Abstract:
Systems and methods to perform privacy-aware computer-vision-based human activity monitoring with real-time haptic feedback. The system and method described in this disclosure employing a registration process for consenting human subjects before their activities are monitored. The registration process involves the corroboration of human motion captured in different modalities, i.e., computer-vision-based via the programmable computer-vision-based motion sensor and accelerometer-based via the wearable device. The tracked human activities are assessed in real-time and upon detection of activities that violated predefined rules, haptic feedback is delivered in real-time to the tracked human subject via the wearable device worn by the caregiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit to U.S. Provisional Patent Application No. 62/183,515, filed Jun. 23, 2015, which is hereby incorporated by reference herein in its entirety. 
     
    
     INTRODUCTION 
       [0002]    The present disclosure generally relates to the field of motion tracking of users. More specifically, the present disclosure is directed to systems and methods of utilizing motion sensors, wearable devices, and smart phones, to perform human motion tracking with real-time haptic feedback, such as an alarm or a tactile indication based on tracked activities of the user. The system may be designed to improve job performance of a user, reduce likelihood of injuries, and/or to alert a user of an otherwise improper movement and/or posture. The disclosure additionally relates to methods and systems to respect privacy concerns of other individuals that are proximate to the tracked user, thereby avoiding improper data collection of data due to the privacy concern and governmental regulations. The disclosure further relates to novel methods for registering a user utilizing motion detection in conjunction with other technologies. Systems and method disclosed herein allow for real-time feedback to a user so that the user may be warned of potential injuries and/or other improper activities before they occur. 
       BACKGROUND 
       [0003]    Computer-vision based human motion tracking has undergone intensive research for the past several decades. Today, inexpensive portable computer-vision based motion sensors can now be used to accurately track human motions. Such technology could includes benefits. For example, many of the work-related injuries could have been prevented or minimized if the workers follow best practices (such as using proper lifting equipment and following proper gaits and postures). 
         [0004]    Computer-vision based human motion tracking technology could be used to track workers&#39; activities and detect violations of best practices. A system based on the technology could provide instant alerts, for example, via vibration and message notification on the display of the wearable device worn by the worker in this case, and therefore, could potentially reduce the occurrences of such violations in the future. 
         [0005]    Unfortunately, such computer-vision based technology can rarely used in workplaces, particularly in venues such as hospitals and nursing homes, to monitor workers&#39; activities because of privacy-related governmental regulations such as such as the Health Insurance Portability and Accountability Act of 1996 (HIPAA). Even if a worker has consented to being monitored, a vision-based motion sensor cannot guarantee that only the consenting person is tracked due to the indiscriminative nature of the computer-vision technology itself: anyone in its view might be automatically tracked. 
         [0006]    Inertial sensor-based devices, such as wearable devices, can be used to track some form of human activity, such as steps taken, while preserving the privacy of those who are not wearing such devices. However, only a small set of such devices cannot be used to accurately track more sophisticated human activities that involve multiple joints and where trajectory of the movement matters. Furthermore, although multi-modal motion tracking based on both computer-vision and inertial sensors has been explored previously, it is used solely used to improve the accuracy of the motion tracking itself, not to enable the tracking of specific human subjects. 
         [0007]    What is needed is a system and method that enables the monitoring of only consenting human subjects, which preserves the privacy of those who have not consented. 
       SUMMARY 
       [0008]    Systems and methods to facilitate privacy-aware human activity monitoring are provided herein. A consenting human subject will be required to wear a programmable wearable device, such as a smart watch. One or more programmable computer-vision based motion sensors, such as a Microsoft Kinect sensor, will be used to track the activities of the consenting human subject. Discriminative tracking is achieved by a registration mechanism executed when the human subject enters the view of a camera and periodically while the subject stays in the view. The registration mechanism identifies the consenting subject in the view of the camera by matching a predefined gesture that is simultaneously captured by both the wearable device and the computer-vision based motion sensor. After the registration step, only the consenting subject is tracked and the motion data collected for all non-consenting subjects will be discarded immediately. Before the initial registration step, a frame supplied by the motion sensor is dropped immediately, or only a finite set of most recent frames are cached for the purpose of registration. 
         [0009]    The system has also mechanisms that remind and guide the consenting human subject to register (in case he/she forgets to register) and to register properly (in case he/she did not come to the view of the motion sensor). The system sends alerts to the consenting human subject upon detection of violations of best practices via the wearable device worn by the subject using haptic feedback (i.e., vibrations) and text-based notifications (on the screen display of the wearable device). 
         [0010]    In one aspect, a system to monitor only consenting human subjects is provided and includes one or more computer-vision based programmable motion sensors, one or more programmable wearable devices, one or more smart phones, and one or more processors. The one or more computer-vision based programmable motion sensors identify a consenting human subject that is wearing one of the programmable wearable devices and identify a non-consenting human subject. The one or more processors ignore the non-consenting human subject and monitor the consenting human subject for violations of best practices and provide violation alerts to the consenting human subject when a violation is detected. Such a system may also include a wristband having a reflective material which is worn by consenting human subjects and the one or more computer-vision based programmable motion sensors identify the human subject by identifying the wristband. 
         [0011]    In another aspect, a system for alerting a person of improper actions is provided and includes a plurality of motion sensors that communicate to send a stream of images of a viewing area of the motion sensors, a wearable device that is associated with the user and capable of sending and receiving a signal indicative of the person in a field of view of the motion sensors, and a central processor that receives the signal from the wearable device indicating the presence of the person in the viewing area, monitors the images from the motion sensors to identify the person, tracks one or more orientations of the person, identifies an improper orientation, and sends a warning signal based on the identified improper orientation. 
         [0012]    In still another aspect, a method for identifying a consenting human subject is provided and includes recognizing via one or more sensors a predefined gesture performed by a consenting human subject who is wearing a detectable wearable device, providing a registration request including an indication that the consenting human subject has interest in being monitored, receiving vision-based motion data from one or more motion sensors, recognizing a gesture by the consenting human subject from the vision-based motion data, and providing a confirmation message to the consenting human subject via haptic feedback a short message displayed on the wearable device. The gesture may be a tapping motion on the wearable device by one or more fingers of the opposite hand which is detected by one or more accelerometers in the wearable device and compared against a predefined configurable threshold. 
         [0013]    In yet another aspect, a method for alerting a person of improper actions is provided and includes receiving from one or more user devices an indication that a user is present in a viewing area, activating in response to the indication one or more motion sensors to monitor the viewing area, receiving the image data from the one or more sensors, analyzing the image data to identify the user, tracking the movements of the user based on the image data, identifying a posture that is indicative of potential harm to the user, and sending a warning signal to one or more alert systems. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is an exemplary environment for an implementation of the present invention. 
           [0015]      FIG. 2  is a diagram illustrating the interaction pattern between different software components in accordance with one embodiment of the present invention. 
           [0016]      FIG. 3  is flow chart illustrating the registration mechanism components in accordance with one embodiment of the present invention. 
           [0017]      FIG. 4  is a flow chart illustrating the re-synchronization mechanism when the system is in a registered state for a consenting human subject in accordance with one embodiment of the present invention. 
           [0018]      FIG. 5  is a diagram illustrating different types of notifications generated by the system in accordance with one embodiment of the present invention. 
           [0019]      FIG. 6  is a diagram illustrating an example gesture that could be used to register a human subject to the system in accordance with one embodiment of the present invention. 
           [0020]      FIG. 7  is a diagram illustrating an alternative method for automated registration without using any gesture. 
           [0021]      FIG. 8  is a diagram illustrating how to anonymize non-consenting human subjects in color frames in accordance with one embodiment of the present invention. 
           [0022]      FIG. 9  is a block diagram of an example environment is provided in which privacy-aware motion tracking may be performed. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    This Detailed Description merely describes exemplary embodiments of the invention and is not intended to limit the scope of the claims in any way. Indeed, the invention as claimed is broader than the exemplary embodiments, and the terms used in the claims have their full ordinary meaning, unless an express definition is provided herein. 
         [0024]    Referring to  FIG. 9 , a block diagram of an example environment is provided in which privacy-aware motion tracking may be performed. The environment includes a network communication  901 . The communication network  901  facilitates communication between the various components in the environment. In some implementations, the communication network  901  may include the Internet, one or more intranets, and/or one or more bus subsystems. The communication network  901  may optionally utilize one or more standard communications technologies, protocols, and/or inter-process communication techniques. For example, network communication  901  may include communication via Wi-Fi, BLUETOOTH, RF, and/or one or more alternate communication protocols. The example environment also includes personal device  905 , which may include, for example, a cellular phone, a smart phone, a tablet computing device, and/or one or more wearable devices (e.g., a fitness tracking device, a smart watch, an electronic tag). The personal device  905  may include one or more movement sensors  906  that may record movements of a user that is associated with the wearable device  906 . For example, movement sensors  906  may include accelerometers, gyroscopes, location sensors, and/or one or more other sensors that can detect movements of the associated user. Personal device  905  may additionally be executing one or more applications  907 . Applications  907  may include one or more applications associated with executing, analyzing, processing, and/or transmitting data from movement sensors  906 . Additionally or alternatively, applications  907  may include one or more components of the system described herein. For example, one or more of the components described as components of system  920  may be executing, wholly or in part, on personal device  905 . 
         [0025]    Motion sensors  910  include one or more components that transmit image data to one or more components. In some implementations, motion sensors  910  may analyze image data to identify objects that are in proximity to the motion sensor  910 . For example, referring to  FIG. 1 , motion sensors  102  and  104  may each emit a signal to identify objects within the view of the sensors. For example, an image of worker  130  and/or one or more objects nearby worker  130  may be identified by sensors  102  and  104  via, for example, image data, infrared data, and/or one or more other visual image identification protocols. 
         [0026]    Referring again to  FIG. 9 , the environment includes a database  915 . Database  915  may store information related to one or more users of the system  920 . For example, database  915  may include login information, user biometrics (e.g., body size, joint locations, facial feature information), and/or other user data. In some implementations, one or more user records in database  915  may be associated with additional information related to past sessions of the user interacting with the system. For example, a record for a user may include information related to movements that were observed by motion sensors  910  in previous sessions and/or movements of the user that were identified by movement sensors  906 . 
         [0027]    System  920  includes one or more components that work in conjunction with other components of the example environment to identify a user that is visible to motion sensors and track movements of the user in a privacy-aware environment. In some implementations, one or more of the component and/or steps performed by system  920  may additionally and/or alternatively be performed on one or more other computing devices. For example, one or more of the components illustrated as part of system,  920  may be performed by personal device  905 , motion sensors  910 , and/or one or more other computing devices (such as computer  120  of  FIG. 1 ). 
         [0028]    Sensor engine  924  may receive information related to the motion sensors  910  and analyze and/or otherwise process the motion sensor information. For example, sensor engine  924  may receive sensor information indicative of one or more objects that are moving within the proximate view of one or more motion sensors  910 . The sensor engine  924  may determine, based on one or more methods, which objects that are identifiable from the data are users of the system and then track those users. In some implementations, sensor engine  924  may utilize information from one or more other components to determine which moving objects are users. For example, sensor engine  924  may additionally utilize a signal from a personal device  905  to determine that a user is present, where the user is present, and/or an indication of one or more movements that are currently being performed by the user (that may be detected via, for example, a movement sensor  906 ). 
         [0029]    Registration monitor  922  may receive image information from the sensor engine  924  that indicates that a user is present for identification. In some implementations, the user may first activate the personal device  905  to send a signal to sensor engine  924  indicating that the associated user desires to be tracked by the system. The sensor engine  924  may then monitor the images being received from the motion sensors  910  to start to identify the user. In some implementations, the user may be required to perform a particular movement to signal to the sensor engine  924  which is the user from a plurality of potential objects that may be the user. For example, the user may hold his hands up in a particular position and/or make some other bodily movement that may be assist the sensor engine  924  in identifying the user. 
         [0030]    The registration monitor  922  may identify information related to the now-tracked user in database  915 . The registration monitor  922  may identify, for example, the user&#39;s name, personal information, information regarding previous tracking sessions, biometric information, and/or other information that may be utilized in conjunction with monitoring the user&#39;s movements during the session. In some implementations, the signal from the personal device  905  may indicate which user is being tracked and that information may be utilized by the registration monitor  922  to identify user information in database  915 . In some implementations, registration monitor  922  may utilize image information from the sensor engine  924  to identify potential users from the image data, and then utilize defining characteristics of the user (e.g., biometrics) to identify the user. 
         [0031]    Metric recorder  928  may utilize the motion sensor information related to a tracked user to determine the movements of the user. In some implementations, the metric recorder  928  will only track the movements of users who have been registered with the system. For example, referring to  FIG. 1 , worker  130  and worker  140  may be tracked by the system and metric recorder  928  may record and monitor their movements, whereas patient  150  may not be monitored because the patient  150  has not registered with the system. In this way, the system  920  may monitor movements of some objects without invading privacy of any users who do not wish to or have not consented to being monitored. 
         [0032]    Metric recorder  928  may utilize motion information to determine the movements of users. For example, metric recorder  928  may identify the limbs of the monitored user, the joint locations of the monitored users, the location of key body parts of the user, the location of the user in a room, and/or other information related to the movements of the tracked users. For example, the worker  130  may start from a first position, approach the patient  150 , and move the patient  150  in some way. Metric recorder  928  may identify each of these movements based on the image information. 
         [0033]    Alert engine  926  may receive metrics of the movements of users from metric recorder  928  and may analyze the movements to determine if the user has performed, in the process of performing, and/or is about to perform an improper movement. For example, worker  130  may squat down to pick up a large object. Metric recorder  928  may identify the movements of the user and transmit the movement information to alert engine  926 . If the alert engine  926  identifies that the user is in a position that may result in an injury, the alert engine  926  may produce an alert signal. The alert signal may result in, for example, a haptic alarm on the personal device  905 , an audible alarm, a visual warning, and/or one or more other types of alarms. 
         [0034]      FIGS. 1 through 8  illustrate additional implementations of the system. In some implementations, components similar or identical to components of the system illustrated in  FIG. 9  may be utilized in  FIGS. 1 to 8 . In some implementations, one or more processes and/or steps may be performed by an alternate component and/or hardware system. The embodiments described herein are merely an additional explanation of the present invention and may be utilized in conjunction with or as an alternative to any component of  FIG. 9 . 
         [0035]      FIG. 1  illustrates a system according to one embodiment of the present invention. The system comprises one or more computer-vision based motion tracking sensors  102  and  104  (which may share one or more characteristics with motion sensors  1010 ), one or more human subjects  130  and  140  that have been consented to being monitored, one or more wearable devices  106  and  108  worn by consenting human subjects (which may share one or more characteristics with personal device  1005 ), one or more smart phones  110  (which may execute one or more components of personal device  1005  and/or system  1020 ), and a computer  120  (which may execute one or more of the components of system  1020 ). Non-consenting human subjects  150  might be present in the view of the vision-based motion sensors  102  and  104 . The wearable devices  106  and  108  communicate with the smart phone  110  via low-energy Bluetooth  160  and  170 , and the smart phone  110  relays the messages received to the computer  120  via 802.11 (wifi) wireless communication protocols  180 . 
         [0036]      FIG. 2  illustrates the software components in the system and how they interact with each other. A wearable application  210  runs on each wearable device  270 . The wearable application  210  has two-way communications with a mobile application  220  running on the smart phone  260 . The mobile application  220  has two-way communications with the server application  296  running on the computer  250 . The server application  296  receives motion-sensing data collected by the motion sensor  230  attached to the computer  250 , such as the skeleton stream  240 . Typically, a programmable computer-vision based motion sensor provides at least four types of frames to the server application, including the color frames showing color images of its view, infrared (IR) frames showing the images collected by its IR camera, depth frames that contains the distance of each pixel from the sensor, and the skeleton (also referred to as body) frames that contains the skeleton joints of each tracked human subject. The number of consenting human subjects can be tracked by the system is limited by the type of motion sensors and the number of motion sensors used. 
         [0037]    The communication loop between the three main software components  210 ,  220 , and  296  is driven by the wearable application  210 . During registration, the wearable application  210  sends a registration request message  280  to the mobile application  220  upon detection of a predefined gesture using the accelerometers equipped with the wearable device  270 . The mobile application  220  would then relay the registration request in message  292  to the server application  296 . The server application  296  then examines the next frame or the cached set of frames  240  to determine whether or not the corresponding gesture is performed by any of the fully tracked users. If one and only one user is detected, the registration succeeds and the server application  296  labels that particular user as being monitored from now on. The status of the registration will be included in messages  294  and  290 . Upon receiving message  290 , the wearable application  210  generates an appropriate vibration and short message for display according to the result of the registration request. 
         [0038]    The server application  296  continuously monitors all registered human subjects and logs detected violations of best practices including the nature of the violation and the timestamp of the incidence in its own durable storage as well as its memory (RAM). The server application  296  may additionally monitor other information regarding registered human subjects, such as the duration, starting and ending timestamps, of each registration session, as well as the number of activities that have been carried out successfully for each registered subject. 
         [0039]    Each tracked user by the motion sensor is assigned a unique user identifier. When a user leaves the view of the motion sensor, the corresponding skeleton (or body) cedes to exist in the depth and skeleton (or body) frames. Therefore, the monitoring would naturally stop when the registered user leaves the view of the motion sensor. If the previously registered user comes back to the view of the motion sensor, the motion sensor assigns a new user identifier to the user, thereby necessitating a new round of registration before the user can be monitored again. 
         [0040]    After a human subject successfully registers with the system, the communication loops continues to operate. The wearable application  210  periodically polls the mobile application  220 , which in turn queries the server application  296 . Upon receiving message  292 , the server application returns the status of the subject. In turn, the mobile application  220  relays the response to the wearable application  210  in the message  290 . If a violation is detected, the wearable application  270  generates a vibration and displays a corresponding message on the display of the wearable device, if one is available. 
         [0041]      FIG. 3  illustrates a flow chart of an exemplary registration method. In some embodiments, the wearable application  210  (in  FIG. 2 ) drives the registration process. The wearable application  210  (in  FIG. 2 ) may receive a notification when the wearable device  270  is able to establish a communication connection to the smart phone  260  (in  FIG. 2 ). The wearable application  210  (in  FIG. 2 ) may then launch the registration method described in  FIG. 3  when it learns that the wearable device is in the connected state  302 . The wearable application  210  (in  FIG. 2 ) receives accelerometer-related data and events from the wearable device  270 . Based on the collected information, the wearable application may detect whether or not a predefined gesture has happened. If such a gesture is detected  304 , the wearable application  210  (in  FIG. 2 ) may send a registration request to the server application  296  (in  FIG. 2 ) via the mobile application  220  (in  FIG. 2 ). The server application then tries to detect the corresponding gesture based on the next frame or the cached frames. If one is detected  306 , in step  320 , the server application  296  (in  FIG. 2 ) may generate a corresponding response and send the response to the wearable application  210  (in  FIG. 2 ) via the mobile application  220  (in  FIG. 2 ). 
         [0042]    If the server application  296  (in  FIG. 2 ) fails to detect the corresponding gesture, or it detects two of more users in its view that have performed the same gesture, the registration may fail and a failure notification may be sent to the wearable application  210  (in  FIG. 2 ) in step  312 . 
         [0043]    In some instances, a consenting human subject may forget to register upon arriving at a predefined location. In those instances, the wearable application  210  (in  FIG. 2 ) may take a timestamp when it learns that the wearable device  270  (in  FIG. 2 ) has connected to the smart phone  260  (in  FIG. 2 ), and furthermore maintain a configurable threshold for registration. Periodically, the wearable application  210  (in  FIG. 2 ) may monitor the time that has elapsed before the registration is completed. If the time elapsed since an initial communication connection exceeds the threshold in step  308 , the wearable application  210  (in  FIG. 2 ) may generate a notification in the form of a vibration and/or a short message for display in step  310 . 
         [0044]      FIG. 4  illustrates a flow chart of a method to periodically re-register a consenting human subject (referred to as re-synchronization). Additionally, the flow chart illustrates steps that may be utilized when a registered subject leaves the view of the vision-based motion sensor. When a human subject has registered  402 , the wearable device  210  (in  FIG. 2 ) periodically monitors to determine whether re-registration is required (step  404 ). The wearable device  210  (in  FIG. 2 ) may record a timestamp in memory each time the subject successfully registers. The wearable application  210  (in  FIG. 2 ) maintains another configurable parameter as the threshold for re-registration. If the time since the last recorded timestamp satisfies the registration threshold parameter at re-registration  404 , the wearable application  210  (in  FIG. 2 ) monitors for the subject to perform a predefined gesture. If the requisite gesture is detected and it is successful  406 , the timestamp is updated and a confirmation is generated  408 . Otherwise, a notification for re-registration is generated  410 . 
         [0045]    The server application  296  (in  FIG. 2 ) monitors whether or not the subject is still in its view  412 . If the registered human subject is no longer in its view, the server application  296  (in  FIG. 2 ) logs the event. The wearable application  210  (in  FIG. 2 ) would learn this status change the next time it polls the server application  296  (in  FIG. 2 ). It subsequently generates a notification for the subject to register again  414  when the wearable device is connected to the smart phone. 
         [0046]      FIG. 5  shows three types of haptic feedback  510  that may be used in the system in one embodiment of the present invention. A programmable wearable device typically offers different levels of haptic feedback in terms of the duration and/or intensity of generated vibrations. For example, if such a device offers three levels of haptic feedback, as does in the Pebble Smart Watch, the system may use a short vibration  522  for notification of successful registration  520 , a normal vibration  532  for notification for a human subject to register or re-register  530 , and a long vibration  542  for notification of a violation of best practices. Also, for example, if a wearable device has two levels of haptic feedback, then notification  520  and notification  530  could both use the same shorter vibration and the long vibration may be utilized for notification  540 . 
         [0047]      FIG. 6  illustrates one particular gesture that can be used for registration. Other gestures could be designed for the purpose of registration. To register, a human subject could tap his or her wearable device  610  worn on his or her left or right wrist using the finger of the other hand. The tapping event may be detected by accelerometers in the wearable device  620  and/or via one or more other sensors. When a subject begins to motion to tap his or her wearable device, the distance between the left and right wrists  630  and  640  will decrease. In some embodiments, the computer-vision based motion sensor could detect this gesture by determining the wrist-to-wrist distance with respect to a configurable threshold parameter. If the wrist-to-wrist distance is smaller than a threshold value  650 , then the vision-based motion sensor detects the tapping gesture  660  using a single frame. In instances where another non-consenting human subject is in the view of the motion sensor, he or she might also satisfy the wrist-to-wrist distance criteria (i.e., the wrists of the non-consenting human may be close together, but not intended to be positioned for registration purposes). As the result, the motion sensor might find that two or more users have performed the tapping gesture. In this case, the registration would fail because the motion sensor would be unable to determine which of the detected humans has consented to monitoring. 
         [0048]    In some instances, the consenting subject (i.e., the one intending to register) may be occluded by a non-consenting subject, and the wrong subject may be registered. To minimize the probability of this from happening, the entire tapping gesture could be recognized by the server application. The tapping gesture involves two monotonic movement segments: (1) the wrist-to-wrist distance is reduced from a value larger than a predefined value down to below a threshold value as the wearer moves one hand closer to the other to tap; and (2) after a momentary pause at a minimum wrist-to-wrist distance (for tapping), the wrist-to-wrist distance increases beyond a predefined value. To capture the entire tapping gesture, a set of frames that expand the duration of the gesture may be cached. As an example, if the motion sensor has a frame rate of 30 per second and the gesture takes 2 seconds, then 60 frames will need to be cached. 
         [0049]      FIG. 7  illustrates an alternative method for registration. In this method, consenting human subject wears a wristband that includes an infrared reflective material  720  in addition to a wearable device  710 . In some embodiments, only consenting human subjects may wear such a wristband. The computer-vision based motion sensor performs object recognition for the wristband in every depth frame received. If such a wristband is detected, then the user who wears the wristband is automatically registered and monitored. The programmable wearable device  710  is still needed for driving the monitoring system and for user notification of violations of best practices. 
         [0050]      FIG. 8  illustrates how to anonymize non-consenting human subjects in color frames in accordance with one embodiment of the present invention. Each tracked user is assigned a unique user identifier, such as user # 1   840  and user # 2   850 . The user identifier is encoded in both the skeleton (or body) frame  810  and the corresponding depth frame  820 . User identifier information is not included in color frames  830 . However, in the depth frame  820 , every pixel contains user identifier information  840  and  850 . If a pixel does not belong to any user tracked by the motion sensor, it may include a predefined value indicating that the pixel belongs to the profile of a non-tracked individual. Furthermore, the depth pixel position can be mapped to that of the color frame. Based on this mapping, one can associate each color pixel that is within the range of the depth frame (because the color frame might be set to a higher resolution than that of the depth frame) to any user tracked by the motion sensor. One can further identify which color pixel belongs to the registered human subject. With such identification information, color pixels that belong to non-consenting human subjects  840  can be rendered a monotonic color, or any desirable color pattern, while color pixels that belong to the registered human subject  850  can keep the original colors. 
         [0051]    While particular embodiments and applications of the present invention have been illustrated and described herein, it is to be understood that the invention is not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatuses of the present invention without departing from the spirit and scope of the invention as it is defined in the appended claims.