Patent Publication Number: US-2022239811-A1

Title: Camera with reconfigurable lens assembly

Description:
TECHNICAL FIELD 
     This disclosure relates to cameras with a reconfigurable lens assembly. 
     BACKGROUND 
     Image capture devices, such as cameras, may capture content as images (e.g., still images or frames of video). Light may be received and focused via a lens and may be converted to an electronic image signal by an image sensor. The image signal may be processed by an image signal processor (ISP) to form an image, which may be stored and/or encoded. In some implementations, multiple images or video frames may include spatially adjacent or overlapping content. Optical properties of a lens of an image capture device may limit applications of the image capture device. Signal processing may be applied to captured images to optical distortion caused by a lens used to capture the image. 
     SUMMARY 
     Disclosed herein are implementations of cameras with a reconfigurable lens assembly. 
     In a first aspect, the subject matter described in this specification can be embodied in systems that include an image capture device including a mother lens and an image sensor configured to detect light incident through the mother lens; an accessory lens structure including an accessory lens and a retaining mechanism configured to fasten the accessory lens in a position covering the mother lens in a first arrangement and configured to disconnect the accessory lens from the image capture device in a second arrangement, wherein the accessory lens augments optical properties of a lens stack over the image sensor that includes the mother lens when the retaining mechanism is in the first arrangement; a non-volatile memory storing more than two bits of data that is integrated in the accessory lens structure; and a processing apparatus that is integrated in the image capture device and configured to: receive data that is stored in the non-volatile memory when the retaining mechanism is in the first arrangement. 
     In the first aspect, the non-volatile memory may store an identifier of the accessory lens. In the first aspect, the non-volatile memory may store calibration data of the accessory lens. In the first aspect, the non-volatile memory may store optical parameters of the accessory lens. In the first aspect, the systems may further include a communication interface that is integrated in the accessory lens structure, and the processing apparatus may be configured to receive data stored in the non-volatile memory as signals transmitted via the communications interface. In the first aspect, the communications interface may include a radio-frequency identification tag and the image capture device includes a radio-frequency identification reader configured to read signals from the radio-frequency identification tag. In the first aspect, the communications interface may include one or more electrical conductors configured to contact one or more corresponding electrical conductors on the image capture device when the retaining mechanism is in the first arrangement. In the first aspect, the processing apparatus may be configured to determine a warp mapping based on the data received from the non-volatile memory; and apply the warp mapping to an image captured using the image sensor when the retaining mechanism is in the first arrangement. In the first aspect, the processing apparatus may be configured to automatically detect when the retaining mechanism is in the first arrangement. In the first aspect, the processing apparatus may be configured to, responsive to detecting that the accessory lens structure has been mounted, prompt a user, via a user interface, to confirm a lens configuration change. In the first aspect, the processing apparatus may be configured to, responsive to detecting that the accessory lens structure has been mounted, automatically identify the accessory lens from among a set of multiple supported accessory lenses. In the first aspect, a field of view of the lens stack may be projected as a circle within a detectable area of the image sensor when the retaining mechanism is in the first arrangement, and the processing apparatus may be configured to access an image captured using the image sensor when the retaining mechanism is in the first arrangement; apply an electronic image stabilization rotation to the image to obtain a stabilized image; and crop the stabilized image to a rectangular output image from within the circle. The first aspect may include any combination of the features described in this paragraph. 
     In a second aspect, the subject matter described in this specification can be embodied in methods that include automatically detecting that an accessory lens structure has been mounted to an image capture device including a mother lens and an image sensor configured to detect light incident through the mother lens, such that an accessory lens of the accessory lens structure is positioned covering the mother lens; responsive to detecting that the accessory lens structure has been mounted, automatically identifying the accessory lens from among a set of multiple supported accessory lenses; accessing an image captured using the image sensor when the accessory lens structure is positioned covering the mother lens; determining a warp mapping based on identification of the accessory lens; applying the warp mapping to the image to obtain a warped image; and transmitting, storing, or displaying an output image based on the warped image. 
     In the second aspect, when the accessory lens structure is positioned covering the mother lens, a field of view of a lens stack including the accessory lens and the mother lens is projected as a circle within a detectable area of the image sensor, the method may include applying an electronic image stabilization rotation to the image to obtain a stabilized image; and cropping the stabilized image to a rectangular output image from within the circle. In the second aspect, the method may include, responsive to detecting that the accessory lens structure has been mounted, prompting a user, via a user interface, to confirm a lens configuration change. In the second aspect, automatically detecting that the accessory lens structure has been mounted to the image capture device may include using a proximity sensor integrated in the image capture device. In the second aspect, automatically detecting that the accessory lens structure has been mounted to the image capture device may include detecting a change in image sensor coverage of the image sensor. In the second aspect, automatically identifying the accessory lens may include receiving data from a non-volatile memory integrated in the accessory lens structure. In the second aspect, automatically identifying the accessory lens may include comparing image sensor coverage of the image sensor to an image sensor coverage profile associated with the accessory lens. The second aspect may include any combination of the features described in this paragraph. 
     In a third aspect, the subject matter described in this specification can be embodied in systems that include an image capture device including a mother lens and an image sensor configured to detect light incident through the mother lens; an accessory lens structure including an accessory lens and a retaining mechanism configured to fasten the accessory lens in a position covering the mother lens in a first arrangement and configured to disconnect the accessory lens from the image capture device in a second arrangement, wherein the accessory lens augments optical properties of a lens stack over the image sensor that includes the mother lens, such that a field of view of the lens stack is projected as a circle within a detectable area of the image sensor, when the retaining mechanism is in the first arrangement; and a processing apparatus that is integrated in the image capture device and configured to: access an image captured using the image sensor when the retaining mechanism is in the first arrangement; apply an electronic image stabilization rotation to the image to obtain a stabilized image; and crop the stabilized image to a rectangular output image from within the circle. 
     In the third aspect, the processing apparatus may be configured to automatically detect when the retaining mechanism is in the first arrangement. In the third aspect, the processing apparatus may be configured to, responsive to detecting that the accessory lens structure has been mounted, prompt a user, via a user interface, to confirm a lens configuration change. In the third aspect, the processing apparatus may be configured to, responsive to detecting that the accessory lens structure has been mounted, automatically identify the accessory lens from among a set of multiple supported accessory lenses. The third aspect may include any combination of the features described in this paragraph. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
         FIGS. 1A-D  are isometric views of an example of an image capture device. 
         FIGS. 2A-B  are isometric views of another example of an image capture device. 
         FIG. 2C  is a cross-sectional view of the image capture device of  FIGS. 2A-B . 
         FIGS. 3A-B  are block diagrams of examples of image capture systems. 
         FIG. 4A  illustrates a cross-sectional side view of an example of lens assembly including a mother lens and an image sensor. 
         FIG. 4B  illustrates a cross-sectional side view of an example of a system including an accessory lens structure mounted over a lens assembly including a mother lens and an image sensor. 
         FIG. 5A  illustrates an example of an accessory lens structure including a bayonet mechanism. 
         FIG. 5B  illustrates an example of an accessory lens structure including a threaded mechanism. 
         FIG. 5C  illustrates an example of an accessory lens structure including a snap-ring mechanism. 
         FIG. 5D  illustrates an example of an accessory lens structure including screw holes. 
         FIG. 6  is a flowchart of an example of a process for using an accessory lens structure with an image capture device. 
         FIG. 7  is a flowchart of an example of a process for improving electronic image stabilization using an accessory lens structure with an image capture device. 
     
    
    
     DETAILED DESCRIPTION 
     Systems and methods for cameras with a reconfigurable lens are described below. As built, a single imaging head camera&#39;s functionality is limited by its sensor resolution and lens field of view. While many uses can be derived from such a singular configuration, a lot of other use cases are out of bounds. This in effect limits the usability of such a camera. 
     Reconfigurable lens cameras are described herein, in which, by adding an accessory lens in front of the main outer lens, or mother lens, optical parameters of a lens stack including the mother lens are significantly altered. For example, the resulting reconfigured lens may have a significantly different field of view and/or distortion than those of the mother lens. For example, the mother lens can work without an accessory lens to offer a specific set of modes and use cases, but also in combination with an accessory lens, to offer a different set of modes supporting different use cases. 
     When the mother lens is reconfigured with the accessory lens, the image capture device (e.g., a main camera including the mother lens) identifies the reconfigured lens using one or more of a variety of available sensing modalities. For example, proximity sensing (e.g., using a magnetically actuated switch) may be used to detect the presence of an accessory lens. For example, changes in imaging sensor coverage caused by the addition of the accessory lens may be detected to detect the presence of an accessory lens. The image capture device may then reconfigure an internal image processing pipeline to work with the new reconfigured lens to offer the user access to a new sets of modes. For example, these new modes may include new image processing configurations and tuning. 
     In addition to detection of the accessory lens as present covering the mother lens, the image capture device may also identify which accessory lens is mounted over the mother lens (e.g., where multiple accessory lenses are built to work with the mother lens and provide for additional use cases). In some implementations, it can be useful that specific accessory lens information is loaded in non-volatile storage present with the accessory lens as part of an accessory lens structure used to mount the accessory lens over the mother lens. Such information may include, for example, an accessory lens identifier, identification of a mother lens the accessory lens is designed to work with, accessory lens characteristics (e.g., optical parameters) and/or accessory lens calibration data. This information stored in the non-volatile memory may be read (e.g., using a communication interface built into the accessory lens structure) by the image capture device (e.g., a camera) and aid in the image capture device reconfiguring itself to work with the reconfigured lens. 
       FIGS. 1A-D  are isometric views of an example of an image capture device  100 . The image capture device  100  may include a body  102  having a lens  104  structured on a front surface of the body  102 , various indicators on the front of the surface of the body  102  (such as LEDs, displays, and the like), various input mechanisms (such as buttons, switches, and touch-screen mechanisms), and electronics (e.g., imaging electronics, power electronics, etc.) internal to the body  102  for capturing images via the lens  104  and/or performing other functions. The image capture device  100  may be configured to capture images and video and to store captured images and video for subsequent display or playback. 
     The image capture device  100  may include various indicators, including LED lights  106  and LCD display  108 . The image capture device  100  may also include buttons  110  configured to allow a user of the image capture device  100  to interact with the image capture device  100 , to turn the image capture device  100  on, to operate latches or hinges associated with doors of the image capture device  100 , and/or to otherwise configure the operating mode of the image capture device  100 . The image capture device  100  may also include a microphone  112  configured to receive and record audio signals in conjunction with recording video. 
     The image capture device  100  may include an I/O interface  114  (e.g., hidden as indicated using dotted lines). As best shown in  FIG. 1B , the I/O interface  114  can be covered and sealed by a removable door  115  of the image capture device  100 . The removable door  115  can be secured, for example, using a latch mechanism  115   a  (e.g., hidden as indicated using dotted lines) that is opened by engaging the associated button  110  as shown. 
     The removable door  115  can also be secured to the image capture device  100  using a hinge mechanism  115   b , allowing the removable door  115  to pivot between an open position allowing access to the I/O interface  114  and a closed position blocking access to the I/O interface  114 . The removable door  115  can also have a removed position (not shown) where the entire removable door  115  is separated from the image capture device  100 , that is, where both the latch mechanism  115   a  and the hinge mechanism  115   b  allow the removable door  115  to be removed from the image capture device  100 . 
     The image capture device  100  may also include another microphone  116  integrated into the body  102  or housing. The front surface of the image capture device  100  may include two drainage ports as part of a drainage channel  118 . The image capture device  100  may include an interactive display  120  that allows for interaction with the image capture device  100  while simultaneously displaying information on a surface of the image capture device  100 . As illustrated, the image capture device  100  may include the lens  104  that is configured to receive light incident upon the lens  104  and to direct received light onto an image sensor internal to the lens  104 . 
     The image capture device  100  of  FIGS. 1A-D  includes an exterior that encompasses and protects internal electronics. In the present example, the exterior includes six surfaces (i.e. a front face, a left face, a right face, a back face, a top face, and a bottom face) that form a rectangular cuboid. Furthermore, both the front and rear surfaces of the image capture device  100  are rectangular. In other embodiments, the exterior may have a different shape. The image capture device  100  may be made of a rigid material such as plastic, aluminum, steel, or fiberglass. The image capture device  100  may include features other than those described here. For example, the image capture device  100  may include additional buttons or different interface features, such as interchangeable lenses, cold shoes and hot shoes that can add functional features to the image capture device  100 , etc. 
     The image capture device  100  may include various types of image sensors, such as a charge-coupled device (CCD) sensors, active pixel sensors (APS), complementary metal-oxide-semiconductor (CMOS) sensors, N-type metal-oxide-semiconductor (NMOS) sensors, and/or any other image sensor or combination of image sensors. 
     Although not illustrated, in various embodiments, the image capture device  100  may include other additional electrical components (e.g., an image processor, camera SoC (system-on-chip), etc.), which may be included on one or more circuit boards within the body  102  of the image capture device  100 . 
     The image capture device  100  may interface with or communicate with an external device, such as an external user interface device, via a wired or wireless computing communication link (e.g., the I/O interface  114 ). The user interface device may, for example, be the personal computing device  360  described below with respect to  FIG. 3B . Any number of computing communication links may be used. The computing communication link may be a direct computing communication link or an indirect computing communication link, such as a link including another device or a network, such as the internet, may be used. 
     In some implementations, the computing communication link may be a Wi-Fi link, an infrared link, a Bluetooth (BT) link, a cellular link, a ZigBee link, a near field communications (NFC) link, such as an ISO/IEC 20643 protocol link, an Advanced Network Technology interoperability (ANT+) link, and/or any other wireless communications link or combination of links. 
     In some implementations, the computing communication link may be an HDMI link, a USB link, a digital video interface link, a display port interface link, such as a Video Electronics Standards Association (VESA) digital display interface link, an Ethernet link, a Thunderbolt link, and/or other wired computing communication link. 
     The image capture device  100  may transmit images, such as panoramic images, or portions thereof, to the user interface device (not shown) via the computing communication link, and the user interface device may store, process, display, or a combination thereof the panoramic images. 
     The user interface device may be a computing device, such as a smartphone, a tablet computer, a phablet, a smart watch, a portable computer, and/or another device or combination of devices configured to receive user input, communicate information with the image capture device  100  via the computing communication link, or receive user input and communicate information with the image capture device  100  via the computing communication link. 
     The user interface device may display, or otherwise present, content, such as images or video, acquired by the image capture device  100 . For example, a display of the user interface device may be a viewport into the three-dimensional space represented by the panoramic images or video captured or created by the image capture device  100 . 
     The user interface device may communicate information, such as metadata, to the image capture device  100 . For example, the user interface device may send orientation information of the user interface device with respect to a defined coordinate system to the image capture device  100 , such that the image capture device  100  may determine an orientation of the user interface device relative to the image capture device  100 . 
     Based on the determined orientation, the image capture device  100  may identify a portion of the panoramic images or video captured by the image capture device  100  for the image capture device  100  to send to the user interface device for presentation as the viewport. In some implementations, based on the determined orientation, the image capture device  100  may determine the location of the user interface device and/or the dimensions for viewing of a portion of the panoramic images or video. 
     The user interface device may implement or execute one or more applications to manage or control the image capture device  100 . For example, the user interface device may include an application for controlling camera configuration, video acquisition, video display, or any other configurable or controllable aspect of the image capture device  100 . 
     The user interface device, such as via an application, may generate and share, such as via a cloud-based or social media service, one or more images, or short video clips, such as in response to user input. In some implementations, the user interface device, such as via an application, may remotely control the image capture device  100  such as in response to user input. 
     The user interface device, such as via an application, may display unprocessed or minimally processed images or video captured by the image capture device  100  contemporaneously with capturing the images or video by the image capture device  100 , such as for shot framing, which may be referred to herein as a live preview, and which may be performed in response to user input. In some implementations, the user interface device, such as via an application, may mark one or more key moments contemporaneously with capturing the images or video by the image capture device  100 , such as with a tag, such as in response to user input. 
     The user interface device, such as via an application, may display, or otherwise present, marks or tags associated with images or video, such as in response to user input. For example, marks may be presented in a camera roll application for location review and/or playback of video highlights. 
     The user interface device, such as via an application, may wirelessly control camera software, hardware, or both. For example, the user interface device may include a web-based graphical interface accessible by a user for selecting a live or previously recorded video stream from the image capture device  100  for display on the user interface device. 
     The user interface device may receive information indicating a user setting, such as an image resolution setting (e.g., 3840 pixels by 2160 pixels), a frame rate setting (e.g., 60 frames per second (fps)), a location setting, and/or a context setting, which may indicate an activity, such as mountain biking, in response to user input, and may communicate the settings, or related information, to the image capture device  100 . 
       FIGS. 2A-B  illustrate another example of an image capture device  200 . The image capture device  200  includes a body  202  and two camera lenses  204 ,  206  disposed on opposing surfaces of the body  202 , for example, in a back-to-back or Janus configuration. 
     The image capture device may include electronics (e.g., imaging electronics, power electronics, etc.) internal to the body  202  for capturing images via the lenses  204 ,  206  and/or performing other functions. The image capture device may include various indicators such as an LED light  212  and an LCD display  214 . 
     The image capture device  200  may include various input mechanisms such as buttons, switches, and touchscreen mechanisms. For example, the image capture device  200  may include buttons  216  configured to allow a user of the image capture device  200  to interact with the image capture device  200 , to turn the image capture device  200  on, and to otherwise configure the operating mode of the image capture device  200 . In an implementation, the image capture device  200  includes a shutter button and a mode button. It should be appreciated, however, that, in alternate embodiments, the image capture device  200  may include additional buttons to support and/or control additional functionality. 
     The image capture device  200  may also include one or more microphones  218  configured to receive and record audio signals (e.g., voice or other audio commands) in conjunction with recording video. 
     The image capture device  200  may include an I/O interface  220  and an interactive display  222  that allows for interaction with the image capture device  200  while simultaneously displaying information on a surface of the image capture device  200 . 
     The image capture device  200  may be made of a rigid material such as plastic, aluminum, steel, or fiberglass. In some embodiments, the image capture device  200  described herein includes features other than those described. For example, instead of the I/O interface  220  and the interactive display  222 , the image capture device  200  may include additional interfaces or different interface features. For example, the image capture device  200  may include additional buttons or different interface features, such as interchangeable lenses, cold shoes and hot shoes that can add functional features to the image capture device  200 , etc. 
       FIG. 2C  is a cross-sectional view of the image capture device  200  of  FIGS. 2A-B . The image capture device  200  is configured to capture spherical images, and accordingly, includes a first image capture device  224  and a second image capture device  226 . The first image capture device  224  defines a first field-of-view  228  as shown in  FIG. 2C  and includes the lens  204  that receives and directs light onto a first image sensor  230 . 
     Similarly, the second image capture device  226  defines a second field-of-view  232  as shown in  FIG. 2C  and includes the lens  206  that receives and directs light onto a second image sensor  234 . To facilitate the capture of spherical images, the image capture devices  224 ,  226  (and related components) may be arranged in a back-to-back (Janus) configuration such that the lenses  204 ,  206  face in generally opposite directions. 
     The fields-of-view  228 ,  232  of the lenses  204 ,  206  are shown above and below boundaries  236 ,  238 , respectively. Behind the first lens  204 , the first image sensor  230  may capture a first hyper-hemispherical image plane from light entering the first lens  204 , and behind the second lens  206 , the second image sensor  234  may capture a second hyper-hemispherical image plane from light entering the second lens  206 . 
     One or more areas, such as blind spots  240 ,  242  may be outside of the fields-of-view  228 ,  232  of the lenses  204 ,  206  so as to define a “dead zone.” In the dead zone, light may be obscured from the lenses  204 ,  206  and the corresponding image sensors  230 ,  234 , and content in the blind spots  240 ,  242  may be omitted from capture. In some implementations, the image capture devices  224 ,  226  may be configured to minimize the blind spots  240 ,  242 . 
     The fields-of-view  228 ,  232  may overlap. Stitch points  244 ,  246 , proximal to the image capture device  200 , at which the fields-of-view  228 ,  232  overlap may be referred to herein as overlap points or stitch points. Content captured by the respective lenses  204 ,  206 , distal to the stitch points  244 ,  246 , may overlap. 
     Images contemporaneously captured by the respective image sensors  230 ,  234  may be combined to form a combined image. Combining the respective images may include correlating the overlapping regions captured by the respective image sensors  230 ,  234 , aligning the captured fields-of-view  228 ,  232 , and stitching the images together to form a cohesive combined image. 
     A slight change in the alignment, such as position and/or tilt, of the lenses  204 ,  206 , the image sensors  230 ,  234 , or both, may change the relative positions of their respective fields-of-view  228 ,  232  and the locations of the stitch points  244 ,  246 . A change in alignment may affect the size of the blind spots  240 ,  242 , which may include changing the size of the blind spots  240 ,  242  unequally. 
     Incomplete or inaccurate information indicating the alignment of the image capture devices  224 ,  226 , such as the locations of the stitch points  244 ,  246 , may decrease the accuracy, efficiency, or both of generating a combined image. In some implementations, the image capture device  200  may maintain information indicating the location and orientation of the lenses  204 ,  206  and the image sensors  230 ,  234  such that the fields-of-view  228 ,  232 , stitch points  244 ,  246 , or both may be accurately determined, which may improve the accuracy, efficiency, or both of generating a combined image. 
     The lenses  204 ,  206  may be laterally offset from each other, may be off-center from a central axis of the image capture device  200 , or may be laterally offset and off-center from the central axis. As compared to image capture devices with back-to-back lenses, such as lenses aligned along the same axis, image capture devices including laterally offset lenses may include substantially reduced thickness relative to the lengths of the lens barrels securing the lenses. For example, the overall thickness of the image capture device  200  may be close to the length of a single lens barrel as opposed to twice the length of a single lens barrel as in a back-to-back configuration. Reducing the lateral distance between the lenses  204 ,  206  may improve the overlap in the fields-of-view  228 ,  232 . 
     Images or frames captured by the image capture devices  224 ,  226  may be combined, merged, or stitched together to produce a combined image, such as a spherical or panoramic image, which may be an equirectangular planar image. In some implementations, generating a combined image may include three-dimensional, or spatiotemporal, noise reduction (3DNR). In some implementations, pixels along the stitch boundary may be matched accurately to minimize boundary discontinuities. 
       FIGS. 3A-B  are block diagrams of examples of image capture systems. 
     Referring first to  FIG. 3A , an image capture system  300  is shown. The image capture system  300  includes an image capture device  310  (e.g., a camera or a drone), which may, for example, be the image capture device  200  shown in  FIGS. 2A-C . 
     The image capture device  310  includes a processing apparatus  312  that is configured to receive a first image from a first image sensor  314  and receive a second image from a second image sensor  316 . The image capture device  310  includes a communications interface  318  for transferring images to other devices. The image capture device  310  includes a user interface  320  to allow a user to control image capture functions and/or view images. The image capture device  310  includes a battery  322  for powering the image capture device  310 . The components of the image capture device  310  may communicate with each other via the bus  324 . 
     The processing apparatus  312  may be configured to perform image signal processing (e.g., filtering, tone mapping, stitching, and/or encoding) to generate output images based on image data from the image sensors  314  and  316 . The processing apparatus  312  may include one or more processors having single or multiple processing cores. The processing apparatus  312  may include memory, such as a random-access memory device (RAM), flash memory, or another suitable type of storage device such as a non-transitory computer-readable memory. The memory of the processing apparatus  312  may include executable instructions and data that can be accessed by one or more processors of the processing apparatus  312 . 
     For example, the processing apparatus  312  may include one or more dynamic random access memory (DRAM) modules, such as double data rate synchronous dynamic random-access memory (DDR SDRAM). In some implementations, the processing apparatus  312  may include a digital signal processor (DSP). In some implementations, the processing apparatus  312  may include an application specific integrated circuit (ASIC). For example, the processing apparatus  312  may include a custom image signal processor. 
     The first image sensor  314  and the second image sensor  316  may be configured to detect light of a certain spectrum (e.g., the visible spectrum or the infrared spectrum) and convey information constituting an image as electrical signals (e.g., analog or digital signals). For example, the image sensors  314  and  316  may include CCDs or active pixel sensors in a CMOS. The image sensors  314  and  316  may detect light incident through a respective lens (e.g., a fisheye lens). In some implementations, the image sensors  314  and  316  include digital-to-analog converters. In some implementations, the image sensors  314  and  316  are held in a fixed orientation with respective fields of view that overlap. 
     The communications interface  318  may enable communications with a personal computing device (e.g., a smartphone, a tablet, a laptop computer, or a desktop computer). For example, the communications interface  318  may be used to receive commands controlling image capture and processing in the image capture device  310 . For example, the communications interface  318  may be used to transfer image data to a personal computing device. For example, the communications interface  318  may include a wired interface, such as a high-definition multimedia interface (HDMI), a universal serial bus (USB) interface, or a FireWire interface. For example, the communications interface  318  may include a wireless interface, such as a Bluetooth interface, a ZigBee interface, and/or a Wi-Fi interface. 
     The user interface  320  may include an LCD display for presenting images and/or messages to a user. For example, the user interface  320  may include a button or switch enabling a person to manually turn the image capture device  310  on and off. For example, the user interface  320  may include a shutter button for snapping pictures. 
     The battery  322  may power the image capture device  310  and/or its peripherals. For example, the battery  322  may be charged wirelessly or through a micro-USB interface. 
     The image capture system  300  may implement some or all of the techniques described in this disclosure, such as the process  600  described in  FIG. 6  and/or the process  700  described in  FIG. 7 . 
     Referring to  FIG. 3B , another image capture system  330  is shown. The image capture system  330  includes an image capture device  340  and a personal computing device  360  that communicate via a communications link  350 . The image capture device  340  may, for example, be the image capture device  100  shown in  FIGS. 1A-D . The personal computing device  360  may, for example, be the user interface device described with respect to  FIGS. 1A-D . 
     The image capture device  340  includes an image sensor  342  that is configured to capture images. The image capture device  340  includes a communications interface  344  configured to transfer images via the communication link  350  to the personal computing device  360 . 
     The personal computing device  360  includes a processing apparatus  362  that is configured to receive, using a communications interface  366 , images from the image sensor  342 . The processing apparatus  362  may be configured to perform image signal processing (e.g., filtering, tone mapping, stitching, and/or encoding) to generate output images based on image data from the image sensor  342 . 
     The image sensor  342  is configured to detect light of a certain spectrum (e.g., the visible spectrum or the infrared spectrum) and convey information constituting an image as electrical signals (e.g., analog or digital signals). For example, the image sensor  342  may include CCDs or active pixel sensors in a CMOS. The image sensor  342  may detect light incident through a respective lens (e.g., a fisheye lens). In some implementations, the image sensor  342  includes digital-to-analog converters. Image signals from the image sensor  342  may be passed to other components of the image capture device  340  via a bus  346 . 
     The communications link  350  may be a wired communications link or a wireless communications link. The communications interface  344  and the communications interface  366  may enable communications over the communications link  350 . For example, the communications interface  344  and the communications interface  366  may include an HDMI port or other interface, a USB port or other interface, a FireWire interface, a Bluetooth interface, a ZigBee interface, and/or a Wi-Fi interface. For example, the communications interface  344  and the communications interface  366  may be used to transfer image data from the image capture device  340  to the personal computing device  360  for image signal processing (e.g., filtering, tone mapping, stitching, and/or encoding) to generate output images based on image data from the image sensor  342 . 
     The processing apparatus  362  may include one or more processors having single or multiple processing cores. The processing apparatus  362  may include memory, such as RAM, flash memory, or another suitable type of storage device such as a non-transitory computer-readable memory. The memory of the processing apparatus  362  may include executable instructions and data that can be accessed by one or more processors of the processing apparatus  362 . For example, the processing apparatus  362  may include one or more DRAM modules, such as DDR SDRAM. 
     In some implementations, the processing apparatus  362  may include a DSP. In some implementations, the processing apparatus  362  may include an integrated circuit, for example, an ASIC. For example, the processing apparatus  362  may include a custom image signal processor. The processing apparatus  362  may exchange data (e.g., image data) with other components of the personal computing device  360  via a bus  368 . 
     The personal computing device  360  may include a user interface  364 . For example, the user interface  364  may include a touchscreen display for presenting images and/or messages to a user and receiving commands from a user. For example, the user interface  364  may include a button or switch enabling a person to manually turn the personal computing device  360  on and off. In some implementations, commands (e.g., start recording video, stop recording video, or capture photo) received via the user interface  364  may be passed on to the image capture device  340  via the communications link  350 . 
     The image capture device  340  and/or the personal computing device  360  may be used to implement some or all of the techniques described in this disclosure, such as the process  600  of  FIG. 6  and/or the process  700  described in  FIG. 7 . 
       FIGS. 4A and 4B  illustrate an example of a lens assembly  400  with ( 4 B) and without ( 4 A) an optional accessory lens  470  attached to alter the optical properties of the lens assembly  400 . 
       FIG. 4A  illustrates a cross-sectional side view of an example of a lens assembly  400  including a mother lens  420  and an image sensor  430 . The lens assembly  400  includes a lens barrel  410  including multiple inner lenses  411 ,  412 ,  413 , and  414 ; a mother lens  420 ; and an image sensor  430 . For example, the lens assembly  400  may be implemented as part of an image capture device, such as the image capture device  100  of  FIGS. 1A-1D , the image capture device  200  of  FIGS. 2A-2B , the image capture device  310  of  FIG. 3A , or the image capture device  340  of  FIG. 3B . 
     The lens assembly  400  includes a lens barrel  410  in a body of an image capture device. The lens barrel  410  may be an integrated part of a body of an image capture device. The lens barrel  410  includes multiple inner lenses  411 ,  412 ,  413 , and  414 . In some implementations, at least one of the multiple inner lenses  411 ,  412 ,  413 , and  414  is curved. In the depicted example, the lens barrel  410  includes a curved inner lens  412 . The curved inner lens  412  may refract light propagating through the lens barrel  410  to focus the light for capture by the image sensor  430 . The lens barrel  410  includes a second curved inner lens  414 . For example, the inner lenses  411 ,  412 ,  413 , and  414  may be attached (e.g., using glue and/or ledges and flanges (not shown)) to inner walls of the lens barrel  410 . The inner lenses  411 ,  412 ,  413 , and  414  may be oriented to direct light from a first end of the lens barrel  410 , roughly parallel to an optical axis  416  of the lens barrel  410  to a second end of the lens barrel  410 , where the light may be detected by the image sensor  430  to capture an image. 
     The lens assembly  400  includes a mother lens  420  positioned at an opposite end of the lens barrel from the image sensor  430 . The mother lens  420  is an outer (L1) lens of the lens assembly  400 . The lens assembly  400  may be used to capture images with the mother lens  420  exposed as the outer lens. The lens assembly  400 , with the mother lens  420  as the outer lens, has optical parameters (e.g., a field of view and a distortion profile) that can be used to support a first set of image capture modes. An image capture device that includes the lens assembly  400  may include a processing apparatus (e.g., the processing apparatus  312 ) that is configured to perform signal processing on images captured using the lens assembly  400  including applying a warp based on optical parameters of the lens assembly  400 . For example, the lens assembly  400 , with the mother lens  420  as the outer lens, may have a narrow field of view or a wide field of view, and it may have one of many possible distortion profiles (e.g., rectilinear, fisheye, or anamorphic). 
     The lens assembly  400  includes an image sensor  430  mounted within a body of an image capture device at a second end of the lens barrel  410 . The image sensor  430  may be configured to capture images based on light incident on the image sensor through the mother lens  420  and the inner lenses  411 ,  412 ,  413 , and  414 . The image sensor  430  may be configured to detect light of a certain spectrum (e.g., the visible spectrum or the infrared spectrum) and convey information constituting an image as electrical signals (e.g., analog or digital signals). For example, the image sensor  430  may include charge-coupled devices (CCDs) or active pixel sensors in complementary metal-oxide-semiconductor (CMOS). In some implementations, the image sensor  430  includes a digital-to-analog converter. For example, the image sensor  430  may be configured to capture image data using a plurality of selectable exposure times. 
       FIG. 4B  illustrates a cross-sectional side view of an example of a system  450  including an accessory lens structure  470  mounted over the lens assembly  400  including the mother lens  420  and the image sensor  430 . For example, the lens assembly  400  may be implemented as part of an image capture device, such as the image capture device  100  of  FIGS. 1A-1D , the image capture device  200  of  FIGS. 2A-2B , the image capture device  310  of  FIG. 3A , or the image capture device  340  of  FIG. 3B . The accessory lens structure  470  includes an accessory lens  472  and a retaining mechanism  480  configured to fasten the accessory lens  472  in a position covering the mother lens  420  in a first arrangement and configured to disconnect the accessory lens  472  from the image capture device in a second arrangement. The accessory lens structure  470  includes an interface ring  474  attached to a base of the accessory lens  472  and configured to support the accessory lens  472  in position over the mother lens  420  at the end of the lens barrel  410  when the retaining mechanism  480  is in the first arrangement. The system  450  includes an O-ring  482  for waterproofing. The system  450  includes a non-volatile memory  490  storing more than two bits of data that is integrated in the accessory lens structure  470 ; and a communication interface  492  integrated in the accessory lens structure  470 . For example, the non-volatile memory  490  may store data that identifies the accessory lens  472 , which can be read, via the communications interface  492 , by a processing apparatus of the image capture device and used to configure an image processing pipeline of the image capture device to process images captured using the accessory lens  472 . For example, system  450  may implement some or all of the techniques described in this disclosure, such as the process  600  described in  FIG. 6  and/or the process  700  described in  FIG. 7 . 
     The accessory lens structure  470  includes an accessory lens  472  and a retaining mechanism  480  configured to fasten the accessory lens  472  in a position covering the mother lens  420  in a first arrangement and configured to disconnect the accessory lens  472  from the image capture device in a second arrangement. The accessory lens  472  augments optical properties of a lens stack over the image sensor that includes the mother lens  420  when the retaining mechanism is in the first arrangement. For example, the accessory lens  472  may be used to provide a different field of view (e.g., fisheye, narrow, portrait, macro, or telephoto) for the image capture device than the field of view with the mother lens  420  serving as the outer lens. For example, the accessory lens  472  may be used to provide a different optical distortion (e.g., rectilinear, fisheye, or anamorphic) for the image capture device than the optical distortion with the mother lens  420  serving as the outer lens. For example, the accessory lens  472  may augment the optical properties of the lens stack including the mother lens  420  in such a way as to facilitate robust image stabilization processing. For example, when the retaining mechanism  480  is in the first arrangement, a field of view of the lens stack may be projected as a circle within a detectable area of the image sensor  430 . In some implementations, the processing apparatus is configured to: access an image captured using the image sensor  430  when the retaining mechanism  480  is in the first arrangement; apply an electronic image stabilization rotation to the image to obtain a stabilized image; and crop the stabilized image to a rectangular output image from within the circle. 
     The retaining mechanism  480  may include a fastening mechanism configured to facilitate transition between the first arrangement and the second arrangement by removably fastening the retaining mechanism  480  to the lens barrel  410  or another nearby portion of the body of the image capture device. In the example depicted in  FIG. 4B , a threaded mechanism is employed to fasten the retaining mechanism  480  to the lens barrel  410  and fasten the accessory lens  472  in a position covering a first end of the lens barrel  410 . In some implementations (not shown in  FIG. 4B ), a retaining mechanism  480  may employ other fastening mechanisms to secure a retaining ring to a body of an image capture device. For example, a retaining mechanism may include a bayonet mechanism (e.g., such as the bayonet mechanism described in relation to  FIG. 5A ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining mechanism may include a threaded mechanism (e.g., such as the threaded mechanism described in relation to  FIG. 5B ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining mechanism may include a snap-ring mechanism (e.g., such as the snap-ring mechanism described in relation to  FIG. 5C ) configured to facilitate transition between the first arrangement and the second arrangement. For example, a retaining mechanism may include screw holes that enable screws to fasten the retaining ring to the body in the first arrangement (e.g., as described in relation to  FIG. 5D ). 
     In some implementations, the retaining mechanism  480  is glued to the accessory lens  472 . In some implementations, the accessory lens  472  is secured in the retaining mechanism  480  as a captured mount, such that the accessory lens  472  may be rotated within the retaining mechanism  480 . For example, the accessory lens  472  and the retaining mechanism  480  may be interlocked (e.g., using a flange and slot interface around a circumference of the accessory lens  472 ) and travel together but the accessory lens  472  may still be loose enough to turn inside the retaining mechanism  480  independently. In some implementations, the accessory lens  472  is firmly held in a fixed orientation in the first arrangement by a friction lock formed by pressing the retaining mechanism  480  against the accessory lens  472  in its position covering the first end of the lens barrel  410 . 
     The system  450  includes an O-ring  482  for waterproofing that is positioned radially around the accessory lens  472 . The O-ring may be composed of a rubbery material. For example, the O-ring  482  may be positioned to be compressed between the retaining mechanism  480 , the accessory lens  472  and the body (e.g., the lens barrel  410 ) of the image capture device to form a waterproofing seal. In some implementations, the O-ring  482  may be glued to the retaining mechanism  480  and/or to the accessory lens  472 . 
     Although not shown in  FIG. 4B , the system  450  includes a processing apparatus (e.g., the processing apparatus  312 ), integrated in the image capture device that includes the lens assembly  400 . The processing apparatus is configured to: receive data that is stored in the non-volatile memory  490  when the retaining mechanism is in the first arrangement. For example, the non-volatile memory  490  may store an identifier of the accessory lens  472 . For example, the non-volatile memory  490  may store calibration data of the accessory lens  472 . For example, the non-volatile memory  490  may store optical parameters of the accessory lens  472 . For example, the non-volatile memory  490  may include a read only memory (ROM). For example, the non-volatile memory  490  may include a flash drive. 
     In some implementations, the processing apparatus is configured to automatically detect when the retaining mechanism  480  is in the first arrangement. For example, sensing modalities, such as proximity sensing (e.g., using a capacitive coupling, using electrical contacts between the accessory lens structure  470  and the lens assembly  400 , and/or using a magnetically actuated switch in the image capture device and a magnet in the accessory lens structure  470 ) and/or detecting changes in image sensor coverage caused by the accessory lens  472 , may be used automatically detect when the retaining mechanism  480  is in the first arrangement. In some implementations, the processing apparatus is configured to: determine a warp mapping based on the data received from the non-volatile memory  490 ; and apply the warp mapping to an image captured using the image sensor  430  when the retaining mechanism  480  is in the first arrangement. In some implementations, the processing apparatus is configured to, responsive to detecting that the accessory lens  472  has been mounted, prompt a user, via a user interface (e.g., the user interface  320 ), to confirm a lens configuration change. For example, a confirmation prompt may be presented in the interactive display  120 . In some implementations, the processing apparatus is configured to, responsive to detecting that the accessory lens  472  has been mounted, automatically identify the accessory lens  472  from among a set of multiple supported accessory lenses. For example, the accessory lens  472  may be identified based on data (e.g., a lens identifier) stored in the non-volatile memory  490  that is received by the processing apparatus. 
     The accessory lens structure  470  includes a communication interface  492  integrated in the accessory lens structure  470 . The communication interface  492  may be used to transfer data from the non-volatile memory  490  to the processing apparatus (e.g., the processing apparatus  312 ). For example, the processing apparatus may be configured to receive data stored in the non-volatile memory  490  as signals transmitted via the communications interface  492 . In some implementations, the communications interface  492  includes a radio-frequency identification tag and the image capture device includes a radio-frequency identification reader configured to read signals from the radio-frequency identification tag. In some implementations, the communications interface  492  includes one or more electrical conductors configured to contact one or more corresponding electrical conductors on the image capture device when the retaining mechanism  480  is in the first arrangement. In some implementations, the communications interface  492  includes a capacitive coupling. In some implementations, the communications interface  492  includes an optical coupling. 
     In some implementations (not shown in  FIGS. 4A-4B ), the mother lens  420  is also removeably attached to the lens barrel  410 . For example, this structure may allow the mother lens  420  to be replaced in the event that the mother lens  420  is scratched. For example, the mother lens  420  may be fastened at the end of the lens barrel using a fastening mechanism (e.g., a bayonet mechanism, a threaded mechanism, a snap-ring mechanism, or screws), and the accessory lens structure  470  may be fastened over the mother lens  420  using a fastening mechanism to attached the accessory lens structure  470  to the fastening mechanism of the mother lens  420  or another part of the body of the image capture device. In some implementations (not shown in  FIGS. 4A-4B ), the accessory lens structure  470  includes multiple lens elements stacked over the mother lens  420  when the retaining mechanism  480  is in the first arrangement. 
       FIG. 5A  illustrates an example of an accessory lens structure  500  including a bayonet mechanism. The accessory lens structure  500  includes a lens barrel  510  (e.g., similar to the lens barrel  410  of  FIG. 4B ), which may include a mother lens and one or more inner lenses that may be curved. The lens barrel  510  is part of a body of an image capture device that includes a male bayonet ring  512 , which may be attached to or otherwise integrated with the lens barrel  510  or another portion of the body. The accessory lens structure  500  includes a retaining ring  514  that includes a female bayonet ring. For example, the retaining ring  514  may be pushed onto the male bayonet ring of the body in an unlocked position and turned to a locked position to fasten the retaining ring  514  to the body and fasten an accessory lens  516  (e.g., the accessory lens  472 ) in a position covering a first end of the lens barrel  510 . The accessory lens structure  500  includes an O-ring  518  that may be positioned radially around the accessory lens  516  and compressed between the retaining ring  514  and the accessory lens  516  and/or the body to waterproof the accessory lens structure  500 . The accessory lens structure  500  may offer advantages over alternative lens assemblies, such as robust reusability over many cycles of removing and replacing an accessory lens, over-center locking, an enhanced user experience (e.g., easy to remove/replace), and the retaining ring  514  maybe made sturdy by making the retaining ring  514  out of a strong metal. A drawback may be a relatively large outer diameter of the retaining ring  514 . 
       FIG. 5B  illustrates an example of an accessory lens structure  520  including a threaded mechanism. The accessory lens structure  520  includes a lens barrel  530  (e.g., similar to the lens barrel  410  of  FIG. 4B ), which may include a mother lens and one or more inner lenses that may be curved. The lens barrel  530  is part of a body of an image capture device that includes a male threaded interface  534 , which may be attached to or otherwise integrated with the lens barrel  530  or another portion of the body. The accessory lens structure  520  includes a retaining ring  532  that includes a female threaded interface. For example, the retaining ring  532  may be twisted onto the male threaded interface  534  of the body to fasten the retaining ring  532  to the body and fasten an accessory lens  536  (e.g., the accessory lens  472 ) in a position covering a first end of the lens barrel  530 . The accessory lens structure  520  includes an O-ring  538  that may be positioned inside (e.g., vertically under) the accessory lens  536  and compressed between the accessory lens  536  and the body (e.g., the lens barrel  530 ) to waterproof the accessory lens structure  520 . The accessory lens structure  520  may offer advantages over alternative lens assemblies, such as a low profile. A drawback may be a risk of cross threading or stripping. 
       FIG. 5C  illustrates an example of an accessory lens structure  540  including a snap-ring mechanism. The accessory lens structure  540  includes a lens barrel  550  (e.g., similar to the lens barrel  410  of  FIG. 4B ), which may include a mother lens and one or more inner lenses that may be curved. The lens barrel  550  is part of a body of an image capture device that includes a male snap-ring interface  554 , which may be attached to or otherwise integrated with the lens barrel  550  or another portion of the body. The accessory lens structure  540  includes a retaining ring  552  that includes a female snap-ring interface. For example, the retaining ring  552  may be pushed onto the male snap-ring interface  554  of the body to fasten the retaining ring  552  to the body and fasten an accessory lens  516  (e.g., the accessory lens  472 ) in a position covering a first end of the lens barrel  550 . The accessory lens structure  540  includes an O-ring  558  that may be positioned radially around the accessory lens  556  and compressed between the retaining ring  552  and the accessory lens  556  and/or the body to waterproof the accessory lens structure  540 . The accessory lens structure  540  may offer advantages over alternative lens assemblies, such as ease of installation. A drawback may be greater difficulty in removing the retaining ring  552 . 
       FIG. 5D  illustrates an example of an accessory lens structure  560  including screw holes. The accessory lens structure  560  includes a lens barrel  570  (e.g., similar to the lens barrel  410  of  FIG. 4B ), which may include a mother lens and one or more inner lenses that may be curved. The lens barrel  570  is part of a body of an image capture device that includes screw holes  574 , which may be attached to or otherwise integrated with the lens barrel  570  or another portion of the body. The accessory lens structure  560  includes a retaining ring  572  that includes screw holes. For example, the retaining ring  572  may be fastened to body by driving screws  580  and  582  through the screw holes of the retaining ring  572 , into the screw holes  574  of the body to fasten an accessory lens  516  (e.g., the accessory lens  472 ) in a position covering a first end of the lens barrel  570 . The accessory lens structure  560  includes an O-ring  578  that may be positioned radially around the accessory lens  576  and compressed between the retaining ring  572  and the accessory lens  576  and/or the body to waterproof the accessory lens structure  560 . The accessory lens structure  560  may offer advantages over alternative lens assemblies, such as robust fastening of the retaining ring  572  and the accessory lens  576  into position. A drawback may be a large size and poor aesthetics of the retaining ring  572 . 
       FIG. 6  is a flowchart of an example of a process  600  for using an accessory lens structure (e.g., the accessory lens structure  470 ) with an image capture device. The process  600  includes automatically detecting that an accessory lens structure has been mounted to an image capture device including a mother lens and an image sensor configured to detect light incident through the mother lens, such that an accessory lens of the accessory lens structure is positioned covering the mother lens; responsive to detecting that the accessory lens structure has been mounted, automatically identifying the accessory lens from among a set of multiple supported accessory lenses; accessing an image captured using the image sensor when the accessory lens structure is positioned covering the mother lens; determining a warp mapping based on identification of the accessory lens; applying the warp mapping to the image to obtain a warped image; and transmitting, storing, or displaying an output image based on the warped image. For example, the process  600  may be implemented by an image capture device, such as the image capture device  100  of  FIGS. 1A-1D , the image capture device  200  of  FIGS. 2A-2B , the image capture device  310  of  FIG. 3A , or the image capture device  340  of  FIG. 3B . 
     The process  600  includes automatically detecting  610  that an accessory lens structure (e.g., the accessory lens structure  470 ) has been mounted to an image capture device including a mother lens (e.g., the mother lens  420 ) and an image sensor (e.g., the image sensor  430 ) configured to detect light incident through the mother lens, such that an accessory lens (e.g., the accessory lens  472 ) of the accessory lens structure is positioned covering the mother lens. Mounting of the accessory lens structure may be detected  610  using a variety of sensing modalities. In some implementations, automatically detecting  610  that the accessory lens structure has been mounted to the image capture device includes using a proximity sensor integrated in the image capture device. For example, a magnetically actuated switch may be integrated in the image capture device near the lens assembly including the mother lens, and the magnetically actuated switch may be used to detect  610  the presence of a magnet that is integrated in the accessory lens structure (e.g., in a plastic interface ring attached to a base of the accessory lens). For example, a capacitive coupling between a device integrated in the accessory lens structure and a device integrated in the image capture device may be used to detect  610  when the accessory lens structure has been mounted. For example, the accessory lens structure and a portion of the body of the image capture device (e.g., a lens barrel) may include respective electrical contacts that come into contact with each other when the accessory lens structure is mounted. In some implementations, automatically detecting  610  that the accessory lens structure has been mounted to the image capture device includes detecting a change in image sensor coverage of the image sensor. For example, the image sensor coverage may be monitored and when a change in the coverage corresponding to the mounting of the accessory lens structure may be detected  610  when the accessory lens structure is mounted. In some implementations, the process  600  includes, responsive to detecting  610  that the accessory lens has been mounted, prompting a user, via a user interface (e.g., the user interface  320 ), to confirm a lens configuration change. Prompting a user to confirm the mounting may prevent false detections in some circumstances. 
     The process  600  includes, responsive to detecting that the accessory lens structure has been mounted, automatically identifying  620  the accessory lens from among a set of multiple supported accessory lenses. In some implementations, automatically identifying  620  the accessory lens includes receiving data from a non-volatile memory (e.g., the non-volatile memory  490 ) integrated in the accessory lens structure. For example, the data from the non-volatile memory may include an identifier for the accessory lens or other identifying information, such as optical parameters or configuration parameters for an image signal processor. Data from the non-volatile memory may be received via communications interface integrated in the accessory lens structure with the non-volatile memory. For example, the accessory lens structure may include a radio frequency identification (RFID) tag, and the image capture device may include an RFID reader configured to read data from the non-volatile memory of the RFID tag. Other types of communication interfaces may be used to receive data from the non-volatile memory, such as a capacitive coupling, an optical coupling, one or more electrical conductors that meet at one or more electrical contacts between the accessory lens structure and the image capture device when the accessory lens structure is mounted. In some implementations, a bar code on the accessory lens structure is read by an optical bar code reader integrated in the image capture device when the accessory lens structure is mounted. In some implementations, automatically identifying  620  the accessory lens includes comparing image sensor coverage of the image sensor to an image sensor coverage profile associated with the accessory lens. 
     The process  600  includes accessing  630  an image (e.g., a still image or a frame of video) captured using the image sensor when the accessory lens structure is positioned covering the mother lens. For example, the input image may be accessed  630  from an image sensor (e.g., the image sensor  430  or the image sensor  314 ) via a bus (e.g., the bus  324 ). In some implementations, the input image may be accessed  630  via a communications link (e.g., the communications link  350 ). For example, the input image may be accessed  630  via a wireless or wired communications interface (e.g., Wi-Fi, Bluetooth, USB, HDMI, Wireless USB, Near Field Communication (NFC), Ethernet, a radio frequency transceiver, and/or other interfaces). For example, the input image may be accessed  630  via communications interface  366 . For example, the input image may be accessed  630  via a front ISP that performs some initial processing on the accessed  630  input image. For example, the input image may represent each pixel value in a defined format, such as in a RAW image signal format, a YUV image signal format, or a compressed format (e.g., an MPEG or JPEG compressed bitstream). For example, the input image may be stored in a format using the Bayer color mosaic pattern. 
     The process  600  includes determining  640  a warp mapping based on identification of the accessory lens. For example, the warp mapping may include a lens distortion correction that is determined based on the identification of the accessory lens. For example, identification of the accessory lens may be made based on data read from a non-volatile memory integrated in the accessory lens structure. In some implementations, the data from the non-volatile memory includes parameters of the warp mapping (e.g., parameters of a lens distortion correction transformation) that are used to determine  640  the warp mapping. In some implementations, the data from the non-volatile memory includes optical parameters (e.g., optical parameters of the accessory lens or optical parameters of a lens stack including the accessory lens and the mother lens), and the warp mapping is determined  640  based on these optical parameters. For example, the warp mapping may include a series of transformations, such as lens distortion correction, electronic rolling shutter correction, and parallax correction (for implementations with using two or more image sensors). 
     The process  600  includes applying  650  the warp mapping to the image to obtain a warped image. For example, the warp mapping may specify the determination of image portions (e.g., pixels or blocks of pixels) of the warped image based on linear combinations of one or more corresponding image portions of the image and/or one or more corresponding image portions of an image captured with another image sensor of the image capture device. 
     For example, the accessory lens may be used to facilitate robust electronic image stabilization in some use cases. In some implementations, when the accessory lens structure is positioned covering the mother lens, a field of view of a lens stack including the accessory lens and the mother lens is projected as a circle within a detectable area of the image sensor. Although not explicitly shown in  FIG. 6 , the process  600  may also include applying an electronic image stabilization rotation to the image to obtain a stabilized image; and cropping the stabilized image to a rectangular output image from within the circle (e.g., as described in relation to the process  700  of  FIG. 7 ). 
     The process  600  includes transmitting, storing, or displaying  660  an output image based on the warped image. For example, the output image may be transmitted  660  to an external device (e.g., a personal computing device) for display or storage. For example, the output image may be the same as the warped image. For example, the output image may be a composite image determined by stitching an image based on the output image to one or more images from other image sensors with overlapping fields of view. For example, the output image may be an electronically stabilized image based on the warped image. For example, the output image may be compressed using an encoder (e.g., an MPEG encoder). For example, the output image may be transmitted  660  via the communications interface  318 . For example, the output image may be displayed  660  in the user interface  320  or in the user interface  364 . For example, the output image may be stored  660  in memory of the processing apparatus  312  or in memory of the processing apparatus  362 . 
       FIG. 7  is a flowchart of an example of a process  700  for improving electronic image stabilization using an accessory lens structure with an image capture device. The image capture device includes a mother lens (e.g., the mother lens  420 ) and an image sensor (e.g., the image sensor  430 ) configured to detect light incident through the mother lens. The accessory lens structure (e.g., the accessory lens structure  470 ) includes an accessory lens (e.g., the accessory lens  472 ) and a retaining mechanism (e.g., the retaining mechanism  480 ) configured to fasten the accessory lens in a position covering the mother lens in a first arrangement and configured to disconnect the accessory lens from the image capture device in a second arrangement. In this example, the accessory lens augments optical properties of a lens stack over the image sensor that includes the mother lens, such that a field of view of the lens stack is projected as a circle within a detectable area of the image sensor, when the retaining mechanism is in the first arrangement. The process  700  includes accessing  710  an image captured using the image sensor when the retaining mechanism is in the first arrangement; applying  720  an electronic image stabilization rotation to the image to obtain a stabilized image; and cropping  730  the stabilized image to a rectangular output image from within the circle. For example, the process  600  may be implemented by an image capture device, such as the image capture device  100  of  FIGS. 1A-1D , the image capture device  200  of  FIGS. 2A-2B , the image capture device  310  of  FIG. 3A , or the image capture device  340  of  FIG. 3B . 
     For example, the image capture device may include a processing apparatus integrated in the image capture device. In some implementations, the processing apparatus is configured to automatically detect  610  when the retaining mechanism is in the first arrangement. In some implementations, the processing apparatus is configured to, responsive to detecting that the accessory lens structure has been mounted, prompt a user, via a user interface (e.g., the interactive display  120 ), to confirm a lens configuration change. In some implementations, the processing apparatus is configured to, responsive to detecting that the accessory lens structure has been mounted, automatically identify  620  the accessory lens from among a set of multiple supported accessory lenses. 
     The process  700  includes accessing  710  an image (e.g., a still image or a frame of video) captured using the image sensor when the retaining mechanism is in the first arrangement. For example, the input image may be accessed  710  from an image sensor (e.g., the image sensor  430  or the image sensor  314 ) via a bus (e.g., the bus  324 ). In some implementations, the input image may be accessed  710  via a communications link (e.g., the communications link  350 ). For example, the input image may be accessed  710  via a wireless or wired communications interface (e.g., Wi-Fi, Bluetooth, USB, HDMI, Wireless USB, Near Field Communication (NFC), Ethernet, a radio frequency transceiver, and/or other interfaces). For example, the input image may be accessed  710  via communications interface  366 . For example, the input image may be accessed  710  via a front ISP that performs some initial processing on the accessed  710  input image. For example, the input image may represent each pixel value in a defined format, such as in a RAW image signal format, a YUV image signal format, or a compressed format (e.g., an MPEG or JPEG compressed bitstream). For example, the input image may be stored in a format using the Bayer color mosaic pattern. 
     The process  700  includes applying  720  an electronic image stabilization rotation to the image to obtain a stabilized image. For example, the electronic image stabilization rotation may be applied  720  to a portion (e.g., pixel or block of pixels) of the image. For example, a portion of the stabilized image may be shifted to a new address or position within the stabilized image based on the electronic image stabilization rotation. For example, the electronic image stabilization rotation may be applied  720  to all portions of the image within the field of view. In some implementations, the electronic image stabilization rotation may be determined based on angular rate measurements for the image capture device including the image sensor used to capture the image. For example, the electronic image stabilization rotation may be determined based on motion sensor (e.g., gyroscope and/or accelerometer) measurements from a time associated with the capture of the image. Because the field of view of the lens stack is projected as a circle within a detectable area of the image sensor, the image may be well suited to the application of significant electronic image stabilization rotation, resulting in little or no distortion due to edge effects. 
     The process  700  includes cropping  730  the stabilized image to a rectangular output image from within the circle. For example, the stabilized image may be cropped  730  to a rectangular output image to conform to an image or video encoding format or a display format. 
     While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.