Patent Publication Number: US-2023154042-A1

Title: Skeletal tracking using previous frames

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 17/240,457, filed on Apr. 26, 2021, which is a continuation of U.S. patent application Ser. No. 16/710,980, filed on Dec. 11, 2019, now issued as U.S. Pat. No. 11,036,989, each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to generating virtual objects based on an image depicting a user. 
     BACKGROUND 
     Virtual rendering systems can be used to create engaging and entertaining augmented reality experiences, in which virtual object graphics, such as avatars, appear to be present in the real world. Such systems can be subject to presentation problems due to environmental conditions, user actions, unanticipated visual interruption between a camera and the object being rendered, and the like. This can cause a virtual object to disappear or otherwise behave erratically, which breaks the illusion of the virtual objects being present in the real world. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       in the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced. Some embodiments are illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG.  1    is a block diagram showing an example messaging system for exchanging data (e.g., messages and associated content) over a network, according to example embodiments. 
         FIG.  2    is a schematic diagram illustrating data which may be stored in the database of a messaging server system, according to example embodiments. 
         FIG.  3    is a schematic diagram illustrating a structure of a message generated by a messaging client application for communication, according to example embodiments. 
         FIG.  4    is a block diagram showing an example body pose estimation system, according to example embodiments. 
         FIG.  5    is a diagram showing body joint positions used to determine a body pose, according to example embodiments. 
         FIG.  6    is a flowchart illustrating example operations of the body pose estimation system, according to example embodiments. 
         FIGS.  7 A- 8 C  are illustrative inputs and outputs of the body pose estimation system, according to example embodiments. 
         FIG.  9    is a block diagram illustrating a representative software architecture, which may be used in conjunction with various hardware architectures herein described, according to example embodiments. 
         FIG.  10    is a block diagram illustrating components of a machine able to read instructions from a machine-readable medium (e.g., a machine-readable storage medium) and perform any one or more of the methodologies discussed herein, according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes systems, methods, techniques, instruction sequences, and computing machine program products that embody illustrative embodiments of the disclosure. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide an understanding of various embodiments. It will be evident, however, to those skilled in the art, that embodiments may be practiced without these specific details. In general, well-known instruction instances, protocols, structures, and techniques are not necessarily shown in detail. 
     Typically, virtual reality (VR) and augmented reality (AR) systems display avatars representing a given user by capturing an image of the user and, in addition, obtaining a depth map using a depth sensor of the real-world human body depicted in the image. By processing the depth map and the image together, the VR and AR systems can mimic actions performed by the user. While such systems work well for presenting avatars of a user, the need for a depth sensor limits the scope of their applications. This is because adding depth sensors to user devices for the purpose of displaying avatars increases the overall cost and complexity of the devices, making them less attractive. 
     Also, while certain systems use real-time skeletal tracking trackers to identify actions performed by a user, such trackers are noisy and require temporal filtering to be applied. This reduces their overall efficiency and consumes too many resources to apply them on mobile devices. Filtering based on classical computer vision and signal analysis can improve results slightly but not enough. 
     The disclosed embodiments improve the efficiency of using the electronic device by applying a first machine learning technique to identify skeletal joints of a user&#39;s body from a single image of the user and then filter or improve the identified skeletal joints by applying a second machine learning technique to previously received video frames of the user and current frame image features to predict skeletal joint positions for a current frame, such as the single image. Specifically, a video depicting a user&#39;s body is received. A current frame of the video is processed by a first machine learning technique to identify skeletal joint positions. A set of previous frames, such as 1-2 seconds of video preceding the current frame, is processed by a second machine learning technique to predict skeletal joint positions for a subsequent frame, such as the current frame. A comparison is made between the skeletal joint positions identified for the current frame by the first machine learning technique and the skeletal joint positions predicted by the second machine learning technique based on the previous frames. Any deviation or difference between the skeletal joint positions is then corrected by the second machine learning technique to improve and filter the skeletal joint positions identified for the current frame by the first machine learning technique. 
     The skeletal joints can then be used to modify presentation of one or more virtual objects, such as to mimic a pose corresponding to the skeletal joints. The virtual object (e.g., a three-dimensional object, such as a 3D caption, emoji, character, avatar, animation, looping animation of a personalized avatar or character, looping or non-looping animated graphic such as a dancing hot dog, a stylized word with animation, and so forth) is generated directly from a single red, green, and blue (RGB) image (e.g., a monocular RGB image) or a video of RGB images depicting the real-world user&#39;s body. The disclosed embodiments generate the virtual object without also obtaining a depth map of the real-world user&#39;s body. This enables a user device with a simple RGB camera (without a depth sensor) to accurately and quickly render an animated virtual object based on the real-world user&#39;s body pose within the VR or AR application, allowing the user to interact with the YR or AR content in a more realistic environment. 
     In some embodiments, one such virtual object is selected by a user and added to the RGB image, and a pose of the virtual object is modified to match the pose of the user&#39;s body to provide the illusion that the selected virtual object is part of the real-world scene and is mimicking the user. Specifically, the disclosed embodiments process the image depicting the user&#39;s body, using machine learning techniques, to identify skeletal joints. A pose represented by the identified skeletal joints is determined. Once the pose represented by the skeletal joints is determined, corresponding skeletal joints of an avatar rig are adjusted to change a pose of the avatar to match the pose represented by the identified skeletal joints of the body of the user. The avatar with the modified pose that matches the pose represented by the identified skeletal joints of the body of the user is generated for display to the user. 
       FIG.  1    is a block diagram showing an example messaging system  100  for exchanging data (e.g., messages and associated content) over a network  106 . The messaging system  100  includes multiple client devices  102 , each of which hosts a number of applications, including a messaging client application  104  and a AR/VR. application  105 . Each messaging client application  104  is communicatively coupled to other instances of the messaging client application  104 , the AR/VR application  105 , and a messaging server system  108  via a network  106  (e.g., the Internet). 
     Accordingly, each messaging client application  104  and AR/VR application  105  is able to communicate and exchange data with another messaging client application  104  and AR/VR application  105  and with the messaging server system  108  via the network  106 . The data exchanged between messaging client applications  104 , AR/VR applications  105 , and between a messaging client application  104  and the messaging server system  108  includes functions (e.g., commands to invoke functions) as well as payload data (e.g., text, audio, video, or other multimedia data). 
     AR/VR application  105  is an application that includes a set of functions that allow the client device  102  to access body pose estimation system  124 . In some implementations, the AR/VR application  105  is a component or a feature that is part of the messaging client application  104 . AR/VR application  105  uses an RGB camera to capture a monocular image of a user&#39;s real-world body. The AR/VR application  105  applies various trained machine learning techniques on the captured image of the body and one or more previous frames depicting the body to generate an avatar. For example, the avatar is generated to have a pose that is the same as a pose of the user&#39;s body depicted in the image. As another example, the avatar is generated for simultaneous display with the user, and a position of the avatar changes from one frame to another based on a relative position of the user in the image. For example, the avatar position changes to maintain a constant distance between the avatar and the user so it appears the avatar follows the user around. In some implementations, the AR/VR application  105  continuously captures images of the user&#39;s body in real time or periodically to continuously or periodically update the generated avatar. This allows the user to move around in the real world and see the avatar update in real time. The AR/VR. application  105  presents various content (e.g., messages, games, advertisements, and so forth) and allows the user to modify a pose of the avatar in the AR/VR application  105  to interact with other virtual. content (e.g., the avatar pose can be modified to pick a virtual apple off of a virtual tree). Once the avatar is generated, the user can perform an action or gesture to capture an image of the user and the avatar for transmission to another user. 
     In order for AR/VR application  105  to generate the avatar directly from a captured RGB image, the AR/VR application  105  obtains a first trained machine learning techniques from the body pose estimation system  124  and/or messaging server system  108 . The first trained machine learning technique processes the captured RGB image to extract one or more features from the RGB image that correspond to the body depicted in the captured RGB image. The features are analyzed to identify one or more skeletal joints and their respective alignment relative to one another. Specifically, the features are analyzed to determine the joint positions of a specified set of skeletal joints. The AR/VR application  105  also obtains a second trained machine learning technique from the body pose estimation system  124  and/or messaging server system  108 . The second trained machine learning technique processes one or more previously captured frames (e.g., 1-2 seconds of video frames that immediately precede the RGB image) to estimate or predict skeletal joint positions for a subsequent frame. A threshold number of seconds of video frames (which may be user defined, previously specified, and/or dynamically determined) may continuously or periodically be stored in a buffer, such that the threshold number of seconds worth of video frames that precedes a current RGB image can be accessed by the second trained machine learning technique. The output or prediction of the skeletal joint positions of the second trained machine learning technique is used to filter or improve the skeletal joint positions identified by the first trained machine learning technique. In some cases, the second trained machine learning technique processes the skeletal joint positions identified by the first trained machine learning technique together with the previously captured frames to filter or improve the estimated skeletal joint positions. 
     The joint positions are provided to a database with an offset to identify a pose that is within the offset of the determined joint positions. After the pose is identified, an avatar is retrieved and a skeletal rig of the avatar is adjusted to mimic or copy the identified pose. In some embodiments, the skeletal rig of the avatar is adjusted directly from the joint positions that are determined rather than from an identified pose. The avatar is then generated for display based on the adjusted skeletal rig to mimic the pose of the body depicted in the captured image. 
     In some embodiments, the RGB image is a first frame of a plurality of frames of a video. In such cases, after a user&#39;s body is detected in the first frame using the first and second machine learning techniques, the body pose estimation system  124  estimates where the user&#39;s body will be and at what scale in a second frame of the plurality of frames. The second frame may be adjacent to the first frame. In some implementations, a third machine learning technique is applied to the first frame to predict or estimate the position and scale of the user&#39;s body in the second frame. 
     In training, the body pose estimation system  124  obtains a first plurality of input training images that include different real-world body poses. These training images also provide the ground truth information about the body pose depicted in each image. A first machine learning technique (e.g., a deep neural network) is trained based on features of the plurality of training images. Specifically, the first machine learning technique extracts one or more features from a given training image and estimates a body pose by analyzing joint positions of the body depicted in the given training image. The first machine learning technique obtains the ground truth information corresponding to the training image and adjusts or updates one or more coefficients to improve subsequent estimations of a body pose depicted in a subsequent image. 
     In training, the body pose estimation system  124  obtains a first plurality of input training videos (each having a number of frames corresponding to a threshold video duration, such as 1-2 seconds) that include different real-world body poses. These training videos also provide the ground truth information with skeletal joint positions of the body for a subsequent frame relative to each video. Namely, a first training video may be associated with ground truth information identifying skeletal joint positions of a body depicted in the first training video in a frame immediately subsequent to the last frame in the first training video. A second machine learning technique (e.g., a neural network) is trained based on features of the plurality of training videos. Specifically, the second machine learning technique extracts one or more features from a given training video and estimates or predicts skeletal joint positions in a subsequent frame relative to a last frame of the training video by analyzing joint positions of the body depicted in the given training video. The second machine learning technique obtains the ground truth information corresponding to the training video and adjusts or updates one or more coefficients to improve subsequent estimations of a body pose depicted in a subsequent video. 
     In some implementations, a third machine learning technique (e.g., a deep neural network) extracts one or more features from a given training image and estimates a body pose in a subsequent image that is adjacent to the given training image by analyzing joint positions of the body depicted in the given training image. The third machine learning technique obtains the ground truth information corresponding to the training image that identifies the body pose in the subsequent image and adjusts one or more coefficients to improve subsequent estimations of a body pose depicted in a subsequent image and estimations of body pose and scale in subsequent images. In some implementations, during training, the third machine learning technique obtains reference 3D depth maps for each training image and uses the reference 3D depth map to estimate the body pose. 
     The messaging server system  108  provides server-side functionality via the network  106  to a particular messaging client application  104 . While certain functions of the messaging system  100  are described herein as being performed by either a messaging client application  104  or by the messaging server system  108 , it will be appreciated that the location of certain functionality either within the messaging client application  104  or the messaging server system  108  is a design choice. For example, it may be technically preferable to initially deploy certain technology and functionality within the messaging server system  108 , but to later migrate this technology and functionality to the messaging client application  104  where a client device  102  has a sufficient processing capacity. 
     The messaging server system  108  supports various services and operations that are provided to the messaging client application  104 . Such operations include transmitting data to, receiving data from, and processing data generated by the messaging client application  104 . This data may include message content, client device information, geolocation information, media annotation and overlays, virtual objects, message content persistence conditions, social network information, and live event information, as examples. Data exchanges within the messaging system  100  are invoked and controlled through functions available via user interfaces (UIs) of the messaging client application  104 . 
     Turning now specifically to the messaging server system  108 , an Application Program Interface (API) server  110  is coupled to, and provides a programmatic interface to, an application server  112 . The application server  112  is communicatively coupled to a database server  118 , which facilitates access to a database  120  in which is stored data associated with messages processed by the application server  112 . 
     Dealing specifically with the API server  110 , this server  110  receives and transmits message data (e.g., commands and message payloads) between the client device  102  and the application server  112 . Specifically, the API server  110  provides a set of interfaces (e.g., routines and protocols) that can be called or queried by the messaging client application  104  in order to invoke functionality of the application server  112 . The API server  110  exposes various functions supported by the application server  112 , including account registration; login functionality; the sending of messages, via the application server  112 , from a particular messaging client application  104  to another messaging client application  104 ; the sending of media files (e.g., images or video) from a messaging client application  104  to the messaging server application  114 , and for possible access by another messaging client application  104 ; the setting of a collection of media data (e.g., story); the retrieval of such collections; the retrieval of a list of friends of a user of a client device  102 ; the retrieval of messages and content; the adding and deleting of friends to a social graph; the location of friends within a social graph; access to user conversation data; access to avatar information stored on messaging server system  108 ; and opening an application event (e.g., relating to the messaging client application  104 ). 
     The application server  112  hosts a number of applications and subsystems, including a messaging server application  114 , an image processing system  116 , a social network system  122 , and the body pose estimation system  124 . The messaging server application  114  implements a number of message processing technologies and functions, particularly related to the aggregation and other processing of content (e.g., textual and multimedia content) included in messages received from multiple instances of the messaging client application  104 . As will be described in further detail, the text and media content from multiple sources may be aggregated into collections of content (e.g., called stories or galleries). These collections are then made available, by the messaging server application  114 , to the messaging client application  104 . Other processor- and memory-intensive processing of data may also be performed server-side by the messaging server application  114 , in view of the hardware requirements for such processing. 
     The application server  112  also includes an image processing system  116  that is dedicated to performing various image processing operations, typically with respect to images or video received within the payload of a message at the messaging server application  114 . A portion of the image processing system  116  may also be implemented by the body pose estimation system  124 . 
     The social network system  122  supports various social networking functions and services and makes these functions and services available to the messaging server application  114 . To this end, the social network system  122  maintains and accesses an entity graph within the database  120 . Examples of functions and services supported by the social network system  122  include the identification of other users of the messaging system  100  with which a particular user has relationships or is “following” and also the identification of other entities and interests of a particular user. Such other users may be referred to as the user&#39;s friends.  
     The application server  112  is communicatively coupled to a database server  118 , which facilitates access to a database  120  in which is stored data associated with messages processed by the messaging server application  114 . 
       FIG.  2    is a schematic diagram  200  illustrating data, which may be stored in the database  120  of the messaging server system  108 , according to certain example embodiments. While the content of the database  120  is shown to comprise a number of tables, it will be appreciated that the data could be stored in other types of data structures (e.g., as an object-oriented database). 
     The database  120  includes message data stored within a message table  214 . An entity table  202  stores entity data, including an entity graph  204 . Entities for which records are maintained within the entity table  202  may include individuals, corporate entities, organizations, objects, places, events, and so forth. Regardless of type, any entity regarding which the messaging server system  108  stores data may be a recognized entity. Each entity is provided with a unique identifier, as well as an entity type identifier (not shown). 
     The entity graph  204  furthermore stores information regarding relationships and associations between entities. Such relationships may be social, professional (e.g., work at a common corporation or organization), interest-based, or activity-based, merely for example. 
     Message table  214  may store a collection of conversations between a user and one or more friends or entities. Message table  214  may include various attributes of each conversation, such as the list of participants, the size of the conversation (e.g., number of users and/or number of messages), the chat color of the conversation, a unique identifier for the conversation, and any other conversation related feature(s). 
     The database  120  also stores annotation data, in the example form of filters, in an annotation table  212 . Database  120  also stores annotated content received in the annotation table  212 . Filters for which data is stored within the annotation table  212  are associated with and applied to videos (for which data is stored in a video table  210 ) and/or images (for which data is stored in an image table  208 ). Filters, in one example, are overlays that are displayed as overlaid on an image or video during presentation to a recipient user. Filters may be of various types, including user-selected filters from a gallery of filters presented to a sending user by the messaging client application  104  when the sending user is composing a message. Other types of filters include geolocation filters (also known as geo-filters), which may be presented to a sending user based on geographic location. For example, geolocation filters specific to a neighborhood or special location may be presented within a UI by the messaging client application  104 , based on geolocation information determined by a Global Positioning System (GPS) unit of the client device  102 . Another type of filter is a data filter, which may be selectively presented to a sending user by the messaging client application  104 , based on other inputs or information gathered by the client device  102  during the message creation process. Examples of data filters include current temperature at a specific location, a current speed at which a sending user is traveling, battery life for a client device  102 , or the current time. 
     Other annotation data that may be stored within the image table  208  may be a real-time special effect and sound that may be added to an image or a video. 
     As mentioned above, the video table  210  stores video data which, in one embodiment, is associated with messages for which records are maintained within the message table  214 . Similarly, the image table  208  stores image data associated with messages for which message data is stored in the entity table  202 . The entity table  202  may associate various annotations from the annotation table  212  with various images and videos stored in the image table  208  and the video table  210 . 
     Trained machine learning technique(s)  207  stores parameters that have been trained during training of the body pose estimation system  124 . For example, trained machine learning techniques  207  stores the trained parameters of one or more neural network machine learning techniques. 
     Body pose training images  209  stores a plurality of images of depictions of real-world body poses. The plurality of images stored in the body pose training images  209  includes various depictions of a real-world body pose together with 3D depth information captured from a 3D depth sensor for each image. The plurality of images also include ground truth information identifying the body pose and the ground truth skeletal joint positions of one or more body skeletal joints. Examples of the skeletal joint positions that are identified for a given pose are shown in  FIG.  5   . These skeletal joint positions include a position of the right wrist, right elbow, right shoulder, a nose on a face, a left shoulder, a left elbow, and a left wrist. The skeletal joint positions can be determined relative to one another (e.g., how high one skeletal joint is relative to another or how high or low one skeletal joint is relative to the nose) to determine a given pose. These body pose training images  209  are used by the body pose estimation system  124  to train the first machine learning technique used to determine a body pose and skeletal joint positions from a received RGB monocular image of a user&#39;s body. 
     Body pose training images  209  stores a plurality of videos (1-2 second video segments) of depictions of real-world body poses. The plurality of videos stored in the body pose training images  209  includes various depictions of real-world body poses. The plurality of videos also include ground truth information identifying the ground truth skeletal joint positions of a body depicted in a subsequent frame relative to a last frame in each of the plurality of videos. These body pose training images  209  are used by the body pose estimation system  124  to train the second machine learning technique used to predicts skeletal joint positions for a subsequent frame from a received RGB monocular video of a user&#39;s body. 
     Returning to  FIG.  2   , a story table  206  stores data regarding collections of messages and associated image, video, or audio data, which are compiled into a collection (e.g., a story or a gallery). The creation of a particular collection may be initiated by a particular user (e.g., each user for which a record is maintained in the entity table  202 ). A user may create a “personal story” in the form of a collection of content that has been created and sent/broadcast by that user. To this end, the UI of the messaging client application  104  may include an icon that is user-selectable to enable a sending user to add specific content to his or her personal story. 
     A collection may also constitute a “live story,” which is a collection of content from multiple users that is created manually, automatically, or using a combination of manual and automatic techniques. For example, a “live story” may constitute a curated stream of user-submitted content from various locations and events. Users whose client devices have location services enabled and are at a common location event at a particular time may, for example, be presented with an option, via a UI of the messaging client application  104 , to contribute content to a particular live story. The live story may be identified to the user by the messaging client application  104  based on his or her location. The end result is a “live story” told from a community perspective. 
     A further type of content collection is known as a “location story,” which enables a user whose client device  102  is located within a specific geographic location (e.g., on a college or university campus) to contribute to a particular collection. In some embodiments, a contribution to a location story may require a second degree of authentication to verify that the end user belongs to a specific organization or other entity (e.g., is a student on the university campus). 
       FIG.  3    is a schematic diagram illustrating a structure of a message  300 , according to some embodiments, generated by a messaging client application  104  for communication to a further messaging client application  104  or the messaging server application  114 . The content of a particular message  300  is used to populate the message table  214  stored within the database  120 , accessible by the messaging server application  114 . Similarly, the content of a message  300  is stored in memory as “in-transit” or “in-flight” data of the client device  102  or the application server  112 . The message  300  is shown to include the following components: 
     A message identifier  302 : a unique identifier that identifies the message  300 . 
     A message text payload  304 : text, to be generated by a user via a UI of the client device  102  and that is included in the message  300 . 
     A message image payload  306 : image data, captured by a camera component of a client device  102  or retrieved from memory of a client device  102 , and that is included in the message  300 . 
     A message video payload  308 : video data, captured by a camera component or retrieved from a memory component of the client device  102  and that is included in the message  300 . 
     A message audio payload  310 : audio data, captured by a microphone or retrieved from the memory component of the client device  102 , and that is included in the message  300 . 
     Message annotations  312 : annotation data (e.g., filters, stickers, or other enhancements) that represents annotations to be applied to message image payload  306 , message video payload  308 , or message audio payload  310  of the message  300 . 
     A message duration parameter  314 : parameter value indicating, in seconds, the amount of time for which content of the message (e.g., the message image payload  306 , message video payload  308 , message audio payload  310 ) is to be presented or made accessible to a user via the messaging client application  104 . 
     A message geolocation parameter  316 : geolocation data (e.g., latitudinal and longitudinal coordinates) associated with the content payload of the message. Multiple message geolocation parameter  316  values may be included in the payload, with each of these parameter values being associated with respect to content items included in the content (e.g., a specific image within the message image payload  306 , or a specific video in the message video payload  308 ). 
     A message story identifier  318 : identifier value identifying one or more content collections (e.g., “stories”) with which a particular content item in the message image payload  306  of the message  300  is associated. For example, multiple images within the message image payload  306  may each be associated with multiple content collections using identifier values. 
     A message tag  320 : each message  300  may be tagged with multiple tags, each of which is indicative of the subject matter of content included in the message payload. For example, where a particular image included in the message image payload  306  depicts an animal (e.g., a lion), a tag value may be included within the message tag  320  that is indicative of the relevant animal. Tag values may be generated manually, based on user input, or may be automatically generated using, for example, image recognition. 
     A message sender identifier  322 : an identifier (e.g., a messaging system identifier, email address, or device identifier) indicative of a user of the client device  102  on which the message  300  was generated and from which the message  300  was sent. 
     A message receiver identifier  324 : an identifier (e.g., a messaging system identifier, email address, or device identifier) indicative of user(s) of the client device  102  to which the message  300  is addressed. In the case of a conversation between multiple users, the identifier may indicate each user involved in the conversation. 
     The contents (e.g., values) of the various components of message  300  may be pointers to locations in tables within which content data values are stored. For example, an image value in the message image payload  306  may be a pointer to (or address of) a location within an image table  208 . Similarly, values within the message video payload  308  may point to data stored within a video table  210 , values stored within the message annotations  312  may point to data stored in an annotation table  212 , values stored within the message story identifier  318  may point to data stored in a story table  206 , and values stored within the message sender identifier  322  and the message receiver identifier  324  may point to user records stored within an entity table  202 . 
       FIG.  4    is a block diagram showing an example body pose estimation system  124 , according to example embodiments. Body pose estimation system  124  operates on a set of input data (e.g., a monocular image  401  depicting a real body of a user, body pose training image data  402 , monocular video depicting a body of a user  403 , and body pose training video data  404 ). The set of input data is obtained from body pose training images  209  stored in database(s)  200  during the training phases and is obtained from an RGB camera of a client device  102  when an AR/VR application  105  is being used. Body pose estimation system  124  includes a first machine learning technique module  412 , a skeletal joint position module  414 , a second machine learning technique module  417 , a pose determination module  416 , a virtual object modification module  418 , a virtual object mode selection module  419  and a virtual object display module  420 . 
     During training, according to the disclosed embodiments, body pose estimation system  124  receives a given training image (e.g., monocular image  401  depicting a real-world body, such as an image of a user&#39;s face, arms, torso, hips and legs) from body pose training image data  402 . The body pose estimation system  124  applies one or more machine learning techniques using the first machine learning technique module  412  on the given training image. The first machine learning technique module  412  extracts one or more features from the given training image to estimate skeletal joint positions of the skeletal joints depicted in the image. For example, the first machine learning technique module  412  obtains the given training image depicting a user&#39;s face, arms, torso, hips and legs. The first machine learning technique module  412  extracts features from the image that correspond to the user&#39;s face and arms to identify one or more skeletal joints (e.g., the joints shown in  FIG.  5    including the left/right wrist joints, left/right elbow joints, left/right shoulder joints, and a nose position). 
     The first machine learning technique module  412  determines the relative positions of the identified skeletal joints to determine a pose that corresponds to the skeletal joint positions. In an embodiment, the first machine learning technique module  412  uses depth information associated with the given training image to assist in the determination of the skeletal joint positions and pose of the body. The first machine learning technique module  412  compares the determined skeletal joint positions and the determined pose with the ground truth skeletal joint positions and pose provided as part of the body pose training image data  402 . Based on a difference threshold of the comparison, the first machine learning technique module  412  updates one or more coefficients and obtains one or more additional body pose training images. After a specified number of epochs or batches of training images have been processed and/or when the difference threshold reaches a specified value, the first machine learning technique module  412  completes training and the parameters and coefficients of the first machine learning technique module  412  are stored in the trained machine learning technique(s)  207 . In some embodiments, portions of the first machine learning technique module  412  are implemented by skeletal joint position module  414  and pose determination module  416 . 
     During training, according to the disclosed embodiments, body pose estimation system  124  receives a given training video (e.g., monocular video depicting a body of user  403  depicting a real-world body, such as an image of a user&#39;s face, arms, torso, hips and legs) from body pose training image data  402 . The body pose estimation system  124  applies one or more machine learning techniques using the second machine learning technique module  417  on the given training video. The second machine learning technique module  417  extracts one or more features from the given training video to predict skeletal joint positions for a frame subsequent to the last frame of the video. For example, the second machine learning technique module  417  obtains the given training video depicting movement of a user&#39;s face, arms, torso, hips and legs across a set of frames in 1-2 seconds of video. The second machine learning technique module  417  extracts features from the video that correspond to the user&#39;s face and arms to predict one or more skeletal joints in a frame that is subsequent to the last frame of the video (e.g., the joints shown in  FIG.  5    including the left/right wrist joints, left/right elbow joints, left/right shoulder joints, and a nose position). In some cases, the frame subsequent to the last frame of the video may not be available and not received by the second machine learning technique module  417  but the second machine learning technique module  417  predicts skeletal joint positions for the subsequent frame from the previous frames. 
     The second machine learning technique module  417  predicts skeletal joint positions for one or more subsequent frames that follow the given training video. For example, the second machine learning technique module  417  may process frames  2 - 25  of a given video and frame  26  of the same video to predict skeletal joint positions of a body depicted in frame  26  of the same video. The second machine learning technique module  417  compares the determined/predicted skeletal joint positions with the ground truth skeletal joint positions provided as part of the body pose training image data  402 . The ground truth skeletal joint positions may provide the ground truth real skeletal joint positions for the subsequent frame  26  for movement of a body depicted in frames  2 - 25 . Based on a difference threshold of the comparison, the second machine learning technique module  417  updates one or more coefficients and obtains one or more additional body pose training videos. After a specified number of epochs or batches of training videos have been processed and/or when the difference threshold reaches a specified value, the second machine learning technique module  417  completes training and the parameters and coefficients of the second machine learning technique module  417  are stored in the trained machine learning technique(s)  207 , In some embodiments, portions of the second machine learning technique module  417  are implemented by skeletal joint position module  414  and pose determination module  416 . 
     In an example, the second machine learning technique module  417  is trained to recognize movement of skeletal joint positions across a set of consecutive frames, The second machine learning technique module  417  can receive a current video frame and/or skeletal joint positions determined from that current video frame. The second machine learning technique module  417  can process a set of previous frames that depict movement of the body together with image features of a current frame and predict estimated skeletal joint positions for a next frame. Based on the prediction, the second machine learning technique module  417  compares the predicted estimated skeletal joint positions with the skeletal joint positions determined for the current frame by the first machine learning technique module  412 . The second machine learning technique module  417  can then determine any deviation and correction needed based on the comparison. 
     Specifically, the second machine learning technique module  417  receives a collection of skeletal joint positions that have been determined for a current frame (e.g., from the first machine learning technique module  412 ). The col lection of skeletal joint positions may indicate that the left wrist is at a particular coordinate in two-dimensional (2D) or three-dimensional (3D) space (4, 6) and that the right wrist is at another particular coordinate in the 2D or 3D space (10, 8). The second machine learning technique module  417  processes a sequence of video frames that immediately precede the current frame by 1-2 seconds and image features of a current frame. The second machine learning technique module  417  analyzes movement of the skeletal joints across the sequence of the video frames to predict estimated positions of the skeletal joints in the current frame or for a frame that is subsequent to the current frame. As an example, the second machine learning technique module  417  predicts the coordinates of left wrist to be (4, 7) and the right wrist to be (10, 8). The second machine learning technique module  417  compares the predicted coordinates with the coordinates determined for the current frame (e.g., by the first machine learning technique module  412 ). The second machine learning technique module  417  may filter or correct at least some of the coordinates that do not match. In this example, the second machine learning technique module  417  determines that the left wrist coordinates (4, 6) do not match the coordinates predicted based on the previous video frames (4, 7) and, as such, corrects the skeletal joint positions to be (4, 7) in the collection of skeletal joint positions. 
     After training, according to the disclosed embodiments, body pose estimation system  124  receives an input image  401  (e.g., monocular image depicting a real-world body, such as an image of a user&#39;s face, arms, torso, hips and legs) as a single RGB image from a client device  102 . The body pose estimation system  124  applies the first trained machine learning technique module  412  to the received input image  401  to extract one or more features representing the skeletal joints of the body depicted in the image  401 . The body pose estimation system  124  applies the second trained machine learning technique module  417  to the received monocular video depicting a body of a user  403  to extract one or more features representing the skeletal joints of the  body depicted in the monocular video depicting a body of a user  403  and to generate a prediction or estimation of skeletal joints in a subsequent frame. 
     In some embodiments, the rate at which the features are extracted from a video stream depicting the user&#39;s body is based on how close or far the user is positioned relative to the image capture device. For example, if the user is positioned far from the image capture device and appears really small in the images of the video, the features and as a result a pose of the user&#39;s body are analyzed less frequently (e.g., every 5 frames). If the user is positioned close to the image capture device and appears large in the images of the video, the features and as a result a pose of the user&#39;s body are analyzed more frequently (e.g., every 2 frames). The extracted features are provided to the skeletal joint position module  414 . The skeletal joint position module  414  analyzes the skeletal joint features to determine coordinates of specific skeletal joints. For example, the skeletal joint position module  414  determines the x,y coordinates of a particular point of each skeletal joint, such as the x,y coordinates of the left wrist, the x,y coordinates of the left elbow, the x,y coordinates of the left shoulder, the x,y coordinates of the nose (or other facial feature such as mouth, ears or eyes), the x,y coordinates of the right wrist, the x,y coordinates of the right elbow, and the x,y coordinates of the right shoulder. The skeletal joint position module  414  provides the x,y coordinates of the specified skeletal joints to the second machine learning technique module  417 . In some embodiments, the second machine learning technique module  417  provides the x,y coordinates of the filtered skeletal joints to the virtual object modification module  418 . In an embodiment, the x,y coordinates represent x,y offsets of each skeletal joint relative to a neutral pose of the body. 
     The second machine learning technique module  417  analyzes movement of the skeletal joints across the sequence of the video frames received prior to the monocular image depicting a body of a user  401  to predict estimated positions of the skeletal joints in the monocular image depicting a body of a user  401 . The number of previous video frames or duration of the previously received video segments analyzed by the second machine learning technique module  417  may be set by a user, predetermined, or dynamically adjusted. In some cases, the number of previous video frames that are analyzed may be increased (e.g., from 1 second of video to 2 seconds of video) if the amount of filtering or correction of the skeletal joint positions determined by the first machine learning technique module  412  exceeds a specified threshold. In some cases, the number of previous video frames that are analyzed may be increased (e.g., from 1 second of video to 2 seconds of video) based on a distance between a user and a camera exceeding a specified threshold. The second machine learning technique module  417  may filter or correct at least some of the coordinates of one or more skeletal joint positions provided by the skeletal joint position module  414  that do not match the skeletal joint positions predicted based on previous video frames by the second machine learning technique module  417 . In this example, the second machine learning technique module  417  determines that the left wrist coordinates (4, 6) do not match the coordinates predicted based on the previous video frames (4, 7) and, as such, corrects the skeletal joint positions to be (4, 7) in the collection of skeletal joint positions. 
     Pose determination module  416  determines the relative positions of each of the skeletal joints received from the second machine learning technique module  417 . For example, the pose determination module  416  determines that the left wrist is lower in the y direction than the right wrist by more than a first specified amount but less than second specified amount. Based on this determination, the pose determination module  416  estimates that the pose depicted in the image corresponds to a first pose. As another example, the pose determination module  416  determines that the left wrist is lower in the y direction than the right wrist by more than the first specified amount and the second specified amount. Based on this determination, the pose determination module  416  estimates that the pose depicted in the image corresponds to a second pose. In some embodiments, the pose determination module  416  searches a database based on the x,y coordinates received from the skeletal joint position module  414  to identify a pose that is within a predetermined threshold of the x,y coordinates. 
     Virtual object mode selection module  419  receives from a client device  102  a selection of a virtualization mode. For example, a user of the AR/VR application  105  may be presented with a list of mode options. In response to receiving a user selection of a given mode option from the list, the given mode is provided to the virtual object mode selection module  419  as the selection of the virtualization mode. The mode options may include a single avatar mimic option, a multiple avatar mimic option, an avatar visualization control option, an avatar follow option, and an avatar virtual world interaction option. The virtualization mode selection controls the way in which the skeletal joint positions of the user&#39;s body affect the skeletal rig of the avatar or the position of the avatar in the display relative to the user. The mode options may include a list of avatars of different forms and types for a user to select, The selected avatar is then used to retrieve the corresponding rig to adjust the skeletal rig according to the user&#39;s pose. 
     The virtual object modification module  418  can adjust the skeletal rig of a given avatar based on the mode selected by the virtual object mode selection module  419  and the pose or skeletal joint positions received from the skeletal joint position module  414  and/or pose determination module  416 . The virtual object modification module  418  adjusts the way in which the avatar is presented in an image, such as by changing the pose, a visual attribute and/or a position of the avatar in the image. The adjusted avatar is provided by the virtual object modification module  418  to the virtual object display module  420 . Virtual object display module  420  combines the adjusted avatar into the received monocular image depicting the user&#39;s body so that both the adjusted avatar and the user are simultaneously presented in an image, The image is provided by the virtual object display module  420  to the client device  102  and can then be sent to another user or stored for later access and display. 
     For example, selection of the single avatar mimic option instructs the virtual object modification module  418  to modify the skeletal rig of the avatar based on the relative distances between the skeletal joints of the user&#39;s body. In this way, the skeletal rig is modified to copy or mimic the pose represented by the user&#39;s body. Specifically, if the left wrist is determined to be offset higher from a neutral position of the left wrist by a certain ratio or percentage in the captured RGB image, the corresponding left wrist of the avatar skeletal rig is raised to a position that is also higher from a neutral position of the left wrist of the avatar by the same ratio or percentage. Each skeletal rig joint is similarly adjusted to copy the relative position of the skeletal joint positions of the body depicted in the image. For example, as shown in  FIG.  7 A , a user&#39;s body  723  is identified and the left wrist joint position of the user&#39;s body  723  is determined to be offset lower than a neutral left wrist joint position by a first amount, the right wrist joint position of the user&#39;s body  723  is determined to be offset higher than the neutral right wrist joint position by a second amount. In an embodiment,  FIG.  5    represents the neutral skeletal joint positions of a user&#39;s body. The skeletal joint positions of a rig of the avatar  734  are similarly adjusted relative to their corresponding neutral positions to be offset by similar first and second amounts. As a result, the avatar  734  appears to mimic or copy the pose represented by the user&#39;s body  723 . 
     As another example, selection of the multiple avatar mimic option instructs the virtual object modification module  418  to modify the skeletal rigs of multiple copies of the avatar based on the relative distances between the skeletal joints of the user&#39;s body. The multiple avatar mimic option causes avatars that are depicted in a first neutral position  1020  as shown in image  1011  of  FIG.  8 A  to animate to a pose corresponding to a user&#39;s body as shown in image  1013 . Specifically, multiple avatars shown in image  1011  may appear in different neutral poses (e.g., crawling on the floor on all four legs). In response to selection of the multiple avatar mimic option, the pose estimation system  124  analyzes a sequence of received monocular RGB images to determine when a pose of the user matches a specified pose. In response to determining that the pose of the user matches the specified pose, the pose estimation system  124  causes all of the avatars to copy the pose of the user (e.g., standing on two legs and positioning left and right arms in a similar pose as a user). The skeletal rigs of the avatars are adjusted in a similar manner as done for single avatar when the single avatar mimic option was selected, Another example is shown in images  1019  and  1015 . In image  1013 , avatars  1030  transition from a neutral position (laying flat on the floor) to a pose position  1032  that mimics the pose of the user (e.g., standing on two legs and positioning left and right arms in a similar pose as a user). When the avatar is a collection of papers, the papers are animated as flying around until the papers are arranged in a certain order in front of or behind the user and in the pose that matches the user&#39;s body pose. 
     As another example, selection of the avatar visualization control option instructs the virtual object modification module  418  to modify a visual attribute of the avatar based on a pose of the user. For example, an avatar is presented on a screen as moving at a given rate from top to bottom or from left to right. Specifically, clouds shown in image  1110  of  FIG.  8 B  can be animated moving down across the screen in front of the user, Based on a pose of the user or based on how slowly or quickly a user transitions from one pose to another, the rate at which the clouds move across the screen can be increased or decreased. As another example, an avatar (e.g., clouds) can be positioned over the user&#39;s hands as shown in image  1112 . When the user changes pose from hands being vertical and straight up in the air to having the hands extending horizontally, the avatar continues to follow the user&#39;s hands and be positioned over the user&#39;s hands but a visual attribute of the avatar changes (e.g., the clouds now present a rainbow above the user from a first cloud positioned over one hand to a second cloud positioned over a second hand) as shown in image  1114 . The change in the visual attribute may also include changing a face depicted on the avatar from smiling to frowning or a color of the avatar can be changed based on the change to the user&#39;s skeletal joint positions. 
     As another example, selection of the avatar virtual world interaction instructs the virtual object modification module  418  to cause the avatar to interact with another virtual object that is in the image. For example, the avatar is displayed in an image that includes virtual objects (e.g., a virtual tree and a virtual apple on the tree). The avatar pose and movement track and mimic skeletal joint positions of the user in way that allows the avatar to interact with the virtual objects. Specifically,  FIG.  8 C  shows a virtual apple  810  and an avatar  812  with arms that have the right and left wrists at a particular position level to each other in the vertical direction. The right hand of the avatar  812  in this position is at a first distance away from the virtual apple  810 . When the user&#39;s body  820  depicted in the image raises the right arm, the avatar&#39;s  812  right arm  816  is also raised relative to the left arm, which also raises the right wrist of the avatar  812 . In this position, the right wrist and elbow of the avatar  812  is higher than the left wrist and elbow, and the right hand of the avatar  812  is at a second distance away from the virtual apple  810 . The distance between the right hand of the avatar  812  and the position of the virtual apple  810  is determined to be less than a threshold, and as a result, the virtual apple  810  becomes detached from the virtual tree  814  and is pinned to the right hand of the avatar  812 . As shown, the virtual apple  810  is no longer presented on the virtual tree  814 , and when the user lowers their arms, the avatar&#39;s left and right arms are also lowered to reveal that the right hand is now holding the virtual apple  810 . In this way, the user can cause the avatar  812  to mimic the user&#39;s pose to interact with one or more virtual objects in an image or video. 
     As another example, selection of the avatar follow option instructs the virtual object modification module  418  to maintain a given distance between the avatar and the user. Specifically, this option causes the avatar to follow the user through a sequence of images. For example, the position of the avatar in the image depicting the user&#39;s body is changed as the user&#39;s body position in the image changes. In particular, if the user moves to the right by a certain amount, the position of the displayed avatar also is moved to the right by the same certain amount,  FIG.  8 C  shows an avatar in a first position  830  relative to the user depicted in the image and at a first distance between the avatar and the user in 2D or 3D space. As the user moves to a second position, the avatar is moved to a second position  832  to maintain the same distance from the user depicted in the image. 
       FIG.  6    is a flowchart illustrating example operations of the body pose estimation system  124  in performing process  600 , according to example embodiments. The process  600  may be embodied in computer-readable instructions for execution by one or more processors such that the operations of the process  600  may be performed in part or in whole by the functional components of the messaging server system  108  and/or AR/VR application  105 ; accordingly, the process  600  is described below by way of example with reference thereto. However, in other embodiments, at least some of the operations of the process  600  may be deployed on various other hardware configurations. The process  600  is therefore not intended to be limited to the messaging server system  108  and can be implemented in whole, or in part, by any other component. Some or all of the operations of process  600  can be in parallel, out of order, or entirely omitted. 
     At operation  601 , the body pose estimation system  124  receives a monocular image that includes a depiction of a body of a user. For example, the first machine learning technique module  412  receives the monocular image  401  depicting a body of a user. The first machine learning technique module  412  extracts one or more features from the image indicating skeletal joints. 
     At operation  602 , the body pose estimation system  124  detects a plurality of skeletal joints of the body depicted in the monocular image  401 . For example, the skeletal joint position module  414  processes the features extracted by the first machine learning technique module  412  to determine positions of a set of skeletal joints. The positions may be determined with respect to neutral positions of each skeletal joint. 
     At operation  603 , the body pose estimation system  124  accesses a video feed comprising a plurality of monocular images received prior to the monocular image. For example, pose determination module  416  accesses 1-2 seconds of video that was received prior to the current image that is processed by the first machine learning technique module  412 . 
     At operation  604 , the body pose estimation system  124  filters, using the video feed, the plurality of skeletal joints of the body detected based on the monocular image. For example, the second machine learning technique module  417  predicts skeletal joint positions for a current frame based on skeletal joint positions in one or more previous frames (e.g., based on movement of the body in the previous 1-2 seconds of video). The second machine learning technique module  417  filters or corrects any mismatches between the skeletal joint positions output by the first machine learning technique module  412  based on the actually received current video frame and the predicted skeletal joint positions output by the second machine learning technique module  417  based on the previous video frames and/or image features of the current frame. 
     At operation  605 , the body pose estimation system  124  determines a pose represented by the body depicted in the monocular image based on the filtered plurality of skeletal joints of the body. 
       FIGS.  7 A-C  show illustrative inputs and outputs of the body pose estimation system  124 , according to example embodiments. The inputs and outputs shown in FIGS,  7 A-C can be implemented by the AR/VR application  105 . In some embodiments, a first user accesses the body pose estimation system  124  to exchange images depicting the user and a corresponding avatar to another user. The first user is presented with a screen  711  that includes an avatar selection region and an option to start exchanging images. After the first user selects the avatar and selects the start option, an instruction is presented to the first user in screen  712  to position the first user a specified distance from the image capture device. For example, the first user is instructed to step back so that the user&#39;s body fits within the image captured by the image capture device. 
     In an embodiment, as shown in the screen  712 , the first user is instructed to step far enough away from the image capture device until a predetermined set of skeletal joints are visible but not all of the skeletal joints are visible. Specifically, the body pose estimation system  124  may only need the wrist positions, elbow positions, shoulder positions and nose position to be visible in an image, but not the leg positions. In some embodiments, the skeletal joints of the first user that are visible in the image cause the same corresponding skeletal joints of the avatar to be adjusted. For example, if only the first user&#39;s arms are visible in the image, then only the avatar&#39;s arms are adjusted to mimic the first user&#39;s arm position. If the user&#39;s entire body is visible including the user&#39;s legs, then the entire avatar rig is adjusted including the avatar legs to mimic the first user&#39;s body pose. 
     The user&#39;s body pose is obtained in screen  713  and the body pose estimation system  124  generates for display in screen  714  an avatar  734  with the same or similar pose as the first user. The first user can speak a predetermined word or, if the user maintains the same pose for a threshold period of time, a screenshot or image is captured that features the user in the pose and the avatar mimicking the user&#39;s pose. 
     As shown in  FIG.  7 B , a screenshot  741  is shown to the first user in screen  721 . A blank space  760  may be included in screen  721  indicating that receipt of a corresponding screenshot from a second user is pending. The first user may select or press on the blank space  760  to cause a list of recipients to be presented in screen  722 . Specifically, screen  722  presents a list of the first user&#39;s friends. The first user may select a given friend “Matt” and the body pose estimation system  124  transmits the screenshot  741  to the selected friend “Matt”. 
     As shown in  FIG.  7 C , the second user  731  follows a similar sequence as the first user to cause a second avatar  732  to mimic a pose of the second user  731  as shown in screen  730 . Particularly, screen  730  is provided on a different mobile device that is associated with the second user  731 . The second user  731  selects the second avatar  732  and is instructed to step back so that the body pose estimation system  124  can estimate the body pose of the user  731  and adjust the selected second avatar  732  to mimic the second user&#39;s body pose. The body pose estimation system  124  captures an image  751  depicting the second user  731  and the second avatar  732  in the given pose and presents the captured image  751  in a screen  740 . The captured image  751  is automatically sent to the first user. The captured image  751  depicting the second user  731  and the second avatar  732  in a given pose is presented together with the screenshot  741  depicting the first user and the first avatar in another pose. 
       FIG.  9    is a block diagram illustrating an example software architecture  906 , which may be used in conjunction with various hardware architectures herein described.  FIG.  9    is a non-limiting example of a software architecture and it will be appreciated that many other architectures may be implemented to facilitate the functionality described herein. The software architecture  906  may execute on hardware such as machine  1000  of  FIG.  10    that includes, among other things, processors  1004 , memory  1014 , and input/output (I/O) components  1018 . A representative hardware layer  952  is illustrated and can represent, for example, the machine  1000  of  FIG.  10   . The representative hardware layer  952  includes a processing unit  954  having associated executable instructions  904 . Executable instructions  904  represent the executable instructions of the software architecture  906 , including implementation of the methods, components, and so forth described herein. The hardware layer  952  also includes memory and/or storage modules memory/storage  956 , which also have executable instructions  904 . The hardware layer  952  may also comprise other hardware  958 . 
     In the example architecture of  FIG.  9   , the software architecture  906  may be conceptualized as a stack of layers where each layer provides particular functionality. For example, the software architecture  906  may include layers such as an operating system  902 , libraries  920 , frameworks/middleware  918 , applications  916 , and a presentation layer  914 . Operationally, the applications  916  and/or other components within the layers may invoke API calls  908  through the software stack and receive messages  912  in response to the API calls  908 . The layers illustrated are representative in nature and not all software architectures have all layers. For example, some mobile or special purpose operating systems may not provide a frameworks/middleware  918 , while others may provide such a layer. Other software architectures may include additional or different layers. 
     The operating system  902  may manage hardware resources and provide common services. The operating system  902  may include, for example, a kernel  922 , services  924 , and drivers  926 . The kernel  922  may act as an abstraction layer between the hardware and the other software layers. For example, the kernel  922  may be responsible for memory management, processor management (e.g., scheduling), component management, networking, security settings, and so on. The services  924  may provide other common services for the other software layers. The drivers  926  are responsible for controlling or interfacing with the underlying hardware. For instance, the drivers  926  include display drivers, camera drivers, Bluetooth® drivers, flash memory drivers, serial communication drivers (e.g., Universal Serial Bus (USB) drivers), Wi-Fi® drivers, audio drivers, power management drivers, and so forth depending on the hardware configuration. 
     The libraries  920  provide a common infrastructure that is used by the applications  916  and/or other components and/or layers. The libraries  920  provide functionality that allows other software components to perform tasks in an easier fashion than to interface directly with the underlying operating system  902  functionality (e.g., kernel  922 , services  924  and/or drivers  926 ). The libraries  920  may include system libraries  944  (e.g., C standard library) that may provide functions such as memory allocation functions, string manipulation functions, mathematical functions, and the like. In addition, the libraries  920  may include API libraries  946  such as media libraries (e.g., libraries to support presentation and manipulation of various media format such as MPREG4, H.264, MP3, AAC, AMR, JPG, PNG), graphics libraries (e.g., an OpenGL framework that may be used to render two-dimensional and three-dimensional in a graphic content on a display), database libraries (e.g., SQLite that may provide various relational database functions), web libraries (e.g., WebKit that may provide web browsing functionality), and the like. The libraries  920  may also include a wide variety of other libraries  948  to provide many other APIs to the applications  916  and other software components/modules. 
     The frameworks/middleware  918  (also sometimes referred to as middleware) provide a higher-level common infrastructure that may be used by the applications  916  and/or other software components/modules. For example, the frameworks/middleware  918  may provide various graphic UI (GUI) functions, high-level resource management, high-level location services, and so forth. The frameworks/middleware  918  may provide a broad spectrum of other APIs that may be utilized by the applications  916  and/or other software components/modules, some of which may be specific to a particular operating system  902  or platform. 
     The applications  916  include built-in applications  938  and/or third-party applications  940 . Examples of representative built-in applications  938  may include, but are not limited to, a contacts application, a browser application, a book reader application, a location application, a media application, a messaging application, and/or a game application. Third-party applications  940  may include an application developed using the ANDROID™ or IOS™ software development kit (SDK) by an entity other than the vendor of the particular platform, and may be mobile software running on a mobile operating system such as IOS™, ANDROID™, WINDOWS® Phone, or other mobile operating systems. The third-party applications  940  may invoke the API calls  908  provided by the mobile operating system (such as operating system  902 ) to facilitate functionality described herein. 
     The applications  916  may use built-in operating system functions (e.g., kernel  922 , services  924 , and/or drivers  926 ), libraries  920 , and frameworks/middleware  918  to create UIs to interact with users of the system. Alternatively, or additionally, in some systems, interactions with a user may occur through a presentation layer, such as presentation layer  914 , In these systems, the application/component “logic” can be separated from the aspects of the application/component that interact with a user. 
       FIG.  10    is a block diagram illustrating components of a machine  1000 , according to some example embodiments, able to read instructions from a machine-readable medium (e.g., a machine-readable storage medium) and perform any one or more of the methodologies discussed herein. Specifically,  FIG.  10    shows a diagrammatic representation of the machine  1000  in the example form of a computer system, within which instructions  1010  (e.g., software, a program, an application, an applet, an app, or other executable code) for causing the machine  1000  to perform any one or more of the methodologies discussed herein may be executed. As such, the instructions  1010  may be used to implement modules or components described herein. The instructions  1010  transform the general, non-programmed machine  1000  into a particular machine  1000  programmed to carry out the described and illustrated functions in the manner described. In alternative embodiments, the machine  1000  operates as a standalone device or may be coupled (e.g., networked) to other machines. In a networked deployment, the machine  1000  may operate in the capacity of a server machine or a client machine in a server-client network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine  1000  may comprise, but not be limited to, a server computer, a client computer, a personal computer (PC), a tablet computer, a laptop computer, a netbook, a set-top box (STB), a personal digital assistant (PDA), an entertainment media system, a cellular telephone, a smart phone, a mobile device, a wearable device (e.g., a smart watch), a smart home device (e.g., a smart appliance), other smart devices, a web appliance, a network router, a network switch, a network bridge, or any machine capable of executing the instructions  1010 , sequentially or otherwise, that specify actions to be taken by machine  1000 . Further, while only a single machine  1000  is illustrated, the term “machine” shall also be taken to include a collection of machines that individually or jointly execute the instructions  1010  to perform any one or more of the methodologies discussed herein. 
     The machine  1000  may include processors  1004 , memory/storage  1006 , and I/O components  1018 , which may be configured to communicate with each other such as via a bus  1002 . In an example embodiment, the processors  1004  (e.g., a central processing unit (CPU), a reduced instruction set computing (RISC) processor, a complex instruction set computing (CISC) processor, a graphics processing unit (GPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a radio-frequency integrated circuit (RFIC), another processor, or any suitable combination thereof) may include, for example, a processor  1008  and a processor  1012  that may execute the instructions  1010 . The term “processor” is intended to include multi-core processors  1004  That may comprise two or more independent processors (sometimes referred to as “cores”) that may execute instructions contemporaneously. Although  FIG.  10    shows multiple processors  1004 , the machine  1000  may include a single processor with a single core, a single processor with multiple cores (e.g., a multi-core processor), multiple processors with a single core, multiple processors with multiple cores, or any combination thereof. 
     The memory/storage  1006  may include a memory  1014 , such as a main memory, or other memory storage, and a storage unit  1016 , both accessible to the processors  1004  such as via the bus  1002 . The storage unit  1016  and memory  1014  store the instructions  1010  embodying any one or more of the methodologies or functions described herein. The instructions  1010  may also reside, completely or partially, within the memory  1014 , within the storage unit  1016 , within at least one of the processors  1004  (e.g., within the processor&#39;s cache memory), or any suitable combination thereof, during execution thereof by the machine  1000 . Accordingly, the memory  1014 , the storage unit  1016 , and the memory of processors  1004  are examples of machine-readable media, 
     The components  1018  may include a wide variety of components to receive input, provide output, produce output, transmit information, exchange information, capture measurements, and so on. The specific I/O components  1018  that are included in a particular machine  1000  will depend on the type of machine. For example, portable machines such as mobile phones will likely include a touch input device or other such input mechanisms, while a headless server machine will likely not include such a touch input device. It will be appreciated that the I/O components  1018  may include many other components that are not shown in  FIG.  10   . The I/O components  1018  are grouped according to functionality merely for simplifying the following discussion and the grouping is in no way limiting. In various example embodiments, the I/O components  1018  may include output components  1026  and input components  1028 . The output components  1026  may include visual components (e.g., a display such as a plasma display panel (PDP), a light emitting diode (LED) display, a liquid crystal display (LCD), a projector, or a cathode ray tube (CRT)), acoustic components (e.g., speakers), haptic components (e.g., a vibratory motor, resistance mechanisms), other signal generators, and so forth. The input components  1028  may include alphanumeric input components (e.g., a keyboard, a touch screen configured to receive alphanumeric input, a photo-optical keyboard, or other alphanumeric input components), point-based input components (e.g., a mouse, a touchpad, a trackball, a joystick, a motion sensor, or other pointing instrument), tactile input components (e.g., a physical button, a touch screen that provides location and/or force of touches or touch gestures, or other tactile input components), audio input components (e.g., a microphone), and the like. 
     In further example embodiments, the I/O components  1018  may include biometric components  1039 , motion components  1034 , environmental components  1036 , or position components  1038  among a wide array of other components. For example, the biometric components  1039  may include components to detect expressions (e.g., hand expressions, facial expressions, vocal expressions, body gestures, or eye tracking), measure biosignals (e.g., blood pressure, heart rate, body temperature, perspiration, or brain waves), identify a person (e.g., voice identification, retinal identification, facial identification, fingerprint identification, or electroencephalogram based identification), and the like. The motion components  1034  may include acceleration sensor components (e.g., accelerometer), gravitation sensor components, rotation sensor components (e.g., gyroscope), and so forth. The environmental components  1036  may include, for example, illumination sensor components (e.g., photometer), temperature sensor components (e.g., one or more thermometer that detect ambient temperature), humidity sensor components, pressure sensor components (e.g., barometer), acoustic sensor components (e.g., one or more microphones that detect background noise), proximity sensor components (e.g., infrared sensors that detect nearby objects), gas sensors (e.g., gas detection sensors to detection concentrations of hazardous gases for safety or to measure pollutants in the atmosphere), or other components that may provide indications, measurements, or signals corresponding to a surrounding physical environment. The position components  1038  may include location sensor components (e.g., a GPS receiver component), altitude sensor components (e.g., altimeters or barometers that detect air pressure from which altitude may be derived), orientation sensor components (e.g., magnetometers), and the like. 
     Communication may be implemented using a wide variety of technologies. The I/O components  1018  may include communication components  1040  operable to couple the machine  1000  to a network  1037  or devices  1029  via coupling  1024  and coupling  1022 , respectively. For example, the communication components  1040  may include a network interface component or other suitable device to interface with the network  1037 . In further examples, communication components  1040  may include wired communication components, wireless communication components, cellular communication components, Near Field Communication (NFC) components, Bluetooth® components (e.g., Bluetooth® Low Energy), Wi-Fi® components, and other communication components to provide communication via other modalities. The devices  1029  may be another machine or any of a wide variety of peripheral devices (e.g., a peripheral device coupled via a USB). 
     Moreover, the communication components  1040  may detect identifiers or include components operable to detect identifiers. For example, the communication components  1040  may include Radio Frequency identification (RFID) tag reader components, NFC smart tag detection components, optical reader components (e.g., an optical sensor to detect one-dimensional bar codes such as Universal Product Code (UPC) bar code, multi-dimensional bar codes such as Quick Response (QR) code, Aztec code, Data Matrix, Dataglyph, MaxiCode, PDF417, Ultra Code, UCC RSS-2D bar code, and other optical codes), or acoustic detection components (e.g., microphones to identify tagged audio signals). In addition, a variety of information may be derived via the communication components  1040 , such as, location via Internet Protocol (IP) geo-location, location via Wi-Fi® signal triangulation, location via detecting a NFC beacon signal that may indicate a particular location, and so forth. 
     GLOSSARY 
     “CARRIER SIGNAL” in this context refers to any intangible medium that is capable of storing, encoding, or carrying transitory or non-transitory instructions for execution by the machine, and includes digital or analog communications signals or other intangible medium to facilitate communication of such instructions. Instructions may be transmitted or received over the network using a transitory or non-transitory transmission medium via a network interface device and using any one of a number of well-known transfer protocols. 
     “CLIENT DEVICE” in this context refers to any machine that interfaces to a communications network to obtain resources from one or more server systems or other client devices. A client device may be, but is not limited to, a mobile phone, desktop computer, laptop, PDAs, smart phones, tablets, ultra books, netbooks, laptops, multi-processor systems, microprocessor-based or programmable consumer electronics, game consoles, set-top boxes, or any other communication device that a user may use to access a network. 
     “COMMUNICATIONS NETWORK” in this context refers to one or more portions of a network that may be an ad hoc network, an intranet, an extranet, a virtual private network (VPN), a local area network (LAN), a wireless LAN (WLAN), a wide area network (WAN), a wireless WAN (WWAN), a metropolitan area network (MAN), the Internet, a portion of the Internet, a portion of the Public Switched Telephone Network (PSTN), a plain old telephone service (POTS) network, a cellular telephone network, a wireless network, a Wi-Fi® network, another type of network, or a combination of two or more such networks. For example, a network or a portion of a network may include a wireless or cellular network and the coupling may be a Code Division Multiple Access (CDMA) connection, a Global System for Mobile communications (GSM) connection, or other type of cellular or wireless coupling. In this example, the coupling may implement any of a variety of types of data transfer technology, such as Single Carrier Radio Transmission Technology (1xRTT), Evolution-Data Optimized (EVDO) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for GSM Evolution (EDGE) technology, third Generation Partnership Project (3GPP) including 3G, fourth generation wireless (4G) networks, Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) standard, others defined by various standard setting organizations, other long range protocols, or other data transfer technology. 
     “EPHEMERAL MESSAGE” in this context refers to a message that is accessible for a time-limited duration. An ephemeral message may be a text, an image, a video, and the like. The access time for the ephemeral message may be set by le message sender. Alternatively, the access time may be a default setting or a setting specified by the recipient. Regardless of the setting technique, the message is transitory. 
     “MACHINE-READABLE MEDIUM” in this context refers to a component, device, or other tangible media able to store instructions and data temporarily or permanently and may include, but is not limited to, random-access memory (RAM), read-only memory (ROM), buffer memory, flash memory, optical media, magnetic media, cache memory, other types of storage (e.g., Erasable Programmable Read-Only Memory (EEPROM)) and/or any suitable combination thereof. The term “machine-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) able to store instructions. The term “machine-readable medium” shall also be taken to include any medium, or combination of multiple media, that is capable of storing instructions (e.g., code) for execution by a machine, such that the instructions, when executed by one or more processors of the machine, cause the machine to perform any one or more of the methodologies described herein. Accordingly, a “machine-readable medium” refers to a single storage apparatus or device, as well as “cloud-based” storage systems or storage networks that include multiple storage apparatus or devices. The term “machine-readable medium” excludes signals per se. 
     “COMPONENT” in this context refers to a device, physical entity, or logic having boundaries defined by function or subroutine calls, branch points, APIs, or other technologies that provide for the partitioning or modularization of particular processing or control functions. Components may be combined via their interfaces with other components to carry out a machine process, A component may be a packaged functional hardware unit designed for use with other components and a part of a program that usually performs a particular function of related functions. Components may constitute either software components (e.g., code embodied on a machine-readable medium) or hardware components. A “hardware component” is a tangible unit capable of performing certain operations and may be configured or arranged in a certain physical manner. In various example embodiments, one or more computer systems (e.g., a standalone computer system, a client computer system, or a server computer system) or one or more hardware components of a computer system (e.g., a processor or a group of processors) may be configured by software (e.g., an application or application portion) as a hardware component that operates to perform certain operations as described herein. 
     A hardware component may also be implemented mechanically, electronically, or any suitable combination thereof. For example, a hardware component may include dedicated circuitry or logic that is permanently configured to perform certain operations. A hardware component may be a special-purpose processor, such as a Field-Programmable Gate Array (FPGA) or an ASIC. A hardware component may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations. For example, a hardware component may include software executed by a general-purpose processor or other programmable processor. Once configured by such software, hardware components become specific machines (or specific components of a machine) uniquely tailored to perform the configured functions and are no longer general-purpose processors. It will be appreciated that the decision to implement a hardware component mechanically, in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations. Accordingly, the phrase “hardware component”(or “hardware-implemented component”) should be understood to encompass a tangible entity, be that an entity that is physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a certain manner or to perform certain operations described herein. Considering embodiments in which hardware components are temporarily configured (e.g., programmed), each of the hardware components need not be configured or instantiated at any one instance in time. For example, where a hardware component comprises a general-purpose processor configured by software to become a special-purpose processor, the general-purpose processor may be configured as respectively different special-purpose processors (e.g., comprising different hardware components) at different times. Software accordingly configures a particular processor or processors, for example, to constitute a particular hardware component at one instance of time and to constitute a different hardware component at a different instance of time. 
     Hardware components can provide information to, and receive information from, other hardware components. Accordingly, the described hardware components may be regarded as being communicatively coupled. Where multiple hardware components exist contemporaneously, communications may be achieved through signal transmission (e.g., over appropriate circuits and buses) between or among two or more of the hardware components. In embodiments in which multiple hardware components are configured or instantiated at different times, communications between such hardware components may be achieved, for example, through the storage and retrieval of information in memory structures to which the multiple hardware components have access. For example, one hardware component may perform an operation and store the output of that operation in a memory device to which it is communicatively coupled. A further hardware component may then, at a later time, access the memory device to retrieve and process the stored output. 
     Hardware components may also initiate communications with input or output devices, and can operate on a resource (e.g., a collection of information). The various operations of example methods described herein may be performed, at least partially, by one or more processors that are temporarily configured (e.g., by software) or permanently configured to perform the relevant operations. Whether temporarily or permanently configured, such processors may constitute processor-implemented components that operate to perform one or more operations or functions described herein, As used herein, “processor-implemented component” refers to a hardware component implemented using one or more processors. Similarly, the methods described herein may be at least partially processor-implemented, with a particular processor or processors being an example of hardware. For example, at least some of the operations of a method may be performed by one or more processors or processor-implemented components. Moreover, the one or more processors may also operate to support performance of the relevant operations in a “cloud computing” environment or as a “software as a service” (SaaS). For example, at least some of the operations may be performed by a group of computers (as examples of machines including processors), with these operations being accessible via a network (e.g., the Internet) and via one or more appropriate interfaces (e.g., an API). The performance of certain of the operations may be distributed among the processors, not only residing within a single machine, but deployed across a number of machines. In some example embodiments, the processors or processor-implemented components may be located in a single geographic location (e.g., within a home environment, an office environment, or a server farm). In other example embodiments, the processors or processor-implemented components may be distributed across a number of geographic locations. 
     “PROCESSOR” in this context refers to any circuit or virtual circuit (a physical circuit emulated by logic executing on an actual processor) that manipulates data values according to control signals (e.g., “commands,” “op codes,” “machine code,”, etc) and which produces corresponding output signals that are applied to operate a machine. A processor may, for example, be a Central Processing Unit (CPU), a Reduced Instruction Set Computing (RISC) processor, a Complex Instruction Set Computing (CISC) processor, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), an ASIC, a Radio-Frequency Integrated Circuit (RFIC) or any combination thereof. A processor may further be a multi-core processor having two or more independent processors (sometimes referred to as “cores”) that may execute instructions contemporaneously. 
     “TIMESTAMP” in this context refers to a sequence of characters or encoded information identifying when a certain event occurred, for example giving date and time of day, sometimes accurate to a small fraction of a second. 
     Changes and modifications may be made to the disclosed embodiments without departing from the scope of the present disclosure. These and other changes or modifications are intended to be included within the scope of the present disclosure, as expressed in the following claims.