All-in-focus imager and associated method

A method for imaging of an object includes, for each of a plurality of surface-regions of the object, determining a corresponding image-sensor pixel group of a camera illuminated by light propagating from the surface-region via a lens of the camera. The method also includes, after the step of determining and for each surface-region: (i) changing a distance between the object and the lens such that the surface region intersects an in-focus object-plane of the camera and the lens forms an in-focus surface-region image on the corresponding image-sensor pixel group; (ii) capturing, with the corresponding image-sensor pixel group, the in-focus surface-region image of the surface-region; and (iii) combining the in-focus surface-region images, obtained by performing said capturing for each surface-region, to yield an all-in-focus image of the object.

BACKGROUND

The extent of three-dimensional information captured in a two-dimensional image is dependent on the amount of detail that can be captured laterally and in depth. Lateral information increases with higher resolution systems, where smaller features can be distinguished. This increase in resolution is achieved by using a fast optical system, which requires a low F/#. Depth information increases with larger depth of focus, where more features at different depths can all be in focus at once. This depth resolution is achieved with a slow optical system, requiring a high F/#. Therefore, having high resolution and large depth of focus traditionally becomes a trade-off, where both cannot be achieved at once.

To address the inherent limits, there have been many extended depth of focus (EDOF) systems that attempt to keep high resolution laterally while increasing the depth of focus. Such systems include plenoptic cameras, phase masking, compressed imaging, scanning as in confocal microscopy, or interferometry.

Plenoptic cameras use microlens arrays to capture many sub-images. The user can adjust focus and depth of focus after these many images are captured. Phase masks modify the clear aperture of an imaging system, which changes the shape of its point spread function in a specific, expected way. These changes provide additional scene information in the final image.

Compressed imaging requires less data than is traditionally needed to achieve an image of the same final size. Confocal microscopy is similar to traditional microscopy, but limits imaging from point to point rather than the full field of view. The microscope can focus at a specific point at a specific depth, thus imaging this point very well at the sensor. The microscope is scanned over the full field and through full depth, creating a stack of two-dimensional slices used to create a single in-focus image over the entire depth.

SUMMARY OF THE EMBODIMENTS

Existing EDOF imaging technologies systems, while attempting to circumvent the theoretical limitations, bring forth other issues, including artifacts in final images (e.g., phase masks and compressed imaging), significant post-processing (e.g., plenoptic cameras, phase masking, and compressed imaging), slow operation (e.g., scanning, confocal microscopy, and interferometry), and inability to collect true-color images (e.g., traditional interferometry). Simply, in the attempt to circumvent theoretical limitations in traditional optical imaging (i.e., tradeoff between resolution and depth of field), other issues arise such that to achieve both resolution and depth of field simultaneously has been challenging. What is needed are fast, repeatable, and cost-efficient imaging techniques that achieve high resolution over an extended depth of field. To this end, embodiments disclosed herein employ white-light interferometric imaging to capture all-in-focus images.

In a first aspect, a method for all-in-focus imaging of an object is disclosed. The method includes, for each of a plurality of surface-regions of the object, determining a corresponding image-sensor pixel group of a camera illuminated by light propagating from the surface-region of the object via a lens of the camera. The method also includes, after the step of determining and for each surface-region: (i) changing a distance between the object and the lens such that the surface region intersects an in-focus object-plane of the camera and the lens forms an in-focus surface-region image on the corresponding image-sensor pixel group; (ii) capturing, with the corresponding image-sensor pixel group, the in-focus surface-region image of the surface-region; and (iii) combining a plurality of in-focus surface-region images, obtained by performing said capturing for each of the plurality of surface-regions, to yield an all-in-focus image of the object.

In a second aspect, an all-in-focus imager includes a camera, an interferometer, a second beamsplitter, and an actuator. The camera includes an image sensor. The interferometer includes a reference sensor having a plurality of reference-sensor pixels, a reference mirror terminating a reference arm of the interferometer, and a first beamsplitter. The first beamsplitter is configured to split, at a first beam-splitting interface, an input light beam into (i) a test optical-beam propagating from the first beam-splitting interface to an object, such that the object terminates a test arm of the interferometer and reflects the test optical-beam as a reflected optical-beam, and (ii) a reference beam propagating from the first beam-splitting interface to the reference mirror and from the reference mirror to the reference sensor. The second beamsplitter is configured to direct (i) a first part of the reflected optical-beam to the reference sensor and (ii) a second part of the reflected optical-beam to the camera. The actuator is configured to change a length of the test arm by moving the object.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG.1is a schematic block diagram of an all-in-focus imager100that includes a camera150, an interferometer102, a beamsplitter117, and an actuator108. In embodiments, all-in-focus imager100includes a processing unit160. All-in-focus imager100is configured to generate an all-in-focus image of a surface174of an object170having a plurality of surface regions174(k) at different respective distance ranges from camera150. Interferometer102enables mapping each surface region174(k) to a respective group of image sensor pixels of camera150, after which each surface region174(k), one by one, may be brought into focus of camera150to have its image captured by the respective group of image sensor pixels of camera150. Since the mapping between surface regions174(k) and corresponding image sensor pixel groups is obtained prior to image capture, it is known, for each surface region174(k), which pixels of camera150provides in-focus image data. All-in-focus imager100therefore overcomes the deficiencies of prior-art systems by quickly capturing true-color and artifact-free images that have both high resolution and a long depth of field while not requiring significant post-processing or computational overhead.

The cross-sectional view ofFIG.1is parallel to a plane, hereinafter the y-z plane, formed by orthogonal axes298Y and298Z, each of which is orthogonal to an axis298Z. Herein, the x-y plane is formed by orthogonal axes298X and298Y, and planes parallel to the x-y plane are referred to as transverse planes. Also, a transverse direction refers to one or both of axes298X and298Y.

Camera150includes a lens155configured to form an image on a pixel array153A of an image sensor152. Pixel array153A includes a plurality of pixels153, each of which belongs to a respective one of a plurality of image-sensor pixel groups154. Beamsplitter117includes a beam-splitting interface119, which may be a surface of beamsplitter117, or a material interface of two surfaces of beamsplitter117when beamsplitter117is a beamsplitter cube as in the example depicted inFIG.1.FIG.1denotes a principal axis151, which corresponds to the optical path of an optical ray propagating along the optical axis of lens155A and reflecting off of beam-splitting interface119toward object170. In embodiments, pixel array153is in a plane that is parallel to the x-z plane and perpendicular to principal axis151.

Lens155(e.g., its principal plane) and a light-sensing surface of pixel array153A are separated by an image-distance158along an optical axis of lens155. Lens155has a focal length155F such that camera150forms an in-focus image of objects in an in-focus object-plane157, which is located at an in-focus object-distance d157from lens155along principal axis151. In-focus object-distance d157, image-distance158, and focal length155F may satisfy the Gaussian lens formula.

Interferometer102includes a reference sensor140, a reference mirror111, and a beamsplitter114. Reference sensor140has a pixel array143A that includes a plurality of reference-sensor pixels143, each of which belongs to a respective one of a plurality of reference-sensor pixel groups144, as determined in part by surface174. Beamsplitter114has a beam-splitting interface115. Interferometer102has a reference arm that begins at beam-splitting interface115and ends at reference mirror111. In embodiments, interferometer102includes a compensator113between beamsplitter114and reference mirror111for compensating for dispersion and optical-path-length changes imposed by beam splitter117in the test arm of interferometer102. In embodiments, pixel array143is in a plane parallel to the x-z plane.

In embodiments, all-in-focus imager100also includes at least one beam-shaping optical element, such as a lens, a tube lens for example. For example, all-in-focus imager100may include at least one of a first beam-shaping optical element between object170and beamsplitter117, and a second beam-shaping optical element between reference sensor140and beamsplitter114, and a third beam-shaping optical element between reference mirror111and beamsplitter114

In embodiments, processing unit160includes software, stored in memory163, that determines reference-sensor pixel groups144from a sensor output149generated by reference sensor140. In embodiments, processing unit160also includes software, stored in memory163, that determines image-sensor pixel groups154from reference-sensor pixel groups144.

Beamsplitter114is configured to split, at beam-splitting interface115, an input light beam121into a test optical-beam122and a reference beam132. Reference mirror111retro-reflects reference beam132back to beamsplitter114as reflected beam133, which beamsplitter114reflects as reference beam134, which is detected by reference sensor140. Test optical-beam122propagates from beam-splitting interface115to object170.

In embodiments, all-in-focus imager100includes a light source120configured to generate input light beam121. In embodiments, light source120includes a Kohler illumination source, and input light beam121is Kohler illumination that completely and uniformly illuminates surface174. In embodiments, light source120is a low-coherence source, for example light beam121may have a coherence length less than ten micrometers. Examples of light source120include a tungsten lamp, a mercury lamp, a continuous-output xenon lamp, a superluminescent diode, and any combination thereof.

FIG.1denotes a plurality of object planes177(1, 2, . . . , M), where M is a positive integer greater than one, each of which is displaced from and parallel to in-focus object-plane157. For clarity of illustration, M=5 in the illustration of object170inFIG.1. A distance between adjacent planes177may greater than or equal to a step size of actuator108in direction298Z. In embodiments, the step size of actuator108is between twenty nanometers and fifty nanometers.

In embodiments, a separation between adjacent object planes177is greater than or equal to a depth of field of camera150. This enables camera150to capture an in-focus image of each surface region174as actuator108scans object170in the z direction such that each object plane177is coplanar with in-focus object plane157at a respective time during the scan. That is, while scanning, object planes177move with object170. When the depth of field of camera150exceeds a separation between two adjacent object planes, planes177(1) and177(2) for example, capturing two respective images when planes177(1) and177(2) are coplanar with in-focus plane157is not necessary.

Object170has a front surface174, located in a field of view of camera150, that includes the plurality of surface regions174(1, 2, . . . , N), where N is a positive integer greater than one. In the example shown inFIG.1, front surface174has surface regions174(1-3). Herein, front surface174refers to the surface of object170that includes all of surface regions174(1, 2, . . . , N). In some scenarios, at least one of surface regions174(k) is discontiguous. Herein k is an integer in the range of one to N.

All locations within each surface region174are closest to the same one of object planes177. In the example ofFIG.1, each of surface regions174(1) is closest to object plane177(2), each of surface regions174(2) is closest to object plane177(4), and each of surface regions174(3) is closest to object plane177(5). Parts of a surface region174may be on opposite sides of its closest object plane177. For example,FIG.1denotes two surface regions174(1) that are on opposite sides of object plane177(2).

The coherence length of light beam121determines a depth resolution of all-in-focus imager100. If this coherence length exceeds a spacing between two adjacent object planes177, all-in-focus imager100cannot distinguish between surface regions174that are closest to the adjacent object planes177. Accordingly, in embodiments, the coherence length of light beam121is less than the separation between adjacent object planes177.

Interferometer102has a test arm that begins at beam-splitting interface115and ends at front surface174. The test arm hence has different lengths according to which surface region174it intersects.

Beamsplitter117is configured to direct part of test optical-beam122to front surface174as a test-optical beam123. Front surface174reflects test optical-beam122as a reflected test-beam124, which propagates from front surface174to a beam-splitting interface119of beamsplitter117. Beamsplitter117is configured to direct (i) a first part of reflected test-beam124to reference sensor140and (ii) a second part of reflected test-beam124to camera150.

Beamsplitter117includes four ports118(1-4). When beamsplitter117is a beamsplitter cube, each port118is a respective surface of beamsplitter117perpendicular to the y-z plane. When beamsplitter117is not a beamsplitter cube, and is a plate beamsplitter for example, ports118(1,2) correspond to two perpendicular planes on a first side of beam-splitting interface119such that the two planes and interface119form a right triangle with interface119as the hypotenuse. Similarly, ports (3,4) correspond to two perpendicular planes on a second side of beam-splitting interface119such that the two planes and interface119form a right triangle with interface119as the hypotenuse. In the example ofFIG.1, beamsplitter117transmits reflected test-beam124through port118(1) as a reflected test-beam126, part of which is transmitted by beamsplitter114as a detected test-beam127that is incident on pixel array143A of reference sensor140. Both reference beam134and detected test-beam127are incident on pixel array143A, and form a recombined beam129.

Beamsplitter117reflects reflected test-beam124through port118(4) as a beam126125, which is incident on pixel array153A of camera150. Actuator108is configured to change a length of the test arm by moving object170. In the example ofFIG.1, actuator108is configured to move object170along the z axis.

In an alternative example, the orientation of beamsplitter117is rotated by ninety degrees, as compared to the configuration shown inFIG.1, and the positions of object170and camera150are switched from their positions shown inFIG.1. In such a rotated configuration, port118(3) is between beam-splitting interface119and camera150, and port118(4) is between beam-splitting interface119and object170. In such embodiments, beam-splitting interface119reflects a first part of test-optical beam122as beam125propagating toward object170, and transmits a second part of test-optical beam122as test optical beam123, which propagates toward camera150. In such embodiments, actuator108is configured to move object170along the y axis.

A key characteristic of a beamsplitter is its split ratio, which is the ratio of reflected power R to transmitter power T. In the configuration ofFIG.1, beamsplitter117may have a splitting ratio less than one-half such that it transmits more of incident light than it reflects to ensure that the respective amplitudes of beams127and134are comparable, within a factor of two for example. Maintaining such a split ratio results in adequate fringe visibility in combined beam129. In embodiments, beamsplitter117has a split ratio R/T between 20/80 and 40/60. In the above-mentioned rotated configuration, beamsplitter117may have a split ratio between 80/20 and 60/40.

In embodiments, an optical path length116between beam-splitting interface119and beam-splitting interface115equals an optical path length156along the section of principal axis151between beam-splitting interface119and lens155. Optical path length116traverses a geometric path that is collinear with the section of principal axis151between beam-splitting interface119and surface174. When reference sensor140detects interference in recombined beam129(between detected test-beam127and reference beam134) at a reference-sensor pixel group144(k), this interference corresponds to reflected test-beam124reflected by surface-region174(k).

In embodiments, reference sensor140is an event-based vision sensor. Gallego et al. describe a key difference between event-based vision sensor and a traditional image sensor, or a camera with a traditional image sensor. Event-based vision sensors “work radically different from traditional cameras. Instead of capturing images at a fixed rate, they measure per-pixel brightness changes asynchronously. This results in a stream of events, which encode the time, location and sign of the brightness changes” (“Event-based Vision: A Survey,” arXiv:1904.08405v2). An advantage of reference sensor140being an event-based vision sensor is that such a sensor can more accurately detect interference (e.g., interference fringes) between detected test-beam127and reference beam134as actuator108scans object170along the z axis.

Herein, detection of interference between127and134refers to detection of interference-induced changes in amplitude of recombined beam129, e.g., as actuator108moves object170, resulting from interference between beams127and134. Interference includes at least one of constructive interference, destructive interference, and interference fringes corresponding to transitions between constructive and destructive interference. In embodiments, as actuator108translates object170, the magnitude of the interference fringes (peak modulation between constructive and destructive interferences) associated with a surface region174(k) increases from zero to a peak value, and back to zero, thus forming a correlogram. Detected interference may refer to a peak magnitude of the modulation (peak of the correlogram's envelope), and actuator position109(k) corresponds the position of actuator108resulting in the detection of said peak magnitude.

Processing unit160includes a processor162and a memory163communicatively coupled thereto. Processing unit160is communicatively coupled to both reference sensor140and camera150. In embodiments, processing unit160is also communicatively coupled to actuator108and configured to control actuator108to move object170to locations corresponding to a plurality of actuator positions109(1−N), stores in memory163.

In embodiments, memory163also stores the following measurement outputs indexed by 1−N corresponding to each actuator position109: reference-sensor pixel groups144(1−N), a plurality of sensor outputs149(1−N), a plurality of in-focus surface-regions images159(1−N), and an all-in-focus image199. Memory163also stores computer-readable instructions, such as an image combiner189.

Memory163may be transitory and/or non-transitory and may include one or both of volatile memory (e.g., SRAM, DRAM, computational RAM, other volatile memory, or any combination thereof) and non-volatile memory (e.g., FLASH, ROM, magnetic media, optical media, other non-volatile memory, or any combination thereof). Part or all of memory163may be integrated into processor162.

In embodiments, memory163stores non-transitory computer-readable instructions that, when executed by processor162, control processor162to control actuator108to vary the length of the test arm of interferometer102, for example moves object170along the z axis to vary the length of the test arm.

In embodiments, all-in-focus imager100includes a flash178, which may be located between beamsplitter117and object170, located between camera150and beam-splitting interface119, and/or be part of camera150. Flash178is configured to illuminate object170when camera150captures an image of a surface region174thereof. Illuminating object170with flash178at other times, when camera150is not capturing an image, can interfere with the functioning of all-in-focus imager100. For example, reference sensor140may detect illumination from flash178while also detecting interference in recombined beam129would hamper accurate determination of reference-sensor pixel groups144.

In embodiments, all-in-focus imager100includes a spatial light modulator106along principal axis151, for example, between beamsplitter117and camera150. When capturing each in-focus surface-region image159(k), processing unit160may control spatial light modulator106to transmit only parts of beam125that reach pixels153that are part of image-sensor pixel groups154(k).

FIG.2is a flowchart illustrating a method200for producing an all-in-focus image of an object. Method200includes at least one of steps210,220,230, and240. Method200may be implemented within one or more aspects of all-in-focus imager100. In embodiments, method200is implemented by processor162executing computer-readable instructions stored in memory163.

Step210includes, for each of a plurality of surface-regions of the object, determining a corresponding image-sensor pixel group of a camera illuminated by light propagating from the surface-region of the object via a lens of the camera. In embodiments, all locations within each surface region are closest to a same respective object plane of a plurality of object planes each displaced from and parallel to an in-focus object-plane of the camera. In an example of step210, all-in-focus imager100determines, for each surface region174(k) of object170, a corresponding image-sensor pixel group154(k) of camera150. Camera150is illuminated by beam125.

Steps220and230occur after step210and for each surface region of the plurality of surface regions. In the following examples, the plurality of surface regions are surface regions174.

Step220includes changing a distance between the object and the lens such that the surface region intersects the in-focus object-plane and the lens forms an in-focus surface-region image on the corresponding image-sensor pixel group. In an example of step220, actuator108changes a distance between object170and lens155by moving object170along principal axis151such that, when actuator108is at an actuator position109(k), surface region174(k) intersects in-focus object-plane157and lens155forms an in-focus surface-region image on image-sensor pixel group154(k). In embodiments, processing unit160stores actuator position109(k) in memory163.

Steps220and230are repeated for each surface region174, such that memory163stores a plurality of actuator positions109(1−N) and a corresponding plurality of in-focus surface-region images159(1−N). Each in-focus surface-region image154(k) has been captured at a respective actuator position109(k), where k is an integer in the range of 1 to N.

Step240includes combining a plurality of in-focus surface-region images, obtained by performing said capturing for each of the plurality of surface-regions, to yield an all-in-focus image of the object. In an example of step240, image combiner189combines in-focus surface-region images159to yield an all-in-focus image199.

FIG.3is a schematic block diagram of a processing unit360, which is an example of processing unit160of all-in-focus imager100. Processing unit160includes processor162and a memory363, which is an example of memory163. Like memory163, memory363stores at least one of actuator positions109, reference-sensor pixel groups144, image-sensor pixel groups154, in-focus surface-ration images159, image combiner189, and all-in-focus image199. Memory363also stores at least one of an inter-sensor pixel map388, and additional computer-readable instructions: a pixel grouper382, a pixel grouper384, and a camera controller386.

Inter-sensor pixel map388includes a location-based mapping of reference-sensor pixels143to image-sensor pixels153. In embodiments, pixel array143A has Myrows and Mxcolumns, pixel array153A has Nyrows and Nxcolumns. Each reference-sensor pixel143has a respective pixel coordinate (py, px) and a respective normalized pixel coordinate (py/My, px/Mx), and each pixel153has a respective pixel coordinate (qy, qy) and a respective normalized pixel coordinate (qy/Ny, qx/Nx). In embodiments, inter-sensor pixel map388is a look-up table that (a) maps row pyof pixel array143A to row qyof image-sensor pixel array153A and (b) maps column pxof reference-sensor pixel array143A to column qXimage-sensor pixel array153A, where qyand qxare the integers closest to respective quotients

In embodiments, step210of method200includes utilizing optical interferometry to determine the image-sensor pixel group. For example, step210may include a method400(seeFIG.4). In embodiments, method400is implemented by processor162executing computer-readable instructions stored in memory363. Method400includes steps420,422, and426. In embodiments, method400also includes at least one of steps412,414,416,418,419, and430.

Step412refers to terms introduced in step210, which include the plurality of surface-regions, the test optical beam, the reflected optical-beam, and the plurality of surface-regions. Step412includes illuminating an object with a test optical-beam. The test optical-beam propagates along a test-arm of an interferometer. The plurality of surface-regions collectively reflects the test optical-beam as the reflected optical-beam having a plurality of reflected-beam regions each corresponding to one of the plurality of surface-regions. In an example of step412, test-optical beam123illuminates object170. Surface regions174reflect test-optical beam123as reflected test-beam124.

Step414includes illuminating a reference sensor, located at an output port of the interferometer, with the reference beam propagating from a reference mirror of the interferometer. The reference sensor includes a plurality of reference-sensor pixels. In an example of step414, reference beam134illuminates reference sensor140.

Step416includes splitting the reflected optical-beam into the first part of the reflected optical-beam and a second part of the reflected optical-beam. In an example of step416, beamsplitter117splits reflected test-beam124into optical beams126and125, which are the first part and second part of the reflected optical beam, respectively.

Step418includes illuminating the reference sensor with the first part of the reflected optical-beam, in which each of the plurality of reference-sensor pixels is illuminated by a respective one of the plurality of reflected-beam regions. In an example of step418, beamsplitter114transmits optical beam126as detected test-beam127, which illuminates reference sensor140. Each pixel of the plurality of reference-sensor pixels143is illuminated by a respective one of a plurality of regions of detected test-beam127reflected by a respective one of surface regions174.

Step419includes illuminating the image sensor with the second part of the reflected optical-beam such that each of the plurality of image-sensor pixels is illuminated by a respective one of the plurality of reflected-beam regions, and is therefore mapped to the one of the plurality of reference-sensor pixels illuminated by the respective one of the plurality of reflected-beam regions. In an example of step419, beam125illuminates image sensor152. Each of image-sensor pixels153is illuminated by a respective one of the plurality of regions of beam125. Accordingly, each image-sensor pixel153illuminated by part of beam125reflected by surface region174(k) is mapped to a reference-sensor pixel illuminated by a region of detected test-beam127reflected by surface region174(k), so as to map surface region174(k) to a corresponding image-sensor pixel group154(k).

Step420includes positioning the object at a plurality of positions along an axis parallel to the test optical-beam. In an example of step420, actuator108positions object170at actuator positions109(1-N) along an axis parallel to test-optical beam123. At each of the plurality of positions, a different one of object planes177is closest to—coplanar with, for example—in-focus object plane157.

Steps422and426are executed for each of the plurality of positions of step420. Step422includes determining a group of reference-sensor pixels, of the plurality of reference-sensor pixels, that detect interference between the reference beam and the first part of the reflected optical-beam reflected by one surface-region of the plurality of surface regions. In an example of step422, k is an integer in the range of 1 to M, and pixel grouper382determines reference-sensor pixel group144(k) from sensor output149from reference sensor140when actuator108is at actuator position109(k). Pixel group144(k) includes reference-sensor pixels143that detect interference between reference beam134and part of detected test-beam127reflected by surface region174(k).

In embodiments, step422includes step424, which includes generating, with the reference sensor, a signal in response to changes in amplitude (e.g., optical power or irradiance) of a recombined beam incident on the reference sensor and composed of the reference beam and the first part of the reflected optical-beam. In an example of step424, reference sensor140is an event-based vision sensor that generates sensor output149(k) at a plurality of reference-sensor pixels143corresponding to a reference-sensor pixel group144(k) in response to changes in amplitude of recombined beam129.

Step426includes determining the image-sensor pixel group as a plurality of pixels of the image sensor illuminated by a second part of the reflected optical beam reflected by the one surface-region. In an example of step426, pixel grouper384determines image-sensor pixel group154(k) from reference-sensor pixel group144(k) and inter-sensor pixel map388.

Step430includes repositioning the object at each of the plurality of positions. In an example of step430, actuator108repositions object170at actuator of positions109(1−N) along an axis parallel to the z axis.

In embodiments, step430includes a step432. Step432includes, at each of the plurality of positions, capturing an image of the surface-region of the plurality of surface-regions with the determined image-sensor pixel group. In an example of step432, camera controller386controls camera150to capture, at each of the plurality of positions109(k) and with image-sensor pixel group154(k), k={1, 2, . . . , N}, in-focus surface-region image159(k) of surface region174(k). Step432may also include illuminating, with flash178for example, the plurality of surface-regions when capturing the image thereof.

In step432, camera150may capture an image with more than one image-sensor pixel group154. In such instances, camera150and/or processing unit160extracts in-focus surface-region image159(k) from the captured image. In embodiments, the captured image includes pixel values from all pixels153, such that processing unit160need not control camera150to capture images with a subset of pixels153determined by image-sensor pixel groups154(k).

FIG.5illustrates an example of interference fringes529of recombined beam129detected by reference-sensor pixels143of reference sensor140as a function of an optical path difference between the test arm and the reference arm of interferometer102. Interference fringes529result from interference between beams127and134. In this example, the coherence length of light beam121is approximately ten micrometers. Reference-sensor pixels143of a reference-sensor pixel group144(k) detects interference from surface-region174(k) when actuator108is at actuator position109(k). That is, the optical path difference between the test arm and reference arm of interferometer102are equal in regions of recombined beam129corresponding to regions of reference beam134originating at surface-region174(k).

FIG.6is a schematic block diagram of an all-in-focus imager600, which is an example of all-in-focus imager100,FIG.1, where a single sensor functions as both reference sensor140and image sensor152. All-in-focus imager600is a modification of all-in-focus imager100in which both beamsplitter117and camera150are removed and a reference sensor640replaces reference sensor140. All-in-focus imager600includes a light source620, which is an example of light source120. In embodiments, reference sensor640is identical to reference sensor140, and may be an event-based image sensor. All-in-focus imager600also includes a lens655, which is an example of lens155and is configured to form an image of surface regions174of object170depending on position109of actuator108. In embodiments, all-in-focus imager600includes at least one of beam-shaping optical element604and beam-shaping optical element606.

In embodiments, all-in-focus imager600includes processing unit160. Method200may be implemented within one or more aspects of all-in-focus imager600. In embodiments, method200is implemented by processor162executing computer-readable instructions stored in memory163.

Combinations of Features

Features described above, as well as those claimed below, may be combined in various ways without departing from the scope hereof. The following enumerated examples illustrate some possible, non-limiting combinations.

(A1) A method for all-in-focus imaging of an object includes, for each of a plurality of surface-regions of the object, determining a corresponding image-sensor pixel group of a camera illuminated by light propagating from the surface-region of the object via a lens of the camera. The method also includes, after the step of determining and for each surface-region: (i) changing a distance between the object and the lens such that the surface region intersects the in-focus object-plane and the lens forms an in-focus surface-region image on the corresponding image-sensor pixel group; (ii) capturing, with the corresponding image-sensor pixel group, the in-focus surface-region image of the surface-region; and (iii) combining a plurality of in-focus surface-region images, obtained by performing said capturing for each of the plurality of surface-regions, to yield an all-in-focus image of the object.

(A2) In the method (A1), at least one of the image-sensor pixel groups may be discontiguous.

(A3) In any of methods (A1) and (A2), changing the distance may include moving the object.

(A4) In any of methods (A1)-(A3), a light-sensing plane of the camera may be located at an image-distance from the lens, and in the step of capturing, a focal length of the lens, a distance between the in-focus object-plane and the lens, and the image-distance may collectively satisfy the Gaussian lens formula.

(A5) Any of methods (A1)-(A4) may utilize optical interferometry to perform the step of determining the image-sensor pixel group.

(A6) In method (A5), each pixel group may include a respective plurality of image-sensor pixels, and determining the image-sensor pixel group may include at least one of steps (A7.1), (A7.2), and (A7.3). Step (A7.1) includes positioning the object at a plurality of positions along an axis parallel to a test optical-beam propagating along a test-arm of an interferometer and illuminating the object such that the object reflects the test optical-beam as a reflected optical-beam. Step (A7.2) includes, for each of the plurality of positions, determining a group of reference-sensor pixels, of a reference sensor, located at an output port of the interferometer, that detect interference between a reference beam and a first part of the reflected optical-beam reflected by one surface-region of the plurality of surface regions. Step (A7.3) includes determining the image-sensor pixel group as a plurality of pixels of the image sensor illuminated by a second part of the reflected optical beam reflected by the one surface-region.

(A7) Method (A6) may further include at least one of steps (A7.1)-(A7.5). Step (A7.1) includes illuminating the object with the test optical-beam. The plurality of surface-regions reflect the test optical-beam as the reflected optical-beam having a plurality of reflected-beam regions each corresponding to one of the plurality of surface-regions. Step (A7.2) includes illuminating a reference sensor, located at an output port of the interferometer, with the reference beam propagating from a reference mirror of the interferometer. The reference sensor includes a plurality of reference-sensor pixels. Step (A7.3) includes splitting the reflected optical-beam into the first part of the reflected optical-beam and a second part of the reflected optical-beam. Step (A7.4) includes illuminating the reference sensor with the first part of the reflected optical-beam such that each of the plurality of reference-sensor pixels is illuminated by a respective one of the plurality of reflected-beam regions. Step (A7.5) includes illuminating the image sensor with the second part of the reflected optical-beam such that each of the plurality of image-sensor pixels is illuminated by a respective one of the plurality of reflected-beam regions, and is therefore mapped to the one of the plurality of reference-sensor pixels illuminated by the respective one of the plurality of reflected-beam regions.

(A8) Any of methods (A6) and (A7) may further include, for each of the plurality of positions: repositioning the object at each the plurality of positions and, at each of the plurality of positions, capturing an image of the surface-region of the plurality of surface-regions with the determined image-sensor pixel group.

(A9) In any of methods (A6)-(A8), the step of determining a group of reference-sensor pixels may include generating, with the reference sensor, a signal in response to a change in amplitude of a recombined beam thereon composed of the reference beam and the first part of the reflected optical-beam.

(A10) In any of methods (A1)-(A9), all locations within each surface region may be closest to a same respective object plane of a plurality of object planes each displaced from and parallel to an in-focus object-plane of the camera.

(A11) In method (A10), a separation between adjacent object planes of the plurality of object planes may be greater than or equal to a depth of field of the camera.

(A11) In any of methods (A10) and (A11), a separation between adjacent object planes of the plurality of object planes may be greater than or equal to a coherence length of the test optical-beam.

(B1) An all-in-focus imager includes a camera, an interferometer, a second beamsplitter, and an actuator. The camera includes an image sensor. The interferometer includes a reference sensor having a plurality of reference-sensor pixels, a reference mirror terminating a reference arm of the interferometer, and a first beamsplitter. The first beamsplitter is configured to split, at a first beam-splitting interface, an input light beam into (i) a test optical-beam propagating from the first beam-splitting interface to an object, such that the object terminates a test arm of the interferometer and reflects the test optical-beam as a reflected optical-beam, and (ii) a reference beam propagating from the first beam-splitting interface to the reference mirror and from the reference mirror to the reference sensor. The second beamsplitter is configured to direct (i) a first part of the reflected optical-beam to the reference sensor and (ii) a second part of the reflected optical-beam to the camera. The actuator is configured to change a length of the test arm by moving the object.

(B2) In imager (B1), an optical path length between a second beam-splitting interface of the second beamsplitter and the first beam-splitting interface may be equal to an optical path length between the second beam-splitting interface and a lens of the camera.

(B3) In either of imagers (B1) and (B2), the second beamsplitter may be between the first beamsplitter and a termination of the test arm, and be configured to transmit the first part of the reflected optical-beam and reflect the second part of the reflected optical-beam.

(B4) In either of imagers (B1) and (B2), the second beamsplitter may be between the camera and the first beamsplitter, and be configured to reflect the first part of the reflected optical-beam and transmit the second part of the reflected optical-beam.

(B5) Any of imagers (B1)-(B4) may further include a light source configured to generate the input light beam.

(B6) In any of imagers (B1)-(B5), the reference sensor may be an event-based vision sensor.

(B7) Any of imagers (B1)-(B6) may further include a processor and a memory. The processor is communicatively coupled to the camera, the reference sensor, and the actuator. The memory stores non-transitory computer-readable instructions that, when executed by the processor, control the processor to control the actuator to vary the length of the test arm.

(B8) Any of imagers (B1)-(B6) may further include a processor and a memory. The processor is communicatively coupled to the camera, the reference sensor, and the actuator. The memory stores non-transitory computer-readable instructions that, when executed by the processor, control the processor to execute any of the methods (A1)-(A11).

Changes may be made in the above methods and systems without departing from the scope of the present embodiments. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. Herein, and unless otherwise indicated the phrase “in embodiments” is equivalent to the phrase “in certain embodiments,” and does not refer to all embodiments. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.