Method for obtaining an image stabilised frame

Abstract

A method of obtaining an image stabilised frame by: predicting a motion of an imaging system over a period of time before using the the predicted motion and an actuation range of an actuator assembly

Description

There are a variety of apparatuses in which it is desired to provide control of a movable element. SMA elements, for instance SMA wires, may be advantageous as actuators in such apparatuses, for example due to their high energy density which means that the SMA actuator required to apply a given force to the movable element can be relatively small. One type of apparatus in which SMA wire is known for use as an actuator is in miniature cameras, for example those used in smartphones or other portable electronic devices. WO2011 / 104518 discloses examples of SMA actuation apparatuses which are suitable for use in miniature cameras. The present application relates to a method of obtaining image stabilised frames particularly suited for applications such as computer vision, where obtaining a few high-quality frames is more desirable than obtaining numerous lower-quality frames within a given period. This is particularly relevant for systems where the captured frames are not passed directly to the user, but are processed in some way, for instance processed to detect objects, extract object position data, track object movement, or extract camera orientation or position data. Summary According to an aspect of the present invention, there is provided a method of obtaining one or more image stabilised frames (for instance one or more stabilised 2D or 3D images, that is stabilised snapshots of 2D or 3D visual data) using an imaging system, the imaging system (for instance a computer vision camera) comprising: a support structure, an imaging component, a sensor (or optionally a plurality of sensors) configured to provide data on the motion of the support structure, and an actuator assembly operable to configure the imaging component within a (limited) actuation range so as to provide image stabilisation; the method comprising obtaining each of, or at least one of, the one or more image stabilised frames by: predicting a motion of the support structure over a first period of time, based on data provided by the sensor; based on the predicted motion of the support structure and the (limited) actuation range of the actuator assembly, determining a target configuration for the imaging component, relative to the support structure; driving the actuator assembly to configure the imaging component to the target configuration; and subsequently, capturing a frame, during the first period of time, while the actuator assembly provides image stabilisation. The sensor may suitably be an inertial measurement unit (IMU) or other known motion sensor which is coupled to or otherwise configured to detect motion of the support structure. Motion of the support structure may be indicative of the motion of the imaging system taken as a whole. The imaging component may be an imaging sensor, a lens element or lens assembly configured to focus light onto an imaging sensor or a combination of an imaging sensor and a lens element or lens assembly (such that both move together). For these examples of an imaging component the target configuration of the imaging component may be a position and / or orientation of the imaging sensor relative to the support structure. The actuation range may comprise a range of movement for the imaging component (relative to the support structure). In an alternative (or in addition to these options) the imaging component may comprise or include a deformable lens, and the actuator assembly may be configured to deform the lens to adjust the focal point of light focused by the lens upon an imaging sensor. Accordingly, the target configuration may comprise or include a target deformation of the lens. For each of these examples of imaging component, embodiments of the present invention allow for an imaging system to be configured so that throughout a first period of time image stabilisation can be performed such that a real-world object remains focused at a constant (or approximately constant) location upon an imaging sensor. The target configuration (for instance, target position or orientation or target lens deformation) is selected such that based on the predicted motion of the support structure image stabilisation is achievable throughout the first period of time. For instance, if predicted motion through the first period of time comprise rotation of the imaging system continuously in one direction, it may be appropriate to select an imaging component starting position and orientation such that a real-world object is focused close to one edge of the imaging sensor such that it can track across the imaging sensor through the first period of time. The present invention is not limited to any particular physical structure of imaging system nor indeed any particular type of optical image stabilisation. The first period of time may be an exposure period determined as suitable for capturing a frame using the imaging system. The target configuration may be a target position may be a position that is expected to enable the actuator assembly to provide image stabilisation throughout the first period of time. The target position may be a central position within the range of movement. The target position may not necessarily be a central position within the range of movement. The target position may be a position that is offset from the centre of the range of movement. The target position may even be a position at an end or extremity of the range of movement. Optionally, the first period of time is an exposure period (or 'exposure time') determined as suitable for capturing a (single) frame using the imaging system, for instance at the first period of time. Optionally, the target position is further determined based on the velocity and acceleration capabilities of the actuator assembly. For example, based on the maximum velocity the imaging component is capable of being moved at relative to the support structure by the actuator assembly, and the rates (for instance the maximum rate) at which the velocity of the imaging component can be increased or decreased by the actuator assembly. The target position may be further determined based on the length of the first period of time, for instance the length of the exposure time required for capturing the frame. Alternatively, or additionally, the target position may be further determined based on the relative movement that the imaging component is expected to undergo as the actuating assembly provides image stabilisation during the first period of time. Optionally, the one or more image stabilised frames comprises a sequence of image stabilised frames obtained by the imaging system capturing frames at a frame rate, for instance a constant or a variable frame rate. Optionally, the driving of the actuator assembly is carried out during a blanking period, that is a period between refreshes in the frame rate. Optionally, the driving of the actuator assembly is carried out during a frame period (or 'active period'), that is a period during which the imaging system, more specifically the imaging sensor of the imaging system, usually actively captures imaging data. According to another aspect of the present invention, there is provided a method of obtaining a sequence of image stabilised frames obtained by an imaging system capturing frames at a frame rate (for instance a constant or a variable frame rate), the imaging system comprising: a support structure, an imaging component, one or more sensors configured to provide data on the motion of the support structure, and an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the method comprising obtaining each of, or at least one of, the image stabilised frames by: driving the actuator assembly to configure the imaging component to a target configuration, and subsequently capturing a frame while the actuator assembly provides image stabilisation; wherein the driving of the actuator assembly is carried out during a frame period of the frame rate. As above, the target configuration of the imaging component may comprise a target position or orientation. Optionally, no imaging data is obtained by the imaging system during the frame period (during which the driving of the actuator assembly occurs), or imaging data obtained by the imaging system during the frame period (during which the driving of the actuator assembly occurs) is not processed or stored by the imaging system. Optionally, the actuator assembly starts providing image stabilisation after the imaging component is moved to the target position and before the capturing of the frame, and continues to provide image stabilisation during the capturing of the frame. This can help improve stabilisation performance during the capturing of the frame. According to another aspect of the present invention, there is provided a method of obtaining one or more image stabilised frames using an imaging system, the imaging system comprising: a support structure, an imaging component, one or more sensors configured to provide data on the motion of the support structure, and an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the method comprising obtaining each of, or at least one of, the one or more image stabilised frames by: driving the actuator assembly to configure the imaging component relative to the support structure to a target configuration, and subsequently capturing a frame while the actuator assembly provides image stabilisation; wherein the actuator assembly starts providing image stabilisation after the imaging component is moved to the target configuration and before the capturing of the frame, and continues to provide image stabilisation during the capturing of the frame. As above, the target configuration of the imaging component may comprise a target position or orientation. Optionally, the actuator assembly comprises one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to (directly or indirectly) move the imaging component relative to the support structure; and wherein the driving of the actuator assembly and the providing of image stabilisation involves powering the SMA element of at least one of the actuating units. According to another aspect of the present invention, there is provided a computer vision method comprising: obtaining one or more image stabilised frames according to any of the above-described methods; and identifying features (for instance objects and / or people) from the one or more image stabilised frames. According to another aspect of the present invention, there is provided a (non-transitory) computer-readable medium storing (program) instructions for causing a system to perform any of the abovedescribed methods. According to another aspect of the present invention, there is provided an imaging system (for instance a 2D camera, a computer vision camera, or a 3D sensing system) comprising: a support structure; an imaging component; one or more sensors configured to provide data on the motion of the support structure; an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the above-described computer-readable medium; and a controller configured to execute the instructions stored on the computer-readable medium. As above, the target configuration of the imaging component may comprise a target position or orientation. Optionally, the actuator assembly comprises one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to (directly or indirectly) move the imaging component relative to the support structure. Optionally, the one or more actuating units comprise four actuating units arranged so as to be capable of moving the imaging component relative to the support structure in any direction in a movement plane without applying any net torque to the imaging component about a first axis perpendicular to the movement plane. Optionally, the one or more actuating units comprises a plurality of actuating units arranged such that, for each direction along each axis of a Cartesian coordinate system, there is at least one actuating force with a non-zero component along that direction. Optionally, the one or more actuating units are configured to tilt the imaging component relative to the support structure about at least one axis perpendicular to a first axis of the support structure, wherein the first axis is parallel to the optical axis of the imaging system. Optionally, the imaging system is a computer vision camera. The imaging system may be an RGB camera, IR camera, or a 3D sensing system. The 3D sensing system may be of any known time, including direct time of flight, indirect time of flight, or structured light 3D scanning. Optionally, the imaging component is an imaging sensor. Optionally, the imaging component is a lens assembly or lens element arranged to focus an image on an imaging sensor. The lens element may be an adjustable lens element, for instance a fluid lens. According to another aspect of the present invention, there is provided a head-mounted device comprising any of the above-described imaging systems. Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a flowchart showing the steps involved in a method of obtaining one or more image stabilised frames using an imaging system; Figure 2 is a graph illustrating how the method of Fig. 1 may be used; Figure 3 is a schematic cross-sectional view of an imaging system incorporating an actuator assembly; Figure 4 is a schematic cross-sectional view of an imaging system incorporating an actuator assembly; Figure 5 is a schematic cross-sectional view of an imaging system incorporating an actuator assembly; Figure 6 is a schematic plan view of an arrangement of four actuating units; and Figure 7 is a schematic perspective view of an arrangement of eight actuating units. Detailed description Method of obtaining one or more image stabilised frames using an imaging system Fig. 1 is a flowchart showing the steps involved in a method of obtaining one or more image stabilised frames using an imaging system 1 (for instance, as illustrated in any one of Fig.s 3 to 5), wherein the imaging system 1 comprises a support structure 10, an imaging component (which in some examples includes one or both of a lens element or lens assembly 3 and an imaging sensor) 4, one or more sensors 9 configured to provide data on the motion of the imaging system (specifically, the support structure), and an actuator assembly 20 configured to move or configure the imaging component relative to the support structure 10 within a (limited) range of movement so as to provide image stabilisation. The stabilised frames may be stabilised 2D or 3D images, that is stabilised snapshots of 2D or 3D electromagnetic data. The imaging system 1 may be a computer vision camera, an RGB camera, an IR camera, or a 3D sensing system. The method comprises obtaining each of, or at least one of, the one or more image stabilised frames by: predicting a motion of the imaging system 1 over a first period of time, based on data provided by the one or more sensors S10; based on the predicted motion of the imaging system 1 and the (limited) actuation range of the actuator assembly 20, determining a target position or target configuration for the imaging component to be moved to, relative to the support structure S20; driving the actuator assembly 20 to move or otherwise configure the imaging component relative to the support structure 10 to the target position S30; and subsequently, capturing a frame, during the first period of time, while the actuator assembly 20 provides image stabilisation S40. For embodiments where the target configuration is a target position, this may be is a position and / or orientation of a lens element, lens assembly and / or imaging sensor that is expected to enable the actuator assembly 20 to provide image stabilisation throughout the first period of time. Where the imaging component comprises a deformable lens, the target configuration may be a lens deformation state that is expected to enable image stabilisation throughout the first period of time (through further lens deformation). The majority of the following examples concern imaging systems in which one or more imaging components are moved (such as shifted or tilted) to enable image stabilisation, though the present invention is not limited to this. A target position may be a central position within the range of movement of the actuator assembly 20. The target position may not necessarily be a central position within the range of movement. The target position may be a position that is offset from the centre of the range of movement. The target position may even be a position at an end or extremity of the range of movement. The target position may be further determined based on the velocity and acceleration capabilities of the actuator assembly 20. For example, the target position may be based on the maximum velocity the imaging component is capable of being moved at relative to the support structure 10 by the actuator assembly 20, and the rates (for instance the maximum rate) at which the velocity of the imaging component can be increased or decreased by the actuator assembly 20. The target position may be further determined based on the length of the first period of time, for instance the length of the exposure time required for capturing the frame. Alternatively, or additionally, the target position may be further determined based on the relative movement that the imaging component is expected to undergo as the actuating assembly 20 provides image stabilisation during the first period of time. The first period of time is an exposure period (or 'exposure time') determined as suitable for capturing the frame using the imaging system 1. It will be appreciated that the exposure time will depend on the conditions in which the frame is captured. For example, low light conditions would normally require longer exposure times compared to well-lit or brightly illuminated environments to ensure sufficient light reaches the imaging sensor 4. The one or more image stabilised frames may comprise a sequence of image stabilised frames obtained by the imaging system 1 capturing frames at a frame rate, for instance at a constant or a variable frame rate. Where this is the case, the driving of the actuator assembly 1 to move the imaging component to the target position S30 may be carried out during a blanking period, that is a period between refreshes in the frame rate, or during a frame period (or 'active period'), that is a period during which the imaging system 1, more specifically the imaging sensor 4 of the imaging system 1, usually actively captures imaging data. The driving of the actuator assembly 1 to move the imaging component to the target position S30 may be carried out during a blanking period for some frames and carried out during a frame period for some frames. When the actuator assembly 20 is driven to move the imaging component to the target position during a frame period, the imaging system 1 may be configured to not obtain any imaging data during this frame period, or configured to not process or store any imaging data obtained by the imaging system 1 during this frame period. The actuator assembly 20 may start providing image stabilisation after the imaging component is moved to the target position S30 and before the capturing of the frame S40 and may continue to provide image stabilisation during the capturing of the frame S40. This may help improve stabilisation performance during the capturing of the frame S40. The actuator assembly 20 may comprise one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to, directly or indirectly, move the imaging component relative to the support structure 10. Where this is the case, the driving of the actuator assembly 20 to move the imaging component to the target position S30 and the providing of image stabilisation during the first period of time S40 would involve powering this SMA element. The above-described method of obtaining one or more image stabilised frames may be used as part of a computer vision method comprising the step of identifying features (for instance objects and / or people and / or support structure position) from the one or more image stabilised frames. Example of method in use Fig. 2 is a graph illustrating how the above-described method of obtaining image stabilised frames may be used. The x-axis in this graph represents time in seconds (s). The left and right y-axes respectively represent slew rate in degrees per second (deg / s), and position in degrees (deg). The line CP represents the angular movement (the change in position in degrees) of the support structure 10 (right y-axis). The line CV represents the position of the image being perceived by the imaging sensor of the imaging system (right y-axis). The line CS represents the slew rate of the support structure (left y-axis). The line AS represents the slew rate of the imaging component moved by the actuator assembly (left y-axis). In this example, the imaging system is capturing a plurality of image stabilised frames by using the above-described method. During each period Tl, the imaging component is moved by the actuator assembly to a target position. During each period T2, a frame is captured while the actuator assembly provides image stabilisation. As illustrated by the constant positive gradient of line CP and the flat CS line, the imaging system (specifically, the support structure) is undergoing a steady state panning motion at 39 deg / s. As illustrated by the flat gradient of the line CV and the flat gradient of the line AS during T2 periods, the actuator assembly provides image stabilisation by moving the imaging component at a negative slew rate of -39 deg / s during T2 periods (which compensates for, and effectively reverses the panning motion of the support structure during those periods). As illustrated by the positive gradient of the line CV and the flat gradient of the line AS during T1 periods, the actuator assembly moves the imaging component at a positive slew rate of 39 deg / s to 'catch up' with the position of the support structure during T1 periods. In this example, an image stabilised frame is captured half of the time. Computer-readable medium There may be provided a (non-transitory) computer-readable medium storing (program) instructions for causing a system to perform the above-described method of obtaining one or more image stabilised frames. Imaging system Fig.s 3 to 5 illustrate examples where imaging components are shifted in position or orientation to effect image stabilisation. Fig. 3 is a schematic cross-sectional view of an example of the imaging system 1. As discussed above, the imaging system 1 comprises: a support structure 10; an imaging sensor 4; at least one motion sensor 9 configured to provide data on the motion of the support structure; an actuator assembly 20 configured to move an imaging component comprising the imaging sensor 4 relative to the support structure 10 within a range of movement so as to provide image stabilisation. The imaging system 1 may also comprise the above-described computer-readable medium (not shown), and a controller 8 configured to execute the instructions stored on the computer-readable medium. In this example, the imaging component is an imaging sensor 4, and the imaging system 1 further comprises a lens assembly 3 arranged to focus an image on the imaging sensor 4. In this example, image stabilisation is provided by driving relative movement between the lens assembly 3 and the imaging sensor 4, for instance by shifting the imaging sensor 4 along axes orthogonal to a first axis P as indicated by arrows 2. As shown in Fig. 4, in other examples of the imaging system 1, the actuator assembly 20 may be configured to move the lens assembly 3 (which thus comprises the imaging component) relative to the support structure 10 along axes orthogonal to a first axis P as indicated by arrows 2, instead of the imaging sensor 4 relative to the support structure 10, so as to provide image stabilisation by driving relative movement between the lens assembly 3 and the imaging sensor 4. As shown in Fig. 5, in other examples of the imaging system 1, the actuator assembly 20 may be configured to move an imaging component comprising both the imaging sensor 4 and the lens assembly 3 relative to the support structure 10, so as to provide image stabilisation by tilting the imaging sensor 4 and the lens assembly 3 relative to the support structure 10. This motion may comprise tilting the imaging component about axes orthogonal to a first axis P as indicated by arrows 2. The one or more sensors may comprise a motion sensor such as a 3-axis gyroscope or a 3-axis accelerometer. Actuator assemblies The actuator assembly 20 may comprise one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to, directly or indirectly, move the imaging component relative to the support structure 10. The actuator assembly 20 may comprise four actuating units arranged so as to be capable of moving the imaging component relative to the support structure 10 in any direction in a movement plane without applying any net torque to the imaging component about a first axis P perpendicular to the movement plane. For example, the actuator assembly 20 may comprise four actuating units configured to drive relative movement between the imaging component and the support structure 10 by applying actuating forces F between the imaging component and the support structure 10 as illustrated in Fig. 6. The arrangement of actuating forces F of Fig. 6 corresponds to the arrangement of SMA wires described in WO2013 / 175197 Al, which is herein incorporated by reference to the maximum extent permissible by law. Additionally, or alternatively, the actuator assembly 20 may comprise a plurality of actuating units arranged such that, for each direction along each axis of a Cartesian coordinate system, there is at least one actuating force F with a non-zero component along that direction. For example, the actuator assembly 20 may include eight actuating units configured to drive relative movement between the imaging component and the support structure 10 by applying actuating forces F between the imaging component and the support structure 10 as illustrated in Fig. 7. The eight actuating units may be arranged such that the actuating forces F are oriented or arranged in a manner equivalent to the orientation or arrangement of the forces applied by the eight SMA wires in the actuator assemblies disclosed in WO 2011 / 104518 Al, which is herein incorporated by reference to the maximum extent permissible by law. The one or more actuating units may be configured to tilt the imaging component relative to the support structure 10 about at least one axis perpendicular to a first axis P of the support structure 10, wherein the first axis P is parallel to the optical axis O of the imaging system. Many other actuator arrangements may be suitable for the actuator assembly 20. Head-mounted device There may be provided a head-mounted device comprising the above-described imaging system 1. Other variations It will be appreciated that there may be many other variations of the above-described examples. For example, in certain examples of the imaging system 1, the imaging component may be an adjustable lens element, for instance a fluid lens, arranged to focus an image on an imaging sensor. SMA The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (for instance non-tensile) forces to elements. The SMA element may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling, deposition, sintering or powder fusion. The SMA element may exhibit any shape memory effect, for instance a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, for instance by Joule heating, another heating technique or by applying a magnetic field. The SMA element may typically comprise nitinol (nickel titanium), although generally other types of SMA material may be used. Alternative ways of heating SMA The heating of the heat-activated actuator(s), such as SMA material, in order to cause the moving portion to move, could be achieved in a number of ways. In one arrangement, the material could be heated by passing a current through it. This current might come from a local or external power supply. Alternatively, the current might be induced in the wire by inductive coupling with an external alternating field. Where there are two actuators, the two actuators might be designed so that they couple to two different frequencies of the inductive power source, thus allowing the two actuators to be heated differentially. In another arrangement, the material could be heated by external radiation such as a visible or infra-red laser. The external radiation could be focussed so that one actuator is heated preferentially over another actuator, thus allowing differential actuation. Alternatively, or additionally, different actuators, or portions of the actuators, could be treated (for example with a surface coating) so that the different actuators heat at different rates depending on the nature (for instance, the frequency) of the incident radiation.

Claims

1. A method of obtaining one or more image stabilised frames using an imaging system, the imaging system comprising: a support structure, an imaging component, a sensor configured to provide data on the motion of the support structure, and an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the method comprising obtaining at least one image stabilised frame by:predicting a motion of the support structure over a first period of time, based on data provided by the sensor;based on the predicted motion of the support structure and the actuation range of the actuator assembly, determining a target configuration for the imaging component;driving the actuator assembly to configure the imaging component to the target configuration; andsubsequently, capturing a frame, during the first period of time, while the actuator assembly provides image stabilisation.

2. A method according to claim 1, wherein the first period of time is an exposure period determined as suitable for capturing a frame using the imaging system.

3. A method according to claim 1 or 2, wherein the target configuration is further determined based on the velocity and acceleration capabilities of the actuator assembly.

4. A method according to any preceding claim, wherein the one or more image stabilised frames comprises a sequence of image stabilised frames obtained by the imaging system capturing frames at a frame rate.

5. A method according to claim 4, wherein the driving of the actuator assembly is carried out during a blanking period.

6. A method according to claim 4 or 5, wherein the driving of the actuator assembly is carried out during a frame period.

7. A method of obtaining a sequence of image stabilised frames obtained by an imaging system capturing frames at a frame rate, the imaging system comprising: a support structure, an imaging component, a sensor configured to provide data on the motion of the support structure, and anactuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the method comprising obtaining at least one image stabilised frame by: driving the actuator assembly to configure the imaging component to a target configuration, and subsequently capturing a frame while the actuator assembly provides image stabilisation;wherein the driving of the actuator assembly is carried out during a frame period of the frame rate.

8. A method according to claim 6 or 7, wherein no imaging data is obtained by the imaging system during the frame period; or wherein imaging data obtained by the imaging system during the frame period is not processed or stored by the imaging system.

9. A method according to any preceding claim, wherein the actuator assembly starts providing image stabilisation after the imaging component is configured to the target configuration and before the capturing of the frame, and continues to provide image stabilisation during the capturing of the frame.

10. A method of obtaining one or more image stabilised frames using an imaging system, the imaging system comprising: a support structure, an imaging component, a sensor configured to provide data on the motion of the support structure, and an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation; the method comprising obtaining at least one image stabilised frame by:driving the actuator assembly to configure the imaging component to a target configuration, and subsequently capturing a frame while the actuator assembly provides image stabilisation;wherein the actuator assembly starts providing image stabilisation after the imaging component is configured to the target configuration and before the capturing of the frame, and continues to provide image stabilisation during the capturing of the frame.

11. A method according to any preceding claim, wherein the actuator assembly comprises one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to move the imaging component relative to the support structure or deform the imaging component; and wherein the driving of the actuator assembly and the providing of image stabilisation involves powering the SMA element of at least one of the actuating units.

12. A computer vision method comprising:obtaining one or more image stabilised frames according to the method of any preceding claim;andidentifying features from the one or more image stabilised frames.

13. A computer-readable medium storing instructions for causing a system to perform a method according to any preceding claim.

14. An imaging system comprising:a support structure;an imaging component;a sensor configured to provide data on the motion of the support structure;an actuator assembly operable to configure the imaging component within an actuation range so as to provide image stabilisation;a computer-readable medium according to claim 13; anda controller configured to execute the instructions stored on the computer-readable medium.

15. An imaging system according to claim 14, wherein the actuator assembly comprises one or more actuating units each comprising an SMA (shape memory alloy) element configured, when powered, to move the imaging component relative to the support structure or deform the imaging component.

16. An imaging system according to claim 15, wherein the one or more actuating units comprise four actuating units arranged so as to be capable of moving the imaging component relative to the support structure in any direction in a movement plane without applying any net torque to the imaging component about a first axis perpendicular to the movement plane.

17. An imaging system according to claim 15, wherein the one or more actuating units comprises a plurality of actuating units arranged such that, for each direction along each axis of a Cartesian coordinate system, there is at least one actuating force with a non-zero component along that direction.

18. An imaging system according to any of claims 15 to 17, wherein the one or more actuating units are configured to tilt the imaging component relative to the support structure about at least one axis perpendicular to a first axis of the support structure, wherein the first axis is parallel to the optical axis of the imaging system.

19. An imaging system according to any of claims 14 to 18, wherein the imaging system is a computer vision camera.

20. An imaging system according to any of claims 14 to 19, wherein the imaging component is an imaging sensor;wherein the imaging component is a lens assembly or a lens element arranged to focus an image on an imaging sensor; orwherein the imaging component a combination of an imaging sensor and a lens assembly or a lens element arranged to focus an image on the imaging sensor.

21. A head-mounted device comprising an imaging system according to any of claims 14 to 21.

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