Patent Description:
The human iris of an eye can be used as a source of biometric information. Biometric information can provide authentication or identification of an individual. Biometric information can additionally or alternatively be used to determine a gaze direction for the eye.

<CIT> discloses apparatus, systems, and methods for substantially continuous biometric identification (CBID) of an individual using eye signals in real time. The apparatus is included within a wearable computing device with identification of the device wearer based on iris recognition within one or more cameras directed at one or both eyes, and/or other physiological, anatomical and/or behavioral measures. Verification of device user identity can be used to enable or disable the display of secure information. Identity verification can also be included within information that is transmitted from the device in order to determine appropriate security measures by remote processing units. The apparatus may be incorporated within wearable computing that performs other functions including vision correction, head-mounted display, viewing the surrounding environment using scene camera(s), recording audio data via a microphone, and/or other sensing equipment.

<NPL> discloses an "Explicit Shape Regression" approach for face alignment which directly learns a vectorial regression function to infer the whole facial shape from the imate and explicitly minimize the alignment errors over the training data.

Systems and methods for robust biometric applications using a detailed eye shape model are described.

Throughout the drawings, reference numbers may be re-used to indicate correspondence between referenced elements.

Extracting biometric information from the eye generally includes a procedure for the segmentation of the iris within an eye image. Iris segmentation can involve operations including locating the iris boundaries, including finding the pupillary and limbic boundaries of the iris, localizing upper or lower eyelids if they occlude the iris, detecting and excluding occlusions of eyelashes, shadows, or reflections, and so forth. For example, the eye image can be included in an image of the face or may be an image of the periocular region. To perform iris segmentation, both the boundary of the pupil (the interior boundary of the iris) and the limbus (the exterior boundary of the iris) can be identified as separate segments of image data. In addition to this segmentation of the iris, the portion of the iris that is occluded by the eyelids (upper or lower) can be estimated. This estimation is performed because, during normal human activity, the entire iris of a person is rarely visible. In other words, the entire iris is not generally free from occlusions of the eyelids (e.g., during blinking).

Eyelids may be used by the eye to keep the eye moist, for example, by spreading tears and other secretions across the eye surface. Eyelids may also be used to protect the eye from foreign debris. As an example, the blink reflex protects the eye from acute trauma. As another example, even when the eye is actively viewing the world, the eyelids may protect the eye, for example, by moving automatically in response to changes in the pointing direction of the eye. Such movement by the eyelids can maximize protection of the eye surface while avoiding occlusion of the pupil. However, this movement presents further challenges when extracting biometric information with iris-based biometric measurements such as iris segmentation. For example, to use iris segmentation, the areas of the iris that are occluded by the eyelids may be estimated and masked from identity verification computations or images taken during eyelid blink may be discarded or given lower weight during analysis.

Extracting biometric information has presented challenges, such as estimating the portion of the iris occluded by eyelids. However, using the techniques described herein, the challenges presented in extracting biometric information can be mitigated by first estimating the eye shape. As used herein, the eye shape includes one or more of a shape (e.g., a boundary) of the pupil, iris, upper eyelid, or lower eyelid. This estimation of eye shape can be used as a starting point for iris segmentation. Once the eye shape is estimated, biometric applications may be performed more efficiently and more robustly. For instance, corneal reflections (e.g., glints) found in certain regions of the eye (e.g., the iris) may be used for gaze estimation. Glints in other regions of the eye (e.g., the sclera) are often not used in eye gaze estimation. By calculating a detailed eye shape model using the techniques described herein, glints in the desired regions (e.g., iris) can be located more quickly and efficiently by removing the need to search the entire eye (e.g., iris and sclera), thus producing a more efficient and robust gaze estimation.

To obtain biometric information, algorithms exist for tracking eye movements of a user of a computer. For example, a camera coupled to a monitor of the computer can provide images for identifying eye movements. However, the cameras used for eye tracking are some distance from the eyes of the user. For example, the camera may be placed at the top of a user's monitor coupled to the computer. As a result, the images of the eyes produced by the camera are, often, produced with poor resolution and at differing angles. Accordingly, extracting biometric information from a captured eye image may present challenges.

In the context of a wearable head mounted display (HMD), cameras may be closer to the user's eyes than a camera coupled to a user's monitor. For example, cameras may be mounted on the wearable HMD, which itself is placed on a user's head. The proximity of the eyes to such a camera can result in higher resolution eye imagery. Accordingly, it is possible for computer vision techniques to extract visual features from the user's eyes, particularly at the iris (e.g., an iris feature) or in the sclera surrounding the iris (e.g., a scleral feature). For example, when viewed by a camera near the eye, the iris of an eye will show detailed structures. Such iris features are particularly pronounced when observed under infrared (IR) illumination and can be used for biometric applications, such as gaze estimation or biometric identification. These iris features are unique from user to user and, in the manner of a fingerprint, can be used to identify the user uniquely. Eye features can include blood vessels in the sclera of the eye (outside the iris), which may also appear particularly pronounced when viewed under red or infrared light. Eye features may further include glints and the center of the pupil.

With the techniques disclosed herein, detailed eye shape estimation is used to produce a more robust method of detecting eye features used in biometric applications (e.g., gaze estimation and biometric identification). The use of gaze estimation has significant implications on the future of computer interfaces. Gaze estimation is currently employed in active interfaces (e.g., an interface that receives instructions through eye movements) and passive interfaces (e.g., a virtual reality device that modifies the display based on gaze position). Detecting eye features using conventional eye shape estimation techniques is challenging because of image noise, ambient light, and large variations in appearance when the eye is half-closed or blinking. Therefore, a method of producing a more robust algorithm for determining eye features used in biometric applications, such as gaze estimation or biometric identification, would be advantageous. The following disclosure describes such a method.

The present disclosure will describe a detailed eye shape model calculated using cascaded shape regression techniques, as well as ways that the detailed eye shape model may be used for robust biometric applications. Recently, shape regression has become the state-of-the-art approach for accurate and efficient shape alignment. It has been successfully used in face, hand and ear shape estimation. Regression techniques are advantageous because, for example, they are capable of capturing large variances in appearance; they enforce shape constraint between landmarks (e.g., iris between eyelids, pupil inside iris); and they are computationally efficient.

As used herein, video is used in its ordinary sense and includes, but is not limited to, a recording of a sequence of visual images. Each image in a video is sometimes referred to as an image frame or simply a frame. A video can include a plurality of sequential frames or non-sequential frames, either with or without an audio channel. A video can include a plurality of frames, which are ordered in time or which are not ordered in time. Accordingly, an image in a video can be referred to as an eye image frame or eye image.

<FIG> illustrates an image of an eye <NUM> with eyelids <NUM>, iris <NUM>, and pupil <NUM>. Curve 114a shows the pupillary boundary between the pupil <NUM> and the iris <NUM>, and curve 112a shows the limbic boundary between the iris <NUM> and the sclera <NUM> (the "white" of the eye). The eyelids <NUM> include an upper eyelid 110a and a lower eyelid 110b and eyelashes <NUM>. The eye <NUM> is illustrated in a natural resting pose (e.g., in which the user's face and gaze are both oriented as they would be toward a distant object directly ahead of the user). The natural resting pose of the eye <NUM> can be indicated by a natural resting direction <NUM>, which can be a direction orthogonal to the surface of the eye <NUM> when in the natural resting pose (e.g., directly out of the plane for the eye <NUM> shown in <FIG>) and in this example, centered within the pupil <NUM>.

The eye <NUM> can include eye features <NUM> in the iris or the sclera (or both) that can be used for biometric applications, such as eye tracking. <FIG> illustrates an example of eye features <NUM> including iris features 115a and a scleral feature 115b. Eye features <NUM> can be referred to as individual keypoints. Such eye features <NUM> may be unique to an individual's eye, and may be distinct for each eye of that individual. An iris feature 115a can be a point of a particular color density, as compared to the rest of the iris color, or as compared to a certain area surrounding that point. As another example, a texture (e.g., a texture that is different from texture of the iris nearby the feature) or a pattern of the iris can be identified as an iris feature 115a. As yet another example, an iris feature 115a can be a scar that differs in appearance from the iris <NUM>. Eye features <NUM> can also be associated with the blood vessels of the eye. For example, a blood vessel may exist outside of the iris <NUM> but within the sclera. Such blood vessels may be more prominently visible under red or infrared light illumination. The scleral feature 115b can be a blood vessel in the sclera of the eye. Additionally or alternatively, eye features <NUM> may comprise glints, which comprise corneal reflections of light sources (e.g., an IR light source directed toward the eye for gaze tracking or biometric identification). In some cases, the term eye feature may be used to refer to any type of identifying feature in or on the eye, whether the feature is in the iris <NUM>, the sclera <NUM>, or a feature seen through the pupil <NUM> (e.g., on the retina).

Each eye feature <NUM> can be associated with a descriptor that is a numerical representation of an area surrounding the eye feature <NUM>. A descriptor can also be referred to as an iris feature representation. As yet another example, such eye features may be derived from scale-invariant feature transforms (SIFT), speeded up robust features (SURF), features from accelerated segment test (FAST), oriented FAST and rotated BRIEF (ORB), KAZE, Accelerated KAZE (AKAZE), etc. Accordingly, eye features <NUM> may be derived from algorithms and techniques from the field of computer vision known. Such eye features <NUM> can be referred to as keypoints. In some of the example embodiments described below, the eye features will be described in terms of iris features. This is not a limitation and any type of eye feature (e.g., a scleral feature) can be used, additionally or alternatively, in other implementations.

As the eye <NUM> moves to look toward different objects, the eye gaze (sometimes also referred to herein as eye pose) will change relative to the natural resting direction <NUM>. The current eye gaze can be measured with reference the natural resting eye gaze direction <NUM>. The current gaze of the eye <NUM> may be expressed as three angular parameters indicating the current eye pose direction relative to the natural resting direction <NUM> of the eye. For purposes of illustration, and with reference to an example coordinate system shown in <FIG>, these angular parameters can be represented as α (may be referred to as yaw), β (may be referred to as pitch), and γ (may be referred to as roll). In other implementations, other techniques or angular representations for measuring eye gaze can be used, for example, any other type of Euler angle system.

An eye image can be obtained from a video using any appropriate process, for example, using a video processing algorithm that can extract an image from one or more sequential frames. The pose of the eye can be determined from the eye image using a variety of eye-tracking techniques. For example, an eye pose can be determined by considering the lensing effects of the cornea on light sources that are provided or by calculating a shape of the pupil or iris (relative to a circular shape representing a forward-looking eye).

In some embodiments, display systems can be wearable, which may advantageously provide a more immersive virtual reality (VR), augmented reality (AR), or mixed reality (MR) experience, where digitally reproduced images or portions thereof are presented to a wearer in a manner wherein they seem to be, or may be perceived as, real.

Without being limited by theory, it is believed that the human eye typically can interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited number of depth planes. For example, displays containing a stack of waveguides may be configured to be worn positioned in front of the eyes of a user, or viewer. The stack of waveguides may be utilized to provide three-dimensional perception to the eye/brain by using a plurality of waveguides to direct light from an image injection device (e.g., discrete displays or output ends of a multiplexed display which pipe image information via one or more optical fibers) to the viewer's eye at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide.

In some embodiments, two stacks of waveguides, one for each eye of a viewer, may be utilized to provide different images to each eye. As one example, an augmented reality scene may be such that a wearer of an AR technology sees a real-world park-like setting featuring people, trees, buildings in the background, and a concrete platform. In addition to these items, the wearer of the AR technology may also perceive that he "sees" a robot statue standing upon the real-world platform, and a cartoon-like avatar character flying by which seems to be a personification of a bumble bee, even though the robot statue and the bumble bee do not exist in the real world. The stack(s) of waveguides may be used to generate a light field corresponding to an input image and in some implementations, the wearable display comprises a wearable light field display. Examples of wearable display device and waveguide stacks for providing light field images are described in <CIT>.

<FIG> and <FIG> illustrate examples of a wearable display system <NUM> that can be used to present a VR, AR, or MR experience to the wearer <NUM>. The wearable display system <NUM> may be programmed to capture an image of an eye and perform eye shape estimation to provide any of the applications or embodiments described herein. The display system <NUM> includes a display <NUM> (positionable in front of the user's eye or eyes), and various mechanical and electronic modules and systems to support the functioning of that display <NUM>. The display <NUM> may be coupled to a frame <NUM>, which is wearable by a display system wearer or viewer <NUM> and which is configured to position the display <NUM> in front of the eyes of the wearer <NUM>. The display <NUM> may be a light field display, configured to display virtual images at multiple depth planes from the user. In some embodiments, a speaker <NUM> is coupled to the frame <NUM> and positioned adjacent the ear canal of the user in some embodiments, another speaker, not shown, is positioned adjacent the other ear canal of the user to provide for stereo/shapeable sound control. The display <NUM> is operatively coupled <NUM>, such as by a wired lead or wireless connectivity, to a local data processing module <NUM> which may be mounted in a variety of configurations, such as fixedly attached to the frame <NUM>, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user <NUM> (e.g., in a backpack-style configuration, in a belt-coupling style configuration).

As shown in <FIG>, the wearable display system <NUM> may further include an eye tracking camera 252a disposed within the wearable display system <NUM> and configured to capture images of an eye 100a. The display system <NUM> may further comprise a light source 248a configured to provide sufficient illumination to capture eye features <NUM> of the eye 100a with the eye tracking camera 252a. In some embodiments, the light source 248a illuminates the eye 100a using infrared light, which is not visible to the user, so that the user is not distracted by the light source. The eye tracking camera 252a and light source 248a may be separate components that are individually attached to the wearable display system <NUM>, for instance to the frame <NUM>. In other embodiments, the eye tracking camera 252a and light source 248a may be components of a single housing 244a that is attached to the frame <NUM>. In some embodiments, the wearable display system <NUM> may further comprise a second eye tracking camera 252b and a second light source 248b configured to illuminate and capture images of eye 100b. The eye tracking cameras 252a, 252b can be used to capture the eye images used in eye shape calculation, gaze determination, and biometric identification.

Referring again to <FIG>, the local processing and data module <NUM> may comprise a hardware processor, as well as non-transitory digital memory, such as non-volatile memory e.g., flash memory, both of which may be utilized to assist in the processing, caching, and storage of data. The data include data (a) captured from sensors (which may be, e.g., operatively coupled to the frame <NUM> or otherwise attached to the wearer <NUM>), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros; and/or (b) acquired and/or processed using remote processing module <NUM> and/or remote data repository <NUM>, possibly for passage to the display <NUM> after such processing or retrieval. The local processing and data module <NUM> may be operatively coupled by communication links <NUM>, <NUM>, such as via a wired or wireless communication links, to the remote processing module <NUM> and remote data repository <NUM> such that these remote modules <NUM>, <NUM> are operatively coupled to each other and available as resources to the local processing and data module <NUM>.

In some embodiments, the remote processing module <NUM> may comprise one or more processors configured to analyze and process data and/or image information such as video information captured by an image capture device. The video data may be stored locally in the local processing and data module <NUM> and/or in the remote data repository <NUM>. In some embodiments, the remote data repository <NUM> may comprise a digital data storage facility, which may be available through the internet or other networking configuration in a "cloud" resource configuration. In some embodiments, all data is stored and all computations are performed in the local processing and data module <NUM>, allowing fully autonomous use from a remote module. In some implementations, the local processing and data module <NUM> and/or the remote processing module <NUM> are programmed to perform embodiments of estimating a detailed eye shape model as described herein. For example, the local processing and data module <NUM> or the remote processing module <NUM> can be programmed to perform embodiments of routine <NUM> described with reference to <FIG> below. The local processing and data module <NUM> or the remote processing module <NUM> can be programmed to use eye shape estimation techniques disclosed herein to perform biometric applications, for example to identify or authenticate the identity of the wearer <NUM>. Additionally or alternatively, in gaze estimation or pose determination, for example to determine a direction toward which each eye is looking.

An image capture device can capture video for a particular application (e.g., video of the wearer's eye for an eye-tracking application or video of a wearer's hand or finger for a gesture identification application). The video can be analyzed using the eye shape estimation techniques by one or both of the processing modules <NUM>, <NUM>. With this analysis, processing modules <NUM>, <NUM> can perform eye shape estimation for robust biometric applications. As an example, the local processing and data module <NUM> and/or the remote processing module <NUM> can be programmed to store obtained eye images from the eye tracking cameras 252a, 252b attached to the frame <NUM>. In addition, the local processing and data module <NUM> and/or the remote processing module <NUM> can be programmed to process the eye images using the eye shape estimation techniques described herein (e.g., the routine <NUM>) to extract biometric information of the wearer <NUM> of the wearable display system <NUM>. In some cases, off-loading at least some of the biometric information to a remote processing module (e.g., in the "cloud") may improve efficiency or speed of the computations. Various parameters for eye gaze identification (e.g., weights, bias terms, random subset sampling factors, number, and size of filters (e.g., Sobel derivative operator), etc.) can be stored in data modules <NUM> or <NUM>.

The results of the video analysis (e.g., detailed eye shape model) can be used by one or both of the processing modules <NUM>, <NUM> for additional operations or processing. For example, in various applications, biometric identification, eye-tracking, recognition, or classification of objects, poses, etc. may be used by the wearable display system <NUM>. For example, video of the wearer's eye(s) can be used for eye shape estimation, which, in turn, can be used by the processing modules <NUM>, <NUM> to determine the direction of the gaze of the wearer <NUM> through the display <NUM>. The processing modules <NUM>, <NUM> of the wearable display system <NUM> can be programmed with one or more embodiments of eye shape estimation to perform any of the video or image processing applications described herein.

<FIG> is a flow diagram of an example eye shape estimation routine <NUM>. The eye shape estimation routine <NUM> can be implemented by the local processing and data module <NUM> or the remote processing module <NUM> and data repository <NUM> described with reference to <FIG>. Eye shape estimation can also be referred to as eye shape detection or detailed eye shape modelling. The routine <NUM> begins at block <NUM> when an eye image <NUM> is received. The eye image <NUM> can be received from a variety of sources including, for example, an image capture device, a head mounted display system, a server, a non-transitory computer-readable medium, or a client computing device (e.g., a smartphone). The eye image <NUM> may be received from the eye tracking camera 252a. In some implementations, the eye image <NUM> can be extracted from a video.

At block <NUM>, a detailed eye shape model 400b may be estimated from the eye image <NUM>. In some embodiments, the detailed eye shape model 400b may be estimated using cascaded shape regression as further described below. At block <NUM>, eye features <NUM> are determined based at least in part on the detailed eye shape model 400b estimated in block <NUM>. In some embodiments, eye features <NUM> (some of which are shown in image <NUM>) include pupillary or limbic boundaries, eyelid boundaries, glints, eye keypoints, or a center of the pupil <NUM>. Eye features <NUM> may further include any feature that can be used in a biometric application. The detailed eye shape model 400b estimated in block <NUM> may serve as prior knowledge to improve the robustness of the feature detection at block <NUM>. At block <NUM>, a biometric application (e.g., gaze estimation or biometric identification/authentication) is performed based at least in part on the biometric information obtained at blocks <NUM> and <NUM>. In some embodiments, at block 320a, gaze direction may be estimated based at least in part on the eye features <NUM> determined at block <NUM>. Additionally or alternatively, in some embodiments, at block 320b, biometric identification/authentication may be performed based at least in part on the eye features determined at block <NUM>. Biometric identification or authentication may comprise determining an iris code based at least in part on the eye image and the determined pupillary and limbic boundaries (e.g., the iris code based on the Daugman algorithm).

Given an input image I, with an initial eye shape S<NUM>, cascaded shape regression progressively refines a shape S by estimating a shape increment ΔS stage-by-stage. The initial shape S<NUM> may represent a best guess to the eye shape (e.g., pupillary, limbic, and eyelid boundaries) or a default shape (e.g., circular pupillary and iris boundaries centered at the center of the eye image I). In a generic form, a shape increment ΔSt at stage t is regressed as: <MAT> where ft is a regression function at stage t and Φt is a shape-indexed extraction function. Note that Φt can depend on both the input image I and shape in the previous stage St-<NUM>. The shape-indexed extraction function Φt can handle larger shape variations compared to a "non-shape-indexed" feature. A pairwise pixel comparison feature may be used, which may be invariant to global illumination changes. The regression goes to the next stage t+<NUM> by adding the shape increment ΔSt to the shape in the previous stage St-<NUM> to yield St = St-<NUM> + ΔSt.

Some examples of cascaded shape regression models that can be used to estimate an eye shape can include: Explicit Shape Regression (ESR), Cascaded Pose Regression (CPR), Ensemble of Regression Trees (ERT), Supervised Descent Method (SDM), Local Binary Features (LBF), Probabilistic Random Forests (PRF), Cascade Gaussian Process Regression Trees (cGPRT), Coarse-to-Fine Shape Searching (CFSS), Random Cascaded Regression Copse (R-CR-C), Cascaded Collaborative Regression method (CCR), Spatio-Temporal Cascade Shape Regression (STCSR), or other cascaded shape regression methods.

<FIG> schematically illustrates an example progression of a detailed eye shape model. For simplicity, <FIG> only depicts the shape of an upper and lower eyelid 110a, 110b and does not illustrate the estimated shapes of an iris <NUM> or a pupil <NUM>. However, the shapes of the iris <NUM> and the pupil <NUM> may additionally or alternatively be modeled at this stage (see, e.g., the example results in <FIG>). In some embodiments, the initial estimated eye shape <NUM> may be any eye shape that is similar to the target shape <NUM>. For example, the initial estimated eye shape can be set as a mean shape in the center of the image. <FIG> depicts the eye shape regression from the initial estimated eye shape <NUM> to the target shape <NUM> performed over eleven stages. <FIG> shows the initial (zeroth) stage S<NUM>, the first stage S<NUM>, and the tenth stage S<NUM>. For simplicity, only the intermediate eyelid shape <NUM> is depicted in <FIG>. In some embodiments, the regression model may be programmed to stop after a predetermined number of iterations (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or more). In other embodiments, the regression model may continue iterating until the shape increment ΔSt at stage t is smaller than a threshold. For example, if the relative eye shape change |ΔSt/St| is less than a threshold (e.g., <NUM>-<NUM>, <NUM>-<NUM>, or smaller), the regression model may terminate. In other embodiments, the regression model may continue iterating until the difference between the shape St at stage t and the shape at the previous stage St-<NUM> is smaller than a threshold.

In some embodiments, the detailed eye shape model 400b may comprise a plurality of boundary points <NUM> for the pupillary, limbic, or eyelid boundaries. The boundary points <NUM> may correspond to the estimated eyelid shape <NUM>, the estimated iris shape <NUM>, and the estimated pupil shape <NUM>, respectively. The number of boundary points <NUM> can be in a range of <NUM>-<NUM> or more. In some implementations, the detailed eye shape model 400b can be used to determine whether a received eye image meets certain standards, e.g., quality of the image.

<FIG> illustrates an example of a completed eye shape model using the eye shape estimation routine <NUM> described at block <NUM> of <FIG>. <FIG> illustrates the result of block <NUM> after an eye shape is modeled based on cascaded shape regression that has determined the pupillary, limbic, and eyelid boundaries. These boundaries are overlaid on an image of the periocular region of the eye to show the match between the calculated boundaries and the underlying eye image. As described above, the shape-indexed extraction function Φt can handle larger shape variations compared to a "non-shape-indexed" feature. A pairwise pixel comparison feature may be used, which may be invariant to global illumination changes. <FIG> is an image showing an example of two pairs of shape-indexed features. A local coordinate system (shown as x and y axes <NUM>) is determined by the current eye shape (e.g., the eyelid shape <NUM>). Intensity values from a pair of pixel locations 460a, 460b (the squares connected by arrowed lines; two pair 460a, 460b of such pixel locations are shown) can be compared to provide a binary feature (e.g., a Boolean value such as <NUM> or <NUM>, indicating a match or non-match). For example, a pixel located inside the pupil (e.g., the pupillary pixel in the pair 460b) may be darker in color or contrast than a pixel located outside the pupil (e.g., in the user's iris, sclera, or skin (as shown in <FIG>)). In some implementations, the pixel locations are fixed in the local coordinate system <NUM>, which varies as the eye shape <NUM> is updated during the stages of the regression. In one example system, <NUM> features are constructed from <NUM> pixel locations, all of which are learned from training data <NUM> (described below with reference to <FIG>).

In some embodiments, the regression function ft and the shape-indexed extraction function Φt may be learned from sets of annotated (e.g., labeled) training data. <FIG> illustrates an example of training data <NUM> that includes eight example eye images from different subjects with large shape and appearance variations (indexed as (a) through (h)). The labeled eye images advantageously should show a wide range of eye variations (e.g., normally opened eyes, blinking eyes, eyes pointing in a wide range of directions (up, down, left, right) relative to a natural resting direction, etc.) from a wide range of subjects (of different genders, ethnicities, etc.).

The training data <NUM> are annotated to show the features that are to be learned, which in this example include pupillary, limbic, and eyelid boundaries marked on each of the images. These labeled boundaries in each of the images in the training data <NUM> can be determined using any appropriate pupillary, limbic, or eyelid boundary technique or by hand. Various machine learning algorithms may be used to learn the regression function ft and the shape-indexed extraction function Φt from the annotated training data <NUM>. Supervised machine learning algorithms (e.g., regression-based algorithms) can be used to learn the regression function and shape-indexed extraction function from the annotated data <NUM>. Some examples of machine learning algorithms that can be used to generate such a model can include regression algorithms (such as, for example, Ordinary Least Squares Regression), instance-based algorithms (such as, for example, Learning Vector Quantization), decision tree algorithms (such as, for example, classification and regression trees), Bayesian algorithms (such as, for example, Naive Bayes), clustering algorithms (such as, for example, k-means clustering), association rule learning algorithms (such as, for example, a-priori algorithms), artificial neural network algorithms (such as, for example, Perceptron), deep learning algorithms (such as, for example, Deep Boltzmann Machine, or deep neural network), dimensionality reduction algorithms (such as, for example, Principal Component Analysis), ensemble algorithms (such as, for example, Stacked Generalization), or other machine learning algorithms.

In some embodiments, a set of training images may be stored in the remote data repository <NUM>. The remote processing module <NUM> may access the training images to learn the regression function ft and the shape-indexed extraction function Φt. The local processing and data module <NUM> may then store the regression function ft and the shape-indexed extraction function Φt on the wearable device <NUM>. This reduces the need for the local processing and data module <NUM> to perform the computationally intense process of learning the regression function ft and the shape-indexed extraction function Φt. In some embodiments, biometric information may be taken from the user <NUM> and stored on the local processing and data module <NUM>. The biometric information can then be used by the local processing and data module <NUM> (or the remote processing module <NUM>) to further train the regression function and shape-indexed extraction function based on the user's personalized eye shape and features through, for example, unsupervised learning. Such training personalizes the regression model so that it more particularly matches the features of the user's eyes and periocular region, which can improve accuracy and efficiency.

<FIG> is a flow diagram of an example eye shape training routine <NUM>, used to learn the regression function ft and the shape-indexed extraction function Φt from a set of training images (e.g., the images <NUM> shown in <FIG>). The eye shape training routine <NUM> can be implemented by the processing modules <NUM>, <NUM>, <NUM>. The routine <NUM> begins at block <NUM> when training data (e.g., the data <NUM>) comprising annotated eye images are accessed. The training eye images can be accessed from a non-transitory data store, which stores annotated eye images. The processing module can access the non-transitory data store via wired or wireless techniques. At block <NUM>, a machine learning technique (e.g., supervised learning for annotated or labeled images) is applied to learn the regression function ft and the shape-indexed extraction function Φt. A cascaded shape regression model can then be generated at block <NUM>. This regression model enables routine <NUM> to estimate the detailed eye shape model at block <NUM>. As described above, the cascaded shape regression model can be personalized to a particular user by further training the regression function and shape-indexed extraction function on eye images of the user obtained by the wearable display system <NUM> during use.

<FIG> illustrates boundary points <NUM> of a pupil that is partially occluded by the eyelids. In one embodiment for robust feature detection using a detailed eye shape model, pupil detection may be improved by removing false pupil boundary points <NUM> (shown as the arc of boundary points along the upper eyelid 110a and within the pupil boundary <NUM>). False pupil boundary points <NUM> may be created when an eyelid partially occludes the pupil as shown in <FIG> (where the upper eyelid 110a partially occludes the pupil <NUM>). The points <NUM> therefore reflect the position of the eyelid rather than the true boundary of the pupil (which is occluded by the eyelid). Rather than include the false boundary points <NUM>, which may lead to generation of an inaccurate model of the pupil, the false boundary points <NUM> may be identified and removed before a pupil boundary-finding method is performed. In some embodiments, the false pupil boundary points <NUM> may be any pupil boundary point that is located within a certain distance of the upper or lower eyelid. In some embodiments, the false pupil boundary points <NUM> may be any pupil boundary point that borders the upper or lower eyelid. In some embodiments, once the false pupil boundary points <NUM> are identified and removed, an ellipse may be fitted to the pupil using the remaining pupil boundary points. Algorithms that may be implemented for such an ellipse fitting include: integro-differential operators, least-squares method, random sample consensus (RANSAC), or an ellipse or curve fitting algorithm.

Note, while the above embodiments specifically reference false pupil boundary points, the techniques described above may also be applied to identify and remove false limbic boundary points.

In some embodiments, a detailed eye shape model may be used in conjunction with a pupil boundary finding algorithm such as, e.g., the starburst algorithm, which can be employed to detect many pupil boundary points. Using the eyelid shapes <NUM> of the detailed eye shape model, the boundary points determined using the starburst algorithm that border upper or lower eyelids 110a, 110b are removed, and the remaining boundary points are used to fit a pupil boundary <NUM>. In some embodiments, the limbic boundary points that border the sclera <NUM> may also be identified using the detailed eye shape model. Thereafter, the iris ellipse <NUM> is fit using only the limbic boundary points determined to border the sclera <NUM>. Similarly, the pupil boundary <NUM> may be fit using only the pupil boundary points determined to border the iris <NUM>. In some embodiments, the detailed eye shape model may improve the robustness of the pupil boundary-finding algorithm by providing a better initial "best guess" of the pupil center based on the detailed eye shape model.

In conventional gaze estimation, the pupil boundary (e.g., an ellipse in some techniques) and glints are detected by searching the entire eye image. Given the detailed eye shape model described herein, feature detection can be faster and more efficient by eliminating the need to search the entire eye for features. In some embodiments, by first identifying the different regions of the eye (e.g., sclera, pupil, or iris) the detailed eye shape model may allow feature detection in particular regions of the eye (e.g., selective feature detection). <FIG> illustrates an example of selective feature detection. Glints 115a, 115b may appear in the sclera <NUM>, the iris <NUM>, or the pupil <NUM>. In certain biometric applications, it may be necessary or desirable to identify glints 115a, 115b in certain regions of the eye (e.g., the iris, which represent corneal reflections) while ignoring glints 115a, 115b outside of those regions (e.g., the sclera). For instance, when determining gaze in certain techniques, scleral glints 115b, located in the sclera <NUM>, do not represent the reflection of the light source from the cornea, and their inclusion in the gaze technique leads to inaccuracies in the estimated gaze. Therefore, it may be advantageous to use a detailed eye shape model to search for and identify iris glints 115a located within the iris <NUM> or within the limbic boundary <NUM>. As illustrated in <FIG>, iris glints 115a are within the iris <NUM> and therefore may be preferred for gaze estimation. On the other hand, the scleral glints 115b appear in the sclera <NUM> and therefore may not be preferred for gaze estimation. Accordingly, embodiments of the techniques disclosed herein can be used to identify the eye regions where glints are likely to occur and eye regions outside these regions do not need to be searched, which improves the accuracy, speed, and efficiency of the technique.

In some embodiments, feature detection can be more robust and efficient by using a detailed eye shape model to determine whether a received eye image meets certain quality thresholds. For instance, the detailed eye shape model may be used to determine whether the eye is sufficiently open to estimate a reliable eye shape and to extract features and to perform a biometric application (e.g., gaze finding or biometric authentication/identification). In some embodiments, if the distance between the upper eyelid 110a and the lower eyelid 110b is less than a threshold, the eye image is considered unusable and is discarded, and accordingly no features are extracted for biometric application. In some embodiments, the eye image may be rejected if the upper eyelid 110a and the lower eyelid 110b are separated by no more than <NUM>. In another embodiment, the eye image may be rejected if greater than a certain percentage of the pupil <NUM> or iris <NUM> is occluded by one or more of the eyelids 110a, 110b (e.g., greater than <NUM>%, <NUM>%, <NUM>%, <NUM>%, or more). In another embodiment, the eye image may be rejected if a number of pupil boundary points <NUM> border the upper eyelid 110a or lower eyelid 110b. For instance, if roughly half of the pupil boundary points <NUM> border an eyelid 110a, 110b, it may be concluded that roughly half of the pupil <NUM> is occluded by the eyelid, and thus, the eye image is unsuitable for biometric applications. In other embodiments, rather than rejecting and discarding the eye image, the eye image is assigned a lower weight in a biometric application than eye images in which there is less occlusion of the eye (e.g., images where the distance between the upper eyelid 110a and the lower eyelid 110b is greater than the threshold).

Each of the processes, methods, and algorithms described herein and/or depicted in the attached figures may be embodied in, and fully or partially automated by, code modules executed by one or more physical computing systems, hardware computer processors, application-specific circuitry, and/or electronic hardware configured to execute specific and particular computer instructions. For example, computing systems can include general purpose computers (e.g., servers) programmed with specific computer instructions or special purpose computers, special purpose circuitry, and so forth. A code module may be compiled and linked into an executable program, installed in a dynamic link library, or may be written in an interpreted programming language. In some implementations, particular operations and methods may be performed by circuitry that is specific to a given function.

Further, certain implementations of the functionality of the present disclosure are sufficiently mathematically, computationally, or technically complex that application-specific hardware or one or more physical computing devices (utilizing appropriate specialized executable instructions) may be necessary to perform the functionality, for example, due to the volume or complexity of the calculations involved or to provide results substantially in real-time. For example, a video may include many frames, with each frame having millions of pixels, and specifically programmed computer hardware is necessary to process the video data to provide a desired image processing task, eye shape model, or biometric application in a commercially reasonable amount of time.

Code modules or any type of data may be stored on any type of non-transitory computer-readable medium, such as physical computer storage including hard drives, solid state memory, random access memory (RAM), read only memory (ROM), optical disc, volatile or non-volatile storage, combinations of the same and/or the like. The methods and modules (or data) may also be transmitted as generated data signals (e.g., as part of a carrier wave or other analog or digital propagated signal) on a variety of computer-readable transmission mediums, including wireless-based and wired/cable-based mediums, and may take a variety of forms (e.g., as part of a single or multiplexed analog signal, or as multiple discrete digital packets or frames). The results of the disclosed processes or process steps may be stored, persistently or otherwise, in any type of non-transitory, tangible computer storage or may be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flow diagrams described herein and/or depicted in the attached figures should be understood as potentially representing code modules, segments, or portions of code which include one or more executable instructions for implementing specific functions (e.g., logical or arithmetical) or steps in the process. The various processes, blocks, states, steps, or functionalities can be combined, rearranged, added to, deleted from, modified, or otherwise changed from the illustrative examples provided herein. In some embodiments, additional or different computing systems or code modules may perform some or all of the functionalities described herein. The methods and processes described herein are also not limited to any particular sequence, and the blocks, steps, or states relating thereto can be performed in other sequences that are appropriate, for example, in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. Moreover, the separation of various system components in the implementations described herein is for illustrative purposes and should not be understood as requiring such separation in all implementations. It should be understood that the described program components, methods, and systems can generally be integrated together in a single computer product or packaged into multiple computer products. Many implementation variations are possible.

The processes, methods, and systems may be implemented in a network (or distributed) computing environment. Network environments include enterprise-wide computer networks, intranets, local area networks (LAN), wide area networks (WAN), personal area networks (PAN), cloud computing networks, crowd-sourced computing networks, the Internet, and the World Wide Web. The network may be a wired or a wireless network or any other type of communication network.

The systems and methods of the disclosure each have several innovative aspects, no single one of which is solely responsible or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure.

Certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. No single feature or group of features is necessary or indispensable to each and every embodiment.

Conditional language used herein, such as, among others, "can," "could," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. In addition, the articles "a," "an," and "the" as used in this application and the appended claims are to be construed to mean "one or more" or "at least one" unless specified otherwise.

As an example, "at least one of: A, B, or C" is intended to cover: A, B, C, A and B, A and C, B and C, and A, B, and C. Conjunctive language such as the phrase "at least one of X, Y and Z," unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be at least one of X, Y or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require at least one of X, at least one of Y and at least one of Z to each be present.

Claim 1:
A wearable display system (<NUM>) comprising:
an infrared light source (248a, 248b) configured to illuminate an eye (100a, 100b) of a user;
an image capture device (252a, 252b) configured to capture an eye image of the eye;
non-transitory memory configured to store the eye image; and
a hardware processor in communication with the non-transitory memory, the hardware processor programmed to:
receive the eye image from the non-transitory memory; characterized in that the hardware processor is further programmed to:
estimate an eye shape from the eye image using cascaded shape regression, the eye shape comprising a pupil shape (<NUM>), an iris shape (<NUM>), or an eyelid shape (<NUM>), wherein, to estimate the eye shape from the eye image using cascaded shape regression, the hardware processor is programmed to iterate a regression function for determining a shape increment over a plurality of stages, the regression function comprising a shape-indexed extraction function, and wherein, to iterate the regression function, the hardware processor is programmed to evaluate <MAT>
for a shape increment ΔSt at stage t of the iteration, where ft is the regression function at stage t , Φt is the shape-indexed extraction function at stage t, I is the eye image, and St-<NUM> is the eye shape at stage t-<NUM> of the iteration.