diagrammatically shows how the frequency of the control signal varies as a function of the scanning angle Up With such a frequency dependent relation, the delay 125 introduced will exhibit at the maximum angle Pm the longest difference from so = O (vertically under the airplane) required for that threshold angle It is thus possible to cause the delay to vary in dependence on the scanning 130 1 564 999 angle according to a sinusoidal function.
The signals from the detector elements, thus delayed in the desired manner, are supplied via processing means A, -A 4 to a plurality of light modulator units L, -L 4.
These light modulator units can generate a plurality of separate light beams, each of which is modulated in brightness with the signal from the associated detector element.
According to a further aspect of the present invention, these light modulator units L, -L 4 are optically coupled to a prism unit, comprising, in the embodiment shown, three prism sub-units PSI, P 52 and P 53 Each of these sub-units comprises a pair of prisms cemented together at their oblique faces A reflective layer of suitable, i e elliptic, shape is provided in this boundary surface of the prisms thus cemented together It is thus possible, by means of such a sub-unit, for two separate light beams, such as from two light modulator units, to be, as it were, concentrically combined, the two light beams being co-axially shifted one into the other to form a rotationsymmetrical beam composed of two component beams By disposing the sub-units as shown diagrammatically in Figure 2 and providing them with suitable reflective layers on the boundary faces, it is possible to combine the four separate light beams referred to in this example, in the manner described above, to form a single composite light beam suitable to be supplied to a known per se reproducing apparatus equipped with large-aperture optics and with facilities for controlling the light spot for reproduction or recording in dependence on the film speed, using the well-known principle of slit control for the overall dimension of the imaging slit.
The light modulators L, -L 4 and the prism sub-units PSI -P 53 should be arranged in such interrelationship that the light beams from the light modulators pass along equally long transmission paths having substantially identical transmission characteristics and extending to the output end of the prism sub-unit serving as the output sub-unit, such as P 53.
Claims (4)
WHAT WE CLAIM IS:-
1 Apparatus for scanning with a scanning beam an area emitting a given kind of radiation, and for processing the radiation thus collected into a form suitable for reproduction and recording, which comprises one or more surfaces reflecting the radiation, which surfaces are rotatable about an axis of rotation; a configuration of detector elements with an array of N elements for simultaneously scanning N field lines of field transversely to said axis of rotation; and N light modulator units each responsive to an output signal derived from an associated one of said n detector elements; and characterized in that each of said reflecting surfaces is at a fixed angle, of preferably 450, to said axis of 65 rotation; each of a plurality of the detector elements is coupled to a separate delay device serving to delay the signal from the associated detector element by a time interval varying with the scanning angle p (as hereinbefore 70 defined) according to a pre-determined function, the arrangement being such that field elements located in a row parallel to said axis of rotation, are effective to produce, isochronous signals at the respective outputs 75 of the delay devices; and in that said light modulator units are optically coupled at their output end to prism means for combining the N separate beams of radiation generated by the N light modulator units, each of which 80 light beams has been modulated with the appropriately delayed output signal from an associated one of said detector elements, to form a beam comprising N rotation-symmetrical component beams co-axially shifted together 85
2 Apparatus according to claim 1, wherein a delay device is formed as a shift register arranged to cooperate with means for varying the shift frequency at a periodicity corresponding to the scan rate and in inversely proportional 90 relationship to the scanning angle p.
3 Apparatus according to claim 2, wherein a shift register is formed as a charge-coupled device, the number of stages of which is determined by the sequential number of the 95 associated detector element in said array.
4 Apparatus according to any one of claims 1-3, wherein the prism unit comprises n-l sub-units, each comprising a pair of triangular prisms cemented together at their oblique faces, 100 with a reflective layer being applied at the boundary face, the form of said layer being suited to the component beams to be combined.
Apparatus according to claim 4, wherein the light modulators and said sub-units of the 105 prism unit are arranged in such interrelationship that the light beams from the light modulators pass along equally long transmission paths to the output face of the prism sub-unit serving as the output sub-unit of said prism unit 110 6 Apparatus constructed, arranged and adapted to operate substantially as described herein with reference to the accompanying Figure 2.
RAWORTH, MOSS & COOK Chartered Patent Agents Agents for the Applicants 36 Sydenham Road, Croydon, Surrey CR O 2 EF 120 Printed for Her Majesty's Stationery Office by MULTIPLEX techniques ltd, St Mary Cray, Kent 1980 Published at the Patent Office, 25 Southampton Buildings, London WC 2 l AY, from which copies may be obtained.
GB49513/77A
1976-12-03
1977-11-29
Line-scanning systems
Expired
GB1564999A
(en)
Applications Claiming Priority (1)
Application Number
Priority Date
Filing Date
Title
NL7613491A
NL7613491A
(en)
1976-12-03
1976-12-03
SYSTEM FOR THE SIGNAL SENSING OF A PARTICULAR TYPE OF A RADIATION EMITTING AREA, AND PROCESSING THE RADIATION RECEIVED INTO A FORM SUITABLE FOR DISPLAY OR RECORDING.
Publications (1)
Publication Number
Publication Date
GB1564999A
true
GB1564999A
(en)
1980-04-16
Family
ID=19827329
Family Applications (1)
Application Number
Title
Priority Date
Filing Date
GB49513/77A
Expired
GB1564999A
(en)
1976-12-03
1977-11-29
Line-scanning systems
Country Status (5)
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Link
US
(1)
US4152725A
(en)
DE
(1)
DE2752828C2
(en)
FR
(1)
FR2373041A1
(en)
GB
(1)
GB1564999A
(en)
NL
(1)
NL7613491A
(en)
Cited By (1)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
GB2149258A
(en)
*
1983-11-04
1985-06-05
Ferranti Plc
Image correction system
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US4231062A
(en)
*
1978-11-28
1980-10-28
Rca Corporation
Charge-coupled device imager system
FR2517839A1
(en)
*
1981-12-07
1983-06-10
Thomson Csf
HETERODYNE DETECTION DEVICE OF AN OPTICAL IMAGE
EP0110282A1
(en)
*
1982-11-23
1984-06-13
Tektronix, Inc.
Image distortion correction method and apparatus
US4524390A
(en)
*
1983-03-07
1985-06-18
Eastman Kodak Company
Imaging apparatus
EP0135345B1
(en)
*
1983-08-12
1988-11-02
Nec Corporation
Image pickup system capable of reproducing a stereo and/or a nonstereo image by the use of a single optical system
US4571631A
(en)
*
1984-04-02
1986-02-18
The United States Of America As Represented By The Secretary Of The Navy
CIG Distortion correction with delay lines
FR2577371B1
(en)
*
1985-02-12
1988-06-24
Centre Nat Rech Scient
WIDE SCREEN TELEVISION IMAGE PROJECTION DEVICE
GB2180714B
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*
1985-08-22
1989-08-16
Rank Xerox Ltd
Image apparatus
GB2188205B
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*
1986-03-20
1990-01-04
Rank Xerox Ltd
Imaging apparatus
CH682698A5
(en)
*
1990-11-01
1993-10-29
Fisba Optik Ag Bystronic Laser
Method in which several, arranged in one or more rows of radiation sources are imaged and apparatus therefor.
US5481479A
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*
1992-12-10
1996-01-02
Loral Fairchild Corp.
Nonlinear scanning to optimize sector scan electro-optic reconnaissance system performance
US5278402A
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*
1993-06-09
1994-01-11
Litton Systems
Real-scene dispersion sensor detecting two wavelengths and determining time delay
DE4402775C1
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*
1994-01-27
1995-07-20
Mannesmann Ag
Video camera system for surveillance and inspection purposes
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*
1996-09-24
2000-05-30
Alliedsignal Inc.
Dynamic optical scanning correction device
CN105824004A
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*
2016-04-29
2016-08-03
深圳市虚拟现实科技有限公司
Method and system for positioning interactive space
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Assignee
Title
US3078340A
(en)
*
1954-11-09
1963-02-19
Servo Corp Of America
Means for infrared imaging in color
US3632870A
(en)
*
1966-01-03
1972-01-04
Texas Instruments Inc
Scanner system
NL153679B
(en)
*
1968-08-29
1977-06-15
Tno
DEVICE FOR FILMS OF A TERRAIN FROM AN AIRPLANE, IN WHICH THE TERRAIN IS SCANNED AND SHOWN ON A FILM USING MODULATED LIGHT SOURCES.
US3723642A
(en)
*
1971-05-28
1973-03-27
Hughes Aircraft Co
Thermal imaging system
1976
1976-12-03
NL
NL7613491A
patent/NL7613491A/en
not_active
Application Discontinuation
1977
1977-11-26
DE
DE2752828A
patent/DE2752828C2/en
not_active
Expired
1977-11-28
US
US05/855,163
patent/US4152725A/en
not_active
Expired - Lifetime
1977-11-29
GB
GB49513/77A
patent/GB1564999A/en
not_active
Expired
1977-12-02
FR
FR7736431A
patent/FR2373041A1/en
active
Granted
Cited By (2)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
GB2149258A
(en)
*
1983-11-04
1985-06-05
Ferranti Plc
Image correction system
US4630111A
(en)
*
1983-11-04
1986-12-16
Ferranti Plc
Image distortion correction system for electro-optic sensors
Also Published As
Publication number
Publication date
US4152725A
(en)
1979-05-01
NL7613491A
(en)
1978-06-06
FR2373041A1
(en)
1978-06-30
DE2752828C2
(en)
1986-08-14
FR2373041B3
(en)
1980-09-12
DE2752828A1
(en)
1978-06-08
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Legal Events
Date
Code
Title
Description
1980-08-28
PS
Patent sealed [section 19, patents act 1949]
1988-07-20
PCNP
Patent ceased through non-payment of renewal fee
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