Calibration of a head mounted device

Abstract

A calibration method, consisting of providing an electronic lens having an array of transparent pixels, a refractive index of each pixel being electrically tunable, and, while a user is looking through the electronic lens toward a target, receiving feedback from the user regarding a visibility of the target while modulating selected pixels of the array to perturb light transmission therethrough. The method further includes, in response to the feedback from the user, identifying one or more pixels of the array that correspond to a line of sight of the user, thereby calibrating an optical center of the electronic lens for the user.

Description

[0001] CALIBRATION OF A HEAD MOUNTED DEVICE

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit of U.S. Patent Application 63 / 507,992, filed 14 June 2023, which is incorporated herein by reference.

[0004] FIELD OF THE INVENTION

[0005] This invention relates generally to optical calibration, and specifically to calibration of an electronic lens of a head-mounted device.

[0006] BACKGROUND OF THE INVENTION

[0007] An electrically-tunable lens, herein also termed an electronic lens, comprises a pixel grid, wherein the effective refractive index of each pixel can be modified electrically. The optical parameters of the electronic lens can thus be tuned electronically, including the lens optical power and the lens aperture.

[0008] PCT International Patent Publication WO 2015 / 186010, to Yadin et al., describes electronic lenses as used in a pair of spectacles. Control circuitry is configured to receive an input indicative of a distance from an eye of a person wearing the spectacles to an object viewed by the person, and to tune the lenses in response to the input.

[0009] SUMMARY OF THE INVENTION

[0010] An embodiment of the present invention provides a calibration method, including: providing an electronic lens consisting of an array of transparent pixels, a refractive index of each pixel being electrically tunable; while a user is looking through the electronic lens toward a target, receiving feedback from the user regarding a visibility of the target while modulating selected pixels of the array to perturb light transmission therethrough; and in response to the feedback from the user, identifying one or more pixels of the array that correspond to a line of sight of the user, thereby calibrating an optical center of the electronic lens for the user. Typically the method includes applying the calibrated optical center in controlling the electronic lens.

[0011] In a disclosed embodiment modulating selected pixels includes electrically modulating the selected pixels so as to modulate an amplitude of light transmitted through the selected pixels. The method may include not electrically modulating pixels of the array other than the selected pixels so as to render the pixels of the array other than the selected pixels transparent to the light transmission. The feedback may include the user indicating that the target is visible through the pixels of the array other than the selected pixels. Alternatively, the feedback may include the user indicating that the selected pixels obscure the visibility of the target.

[0012] In another disclosed embodiment modulating selected pixels includes electrically modulating the selected pixels so as to apply a spatially varying phase to the light transmitted through the selected pixels. The method may further include applying a spatially uniform phase variation to the pixels of the array other than the selected pixels so as to render the pixels of the array other than the selected pixels transparent to the light transmission. The feedback may include the user indicating that the target is visible through the pixels of the array other than the selected pixels. Alternatively, the feedback may include the user indicating that the selected pixels obscure the visibility of the target.

[0013] In a yet other disclosed embodiment the pixels of the array are formed as a rectangular array of rows and columns, and the selected pixels of the array are formed as a one-dimensional group comprising all pixels in at least one row or all pixels in at least one column. Identifying the one or more pixels of the array may include identifying that the optical center lies on the one-dimensional group.

[0014] In an alternative embodiment the pixels of the array are formed as a rectangular array of rows and columns, and the selected pixels of the array are formed within a two- dimensional (2D) contiguous sub-group of the pixels, wherein the 2D sub-group does not include all the pixels in any given column, or all the pixels in any given row. Identifying the one or more pixels of the array may include identifying that the optical center corresponds to a center of the two-dimensional sub-group. In a further alternative embodiment the line of sight of the user consists of a single, predetermined, line of sight.

[0015] There is further provided, according to an alternative embodiment of the present invention, a calibration method, including: providing an electronic lens consisting of an array of transparent pixels, a refractive index of each pixel being electrically tunable; while a user is looking through the electronic lens toward a target along multiple different lines of sight, recording respective parameters indicative of the different lines of sight and receiving feedback regarding a visibility of the target for each different line of sight while modulating selected pixels of the array to perturb light transmission therethrough; in response to the feedback, identifying respective pixels of the array that lie on the different lines of sight; and forming a correlation between the respective pixels of the array and the respective parameters.

[0016] In a disclosed embodiment the identified respective pixels correspond to an optical center of the electronic lens for the user. The method may include applying the optical center in controlling the electronic lens.

[0017] In a further disclosed embodiment the respective parameters include a location of a pupil of an eye of the user. Alternatively the respective parameters include a gaze direction of an eye of the user.

[0018] In a yet further disclosed embodiment the feedback is provided by the user. Alternatively, the feedback includes a given parameter indicative of the line of sight stabilizing.

[0019] There is further provided, according to an alternative embodiment of the present invention, a calibration apparatus, consisting of: an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; and a processor, configured to: while a user is looking through the electronic lens toward a target, receive feedback from the user regarding a visibility of the target while modulating selected pixels of the array to perturb light transmission therethrough, and in response to the feedback from the user, identify one or more pixels of the array that correspond to a line of sight of the user, thereby calibrating an optical center of the electronic lens for the user.

[0020] There is further provided, according to an alternative embodiment of the present invention, a calibration apparatus, consisting of: an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; and a processor, configured to: while a user is looking through the electronic lens toward a target along multiple different lines of sight, record respective parameters indicative of the different lines of sight and receive feedback regarding a visibility of the target for each different line of sight while modulating selected pixels of the array to perturb light transmission therethrough, in response to the feedback, identify respective pixels of the array that lie on the different lines of sight, and form a correlation between the respective pixels of the array and the respective parameters.

[0021] The present disclosure will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, in which:

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Fig. 1 is a schematic pictorial illustration showing adaptive spectacles worn by a user 21, according to an embodiment of the present invention;

[0024] Fig. 2 is a schematic cross-section of lenses of the spectacles, according to an embodiment of the present invention; Fig. 3 is a schematic block diagram illustrating a spatial light modulator (SLM), according to an embodiment of the present invention;

[0025] Fig. 4 is a two-dimensional representation of bounds of a user’s field of view when the user is looking through a lens, according to an embodiment of the present invention;

[0026] Figs. 5A and 5B illustrate examples of two-dimensional (2D) perturbed and non=perturbed regions on a spatial light modulator, and the corresponding images on the retina of a user, according to an embodiment of the present invention;

[0027] Fig. 6 is a flowchart showing how perturbed SLMs, may be used to calibrate a given lens, according to an embodiment of the present invention.

[0028] Figs. 7A, 7B, 7C and 7D illustrate examples of one-dimensional (ID) perturbed and non=perturbed regions on a spatial light modulator, and the corresponding images on the retina of a user, according to an embodiment of the present invention;

[0029] Figs. 8 A, 8B, and 8C are schematic diagrams illustrating locations on a lens of a target being viewed by a user, according to an embodiment of the present invention;

[0030] Fig. 9 is a schematic diagram illustrating the relation between an image of the eye of a user, and the eye’s line of sight, according to an embodiment of the present invention;

[0031] Fig. 10 is a flowchart showing how an SLM may be used to calibrate a lens for multiple lines of sight, according to an embodiment of the present invention; and

[0032] Figs. 11A and 11B are schematic diagrams illustrating possible orders of clear area positions for an SLM, according to an embodiment of the present invention.

[0033] DETAILED DESCRIPTION OF EMBODIMENTS

[0034] Overview

[0035] A person with defective vision, such as myopia, hyperopia, or presbyopia, may wear eyeglasses, or another head mounted device (HMD), with lenses selected to correct the vision defect. For optimal correction the optical axis of each correcting lens should align with the person’s line of sight. The alignment eliminates prismatic effects, improves the person’s experience, and increases the field of view. The optical axis of the correcting lens originates at a point in the lens herein termed the lens optical center, so that at the optimal alignment the person’s line of sight passes through the optical center. (Typically, when being fitted for a correcting lens, a prescribing optometrist will mark the lens optical center on a temporary prescription lens being worn by a client, by observing where the client’s pupil appears to be when the client looks straight ahead at the optometrist.)

[0036] In embodiments of the present invention each lens used for the vision correction is an electronic lens, i.e., a lens that comprises an array of transparent pixels, arranged in a pixel grid, coupled to a processor. When being operated as a correcting lens, the processor is configured to be able to tune the pixels, i.e., to adjust the refractive index of each pixel electrically so that the processor may adjust the overall lens optical power, the lens aperture, and the lens optical center.

[0037] In the embodiments, rather than adjusting the refractive index of selected pixels so that the pixel array acts as a correcting lens, the processor is configured to be able to electrically modulate the pixels so as to modulate the amplitude and / or the phase of light passing through each selected pixel in a spatially varying manner. When operated in this configuration, an electronic lens is herein also termed a spatial light modulator (SLM). The amplitude or phase modulation of the SLM may be used, in embodiments of the present invention, to effectively “blank” the selected pixels so that light transmission through the selected pixels is perturbed.

[0038] In an embodiment the spatial variation is random, causing, in the case of phase variation, an image formed on the retina of an eye to be blurred. In an alternative embodiment, the spatial variation is periodic that is configured to create image duplication.

[0039] While modulating a selected group of pixels, and typically changing the size and / or the shape of the group, the processor may use feedback from a user wearing the electronic lens to identify the position of the lens optical center when the user is looking directly ahead. The identification replaces the manual marking of a lens by an optometrist, described above.

[0040] The processor may then use, possibly at some later date, the identified position of the optical center to operate the electronic lens as a correcting lens for the user with the center aligned with the user’s line of sight. In an alternative embodiment of the present invention, a camera or other eye tracking system is attached to the HMD and is used to track the pupil location and direction of gaze of a user’s eye. The processor finds the optical center of the electronic lens for the user looking in different directions, not just straight ahead, and forms a correlation between the user’s pupil location or gaze direction and the lens optical center.

[0041] When the electronic lens is operated as a correcting lens, the processor may use the correlation to identify the optical center of the correcting lens, according to the pupil location or gaze direction, when the user is looking in different directions, and construct the correcting lens accordingly.

[0042] Detailed Description

[0043] In the following description, like elements in the drawings are identified by like numerals. In addition, all directional references (e.g., upper, lower, upward, downward, left, right, top, bottom, above, below, vertical, and horizontal) are only used for identification purposes to aid the reader’s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of embodiments of the invention.

[0044] Fig. 1 is a schematic pictorial illustration showing adaptive spectacles 20 worn by a user 21, according to an embodiment of the present invention. Spectacles 20 comprise a frame 23, comprising a front piece 24 and temples 26 connected to respective edges of the front piece.

[0045] Right and left electrically tunable lenses 30A and 30B, also collectively referred to herein as lenses 30, are contained in respective transparent envelopes 22, which are mounted in front piece 24. Each lens 30 is formed of a respective rectangular array of pixels 37 constructed on sets of orthogonal electrodes, i.e., there is a set of vertical electrodes having vertical addresses for vertical columns of pixels, and another set of horizontal electrodes having horizontal addresses for horizontal rows of pixels. The refractive index of each pixel may be set by a processor 36, which in a disclosed embodiment is assumed to be mounted on one of temples 26, activating the respective pair of electrodes of the pixel. In the description herein processor 36 is assumed to comprise associated memory wherein operating instructions for lenses 30 are stored.

[0046] As long as lenses 30 are switched off, user 21 is able to see through the entire area of envelopes 22 without distortion (or possibly with a fixed refractive correction, such as a negative correction for myopia, for example).

[0047] When lenses 30 are switched on, processor 36 is configured to set the refractive index of pixels 37 so as to provide a vision correction for user 21, typically by tuning the pixels to add a predetermined positive or a negative refractive power to the lenses. (The added power is typically established by prior evaluation of the eyesight of user 21.) The active areas of electrically tunable lenses 30 may completely fill the entire area of envelopes 22, although in alternative embodiments the active areas of the electrically tunable lenses may have other shapes, less than the entire area.

[0048] In this situation, i.e., when lenses 30 are switched on to provide vision correction, the lenses may also be referred to herein as correcting lenses.

[0049] To view a nearby object, such as a screen 40 of a smartphone 44, user 21 turns on electrically tunable lenses 30 by activating processor 36. The activation may be mechanical, for example using a switch, and / or via a software application running on a mobile computing device, such as smartphone 44. Smartphone 44 comprises its own processor 48, which operates the smartphone as well as running the application. The application may communicate with processor 36 over a wireless link, such as a Bluetooth™ link and / or over a network 46, such as the Internet, with a server 50. Such communication enables processor 36 to receive and install firmware updates for spectacles 20, and the firmware may be stored in the memory associated with the processor.

[0050] When lenses 30 are turned on to act as correcting lenses, processor 36 sets the refractive index of each pixel 37 according to the predetermined power correction of the lenses. For optimal operation of lenses 30, the optic axis of each lens should coincide with the line of sight of the respective eye of user 21. Consequently, the optical center of each lens should lie on the line of sight of each eye of user 21. As is explained below, embodiments of the present invention determine, in a calibration process, the position of the optical center of each lens so that the center does lie on the user’s line of sight.

[0051] In some embodiments spectacles 20 comprise cameras 52 and 54, mounted on frame 23, that are configured to respectively image left eye 62 and right eye 64 of user 21. Use of the images formed by the cameras 52 and 54 is described further below.

[0052] It will be understood that spectacles 20, comprising frame 23, are one example of a head mounted device (HMD) for user 21 that retains electronic lenses 30. Other HMDs, such as a helmet for user 21 that is configured to retain the lenses, will be apparent those having ordinary skill in the art, and all such HMDs are assumed to be comprised within the scope of the present invention. For simplicity, the description herein is directed to an HMD comprising a spectacle frame, and may be adapted, mutatis mutandis, for other types of HMD such as a helmet.

[0053] Fig. 2 is a schematic cross-section of lenses 30, according to an embodiment of the present invention. An xyz set of Cartesian axes has been drawn for the figure where the plane of the paper is assumed to be in an xz plane, and, for simplicity, the lenses are assumed to lie in a common plane xy plane. The figure illustrates left eye 62 and right eye 64 of user 21, and the user is assumed to be looking directly ahead, towards a target 66 on screen 40. Eye 62 looks along a line of sight 70, and eye 64 looks along a line of sight 72. As stated above, for optimal operation of lenses 30 as correcting lenses, the optical centers of the lenses should lie on the lines of sight, so that an optical center 76 of lens 30A is on line of sight 72, and an optical center 78 of lens 30B is on line of sight 70.

[0054] As is described in more detail below, to identify the positions of the optical center for each lens 30, processor 36 perturbs the light transmission through different selected pixels 37 of the lenses, i.e., different spatial regions of the lenses, while receiving feedback from user 21 as to the effect of the perturbation on the visibility of target 66. The system of processor 36 perturbing the light transmission through selected pixels 37 of a lens 30, is herein termed a spatial light modulator, and spatial light modulators are described below.

[0055] As illustrated by a double headed arrow in the figure, the distance between optical centers 76 and 78 corresponds to an interpupillary distance (IPD) 80 of user 21. Thus, once processor 36 has identified the positions of both optical centers, and from a knowledge of the dimensions of front piece 24, the processor is able to calculate IPD 80.

[0056] Spatial Light Modulator

[0057] Fig. 3 is a schematic block diagram illustrating a spatial light modulator (SLM) 100, according to an embodiment of the present invention. SLM 100 comprises processor 36 and lens 30, the lens in turn comprising pixels 37 arranged in a rectangular array 38. Code for operating lens 30 as an SLM is stored in the memory associated with processor 36. In operation of SLM 100, processor 36 controls voltages applied to pixels 37 independently, thus implementing spatially varying light modulation as described below.

[0058] The figure illustrates how one lens 30 is operated as an SLM by processor 36. In the description herein, when an electronic lens is being operated as an SLM, the lens itself may be referred to as an SLM. (This is in contrast to the case when a processor is operating the electronic lens as a vision correction lens, in which case the lens is referred to as a correcting lens.) It will be understood that processor 36 may be configured to operate two or more lenses 30 as independent SLMs. The operation as independent SLMs may be implemented concurrently or sequentially.

[0059] In a disclosed embodiment processor 36 implements the light transmission perturbation by modulating the amplitude of the light transmitted through the selected pixels; alternatively or additionally the processor implements the perturbation by modulating the phase of the transmitted light.

[0060] The processor effects both types of modulation by applying appropriate voltages to pixels 37. A voltage applied to a given pixel may change the phase of the transmitted light as well as the polarization of the light.

[0061] To implement amplitude modulation a polarizing plate 104 may be attached to lens 30, so that the voltage change on a given pixel 37, which changes the polarization of the transmitted light, changes the amplitude of the light.

[0062] To implement phase modulation no polarizing plate is required, since the voltage change on a given pixels 37 changes the transmitted phase. In the calibration process described herein, to identify the position of the optical center of a given lens 30, the lens is operated as an SLM. The SLM is used to implement a spatially varying modulation profile, including at least two areas - a non-perturbed area and a perturbed area, in the lens. The perturbed area is the area where the light transmission is altered or restricted. The non-perturbed area is the area where there is no alteration or restriction on the light transmission. Each area - perturbed or nonperturbed - comprises a corresponding sub-group of pixels 37.

[0063] When the SLM is configured to modulate the amplitude of light, the nonperturbed area is configured to be transparent, i.e., to have low or even no attenuation, and the perturbed area is configured to attenuate light. When the SLM modulates the phase of light, the non-perturbed area has uniform phase modulation, while the perturbed area has a spatially varying phase modulation profile.

[0064] In an embodiment the spatially varying phase modulation is configured to be random, so that the perturbation of the light transmission causes an image formed on the retina of an eye to be blurred. In an alternative embodiment the spatially varying phase modulation is periodic, and is adjusted so that the perturbation of the light transmission causes an image formed on the retina of an eye to be different from that of correcting lens; for example, the image formed may be duplicated.

[0065] In some embodiments, during a calibration process using SLM 100, processor 36 may set pixels 37 of non-perturbed areas of lens 30 to have refractive indices according a predetermined vision correction for user 21. In other embodiments the refractive indices of pixels 37 of non-perturbed areas are not set according to the vision correction of user 21.

[0066] Referring back to Fig. 2, it will be understood that regardless of whether or not non-perturbed areas of a lens have refractive indices set according to the vision correction needed for user 21, because of the non-zero diameter of the eye’s pupil, the edge between the perturbed and non-perturbed regions is not focused on the retina of the eye, and thus is inherently blurred on the retina. The images on the retina are described in more detail below.

[0067] Fig. 4 is a two-dimensional representation of bounds of a user’s field of view when the user is looking through a lens, according to an embodiment of the present invention. The user’s field of view is a three-dimensional, generally conical, field of view having its apex at the user’s eye, but for simplicity the figure is drawn in two- dimensions. The figure shows eye 64 looking through lens 30A at target 66, and the lens is assumed to be operating as SLM 100. The bounds of the user’s field of view of the target are lines 80 and 84, and the bounds cross SLM 100, i.e., lens 30A, at points 80A and 84A.

[0068] If a perturbation is implemented in SLM 100 in the area between the points 80A and 84A, light from target 66 will pass through the perturbed area before reaching the eye, and therefore at least part of the target will not be clear to the user. If the entire area between points 80A and 84A is kept clear, i.e., is unperturbed, the target will be seen clearly.

[0069] Lens Calibration Using an SLM With 2D Perturbations

[0070] Figs. 5A and 5B illustrate examples of two-dimensional (2D) perturbed and non=perturbed regions on a spatial light modulator, and the corresponding images on the retina of a user, according to an embodiment of the present invention. In the figures, user 21 is assumed to be observing a rectangular target 120 through a given lens 30, the lens comprising pixels 37 and being operated as SLM 100. A rectangle 132 on lens 30 shows the bounds of target 120, as seen through the lens.

[0071] In the following description the perturbed regions are assumed to comprise regions having a randomly spatially varied phase modulation profile, causing significant scatter of light passing through these regions, and the non-perturbed regions are assumed to have a uniform phase modulation profile. Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, if for the perturbed regions the phase modulation is spatially periodic, and / or the amplitude of the light transmission is attenuated, and is not attenuated for non-perturbed regions.

[0072] In Fig. 5 A a circular area 124 of SLM 100 is assumed to comprise a perturbed region, while the remaining area 128 of the SLM comprises a non-perturbed region. The figure shows an image 136 of target 120 on the retina of the eye of user 21. As is illustrated in image 136, most of the image, in a region 140 corresponding to the nonperturbed region within rectangle 132, is a focused section of the image on the retina. However, a circular region 144, corresponding to perturbed region 124 is blurred, so that the corresponding part of the target is obscured. Because, as explained above, the pupil of the eye has a finite diameter, region 144 is surrounded by an at least partially blurred perimeter 148.

[0073] In Fig. 5B a circular area 154 of SLM 100 is assumed to comprise a nonperturbed region, while the remaining area 158 of the SLM comprises a perturbed region. The figure shows an image 166 of target 120 on the retina of the eye of user 21. As is illustrated in image 166, most of the image, in a region 174 corresponding to the perturbed region within rectangle 132, is a blurred section of the image on the retina, so that this section of the image is obscured. A circular region 178, corresponding to non-perturbed region 154 is not blurred, so that the corresponding part of the target is visible. Region 178 is surrounded by an at least partially blurred perimeter 182.

[0074] Areas 124 and 154 are examples of 2D contiguous regions that processor 36 may generate by addressing selected sub-groups of pixels 37 in array 38. In contrast to the one-dimensional (ID) regions described below, the 2D contiguous regions do not include all the pixels in any given vertical column, or all the pixels in any given horizontal row.

[0075] Areas 124 and 154 are circular. Those having ordinary skill in the art will be aware of non-circular 2D continuous regions, such as regular or irregular polygons, that do not include all the pixels in any given vertical column, or all the pixels in any given horizontal row, and all such regions are assumed to be within the scope of the present invention.

[0076] Fig. 6 is a flowchart 200 showing how perturbed SLMs, such as those of Figs. 5A and 5B, may be used to calibrate a given lens 30, i.e., to determine the optical center of the given lens, according to an embodiment of the present invention. For simplicity, the description of flowchart 200 is directed to finding the optical center of lens 30A (Fig. 2) in front of the right eye of user 21, using perturbations similar to those of Fig. 5A. Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, for lens 30B (in front of the left eye of the user), and / or for perturbations such as those of Fig. 5B, or for amplitude perturbations, rather than the spatially varied phase perturbations of Figs. 5A and 5B. The calibration may use smartphone 40 and may be conveniently performed under overall control of processor 48 of the smartphone, the smartphone processor communicating, as necessary with processor 36 of lens 30A and lens 30B.

[0077] As is described further below, processor 36 applies perturbations to lens 30A when it is operated as an SLM, and user 21 provides feedback to the smartphone processor 48 regarding the effect of the perturbations on the visibility of a target. When not operated as an SLM, processor 36 may set the refractive index of pixels 37 according to the vision correction required by user 21, typically, as described above, by prior evaluation of the eyesight of user 21.

[0078] In an initial step 204 user 21 puts on spectacles 20, and places a target, herein by way of example assumed to be target 120 of Fig. 5 A, at a convenient distance in front of the user. The target may be generated on the screen of smartphone 40, and the smartphone may be held at or beyond the near point of user 21, such as at a distance of 40 cm from the user. Processor 36 is configured so that both lenses 30 of the spectacles operate as SLMs, and so that the processor is in communication with smartphone processor 48.

[0079] In a blocking perturbation step 208, processor 36 applies a spatially varying phase modulation over the whole of lens 30B (in front of left eye 62). The spatially varying modulation is a perturbation that alters light transmission through lens 30B, blocking the left eye from viewing target 120.

[0080] In a calibrating step 212, processor 36 applies a spatially varied phase perturbation to a region of lens 30A, in front of the user’s right eye, similar to that illustrated in Fig. 5A.

[0081] Smartphone processor 48 records the position of the region, and user 21 provides feedback to the smartphone processor as to whether the perturbation obscures a part of target 120. The feedback may be any convenient feedback known in the art, such as tapping on a button or the screen of smartphone 40, and / or using a gesture, and / or vocalizing a response. The feedback may also indicate situations when the perturbation does not obscure the target, i.e. when the perturbation is visible but is outside the bounds of the target as viewed by the user, as well as when the perturbation partially obscures the target. As indicated by arrow 214, processor 36 and smartphone processor 48 iterate step 212 and on each iteration the smartphone processor records the feedback for a given position of the perturbed region. Typically, for each iteration the position of the perturbed region is different from previous positions.

[0082] In an analysis step 216 smartphone processor 48 uses the results from step 212 to formulate the location of a closed region on lens 30A corresponding to the field of view of target 120, as viewed by right eye 64. A cross-section of this closed region corresponds to the area between points 80A and 84A in Fig. 4. The formulation may comprise generating a perimeter of a region surrounding the positions recorded when a perturbation obscured the target, as well as not including positions where the perturbation did not obscure the target. Typically the formulation produced by smartphone processor 48 takes into account the possibility of outlier positions in the results, and removes the outliers. In addition, it will be understood that the generated perimeter of the closed region corresponds to rectangle 132, and is theoretically similar to the shape of target 120, so that processor 48 may be configured to generate the perimeter accordingly.

[0083] In a final, application, step 220, smartphone processor 48 calculates a centroid of the closed region, which corresponds to the position on the SLM through which the user’s line-of-sight passes when looking at the center of the target. The smartphone processor may provide the location of the centrode to processor 36. Processor 36 may then use the location, when operating lens 30A as a correcting lens, possibly at a time different from the time of the calibration, to set the refractive indices of pixels 37 according to the vision correction required for the right eye of user 21.

[0084] Smartphone processor 48 and processor 36 may use flowchart 200 to evaluate the locations of the optical center of lens 30B as well as the optical center of lens 30A, for user 21 gazing along a specific, predetermined, direction. In an embodiment the calibration for the two eyes is performed simultaneously, by alternately recording a calibration point for the left eye, and then for the right eye. Alternatively, the calibration for the two eyes may be performed sequentially, by calibrating the second eye after completing calibration of the first eye. Assuming the dimensional parameters of frame 23 are known, it will be understood that smartphone processor 48 can calculate the interpupillary distance (IPD) of user 21 for the predetermined gaze direction and distance, as is illustrated in Fig. 2.

[0085] The above description of flowchart 200 assumes that two-dimensional (2D) perturbations, as are exemplified by Figs. 5 A and 5B, are used to identify and delineate the field of view of user 21, and to use the field of view to demarcate the optical center of lenses 30A and 30B. The 2D perturbations and derived results are used in step 212 and subsequent steps of the flowchart.

[0086] Lens Calibration Using an SLM With ID Perturbations

[0087] In an alternative embodiment, one-dimensional (ID) perturbations and / or nonperturbations, depicted in Figs. 7A - 7D described below, may be used to identify the field of view, and the lens optical centers.

[0088] In SLM 100 pixels 37 are formed as rectangular array 38. In the ID regions referred to herein, all the pixels in one or more contiguous vertical columns, or all the pixels in one or more contiguous horizontal rows, are selected. In a disclosed embodiment the number of rows or columns in a ID region is up to 10 rows or columns, although in other embodiments there may be more than 10 rows or columns.

[0089] Figs. 7A, 7B, 7C and 7D illustrate examples of one-dimensional (ID) perturbed and non=perturbed regions on a spatial light modulator, and the corresponding images on the retina of a user, according to an embodiment of the present invention.

[0090] As for Figs 5A and 5B, in Figs. 7A - 7D user 21 is assumed to be observing rectangular target 120 (Figs. 5A, 5B) through a lens 30, the lens comprising pixels 37 and being operated as SLM 100. Rectangle 132 on lens 30 shows the bounds of target 120, as seen through the lens.

[0091] In Figs. 7A - 7D perturbed regions 250A, 250B, 250C, 250D are assumed to comprise regions having a spatially varied phase modulation profile, and ID slit-like non-perturbed regions 254A, 254B, 254C, 254D are assumed to have a uniform phase modulation profile. The corresponding images, seen through rectangle 132, on the retina of user 21 are images 258A, 258B, 258C, and 258D. The target is visible through the non perturbed regions 254A, 254B, 254C, 254D, but is not visible through the perturbed regions 250A, 250B, 250C, 250D. Thus images 258A, 258B, and 258D show respective ID sections 262A, 262B, and 262D of the target, each section being respectively bounded by an at least partially blurred region 266A, 266B, and 266D. Image 258C does not have any visible section of the target, since non-perturbed region 254C is disjoint from rectangle 132.

[0092] In Figs. 7A, 7B, 7C the non perturbed regions 254A, 254B, 254C are vertical, and, as is described below, SLMs with non-perturbed vertical regions may be used to find the vertical bounds of rectangle 132, i.e., the x-locations of the vertical sides of the rectangle. In Fig. 7D the non-perturbed region 254D is horizontal, and SLMs with nonperturbed horizontal regions may be used to find the horizontal bounds of rectangle 132, i.e., the y-locations of the horizontal sides of the rectangle.

[0093] To determine the x-locations and the y-locations of rectangle 132, for the eyes of user 21 the steps described for flowchart 200 are generally as stated above, except for the differences described below.

[0094] For the x-locations for the right eye, the processor blocks the target visibility to the left eye. Then, in calibrating step 212 the processor iteratively applies slits, having ID non-perturbed regions similar to those of Figs. 7A, 7B, 7C, to the lens, in front of the right eye, being calibrated. Each iteration changes the x-value of the slit. At each iteration the processor records the slit x-position, and also records the feedback from user 21 as to whether the target is visible. The lens for the left eye may be calibrated similarly, blocking target visibility to the right eye.

[0095] The y-locations for the left and right eye may be determined separately, generally as described above for the x-locations, using ID non-perturbed regions similar to those of Fig. 7D. Alternatively, the calibration for the y-locations can typically be done on both eyes simultaneously, since both eyes usually view through approximately the same Y coordinates in the lenses. Thus, there is no need to block the view of one of the eyes.

[0096] Typical results, after removal of outlier measurements, for the x-location and y- location calibration of lens 30A, the lens of the right eye of user 21, and of lens 30B, the lens of the left eye of the user, are shown in Figs. 8A - 8C, described below. Figs. 8 A, 8B, and 8C are schematic diagrams illustrating locations on a lens of a target being viewed by a user, according to an embodiment of the present invention. Each point on all three diagrams shows the distance of the center of a slit being formed on the lens with respect to the physical center of the lens being calibrated. As stated above, the different slit locations are displayed iteratively to the user, as the calibration is being performed.

[0097] The figures indicate, for each iteration, whether the target being viewed is visible or not for each slit displayed.

[0098] Fig. 8A, showing the x-axis calibration results for the left eye, indicates that the x-bounds of rectangle 132 are +4 mm and -3 mm with respect to the physical center of the lens, so that the center of rectangle 132 has an x-value of +0.5mm.

[0099] Fig. 8B, showing the x-axis calibration results for the right eye, indicates that the x-bounds of rectangle 132 are +1 mm and -3 mm with respect to the physical center of the lens, so that the center of rectangle 132 has an x-value of -1.

[0100] Fig. 8C shows the y-axis calibration results when the calibration is performed on both eyes simultaneously. The results indicate that the y-bounds of rectangle 132 are 0 mm and +4 mm with respect to the physical center of the lens, so that the center of rectangle 132 has a y-value of +2.

[0101] In flowchart 200, in the final application step 220, processor 36 uses the identified x-location and y-location of the centers of rectangles 132 as the optical centers of the lenses. The processor then controls operation of the electronic lenses by setting the refractive indices of pixels 37 of each of the lenses according to the vision correction for the eyes of user 21.

[0102] Lens Calibration for Multiple Lines of Sight

[0103] The description above assumes that lenses 30 are calibrated for user 21 looking in one direction. In embodiments comprising eye tracking, for example using cameras 52 and 54 (Fig. 1), the images of eyes 62 and 64 may be used as indications of the line of sight of user 21 for multiple directions. When lenses 30 are calibrated, as described below, to identify the line of sight from the camera images, lenses 30 may be set so that their optical center corresponds to the identified line of sight, and also so that the refractive indices of pixels 37 of the lenses comply with the vision correction required for the eyes of user 21.

[0104] Fig. 9 is a schematic diagram illustrating the relation between an image of the eye of user 21, and the eye’s line of sight, according to an embodiment of the present invention. An upper section 300 of the figure illustrates a similar situation to that shown in Fig. 2 for left eye 62, where the eye is looking straight ahead through lens 30B along line of sight 70. Line of sight 70 crosses lens 30B at a pixel 37A in the lens. Camera 52, having field of view bounds 52A, 52B produces an image 304, wherein a pupil 308 of an image 312 of eye 62 is centered on image 312.

[0105] A lower section 320 of Fig. 9 illustrates left eye 62 looking left along a line of sight 324. Line of sight 324 crosses lens 30B at a pixel 37B in the lens, so that pixel 37B lies on line of sight 324. For this case, camera 52 produces an image 328, wherein pupil 308 of image 312 of eye 62 is shifted to the right in image 312.

[0106] As is described below, for calibration lens 30B is operated as an SLM. While being operated as an SLM a correlation is generated between lines of sight of eye 62, as indicated by a position of the pupil in an image of the eye, and pixels of the SLM. The correlation enables the optical center of lens 30B to be set, as well as the refractive indices of the pixels of the lens, according to the line of sight of eye 62.

[0107] Fig. 10 is a flowchart 400 showing how an SLM may be used to calibrate a lens 30 for multiple lines of sight, i.e., to determine the optical center of the lens for a given line of sight, according to an embodiment of the present invention. For simplicity, the description of flowchart 400 is directed to finding the optical centers of lens 30B, in front of left eye 62 of user 21 (Figs. 2 and 9), for multiple lines of sight. Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, for lens 30A (in front of the right eye of the user).

[0108] The following description assumes, for clarity and simplicity, that images acquired by cameras 52 and 54 are used to identify the pupil position and gaze direction of eyes 62 and 64. However, those having ordinary skill in the art will be aware of other systems, such as arrays of diodes, that are also able to identify pupil position and gaze direction, and they will be able to modify the description, mutatis mutandis, to accommodate the other systems. Thus, all such systems are assumed to be included within the scope of the present invention.

[0109] As for flowchart 200, the calibration performed by flowchart 400 may use smartphone 40 and may be conveniently performed under overall control of processor 48 of the smartphone, the smartphone processor communicating, as necessary with processor 36 of lens 30A and lens 30B.

[0110] An initial step 404 is substantially similar to step 204 of flowchart 200, so that each lens 30 is operated as an SLM 100, and user 21 views target 120 through the lenses. In addition, camera 52 for left eye 62 is configured, together with smartphone processor 48 and / or processor 36, to operate as an eye tracker of the left eye, i.e., to provide the pupil location and the line of sight, also herein termed the gaze direction, of the left eye. Camera 54 may also be similarly configured to operate as an eye tracker of right eye 64. Thus, in the following description cameras 52 and 54 are also referred to as eye trackers 52 and 54.

[0111] The following steps of the flowchart are assumed to be under the overall control of smartphone processor 48.

[0112] In a perturbation step 408 a perturbation is applied to pixels 37 of the SLM 100 of the right eye, to perturb visibility through the SLM.

[0113] In a data acquisition step 412 processor 36 iteratively applies a perturbation, similar to that illustrated in Fig. 5B, to pixels 37 of the SLM 100 in front of left eye 62. As shown in Fig. 5B the perturbation leaves a small, clear, transparent region 154 in the SLM through which target 120 is visible. (The Appendix below provides more details of how the processor may implement the perturbations.) In some embodiments the clear region has a diameter of approximately 5 mm; in other embodiments the clear region has a diameter of approximately 2 mm; in yet other embodiments the clear region diameter may be larger or smaller than these values.

[0114] At each iteration, illustrated in the flowchart by the arrow 414, processor 36 shifts the location of region 154 and records the locations of the pixels of the region. At each iteration, user 21 gazes through transparent region 154 to see the visible portion of target 120. In a disclosed embodiment, once the readings of eye tracker 52 have stabilized, so providing feedback to smartphone processor 48 indicating that the user is gazing through region 154 at target 120, the smartphone processor records the eye tracker output, i.e., the values of the pupil location and the gaze direction of eye 62. It will be understood that when the eye tracker readings have stabilized, the pixels of region 154 include pixels that lie on the line of sight of user 21.

[0115] In an alternative embodiment, smartphone processor 48 may use any convenient method of feedback known in the art, indicating that the user is gazing at the visible portion, and then record the eye tracker readings.

[0116] In an analysis step 416 the smartphone processor forms a correlation between the eye tracker readings and the pixel locations of the centers of region 154.

[0117] In a disclosed embodiment the pupil locations of the eye tracker readings are used, and the correlation assumes that the centers of region 154 are linearly related to the coordinates of the pupil location of the eye according to the homography:

[0118] [Si] = [T,] ■ [Ci] (1) where [Si], l<i<n are vectors of the locations of the centers of region 154 in SLM 100, as measured in iteration i, n being the number of iterations in the process;

[0119] [Ci], l<i<n are vectors of the pupil locations as identified by the eye tracker; and

[0120] [Tj] is a transformation matrix correlating [Si] with [Ci], also herein termed a pupil correlation matrix.

[0121] [Si] and [Ci] are two-dimensional vectors that may be rewritten: where (x$ p y$ j ) and (x^ p VQ' j ) are Cartesian coordinates respectively of the

[0122] SLM transparent region and of the pupil location as indicated by the eye tracker. Using expressions (2), equation (1) may be rewritten: xs,ii rxc,i

[0123] Ys,i = [T ■ yc,i (3)

[0124] 1 1

[0125] Smartphone processor 48 uses equation (3) and the data acquired in step 412 to evaluate the elements of pupil correlation matrix [T 1 1 that best fit the n measurements acquired in step 412. In the evaluation, the processor may use any convenient method known in the art to minimize error, for example using a random sample consensus (RANSAC) method for the evaluation.

[0126] In an alternative embodiment the gaze directions of the eye tracker readings are used, and the correlation assumes that the centers of region 154 are linearly related to the gaze directions of the eye according to the homography:

[0127] [Si] = [T2] ■ [Di] (4) where [Si], l<i<n are as defined above in equation (1);

[0128] [Di], l<i<n are vectors of the eye gaze direction as identified by the eye tracker; and

[0129] [T2] is a transformation matrix, correlating [Si] with [Di], also herein termed a gaze direction correlation matrix.

[0130] Smartphone processor 48 may provide the elements of matrices [Tl] and [T2] to processor 36.

[0131] In an operational step 420, which may be performed at a time different from the time for calibration steps 408 - 416, once the elements of matrix [Tj] or matrix [T2] have been provided to processor 36, the processor may operate lens 30B as an electronic lens. During the operation, camera 52 is operated as an eye tracker of left eye 62 of user 21.

[0132] Processor 36 uses equation (3) or equation (4), and the coordinates of the pupil or the eye gaze direction, to calculate the coordinates of the pixel optical center to be applied to lens 30B. In addition, the processor controls operation of the electronic lens by setting the refractive indices of pixels 37 according to the visual correction required for the user’s left eye.

[0133] For simplicity the description above applies to the left eye of user 21; those having ordinary skill in the art will be able to adapt the description so that it applies to the right eye of the user.

[0134] Appendix

[0135] Initial position of clear area

[0136] Due to anatomical differences between users, such as different interpupillary distances, the area in the SLM located opposite the pupil is user dependent. A small clear area at a certain position in the SLM can fall within the field of view of one user, but outside of the field of view of a different user.

[0137] In a disclosed embodiment processor 36 is configured to estimate the initial position in which the clear area is to be positioned by using eye tracker measurements, derived from images from cameras 52 and 54, before starting the calibration process. The pupil coordinates are transformed to an estimated position in the SLM based on the mechanical parameters of spectacles 20.

[0138] In an alternative embodiment the processor is configured to determine where to position the clear area in the beginning of the iterative process by starting with a large clear area, and gradually reduce the size of the area. The user may be enabled to move the clear area, for example by moving a mouse or sliding a finger on smartphone screen 40, that is configured communicate with the processor.

[0139] Transition between points

[0140] Once the initial position is determined, in an embodiment processor 36 is configured to iteratively move the clear area to other positions in the SLM, while the user follows the movement and looks through the clear area. The displacement of the clear area location between consecutive iterations should be small enough for the user to find the clear area easily, but large enough to cover a large area of the SLM without resorting to many iterations. In an embodiment the displacement of the clear area between consecutive steps is no more than 10 mm and no less than 1 mm, but in other embodiments the displacement may be smaller or larger than these values.

[0141] In a disclosed embodiment, to make it easier for the user to locate a new position of the clear area, the processor is configured switch back and forward several times between the new position and the present position.

[0142] In an alternative embodiment, to make it easier for the user to locate a new position of the clear area, the processor is configured to switch between clear area locations in an orderly manner, to help the user predict the next position. Figs. 11 A and 1 IB are schematic diagrams illustrating possible orders of clear area positions for an SLM, according to an embodiment of the present invention.

[0143] Eye tracker sampling

[0144] When the clear area is moved on the SLM, it may take the user time to rotate his / her eye to the correct position, especially if the displacement of the clear area is large. Furthermore, even when the user is looking through the correct position, the eye may still move a little causing the eye tracking measurements to be noisy.

[0145] In an embodiment, to reduce the noise, the processor is configured to present a large number of clear areas, with small displacements between consecutive areas, thus creating enough redundancy in the data to reduce the noise.

[0146] In an alternative embodiment, the processor may wait after each clear area movement before collecting eye tracker data. In one embodiment the wait time after a movement is set at 500 ms, and the eye tracker is activated for 1 s, but other embodiments may have times smaller or larger than these times. Typically, the processor analyzes the eye tracker images to reduce noise, using any convenient method known in the art. In some cases, if the noise is not sufficiently reduced, the processor may repeat the eye tracker activation.

[0147] It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims

CLAIMS1. A calibration method, comprising: providing an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; while a user is looking through the electronic lens toward a target, receiving feedback from the user regarding a visibility of the target while modulating selected pixels of the array to perturb light transmission therethrough; and in response to the feedback from the user, identifying one or more pixels of the array that correspond to a line of sight of the user, thereby calibrating an optical center of the electronic lens for the user.

2. The calibration method according to claim 1, and comprising applying the calibrated optical center in controlling the electronic lens.

3. The calibration method according to claim 1, wherein modulating selected pixels comprises electrically modulating the selected pixels so as to modulate an amplitude of light transmitted through the selected pixels.

4. The calibration method according to claim 3, further comprising not electrically modulating pixels of the array other than the selected pixels so as to render the pixels of the array other than the selected pixels transparent to the light transmission.

5. The calibration method according to claim 4, wherein the feedback comprises the user indicating that the target is visible through the pixels of the array other than the selected pixels.

6. The calibration method according to claim 4, wherein the feedback comprises the user indicating that the selected pixels obscure the visibility of the target.

7. The calibration method according to claim 1, wherein modulating selected pixels comprises electrically modulating the selected pixels so as to apply a spatially varying phase to the light transmitted through the selected pixels.

8. The calibration method according to claim 7, further comprising applying a spatially uniform phase variation to the pixels of the array other than the selected pixelsso as to render the pixels of the array other than the selected pixels transparent to the light transmission.

9. The calibration method according to claim 8, wherein the feedback comprises the user indicating that the target is visible through the pixels of the array other than the selected pixels.

10. The calibration method according to claim 8, wherein the feedback comprises the user indicating that the selected pixels obscure the visibility of the target.

11. The calibration method according to claim 1, wherein the pixels of the array are formed as a rectangular array of rows and columns, and wherein the selected pixels of the array are formed as a one-dimensional group comprising all pixels in at least one row or all pixels in at least one column.

12. The calibration method according to claim 11, wherein identifying the one or more pixels of the array comprises identifying that the optical center lies on the onedimensional group.

13. The calibration method according to claim 1, wherein the pixels of the array are formed as a rectangular array of rows and columns, and wherein the selected pixels of the array are formed within a two-dimensional (2D) contiguous sub-group of the pixels, wherein the 2D sub-group does not include all the pixels in any given column, or all the pixels in any given row.

14. The calibration method according to claim 13, wherein identifying the one or more pixels of the array comprises identifying that the optical center corresponds to a center of the two-dimensional sub-group.

15. The calibration method according to claim 1, wherein the line of sight of the user comprises a single, predetermined, line of sight.

16. A calibration method, comprising: providing an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; while a user is looking through the electronic lens toward a target along multiple different lines of sight, recording respective parameters indicative of the different linesof sight and receiving feedback regarding a visibility of the target for each different line of sight while modulating selected pixels of the array to perturb light transmission therethrough; in response to the feedback, identifying respective pixels of the array that lie on the different lines of sight; and forming a correlation between the respective pixels of the array and the respective parameters.

17. The calibration method according to claim 16, wherein the identified respective pixels correspond to an optical center of the electronic lens for the user.

18. The calibration method according to claim 17, and comprising applying the optical center in controlling the electronic lens.

19. The calibration method according to claim 16, wherein the respective parameters comprise a location of a pupil of an eye of the user.

20. The calibration method according to claim 16 wherein the respective parameters comprise a gaze direction of an eye of the user.

21. The calibration method according to claim 16, wherein the feedback is provided by the user.

22. The calibration method according to claim 16, wherein the feedback comprises a given parameter indicative of the line of sight stabilizing.

23. A calibration apparatus, comprising: an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; and a processor, configured to: while a user is looking through the electronic lens toward a target, receive feedback from the user regarding a visibility of the target while modulating selected pixels of the array to perturb light transmission therethrough, and in response to the feedback from the user, identify one or more pixels of the array that correspond to a line of sight of the user, thereby calibrating an optical center of the electronic lens for the user.

24. The calibration apparatus according to claim 23, and comprising configuring the processor to apply the calibrated optical center in controlling the electronic lens.

25. The calibration apparatus according to claim 23, wherein modulating selected pixels comprises electrically modulating the selected pixels so as to modulate an amplitude of light transmitted through the selected pixels.

26. The calibration apparatus according to claim 25, further comprising configuring the processor to not electrically modulate pixels of the array other than the selected pixels so as to render the pixels of the array other than the selected pixels transparent to the light transmission.

27. The calibration apparatus according to claim 26, wherein the feedback comprises the user indicating that the target is visible through the pixels of the array other than the selected pixels.

28. The calibration apparatus according to claim 26, wherein the feedback comprises the user indicating that the selected pixels obscure the visibility of the target.

29. The calibration apparatus according to claim 23, wherein modulating selected pixels comprises electrically modulating the selected pixels so as to apply a spatially varying phase to the light transmitted through the selected pixels.

30. The calibration apparatus according to claim 29, further comprising configuring the processor to apply a spatially uniform phase variation to the pixels of the array other than the selected pixels so as to render the pixels of the array other than the selected pixels transparent to the light transmission.

31. The calibration apparatus according to claim 30, wherein the feedback comprises the user indicating that the target is visible through the pixels of the array other than the selected pixels.

32. The calibration apparatus according to claim 30, wherein the feedback comprises the user indicating that the selected pixels obscure the visibility of the target.

33. The calibration apparatus according to claim 23, wherein the pixels of the array are formed as a rectangular array of rows and columns, and wherein the selected pixelsof the array are formed as a one-dimensional group comprising all pixels in at least one row or all pixels in at least one column.

34. The calibration apparatus according to claim 33, wherein identifying the one or more pixels of the array comprises identifying that the optical center lies on the onedimensional group.

35. The calibration apparatus according to claim 23, wherein the pixels of the array are formed as a rectangular array of rows and columns, and wherein the selected pixels of the array are formed within a two-dimensional (2D) contiguous sub-group of the pixels, wherein the 2D sub-group does not include all the pixels in any given column, or all the pixels in any given row.

36. The calibration apparatus according to claim 35, wherein identifying the one or more pixels of the array comprises identifying that the optical center corresponds to a center of the two-dimensional sub-group.

37. The calibration apparatus according to claim 23, wherein the line of sight of the user comprises a single, predetermined, line of sight.

38. A calibration apparatus, comprising: an electronic lens comprising an array of transparent pixels, a refractive index of each pixel being electrically tunable; and a processor, configured to: while a user is looking through the electronic lens toward a target along multiple different lines of sight, record respective parameters indicative of the different lines of sight and receive feedback regarding a visibility of the target for each different line of sight while modulating selected pixels of the array to perturb light transmission therethrough, in response to the feedback, identify respective pixels of the array that lie on the different lines of sight, and form a correlation between the respective pixels of the array and the respective parameters.

39. The calibration apparatus according to claim 38, wherein the identified respective pixels correspond to an optical center of the electronic lens for the user.

40. The calibration apparatus according to claim 39, and comprising configuring the processor to apply the optical center in controlling the electronic lens.

41. The calibration apparatus according to claim 38, wherein the respective parameters comprise a location of a pupil of an eye of the user.

42. The calibration apparatus according to claim 38 wherein the respective parameters comprise a gaze direction of an eye of the user.

43. The calibration apparatus according to claim 38, wherein the feedback is provided by the user.

44. The calibration apparatus according to claim 38, wherein the feedback comprises a given parameter indicative of the line of sight stabilizing.

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