Apparatus and method for imaging
Apparatus and method for compiling an image is disclosed. The apparatus comprises a deflector, a detector, and a processor. The deflector is operable to deflect light incident thereon by a controllable angular deflection, and is arranged to receive light from a moveable field of view within a field of regard by controlling the angular deflection. The detector is arranged to receive deflected light and output an image component composed from the deflected light. The processor is arranged to control the angular deflection to select a part of the field of regard to be received at the detector, and to receive a sequence of such image components from the detector. The apparatus is configured to receive each image component passively, and the processor is operable to compile the sequence of image components to form a composite image of at least a part of the field of regard.
1 . Apparatus for compiling an image, the apparatus comprising:
a) a deflector operable to deflect light incident thereon by a controllable angular deflection and arranged to receive light from a field of view, which field of view is moveable within a field of regard by controlling the angular deflection;
b) a detector arranged to receive deflected light from the deflector and operable to output an image component composed from the deflected light; and
c) a processor arranged to control at least one of a staretime for each image component or dwell times for the deflector within the staretime for each image component such that a size of each image component with respect to the field of regard is variable, whereby the control selects a part of the field of regard to be received at the detector for each image component, and to receive a sequence of such image components from the detector;
wherein the apparatus is configured to receive each image component passively, and wherein the processor is operable to compile the sequence of image components to form a composite image of at least a part of the field of regard.
2 . The apparatus as claimed in claim 1 , wherein the deflector comprises one or more acousto-optic deflectors.
3 . The apparatus as claimed in claim 2 , wherein the deflector comprises two acousto-optic deflectors immediately adjacent one another.
4 . The apparatus as claimed in claim 2 , wherein the deflector comprises two spaced apart acousto-optic deflectors, and further comprises a relay lens between the two spaced apart acousto-optic deflectors arranged to focus light deflected by one of the acousto-optic deflectors onto the other of the acousto-optic deflectors.
5 . The apparatus as claimed in claim 2 , wherein the deflector comprises a single acousto-optic deflector operable to deflect light across a two dimensional field of regard.
6 . The apparatus as claimed in claim 2 , further comprising one or more stops arranged to prevent light passing through the one or more acousto-optic deflectors without deflection from reaching the detector.
7 . The apparatus as claimed in claim 6 , wherein the one or more stops comprises one or more mirrors arranged such that an image of the detector is formed at the detector.
8 . The apparatus as claimed in claim 6 , wherein the one or more stops comprises an arrangement of mirrors configured to retroreflect rays originating at the detector.
9 . The apparatus as claimed in claim 1 , further comprising a filter configured to filter light incident on the detector.
10 . The apparatus as claimed in claim 9 , wherein the filter is a variable filter.
11 . The apparatus as claimed in claim 1 , wherein the detector is configured to detect radiation in a long wavelength infrared band.
12 . The apparatus as claimed in claim 1 , wherein the detector comprises between one and one thousand pixels.
13 . The apparatus as claimed in claim 12 , wherein the detector is a single pixel detector.
14 . The apparatus as claimed in claim 12 , wherein the deflector is operable such that a first field of view recorded by a first image component is displaced from a second field of view recorded by a second image component by a non-integer number of pixels.
15 . The apparatus as claimed claim 1 , wherein the detector comprises a number of pixels each operable to detect a different wavelength of electromagnetic radiation.
16 . The apparatus as claimed in claim 1 , wherein the detector is cooled.
17 . The apparatus as claimed in claim 1 , wherein at least the detector and the deflector are mounted on a gimbal.
18 . The apparatus as claimed in claim 1 , further comprising an optical arrangement configured to alter the field of regard.
19 . The apparatus as claimed in claim 18 , wherein the optical arrangement comprises an afocal telescope configured to expand the field of regard.
20 . The apparatus as claimed in claim 1 , further comprising a sensor arranged to detect motion of the apparatus and to output detected motion to the processor; and wherein the processor is configured to control the angular deflection so as to compensate for the detected motion.
21 . A seeker for a guided missile comprising the apparatus as claimed in claim 1 .
22 . A passive imaging method for compiling an image, the method using apparatus comprising a detector arranged to receive deflected light from a deflector; the deflector being operable to deflect light incident thereon by a controllable angular deflection, and arranged to receive light from a field of view, which field of view is moveable within a field of regard by controlling the angular deflection; and the method comprising the steps of:
selecting a number of image components;
for each image component, determining a staretime and dwell times, wherein at least one of the staretime and the dwell times of the deflector within the staretime for each image component is variable such that a size of the image component with respect to the field of regard is variable between image components;
determining the deflection required to enable the detector to image each of said image components based on the staretime and the dwell times determined for each image component;
for each determined deflection, applying the deflection to light incident on the apparatus and using the detector to record the image component associated with the deflection; and
compiling the image components to form a composite image of at least a part of the field of regard.
23 . The method as claimed in claim 22 , wherein the deflection is varied during recording of at least one of the image components.
24 . The method as claimed in claim 23 , wherein the deflection takes a number of discrete values during recording of said at least one of the image components, such that said at least one of the image components relates to a set of discrete regions of the field of regard.
25 . The method as claimed in claim 24 , wherein the deflection is maintained at each discrete value for a set dwell time, and wherein the method further comprises the step of selecting the dwell time-times for each of the discrete values, respectively.
26 . The method as claimed in claim 25 . wherein the dwell time is the same for each of the discrete values.
27 . The method as claimed in claim 23 , wherein the deflection is varied continuously during recording of said at least one of the image components.
28 . The method as claimed in claim 22 , wherein the deflection takes a number of discrete values during recording of at least one of the image components, and where the deflection is varied continuously during recording of at least another of the image components.
29 . A method of capturing video, the video comprising a sequence of image frames, wherein each of the sequence of image frames is a composite image obtained using the method of claim 22 .
30 . The method as claimed in claim 29 , wherein the step of determining the deflection required to enable the detector to image each of said image components for one of the image frames comprises the steps of determining motion of the apparatus, and determining the deflection so as to compensate for the motion of the apparatus.
31 . The method as claimed in claim 29 , further comprising the step of tracking a target in the sequence of image frames, and wherein the step of selecting the image components for one of the image frames is performed in dependence on motion of the tracked target determined from a number of preceding image frames.
32 . A computer readable medium comprising instructions that when executed cause a processor to perform the method of claim 22 .
33 . The apparatus as claimed in claim 1 , wherein the processor is configured to control the deflector during recording image components such that the composite image includes gaps in the field of regard.