Abstract:
The present invention relates to computer capture of object motion. More specifically, embodiments of the present invention relate to capturing of facial movement or performance of an actor. Embodiments of the present invention provide a head-mounted camera system that allows the movements of an actor&#39;s face to be captured separately from, but simultaneously with, the movements of the actor&#39;s body. In some embodiments of the present invention, a method of motion capture of an actor&#39;s performance is provided. A self-contained system is provided for recording the data, which is free of tethers or other hard-wiring, is remotely operated by a motion-capture team, without any intervention by the actor wearing the device. Embodiments of the present invention also provide a method of validating that usable data is being acquired and recorded by the remote system.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present invention is related to U.S. application No. ______, filed Sep. 29, 2008, Attorney Docket No. 027274-000100US entitled “ACTOR-MOUNTED MOTION CAPTURE CAMERA”, to U.S. application No. ______, filed Sep. 29, 2008, Attorney Docket No. 027274-001300US entitled “MOUNTING AND BRACKET FOR AN ACTOR-MOUNTED MOTION CAPTURE CAMERA SYSTEM”, and to U.S. application No. ______, filed Sep. 29, 2008, Attorney Docket No. 027274-001800US entitled “METHODS AND APPARATUS FOR DOT MARKER MATCHING”. These applications are incorporated by reference, for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to computer capture of object motion. More specifically, embodiments of the present invention relate to capturing of facial movement or performance of an actor. 
         [0003]    Traditional computer animation of objects is determined by users known as animators. These animators are skilled artists who would specify movement of objects, such as people, within a computer environment. As a model for human movement, many animators often referred to how they moved, through the use of mirrors, video cameras, or the like. 
         [0004]    Animation has also been based more directly upon physical movement of actors. This animation is known in the film industry as motion-capture or performance capture. In such cases, an actor is equipped with a suit with a number of markers, and as the actor moves, a number of cameras track the positions of the markers in space. This technique allows the actor&#39;s movements and expressions to be captured, and the movements and expressions can then be manipulated in a digital environment to produce whatever animation is desired. 
         [0005]    One difficulty with prior motion capture techniques is that they often fail to produce high quality results with respect to capturing facial motion. Facial motion is very detailed and capturing the fine movements of an actor, or failing to do so, has a significant impact on the end product. Simply scaling current techniques to capture more markers is not practical as the data management, storage and processing capabilities are barely able to handle current marker density. High fidelity motion-capture, particularly video based data of the face, generates large volumes of digital data. Further, the fine-grain motion of the face is often lost in the noise inherent in stationary camera motion capture systems. 
         [0006]    One solution to this problem has been to use separate and non-simultaneous face and body motion capture. A drawback to this approach is that it requires substantial duplication of effort by the actor and the crew, as each scene must be performed and captured at least twice. Another difficulty arises in that the actor&#39;s second performance may not correspond closely enough with the first, which affects the appearance and quality of the end result by making the correlation of the data from the multiple performances difficult. 
         [0007]    Another solution is a simultaneous face and body motion capture using fixed position cameras and/or movable platform mounted cameras  100 , such as is shown in  FIG. 1 . Capturing detailed facial motion generally involves tracking a large number of markers  140  placed on the actors&#39; faces throughout a fixed capture volume  120 , which is defined by the stationary motion capture cameras. In addition to the facial markers  140 , markers  130  are placed on the actors&#39; bodies, averaging a total of about  250  marker points per actor. For a scene with several actors, the total number of markers may be well over a thousand. 
         [0008]    This abundance of markers creates a correspondingly large amount of data to be processed. It is sometimes difficult to accurately identify the markers associated with each actor  110  in a scene and obtaining sufficient resolution of the closely spaced facial markers  140  presents further complexities. In addition, because data from both the face and the body is captured together, it is necessary to process all of the data in order to determine whether sufficient facial motion data was recorded. Similarly, feedback cannot be given to the director or actor regarding the overall movement in the scene until all of the data has been processed. Waiting for the combined facial and body data to be processed significantly increases the delay between the initial capture and any reshoots that are necessary, likely causing production and scheduling problems, as well as increasing costs. 
         [0009]    Prior head-mounted cameras have had several obstacles, such as interfering with the performance of the actor, either due to the discomfort of wearing the device or from the mere presence of the device in front of the actor&#39;s eyes or mouth, or failing to capture images of an adequate portion of the face for quality reconstruction. In addition, prior head-mounted cameras experience difficulty in maintaining position or in repositioning the camera. Other drawbacks to previous solutions include limitations on the actors&#39; movements due to tethers or hard-wiring of a motion capture camera, as well as requiring operational intervention by the actor wearing the device. 
         [0010]    Accordingly, an improved system for capturing and processing facial motions of an actor that increases accuracy while minimizing processing time and difficulty is desired. In addition, it would be desirable to provide a process for confirming that usable data is being acquired and recorded during the acquisition. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The present invention relates to computer capture of object motion. More specifically, embodiments of the present invention relate to capturing of facial movement or performance of an actor. Embodiments of the present invention provide a head-mounted camera system that allows the movements of an actor&#39;s face to be captured separately from, but simultaneously with, the movements of the actor&#39;s body. In some embodiments of the present invention, a method of motion capture of an actor&#39;s performance is provided. A self-contained system is provided for recording the data, which is free of tethers or other hard-wiring, is remotely operated by a motion-capture team, without any intervention by the actor wearing the device. Embodiments of the present invention also provide a method of validating that usable data is being acquired and recorded by the remote system. 
         [0012]    In a first aspect, embodiments of the present invention provide a method of motion capture animation of an actor&#39;s performance. The method includes placing body markers on the actor&#39;s body and facial markers on the actor&#39;s face. A head-mounted motion capture camera system is positioned on the actor&#39;s head. Body image data corresponding to the body markers is acquired during the actor&#39;s performance. At substantially the same time, facial image data corresponding to the facial markers during the actor&#39;s performance is acquired with the head-mounted motion capture camera system. The body image data is stored on a server, while the facial image data is stored on a data logger, where the facial image data comprises camera images of the actor&#39;s face. A camera image of the actor&#39;s face is selected and transmitted to a wireless receiver. The camera image is then reviewed at a remote workstation. 
         [0013]    In some embodiments, the head-mounted motion capture camera system comprises at least two cameras. In many embodiments, the head-mounted motion capture camera system comprises at least four cameras. The head-mounted motion capture camera system may be configured to acquire image data from at least two views of each side of the actor&#39;s face. 
         [0014]    In some embodiments, the step of transmitting the camera image to a wireless receiver uses a protocol selected from at least one of: Bluetooth, Zigbee, WiFi, WiMax and IR. 
         [0015]    In some embodiments, the step of reviewing the camera image also includes validating the facial image data stored on the data logger. 
         [0016]    In some embodiments, the method also includes transmitting the facial image data from the data logger to the server, which may use a USB or FireWire connection. 
         [0017]    In many embodiments, the method also includes processing the body image data and generating an initial viewing sequence from the processed body image data. The initial viewing sequence is then transmitted to a display. The facial image data is also processed, the processed facial image data and the processed body image data are combined to generate animated images. 
         [0018]    In another aspect, embodiments of the present invention provide a method of asynchronous streaming of data for validation. The method includes positioning a plurality of cameras each at one of a plurality of angles and acquiring image data with the plurality of cameras. The image data is stored locally on a data logger. A camera image is selected from the image data and wirelessly transmitted from the data logger to a receiver, where the receiver is coupled to a processor and a display. The camera image is displayed for review to validate that the image data has been acquired and stored. The image data is then transferred from the data logger to a server. 
         [0019]    In some embodiments, the plurality of cameras are mounted on a head-mounted camera system, where the head-mounted camera system is positioned on an actor&#39;s head and the plurality of cameras are configured to capture images of the actor&#39;s face. In some embodiments, the plurality of cameras includes at least two cameras. In many embodiments, the plurality of cameras includes at least four cameras. The at least four cameras may be configured to acquire image data from at least two views of each side of the actor&#39;s face. 
         [0020]    In some embodiments, the steps of selecting a camera image, wirelessly transmitting the camera image, and displaying the camera image are repeated sequentially at intervals throughout a period of time while the steps of acquiring image data and storing the image data are ongoing. As the step of selecting a camera image is repeated, an image is selected from a different camera during each sequential cycle. 
         [0021]    In a further aspect, embodiments of the present invention provide a method of asynchronous streaming of image data for validation. The method includes positioning a head-mounted motion capture camera system on an actor&#39;s head, where marker dots have been placed on the actor&#39;s face. Image data is continuously acquired with the head-mounted motion capture camera system at an acquisition speed over an acquisition period. The image data includes marker data and is stored locally on a data logger. Camera images are selected from the image data at successive intervals during the acquisition period. Each of the camera images is wirelessly transmitted as it is selected from the data logger to a receiver, where the receiver is coupled to a processor and a display. Each of the camera images is displayed for review to validate that the image data is being acquired and stored. The image data is then transmitted from the data logger to a server at the end of the acquisition period. 
         [0022]    In many embodiments, the head-mounted motion capture camera system includes at least four cameras. The head-mounted motion capture camera system may be configured to acquire image data from at least two views of each side of the actor&#39;s face. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  depicts a prior art motion capture camera system. 
           [0024]      FIG. 2  shows a motion capture camera system according to an embodiment of the present invention. 
           [0025]      FIG. 3  shows a head-mounted camera system according to an embodiment of the present invention. 
           [0026]      FIG. 4  depicts an enlarged view of a universal joint connecting a mounting rod and helmet. 
           [0027]      FIG. 5  shows a side view of an embodiment of a head-mounted motion capture camera system. 
           [0028]      FIG. 6  shows a rear view of the head-mounted motion capture camera system. 
           [0029]      FIGS. 7A and 7B  show enlarged views of a universal joint. 
           [0030]      FIGS. 8A-8D  show enlarged views of a camera and universally pivoting ball joint according to an embodiment of the invention. 
           [0031]      FIGS. 9A-9D  show a method of motion capture animation and data validation according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Embodiments of the present invention relate to computer capture of object motion. 
         [0033]    Although embodiments make specific reference to capturing of facial movement or performance of an actor, the system methods and device described herein may be applicable to any application in which computer capture of fine movements is required. 
         [0034]      FIG. 2  shows a motion capture camera system according to an embodiment of the present invention. A head-mounted motion capture camera system  250  is positioned on the actor&#39;s head for capturing data from the facial movement of the actor  210 . The head-mounted camera system includes cameras  240  and a helmet  245 . The cameras  240  are connected via cable  270  to a data logger  260 , which is attached to the actor. The data logger  260  may be worn on a belt or otherwise as part of the actor&#39;s clothing to prevent the data logger from becoming disconnected during the actor&#39;s performance. The data logger  260  is in wireless communication with a processor  280  via a wireless receiver  290 . 
         [0035]    For capturing the data from the body movement of an actor  210 , the system in  FIG. 2  is similar to that shown in  FIG. 1 . Fixed or platform-mounted movable cameras  200  are positioned around an actor  210 , defining a capture volume  220 . The cameras  200  capture images of the actor&#39;s movement using body markers  230 . 
         [0036]      FIG. 3  shows one embodiment of a head-mounted motion capture camera system  300  in more detail. A helmet  310  is secured to the head of an actor. Mounting rods  320  are attached to the helmet  310  via universal joints  330 . In some embodiments, the mounting rods  320  will be attached to the helmet  310  approximately above the temples of the actor. Mounted on the mounting rods  320  are cameras  340 . The cameras  340  are secured to the mounting rods  320  with universally pivoting ball joints  350 . The mounting rods  320  are preferably made from carbon fiber tubes and/or stainless steel to minimize weight, while maintaining the strength of the rods. Adjustment screws  360  and  370  are provided to adjust the orientation of the mounting rod  320  and cameras  340 , respectively. The cameras  340  are connected via cables  380  to the data logger (not shown). 
         [0037]    In  FIG. 4 , an enlarged side view of an embodiment of a head-mounted motion capture camera system is shown. Mounting rod  410  is connected via a universal joint  420  to helmet  430 . The universal joint includes a bracket  440 , which holds the mounting rod  410  in a channel extending lengthwise through the bracket. Set screws  450  maintain pressure on the mounting rod  410  to hold it in position within the bracket  440 . The bracket  440  is connected to an inner circular portion  460  of the universal joint  420 . The inner circular portion  460  is positioned concentrically inside an outer circular portion  470 . Outer circular portion  470  is affixed to the helmet  430  using screws  480 . The outer circular portion  470  does not move with respect to the helmet and is preferably configured to affix to the helmet  430  in a singular orientation. Inner circular portion  460  is rotatable with respect to the outer circular portion  470 , allowing one degree of freedom of movement for the mounting rod, such that its orientation may be adjusted to position the cameras (not shown) higher or lower in front of the actor&#39;s face. Set screws  490  are used to lock the inner circular portion  460  into a fixed position with respect to the outer circular portion  470 . 
         [0038]    A side view of an embodiment of a head-mounted motion capture camera system  500  is shown in  FIG. 5 . Approximately  75  makeup dots  560  will be placed on the face of the actor. The makeup dots are not reflective and so are not captured by the fixed motion capture cameras described above (e.g.  100  in  FIG. 1 ). Additionally, unlike the reflective markers used for tracking the body movements, the makeup dots are simple paint that can remain in place for an entire day, without needing to be replaced or repositioned. Cameras  540  are positioned on mounting rods  520 . In a preferred embodiment, the camera system  500  has two mounting rods  520  and each mounting rod has two cameras  540  and the cameras  540  are machine vision micro-cameras. The cameras  540  record grayscale images of the actor&#39;s face, which are then used to track the movement of the face during post-processing. 
         [0039]    The placement of the four cameras around the face allow for stereo reconstruction from both sides of the face because each side of the face is imaged from two different angles. In addition, the cameras move with the actor, keeping the relative position of each camera to the face the same, which minimizes the calculations necessary to identify and track the makeup dots  560  and to process the image data. 
         [0040]      FIG. 6  shows a view of the back of the head-mounted motion capture camera system  600 . The helmet  630  may be secured to the head of the actor, for example by using buckles  640  with a hook-and-loop fastening material  650 , a chin strap (not shown), or a pressurized custom fit. In a preferred embodiment, cables  680  are gathered at the back of the actor&#39;s head and then connected to the data logger (not shown) in order to minimize the chances of the actor becoming entangled by the cables or the cables becoming disconnected. 
         [0041]      FIGS. 7A and 7B  show additional views of an embodiment of the universal joint  710  that connects the mounting rod  720  to the helmet  730 . Bracket  740  holds the mounting rod  720  in a channel  750  that runs through the length of the bracket. By loosening set screws  760 , mounting rod  720  may be rotated around its axis and may be repositioned within the channel  750  to extend a greater or shorter distance from the bracket  740 . The bracket  740  is attached to the inner circular portion  770  with connector  780 , and the bracket may pivot on the connector to adjust the mounting rod  720  to be closer to or further from the actor&#39;s face. A set screw  790  is used to secure the bracket  740  in position with the connector  780 . 
         [0042]    The universal joint  710  provides a connection for the mounting rod that is both easily repositioned by simply loosening the appropriate set screws, and securely held in a fixed position when the set screws are tightened. When necessary, one of the mounting rods  720  may be removed from the helmet  730  by loosening screws  785  to remove the entire assembly from the helmet. This can be useful in scenes where an actor is required to hold an object near one side of his face, for example, or when he is required to rest his head on a surface, such as a pillow. After that portion of the performance has been captured, the mounting rod  720  and universal joint  710  assembly can be replaced in exactly the same position and orientation as it was previously arranged by reattaching the set screws  785 . Because the outer circular portion  795  does not move with respect to the helmet  730 , as discussed above, when it is placed on the helmet again with the screws, it will adopt its original orientation. 
         [0043]    In  FIGS. 8A-8D , enlarged views of a camera and universally pivoting ball joint according to an embodiment of the invention are shown. Camera  800  is attached to mounting rod  810  via a universally pivoting ball joint  820 . The universally pivoting ball joint  820  comprises a ball  930  that fits inside a socket  940 , which allows the camera to be oriented in a wide range of directions. The ball  930  of the ball joint  820  is connected via a stem  950  to the housing of the camera  800 , while the socket  940  is connected to the mounting rod  810 . Once an orientation is selected for the camera, based on the requirements of the actor&#39;s face or other considerations, the ball  930  may be locked into that position in the socket  940  using set screw  920 . 
         [0044]    Set screws  900  hold the camera  800  in place on the stem  950  of the universally pivoting ball joint  820 . The camera  800  may be removed, for example to replace a defective or non-functioning camera, by simply loosening the set screws  900 . It is not necessary to adjust the ball joint  820  or the mounting rod  810  to remove the camera, thus when a camera  800  (either the same or a different camera) is placed onto the ball joint  820 , it will be in the same position and orientation as the original camera. Similarly, set screws  910  hold the lens  860  in place and allow it to be removed and replaced without changing its position or orientation. 
         [0045]    This consistency, along with the consistent positioning of the mounting rod as discussed above, is exceptionally helpful in minimizing the computational requirements for processing the image data. Processing can be performed using techniques described in co-pending U.S. patent application No. ______ (Attorney Docket No.: 027274-001800US, filed Sep. 29, 2008, entitled “Methods and apparatus for dot marker matching”). The tolerance for maintaining the positions of each of the elements is to within portions of a millimeter. It is important to maintain the position and orientation of the cameras and mounting rods in order to keep the angle of view of the face from each camera the same, as well as to keep the angles between each of the cameras constant. Because the cameras remain in a known, fixed position, even after a replacement, it is easier to identify and correlate the makeup dots on the actor&#39;s face, and thus to process the images for the animation. Further, because the cameras are fixed relative to the face, they have a much higher effective resolution, yielding a better signal to noise ratio. 
         [0046]    Also in  FIGS. 8A-8D , cable  830  is shown connecting the camera  800  to the data logger (not shown). A front portion  850  of the camera  800  comprises a lens  860 , which may be covered by a lens cap  870  for protection when not in use. Screws  840  secure the front portion  850  to the rear portion  880  of camera  800 . In some embodiments, the camera  800  comprises a charge-coupled device (“CCD”) element. The CCD element (not shown) is permanently secured within the rear portion  880  by a resin  890 . 
         [0047]    Advantages of the present invention include both the data processing aspects and the performance aspects of motion capture technology. The head-mounted camera system of the present invention captures images that show much greater detail about the movement of the face, which provides a greater effective resolution of the face for use in creating the final animation product. This greater detail is achieved in part because the cameras are able to maintain a close view of the face at all times, even when an actor&#39;s face would otherwise be blocked from view if using only the fixed cameras. The greater detail is also due in part to the larger number of markers that may be captured using the head-mounted camera system, versus the number that can be captured with previous systems. Further, because the time needed to process the body image data is no longer tied to processing the facial image data, it is possible to capture more data than in previous systems. As discussed in more detail below with respect to  FIGS. 9A-9D , only selected images of the face are viewed in near to real-time, the rest are stored and processed later. Thus, the frame rate for acquiring image data can be increased, improving resolution. 
         [0048]    In addition, because the head-mounted camera system captures the facial image data at the same time as the body capture, the system has the artistic advantages of prior simultaneous capture solutions while using manageable data capture and processing requirements. For example, an actor need not attempt to duplicate his performance precisely for separate captures of the face and the body. In addition, the placement of the cameras at the sides of the face allow for a less obstructed line of sight for the actor, which is preferred by actors and contributes to their comfort in performing using motion capture equipment. The placement also allows unobstructed access to the actor&#39;s mouth, which is helpful, for example, in scenes where the actor is expected to eat or drink. 
         [0049]      FIGS. 9A-9D  show a method of motion capture animation and data validation according to an embodiment of the present invention. The method begins in  FIG. 9A  with step  1000 , placing markers on an actor&#39;s face and body. A head-mounted camera system is positioned on the actor such that the cameras capture images of the actor&#39;s face in step  1010 . The actor then performs in step  1020  and the performance is acquired by the motion capture system. In step  1030 , external cameras capture image data corresponding to the markers on the body of the actor. At substantially the same time, the head-mounted camera system acquires two views of each side of the actor&#39;s face in step  1050 . As discussed above, the facial image data acquired includes marker data. 
         [0050]    In step  1040 , the body image data is stored on a server. Proceeding past reference point C, in step  1070  it is determined whether all of the scenes have been finished. If not, the actor continues to perform in step  1020  and the subsequent steps are repeated. If all of the scenes have been finished, the method continues at reference point D in  FIG. 9C , which is discussed below. 
         [0051]    Continuing in  FIG. 9A , in step  1060  the facial image data is stored on the data logger. Moving to reference point B in  FIG. 9B , a camera image is selected in step  1080 . In step  1090 , the selected camera image is transmitted to a wireless receiver that is connected to a remote workstation. The wireless transmission may use one of several known protocols, such as Bluetooth, Zigbee, WiFi, WiMax or IR. The transmission comprises a low resolution, lossy-compressed data stream that may be sub-sampled in time, width or height. The data stream may contain time code information, the total number of frames recorded by the data logger, the data logger&#39;s battery life and recording capacity remaining and other pertinent data. 
         [0052]    In step  1100 , the selected camera image and related data is then inspected by an operator or automatic computer software to verify that the cameras are acquiring and the data logger is storing usable data. The inventors of the present invention have sometimes discovered that after a full day of shooting, one or more cameras are defective and the image data has not been captured, that the cameras&#39; lenses have become dirty because of oil, saliva, food or other obstructions, or that problems occurred with the data logger on the actor&#39;s back. This validation is an important step in the process because it ensures that these kinds of problems with the portable head-mounted camera system or with the acquired data are caught as quickly as possible, minimizing wasted time and effort by the actors, director and crew by reducing the need for retakes. 
         [0053]    If the data on the data logger is determined to be valid in step  1110 , then the method continues at reference point C in  FIG. 9A . If the data is determined to be invalid for any reason, then the source of the problem is determined in step  1120 . In step  1130 , the problem is fixed, for example, by replacing a defective or damaged camera or by changing the batteries of the data logger. After the problem has been resolved, the method continues at reference point C in  FIG. 9A . 
         [0054]    Moving to reference point C in  FIG. 9A , step  1070  determines whether all of the scenes are finished, as described above. After the scenes are finished, the method continues at reference point D in  FIG. 9C . In step  1140 , the data from the data logger is transmitted to the server. The transmission may be via a USB, FireWire or similar type of connection. At step  1150 , both the facial image data and the body image data are stored on the server. The body image data is processed in step  1160  to generate an initial viewing sequence or “rough cut” for the director in step  1170 . Because the body image data is processed alone, without the facial image data, the processing can be completed much faster. In addition, the body markers are easily identified for processing, in comparison with the identification of previous facial markers in a conventional motion capture system, such as shown in  FIG. 1 . Accordingly, because the body markers are more easily identified, they require less manual identification by an operator. 
         [0055]    In step  1180 , the director views the rough cut to determine whether any changes or reshoots are needed. If the director does not approve the rough cut in step  1200 , then the process returns to reference point C to repeat the earlier steps of the method. If the rough cut was approved, then the body image data and the facial image data are combined in step  1210  to produce an animated image. After the animation is produced, the method continues at reference point E in  FIG. 9D . 
         [0056]    In step  1220  in  FIG. 9D , a representation of the animated image is stored on a tangible medium. The representation is the retrieved from the tangible medium in step  1230  and displayed to a user in step  1240 . The user may be the director, the studio executives, an audience at the theater, etc. 
         [0057]    While the exemplary embodiments have been described in some detail, by way of example and for clarity of understanding, those of skill in the art will recognize that a variety of modifications, adaptations, and changes may be employed. Hence, the scope of the present invention should be limited solely by the appended claims.