Patent Publication Number: US-2023152883-A1

Title: Scene processing for holographic displays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE 
     This patent application claims the priority benefit of U.S. Provisional Pat. App. 63/277,519 filed 9 Nov. 2021 (Attorney Docket MNE-124-PR). 
     This patent application is a continuation-in-part (CIP) of commonly owned PCT patent application PCT/US16/23433 entitled “Virtual 3D Methods, Systems And Software” (Atty. Dkt. MNE-111-PCT), published as WO/2016/154123 (which claims priority benefit of U.S. Provisional Application for Patent 62/136,494 (Atty. Dkt. MNE-111-PR)), both incorporated by reference herein. 
     This patent application is also a CIP of commonly owned U.S. patent application Ser. No. 17/460,246 (Atty. Dkt. MNE-111-US-3), which is a continuation of U.S. patent application Ser. No. 16/749,989 (now U.S. Pat. No. 11,106,275) (Atty. Dkt. MNE-111-US-2), both incorporated by reference herein. 
     U.S. patent application Ser. No. 16/749,989 is a continuation of U.S. patent application Ser. No. 15/560,019 (now U.S. Pat. No. 10,551,913) (Atty. Dkt. MNE-111-US), which is a U.S. national entry of above-noted PCT/US16/23433, both incorporated by reference herein. 
     This patent application is also related to the following commonly owned patent applications incorporated by reference herein: 
     PCT/US16/32213 entitled “Facial Signature Methods, Systems and Software” (Atty. Dkt. MNE-113-PCT), published as WO/2016/183380; 
     PCT/US18/19243 entitled “Image Reconstruction Methods, Systems And Software for Virtual 3D” (Atty. Dkt. MNE-115-PCT), published as WO 2018/164852; 
     PCT/US18/63699 entitled “Stereo Correspondence Search” (Atty. Dkt. MNE-118-PCT), published as WO/2019/109106; 
     PCT/US18/48197 entitled “Visual Communications Methods, Systems And Software” (Atty. Dkt. MNE-119-PCT), published as WO/2019/067134; 
     PCT/US18/63531 entitled “Temporal De-Noising” (Atty. Dkt. MNE-120-PCT), published as WO/2019/109061; 
     PCT/US18/64077 entitled “Disparity Cache” (Atty. Dkt. MNE-121-PCT), published as WO/2019/113215: 
     PCT/US20/47276 entitled “Camera System Utilizing Auxiliary Image Sensors” (Atty. Dkt. MNE-122-PCT), published as WO/2021/035095; and 
     U.S. patent application Ser. No. 17/858,954 entitled “Asymmetric Communication System With Viewer Position Indications” (Atty. Dkt. MNE-123-US). 
     Each of the above-listed applications is incorporated by reference herein as if set forth herein in its entirety, including all text and drawings thereof. In the event of an inconsistent description between this document and any of the documents incorporated by reference, the description in the incorporated document(s) shall be considered merely supplementary to the description set forth herein, and the description set forth herein shall control. 
    
    
     BACKGROUND OF THE INVENTION 
     It would be desirable to provide methods, systems, devices and computer software/program code products that enable efficient, high-quality display of scene content on holographic display devices. 
     It would be desirable to provide methods, systems, devices and computer software/program code products that enable, in a visual communications system involving a plurality of holographic display devices usable by respective users, efficient, high-quality display of scene content on such holographic display devices. 
     It would also be desirable to provide such functions at reasonable computational cost. 
     The present invention provides methods, systems, devices and computer software/program code products that enable the foregoing aspects and others. 
     Some embodiments and practices of the present invention can be implemented in conjunction with V3D aspects disclosed and claimed in commonly-owned U.S. Pat. No. 10,551,913 and related commonly-owned U.S. patent applications, and may utilize aspects of the V3D subject matter. However, the present invention can also be practiced in environments other than those disclosed in the noted, commonly-owned U.S. patents and U.S./PCT patent applications. 
     Thus, although embodiments and practices of the present invention discussed herein can be used in conjunction with practices and embodiments of the Virtual 3D (“V3D”) inventions described in the above-noted, commonly-owned patent applications incorporated herein by reference, they may also be useful in other systems and in connection with other technologies, and are not limited to application in connection with the V3D inventions described in the patent applications incorporated by reference herein. 
     Aspects, examples, embodiments and practices of the invention, whether in the form of methods, devices, systems or computer software/program code products, will next be described in greater detail in the following Detailed Description of the invention, in conjunction with the attached drawing figures. 
     Those skilled in the art will appreciate that while the following detailed description provides sufficient detail to enable one skilled in the art to practice the present invention, the various examples, embodiments and practices of the present invention that are discussed and described below, in conjunction with the attached drawing figures, are provided by way of example, and not by way of limitation. Numerous variations, additions, and other modifications or different implementations of the present invention are possible, and are within the spirit and scope of the invention. 
     The Detailed Description of the Invention section set forth below first discusses V3D aspects, in connection with which aspects of the present invention may be practiced, and then discusses embodiments and practices of the present invention relating to processing scene content in preparation for display on holographic display devices. 
     SUMMARY OF THE INVENTION 
     The following discussion, detailed description and accompanying drawing figures describe systems, methods and computer program code products (software) for processing scene content in preparation for display on a holographic display device. Some aspects of the invention pertain to automatically selecting rendering parameters or performing scene transformations in order to render images for display on a holographic display device. 
     The following discussion, detailed description and accompanying drawing figures also describe a communication system, and related methods and computer program code products, in which a rich representation of one or more users is captured and the user&#39;s or users&#39; likeness is displayed in a remote location using one or more holographic display devices. 
     This invention may be useful to facilitate remote meetings, conferences, live performances including musical performances, sporting events, and additional use cases that would be enhanced by real-time immersion in a remote location or real-time interaction with a remote person, persons, or objects. 
     Where the word “connected” is used herein, it should be understood to include virtual connections, such as connections using a wireless communication link or a connection facilitated by a network, which may include some degree of virtualization. 
     One aspect of the invention relates to methods, systems, and computer program products (software) for rendering scene content in a form configured for visually improved presentation on at least one holographic display device, wherein an exemplary method aspect comprises: (A) recognizing at least one meaningful element within the scene content; (B) selecting, from the at least one recognized meaningful element, at least one selected meaningful scene element; (C) determining, based at least in part on the at least one selected meaningful scene element, at least one scene transform; and (D) utilizing the at least one determined scene transform, rendering multiple 2-dimensional perspectives of the content, the multiple 2-dimensional perspectives being configured for visually improved presentation on at least one holographic display device. 
     In one aspect of the invention, a meaningful scene element comprises a head. In another aspect, a meaningful scene element comprises any of: human head, animal head, caricature of a head, or avatar&#39;s head. In another aspect, a meaningful scene element comprises a hand. In another aspect, a meaningful scene element comprises an object held by a hand. In another aspect of the invention a meaningful scene element comprises an object bearing a selected pattern. In another aspect, a meaningful scene element comprises an object within a set of possible objects. In another aspect of the invention, a meaningful scene element comprises an entire scene. In another aspect, a meaningful scene element comprises any of: the area within a bounding box, the area within a projected bounding rectangle, or the area within a bounding volume. In yet another aspect, a meaningful scene element comprises a subset of the scene content. 
     Another aspect of the invention comprises blurring at least one element within the scene content. Another aspect comprises reducing the visibility of at least one element within the scene content. Yet another aspect comprises applying a blur effect to at least one region of at least one rendered 2-dimensional image. In a related aspect, applying a blur effect comprises applying a distance-controlled blur effect. In another aspect, applying a distance-controlled blur effect comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in a 3D scene reference frame. Another aspect of the invention comprises reducing the visibility of at least two regions of at least one rendered 2-dimensional image. 
     In another aspect of the present invention, the determining of at least one scene transform is configured to minimize blur or visibility reduction of at least one selected scene element. 
     Another aspect of the invention comprises displaying the multiple 2-dimensional perspectives of the content on a holographic display device. A related aspect comprises providing at least one holographic display device such that at least one viewing user can view the at least one holographic display device. 
     Another aspect of the invention comprises receiving an indication of use corresponding to at least one viewing user of at least one holographic display device. In a related aspect, an indication of use comprises any of: a user&#39;s attentional focus, a user&#39;s eye position, a user&#39;s gaze direction, a user&#39;s gestures, input from a user through a user interface, or a user&#39;s actions sensed by a sensor. In another aspect, the sensor comprises a touch-sensitive sensor. 
     A further aspect of the invention comprises stabilizing a scene transform prior to rendering. In another aspect, the stabilizing comprises utilizing change integration logic. In a related aspect, the stabilizing comprises utilizing a heuristic. In another aspect, the stabilizing comprises utilizing logic to establish any of: an acceptable depth range or an acceptable deviance from a prior transform value. In another aspect, the stabilizing comprises utilizing logic to maintain a running average over a time window. In another aspect, the stabilizing comprises utilizing logic to calculate a smooth path from a prior transform. In yet another aspect of the invention, the stabilizing comprises utilizing any combination of: interpolation, cubic Hermite interpolation, splines, Catmull-Rom splines. In another aspect, the stabilizing comprises utilizing logic to detect conditions for an abrupt transition. In another aspect, the logic to detect conditions for an abrupt transition comprises logic to detect a change in at least one meaningful scene element. In another aspect, the logic comprises electronic logic elements. 
     In one aspect of the invention, the at least one holographic display device comprises a lenticular lens array. In another aspect, the at least one holographic display device comprises a parallax barrier display device. In another aspect of the invention, the at least one holographic display device comprises eyewear. 
     Another aspect of the invention further comprises utilizing a second, additional scene transform to render additional 2-dimensional perspectives of the content, the additional 2-dimensional perspectives being configured for display on at least a second holographic display device. 
     In another aspect of the invention, the scene content comprises a moving scene. In another aspect, the scene content comprises at least one frame from a stream representative of a moving scene. In yet another aspect, the scene content comprises at least one head. In another aspect, the scene content comprises the output of a light-field camera. In still another aspect of the invention, the scene content comprises the output of at least one array of cameras. In another aspect, the scene content comprises the output of at least one depth-sensing camera. In yet another aspect, the scene content comprises a 3-dimensional model. In another aspect of the invention, the scene content comprises any of: a polygonal mesh, voxel data, point data, or light-field data. In a further aspect, the scene content comprises at least one image containing depth information. In another aspect, the scene content comprises at least one image containing disparity information. In another aspect, the scene content comprises metadata. In a related aspect, the scene content comprises metadata, the metadata identifying objects within the scene content. In another aspect, the scene content comprises information about a prior configuration of the scene content. In yet another aspect of the invention, the scene content comprises historical information, the historical information comprising any of: prior scene transform information or an aggregate representation of prior scene transform information. In another aspect, the scene content comprises motion information. In still another aspect of the invention, the scene content comprises a representation of a physical scene. In another aspect, the scene content comprises a representation of a physical scene, and the representation of a physical scene comprises images of at least one captured user. In another aspect, the scene content comprises a real-time streaming representation ofa live physical scene. In a further aspect of the invention, the scene content further comprises a real-time streaming representation of live humans. In another aspect, the scene content further comprises information corresponding to at least one viewer of the holographic output. 
     In one aspect of the invention, the recognizing of at least one meaningful element within the scene content comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in a 3D scene reference frame. In another aspect, the recognizing comprises recognizing geometric features. In another aspect, the recognizing comprises utilizing 2-dimensional image recognition. In another aspect of the invention, the recognizing comprises utilizing facial recognition. In another aspect, the recognizing comprises any combination of 2-dimensional and 3-dimensional recognition algorithm(s). 
     In one aspect of the invention, the selecting of at least one selected meaningful scene element, from the at least one recognized meaningful scene element, comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in the 3D scene. In another aspect, the selecting comprises utilizing facial analysis. In another aspect, the selecting comprises evaluating the position of a scene element in relation to the entire scene content. In another aspect of the invention, the selecting comprises evaluating the position of a scene element in relation to the frame of a holographic display. In yet another aspect, the selecting comprises evaluating the size of a scene element in relation to the entire scene content. In another aspect of the invention, the selecting comprises evaluating the size of a scene element as it would be projected onto a holographic display. In another aspect, the selecting comprises evaluation of the gaze direction of a head. In another aspect, the selecting comprises evaluating the status of a head as an active speaker or as a recent speaker. In still another aspect, the selecting comprises evaluation of additional indications from at least one captured user. In a related aspect, the additional indications from at least one captured user comprise any of: the attentional focus of at least one captured user or gestures by at least one captured user. In another aspect, the selecting comprises evaluating additional indications from at least one viewing user. In a related aspect, the additional indications from at least one viewing user comprise the attentional focus of at least one viewing user. In yet another aspect, the selecting comprises utilizing heuristics. In another aspect, the selecting comprises utilizing data corresponding to identity of a specific captured user. In another aspect, the selecting comprises utilizing metadata obtained from the scene content. In another aspect of the invention, the selecting comprises selecting all recognized meaningful scene elements. In yet another aspect, the selecting comprises visually recognizing any of an object or a class of objects. In another aspect, the selecting comprises utilizing any of: data transmitted wirelessly, data transmitted via Bluetooth, data transmitted via WiFi, or RFID data. In a further aspect, the selecting comprises detecting motion. In another aspect, the selecting comprises utilizing indications supplied by a director user, wherein the director user is not a captured user or a primary viewing user. 
     In one aspect of the present invention, a scene transform comprises an asymmetric or sheared view frustum. In another aspect, the scene transform comprises a sheared view frustum, and the sheared view frustum enables selection of a plane of zero parallax. In a related aspect, the plane of zero parallax defines a Z-axis distance at which a scene feature is presented at the same spatial position on the holographic plane such that its presentation does not change with respect to viewing angle. Another aspect of the invention comprises dynamically shifting the holographic plane in real-time to maximize viewing quality of a given scene feature. Another aspect comprises applying a blur effect. In another aspect, a scene transform comprises a baseline depth. In another aspect, a scene transform comprises a depth displacement. In another aspect, a scene transform comprises a scene translation. In another aspect, a scene transform comprises a rotation. In another aspect, a scene transform comprises an affine transform. In yet another aspect, a scene transform comprises a scale factor. In another aspect of the invention, a scene transform comprises a re-projection function. In another aspect, a scene transform comprises any of a distortion function or an anti-distortion function. In another aspect, a scene transform comprises rendering parameters. In yet another aspect, a scene transform comprises a blur magnitude parameter 
     In one aspect of the present invention, determining at least one scene transform comprises adjusting a 3D position of a viewing frustum in a 3D scene reference frame. In another aspect, determining at least one scene transform comprises evaluating the position of a selected scene element. In another aspect, determining at least one scene transform comprises evaluating the position of a head. In yet another aspect, determining at least one scene transform comprises analyzing facial features. In another aspect, determining at least one scene transform comprises computing a scale factor to optimize for presentation on a holographic display device. In another aspect of the invention, determining at least one scene transform comprises evaluating a selected scene element and an un-blurred band. In another aspect, determining at least one scene transform comprises the removal of selected scene elements. 
     In one aspect of the invention, rendering multiple 2-dimensional perspectives of the content comprises executing rendering utilizing any combination of 3D projection algorithm, rasterization algorithm, ray tracing algorithm. In another aspect, rendering multiple 2-dimensional perspectives of the content comprises applying a visual effect to a subset of elements of the rendered scene. In a related aspect, the visual effect comprises any combination of: transparency, blur, confusion, bokeh, gaussian blur, rejection. In another aspect, rendering multiple 2-dimensional perspectives of the content comprises applying a pixel re-mapping function to arrange the perspectives such that they are transferable through holographic display optics of the holographic display device so as to provide a visually improved display to a human viewing user. In another aspect, rendering multiple 2-dimensional perspectives of the content comprises applying a swizzle function. In another aspect, the re-mapping function comprises a swizzle function. In another aspect of the invention, applying a pixel re-mapping function comprises utilizing digital logic elements to re-map at least one individual pixel component. In another aspect, applying a swizzle function comprises utilizing digital logic elements to re-map at least one individual pixel component. 
     One aspect of the invention relates to methods, systems, and computer program products (software) for enabling remote communication utilizing a holographic display, wherein exemplary system aspects comprise: (A) a scene capture device, operable to capture rich scene information representative of a scene; (B) a communication link, operable to transmit rich scene information; (C) a scene processing device operable to: (1) select at least one scene transform operable on the rich scene information; and (2) render multiple scene viewpoints, based on the rich scene information, utilizing the at least one selected scene transform; and (D) a holographic display device, operable to provide a holographic display of the scene, based at least in part on the rendered scene viewpoints. Another aspect of the invention relates to such systems operable to execute any of the methods discussed herein. 
     In another aspect of the invention, the scene capture device is operable to capture a digital representation of at least one captured user. In another aspect, the holographic display device is operable to display the rendered scene, based at least in part on the rendered scene viewpoints, for viewing by at least one viewing user. In another aspect, the scene capture device comprises at least two cameras arranged as a stereo pair. In still another aspect, the scene capture device comprises any combination of: a depth-sensing camera, a structured light camera, an infrared pattern emitter, a time-of-flight camera, a light-field camera. In a further aspect, the scene capture device comprises a microphone or an array of microphones. In yet another aspect, the scene capture device comprises an army of cameras. In a related aspect, cameras of the array of cameras are mounted around the perimeter of a holographic display. 
     In one aspect of the invention, the rich scene information comprises any combination of: a 2-dimensional image, a depth map, a 3-dimensional polygonal mesh, voxel data, point data, point-cloud data, displacement data, light field data. 
     In one aspect of the invention, the communication link comprises a digital processing network. In another aspect, the communication link comprises a telecommunications network. In another aspect, the communication link comprises a wireless communication link. In another aspect, the communication link comprises digital processing elements operable in accordance with a computer peripheral connection standard. In yet another aspect, the communication link comprises a data storage device. 
     In one aspect of the invention, the scene processing device comprises any combination of: a digital signal processor, an embedded system-on-chip, a digital computer, a GPU, a mobile computational device, a cloud-computing device. In another aspect, the scene processing devices comprises at least two elements selected from a group comprising: a digital signal processor, an embedded system-on-chip, a digital computer, a GPU, a mobile computational device, a cloud-computing device. In a further aspect, the scene processing device comprises digital processor-executable program code executing on at least one general-purpose computational device. In another aspect, the scene processing device comprises at least two computational units. In yet another aspect, the scene processing device comprises at least two computational units, and the multiple computational units are geographically separate from each other and communicate via a communication link. In still another aspect of the invention, the scene processing device comprises digital logic operable to recognize any of: heads, faces, hands, or selected objects in the scene. In another aspect, the scene processing device comprises digital logic operable to select at least one meaningful object in the scene. In another aspect, the scene processing device comprises digital logic operable to execute selected functions responsive to received indications corresponding to a captured user or captured users. In another aspect, the scene processing device comprises digital logic operable to execute selected functions responsive to received indications pertaining to a viewing user or viewing users. In yet another aspect of the invention, the scene processing device comprises digital logic operable to determine at least one scene transform. In another aspect, the scene processing device comprises digital logic operable to apply a visual effect to a subset of the rich scene information. In another aspect, the scene processing device comprises digital logic operable to render the rich scene information for display on a holographic display device. In a further aspect, the scene processing device comprises digital logic operable to apply a swizzle function. In another aspect, the scene processing device comprises digital logic operable to apply a pixel re-mapping function. In another aspect, the swizzle function is operable to configure scene data corresponding to multiple 2-dimensional perspectives such that the 2-dimensional perspectives are transferable through holographic display optics of the holographic display device so as to provide an optimized, or visually improved, display to a human viewing user. In another aspect of the invention, the pixel re-mapping function is operable to configure scene data corresponding to multiple 2-dimensional perspectives such that the 2-dimensional perspectives are transferable through holographic display optics of the holographic display device so as to provide an optimized, or visually improved, display to a human viewing user. In yet a further aspect of the invention, the digital logic operable to apply a swizzle function comprises digital logic elements operable to re-map at least one individual pixel component. In another aspect, the digital logic operable to apply a pixel re-mapping function comprises digital logic elements operable to re-map at least one individual pixel component. In still another aspect of the invention, the scene processing device comprises digital logic operable to output any combination of: a set of 2-dimensional rendered frames, a swizzled image incorporating multiple 2-dimensional rendered frames, an encoded representation of multiple 2-dimensional rendered frames. 
     In one aspect of the invention, the holographic display device comprises any of: a parallax barrier display device, a lenticular lens array, or a slanted lens array. In another aspect, the holographic display device comprises dedicated eyewear. In another aspect, the holographic display device comprises a display device for which the angle at which a viewer views an image displayed by the device affects the image seen by the viewer. A related aspect of the invention further comprises a sound-producing element operable to reproduce sound captured by a microphone device. Another aspect further comprises at least two sound-producing elements operable to reconstruct spatially localized sound captured by multiple microphone elements. Another aspect of the invention further comprises at least a second scene capture device operable to capture a digital representation of at least one viewing user. A related aspect further comprises at least a second holographic display device operable to display a representation of the scene captured by the second scene capture device, for viewing by at least one captured user. A further aspect of the invention is configured to enable real-time interactions between at least one captured user and at least one viewing user. 
     Another aspect of the present invention comprises (A) a camera, operable to capture a digital image of at least one viewing user; and (B) a non-holographic display, operable to present the digital image to at least one captured user. 
     Another aspect of the invention further comprises at least one additional endpoint, wherein an additional endpoint comprises any combination of: a holographic display; a scene capture device; a communication link. In a related aspect of the invention, (1) a respective scene capture device is associated with a respective endpoint; and (2) the scene processing device is operable to select among scenes captured by the respective scene capture devices associated with the respective endpoints. In another aspect, the scene processing device is operable to integrate information from multiple scenes captured by the respective scene capture devices associated with the respective endpoints. 
     Another aspect of the present invention further comprises a user interface; the user interface operable to provide information to the scene processing device. In another aspect, the user interface comprises a touch-sensitive device. In another aspect, the user interface comprises an eye tracking device. 
     In another aspect of the present invention, the scene processing device is operable to identify any combination of: a speaking user; speaking users; an endpoint associated with a speaking user, wherein an endpoint comprises any combination of holographic display, scene capture device, communication link. In a related aspect, at least one endpoint is designated as a moderator endpoint. In another aspect, a holographic display device is operable to present rendered output from multiple scene capture devices simultaneously. In another aspect, a holographic display device is operable to present a view of a specific individual user. Yet another aspect of the invention further comprises a storage medium; the storage medium operable to store any combination of: rich scene information, rendered scene viewpoints, scene transform information. 
     One embodiment of the invention relates to a system for rendering scene content in a form configured for visually improved presentation on at least one holographic display device, the system comprising a digital processing resource, the digital processing resource comprising at least one digital processor, the digital processing resource being configured to (A) recognize at least one meaningful element within the scene content; (B) select, from the at least one recognized meaningful element, at least one selected meaningful scene element; (C) determine, based at least in part on the at least one selected meaningful scene element, at least one scene transform; and (D) utilizing the at least one determined scene transform, render multiple 2-dimensional perspectives of the content, the multiple 2-dimensional perspectives being configured for visually improved presentation on at least one holographic display device. 
     Another embodiment of the invention relates to a program product for use with a digital processing system to enable the digital processing system to render scene content in a form configured for visually improved presentation on at least one holographic display device, the digital processing system comprising at least one digital processor, the program product comprising digital processor-executable program instructions stored on at least one non-transitory digital processor readable medium, which when executed in the digital processing system cause the digital processing system to (A) recognize at least one meaningful element within the scene content; (B) select, from the at least one recognized meaningful element, at least one selected meaningful scene element; (C) determine, based at least in part on the at least one selected meaningful scene element, at least one scene transform; and (D) utilizing the at least one determined scene transform, render multiple 2-dimensional perspectives of the content, the multiple 2-dimensional perspectives being configured for visually improved presentation on at least one holographic display device. 
     Another practice of the invention relates to a method for remote communication utilizing a holographic display, the method comprising (A) providing a scene capture device operable to capture rich scene information representative of a scene; (B) providing a communication link, operable to transmit rich scene information; (C) providing a scene processing device operable to (1) select at least one scene transform operable on the rich scene information; and (2) render multiple scene viewpoints, based on the rich scene information, utilizing the at least one selected scene transform; and (D) providing a holographic display device, operable to provide a holographic display of the scene, based at least in part on the rendered scene viewpoints. 
     Another aspect of the invention relates to a program product for use with a digital processing system to enable the digital processing system to provide remote communication utilizing a holographic display, the digital processing system comprising at least one digital processor, the digital processing system being operable to communicate with (1) a scene capture device, (2) a communication link, and (3) a holographic display device, the program product comprising digital processor-executable program instructions stored on at least one non-transitory digital processor readable medium, which when executed in the digital processing system cause the digital processing system to (A) enable the scene capture device to capture rich scene information representative of a scene; (B) enable the communication link to transmit rich scene information captured by the scene capture device: (C) execute scene processing operations comprising (1) selecting at least one scene transform operable on the rich scene information; and (2) rendering multiple scene viewpoints, based on the rich scene information, utilizing the at least one selected scene transform; and (D) transmit the rendered scene viewpoints to the holographic display device via the communication link, to enable the holographic display device to provide a holographic display of the scene, based at least in part on the rendered scene viewpoints. 
     Although embodiments and practices of the present invention discussed herein can be used in conjunction with practices and embodiments of the Virtual 3D (“V3D”) inventions described in the above-noted, commonly-owned patent applications incorporated herein by reference, they may also be useful in other systems and in connection with other technologies, and are not limited to implementation in connection with the V3D inventions described in the patent applications incorporated by reference herein. 
     These and other aspects, examples, embodiments and practices of the invention, whether in the form of methods, devices, systems or computer software/program code products, will be discussed in greater detail below in the following Detailed Description of the Invention and in connection with the attached drawing figures. 
     In various aspects and practices of the invention described herein, the image processing methods described are executable by digital processors, which can include graphics processor units (GPUs), including general purpose graphics processor units (GPGPUs) such as those commercially available on cellphones, smartphones, tablets and other commercially available telecommunications and computing devices, as well as in digital display devices and digital cameras. Those skilled in the art to which this invention pertains will understand the structure and operation of digital processors, GPGPUs and similar digital graphics processor units. 
     Those skilled in the art will appreciate that while the following detailed description provides sufficient detail to enable one skilled in the art to practice the present invention, the various examples, embodiments and practices of the present invention that are discussed and described below, in conjunction with the attached drawing figures, are provided by way of example, and not by way of limitation. Numerous variations, additions, and other modifications or different implementations of the present invention are possible, and are within the spirit and scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a camera configuration useful in an exemplary practice of V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  2 A and  2 B- 6 A and  6 B  are schematic diagrams illustrating exemplary V3D-related aspects in connection with which the present invention may be practiced. 
         FIG.  7    is a flowchart showing exemplary V3D-related aspects in connection with which the present invention may be practiced. 
         FIG.  8    is a block diagram depicting exemplary V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  9 - 18 A,  18 B,  18 C and  18 D  are schematic diagrams illustrating exemplary V3D-related aspects in connection with which the present invention may be practiced. 
         FIG.  19    is a graph in accordance with V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  20 A and  20 B- 45    are schematic diagrams illustrating V3D-related aspects in connection with which the present invention may be practiced. 
         FIG.  46    is a graph in accordance with V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  47 A and  47 B- 54    are schematic diagrams illustrating V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  55 - 80    are flowcharts depicting V3D-related aspects in connection with which the present invention may be practiced. 
         FIGS.  81 A- 82 B  are schematic diagrams depicting exemplary practices of the invention relating to scene processing for holographic displays. 
         FIGS.  83 - 84    are flowcharts depicting exemplary practices of the invention relating to scene processing for holographic displays. 
         FIG.  85    is a schematic diagram exemplary practices of the invention relating to scene processing for holographic displays. 
         FIGS.  86 - 103    are flowcharts depicting exemplary practices of the invention relating to scene processing for holographic displays. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As noted above, various embodiments and practices of the present invention can be implemented in conjunction with V3D aspects disclosed and claimed in the commonly-owned U.S. Pat. No. 10,551,913 and related commonly-owned U.S./PCT patent applications, and may utilize aspects of the V3D subject matter. However, it is also noted that the present invention can also be practiced in environments other than those disclosed in the noted, commonly-owned U.S. patents and U.S./PCT patent applications. 
     Thus, although embodiments and practices of the present invention discussed herein can be used in conjunction with practices and embodiments of the Virtual 3D (“V3D”) inventions described in the above-noted, commonly-owned patent applications incorporated herein by reference, they may also be useful in other systems and in connection with other technologies, and are not limited to application in connection with the V3D inventions described in the patent applications incorporated by reference herein. 
     The following discussion first addresses V3D aspects, and then discusses embodiments and practices of the invention relating to processing scene content for display on holographic display devices. 
     I. V3D Aspects: 
     1. Overview of V3D Aspects 
     Introduction—V3D 
     Current video conferencing systems such as Apple&#39;s Facetime, Skype or Google Hangouts have a number of limitations which make the experience of each user&#39;s presence and environment significantly less engaging than being physically present on the other side. These limitations include (1) limited bandwidth between users, which typically results in poor video and audio quality; (2) higher than ideal latency between users (even if bandwidth is adequate, if latency is excessive, a first user&#39;s perception of the remote user&#39;s voice and visual actions will be delayed from when the remote user actually performed the action, resulting in difficult interaction between users; and (3) limited sensory engagement (of the five traditionally defined senses, even the senses of sight and sound are only partially served, and of course taste, smell and touch are unaccounted-for). 
     The first two issues can be addressed by using a higher performing network connection and will likely continue to improve as the underlying communications infrastructure improves. As for the third issue, the present invention, referred to herein as “V3D”, aims to address and radically improve the visual aspect of sensory engagement in teleconferencing and other video capture settings, while doing so with low latency. 
     The visual aspect of conducing a video conference is conventionally achieved via a camera pointing at each user, transmitting the video stream captured by each camera, and then projecting the video stream(s) onto the two-dimensional (2D) display of the other user in a different location. Both users have a camera and display and thus is formed a full-duplex connection where both users can see each other and their respective environments. 
     The V3D of the present invention aims to deliver a significant enhancement to this particular aspect by creating a “portal” where each user would look “through” their respective displays as if there were a “magic” sheet of glass in a frame to the other side in the remote location. This approach enables a number of important improvements for the users (assuming a robust implementation:
         1. Each user can form direct eye contact with the other.   2. Each user can move his or her head in any direction and look through the portal to the other side. They can even look “around” and see the environment as if looking through a window.   3. Device shaking is automatically corrected for since each user sees a view from their eye directly to the other side. Imagine if you looked through a window and shook the frame: there would be no change in the image seen through it.   4. Object size will be accurately represented regardless of view distance and angle.       

     The V3D aspects of the invention can be configured to deliver these advantages in a manner that fits within the highly optimized form factors of today&#39;s modern mobile devices, does not dramatically alter the economics of building such devices, and is viable within the current connectivity performance levels available to most users. 
     By way of example of the invention,  FIG.  1    shows a perspective view of an exemplary prototype device  10 , which includes a display  12  and three cameras: a top right camera  14 , and bottom right camera  16 , and a bottom left camera  18 . In connection with this example, there will next be described various aspects of the invention relating to the unique user experience provided by the V3D invention. 
     Overall User Experience 
     Communication (Including Video Conferencing) with Eye Contact 
     The V3D system of the invention enables immersive communication between people (and in various embodiments, between sites and places). In exemplary practices of the invention, each person can look “through” their screen and see the other place. Eye contact is greatly improved. Perspective and scale are matched to the viewer&#39;s natural view. Device shaking is inherently eliminated. As described herein, embodiments of the V3D system can be implemented in mobile configurations as well as traditional stationary devices. 
       FIGS.  2 A-B ,  3 A-B, and SA-B are images illustrating an aspect of the invention, in which the V3D system is used in conjunction with a smartphone  20 , or like device. Smartphone  20  includes a display  22 , on which is displayed an image of a face  24 . The image may be, for example, part of video/telephone conversation, in which a video image and sound conversation is being conducted with someone in a remote location, who is looking into the camera of their own smartphone. 
       FIGS.  2 A and  2 B  illustrate a feature of the V3D system for improving eye contact.  FIG.  2 A  shows the face image prior to correction. It will be seen that the woman appears to be looking down, so that there can be no eye contact with the other user or participant.  FIG.  1 B  shows the face image after correction. It will be seen that in the corrected image, the woman appears to be making eye contact with the smartphone user. 
       FIGS.  3 A- 3 B  are a pair of diagrams illustrating the V3D system&#39;s “move left” ( FIG.  3 A ) and “move right” ( FIG.  3 B ) corrections.  FIGS.  4 A- 4 B  are a pair of diagrams of the light pathways  26   a ,  26   b  in the scene shown respectively on display  22  in  FIGS.  3 A- 3 B  (shown from above, with the background at the top) leading from face  24  and surrounding objects to viewpoints  28   a ,  28   b  through the “window” defined by display  22 . 
       FIGS.  5 A- 5 B  are a pair of diagrams illustrating the V3D system&#39;s “move in” ( FIG.  5 A ) and “move out” ( FIG.  5 B ) corrections.  FIGS.  6 A- 6 B  are a pair of diagrams of the light pathways  26   c ,  26   d  in the scene shown respectively on display  22  in  FIGS.  3 A- 3 B  (shown from above, with the background at the top) leading from face  24  and surrounding objects to viewpoints  28   c ,  28   d  through the “window” defined by display  22 . 
     Self Portraiture Example 
     Another embodiment of the invention utilizes the invention&#39;s ability to synthesize a virtual camera view of the user to aid in solving the problem of “where to look” when taking a self-portrait on a mobile device. This aspect of the invention operates by image-capturing the user per the overall V3D method of the invention described herein, tracking the position and orientation of the user&#39;s face, eyes or head, and by using a display, presenting an image of the user back to themselves with a synthesized virtual camera viewpoint, as if the user were looking in a mirror. 
     Photography Composition 
     Another embodiment of the invention makes it easier to compose a photograph using a rear-facing camera on a mobile device. It works like the overall V3D method of invention described herein, except that the scene is captured through the rear-facing camera(s) and then, using the user&#39;s head location, a view is constructed such that the scale and perspective of the image matches the view of the user, such that the device display frame becomes like a picture frame. This results in a user experience where the photographer does not have to manipulate zoom controls or perform cropping, since they can simply frame the subject as they like within the frame of the display, and take the photo. 
     Panoramic Photography 
     Another embodiment of the invention enables the creation of cylindrical or spherical panoramic photographs, by processing a series of photographs taken with a device using the camera(s) running the V3D system of the invention. The user can then enjoy viewing the panoramic view thus created, with an immersive sense of depth. The panorama can either be viewed on a 2D display with head tracking, a multi-view display or a binocular virtual reality (VR) headset with a unique perspective shown for each eye. If the binocular VR headset has a facility to track head location, the V3D system can re-project the view accurately. 
     2. Overall V3D Processing Pipeline 
       FIG.  7    shows a general flow diagram illustrating the overall V3D pipeline  70 , which incorporates the following aspects to deliver the user experience described above: 
       71 : Image Capture: One or more images of a scene, which may include a human user, are collected instantaneously or over time via one or more cameras and fed into the system. Wide-angle lenses are generally preferred due to the ability to get greater stereo overlap between images, although this depends on the application and can in principle work with any focal length. 
       72 : Image Rectification: In order to compensate for optical lens distortion from each camera and relative misalignment between the cameras in the multi-view system, image processing is performed to apply an inverse transform to eliminate distortion, and an affine transform to correct misalignment between the cameras. In order to perform efficiently and in real-time, this process can be performed using a custom imaging pipeline or implemented using the shading hardware present in many conventional graphical processing units (GPUs) today, including GPU hardware present in devices such as iPhones and other commercially available smartphones. Additional detail and other variations of these operations will be discussed in greater detail herein. 
       73 : Feature Correspondence: With the exception of using time-of-flight type sensors in the image Capture phase that provide depth information directly, this process is used in order to extract parallax information present in the stereo images from the camera views. This process involves detecting common features between multi-view images and measuring their relative distance in image space to produce a disparity measurement. This disparity measurement can either be used directly or converted to actual depth based on knowledge of the camera field-of-view, relative positioning, sensor size and image resolution. Additional detail and other variations of these operations will be discussed in greater detail herein. 
       74 : Representation: Once disparity or depth information has been acquired, this information, combined with the original images must be represented and potentially transmitted over a network to another user or stored. This could take several forms as discussed in greater detail herein. 
       75 : Reconstruction: Using the previously established representation, whether stored locally on the device or received over a network, a series of synthetic views into the originally captured scene can be generated. For example, in a video chat, the physical image inputs may have come from cameras surrounding the head of the user in which no one view has a direct eye contact gaze vector to the user. Using reconstruction, a synthetic camera view placed potentially within the bounds of the device display enabling the visual appearance of eye contact can be produced. 
       76 : Head Tracking: Using the image capture data as an input, many different methods exist to establish an estimate of the viewer&#39;s head or eye location. This information can be used to drive the reconstruction and generate a synthetic view which looks valid from the user&#39;s established head location. Additional detail and various forms of these operations will be discussed in greater detail herein. 
       77 : Display: Several types of display can be used with the V3D pipeline in different ways. The currently employed method involves a conventional 2D display combined with head tracking to update the display project in real-time so as to give the visual impression of being three-dimensional (3D) or a look into a 3D environment. However, binocular stereo displays (such as the commercially available Oculus Rift) can be employed used, or still further, a lenticular type display can be employed, to allow auto-stereoscopic viewing. 
     3. Pipeline Details 
       FIG.  8    is a diagram of an exemplary V3D pipeline  80  configured in accordance with the invention, for immersive communication with eye contact. The depicted pipeline is full-duplex, meaning that it allows simultaneous two-way communication in both directions. 
     Pipeline  80  comprises a pair of communication devices  81 A-B (for example, commercially available smartphones such as iPhones) that are linked to each other through a network  82 . Each communication device includes a decoder end  83 A-B for receiving and decoding communications from the other device and an encoder end  84 A-B for encoding and sending communications to the other device  81 A-B. 
     The decoder end  83 A-B includes the following components:
         a Receive module  831 A-B;   a Decode module  832 A-B;   a View Reconstruction module  833 A-B; and   a Display  834 A-B.       

     The View Reconstruction module  833 A-B receives data  835 A-B from a Head Tracking Module  836 -B, which provides x-, y-, and z-coordinate data with respect to the user&#39;s head that is generated by camera 0    841 A-B. 
     The encoder end  84 -B comprises a multi-camera array that includes camera 0    841 A-B, camera,  841 A-B, and additional camera(s)  842 A-B. (As noted herein, it is possible to practice various aspects of the invention using only two cameras.) The camera array provides data in the form of color camera streams  843 A-B that are fed into a Color Image Redundancy Elimination module  844 A-B and an Encode module. The output of the camera array is also fed into a Passive Feature Disparity Estimation module  845 A-B that provides disparity estimation data to the Color Image Redundancy Elimination module  846 A-B and the Encode module  847 A-B. The encoded output of the device is then transmitted over network  82  to the Receive module  831 A-B in the second device  81 A-B. 
     These and other aspects of the invention are described in greater detail elsewhere herein. 
     Image Capture 
     The V3D system requires an input of images in order to capture the user and the world around the user. The V3D system can be configured to operate with a wide range of input imaging device. Some devices, such as normal color cameras, are inherently passive and thus require extensive image processing to extract depth information, whereas non-passive systems can get depth directly, although they have the disadvantages of requiring reflected IR to work, and thus do not perform well in strongly naturally lit environments or large spaces. Those skilled in the art will understand that a wide range of color cameras and other passive imaging devices, as well as non-passive image capture devices, are commercially available from a variety of manufacturers. 
     Color Cameras 
     This descriptor is intended to cover the use of any visible light camera that can feed into a system in accordance with the V3D system. 
     IR-Structured Light 
     This descriptor is intended to cover the use of visible light or infrared specific cameras coupled with an active infrared emitter that beams one of many potential patterns onto the surfaces of objects, to aid in computing distance. IR-Structured Light devices are known in the art. 
     IR Time of Flight 
     This descriptor covers the use of time-of-flight cameras that work by emitting a pulse of light and then measuring the time taken for reflected light to reach each of the camera&#39;s sensor elements. This is a more direct method of measuring depth, but has currently not reached the cost and resolution levels useful for significant consumer adoption. Using this type of sensor, in some practices of the invention the feature correspondence operation noted above could be omitted, since accurate depth information is already provided directly from the sensor. 
     Single Camera Over Time 
     The V3D system of the invention can be configured to operate with multiple cameras positioned in a fixed relative position as part of a device. It is also possible to use a single camera, by taking images over time and with accurate tracking, so that the relative position of the camera between frames can be estimated with sufficient accuracy. With sufficiently accurate positional data, feature correspondence algorithms such as those described herein could continue to be used. 
     View-Vector Rotated Camera Configuration to Improve Correspondence Quality 
     The following describes a practice of the V3D invention that relates to the positioning of the cameras within the multi-camera configuration, to significantly increase the number of valid feature correspondences between images captured in real world settings. This approach is based on three observations:
         1. Users typically orient their display, tablet or phone at a rotation that is level with their eyes.   2. Many features in man-made indoor or urban environments consist of edges aligned in the three orthogonal axes (x, y, z).   3. In order to have a practical search domain, feature correspondence algorithms typically perform their search along horizontal or vertical epipolar lines in image space.       

     Taken together, these observations lead to the conclusion that there are often large numbers of edges for which there is no definite correspondence. This situation can be significantly improved while keeping the image processing overhead minimal, by applying a suitable rotation angle (or angular displacement) to the arrangement of the camera sensors, while also ensuring that the cameras are positioned relative to each other along epipolar lines. The amount of rotation angle can be relatively small. (See, for example,  FIGS.  9 ,  10  and  11   .) 
     After the images are captured in this alternative “rotated” configuration, the disparity values can either be rotated along with the images, or the reconstruction phase can be run, and the final image result rotated back to the correct orientation so that the user does not even perceive or see the rotated images. 
     There are a variety of spatial arrangements and orientations of the sensors that can accomplish a range of rotations while still fitting within many typical device form factors.  FIGS.  9 ,  10 , and  11    show three exemplary sensor configurations  90 ,  100 ,  110 . 
       FIG.  9    shows a handheld device  90  comprising a display screen  91  surrounded by a bezel  92 . Sensors  93 ,  94 , and  95  are located at the corners of bezel  92 , and define a pair of perpendicular axes: a first axis  96  between sensors  93  and  94 , and a second axis  97  between cameras  94  and  95 . 
       FIG.  10    shows a handheld device  100  comprising display  101 , bezel  102 , and sensors  103 ,  104 ,  105 . In  FIG.  10   , each of sensors  103 ,  104 ,  105  is rotated by an angle θ relative to bezel  102 . The position of the sensors  103 ,  104 , and  105  on bezel  102  has been configured so that the three sensors define a pair of perpendicular axes  106 ,  107 . 
       FIG.  11    shows a handheld device  110  comprising display  111 , bezel  112 , and sensors  113 ,  114 ,  115 . In the alternative configuration shown in  FIG.  11   , the sensors  113 ,  114 ,  115  are not rotated. The sensors  113 ,  114 ,  115  are positioned to define perpendicular axes  116 ,  117  that are angled with respect to bezel  112 . The data from sensors  113 ,  114 ,  115  are then rotated in software such that the correspondence continues to be performed along the epipolar lines. 
     Although an exemplary practice of the V3D invention uses 3 sensors to enable vertical and horizontal cross correspondence, the methods and practices described above are also applicable in a 2-camera stereo system. 
       FIGS.  12  and  13    next highlight advantages of a “rotated configuration” in accordance with the invention. In particular,  12 A shows a “non-rotated” device configuration  120 , with sensors  121 ,  122 ,  123  located in three corners, similar to configuration  90  shown in  FIG.  9   .  FIGS.  12 B,  12 C, and  12 D  (collectively,  FIGS.  12 A- 12 D  being referred to as “ FIG.  12   ”) show the respective scene image data collected at sensors  121 ,  122 ,  123 . 
     Sensors  121  and  122  define a horizontal axis between them, and generate a pair of images with horizontally displaced viewpoints. For certain features, e.g., features H 1 , H 2 , there is a strong correspondence (i.e., the horizontally-displaced scene data provides a high level of certainty with respect to the correspondence of these features). For other features, e.g., features H 3 , H 4 , the correspondence is weak, as shown in  FIG.  12    (i.e., the horizontally-displaced scene data provides a low level of certainty with respect to the correspondence of these features). 
     Sensors  122  and  123  define a vertical axis that is perpendicular to the axis defined by sensors  121  and  122 . Again, for certain features, e.g., feature V 1  in  FIG.  12   , there is a strong correspondence. For other features, e.g. feature V 2  in  FIG.  12   , the correspondence is weak. 
       FIG.  13 A  shows a device configuration  130 , similar to configuration  100  shown in  FIG.  10   , with sensors  131 ,  132 ,  133  positioned and rotated to define an angled horizontal axis and an angled vertical axis. As shown in  FIGS.  13 B,  13 C, and  13 D , the use of an angled sensor configuration eliminates the weakly corresponding features shown in  FIGS.  128 ,  12 C, and  12 D . As shown by  FIGS.  12  and  13   , a rotated configuration of sensors in accordance with an exemplary practice of the invention enables strong correspondence for certain scene features where the non-rotated configuration did not. 
     Multi-Exposure Cycling 
     In accordance with the invention, during the process of calculating feature correspondence, a feature is selected in one image and then scanned for a corresponding feature in another image. During this process, there can often be several possible matches found and various methods are used to establish which match (if any) has the highest likelihood of being the correct one. 
     As a general fact, when the input camera(s) capture an image, a choice is made to ensure that the camera exposure settings (such as gain and shutter speed) are selected according to various heuristics, with the goal of ensuring that a specific region or the majority of the image is within the dynamic range of the sensing element. Areas that are out of this dynamic range will either get clipped (overexposed regions) or suffer from a dominance of sensor noise rather than valid image signal. 
     During the process of feature correspondence and image reconstruction in an exemplary practice of the V3D invention, the correspondence errors in the excessively dark or light areas of the image can cause large-scale visible errors in the image by causing the computing of radically incorrect disparity or depth estimates. 
     Accordingly, another practice of the invention involves dynamically adjusting the exposure of the multi-view camera system on a frame-by-frame basis in order to improve the disparity estimation in areas out of the exposed region viewed by the user. Within the context of the histogram-based disparity method of the invention, described elsewhere herein, exposures taken at darker and lighter exposure settings surrounding the visibility optimal exposure would be taken, have their disparity calculated and then get integrated in the overall pixel histograms which are being retained and converged over time. The dark and light images could be, but are not required to be, presented to the user and would serve only to improve the disparity estimation. 
     Another aspect of this approach, in accordance with the invention, is to analyze the variance of the disparity histograms on “dark” pixels, “mid-range” pixels and “light pixels”, and use this to drive the exposure setting of the cameras, thus forming a closed loop system between the quality of the disparity estimate and the set of exposures which are requested from the input multi-view camera system. For example, if the cameras are viewing a purely indoor environment, such as an interior room, with limited dynamic range due to indirect lighting, only one exposure may be needed. If, however, the user were to (e.g.) open curtains or shades, and allow direct sunlight to enter into the room, the system would lack a strong disparity solution in those strongly lit areas and in response to the closed loop control described herein, would choose to occasionally take a reduced exposure sample on occasional video frames. 
     Image Rectification 
     An exemplary practice of the V3D system executes image rectification in real-time using the GPU hardware of the device on which it is operating, such as a conventional smartphone, to facilitate and improve an overall solution. 
     Typically, within a feature correspondence system, a search must be performed between two cameras arranged in a stereo configuration in order to detect the relative movement of features in the image due to parallax. This relative movement is measured in pixels and is referred to as “the disparity”. 
       FIG.  14    shows an exemplary pair of unrectified and distorted camera (URD) source camera images  140 A and  140 B for left and right stereo. As shown in  FIG.  14   , the image pair includes a matched feature, i.e., the subject&#39;s right eye  141 A,  140 B. The matching feature has largely been shifted horizontally, but there is also a vertical shift because of slight misalignment of the cameras and the fact that there is a polynomial term resulting from lens distortion. The matching process can be optimized by measuring the lens distortion polynomial terms, and by inferring the affine transform required to apply to the images such that they are rectified to appear perfectly horizontally aligned and co-planar. When this is done, what would otherwise be a freeform 2D search for a feature match can now be simplified by simply searching along the same horizontal row on the source image to find the match. 
     Typically, this is done in one step, in which the lens distortion and then affine transform coefficients are determined and applied together to produce the corrected images. One practice of the invention, however, use a different approach, which will next be described. First, however, we define a number of terms used herein to describe this approach and the transforms used therein, as follows: 
     URD (Unrectified, Distorted) space: This is the image space in which the source camera images are captured. There is both polynomial distortion due to the lens shape and an affine transform that makes the image not perfectly co-planar and axis-aligned with the other stereo image. The number of URD images in the system is equal to the number of cameras in the system. 
     URUD (Unrectified, Undistorted) space: This is a space in which the polynomial lens distortion is removed from the image but the images remain unrectified. The number of URUD images in the system is equal to number of URD images and therefore, cameras, in the system. 
     RUD (Rectified, Undistorted) space: This is a space in which both the polynomial lens distortion is removed from the image and an affine transform is applied to make the image perfectly co-planar and axis aligned with the other stereo image on the respective axis. RUD always exist in pairs. As such, for example, in a 3 camera system where the cameras are arranged in a substantially L-shaped configuration (having two axes intersecting at a selected point), there would be two stereo axes, and thus 2 pairs of RUD images, and thus a total of 4 RUD images in the system. 
       FIG.  15    is a flow diagram  150  providing various examples of possible transforms in a 4-camera V3D system. Note that there are 4 stereo axes. Diagonal axes (not shown) would also be possible. 
     The typical transform when sampling the source camera images in a stereo correspondence system is to transform from RUD space (the desired space for feature correspondence on a stereo axis) to URD space (the source camera images). 
     In an exemplary practice of the V3D invention, it is desirable to incorporate multiple stereo axes into the solution in order to compute more accurate disparity values. In order to do this, it is appropriate to combine the disparity solutions between independent stereo axes that share a common camera. As such, an exemplary practice of the invention makes substantial use of the URUD image space to connect the stereo axes disparity values together. This is a significant observation, because of the trivial invertibility of the affine transform (which is simply, for example, a 3×3 matrix). We would not be able to use the URD space to combine disparities between stereo axes because the polynomial lens distortion is not invertible, due to the problem of multiple roots and general root finding. This process of combining axes in the V3D system is further described below, in “Combining Correspondences on Additional Axes”. 
       FIG.  16    sets forth a flow diagram  160 , and  FIGS.  17 A-C  are a series of images that illustrate the appearance and purpose of the various transforms on a single camera image. 
     Feature Correspondence Algorithm 
     The “image correspondence problem” has been the subject of computer science research for many years. However, given the recent advent of the universal availability of low cost cameras and massively parallel computing hardware (GPUs) contained in many smartphones and other common mobile devices, it is now possible to apply brute force approaches and statistically based methods to feature correspondence, involving more than just a single stereo pair of images, involving images over the time dimension and at multiple spatial frequencies, to execute feature correspondence calculations at performance levels not previously possible. 
     Various exemplary practices of the invention will next be described, which are novel and represent significant improvement to the quality and reliability attainable in feature correspondence. A number of these approaches, in accordance with the invention, utilize a method of representation referred to herein as “Disparity Histograms” on a per-pixel (or pixel group) basis, to integrate and make sense of collected data. 
     Combining Correspondences on Additional Axes 
     An exemplary practice of the invention addresses the following two problems: 
     Typical correspondence errors resulting from matching errors in a single stereo image pair. 
     Major correspondence errors that occur when a particular feature in one image within the stereo pair does not exist in the other image. 
     This practice of the invention works by extending the feature correspondence algorithm to include one or more additional axes of correspondence and integrating the results to improve the quality of the solution. 
       FIGS.  18 A-D  illustrate an example of this approach.  FIG.  18 A  is a diagram of a sensor configuration  180  having 3 cameras  181 ,  182 ,  183  in a substantially L-shaped configuration such that a stereo pair exists on both the horizontal axis  185  and vertical axis  186 , with one camera in common between the axes, similar to the configuration  90  shown in  FIG.  9   . 
     Provided the overall system contains a suitable representation to integrate the multiple disparity solutions (one such representation being the “Disparity Histograms” practice of the invention discussed herein), this configuration will allow for uncertain correspondences in one stereo pair to be either corroborated or discarded through the additional information found by performing correspondence on the other axis. In addition, certain features which have no correspondence on one axis, may find a correspondence on the other axis, allowing for a much more complete disparity solution for the overall image than would otherwise be possible. 
       FIGS.  18 B,  18 C, and  18 D  are depictions of three simultaneous images received respectively by sensors  181 ,  182 ,  183 . The three-image set is illustrative of all the points mentioned above. 
     Feature (A), i.e., the human subject&#39;s nose, is found to correspond both on the horizontal stereo pair ( FIGS.  18 B and  18 C ) and the vertical stereo pair ( FIGS.  18 C and  18 D ). Having the double correspondence helps eliminate correspondence errors by improving the signal-to-noise ratio, since the likelihood of the same erroneous correspondence being found in both axes is low. 
     Feature (B), i.e., the spool of twine, is found to correspond only on the horizontal stereo pairs. Had the system only included a vertical pair, this feature would not have had a depth estimate because it is entirely out of view on the upper image. 
     Feature (C), i.e., the cushion on the couch, is only possible to correspond on the vertical axis. Had the system only included a horizontal stereo pair, the cushion would have been entirely occluded in the left image, meaning no valid disparity estimate could have been established. 
     An important detail is that in many cases the stereo pair on a particular axis will have undergone a calibration process such that the epipolar lines are aligned to the rows or columns of the images. Each stereo axis will have its own unique camera alignment properties and hence the coordinate systems of the features will be incompatible. In order to integrate disparity information on pixels between multiple axes, the pixels containing the disparity solutions will need to undergo coordinate transformation to a unified coordinate system. In an exemplary practice of the invention, this means that the stereo correspondence occurs in the RUD space but the resultant disparity data and disparity histograms would be stored in the URUD (Unrectified, Undistorted) coordinate system and a URUD to RUD transform would be performed to gather the per-axis disparity values. 
     Correspondence Refinement Over Time 
     This aspect of the invention involves retaining a representation of disparity in the form of the error function or, as described elsewhere herein, the disparity histogram, and continuing to integrate disparity solutions for each frame in time to converge on a better solution through additional sampling. 
     Filling Unknowns with Historical Data from Previous Frames 
     This aspect of the invention is a variation of the correspondence refinement over time aspect. In cases where a given feature is detected but for which no correspondence can be found in another camera, if there was a prior solution for that pixel from a previous frame, this can be used instead. 
     Histogram-Based Disparity Representation Method 
     This aspect of the invention provides a representation to allow multiple disparity measuring techniques to be combined to produce a higher quality estimate of image disparity, potentially even over time. It also permits a more efficient method of estimating disparity, taking into account more global context in the images, without the significant cost of large per pixel kernels and image differencing. 
     Most disparity estimation methods for a given pixel in an image in the stereo pair involve sliding a region of pixels (known as a kernel) surrounding the pixel in question from one image over the other in the stereo pair, and computing the difference for each pixel in the kernel, and reducing this to a scalar value for each disparity being tested. 
     Given a kernel of reference pixels and a kernel of pixels to be compared with the reference, a number of methods exist to produce a scalar difference between them, including the following:
         1. Sum of Absolute Differences (SAD)   2. Zero-mean Sum of Absolute Differences (ZSAD)   3. Locally scaled Sum of Absolute Differences (LSAD)   4. Sum of Squared Differences (SSD)   5. Zero-mean Sum of Squared Differences (ZSSD)   6. Locally scaled Sum of Squared Differences (LSSD)   7. Normalized Cross Correlation (NCC)   8. Zero-Mean Normalized Cross Correlation (ZNCC)   9. Sum of Hamming Distances (SHD)       

     This calculation is repeated as the kernel is slid over the image being compared. 
       FIG.  19    is a graph  190  of cumulative error for a 5×5 block of pixels for disparity values between 0 and 128 pixels. In this example, it can be seen that there is a single global minimum that is likely to be the best solution. 
     In various portions of this description of the invention, reference may be made to a specific one of the image comparison methods, such as SSD (Sum of Square Differences). Those skilled in the art will understand that in many instances, others of the above-listed image comparison error measurement techniques could be used, as could others known in the art. Accordingly, this aspect of the image processing technique is referred to herein as a “Fast Dense Disparity Estimate”, or “FDDE”. 
     Used by itself, this type of approach has some problems, as follows: 
     Computational Overhead 
     Every pixel for which a disparity solution is required must perform a large number of per pixel memory access and math operations. This cost scales approximately with the square of the radius of the kernel multiplied by the number of possible disparity values to be tested for. 
     Non-Uniform Importance of Individual Features in the Kernel 
     With the exception of the normalized cross correlation methods, the error function is significantly biased based on image intensity similarity across the entire kernel. This means that subtle features with non-extreme intensity changes will fail to attain a match if they are surrounded by areas of high intensity change, since the error function will tend to “snap” to the high intensity regions. In addition, small differences in camera exposure will bias the disparity because of the “non-democratic” manner in which the optimal kernel position is chosen. 
     An example of this is shown in  FIGS.  20 A-B  and  21 A-B.  FIGS.  20 A and  20 B  are two horizontal stereo images.  FIGS.  21 A and  21 B , which correspond to  FIGS.  20 A and  20 B , show a selected kernel of pixels around the solution point for which we are trying to compute the disparity. It can be seen that for the kernel at its current size, the cumulative error function will have two minima, one representing the features that have a small disparity since they are in the image background, and those on the wall which are in the foreground and will have a larger disparity. In the ideal situation, the minima would flip from the background to the foreground disparity value as close to the edge of the wall as possible. In practice, due to the high intensity of the wall pixels, many of the background pixels snap to the disparity of the foreground, resulting in a serious quality issue forming a border near the wall. 
     Lack of Meaningful Units 
     The units of measure of “error”, i.e. the Y-axis on the example graph, is unscaled and may not be compatible between multiple cameras, each with its own color and luminance response. This introduces difficulty in applying statistical methods or combining error estimates produced through other methods. For example, computing the error function from a different stereo axis would be incompatible in scale, and thus the terms could not be easily integrated to produce a better error function. 
     This is an instance in which the disparity histogram method of the invention becomes highly useful, as will next be described. 
     Operation of the Disparity Histogram Representation 
     One practice of the disparity histogram solution method of the invention works by maintaining a histogram showing the relative likelihood of a particular disparity being valid for a given pixel. In other words, the disparity histogram behaves as a probability density function (PDF) of disparity for a given pixel, higher values indicating a higher likelihood that the disparity range is the “truth”. 
       FIG.  22    shows an example of a typical disparity histogram for a pixel. For each pixel histogram, the x-axis indicates a particular disparity range and the scaley-axis is the number of pixels in the kernel surrounding the central pixel that are “voting” for that given disparity range. 
       FIGS.  23  and  24    show a pair of images and associated histograms. As shown therein, the votes can be generated by using a relatively fast and low-quality estimate of disparity produced using small kernels and standard SSD type methods. According to an aspect of the invention, the SSD method is used to produce a “fast dense disparity map” (FDDE), wherein each pixel has a selected disparity that is the lowest error. Then, the algorithm would go through each pixel, accumulating into the histogram a tally of the number of votes for a given disparity in a larger kernel surrounding the pixel. 
     With a given disparity histogram, many forms of analysis can be performed to establish the most likely disparity for the pixel, confidence in the solution validity, and even identify cases where there are multiple highly likely solutions. For example, if there is a single dominant mode in the histogram, the x coordinate of that peak denotes the most likely disparity solution. 
       FIG.  25    shows an example of a bi-modal disparity histogram with 2 equally probable disparity possibilities. 
       FIG.  26    is a diagram of an example showing the disparity histogram and associated cumulative distribution function (CDF). The interquartile range is narrow, indicating high confidence. 
       FIG.  27    is a contrasting example showing a wide interquartile range in the CDF and thus a low confidence in any peak within that range. 
     By transforming the histogram into a cumulative distribution function (CDF), the width of the interquartile range can be established. This range can then be used to establish a confidence level in the solution. A narrow interquartile range (as in  FIG.  26   ) indicates that the vast majority of the samples agree with the solution, whereas a wide interquartile range (as in  FIG.  27   ) indicates that the solution confidence is low because many other disparity values could be the truth. 
     A count of the number of statistically significant modes in the histogram can be used to indicate “modality.” For example, if there are two strong modes in the histogram (as in  FIG.  25   ), it is highly likely that the point in question is right on the edge ofa feature that demarks a background versus foreground transition in depth. This can be used to control the reconstruction later in the pipeline to control stretch versus slide (discussed in greater detail elsewhere herein). 
     Due to the fact that the y-axis scale is now in terms of votes for a given disparity rather than the typical error functions, the histogram is not biased by variation in image intensity at all, allowing for high quality disparity edges on depth discontinuities. In addition, this permits other methods of estimating disparity for the given pixel to be easily integrated into a combined histogram. 
     If we are processing multiple frames of images temporally, we can preserve the disparity histograms over time and accumulate samples into them to account for camera noise or other spurious sources of motion or error. 
     If there are multiple cameras, it is possible to produce fast disparity estimates for multiple independent axes and combine the histograms to produce a much more statistically robust disparity solution. With a standard error function, this would be much more difficult because the scale would make the function less compatible. With the histograms of the present invention, in contrast, everything is measured in pixel votes, meaning the results can simply be multiplied or added to allow agreeing disparity solutions to compound, and for erroneous solutions to fall into the background noise. 
     Using the histograms, if we find the interquartile range of the CDF to be wide in areas of a particular image intensity, this may indicate an area of poor signal to noise, i.e., underexposed to overexposed areas. Using this, we can control the camera exposures to fill in poorly sampled areas of the histograms. 
     Computational performance is another major benefit of the histogram based method. The SSD approach (which is an input to the histogram method) is computationally demanding due to the per pixel math and memory access for every kernel pixel for every disparity to be tested. With the histograms, a small SSD kernel is all that is needed to produce inputs to the histograms. This is highly significant, since SSD performance is proportional to the square of its kernel size multiplied by the number of disparity values being tested for. Even through the small SSD kernel output is a noisy disparity solution, the subsequent voting, which is done by a larger kernel of the pixels to produce the histograms, filters out so much of the noise that it is, in practice, better than the SSD approach, even with very large kernels. The histogram accumulation is only an addition function, and need only be done once per pixel per frame and does not increase in cost with additional disparity resolution. 
     Another useful practice of the invention involves testing only for a small set of disparity values with SSD, populating the histogram, and then using the histogram votes to drive further SSD testing within that range to improve disparity resolution over time. 
     One implementation of the invention involves each output pixel thread having a respective “private histogram” maintained in on-chip storage close to the computation units (e.g., GPUs). This private histogram can be stored such that each pixel thread will be reading and writing to the histogram on a single dedicated bank of shared local memory on a modern programmable GPU. In addition, if the maximum possible number of votes is known, multiple histogram bins can be packed into a single word of the shared local memory and accessed using bitwise operations. These details can be useful to reduce the cost of dynamic indexing into an array during the voting and the summation. 
     Multi-Level Histogram Voting 
     This practice of the invention is an extension of the disparity histogram aspect of the invention, and has proven to be an highly useful part of reducing error in the resulting disparity values, while still preserving important detail on depth discontinuities in the scene. 
     Errors in the disparity values can come from many sources. Multi-level disparity histograms reduce the contribution from several of these error sources, including:
         1. Image sensor noise.   2. Repetitive patterns at a given image frequency.       

     As with the idea of combining multiple stereo axes&#39; histogram votes into the disparity histogram for the purpose of “tie-breaking” and reducing false matches, the multi-level voting scheme applies that same concept, but across descending frequencies in the image space. 
       FIGS.  28 A and  28 B  shows an example of a horizontal stereo image pair.  FIGS.  28 C and  28 D  show, respectively, the resulting disparity data before and after application of the described multi-level histogram technique. 
     This aspect of the invention works by performing the image pattern matching (FDDE) at several successively low-pass filtered versions of the input stereo images. The term “level” is used herein to define a level of detail in the image, where higher level numbers imply a lower level of detail. In one practice of the invention, the peak image frequencies at level[n] will be half that of level[n−1]. 
     Many methods can be used to downsample, and such methods known in the area of image processing. Many of these methods involve taking a weighed summation of a kernel in level[n−1] to produce a pixel in level[n]. In one practice of the invention, the approach would be for the normalized kernel center position to remain the same across all of the levels. 
       FIGS.  30 A-E  are a series of exemplary left and right multi-level input images. Each level[n] is a downsampled version of level [n−1]. In the example of  FIG.  30   , the downsampling kernel is a 2×2 kernel with equal weights of 0.25 for each pixel. The kernel remains centered at each successive level of downsampling. 
     In this practice of the invention, for a given desired disparity solution at the full image resolution, the FDDE votes for every image level are included. Imagine a repetitive image feature, such as the white wooden beams on the cabinets shown in the background of the example of  FIG.  30   . At Level[ 0 ] (the full image resolution), several possible matches may be found by the FDDE image comparisons since each of the wooden beams looks rather similar to each other, given the limited kernel size used for the FDDE. 
       FIG.  31    depicts an example of an image pair and disparity histogram, illustrating an incorrect matching scenario and its associated disparity histogram (see the notation “Winning candidate: incorrect” in the histogram of  FIG.  31   ). 
     In contrast, and in accordance with an exemplary practice of the invention,  FIG.  32    shows the same scenario, but with the support of 4 lower levels of FDDE votes in the histogram, resulting in a correct winning candidate (see the notation “Winning candidate: correct” in the histogram of  FIG.  31   ). Note that the lower levels provide support for the true candidate at the higher levels. As shown in  FIG.  32   , if one looks at a lower level (i.e., a level characterized by reduced image resolution via low-pass filtering), the individual wooden beams shown in the image become less pronounced, and the overall form of the broader context of that image region begins to dominate the pattern matching. By combining together all the votes at each level, where there may have been multiple closely competing candidate matches at the lower levels, the higher levels will likely have fewer potential candidates, and thus cause the true matches at the lower levels to be emphasized and the erroneous matches to be suppressed. This is the “tie-breaking” effect that this practice of the invention provides, resulting in a higher probability of correct winning candidates. 
       FIG.  33    is a schematic diagram of an exemplary practice of the invention. In particular,  FIG.  33    depicts a processing pipeline showing the series of operations between the input camera images, through FDDE calculation and multi-level histogram voting, into a final disparity result. As shown in  FIG.  33   , multiple stereo axes (e.g.,  0  through n) can be included into the multi-level histogram. 
     Having described multi-level disparity histogram representations in accordance with the invention, the following describes how the multi-level histogram is represented, and how to reliably integrate its results to locate the final, most likely disparity solution. 
     Representation of the Multi-Level Histogram 
       FIG.  34    shows a logical representation of the multi-level histogram after votes have been placed at each level.  FIG.  35    shows a physical representation of the same multi-level histogram in numeric arrays in device memory, such as the digital memory units in a conventional smartphone architecture. In an exemplary practice of the invention, the multi-level histogram consists of a series of initially independent histograms at each level of detail. Each histogram bin in a given level represents the votes for a disparity found by the FDDE at that level. Since level[n] has a fraction the resolution as that of level[n−1], each calculated disparity value represents a disparity uncertainty range which is that same fraction as wide. For example, in  FIG.  34   , each level is half the resolution as the one above it. As such, the disparity uncertainty range represented by each histogram bin is twice as wide as the level before it. 
     Sub-Pixel Shifting of Input Images to Enable Multi-Level Histogram Integration 
     In an exemplary practice of the invention, a significant detail to render the multi-level histogram integration correct involves applying a sub-pixel shift to the disparity values at each level during downsampling. As shown in  FIG.  34   , if we look at the votes in level[ 0 ], disparity bin  8 , these represent votes for disparity values 8-9. At level[ 1 ], the disparity bins are twice as wide. As such, we want to ensure that the histograms remain centered under the level above. Level[ 1 ] shows that the same bin represents 7.5 through 9.5. This half-pixel offset is highly significant, because image error can cause the disparity to be rounded to the neighbor bin and then fail to receive support from the level below. 
     In order to ensure that the histograms remain centered under the level above, an exemplary practice of the invention applies a half pixel shift to only one of the images in the stereo pair at each level of down sampling. This can be done inline within the weights of the filter kernel used to do the downsampling between levels. While it is possible to omit the half pixel shift and use more complex weighting during multi-level histogram summation, it is very inefficient. Performing the half pixel shift during down-sampling only involves modifying the filter weights and adding two extra taps, making it almost “free”, from a computational standpoint. 
     This practice of the invention is further illustrated in  FIG.  36   , which shows an example of per-level downsampling according to the invention, using a 2×2 box filter. On the left is illustrated a method without a half pixel shift. On the right of  FIG.  36    is illustrated the modified filter with a half pixel shift, in accordance with an exemplary practice of the invention. Note that this half pixel shift should only be applied to one of the image in the stereo pair. This has the effect of disparity values remaining centered at each level in the multi-level histogram during voting, resulting in the configuration shown in  FIG.  34   . 
     Integration of the Multi-Level Histogram 
       FIG.  37    illustrates an exemplary practice of the invention, showing an example of the summation of the multi-level histogram to produce a combined histogram in which the peak can be found. Provided that the correct sub-pixel shifting has been applied, the histogram integration involves performing a recursive summation across all of the levels as shown in  FIG.  37   . Typically, only the peak disparity index and number of votes for that peak are needed and thus the combined histogram does not need to be actually stored in memory. In addition, maintaining a summation stack can reduce summation operations and multi-level histogram memory access. 
     During the summation, the weighting of each level can be modified to control the amount of effect that the lower levels in the overall voting. In the example shown in  FIG.  37   , the current value at level[n] gets added to two of the bins above it in level[n−1] with a weight of ½ each. 
     Extraction of Sub-Pixel Disparity Information from Disparity Histograms 
     An exemplary practice of the invention, illustrated in  FIGS.  39 - 40   , builds on the disparity histograms and allows for a higher accuracy disparity estimate to be acquired without requiring any additional SSD steps to be performed, and for only a small amount of incremental math when selecting the optimal disparity from the histogram. 
       FIG.  38    is a disparity histogram for a typical pixel. In the example, there are 10 possible disparity values, each tested using SSD and then accumulated into the histogram with 10 bins. In this example, there is a clear peak in the 4th bin, which means that the disparity lies between 3 and 4 with a center point of 3.5. 
       FIG.  39    is a histogram in a situation in which a sub-pixel disparity solution can be inferred from the disparity histogram. We can see that an even number of votes exists in the 3rd and 4th bins. As such, we can say that the true disparity range lies between 3.5 and 4.5 with a center point of 4.0. 
       FIG.  40    is a histogram that reveals another case in which a sub-pixel disparity solution can be inferred. In this case, the 3rd bin is the peak with 10 votes. Its directly adjacent neighbor is at 5 votes. As such, we can state that the sub-pixel disparity is between these two and closer to the 3rd bin, ranging from 3.25 to 4.25, using the following equation: 
     
       
         
           
             SubpixelOffset 
             = 
             
               
                 Votes 
                 
                   2 
                   ⁢ 
                   ndBest 
                 
               
               
                 2 
                 ⁢ 
                 
                   ( 
                   
                     Votes 
                     Best 
                   
                   ) 
                 
               
             
           
         
       
     
     Center-Weighted SSD Method 
     Another practice of the invention provides a further method of solving the problem where larger kernels in the SSD method tend to favor larger intensity differences with the overall kernel, rather than for the pixel being solved. This method of the invention involves applying a higher weight to the center pixel with a decreasing weight proportional to the distance of the given kernel sample from the center. By doing this, the error function minima will tend to be found closer to the valid solution for the pixel being solved. 
     Injective Constraint 
     Yet another aspect of the invention involves the use of an “injective constraint”, as illustrated in  FIGS.  41 - 45   . When producing a disparity solution for an image, the goal is to produce the most correct results possible. Unfortunately, due to imperfect input data from the stereo cameras, incorrect disparity values will get computed, especially if only using the FDDE data produced via image comparison using SSD, SAD or one of the many image comparison error measurement techniques. 
       FIG.  41    shows an exemplary pair of stereoscopic images and the disparity data resulting from the FDDE using SAD with a 3×3 kernel. Warmer colors represent closer objects. A close look at  FIG.  41    reveals occasional values which look obviously incorrect. Some of the factors causing these errors include camera sensor noise, image color response differences between sensors and lack of visibility of a common feature between cameras. 
     In accordance with the invention, one way of reducing these errors is by applying “constraints” to the solution which reduce the set of possible solutions to a more realistic set of possibilities. As discussed elsewhere herein, solving the disparity across multiple stereo axes is a form of constraint, by using the solution on one axis to reinforce or contradict that of another axis. The disparity histograms are another form of constraint by limiting the set of possible solutions by filtering out spurious results in 2D space. Multi-level histograms constrain the solution by ensuring agreement of the solution across multiple frequencies in the image. 
     The injective constraint aspect of the invention uses geometric rules about how features must correspond between images in the stereo pair to eliminate false disparity solutions. It maps these geometric rules on the concept of an injective function in set theory. 
     In set theory there are four major categories of function type that map one set of items (the domain) onto another set (the co-domain):
         1. Injective, surjective function (also known as a bijection): All elements in the co-domain are reference exactly once by elements in the domain.   2. Injective, non-surjective function: Some elements in the co-domain are references at most once by elements in the domain. This means that not all elements in the co-domain have to be referenced, but no element will be referenced more than once.   3. Non-injective, surjective function: All elements in the co-domain are referenced one or more times by elements in the domain.   4. Non-injective, non-surjective function: Some elements in the co-domain are referenced one or more times by elements in the domain. This means that not all elements in the co-domain have to be referenced.       

     In the context of feature correspondence, the domain and co-domain are pixels from each of the stereo cameras on an axis. The references between the sets are the disparity values. For example, if every pixel in the domain (image A) had a disparity value of “0”, then this means that a perfect bijection exists between the two images, since every pixel in the domain maps to the same pixel in the co-domain. 
     Given the way that features in an image are shifted between the two cameras, we know that elements in the co-domain (image B) can only shift in one direction (i.e. disparity values are ≥0) for diffuse features in the scene. When features exist at the same depth they will all shift together at the same rate, maintaining a bijection. 
       FIG.  42    shows an example of a bijection where every pixel in the domain maps to a unique pixel in the co-domain. In this case, the image features are all at infinity distance and thus do not appear to shift between the camera images. 
       FIG.  43    shows another example of a bijection. In this case all the image features are closer to the cameras, but are all at the same depth and hence shift together. 
     However, since features will exist at different depths, some features will shift more than others and will sometimes even cross over each other. In this situation, occlusions in the scene will be occurring which means that sometimes, a feature visible in image “A” will be totally occluded by another object in the image “B”. 
     In this situation, not every feature in the co-domain image will be referenced if it was occluded in the domain image. Even still, it is impossible for a feature in the co-domain to be referenced more than one time by the domain. This means that while we cannot enforce a bijective function, we can assert that the function must be injective. This is where the name “injective constraint” is derived. 
       FIG.  44    shows an example of an image with a foreground and background. Note that the foreground moves substantially between images. This causes new features to be revealed in the co-domain that will have no valid reference in the domain. This is still an injective function, but not a bijection. 
     In accordance with the invention, now that we know we can enforce this constraint, we are able to use it as a form of error correction in the disparity solution. In an exemplary practice of the invention, a new stage would be inserted in the feature correspondence pipeline (either after the FDDE calculation but before histogram voting, or perhaps after histogram voting) that checks for violations of this constraint. By maintaining a reference count for each pixel in the co-domain and checking to ensure that the reference count never exceeds 1, we can determine that a violation exists. (See, e.g.,  FIG.  45   , which shows an example of a detected violation of the injective constraint.) 
     In accordance with the invention, if such a violation is detected, there are several ways of addressing it. These approaches have different performance levels, implementation complexity and memory overheads that will suggest which are appropriate in a given situation. They include the following: 
     1. First come, first served: The first element in the domain to claim an element in co-domain gets priority. If a second element claims the same co-domain element, we invalidate that match and mark it as “invalid”. Invalid disparities would be skipped over or interpolated across later in the pipeline. 
     2. Best match wins: The actual image matching error or histogram vote count are compared between the two possible candidate element in the domain against the contested element in the co-domain. The one with the best match wins. 
     Smallest disparity wins: During image reconstruction, typically errors caused by too small a disparity are less noticeable than errors with too high a disparity. As such, if there is contest for a given co-domain element, select the one with the smallest disparity and invalidate the others. 
     Seek alternative candidates: Since each disparity value is the result of selecting a minimum in the image comparison error function or histogram peak vote count, this means there may be alternative possible matches, which didn&#39;t score as well. As such, if there is a contest for a given co-domain element, select the 2nd or 3rd best candidate in that order. This approach may need to iterate several times in order to ensure that all violations are eliminated across the entire domain. If after a given number of fall back attempts, the disparity value could be set to “invalid” as described in (1). This attempt threshold would be a tradeoff between finding the ideal solution and computation time. 
     The concept of alternative match candidates is illustrated, by way of example, in  FIG.  46   , which shows a graph of an exemplary image comparison error function. As shown therein, in addition to the global minimum error point, there are other error minimums that could act as alternative match candidates. 
     The Representation Stage 
     Disparity and Sample Buffer Index at 2D Control Points 
     An exemplary practice of the invention involves the use of a disparity value and a sample buffer index at 2D control points. This aspect works by defining a data structure representing a 2D coordinate in image space and containing a disparity value, which is treated as a “pixel velocity” in screen space with respect to a given movement of the view vector. 
     With a strong disparity solution, that single scalar value can be modulated with a movement vector to slide around a pixel in the source image in any direction in 2D, and it will produce a credible reconstruction of 3D image movement as if it had been taken from that different location. 
     In addition, the control points can contain a sample buffer index that indicates which of the camera streams to take the samples from. For example, a given feature may be visible in only one of the cameras in which case we will want to change the source that the samples are taken from when reconstructing the final reconstructed image. 
     Not every pixel must have a control point since the movement of most pixels can be approximated by interpolating the movement of key surrounding pixels. As such, there are several methods that can be used to establish when a pixel should be given a control point. Given that the control points are used to denote an important depth change, the control points should typically be placed along edges in the image, since edges often correspond to depth changes. 
     Computing edges is a known technique already present in commercially available camera pipelines and image processing. Most conventional approaches are based on the use of image convolution kernels such as the Sobel filter, and its more complex variants and derivatives. These work by taking the first derivative of the image intensity to produce a gradient field indicating the rate of change of image intensity surrounding each pixel. From this a second derivative can be taken, thus locating the peaks of image intensity change and thus the edges as would be perceived by the human vision system. 
     Extraction of Unique Samples for Streaming Bandwidth Reduction 
     This aspect of the invention is based on the observation that many of the samples in the multiple camera streams are of the same feature and are thus redundant. With a valid disparity estimate, it can be calculated that a feature is either redundant or is a unique feature from a specific camera and features/samples can be flagged with a reference count of how many of the views “reference” that feature. 
     Compression Method for Streaming with Video 
     Using the reference count established above, a system in accordance with the invention can choose to only encode and transmit samples exactly one time. For example, if the system is capturing 4 camera streams to produce the disparity and control points and have produced reference counts, the system will be able to determine whether a pixel is repeated in all the camera views, or only visible in one. As such, the system need only transmit to the encoder the chunk of pixels from each camera that are actually unique. This allows for a bandwidth reduction in a video streaming session. 
     Head Tracking 
     Tracking to Control Modulation of Disparity Values 
     Using conventional head tracking methods, a system in accordance with the invention can establish an estimate of the viewer&#39;s head or eye location and/or orientation. With this information and the disparity values acquired from feature correspondence or within the transmitted control point stream, the system can slide the pixels along the head movement vector at a rate that is proportional to the disparity. As such, the disparity forms the radius of a “sphere” of motion for a given feature. 
     This aspect allows a 3D reconstruction to be performed simply by warping a 2D image, provided the control points are positioned along important feature edges and have a sufficiently high quality disparity estimate. In accordance with this method of the invention, no 3D geometry in the form of polygons or higher order surfaces is required. 
     Tracking to Control Position of 2D Crop Box Location and Size in Reconstruction 
     In order to create the appearance of an invisible device display, the system of the invention must not only re-project the view from a different view origin, but must account for the fact that as the viewer moves his or her head, they only see an aperture into the virtual scene defined by the perimeter of the device display. In accordance with a practice of the invention, a shortcut to estimate this behavior is to reconstruct the synthetic view based on the view origin and then crop the 2D image and scale it up to fill the view window before presentation, the minima and maxima of the crop box being defined as a function of the viewer head location with respect to the display and the display dimensions. 
     Hybrid Markerless Head Tracking 
     An exemplary practice of the V3D invention contains a hybrid 2D/3D head detection component that combines a fast 2D head detector with the 3D disparity data from the multi-view solver to obtain an accurate viewpoint position in 3D space relative to the camera system. 
       FIGS.  47 A-B  provide a flow diagram that illustrates the operation of the hybrid markerless head tracking system. As shown in  FIGS.  47 A-B , starting with an image captured by one of the color cameras, the system optionally converts to luminance and downsamples the image, and then passes it to a basic 2D facial feature detector. The 2D feature detector uses the image to extract an estimate of the head and eye position as well as the face&#39;s rotation angle relative to the image plane. These extracted 2D feature positions are extremely noisy from frame to frame which, if taken alone as a 3D viewpoint, would not be sufficiently stable for the intended purposes of the invention. Accordingly, the 2D feature detection is used as a starting estimate of a head position. 
     The system uses this 2D feature estimate to extract 3D points from the disparity data that exists in the same coordinate system as the original 2D image. The system first determines an average depth for the face by extracting 3D points via the disparity data for a small area located in the center of the face. This average depth is used to determine a reasonable valid depth range that would encompass the entire head. 
     Using the estimated center of the face, the face&#39;s rotation angle, and the depth range, the system then performs a 2D ray march to determine a best-fit rectangle that includes the head. For both the horizontal and vertical axis, the system calculates multiple vectors that are perpendicular to the axis but spaced at different intervals. For each of these vectors, the system tests the 3D points starting from outside the head and working towards the inside, to the horizontal or vertical axis. When a 3D point is encountered that falls within the previously designated valid depth range, the system considers that a valid extent of the head rectangle. 
     From each of these ray marches along each axis, the system can determine a best-fit rectangle for the head, from which the system then extracts all 3D points that lie within this best-fit rectangle and calculates a weighted average. If the number of valid 3D points extracted from this region pass a threshold in relation to the maximum number of possible 3D points in the region, then there is designated a valid 3D head position result. 
       FIG.  48    is a diagram depicting this technique for calculating the disparity extraction two-dimensional rectangle (i.e., the “best-fit rectangle”). 
     To compensate for noise in the 3D position, the system can interpolate from frame-to-frame based on the time delta that has passed since the previous frame. 
     Reconstruction 
     2D Warping Reconstruction of Specific View from Samples and Control Points 
     This method of the invention works by taking one or more source images and a set of control points as described previously. The control points denote “handles” on the image which we can then move around in 2D space and interpolate the pixels in between. The system can therefore slide the control points around in 2D image space proportionally to their disparity value and create the appearance of an image taken from a different 3D perspective. The following are details of how the interpolation can be accomplished in accordance with exemplary practices of the invention. 
     Lines 
     This implementation of 2D warping uses the line drawing hardware and texture filtering available on modern GPU hardware, such as in a conventional smartphone or other mobile device. It has the advantages of being easy to implement, fast to calculate, and avoiding the need to construct complex connectivity meshes between the control points in multiple dimensions. 
     It works by first rotating the source images and control points coordinates such that the rows or columns of pixels are parallel to the vector between the original image center and the new view vector. For purposes of this explanation, assume the view vector is aligned to image scanlines. Next, the system iterates through each scanline and goes through all the control points for that scanline. The system draws a line beginning and ending at each control point in 2D image space, but adds the disparity multiplied by the view vector magnitude with the x coordinate. The system assigns a texture coordinate to the beginning and end points that is equal to their original 2D location in the source image. 
     The GPU will draw the line and will interpolate the texture coordinates linearly along the line. As such, image data between the control points will be stretched linearly. Provided control points are placed on edge features, the interpolation will not be visually obvious. 
     After the system has drawn all the lines, the result is a re-projected image, which is then rotated back by the inverse of the rotation originally applied to align the view vector with the scanlines. 
     Polygons 
     This approach is related to the lines but works by linking control points not only along a scanline but also between scanlines. In certain cases, this may provide a higher quality interpolation than lines alone. 
     Stretch/Slide 
     This is an extension of the control points data structure and effects the way the reconstruction interpolation is performed. It helps to improve the reconstruction quality on regions of large disparity/depth change. In such regions, for example on the boundary of a foreground and background object, it is not always idea to interpolate pixels between control points, but rather to slide the foreground and background independently of each other. This will open up a void in the image, but this gets filled with samples from another camera view. 
     The determination of when it is appropriate to slide versus the default stretching behavior can be made by analyzing the disparity histogram and checking for multi-modal behavior. If two strong modes are present, this indicates the control point is on a boundary where it would be better to allow the foreground and background to move independently rather than interpolating depth between them. 
     Other practices of the invention can include a 2D crop based on head location (see the discussion above relating to head tracking), and rectification transforms for texture coordinates. Those skilled in the art will understand that the invention can be practiced in connection with conventional 2D displays, or various forms of head-mounted stereo displays (HMDs), which may include binocular headsets or lenticular displays. 
     Digital Processing Environment in which Invention can be Implemented 
     Those skilled in the art will understand that the above described embodiments, practices and examples of the invention can be implemented using known network, computer processor and telecommunications devices, in which the telecommunications devices can include known forms of cellphones, smartphones, and other known forms of mobile devices, tablet computers, desktop and laptop computers, and known forms of digital network components and server/cloud/network-client architectures that enable communications between such devices. 
     Those skilled in the art will also understand that method aspects of the present invention can be executed in commercially available digital processing systems, such as servers, PCs, laptop computers, tablet computers, cellphones, smartphones and other forms of mobile devices, as well as known forms of digital networks, including architectures comprising server, cloud, network, and client aspects, for communications between such devices. 
     The terms “computer software,” “computer code product,” and “computer program product” as used herein can encompass any set of computer-readable programs instructions encoded on a non-transitory computer readable medium. A computer readable medium can encompass any form of computer readable element, including, but not limited to, a computer hard disk, computer floppy disk, computer-readable flash drive, computer-readable RAM or ROM element or any other known means of encoding, storing or providing digital information, whether local to or remote from the cellphone, smartphone, tablet computer, PC, laptop, computer-driven television, or other digital processing device or system. Various forms of computer readable elements and media are well known in the computing arts, and their selection is left to the implementer. 
     In addition, those skilled in the art will understand that the invention can be implemented using computer program modules and digital processing hardware elements, including memory units and other data storage units, and including commercially available processing units, memory units, computers, servers, smartphones and other computing and telecommunications devices. The term “modules”, “program modules”, “components”, and the like include computer program instructions, objects, components, data structures, and the like that can be executed to perform selected tasks or achieve selected outcomes. The various modules shown in the drawings and discussed in the description herein refer to computer-based or digital processor-based elements that can be implemented as software, hardware, firmware and/or other suitable components, taken separately or in combination, that provide the functions described herein, and which may be read from computer storage or memory, loaded into the memory of a digital processor or set of digital processors, connected via a bus, a communications network, or other communications pathways, which, taken together, constitute an embodiment of the present invention. 
     The terms “data storage module”, “data storage element”, “memory element” and the like, as used herein, can refer to any appropriate memory element usable for storing program instructions, machine readable files, databases, and other data structures. The various digital processing, memory and storage elements described herein can be implemented to operate on a single computing device or system, such as a server or collection of servers, or they can be implemented and inter-operated on various devices across a network, whether in a server-client arrangement, server-cloud-client arrangement, or other configuration in which client devices can communicate with allocated resources, functions or applications programs, or with a server, via a communications network. 
     It will also be understood that computer program instructions suitable for a practice of the present invention can be written in any of a wide range of computer programming languages, including Java, C++, and the like. It will also be understood that method operations shown in the flowcharts can be executed in different orders, and that not all operations shown need be executed, and that many other combinations of method operations are within the scope of the invention as defined by the attached claims. Moreover, the functions provided by the modules and elements shown in the drawings and described in the foregoing description can be combined or sub-divided in various ways, and still be within the scope of the invention as defined by the attached claims. 
     The Applicant has implemented various aspects and exemplary practices of the present invention, using, among others, the following commercially available elements:
         1. A 7″ 1280×800 IPS display.   2. Three PointGrey Chameleon3 (CM3-U3-13S2C-CS) 1.3 Megapixel camera modules with ⅓″ sensor size assembled on a polycarbonate plate with shutter synchronization circuit.   3. Sunex DSL377A-650-F/2.8 M12 wide-angle lenses.   4. An Intel Core i7-4650U processor which includes on-chip the following:
           a. An Intel HD Graphics 5000 Integrated Graphics Processing Unit; and   b. An Intel QuickSync video encode and decode hardware pipeline.   
           5. OpenCL API on an Apple Mac OS X operating system to implement, in accordance with exemplary practices of the invention described herein, Image Rectification, Fast Dense Disparity Estimate(s)(FDDE) and Multi-level Disparity Histogram aspects.   6. Apple CoreVideo and VideoToolbox APIs to access QuickSync video compression hardware.   7. OpenCL and OpenGL API(s) for V3D view reconstruction in accordance with exemplary practices of the invention described herein.       

     The attached schematic diagrams  FIGS.  49 - 54    depict system aspects of the invention, including digital processing devices and architectures in which the invention can be implemented. By way of example,  FIG.  49    depicts a digital processing device, such as a commercially available smartphone, in which the invention can be implemented;  FIG.  50    shows a full-duplex, bi-directional practice of the invention between two users and their corresponding devices;  FIG.  51    shows the use of a system in accordance with the invention to enable a first user to view a remote scene;  FIG.  52    shows a one-to-many configuration in which multiple users (e.g., audience members) can view either simultaneously or asynchronously using a variety of different viewing elements in accordance with the invention;  FIG.  53    shows an embodiment of the invention in connection with generating an image data stream for the control system of an autonomous or self-driving vehicle; and  FIG.  54    shows the use of a head-mounted display (HMD) in connection with the invention, either in a pass-through mode to view an actual, external scene (shown on the right side of  FIG.  54   ), or to view prerecorded image content. 
     Referring now to  FIG.  49   , the commercially available smartphone, tablet computer or other digital processing device  492  communicates with a conventional digital communications network  494  via a communications pathway  495  of known form (the collective combination of device  492 , network  494  and communications pathway(s)  495  forming configuration  490 ), and the device  492  includes one or more digital processors  496 , cameras  4910  and  4912 , digital memory or storage element(s)  4914  containing, among other items, digital processor-readable and processor-executable computer program instructions (programs)  4916 , and a display element  498 . In accordance with known digital processing techniques, the processor  496  can execute programs  4916  to carry out various operations, including operations in accordance with the present invention. 
     Referring now to  FIG.  50   , the full-duplex, bi-directional practice of the invention between two users and their corresponding devices (collectively forming configuration  500 ) includes first user and scene  503 , second user and scene  505 , smartphones, tablet computers or other digital processing devices  502 ,  504 , network  506  and communications pathways  508 ,  5010 . The devices  502 ,  504  respectively include cameras  5012 ,  5014 ,  5022 ,  5024 , displays  5016 ,  5026 , processors  5018 ,  5028 , and digital memory or storage elements  5020 ,  5030  (which may store processor-executable computer program instructions, and which may be separate from the processors). 
     The configuration  510  of  FIG.  51   , in accordance with the invention, for enabling a first user  514  to view a remote scene  515  containing objects  5022 , includes smartphone or other digital processing device  5038 , which can contain cameras  5030 , 5032 , a display  5034 , one or more processor(s)  5036  and storage  5038  (which can contain computer program instructions and which can be separate from processor  5036 ). Configuration  510  also includes network  5024 , communications pathways  5026 ,  5028 , remote cameras  516 ,  518  with a view of the remote scene  515 , processor(s)  5020 , and digital memory or storage element(s)  5040  (which can contain computer program instructions, and which can be separate from processor  5020 ). 
     The one-to-many configuration  520  of  FIG.  52   , in which multiple users (e.g., audience members) using smartphones, tablet computers or other devices  526 . 1 ,  526 . 2 ,  526 . 3  can view a remote scene or remote first user  522 , either simultaneously or asynchronously, in accordance with the invention, includes digital processing device  524 , network  5212  and communications pathways  5214 ,  5216 . 1 ,  5216 . 2 ,  5216 . 3 . The smartphone or other digital processing device  524  used to capture images of the remove scene or first user  522 , and the smartphones or other digital processing devices  526 . 1 ,  526 . 2 ,  526 . 3  used by respective viewers/audience members, include respective cameras, digital processors, digital memory or storage element(s) (which may store computer program instructions executable by the respective processor, and which may be separate from the processor), and displays. 
     The embodiment or configuration  530  of the invention, illustrated in  FIG.  53   , for generating an image data stream for the control system  5312  of an autonomous or self-driving vehicle  532 , can include camera(s)  5310  having a view of scene  534  containing objects  536 , processor(s)  538  (which may include or have in communication therewith digital memory or storage elements for storing data and/or processor-executable computer program instructions) in communication with vehicle control system  5312 . The vehicle control system  5312  may also include digital storage or memory element(s)  5314 , which may include executable program instructions, and which may be separate from vehicle control system  5312 . 
     HMD-related embodiment or configuration  540  of the invention, illustrated in  FIG.  54   , can include the use of a head-mounted display (HMD)  542  in connection with the invention, either in a pass-through mode to view an actual, external scene  544  containing objects  545  (shown on the right side of  FIG.  54   ), or to view prerecorded image content or data representation  5410 . The HMD  542 , which can be a purpose-built HMD or an adaptation of a smartphone or other digital processing device, can be in communication with an external processor  546 , external digital memory or storage element(s)  548  that can contain computer program instructions  549 , and/or in communication with a source of prerecorded content or data representation  5410 . The HMD  542  shown in  FIG.  54    includes cameras  5414  and  5416  which can have a view of actual scene  544 ; left and right displays  5418  and  5420  for respectively displaying to a human user&#39;s left and right eyes  5424  and  5426 ; digital processor(s)  5412 , and a head/eye/face tracking element  5422 . The tracking element  5422  can consist of a combination of hardware and software elements and algorithms, described in greater detail elsewhere herein, in accordance with the present invention. The processor element(s)  5412  of the HMD can also contain, or have proximate thereto, digital memory or storage elements, which may store processor-executable computer program instructions. 
     In each of these examples, illustrated in  FIGS.  49 - 54   , digital memory or storage elements can contain digital processor-executable computer program instructions, which, when executed by a digital processor, cause the processor to execute operations in accordance with various aspects of the present invention. 
     Flowcharts of Exemplary Practices of the Invention 
       FIGS.  55 - 80    are flowcharts illustrating V3D aspects in connection with which the invention may be practiced. The methods depicted in these flowcharts are examples only: the organization, order and number of operations in the exemplary practices can be varied; and the exemplary practices and methods can be arranged or ordered differently, and include different functions, whether singly or in combination, while still being within the spirit and scope of the present invention. Items described below in parentheses are, among other aspects, optional in a given practice of the invention. 
       FIG.  55    is a flowchart of a V3D method  550  according to an exemplary practice of the invention, including the following operations:
       551 : Capture images of second user;     552 : Execute image rectification;     553 : Execute feature correspondence, by detecting common features;     554 : Generate data representation;     555 : Reconstruct synthetic view of second user based on representation;     556 : Use head tracking as input to reconstruction;     557 : Estimate location of user&#39;s head/eyes;     558 : Display synthetic view to first user on display screen used by first user; and     559 : Execute capturing, generating, reconstructing, and displaying such that the first user can have direct virtual eye contact with second user through first user&#39;s display screen, by reconstructing and displaying synthetic view of second user in which second user appears to be gazing directly at first user even if no camera has direct eye contact gaze vector to second user;
       (Execute such that first user is provided visual impression of looking through display screen as a physical window to second user and visual scene surrounding second user, and first user is provided immersive visual experience of second user and scene surrounding the second user);   (Camera shake effects are inherently eliminated, in that capturing, detecting, generating, reconstructing and displaying are executed such that first user has virtual direct view through his display screen to second user and visual scene surrounding second user; and scale and perspective of image of second user and objects in visual scene surrounding second user are accurately represented to first user regardless of user view distance and angle).       

       FIG.  56    is a flowchart of another V3D method  560  according to an exemplary practice of the invention, including the following operations:
       561 : Capture images of remote scene;     562 : Execute image rectification;     563 : Execute feature correspondence function by detecting common features and measuring relative distance in image space between common features, to generate disparity values;     564 : Generate data representation, representative of captured images and corresponding disparity values:     565 : Reconstruct synthetic view of the remote scene, based on representation;     566 : Use head tracking as input to reconstruction;     567 : Display synthetic view to first user (on display screen used by first user);
       (Estimate location of user&#39;s head/eyes);         568 : Execute capturing, detecting, generating, reconstructing, and displaying such that user is provided visual impression of looking through display screen as physical window to remote scene, and user is provided an immersive visual experience of remote scene);
       (Camera shake effects are inherently eliminated, in that capturing, detecting, generating, reconstructing and displaying are executed such that first user has virtual direct view through his display screen to remote visual scene; and scale and perspective of image of and objects in remote visual scene are accurately represented regardless of view distance and angle).       

       FIG.  57    is a flowchart of a self-portraiture V3D method  570  according to an exemplary practice of the invention, including the following operations:
       571 : Capture images of user during setup time (use camera provided on or around periphery of display screen of user&#39;s handheld device with view of users face during self-portrait setup time);     572 : Generate tracking information (by estimating location of user&#39;s head or eyes relative to handheld device during setup time);     573 : Generate data representation representative of captured images;     574 : Reconstruct synthetic view of user, based on the generated data representation and generated tracking information;     575 : Display to user the synthetic view of user (on the display screen during the setup time) (thereby enabling user, while setting up self-portrait, to selectively orient or position his gaze or head, or handheld device and its camera, with real-time visual feedback);     576 : Execute capturing, estimating, generating, reconstructing and displaying such that, in self-portrait, user can appear to be looking directly into camera, even if camera does not have direct eye contact gaze vector to user.   

       FIG.  58    is a flowchart of a photo composition V3D method  580  according to an exemplary practice of the invention, including the following operations:
       581 : At photograph setup time, capture images of scene to be photographed (use camera provided on a side of user&#39;s handheld device opposite display screen side of user&#39;s device);     582 : Generate tracking information (by estimating location of user&#39;s head or eyes relative to handheld device during setup time) (wherein estimating a location of the user&#39;s head or eyes relative to handheld device uses at least one camera on display side of handheld device, having a view of user&#39;s head or eyes during photograph setup time);     583 : Generate data representation representative of captured images;     584 : Reconstruct synthetic view of scene, based on generated data representation and generated tracking information (synthetic view reconstructed such that scale and perspective of synthetic view have selected correspondence to users viewpoint relative to handheld device and scene);     585 : Display to user the synthetic view of the scene (on display screen during setup time) (thereby enabling user, while setting up photograph, to frame scene to be photographed, with selected scale and perspective within display frame, with real-time visual feedback) (wherein user can control scale and perspective of synthetic view by changing position of handheld device relative to position of user&#39;s head).   

       FIG.  59    is a flowchart of an HMD-related V3D method  590  according to an exemplary practice of the invention, including the following operations:
       591 : Capture or generate at least two image streams;
       (using at least one camera attached or mounted on or proximate to external portion or surface of HMD);   (wherein captured image streams contain images of a scene);   (wherein at least one camera is panoramic, night-vision, or thermal imaging camera);   (at least one IR TOF camera or imaging device that directly provides depth);         592 : Execute feature correspondence function;     593 : Generate data representation representative of captured images contained in the captured image streams;
       (Representation can also be representative of disparity values or depth information);         594 : Reconstruct two synthetic views, based on representation;
       (use motion vector to modify respective view origins, during reconstructing, so as to produce intermediate image frames to be interposed between captured image frames in the captured image streams and interpose the intermediate image frames between the captured image frames so as to reduce apparent latency);         595 : Display synthetic views to the user, via HMD;     596 : (Track location/position of user&#39;s head/eyes to generate motion vector usable in reconstructing synthetic views);     597 : Execute reconstructing and displaying such that each of the synthetic views has respective view origin corresponding to respective virtual camera location, wherein the respective view origins are positioned such that the respective virtual camera locations coincide with respective locations of user&#39;s left and right eyes, so as to provide user with substantially natural visual experience of perspective, binocular stereo and occlusion exemplary practices of the scene, substantially as if user were directly viewing scene without an HMD.   

       FIG.  60    is a flowchart of another HMD-related V3D method  600  according to an exemplary practice of the invention, including the following operations:
       601 : Capture or generate at least two image streams;
       (using at least one camera);   (wherein captured image streams can contain images of a scene);   (wherein captured image streams can be pre-recorded image content);   (wherein at least one camera is panoramic, night-vision, or thermal imaging);   (wherein at least one JR TOF that directly provides depth);         602 : Execute feature correspondence function;     603 : Generate data representation representative of captured images contained in captured image streams;
       (representation can also be representative of disparity values or depth information);   (data representation can be pre-recorded);         604 : Reconstruct two synthetic views, based on representation;
       (use motion vector to modify respective view origins, during reconstructing, so as to produce intermediate image frames to be interposed between captured image frames in the captured image streams and interpose the intermediate image frames between the captured image frames so as to reduce apparent latency);   (track location/position of user&#39;s head/eyes to generate motion vector usable in reconstructing synthetic views);         605 : Display synthetic views to the user, via HMD;     606 : Execute reconstructing and displaying such that each of the synthetic views has respective view origin corresponding to respective virtual camera location, wherein the respective view origins are positioned such that the respective virtual camera locations coincide with respective locations of user&#39;s left and right eyes, so as to provide user with substantially natural visual experience of perspective, binocular stereo and occlusion exemplary practices of the scene, substantially as if user were directly viewing scene without an HMD.   

       FIG.  61    is a flowchart of a vehicle control system-related method  610  according to an exemplary practice of the invention, including the following operations:
       611 : Capture images of scene around at least a portion of vehicle (using at least one camera having a view of scene);     612 : (Execute image rectification);     613 : Execute feature correspondence function;
       (by detecting common features between corresponding images captured by the at least one camera and measuring a relative distance in image space between conunon features, to generate disparity values);   (detect common features between images captured by single camera over time);   (detect common features between corresponding images captured by two or more cameras);         614 : Calculate corresponding depth information based on disparity values;
       (or obtain depth information using IR TOF camera);         615 : Generate from the images and corresponding depth information an image data stream for use by the vehicle control system.   

       FIG.  62    is a flowchart of another V3D method  620  according to an exemplary practice of the invention, which can utilize a view vector rotated camera configuration and/or a number of the following operations:
       621 : Execute image capture;     622 : (of other user);     623 : (of other user and scene surrounding other user);     624 : (of remote scene);     625 : (Use single camera (and detect common features between images captured over time));     626 : (Use at least one color camera);     627 : (Use at least one infrared structured light emitter);     628 : (Use at least one camera which is an infra-red time-of-flight camera that directly provides depth information);     629 : (Use at least two cameras (and detect common features between corresponding images captured by respective cameras);     6210 : (Camera[s] for capturing images of the second user are located at or near the periphery or edges of a display device used by second user, display device used by second user having display screen viewable by second user and having a geometric center; synthetic view of second user corresponds to selected virtual camera location, selected virtual camera location corresponding to point at or proximate the geometric center):     6211 : (Use a view vector rotated camera configuration in which the locations of first and second cameras define a line; rotate the line defined by first and second camera locations by a selected amount from selected horizontal or vertical axis to increase number of valid feature correspondences identified in typical real-world settings by feature correspondence function) (first and second cameras positioned relative to each other along epipolar lines);     6212 : (Subsequent to capturing of images, rotate disparity values back to selected horizontal or vertical orientation along with captured images);     6213 : (Subsequent to reconstructing of synthetic view, rotate synthetic view back to selected horizontal or vertical orientation);     6214 : (Capture using exposure cycling);     6215 : (Use at least three cameras arranged in substantially L-shaped configuration, such that pair of cameras is presented along first axis and second pair of cameras is presented along second axis substantially perpendicular to first axis).   

       FIG.  63    is a flowchart of an exposure cycling method  630  according to an exemplary practice of the invention, including the following operations:
       631 : Dynamically adjust exposure of camera(s) on frame-by-frame basis to improve disparity estimation in regions outside exposed region: take series of exposures, including exposures lighter than and exposures darker than a visibility-optimal exposure; calculate disparity values for each exposure; and integrate disparity values into an overall disparity solution over time, to improve disparity estimation;     632 : The overall disparity solution includes a disparity histogram into which disparity values are integrated, the disparity histogram being converged over time, so as to improve disparity estimation;     633 : (analyze quality of overall disparity solution on respective dark, mid-range and light pixels to generate variance information used to control exposure settings of the camera(s), thereby to form a closed loop between quality of the disparity estimate and set of exposures requested from camera(s));     634 : (overall disparity solution includes disparity histogram: analyze variance of disparity histograms on respective dark, mid-range and light pixels to generate variance information used to control exposure settings of camera(s), thereby to form a closed loop between quality of disparity estimate and set of exposures requested from camera(s)).   

       FIG.  64    is a flowchart of an image rectification method  640  according to an exemplary practice of the invention, including the following operations:
       641 : Execute image rectification;     642 : (to compensate for optical distortion of each camera and relative misalignment of the cameras);     643 : (executing image rectification includes applying 2D image space transform);     644 : (applying 2D image space transform includes using GPGPU processor running shader program).   

       FIGS.  65 A-B  show a flowchart of a feature correspondence method  650  according to an exemplary practice of the invention, which can include a number of the following operations:
       651 : Detect common features between corresponding images captured by the respective cameras:     652 : (Detect common features between images captured by single camera over time; measure relative distance in image space between common features, to generate disparity values);     653 : (Evaluate and combine vertical- and horizontal-axis correspondence information);     654 : (Apply, to image pixels containing disparity solution, a coordinate transformation to a unified coordinate system (un-rectified coordinate system of the captured images));     655 : Use a disparity histogram-based method of integrating data and determining correspondence: constructing disparity histogram indicating the relative probability of a given disparity value being correct for a given pixel;     656 : (Disparity histogram functions as probability density function (PDF) of disparity for given pixel, in which higher values indicate higher probability of corresponding disparity range being valid for given pixel);     657 : (One axis of disparity histogram indicates given disparity range; second axis of histogram indicates number of pixels in kernel surrounding central pixel in question that are voting for given disparity range);     658 : (Votes indicated by disparity histogram initially generated utilizing sum of square differences [SSD] method: executing SSD method with relatively small kernel to produce fast dense disparity map in which each pixel has selected disparity that represents lowest error; then, processing plurality of pixels to accumulate into disparity histogram a tally of number of votes for given disparity in relatively larger kernel surrounding pixel in question);     659 : (Transform the disparity histogram into a cumulative distribution function (CDF) from which width of corresponding interquartile range can be determined, to establish confidence level in corresponding disparity solution);     6510 : (Maintain a count of number of statistically significant modes in histogram, thereby to indicate modality);     6511 : (Use modality as input to reconstruction, to control application of stretch vs. slide reconstruction method)     6512 : (Maintain a disparity histogram over selected time interval; and accumulate samples into histogram, to compensate for camera noise or other sources of motion or error);     6513 : (Generate fast disparity estimates for multiple independent axes; then combine corresponding, respective disparity histograms to produce statistically more robust disparity solution);     6514 : (Evaluate interquartile (IQ) range of CDF of given disparity histogram to produce IQ result; if IQ result is indicative of area of poor sampling signal to noise ratio, due to camera over- or underexposure, then control camera exposure based on IQ result to improve poorly sampled area of given disparity histogram);     6515 : (Test for only a small set of disparity values using small-kernel SSD method to generate initial results; populate corresponding disparity histogram with initial results; then use histogram votes to drive further SSD testing within given range to improve disparity resolution over time);     6516 : (Extract sub-pixel disparity information from disparity histogram: where histogram indicates a maximum-vote disparity range and an adjacent, runner-up disparity range, calculate a weighted average disparity value based on ratio between number of votes for each of the adjacent disparity ranges);     6517 : (The feature correspondence function includes weighting toward a center pixel in a sum of squared differences (SSD) approach: apply higher weight to the center pixel for which a disparity solution is sought, and a lesser weight outside the center pixel, the lesser weight being proportional to distance of given kernel sample from the center);     6518 : (The feature correspondence function includes optimizing generation of disparity values on GPGPU computing structures);     6519 : (Refine correspondence information over time);     6520 : (Retain a disparity solution over a time interval, and continue to integrate disparity solution values for each image frame over the time interval, to converge on improved disparity solution by sampling over time);     6521 : (Fill unknowns in a correspondence information set with historical data obtained from previously captured images: if a given image feature is detected in an image captured by one camera, and no corresponding image feature is found in a corresponding image captured by another camera, then utilize data for a pixel corresponding to the given image feature, from a corresponding, previously captured image).   

       FIG.  66    is a flowchart of a method  660  for generating a data representation, according to an exemplary practice of the invention, which can include a number of the following operations:
       661 : Generate data structure representing 2D coordinates of control point in image space, and containing a disparity value treated as a pixel velocity in screen space with respect to a given movement of a given view vector; and utilize the disparity value in combination with movement vector to slide a pixel in a given source image in selected directions, in 2D, to enable a reconstruction of 3D image movement;     662 : (Each camera generates a respective camera stream; and the data structure contains a sample buffer index, stored in association with control point coordinates, that indicates which camera stream to sample in association with given control point);     663 : (Determine whether a given pixel should be assigned a control point);     664 : (Assign control points along image edges: execute computations enabling identification of image edges);     665 : (Flag a given image feature with a reference count indicating how many samples reference the given image feature, to differentiate a uniquely referenced image feature, and a sample corresponding to the uniquely referenced image feature, from repeatedly referenced image features; and utilize reference count, extracting unique samples, to enable reduction in bandwidth requirements);     666 : (Utilize the reference count to encode and transmit a given sample exactly once, even if a pixel or image feature corresponding to the sample is repeated in multiple camera views, to enable reduction in bandwidth requirements).   

       FIGS.  67 A- 8    show a flowchart of an image reconstruction method  670 , according to an exemplary practice of the invention, which can include a number of the following operations:
       671 : Reconstruct synthetic view based on data representation and tracking information; execute 3d image reconstruction by warping 2D image, using control points: sliding given pixel along a head movement vector at a displacement rate proportional to disparity, based on tracking information and disparity values;     672 : (wherein disparity values are acquired from feature correspondence function or control point data stream);     673 : (Use tracking information to control 2D crop box: synthetic view is reconstructed based on view origin, and then cropped and scaled to fill user&#39;s display screen view window; define minima and maxima of crop box as function of user&#39;s head location with respect to display screen and dimensions of display screen view window);     674 : (Execute 2D warping reconstruction of selected view based on selected control points: designate set of control points, respective control points corresponding to respective, selected pixels in a source image; slide control points in selected directions in 2D space, wherein the control points are slid proportionally to respective disparity values; interpolate data values for pixels between the selected pixels corresponding to the control points; to create a synthetic view of the image from a selected new perspective in 3D space);     675 : (Rotate source image and control point coordinates so that rows or columns of image pixels are parallel to the vector between the original source image center and the new view vector defined by the selected new perspective);     676 : (Rotate the source image and control point coordinates to align the view vector to image scanlines; iterate through each scanline and each control point for a given scanline, generating a line element beginning and ending at each control point in 2D image space, with the addition of the corresponding disparity value multiplied by the corresponding view vector magnitude with the corresponding x-axis coordinate; assign a texture coordinate to the beginning and ending points of each generated line element, equal to their respective, original 2D location in the source image; interpolate texture coordinates linearly along each line element; to create a resulting image in which image data between the control points is linearly stretched);     677 : (Rotate resulting image back by the inverse of the rotation applied to align the view vector with the scanlines);     678 : (Link control points between scanlines, as well as along scanlines, to create polygon elements defined by control points, across which interpolation is executed);     679 : (For a given source image, selectively slide image foreground and image background independently of each other: sliding is utilized in regions of large disparity or depth change);     6710 : (Determine whether to utilize sliding: evaluate disparity histogram to detect multi-modal behavior indicating that given control point is on an image boundary for which allowing foreground and background to slide independent of each other presents better solution than interpolating depth between foreground and background; disparity histogram functions as probability density function (PDF) of disparity for a given pixel, in which higher values indicate higher probability of the corresponding disparity range being valid for the given pixel);     6711 : (Use at least one sample integration function table (sift), the sift including a table of sample integration functions for one or more pixels in a desired output resolution of an image to be displayed to the user; a given sample integration function maps an input view origin vector to at least one known, weighted 2D image sample location in at least one input image buffer).   

       FIG.  68    is a flowchart of a display method  680 , according to an exemplary practice of the invention, which can include a number of the following operations:
       681 : Display synthetic view to user on display screen;     682 : (Display synthetic view to user on a 2D display screen; update display in real-time, based on tracking information, so that display appears to the user to be a window into a 3d scene responsive to user&#39;s head or eye location;     683 : (Display synthetic view to user on binocular stereo display device);     684 : (Display synthetic view to user on lenticular display that enables auto-stereoscopic viewing).   

       FIG.  69    is a flowchart of a method  690  according to an exemplary practice of the invention, utilizing a multi-level disparity histogram, and which can also include the following:
       691 : Capture images of scene, using at least first and second cameras having a view of the scene, the cameras being arranged along an axis to configure a stereo camera pair having a camera pair axis;     692 : Execute feature correspondence function by detecting common features between corresponding images captured by the respective cameras and measuring a relative distance in image space between the common features, to generate disparity values, the feature correspondence function including constructing a multi-level disparity histogram indicating the relative probability of a given disparity value being correct for a given pixel, and the constructing of a multi-level disparity histogram includes executing a fast dense disparity estimate (FDDE) image pattern matching operation on successively lower-frequency downsampled versions of the input stereo images, the successively lower-frequency downsampled versions constituting a set of levels of FDDE histogram votes:
         692 . 1  Each level is assigned a level number, and each successively higher level is characterized by a lower image resolution;     692 . 2  (Downsampling is provided by reducing image resolution via low-pass filtering);     692 . 3  (Downsampling includes using a weighted summation of a kernel in level [n−1] to produce a pixel value in level [n], and the normalized kernel center position remains the same across all levels);     692 . 4  (For a given desired disparity solution at full image resolution, the FDDE votes for every image level are included in the disparity solution);     692 . 5  Maintain in a memory unit a summation stack, for executing summation operations relating to feature correspondence);         693 : Generate a multi-level histogram including a set of initially independent histograms at different levels of resolution:
         693 . 1 : Each histogram bin in a given level represents votes for a disparity determined by the FDDE at that level;     693 . 2 : Each histogram bin in a given level has an associated disparity uncertainty range, and the disparity uncertainty range represented by each histogram bin is a selected multiple wider than the disparity uncertainty range of a bin in the preceding level;         694 : Apply a sub-pixel shift to the disparity values at each level during downsampling, to negate rounding error effect: apply half pixel shift to only one of the images in a stereo pair at each level of downsampling;
         694 . 1 : Apply sub-pixel shift implemented inline, within the weights of the filter kernel utilized to implement the downsampling from level to level;         695 : Execute histogram integration, including executing a recursive summation across all the FDDE levels:
         695 . 1 : During summation, modify the weighting of each level to control the amplitude of the effect of lower levels in overall voting, by applying selected weighting coefficients to selected levels;         696 : Infer a sub-pixel disparity solution from the disparity histogram, by calculating a sub-pixel offset based on the number of votes for the maximum vote disparity range and the number of votes for an adjacent, runner-up disparity range.   

       FIG.  70    is a flowchart of a method  700  according to an exemplary practice of the invention, utilizing RUD image space and including the following operations:
       701 : Capture images of scene, using at least first and second cameras having a view of the scene, the cameras being arranged along an axis to configure a stereo camera pair having a camera pair axis, and for each camera pair axis, execute image capture using the camera pair to generate image data;     702 : Apply/execute rectification and undistorting transformations to transform the image data into RUD image space;     703 : Iteratively downsample to produce multiple, successively lower resolution levels;     704 : Execute FDDE calculations for each level to compile FDDE votes for each level;     705 : Gather FDDE disparity range votes into a multi-level histogram;     706 : Determine the highest ranked disparity range in the multi-level histogram;     707 : Process the multi-level histogram disparity data to generate a final disparity result.   

       FIG.  71    is a flowchart of a method  710  according to an exemplary practice of the invention, utilizing an injective constraint aspect and including the following operations:
       711 : Capture images of a scene, using at least first and second cameras having a view of the scene, the cameras being arranged along an axis to configure a stereo camera pair;     712 : Execute a feature correspondence function by detecting common features between corresponding images captured by the respective cameras and measuring a relative distance in image space between the common features, to generate disparity values, the feature correspondence function including: generating a disparity solution based on the disparity values, and applying an injective constraint to the disparity solution based on domain and co-domain, wherein the domain comprises pixels for a given image captured by the first camera and the co-domain comprises pixels for a corresponding image captured by the second camera, to enable correction of error in the disparity solution in response to violation of the injective constraint, and wherein the injective constraint is that no element in the co-domain is referenced more than once by elements in the domain.   

       FIG.  72    is a flowchart of a method  720  for applying an injective constraint, according to an exemplary practice of the invention, including the following operations:
       721 : Maintain a reference count for each pixel in the co-domain;     722 : Does reference count for the pixels in the co-domain exceed “1”!;     723 : If the count exceeds “1”:     724 : Signal a violation and respond to the violation with a selected error correction approach.   

       FIG.  73    is a flowchart of a method  730  relating to error correction approaches based on injective constraint, according to an exemplary practice of the invention, including one or more of the following:
       731 : First-come, first-served: assign priority to the first element in the domain to claim an element in the co-domain, and if a second element in the domain claims the same co-domain element, invalidating that subsequent match and designating that subsequent match to be invalid;     732 : Best match wins: compare the actual image matching error or corresponding histogram vote count between the two possible candidate elements in the domain against the contested element in the co-domain, and designate as winner the domain candidate with the best match;     733 : Smallest disparity wins: if there is a contest between candidate elements in the domain for a given co-domain element, wherein each candidate element has a corresponding disparity, selecting the domain candidate with the smallest disparity and designating the others as invalid;     734 : Seek alternative candidates: select and test the next best domain candidate, based on a selected criterion, and iterating the selecting and testing until the violation is eliminated or a computational time limit is reached.   

       FIG.  74    is a flowchart of a head/eye/face location estimation method  740  according to an exemplary practice of the invention, including the following operations:
       741 : Capture images of the second user, using at least one camera having a view of the second users face;     742 : Execute a feature correspondence function by detecting common features between corresponding images captured by the at least one camera and measuring a relative distance in image space between the common features, to generate disparity values;     743 : Generate a data representation, representative of the captured images and the corresponding disparity values;     744 : Estimate a three-dimensional (3D) location of the first user&#39;s head, face or eyes, to generate tracking information, which can include the following:
         744 . 1 : Pass a captured image of the first user, the captured image including the first user&#39;s head and face, to a two-dimensional (2D) facial feature detector that utilizes the image to generate a first estimate of head and eye location and a rotation angle of the face relative to an image plane;     744 . 2 : Use an estimated center-of-face position, face rotation angle, and head depth range based on the first estimate, to determine a best-fit rectangle that includes the head;     744 . 3 : Extract from the best-fit rectangle all 3D points that lie within the best-fit rectangle, and calculate therefrom a representative 3D head position;     744 . 4 : If the number of valid 3D points extracted from the best-fit rectangle exceeds a selected threshold in relation to the maximum number of possible 3D points in the region, then signal a valid 3D head position result     745 : Reconstruct a synthetic view of the second user, based on the representation, to enable a display to the first user of a synthetic view of the second user in which the second user appears to be gazing directly at the first user, including reconstructing the synthetic view based on the generated data representation and the generated tracking information.       

       FIG.  75    is a flowchart of a method  750  providing further optional operations relating to the 3D location estimation shown in  FIG.  74   , according to an exemplary practice of the invention, including the following:
       751 : Determine, from the first estimate of head and eye location and face rotation angle, an estimated center-of-face position;     752 : Determine an average depth value for the face by extracting three-dimensional (3D) points via the disparity values for a selected, small area located around the estimated center-of-face position;     753 : Utilize the average depth value to determine a depth range that is likely to encompass the entire head;     754 : Utilize the estimated center-of-face position, face rotation angle, and depth range to execute a second ray march to determine a best-fit rectangle that includes the head;     755 : Calculate, for both horizontal and vertical axes, vectors that are perpendicular to each respective axis but spaced at different interval;     756 : For each of the calculated vectors, test the corresponding 3D points starting from a position outside the head region and working inwards, to the horizontal or vertical axis;     757 : When a 3D point is encountered that falls within the determined depth range, denominate that point as a valid extent of a best-fit head rectangle;     758 : From each ray march along each axis, determine a best-fit rectangle for the head, and extracting therefrom all 3D points that lie within the best-fit rectangle, and calculating therefrom a weighted average;     759 : If the number of valid 3D points extracted from the best-fit rectangle exceed a selected threshold in relation to the maximum number of possible 3D points in the region, signal a valid 3D head position result.   

       FIG.  76    is a flowchart of optional sub-operations  760  relating to 3D location estimation, according to an exemplary practice of the invention, which can include a number of the following:
       761 : Downsample captured image before passing it to the 2D facial feature detector.     762 : Interpolate image data from video frame to video frame, based on the time that has passed from a given video frame from a previous video frame.     763 : Convert image data to luminance values.   

       FIG.  77    is a flowchart of a method  770  according to an exemplary practice of the invention, utilizing URUD image space and including the following operations:
       771 : Capture images of a scene, using at least three cameras having a view of the scene, the cameras being arranged in a substantially “l”-shaped configuration wherein a first pair of cameras is disposed along a first axis and second pair of cameras is disposed along a second axis intersecting with, but angularly displaced from, the first axis, wherein the first and second pairs of cameras share a common camera at or near the intersection of the first and second axis, so that the first and second pairs of cameras represent respective first and second independent stereo axes that share a common camera;     772 : Execute a feature correspondence function by detecting common features between corresponding images captured by the at least three cameras and measuring a relative distance in image space between the common features, to generate disparity values;     773 : Generate a data representation, representative of the captured images and the corresponding disparity values;     774 : Utilize an unrectified, undistorted (URUD) image space to integrate disparity data for pixels between the first and second stereo axes, thereby to combine disparity data from the first and second axes, wherein the URUD space is an image space in which polynomial lens distortion has been removed from the image data but the captured image remains unrectified.   

       FIG.  78    is a flowchart of a method  780  relating to optional operations in RUD/URUD image space according to an exemplary practice of the invention, including the following operations:
       781 : Execute a stereo correspondence operation on the image data in a rectified, undistorted (RUD) image space, and storing resultant disparity data in a RUD space coordinate system;     782 : Store the resultant disparity data in a URUD space coordinate system;     783 : Generate disparity histograms from the disparity data in either RUD or URUD space, and store the disparity histograms in a unified URUD space coordinate system (and apply a URUD to RUD coordinate transformation to obtain per-axis disparity values).   

       FIG.  79    is a flowchart of a method  790  relating to private disparity histograms according to an exemplary practice of the invention, including the following operations:
       791 : Capture images of a scene using at least one camera having a view of the scene;     792 : Execute a feature correspondence function by detecting common features between corresponding images captured by the at least one camera and measuring a relative distance in image space between the common features, to generate disparity values, using a disparity histogram method to integrate data and determine correspondence, which can include:
         792 . 1 : Construct a disparity histogram indicating the relative probability of a given disparity value being correct for a given pixel;     792 . 2 : Optimize generation of disparity values on a GPU computing structure, by generating, in the GPU computing structure, a plurality of output pixel threads and for each output pixel thread, maintaining a private disparity histogram in a storage element associated with the GPU computing structure and physically proximate to the computation units of the GPU computing structure;         793 : Generate a data representation, representative of the captured images and the corresponding disparity values.   

       FIG.  80    is a flowchart of a method  800  further relating to private disparity histograms according to an exemplary practice of the invention, including the following operations:
       801 : Store the private disparity histogram such that each pixel thread writes to and reads from the corresponding private disparity histogram on a dedicated portion of shared local memory in the GPU;     802 : Organize shared local memory in the GPU at least in part into memory words; the private disparity histogram is characterized by a series of histogram bins indicating the number of votes for a given disparity range; and if a maximum possible number of votes in the private disparity histogram is known, multiple histogram bins can be packed into a single word of the shared local memory, and accessed using bitwise GPU access operations.   

     II. Scene Processing for Holographic Displays: 
     Overview 
     The following sections describe systems, methods and computer program code products (software) for processing scene content in preparation for display on a holographic display device. Some aspects of the invention pertain to automatically selecting rendering parameters or performing scene transformations in order to render images for display on a holographic display device. 
     This document also describes a communication system, and related methods and computer program code products, in which a rich representation of one or more users is captured and the user&#39;s or users&#39; likeness is displayed in a remote location using one or more holographic display devices. 
     This invention may be useful to facilitate remote meetings, conferences, live performances including musical performances, sporting events, and additional use cases that would be enhanced by real-time immersion in a remote location or real-time interaction with a remote person, persons, or objects. 
     Where the word “connected” is used herein, it should be understood to include virtual connections, such as connections using a wireless communication link or a connection facilitated by a network, which may include some degree of virtualization. 
     A number of general aspects of the invention will next be described, before turning to more specific elements of the invention. 
     Holographic display devices: Holographic display devices are display devices that are capable of presenting 3D content to a viewer without the need for special eyewear. In principle, the display accomplishes this by emitting light forming a slightly different image in each radial direction from which the display can be viewed. 
     Therefore, a viewer may move their perspective in order to view a different image among the multiple images simultaneously emitted by the display. If the content displayed on the device is intended to represent 3-dimensional content, the different images emitted will each show a different perspective of the same content. A viewer having two eyes will naturally have the eyes positioned to observe different perspectives, and therefore will perceive the displayed content as 3-dimensional. 
     In some applications, the term “hogel” refers to a holographic optical element that appears to be a single colored point of light that is visible from all directions within a display&#39;s intended viewing field. The color and intensity of each hogel will vary depending on the viewing position, and the hogels collectively form the image seen by the viewer. (https://en.wikipedia.org/wiki/Hogel) 
     Parallax barrier display devices are a simple category of holographic display devices that comprise a traditional display positioned behind a medium, known as the parallax barrier, that blocks the light from certain pixels from escaping, except in specific directions. The principle of a parallax barrier is the same as the principle of the pinhole camera, functioning in reverse. The geometry of the device effectively limits the visible pixels to the subset of pixels that can be seen by connecting a straight line from the viewing position, through one of the openings or apertures in the parallax barrier, to the pixel&#39;s emissive element. By changing the viewing position, a different subset of pixels are visible and hence a different image is visible to the viewer. 
     Lenslet-based display devices are similar in effect to parallax barrier display devices, but are comprised of an array of micro-lenses, or lenslets, arranged on the surface of a flat pixel-based display. Unlike the parallax barrier which blocks a pixel&#39;s light in all but the intended directions, the lenslet will instead refocus and direct the pixel&#39;s light in the desired direction. This improves display brightness as well as allowing for thinner display assemblies. 
     In both parallax barrier and lenslet-based displays, a hogel is composed from a collection of pixels arranged such that each pixel emits light in a different direction such that at least one pixel from the collection is capable of emitting light visible to each possible viewing position. 
     Dot Pitch Limitations: Both parallax barrier and lenslet-based display devices fundamentally rely on traditional pixel-based display technology. Therefore the perceived quality of holographic displays is limited by the dot pitch or linear density of pixel elements. From a given viewing perspective, only a subset of the pixels can be seen, and that subset must form a complete image. Therefore the perceived resolution of the display (e.g. visible dots per inch) will be the resolution of the underlying display divided by the number of separate perspectives being emitted. 
     For example, a 30 inch display with 8K resolution, which is a high-end display in 2021, has an effective resolution of approximately 300 dpi (dots per inch), or a dot pitch of 0.0865 mm. In reality the pitch of the pixel-element matrix is likely higher because individual sub-pixels are required to create a pixel&#39;s color. In any case, such a display would appear to have a resolution of only 18 dpi if a lenslet array or parallax barrier divided the pixels into 16 different sub-views in one axis. This is worse than the dot pitch of a 17 inch QVGA display common circa 1990. 
     This effective resolution limitation has limited holographic displays to niches where multi-perspective viewing is more important than image quality—such as medical diagnostic visualizations. 
     Slanted Lenticular Lens Array Displays: Slanted Lenticular Lens Array Displays represent a further sub-category of lenslet-based display devices, in which horizontal radial view perspective density is prioritized over vertical perspective density. This tradeoff is often acceptable as people&#39;s eyes are typically displaced horizontally while remaining at approximately the same height vertically. 
     A Slanted Lenticular Lens Array is an array of cylindrical lenses bonded to a pixel-based display panel, in which the cylindrical lenses are arranged off-axis from the pixel grid of the underlying display panel. This allows pixels that are displaced in both the vertical and horizontal dimensions to affect the light emitted through different cylindrical lenses, thus increasing the effective dpi in the relevant dimension (usually the horizontal dimension). 
     A further discussion of Lenticular Lens Array devices, and Slanted Lenticular Lens Array devices in particular, can be found at the following location, the content of which is incorporated herein by reference:
         https://pure.tue.nl/ws/portalfiles/portal/46936462/640478-1.pdf       

     Content Generation for Holographic Displays: As a general matter, in conventional systems, generating content for holographic display devices is accomplished by first generating many individual perspective images, usually through a 3D rendering process. After each individual perspective has been rendered the output for the pixels of the underlying display panel are created by convolving (also referred to as “swizzling”) together pixels values (or pixel component values) from the individual perspectives in order to form a single image that may be displayed by the underlying pixels. 
     The precise convolution or swizzle function depends on the particulars of the pixel layout and lens configuration. Often, different color channels are swizzled differently to leverage the fact that individual colored (red, green, or blue) sub-pixels are often offset from each other spatially. 
     In some cases, this swizzling process may be integrated into the rendering process. 
     Issues with Viewing. Angle Discretization: All of the above holographic display technologies fundamentally discretize the possible viewing directions to a pre-determined number of perspectives. These perspectives are usually spaced radially to evenly cover the viewing field, although different display geometries may allocate different angular coverage to different perspectives. Typically the angular coverage is chosen to account for a typical viewing distance and a typical person&#39;s eye spacing, such that each eye will observe an entirely different view in order to maintain the 3D effect for the viewer. 
     This discretization means that tiny shifts in viewing perspective lead to no change in the observed image. It also means that intermediate perspectives of the content that fall between two of the rendered perspectives will not be rendered and thus cannot be viewed by a viewer. 
     In an example holographic display, an eye moving from left to right will see one image fade in as the slightly different, previously visible, image fades away. Typically, these images are similar enough to each other that the effect of the discretization will not be noticed. However, when the displayed content has a substantial depth displacement (either toward or away from the viewer) the parallax effect may cause jarring changes in the image from one perspective to the next. Instead of moving continuously, the displaced parts of the content will fade away in one location and reappear in a different location. This also means that intermediate viewing perspectives will see “ghostly” semi-transparent objects within the scene as scene elements fade away in one location and fade in, in a shifted location. 
       FIGS.  81 A- 81 E  depict an example of issues that may be encountered in a conventional system, in connection with limited angular resolution. In particular,  FIG.  81 A  depicts a side-on view of virtual scene geometry  8101  and the positions of 3 different observers  8102 ,  8103 ,  8104 .  FIG.  81 B  depicts the way the geometry  8101  appears to observer  8102 .  FIG.  81 C  depicts the way the geometry  8101  appears to observer  8103 .  FIG.  81 D  depicts the way the geometry  8101  should appear to observer  8104 , if the display device had perfect angular resolution.  FIG.  81 E  depicts the what an observer at position  8104  would actually see on a typical holographic display with limited angular resolution, because the observed image is a blend of the image intended for an observer located at position  8102  and the image intended for the observer at position  8103 . 
     Blurring High Depth Features: To ameliorate the jarring impact of seeing multiple disjoint images superimposed on top of each other, conventional configuration of holographic display content will often choose to blur the areas of the image where this artifact may be observed. Specifically, image regions depicting content features with large depth variance are blurred. Thus, for example, content features that project far out of the display or recess deeply into the display will be blurred more significantly. 
     Often, a blur kernel, radius of blur, or degree of blurring, is chosen by the content renderer, based on the depth (z-value) of each content feature or portion of the image. This results in more blurring for content features that exhibit a higher degree of parallax between adjacent perspective images. Typically no blurring is applied to content features with depth values that fall within a range of acceptable depth divergence. 
     In the following discussion, the term “unblurred band” is utilized to refer to a region of the content to be displayed on a holographic display device. In accordance with this usage, the unblurred band extends from the negative z-depth below which further recessed features must be blurred, to the positive z-depth above which further elevated features must be blurred. The term “unblurred band” is a nomenclature originated by the Applicant in connection with embodiments of the invention, and will be discussed in greater detail below. 
     Overview of Embodiments of the Invention 
     Conventional content creation processes for holographic displays require the selection of a “baseline depth” associated with the content. This baseline depth is sometimes referred to as the “zero depth.” In an exemplary holographic display, content features with positive z-values will appear to project outward from the display, while content features with negative depth values will appear recessed into the display, when the content is rendered and then viewed by a two-eyed observer. 
     This means that any 3-dimensional content feature with a z-value equal or near to the zero depth will appear exactly the same on the holographic display, regardless of which perspective it is viewed from. As a result, there is no need to blur any content features with z-values at or near the zero depth. 
     In previously known holographic display content creation processes, the zero depth is chosen by a person as part of the process of adapting the 3-dimensional content for presentation on the holographic display. 
     The present invention pertains, in part, to selecting appropriate zero-depth values for interactive content. In some situations, additional rendering parameters may also be selected by the invention. These rendering parameters are referred to as “the scene transform,” although they may include more than simply an affine transform. 
     In some embodiments, one aim of the invention is to position the 3D coordinate system of the content such that the unblurred band contains the most meaningful parts of the content being rendered. (Examples of “meaningful” content will be discussed throughout this document.) The present invention enables use cases and products in which it is not possible or otherwise practical for a human artist to select rendering parameters. Various aspects of the invention pertain to enabling automatic rendering of content containing moving faces on a holographic display device, and in particular, enabling interactive video conferencing using a holographic display device. 
     Automatic Selection of Scene Transformation: In a typical embodiment of the present invention, the invention is operable to analyze scene content, select rendering parameters based on the scene content and potentially also consider additional information, and provide those rendering parameters to a rendering algorithm in order to prepare the content for display on a holographic display device. 
     In some embodiments the invention may consider the location, the composition, and/or the orientation of human heads represented within the content. For a typically proportioned human face, an optimal zero-depth plane would be near the cheekbones, although most zero-depth planes that spatially bisect a head will produce acceptable results when displaying features of the head and face. 
     In some embodiments of the present invention, the scene content may be captured by a scene capture device such as a light field camera, depth-sensing camera, or array of multiple cameras, prior to processing. 
     In some embodiments, the holographic display device is remote from the real-life scene being captured, and data is transmitted via a network or communication link such that the holographic display device displays a representation of the real-life scene that was captured. 
     Byway of example,  FIG.  82 A  depicts a top view of a scene  8200  that is captured with a scene capture device  8204 ; and  FIG.  82 B  depicts a rendering of the same scene  8220 , after the present invention has selected an appropriate transformation and the scene has been blurred and rendered in preparation for display on a holographic display device. 
     More particularly,  FIG.  82 A  depicts a real-life scene  8200 , viewed from above, in which real-life people are captured via Scene Capture Device  8204 , producing Scene Content. 
     That scene content contains digital representations of two people, including their respective heads and faces  8201 ,  8202 . In accordance with exemplary practices of the present invention, logic elements or algorithmic elements select a scene transform that positions a selected zero-depth plane at position  8205  within the content. Therefore the Selected Focus Head  8201  will be rendered within the Unblurred Band  208 , between the Foreground Blur Boundary  8207  and the Background Blur Boundary  8206 . This means that the remaining user&#39;s head, i.e. the Unselected Background Head  8202  and the User&#39;s Outstretched Hand  8203  will extend outside the Unblurred Band  8208  and thus will be blurred by the rendering process. 
     (The term “logic” used herein refers to elements or functions that execute or implement selected behaviors or algorithms. The term “logic” can include, but is not limited to, electronic or digital elements capable of executing processing operations to execute or implement the selected behaviors or algorithms. The term “logic” used herein also encompasses algorithms that provide selected behaviors or operations.) 
       FIG.  82 B  depicts the rendered Scene Content  8220 , as it may be seen from one perspective on a holographic display device. Because the Selected Focus Head  8201  ( FIG.  82 A ) is within the Unblurred Band  8208  ( FIG.  82 A ), the head&#39;s face is crisply visible as the Rendered View of Selected Head  8221 . The User&#39;s Outstretched Hand  8203  ( FIG.  82 A ) is rendered in a blurry form in the foreground of the image as the Rendered View of Outstretched Hand  8223 . Similarly, the Unselected Background Head  8202  ( FIG.  82 A ) is behind the Background Blur Boundary  8206  ( FIG.  82 A ) and therefore it is rendered as a blurry object, Rendered View of Unselected Head  8222 , behind the other elements of the scene visible in the rendered view. 
     Description of Exemplary Implementations 
     Selection of Scene Transformation based on a Head Position: In an exemplary embodiment of the invention, a facial recognition algorithm or head recognition algorithm identifies portions of the 3-dimensional content as being faces or human heads. Then, a head selection algorithm selects a “focus head,” the focus head chosen among all identified heads within the content. If only one head is identified then the head selection algorithm is unnecessary. Next, a transform selection algorithm calculates a zero-depth value based on the head selected by the head selection algorithm. 
     After a zero-depth value is selected, the content is rendered with respect to that zero-depth value, and content features that deviate substantially from the selected zero depth value are blurred appropriately. 
     In various practices of the invention, applying a blur effect can comprise applying a distance-controlled blur effect; and applying a distance-controlled blur effect can comprise evaluating the distance to an object at a fixed 2D position relative to the holographic display in a 3D scene reference frame. 
     It should be noted that in various embodiments of the invention, a human head or face is selected as a “meaningful scene element”; but in accordance with various practices of the present invention, meaningful scene elements could be selected to be any of (or any combination of) a wide range of selected elements, such as hands, or other scene objects, or regions of a scene, or even an entire scene, depending on the selected implementation of the present invention. 
       FIG.  83    is a schematic diagram depicting the flow of data, in accordance with exemplary practices of the present invention, to process scene content to display it on a holographic display device. 
     More particularly,  FIG.  83    depicts an example pipeline  8300  for the analysis, processing, rendering and display of Scene Content  8301  on a Holographic Display Device  8312 . In some embodiments, some steps or pipeline stages may be optional or unnecessary, but they are included in this diagram for completeness. For example, an embodiment intended to display content containing only a single object may not require any of: Head Recognition  8302  or Head Selection  8304 . Similarly an embodiment for static content or content that is otherwise constrained in its spatial movement may not require Transform Stabilization  8308 . 
     The Scene Content  8301  may take different forms, depending on the selected practice or embodiment of the present invention. In various embodiments of the invention, the Scene Content may be 3-dimensional data; examples of which include, but are not limited to, a polygonal mesh or meshes, voxel data, or a collection of points or a point cloud. In other embodiments, the Scene Content may be a 2-dimensional image with an associated depth map or an associated displacement map. In other embodiments the scene content may take the form of light-field data; and in such an embodiment, a depth value may be inferred or calculated based on the position of opaque elements within the scene content. 
     In some practices of the invention, all scene content may be considered to comprise three-dimensional data, as it will be possible to convert content in any of the above mentioned formats into a three-dimensional representation. 
     In addition to three-dimensional data, Scene Content  8301  can also comprise at least one of the following:
         meta-Information such as information identifying people of objects within the scene;   calibration information pertaining to the source of the 3-dimensional data;   semantic information, such as information identifying the importance of objects or features within the scene content;   historical information, such as the prior state of the scene content;   historical scene transform information, such as the scene transform data from a prior frame, from prior frames, or an aggregation of past scene transform information;   motion information, such as information representing current and future motion vectors for objects within the scene;   information pertaining to the viewer or viewers of the holographic output, including the viewpoints of the user of users viewing the holographic display device, especially as a relative position in relation to the display device itself.       

     Referring again to  FIG.  83   , in some embodiments, the head recognition algorithm  8302  processes 3-dimensional geometry to identify spatial characteristics associated with heads. In another example, the head recognition algorithm comprises a 2-dimensional recognition algorithm such as the known Viola-Jones technique (https://en.wikipedia.org/wiki/Viola-Jones_object_detection_framework). In yet another example, the head recognition algorithm comprises both 2-dimensional and 3-dimensional algorithms. 
     Head Identifying Data  8303  may comprise 3-dimensional points, 3-dimensional shapes such as bounding boxes, selected subsets of the Scene Content  8301 , or any other data indicative of the position and/or the orientation of the heads within the scene. 
     The Head Selection algorithm  8304  may consider a number of criteria when selecting the focus head. Those criteria may include at least one of the following:
         the position of the head within the overall 3D content;   the size of the head as it would be seen within the frame of the holographic display;   the positioning of the head as it would be seen within the frame of the holographic display, e.g. central placement within the content region being processed for display;   the gaze direction of the head;   whether the head is speaking;   whether the head was recently speaking;   additional feedback from the human owners of the heads (respective humans to whom the respective heads correspond);   additional feedback from a human within the captured scene, including the attentional focus of that person;   additional feedback from a user viewing the holographic display;   additional feedback from a third party:   predefined rules or heuristics;   indications of the identify of a particular head including recognition of the features of a specific person;   indications of the identify of a particular head including external identifiers such as markers or auxiliary tags;   any of the above criteria used in combination with any other criteria.       

     In some embodiments a head or other object may be selected based on its 2-dimensional position within the frame of the holographic display device. 
     Selected Head Identifying Data  8305  may be represented in a format similar to Head Identifying Data  8303  or it may be represented in any other format capable of specifying one focus head or the location of one other focus object. In one embodiment, Selected Head Identifying Data  8305  is a subset of Head Identifying Data  8303 . 
     In various embodiments of the invention, the Focus Object may be an object other than a head. For example, another target object such as a workpiece may be selected as a Focus Object. 
     The Transform Selection algorithm  8306  may calculate the zero-depth value using varying degrees of complexity depending on the requirements of the embodiment. In addition, the characteristics of the rendering algorithm and the specifications of the intended holographic display device may also be considered in the design of the Transform Selection algorithm. 
     In some embodiments, a simple bounding-range for the head&#39;s depth values may be sufficient. For example, if the back of the head is located at an unadjusted coordinate value 5, and if the front of the head (likely the nose) is located at an unadjusted coordinate value 8, then the transform selection algorithm may simply choose 7 as the zero-depth value because 7 is two thirds of the range between 5 and 8. In this example the scene would be shifted (translated) such that the tip of the nose would have a new depth value of +1, and the back of the head would have a new depth value of −2. 
     In another embodiment, the head may be analyzed to locate features, such as the nose, mouth and eyes. More detailed information about the head&#39;s orientation and position may inform a more effective transformation. For example, a given holographic display may have specific recommended parameters, such as the height of the head or spacing between the eyes, and an appropriate transformation could be calculated to optimize for those parameters. 
     In various embodiments, the Scene Transform Data  8307  will likely include translation, i.e. shifting the scene&#39;s coordinate system towards or away from the display in order to align with a selected zero-depth plane. The Scene Transformation Data may also include rotation, uniform or non-uniform scale factors, distortion or anti-distortion, projection, or other scene transformation parameters. 
     Scale factors may be chosen to ensure an entire face is shown without blurring, or they may be selected to allow an entire head, another scene element, or the scene in its entirety, to fit within the frame of the holographic display. 
     Some practices of the invention may include applying a rotation to the content, in order to display the head in a more natural or a more direct orientation on the holographic display. 
     In some embodiments, Scene Transform Data  8307  may comprise an affine transform matrix, while in some embodiments it may comprise a simple depth value. In other embodiments it may comprise a more complex data structure. 
     In some embodiments, the Scene Transform Data  8307  may comprise data defining one view frustum or multiple view frusta. Each of these frusta may be asymmetric or sheared view frusta. Some embodiments of the present invention may remove portions of the scene entirely, in order to render the remaining scene elements more clearly. For example, an embodiment may remove some background objects so only a subset of foreground objects would be rendered. Some embodiments may exclude or remove portions of the scene using one or more clipping planes. Clipping planes may be integrated into view frusta or they may be expressed as individual geometric constructs. 
     Thus, in various practices of the invention, a scene transform may comprise an asymmetric or sheared view frustum. Moreover, the scene transform may comprise a sheared view frustum wherein the sheared view frustum enables selection of a plane of zero parallax, wherein the plane of zero parallax defines a Z-axis distance at which a scene feature is presented at the same spatial position on the holographic plane such that its presentation does not change with respect to viewing angle. Determining the scene transform can comprise adjusting a 3D position of a viewing frustum in the a 3D scene reference frame. The invention enables dynamically shifting the holographic plane in real-time to maximize viewing quality of a given scene feature. In addition, the invention can further apply a blur effect. 
     Referring again to  FIG.  83   , exemplary embodiments of the invention, intended to present moving content, and especially content captured in real-time, may include Transform Stabilization Logic  8308 . Transform Stabilization Logic may consider Scene Transform Data  8307  as well as other data from Scene Content  8301  in order to produce Stabilized Scene Transform Data  8309 . In some situations, Stabilized Scene Transform Data  8309  will be identical to Scene Transform Data  8307 , while in other situations it will be different. See the “Maintaining Temporal Stability” section below, for further discussion. 
     The Scene Rendering algorithm  8310  may comprise any rendering algorithm known in the art, including polygonal rasterization and ray tracing. The rendering algorithm will render the scene from a multitude of viewpoints, consistent with the requirements of the target holographic display device. The scene rendering algorithm may render each individual viewpoint sequentially, or render all required viewpoints simultaneously. 
     The scene rendering algorithm may blur scene features, or portions of scene features, that extend outside of the unblurred band, often in proportion to the degree to which the feature extends beyond the unblurred band. Alternatively, the scene rendering algorithm may choose not to render such features, or to rendering them with increasing transparency. 
     In some embodiments, the scene rendering algorithm may be responsible for applying the swizzle function. 
     In connection with this description of the present invention, when the term “swizzle” is used herein, it is used to connote the re-mapping of pixel components. These can be selected, individual pixel components. 
     In accordance with the present invention, a pixel re-mapping function or swizzle function can involve the use of digital logic elements to re-map at least one individual pixel component. 
     In accordance with the present invention, the pixel re-mapping function or swizzle function (or digital logic elements that execute the pixel re-mapping function or swizzle function) is operable to configure scene data corresponding to multiple 2-dimensional perspectives such that the 2-dimensional perspectives are transferable through holographic display optics of the holographic display device so as to provide an optimized, or visually improved, display to a human viewing user. 
     As shown in  FIG.  83   , the output of the Scene Rendering  8310  is the Device Appropriate Rendered Frame(s)  8311  In some embodiments, the Device Appropriate Rendered Frame(s) may comprise a series of 2-dimensional images, each displaying a different perspective of the scene content. In other embodiments, it may comprise fewer 2-dimensional frames, each frame incorporating multiple perspectives through the use of a pixel re-mapping function or swizzle function. 
     The Display on Holographic Display Device element  8312  may comprise processing needed, in accordance with the invention, prior to presenting the content on a holographic display device, to provide an optimized, or visually improved, display to a human viewing user. In some embodiments, a swizzle function or pixel re-mapping function is applied. Subsequently, the content is presented on a holographic device via the modification of pixel or hogel elements within the holographic display device. 
     Maintaining Temporal Stability: For a given static scene, the transform selection algorithm may include the selecting of an optimal, or at least highly appropriate, transform for display of scene content on the target holographic display device. However, the scene may not be static, and may instead change over time. For example, if the scene represents a real-life scene captured by a scene capture device, then the scene may change in response to the movements of the real-life people within the real-life scene. In response to the scene changes, any of: the head recognition algorithm, the head selection algorithm, the transform selection algorithm, or the rendering algorithm may produce different output. 
     Abrupt or unnatural changes to the output may be jarring to a viewer of the holographic display. For example, if a captured user leans towards the scene capture device, his or her reproduced representation should naturally appear to move “away from” the display and closer to the viewer of the holographic display device. However, a simplistic implementation of the invention may keep the user&#39;s head in the same place relative to the holographic display and instead move the entire remaining scene, including the user&#39;s body, backwards. This may not be desirable. 
     Therefore, various embodiments of the invention will further comprise change integration logic, or transform stabilization logic. Change integration logic comprises a set of behaviors and heuristics intended to balance the goal of maintaining a stable scene transform with the competing goal of selecting the most appropriate scene transform to present the content of the scene. 
     By way of example, change integration logic may comprise at least one of the following:
         logic to establish an acceptable depth range, or acceptable deviance from a prior transform value, within which the scene transform will remain unchanged (this range could be calculated from the parameters defining the unblurred band, or by considering the angular resolution of the holographic display);   logic to maintain a running average over a time window such that changes to the selected scene transform gradually affect the transform used to render the scene;   logic to calculate a smooth path from a prior scene transform to the selected scene transform (this may include the use of a cubic Hermite interpolation or a similar algorithm such as a Catmull-Rom spline. (see, e.g., https://en.wikipedia.org/wiki/Cubic_Hermite_spline#Catmull-Rom_spline);   logic to detect conditions that warrant an abrupt change of transform, such as when another captured user begins speaking;   at least one of the foregoing used in combination with other logic elements.       

     Use Within a Live-Capture System: This present invention is well suited to systems in which the scene content data is captured from a real-life scene using a scene capture device, and particularly to real-time systems. For example, the invention may be practiced within a system for streaming a live performance to a remote holographic display, via a network or another communication medium. 
     By way of example,  FIG.  84    is a schematic diagram  8400  depicting the flow of data from a scene capture device  8401 , through a scene processing device  8403 , and to a holographic display device  8405  for display, in accordance with the present invention. 
     As shown in  FIG.  84   , Scene Capture Device  8401  may include any device or system capable of capturing data from a real-life scene. This may be a simple camera with an additional capability to infer depth information. However, in most embodiments, the Scene Capture Device will comprise an additional sensor or sensors. For example, a Scene Capture Device  8401  in accordance with the invention can comprise at least one of the following:
         at least one depth sensing camera;   LIDAR;   pattern emitter;   time-of-flight (TOF) measurement device;   light field camera;   multiple cameras oriented to observe the scene from different perspectives;   processing modules to calculate or infer depth from captured images;   multiple instances of any of the above or any of the above in combination.       

     Referring again to  FIG.  84   , Scene Capture Device  8401  produces Scene Content  8402 , which comprises data representative of the captured scene. In accordance with the invention, Scene Content  8402  can comprise at least one of the following:
         2-dimensional Image(s);   depth map(s);   3-dimensional polygonal mesh(es);   voxel data:   point data or point cloud data;   displacement data;   light field data;   multiple instances of any of the above; or any of the above in combination.       

     The Scene Processing Device  8403  is operable to analyze Scene Content  8402  and produce Device-Appropriate Rendered Frames  8404  in preparation for displaying a rendered representation of the scene on a Holographic Display Device  8405 . The Scene Processing Device may comprise a digital processing device such as a computer or embedded processing element. 
     The Scene Processing Device can comprise at least one of the following:
         logic to recognize human heads or human faces;   logic to select a focus head, focus face, or other focus object;   logic to select a rendering transform;   logic to apply a blur to selected scene features;   logic to render Scene Content into Device-Appropriate Rendered Frames;   multiple instances of any of the above, or any the above in combination.       

     Device-Appropriate Rendered Frames  8404  can comprise at least one of the following:
         a set of 2-dimensional images representing different views of the captured scene;   a swizzled image integrating multiple views of the captured scene;   an encoded representation from which multiple views of the captured scene may be extracted;   multiple instances of any of the above, or any of the above in combination.       

     A Holographic Display Device  8405  in accordance with various practices and embodiments of the invention can comprise any display device for which the image displayed depends on the viewing angle of the observer. A Holographic Display Device can comprise at least one of:
         a parallax barrier display device;   a lenticular lens array display;   a slanted lens array;   a head-mounted display;   a display with dedicated eyewear;   a future form of display device for which the viewing angle affects the displayed image;   multiple instances of any of the above, or any of the above in combination.       

     Various embodiments or practices of the invention can include execution of Scene Processing  8403  in different locations or on different computational devices. For example, some aspects of Scene Processing can be performed by a digital processor near to the Scene Capture Device  8401  and some aspects of the Scene Processing may be performed by a digital processor proximate to the Holographic Display Device  8405 ) This disclosure should not be interpreted to limit the Scene Processing functionality to be in a single digital processing device. 
     In some embodiments, a first user or a first set of users may have their likeness captured by a Scene Capture Device. Then data may be transmitted across a network or communication link for display to a second user or second set of users on a holographic display device. 
     In some embodiments, Scene Processing may utilize criteria or parameters associated with the first user or first set of users. In some embodiments Scene Processing may utilize criteria or parameters associated with the second user or second set of users. In some embodiments Scene Processing may utilize criteria or parameters associated with both the first user or first set of users and the second user or second set of users. Said more plainly, sometimes the performers or content director may indicate which aspects of the scene should receive focus, while in other situations, it may be appropriate to base the selection of focal elements on the preferences or particulars of the audience or viewer. 
     Some embodiments may save, to a storage medium, data representing Scene Content  8402 , Device-Appropriate Rendered Frames  8404 , or data representing some combination of Scene Content  8402  and Device-Appropriate Rendered Frames  8404 . Then, the embodiment may be operable to display images constructed from the saved data, on a holographic display, at a future time. In such an embodiment, parameters and criteria may be different when the Scene Content is displayed versus their values when the Scene Content was captured. For example, the parameters of the holographic display device may be different, or the criteria used by a Head Selection Algorithm may be different. 
     Embodiment within a Teleconferencing Product. Device or System: The invention may be embodied in a remote conferencing system, such as a two-way teleconferencing system or a multi-way group teleconferencing system. 
     In some asymmetric embodiments, a first user or first set of users may have their likeness captured by a Scene Capture Device while simultaneously viewing a flat image of a second user or second set of users on a standard display device. Alternatively the first user or first set of users may simply hear sound of the second user or second set of users. The second user or second set of users may view the first user or first set of users on a holographic display device while the image of the second user of second set of users is captured by a simple camera and/or a microphone. 
     In other “full-duplex” embodiments, a first user or a first set of users may have their likeness captured by a Scene Capture Device while simultaneously viewing a representation of a second user or second set of users via a Holographic Display Device. The second user or second set of users may, in turn, view the first user or first set of users via a Holographic Display Device while their own likeness is captured by a Scene Capture Device. 
     Other embodiments or practices of the invention may support bidirectional communication or enable realtime interactions between a first user or first set of users and a second user or second set of users, potentially across large distances. 
     In some embodiments, a Scene Capture Device may be integrated with a Holographic Display Device to provide a teleconferencing product. 
     By way of example,  FIG.  85    is a schematic diagram depicting an example oaf teleconferencing product or system comprising a holographic display and a scene capture device  8500 , in accordance with the present invention. The product or system depicted in  FIG.  85    comprises a Holographic Display Panel  8501 , a Scene Capture Device which, in the depicted embodiment comprises an array of Camera Lenses  8502 , and a Sound Capture Device, which is in the depicted embodiment comprises a pair of Microphone Pickups  8503 . 
     In one example embodiment, a Scene Capture Device comprises a color (RGB) camera in addition to a depth-sensing camera. 
     In another example embodiment, multiple cameras are oriented to observe the user or users from multiple perspectives. The images captured by each individual camera are compared with images captured by other cameras to produce disparity or depth information. 
     Some products that embody the invention will mount multiple cameras in a bezel surrounding a holographic display device. The position of the cameras will likely be such that the display device does not interfere with the visibility of the scene from the perspective of each camera, accounting for the cameras respective fields-of-view, while simultaneously ensuring the cameras and associated lenses don&#39;t interfere with the ability of a user to observe the holographic display from an oblique viewing position. 
     In some exemplary embodiments of the invention, the techniques presented in commonly-owned PCT application PCT/US16/23433 (Attorney Docket MNE-111-PCT), incorporated by reference herein and set forth herein, may be used to process the captured images to create disparity information or depth information. 
     In some embodiments, the techniques presented in commonly-owned PCT application PCT/US18/19243 (Attorney Docket MNE-115-PCT), incorporated by reference herein, may be used to reconstruct synthetic viewpoints of the scene captured by the multiple cameras, such that each viewpoint is appropriate for display on a Holographic Display Panel. The Holographic Display Panel may be associated with a second device that is connected by a communication link with the first device. 
     In some exemplary embodiments, one or more microphone devices can be integrated into the teleconferencing device. The microphone devices may record sound information which may then be transmitted to another device via a communication link. 
     Some example embodiments include more than one microphone pickup. These devices may transmit 3-dimensional sound, which may then be reproduced by another device that receives the sound information via a communication link. 
     Embodiment Within a Group Teleconferencing System: In some embodiments, the invention may be used to facilitate conferencing among more than two participants, where two or more participants are located in the same physical space. 
     In some embodiments, a viewing device may expose a user interface to permit a viewing user to select which subject should receive focus. For example a viewing user may indicate that a specific content feature or a specific other user should be preferred by Focus Object Selection Logic or Focus Head Selection Logic. 
     In other embodiments, a viewing user may indicate that a specific head or object within the content should receive focus through the gaze of the viewing user, as measured by a camera or an additional eye tracking mechanism associated with the viewing device. 
     In additional embodiments, Focus Object Selection Logic or Focus Head Selection Logic may monitor other cues such as listening for the name of an individual person or a specific object being spoken. 
     Some embodiments may provide the captured participants with a means to affect the Focus Object Selection Logic or Focus Head Selection Logic. For example, the Focus Object Selection Logic or Focus Head Selection Logic may focus on the user who is currently speaking. 
     In another example, a user may designate themselves as the Focus Head or Focus Object through the use of a user interface on the capture device. Such a user interface may also include auxiliary control hardware such as a wireless controller. 
     In yet another example, a moderator who is neither a viewing user nor a captured user may control the Focus Head or Focus Object. In some cases moderation logic may be applied automatically, such as designating a specific individual as the sanctioned speaker or providing a specific individual with a focus time allotment. 
     In some embodiments a given display may show renderings from multiple transformed coordinate systems simultaneously. For example, a display may be bisected in order to show two focus users. The users may be together in the same captured scene or they may be in entirely different locations as part of a multi-party conference. In such an example the relative positioning between the users on the display would no longer reflect the users&#39; relationship to each other in real-life space but both users could then be shown together in crisp fidelity on the holographic display. 
     It is also possible to divide a display into quadrants to show four separate spatial transformations and therefore four separate focus objects or focus users on a holographic display. 
     In some embodiments, a given sub-view may maintain focus on an individual user or specific object, regardless of how that individual user or object moves in relationship to other elements within the scene. Some embodiments may associate a given sub-view with a given captured user. 
     Some embodiments may permit multiple holographic displays to be used for viewing. In such an embodiment, specific displays may each have their own parameters for selecting a focus object or focus head, as well as performing the required rendering. All of the possible applications of sub-views on a single holographic display also apply an entire holographic display panel used in conjunction with multiple other displays. 
     Digital Processing Environment in which Invention can be Implemented 
     Those skilled in the art will understand that the above described embodiments, practices and examples of the invention can be implemented using known network, computer processor and telecommunications devices, in which the telecommunications devices can include known forms of cellphones, smartphones, and other known forms of mobile devices, tablet computers, desktop and laptop computers, and known forms of digital network components and server/cloud/network/client architectures that enable communications between such devices. 
     Those skilled in the art will also understand that method aspects of the present invention can be executed in, or using, commercially available digital processing systems, such as servers, PCs, laptop computers, tablet computers, cellphones, smartphones and other forms of mobile devices, as well as known forms of digital networks, including architectures comprising server, cloud, network, and client aspects, for communications between such devices. 
     It should be noted that the method aspects described herein and depicted in the accompanying drawing figures can be embodied in devices, systems or computer software/program code operable in accordance with such method aspects of the invention; and that to one skilled in the technology of digital processors and computer software/program code for digital image or signal processing, the teachings of the method aspects described herein are also teachings of the configuring of devices, systems or computer software/program code operable in accordance with such method aspects of the invention. 
     The terms “computer software,” “computer code product,” and “computer program product” as used herein can encompass any set of computer-readable programs instructions encoded on a non-transitory computer readable medium. A computer readable medium can encompass any form of computer readable element, including, but not limited to, a computer hard disk, computer floppy disk, computer-readable flash drive, computer-readable RAM or ROM element or any other known means of encoding, storing or providing digital information, whether local to or remote from the cellphone, smartphone, tablet computer, PC, laptop, computer-driven television, or other digital processing device or system. Various forms of computer readable elements and media are well known in the computing arts, and their selection is left to the implementer. 
     In addition, those skilled in the art will understand that the invention can be implemented using computer program modules and digital processing hardware elements, including memory units and other data storage units, and including commercially available processing units, memory units, computers, servers, smartphones and other computing and telecommunications devices. The term “modules”, “program modules”, “components”, and the like include computer program instructions, objects, components, data structures, and the like that can be executed to perform selected tasks or achieve selected outcomes. The various modules shown in the drawings and discussed in the description herein refer to computer-based or digital processor-based elements that can be implemented as software, hardware, firmware and/or other suitable components, taken separately or in combination, that provide the functions described herein, and which may be read from computer storage or memory, loaded into the memory of a digital processor or set of digital processors, connected via a bus, a communications network, or other communications pathways, which, taken together, constitute an embodiment of the present invention. 
     The terms “data storage module”, “data storage element”, “memory clcmcnt” and the like, as used herein, can refer to any appropriate memory element usable for storing program instructions, machine readable files, databases, and other data structures. The various digital processing, memory and storage elements described herein can be implemented to operate on a single computing device or system, such as a server or collection of servers, or they can be implemented and inter-operated on various devices across a network, whether in a server-client arrangement, server-cloud-client arrangement, or other configuration in which client devices can communicate with allocated resources, functions or applications programs, or with a server, via a communications network. 
     It will also be understood that computer program instructions suitable for a practice of the present invention can be written in any of a wide range of computer programming languages, including Java, C++, and the like. It will also be understood that method operations shown in the flowcharts can be executed in different orders, and that not all operations shown need be executed, and that many other combinations of method operations are within the scope of the invention as defined by the attached claims. Moreover, the functions provided by the modules and elements shown in the drawings and described in the foregoing description can be combined or sub-divided in various ways, and still be within the scope of the invention as defined by the attached claims. 
     Flowcharts of Exemplary Practices of the Invention 
       FIGS.  86 - 103    are flowcharts illustrating method aspects and exemplary practices of the invention. The methods depicted in these flowcharts are examples only; the organization, order and number of operations in the exemplary practices can be varied; and the exemplary practices and methods can be arranged or ordered differently, and include different or additional functions, whether singly or in combination, while still being within the spirit and scope of the present invention. Elements shown in the flowcharts in parentheses ( ) are, among other aspects, optional in a given practice of the invention. 
     It will also be understood that method operations shown in the flowcharts can be executed in different orders, and that not all operations shown need be executed, and that many other combinations of method operations are within the scope of the invention as defined by the attached claims. Moreover, the functions provided by the modules and elements shown in the drawings and described in the foregoing description can be combined or sub-divided in various ways, and still be within the scope of the invention as defined by the attached claims. 
     All the text and respective textual elements of the accompanying flowcharts are incorporated by reference into this Detailed Description of the Invention as if set forth in their entireties in this Detailed Description of the Invention, in the respective order in which they appear in the flowcharts, while noting that the organization, order and number of operations in the exemplary practices can be varied; and the exemplary practices and methods can be arranged or ordered differently, and include different or additional functions. 
     Referring now to the flowcharts,  FIG.  86    depicts aspects of a method for rendering scene content in accordance with an exemplary practice of the invention, as follows: 
       8600 . Method for Rendering Scene Content: 
     
         
         ( 8601 . Receive scene content;) 
           8602 . Recognize at least one meaningful element within the scene content; 
           8603 . Select, from the at least one recognized meaningful element, at least one selected meaningful scene element; 
           8604 . Determine, based at least in part on the at least one selected meaningful scene element, at least one scene transform; and 
           8605 . Render multiple 2-dimensional perspectives of the content, using the at least one determined scene transform, the multiple 2-dimensional perspectives being configured for visually improved presentation on at least one holographic display device. 
       
    
       FIG.  87    depicts examples of meaningful scene elements in accord with the invention, as follows: 
       8700 . Meaningful Scene Elements: 
     
         
         ( 8701 . Meaningful scene element comprises a head.) 
         ( 8702 . Meaningful scene element comprises any of: human head, animal head, caricature of a head, or avatar&#39;s head.) 
         ( 8703 . Meaningful scene element comprises a hand.) 
         ( 8704 . Meaningful scene element comprises an object held by a hand.) 
         ( 8705 . Meaningful scene element comprises an object bearing a selected pattern.) 
         ( 8706 . Meaningful scene element comprises an object within a set of possible objects.) 
         ( 8707  Meaningful scene element comprises an entire scene.) 
         ( 8708  Meaningful scene element comprises any of: the area within a bounding box, the area within a projected bounding rectangle, or the area within a bounding volume.) 
         ( 8709  Meaningful scene element comprises a subset of the scene content.) 
       
    
       FIG.  88    depicts examples of blur/visibility effects in accord with the invention, as follows: 
       8800 . Blur/Visibility Effects: 
     
         
         ( 8801 . Blur at least one element within the scene content.) 
         ( 8802 . Reduce visibility of at least one element within the scene content.) 
         ( 8803 . Apply blur effect to at least one region of at least one rendered 2-dimensional image.) 
         ( 8804 . Applying blur effect comprises applying a distance-controlled blur effect.) 
         ( 8805 . Applying a distance-controlled blur effect comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in a 3D scene reference frame.) 
         ( 8806 . Reduce the visibility of at least two regions of at least one rendered 2-dimensional image.) 
         ( 8807 . The determining of at least one scene transform can be configured to minimize blur or visibility reduction of at least one selected scene element.) 
       
    
       FIG.  89    depicts aspects of holographic display devices in accord with the invention, as follows: 
       8900 . Aspects Relating to Holographic Display Devices: 
     
         
         ( 8901 . Display multiple 2-dimensional perspectives of the content on a holographic display device.) 
         ( 8902 . Provide at least one holographic display device such that at least one viewing user can view the at least one holographic display device.) 
         ( 8903 . Receive indication of use corresponding to at least one viewing user of at least one holographic display device.) 
         ( 8904 . Indication of use can comprise any of: a user&#39;s attentional focus, a users eye position, a user&#39;s gaze direction, a users gestures, input from a user through a user interface, or a use/s actions sensed by a sensor.) 
         ( 8905 . Sensor comprises a touch-sensitive sensor.) 
         ( 8906 . The at least one holographic display device comprises a lenticular lens array.) 
         ( 8907 . The at least one holographic display device comprises a parallax barrier display device.) 
         ( 8908 . The at least one holographic display device comprises eyewear.) 
         ( 8909 . Utilize a second, additional scene transform to render additional 2-dimensional perspectives of the content, the additional 2-dimensional perspectives being configured for display on at least a second holographic display device.) 
       
    
       FIG.  90    depicts stabilizing aspects in accord with the invention, as follows: 
       9000 . Stabilizing: 
     
         
         ( 9001 . Stabilize a scene transform prior to rendering.) 
         ( 9002 . Stabilizing comprises utilizing change integration logic.) 
         ( 9003 . Stabilizing comprises utilizing a heuristic.) 
         ( 9004 . Stabilizing comprises utilizing logic to establish any of: an acceptable depth range or an acceptable deviance from a prior transform value.) 
         ( 9005 . Stabilizing comprises utilizing logic to maintain a running average over a time window.) 
         ( 9006 . Stabilizing comprises utilizing logic to calculate a smooth path from a prior transform.) 
         ( 9007 . Stabilizing comprises utilizing any combination of: interpolation, cubic Hermite interpolation, splines. Catmull-Rom splines.) 
         ( 9008 . Stabilizing comprises utilizing logic to detect conditions for an abrupt transition.) 
         ( 9009 . Logic to detect conditions for an abrupt transition comprises logic to detect a change in at least one meaningful scene element.) 
         ( 9010 . Logic comprises electronic logic elements.) 
       
    
       FIG.  91    (consisting of  FIGS.  91 A and  91 B ) depicts scene content aspects in accord with the invention, as follows: 
       9100 . Scene Content: 
     
         
         ( 9101 . Scene content comprises a moving scene.) 
         ( 9102 . Scene content comprises at least one frame from a stream representative of a moving scene.) 
         ( 9103 . Scene content comprises at least one head.) 
         ( 9104 . Scene content comprises the output of a light-field camera.) 
         ( 9105 . Scene content comprises the output of at least one array of cameras.) 
         ( 9106 . Scene content comprises the output of at least one depth-sensing camera.) 
         ( 9107 . Scene content comprises a 3-dimensional model.) 
         ( 9108 . Scene content comprises any of: a polygonal mesh, voxel data, point data, or light-field data.) 
         ( 9109 . Scene content comprises at least one image containing depth information.) 
         ( 9110 . Scene content comprises at least one image containing disparity information.) 
         ( 9111 . Scene content comprises metadata.) 
         ( 9112 . Scene content comprises metadata, the metadata identifying objects within the scene content.) 
         ( 9113 . Scene content comprises information about a prior configuration of the scene content.) 
         ( 9114 . Scene content comprises historical information, the historical information comprising any of prior scene transform information or an aggregate representation of prior scene transform information.) 
         ( 9115 . Scene content comprises motion information.) 
         ( 9116 . Scene content comprises a representation of a physical scene.) 
         ( 9117 . Scene content comprises a representation of a physical scene, and the representation of a physical scene comprises images of at least one captured user.) 
         ( 9118 . Scene content comprises a real-time streaming representation of a live physical scene.) 
         ( 9119 . Scene content further comprises a real-time streaming representation of live humans.) 
         ( 9120 . Scene content further comprises information corresponding to at least one viewer of the holographic output.) 
       
    
       FIG.  92    depicts “recognizing” aspects in accord with the invention (see  8602  above: “recognize at least one meaningful element within the scene content”), as follows: 
       9200 . Recognizing: 
     
         
         ( 9201 . The recognizing comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in a 3D scene reference frame.) 
         ( 9202 . The recognizing comprises recognizing geometric features.) 
         ( 9203 . The recognizing comprises utilizing 2-dimensional image recognition.) 
         ( 9204 . The recognizing comprises utilizing facial recognition.) 
         ( 9205 . The recognizing comprises any combination of 2-dimensional and 3-dimensional recognition algorithm(s).) 
       
    
       FIG.  93    (consisting of  FIGS.  93 A and  93 B ) depicts “selecting” aspects in accord with the invention (see  8603  above: “select, from the at least one recognized meaningful element, at least one selected meaningful scene element”), as follows: 
       9300 . Selecting: 
     
         
         ( 9301 . The selecting comprises evaluating the distance to an object at a fixed 2D position relative to the holographic display in the 3D scene.) 
         ( 9302 . The selecting comprises utilizing facial analysis.) 
         ( 9303 . The selecting comprises evaluating the position of a scene element in relation to the entire scene content.) 
         ( 9304 . The selecting comprises evaluating the position of a scene element in relation to the frame of a holographic display.) 
         ( 9305 . The selecting comprises evaluating the size of a scene element in relation to the entire scene content.) 
         ( 9306 . The selecting comprises evaluating the size of a scene element as it would be projected onto a holographic display.) 
         ( 9307 . The selecting comprises evaluation of the gaze direction of a head.) 
         ( 9308 . The selecting comprises evaluating the status of a head as an active speaker or as a recent speaker.) 
         ( 9309 . The selecting comprises evaluation of additional indications from at least one captured user.) 
         ( 9310 . The additional indications from at least one captured user comprise any of: the attentional focus of at least one captured user or gestures by at least one captured user.) 
         ( 9311 . The selecting comprises: evaluating additional indications from at least one viewing user.) 
         ( 9312 . The additional indications from at least one viewing user comprise the attentional focus of at least one viewing user.) 
         ( 9313 . The selecting comprises utilizing heuristics.) 
         ( 9314 . The selecting comprises utilizing data corresponding to identity of a specific captured user.) 
         ( 9315 . The selecting comprises utilizing metadata obtained from the scene content.) 
         ( 9316 . The selecting comprises selecting all recognized meaningful scene elements.) 
         ( 9317 . The selecting comprises visually recognizing any of an object or a class of objects.) 
         ( 9318 . The selecting comprises utilizing any of: data transmitted wirelessly, data transmitted via Bluetooth, data transmitted via WiFi, or RFID data.) 
         ( 9319 . The selecting comprises detecting motion.) 
         ( 9320 . The selecting comprises utilizing indications supplied by a director user, wherein the director user is not a captured user or a primary viewing user.) 
       
    
       FIG.  94    depicts scene transform aspects in accord with the invention, as follows: 
       9400 . Scene Transform: 
     
         
         ( 9401 . Scene transform comprises an asymmetric or sheared view frustum.) 
         ( 9402 . Scene transform comprises a sheared view frustum, and wherein the sheared view frustum enables selection of a plane of zero parallax.) 
         ( 9403 . Plane of zero parallax defines a Z-axis distance at which a scene feature is presented at the same spatial position on the holographic plane such that its presentation does not change with respect to viewing angle.) 
         ( 9404 . Dynamically shifting the holographic plane in real-time to maximize viewing quality of a given scene feature.) 
         ( 9405 . Further comprising applying a blur effect.) 
         ( 9406 . Scene transform comprises a baseline depth.) 
         ( 9407 . Scene transform comprises a depth displacement.) 
         ( 9408 . Scene transform comprises a scene translation.) 
         ( 9409 . Scene transform comprises a rotation.) 
         ( 9410 . Scene transform comprises an affine transform.) 
         ( 9411 . Scene transform comprises a scale factor.) 
         ( 9412 . Scene transform comprises a re-projection function.) 
         ( 9413 . Scene transform comprises any of: a distortion function or an anti-distortion function.) 
         ( 9414 . Scene transform comprises rendering parameters.) 
         ( 9415 . Scene transform comprises a blur magnitude parameter.) 
       
    
       FIG.  95    depicts aspects of determining at least one scene transform in accord with the invention, as follows: 
       9500 : Determining Scene Transform: 
     
         
         ( 9501 . Determining at least one scene transform comprises adjusting a 3D position of a viewing frustum in a 3D scene reference frame.) 
         ( 9502 . Determining at least one scene transform comprises evaluating the position of a selected scene element.) 
         ( 9503 . Determining at least one scene transform comprises evaluating the position of a head.) 
         ( 9504 . Determining at least one scene transform comprises analyzing facial features.) 
         ( 9505 . Determining at least one scene transform comprises computing a scale factor to optimize for presentation on a holographic display device.) 
         ( 9506 . Determining at least one scene transform comprises evaluating a selected scene element and an un-blurred band.) 
         ( 9507 . Determining at least one scene transform comprises the removal of selected scene elements.) 
       
    
       FIG.  96    depicts aspects of rendering multiple 2-dimensional perspectives in accord with the invention, as follows: 
       9600 : Rendering Multiple 2-Dimensional Perspectives: 
     
         
         ( 9601 . Rendering multiple 2-dimensional perspectives of the content comprises executing rendering utilizing any combination of: 3D projection algorithm, rasterization algorithm, ray tracing algorithm.) 
         ( 9602 . Rendering multiple 2-dimensional perspectives of the content comprises applying a visual effect to a subset of elements of the rendered scene.) 
         ( 9603 . The visual effect comprises any combination of: transparency, blur, confusion, bokeh, gaussian blur, rejection.) 
         ( 9604 . Rendering multiple 2-dimensional perspectives of the content comprises applying a pixel re-mapping function to arrange the perspectives such that they are transferable through holographic display optics of the holographic display device so as to provide a visually improved display to a human viewing user.) 
         ( 9605 . Rendering multiple 2-dimensional perspectives of the content comprises applying a swizzle function.) 
         ( 9606 . The re-mapping function comprises a swizzle function.) 
         ( 9607 . Applying a pixel re-mapping function comprises utilizing digital logic elements to re-map at least one individual pixel component.) 
         ( 9608 . Applying a swizzle function comprises utilizing digital logic elements to re-map at least one individual pixel component.) 
       
    
       FIG.  97    depicts remote communication utilizing a holographic display in accord with the invention, as follows: 
       9700  Remote Communication Utilizing a Holographic Display: 
     
         
           9701 . Provide a scene capture device operable to capture rich scene information representative of a scene; 
           9702 . Provide a communication link, operable to transmit rich scene information; 
           9703 . Provide a scene processing device operable to:
       (1) select at least one scene transform operable on the rich scene information; and   (2) render multiple scene viewpoints, based on the rich scene information, utilizing the at least one selected scene transform; and     
           9704 . Provide a holographic display device, operable to provide a holographic display of the scene, based at least in part on the rendered scene viewpoints. 
       
    
       FIG.  98    depicts scene capture device aspects in accord with the invention, as follows: 
       9800 : Scene Capture Device: 
     
         
         ( 9801 . The scene capture device is operable to capture a digital representation of at least one captured user.) 
         ( 9802 . The scene capture device comprises at least two cameras arranged as a stereo pair.) 
         ( 9803 . The scene capture device comprises any combination of: a depth-sensing camera, a structured light camera, an infrared pattern emitter, a time-of-flight camera, a light-field camera.) 
         ( 9804 . The scene capture device comprises a microphone or an array of microphones.) 
         ( 9805 . The scene capture device comprises an array of cameras.) 
         ( 9806 . Cameras of the array of cameras are mounted around the perimeter of a holographic display.) 
       
    
       FIG.  99    depicts rich scene information and communication link aspects in accord with the invention, as follows: 
       9900 : Rich Scene Information: Communication Link: 
     
         
         ( 9901 . The rich scene information comprises any combination of: a 2-dimensional image, a depth map, a 3-dimensional polygonal mesh, voxel data, point data, point-cloud data, displacement data, light field data.) 
         ( 9902 . The communication link comprises a digital processing network.) 
         ( 9903 . The communication link comprises a telecommunications network.) 
         ( 9904 . The communication link comprises a wireless communication link.) 
         ( 9905 . The communication link comprises digital processing elements operable in accordance with a computer peripheral connection standard.) 
         ( 9906 . The communication link comprises a data storage device.) 
       
    
       FIG.  100    (consisting of  FIGS.  100 A and  100 B ) depicts scene processing aspects in accord with the invention, as follows: 
       10000 : Scene Processing Device: 
     
         
         ( 10001 . The scene processing device comprises any combination of: a digital signal processor, an embedded system-on-chip, a digital computer, a GPU, a mobile computational device, a cloud-computing device.) 
         ( 10002 . The scene processing devices comprises at least two elements selected from a group comprising: a digital signal processor, an embedded system-on-chip, a digital computer, a GPU, a mobile computational device, a cloud-computing device.) 
         ( 10003 : The scene processing device comprises digital processor-executable program code executing on at least one general-purpose computational device.) 
         ( 10004 : The scene processing device comprises at least two computational units.) 
         ( 10005 . The scene processing device comprises at least two computational units, and the multiple computational units are geographically separate from each other and communicate via a communication link.) 
         ( 10006 . The scene processing device comprises digital logic operable to recognize any of: heads, faces, hands, or selected objects in the scene.) 
         ( 10007 . The scene processing device comprises digital logic operable to select at least one meaningful object in the scene.) 
         ( 10008 . The scene processing device comprises digital logic operable to execute selected functions responsive to received indications corresponding to a captured user or captured users.) 
         ( 10009 . The scene processing device comprises digital logic operable to execute selected functions responsive to received indications pertaining to a viewing user or viewing users.) 
         ( 10010 . The scene processing device comprises digital logic operable to determine at least one scene transform.) 
         ( 100011 . The scene processing device comprises digital logic operable to apply a visual effect to a subset of the rich scene information.) 
         ( 10012 . The scene processing device comprises digital logic operable to render the rich scene information for display on a holographic display device.) 
         ( 10013 . The scene processing device comprises digital logic operable to apply a swizzle function.) 
         ( 10014 . The scene processing device comprises digital logic operable to apply a pixel re-mapping function.) 
         ( 10015 . The swizzle function is operable to configure scene data corresponding to multiple 2-dimensional perspectives such that the 2-dimensional perspectives are transferable through holographic display optics of the holographic display device so as to provide a visually improved display to a human viewing user.) 
         ( 10016 . The pixel re-mapping function is operable to configure scene data corresponding to multiple 2-dimensional perspectives such that the 2-dimensional perspectives are transferable through holographic display optics of the holographic display device so as to provide a visually improved display to a human viewing user.) 
         ( 10017 . The digital logic operable to apply a swizzle function comprises digital logic elements operable to re-map at least one individual pixel component.) 
         ( 10018 . The digital logic operable to apply a pixel re-mapping function comprises digital logic elements operable to re-map at least one individual pixel component.) 
         ( 10019 . The scene processing device comprises digital logic operable to output any combination of: a set of 2-dimensional rendered frames, a swizzled image incorporating multiple 2-dimensional rendered frames, an encoded representation of multiple 2-dimensional rendered frames.) 
       
    
       FIG.  101    depicts other display device aspects in accord with the invention, as follows: 
       10100 . Other Display Device Aspects: 
     
         
         ( 10101 . The holographic display device is operable to display the rendered scene, based at least in part on the rendered scene viewpoints, for viewing by at least one viewing user.) 
         ( 10102 . The holographic display device comprises any of: a parallax barrier display device, a lenticular lens array, or a slanted lens array.) 
         ( 10103 . The holographic display device comprises dedicated eyewear.) 
         ( 10104 . The holographic display device comprises a display device for which the angle at which a viewer views an image displayed by the device affects the image seen by the viewer.) 
         ( 10105 . Further comprising a sound-producing element operable to reproduce sound captured by a microphone device.) 
         ( 10106 . Further comprising at least two sound-producing elements operable to reconstruct spatially localized sound captured by multiple microphone elements.) 
         ( 10107 . Further comprising at least a second scene capture device operable to capture a digital representation of at least one viewing user.) 
         ( 10108 . Further comprising at least a second holographic display device operable to display a representation of the scene captured by the second scene capture device, for viewing by at least one captured user.) 
         ( 10109 . Configure system to enable real-time interactions between at least one captured user and at least one viewing user.) 
       
    
       FIG.  102    depicts aspects relating to endpoints and other features in accord with the invention, as follows: 
       10200 : Endpoints. Other Features:
     ( 10201 . Configure system to further comprise a camera, operable to capture a digital image of at least one viewing user; and a non-holographic display, operable to present the digital image to at least one captured user.)   ( 10202 . Configure system to further comprise at least one additional endpoint, wherein an additional endpoint comprises any combination of: a holographic display; a scene capture device; a communication link.)   ( 10203 . Configure system to further comprise:
       (1) a respective scene capture device is associated with a respective endpoint; and   (2) the scene processing device is operable to select among scenes captured by the respective scene capture devices associated with the respective endpoints.)   
       ( 10204 . The scene processing device is operable to integrate information from multiple scenes captured by the respective scene capture devices associated with the respective endpoints.)   ( 10205 . Configure system to further comprise a user interface; the user interface operable to provide information to the scene processing device.)   ( 10206 . The user interface comprises a touch-sensitive device.)   ( 10207 . The user interface comprises an eye tracking device.)   ( 10208 . The scene processing device is operable to identify any combination of: a speaking user; speaking users; an endpoint associated with a speaking user, wherein an endpoint comprises any combination of holographic display, scene capture device, communication link.)   ( 10209 . At least one endpoint is designated as a moderator endpoint.)   ( 10210 . A holographic display device is operable to present rendered output from multiple scene capture devices simultaneously.)   ( 10211 . A holographic display device is operable to present a view of a specific individual user.)   ( 10212 . Further comprising a storage medium; the storage medium operable to store any combination of: rich scene information, rendered scene viewpoints, scene transform information.)   
       FIG.  103    depicts a method of providing a system to render scene content in accord with the invention, as follows: 
       10300 . Providing a System to Render Scene Content: 
     
         
           10301 . Configure a digital processing resource to: 
           10302 . Recognize at least one meaningful element within the scene content; 
           10303 . Select, from the at least one recognized meaningful element, at least one selected meaningful scene element; 
           10304 . Determine, based at least in part on the at least one selected meaningful scene element, at least one scene transform; and 
           10305 . Render multiple 2-dimensional perspectives of the content, utilizing the at least one determined scene transform, the multiple 2-dimensional perspectives being configured for visually improved presentation on at least one holographic display device. 
       
    
     CONCLUSION 
     While the foregoing description and the accompanying drawing figures provide details that will enable those skilled in the art to practice aspects of the invention, it should be recognized that the description is illustrative in nature and that many modifications and variations thereof will be apparent to those skilled in the art having the benefit of these teachings. It is accordingly intended that the invention herein be defined solely by any claims that may be appended hereto and that the invention be interpreted as broadly as permitted by the prior art.