Patent Publication Number: US-7899321-B2

Title: Stereo camera with automatic control of interocular distance

Description:
RELATED APPLICATION INFORMATION 
     This patent is a Continuation-in-Part of application Ser. No. 12/409,316, filed Mar. 23, 2009, entitled STEREO CAMERA WITH AUTOMATIC CONTROL OF INTEROCULAR DISTANCE 
    
    
     NOTICE OF COPYRIGHTS AND TRADE DRESS 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become trade dress of the owner. The copyright and trade dress owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright and trade dress rights whatsoever. 
     BACKGROUND 
     1. Field 
     This disclosure relates to stereoscopy. 
     2. Description of the Related Art 
     Humans view the environment three-dimensionally using binocular vision. Binocular vision is both a visual system and an analytical system. Our brain perceives both distance and speed based, in part, on triangulating visual light information received by the retinas of our respective laterally separated, forward facing eyes. Since both eyes are forward facing, the fields of view of each of our eyes overlap, with each eye perceiving a slightly different perspective of the same area. As we focus on objects closer to our eyes, our eyes rotate towards each other. As we focus on objects afar, our eyes rotate towards a parallel view. The angle between the lines of sight of each eye is commonly termed the convergence angle. The convergence angle is higher when we view objects closer to our eyes and lower when viewing distance object. The convergence angle may be essentially zero, indicating essentially parallel lines of sight, when we view objects at great distance. 
     Three dimensional imaging, also known as stereographic imaging, dates at least as far back as 1838. Historically, stereographic cameras commonly include two lenses spaced laterally apart a similar distance as an average human&#39;s eyes, approximately 65 mm. The effective distance of the lenses from each other is known as the interocular distance. The interocular distance has a strong effect on the apparent depth of a stereographic image. Increasing the interocular spacing increases the apparent depth of a stereographic image. Decreasing the interocular spacing has the effect of decreasing the apparent depth of a stereographic image. 
     The presentation of stereoscopic images is commonly achieved by providing a first image to be seen only by the left eye and a second image to be seen only by the right eye. Differences, or disparity, between the two images may provide an illusion of depth. Two images having disparity may be perceived as three-dimensional. Two images, or portions of two images, exhibiting excessive disparity may not be perceived as three-dimensional, but may simply be seen as two overlapping two-dimensional images. The amount of disparity that a viewer can accommodate, commonly called the disparity limit, varies among viewers. The disparity limit is also known to vary with image content, such as the size of an object, the proximity of objects within an image, the color of objects, and the rate of motion of objects within the image. The disparity limit, expressed as the angle between the lines of sight of the viewer&#39;s eyes, may be about 12-15 minutes of arc for typical stereoscopic images. 
     A variety of techniques, including polarization, filters, glasses, projectors, and shutters have been used to restrict each eye to viewing only the appropriate image. 
     One approach to displaying stereographic images is to form the left-eye image on a viewing screen using light having a first polarization state and to form the right-eye image on the same viewing screen using light having a second polarization state orthogonal to the first polarization state. The images may then be viewed using glasses with polarizing lenses such that the left eye only receives light of the first polarization state and the right eye only receives light of the second polarization state. Stereoscopic displays of this type typically project the two polarized images onto a common projection screen. This technique has been used to present 3-D movies. 
     A second approach to displaying stereographic images is to form the left-eye and right-eye images alternately on a common viewing screen at a high rate. The images may then be viewed using shutter glasses that alternately occult either the right or left eye in synchronism with the alternating images. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a stereographic camera in an environment. 
         FIG. 2  is a schematic drawing of a stereographic camera in an environment including foreground objects. 
         FIG. 3  is a representation of images captured by a stereographic camera. 
         FIG. 4  is a representation of the images of  FIG. 2  presented on a common viewing screen. 
         FIG. 5  is a block diagram of a stereographic camera system. 
         FIG. 6  is a block diagram of a computing device. 
         FIG. 7  is a flow chart of a process for recording stereo images. 
     
    
    
     Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having a reference designator with the same least significant digits. Elements that have similar functions for either the left or right eyes are assigned the same reference designator with a suffix of either “L” or “R” to indicate left-eye or right-eye, respectively. 
     DETAILED DESCRIPTION 
     Description of Apparatus 
     Referring now to  FIG. 1 , a stereographic camera  100  may include a left camera  110 L and a right camera  110 R. The term “camera” is intended to include any device having an optical system to form an image of an object and a medium to receive and detect and/or record the image. The left and right cameras may be film or digital still image cameras, may be film or digital motion picture cameras, or may be video cameras. The left and right cameras  110 L,  110 R may be separated by an interocular distance IOD. Each of the left and right cameras  110 L,  110 R may include a lens  112 L,  112 R. The term “lens” is intended to include any image-forming optical system and is not limited to combinations of transparent refractive optical elements. A lens may use refractive, diffractive, and/or reflective optical elements and combinations thereof. Each lens may have an axis  115 L,  115 R that defines the center of the field of view of each camera  110 L,  110 R. 
     The cameras  110 L,  110 R may be disposed such that the axis  115 L,  115 R are parallel or such that a convergence angle ⊖ is formed between the two axis  115 L,  115 R. The cameras  110 L,  110 R may be disposed such that the axis  115 L,  115 R cross at a convergence distance CD from the cameras. The interocular distance IOD, the convergence distance CD, and the convergence angle ⊖ are related by the formula
 
Θ=2 A  TAN(IOD/2CD), or  (1)
 
CD=IOD/[2 TAN(Θ/2)].  (2)
 
The interocular distance IOD and the convergence distance CD may be measured from a nodal point, which may be the center of an entrance pupil, within each of the lenses  112 L,  112 R. Since the entrance pupils may be positioned close to the front of the lenses  112 L,  112 R, the interocular distance IOD and the convergence distance CD may be conveniently measured from the front of the lenses  112 L,  112 R.
 
     The stereographic camera  100  may be used to form a stereographic image of a scene  105 . As shown in the simplified example of  FIG. 1 , the scene  105  may include a primary subject  130 , which is shown, for example, as a person. The scene  105  may also include other features and objects in the background (behind the primary subject). The distance from the cameras  110 L,  110 R to the furthest background object  140 , which is shown, for example, as a tree, may be termed the extreme object distance EOD. 
     When the images from a stereographic camera, such as the stereographic camera  100 , are displayed on a viewing screen, scene objects at the convergence distance will appear to be in the plane of the viewing screen. Scene objects, such as the primary subject  130  in the example of  FIG. 1 , located closer to the stereographic camera may appear to be in front of the viewing screen. Scene objects, such as the tree  140 , located further from the stereographic camera may appear to be behind the viewing screen. 
     Each lens  115 L,  115 R may have adjustable focus. The stereographic camera may have a focus adjusting mechanism to synchronously adjust the focus of the two lenses such that both lenses  115 L,  115 R may be focused at a common adjustable focus distance FD. The focus adjusting mechanism may couple the focus of the two lenses  115 L,  115 R mechanically, electrically, electromechanically, electronically, or by another coupling mechanism. The focus distance FD may be adjusted manually, or may be automatically adjusted. The focus distance FD may be adjusted such that the cameras  110 L,  110 R are focused on the primary subject  130 . The focus distance may be automatically adjusted in response to a sensor (not shown) that determines the distance from the cameras  110 L,  110 R to the primary subject  130 . The sensor to determine the distance from the cameras to the primary subject may be an acoustic range finder, an optical or laser range finder, or some other distance measuring device. In the case where the cameras  110 L,  110 R are digital still image, motion picture, or video cameras, the focus distance may be adjusted in response to one or more processors (not shown) that analyze one or both of the images sensed by the cameras. The processors may be located within or may be coupled to the cameras. 
     The convergence distance CD and the focus distance FD may commonly be set to the same distance, which may be the distance from the cameras  110 L,  110 R to the primary subject  130 . However, as shown in  FIG. 1 , the convergence distance CD and the focus distance FD may not be the same distance. For example, the focus distance FD may be set at the distance from the cameras to the primary subject and the convergence distance CD may be set slightly longer than the focus distance. In this case, when the images are displayed, the primary subject will be seen to be in front of the plane of the viewing screen. The difference between the focus distance FD and the convergence distance CD may be an adjustable or predetermined offset. The offset may be absolute, in which case the convergence distance may be calculated by the formula
 
CD=FD+α  (3)
 
where α is the offset as an absolute dimension. The offset may be relative, in which case the convergence distance may be calculated by the formula
 
CD=(FD)(1+β)  (4)
 
where β is the offset as a portion of FD. For example, an absolute offset α may be a distance measurement such as one foot or two meters, and a relative offset β may be an expression of a relationship or ratio, such as 5% or 10%. Both the absolute offset and the relative offset may be zero, in which case CD=FD.
 
     Each lens  115 L,  115 R may also have zoom capability, which is to say that the focal length FL of each lens may be adjusted. The stereographic camera  100  may have a focal length adjusting mechanism to synchronously adjust the focal length of the two lenses such that both lenses  115 L,  115 R may always have precisely the same focal length. The focal length adjustment of the two lenses  115 L,  115 R may be coupled mechanically, electrically, electronically, electromechanically, or by another coupling mechanism. Commonly, the focal length of the lenses  115 L,  115 R may be adjusted manually. The focal length of the two lenses  115 R,  115 L may also be adjusted automatically in accordance with a predetermined scenario. 
     Referring now to  FIG. 2 , a stereographic camera  200 , which may be the stereographic camera  100 , may include a left camera  210 L and a right camera  210 R, each including a respective lens  212 L,  212 R. The left and right cameras may be film or digital still image cameras, may be motion picture film cameras, or may be video cameras. The left and right cameras  210 L,  210 R may be separated by an interocular distance IOD. Each lens may have an axis  215 L,  215 R that defines the center of the field of view of each camera  210 L,  210 R. The cameras  210 L,  210 R may be disposed such that the axis  215 L,  215 R cross at a convergence distance CD from the cameras. 
     The stereographic camera  200  may be used to form a stereographic image of a scene  205 . As shown in the simplified example of  FIG. 2 , the scene  205  may include a primary subject  230 , which may be, for example, a person. The scene  205  may also include other features and objects in the foreground and the background. The distance from the cameras  210 L,  210 R to the furthest background object  240 , which is shown, for example, as a tree, may be termed the extreme object distance EOD. The distance from the cameras  210 L,  210 R to the closest foreground object  245 , which is shown, for example, as a plant, may be termed the minimum object distance MOD. 
     Depending on the relationship between EOD, CD, and MOD, the image of either the foreground object  245  or the background object  240  may have the greatest disparity when the scene  205  is presented on a stereographic display. 
     Referring now to  FIG. 3 , an exemplary image captured by a left camera is illustrated as displayed on a screen  320 L and an exemplary image captured by a right camera is illustrated as displayed on a second screen  320 R. The image displayed on the screen  320 L includes an image  330 L of a primary subject near the center of the display screen, and an image  340 L of an extreme background object to the left of the image  330 L. The image displayed on screen  320 R includes an image  330 R of the primary subject near the center of the display screen, and an image  340 R of the extreme background object to the right of the image  330 R. 
     The positional difference, or disparity, between corresponding objects in the left image  320 L and the right image  320 R may provide an illusion of depth when the two images are viewed separately by the left and right eyes of an observer. However, to preserve the illusion of depth, the maximum disparity must be less than a limit value which may be both viewer-dependent and image-dependent. In the example of  FIG. 3 , the largest disparity occurs between the images  340 L,  340 R of the extreme background object. 
     Referring now to  FIG. 4 , the left and right images  440 L,  440 R captured by a stereographic camera, such as the stereographic camera  100 , may be presented on a single display screen  420 . The image  440 R to be seen by the right eye (shown as solid lines) and the image  440 L to be seen by the left eye (shown as dotted lines) may be separated at the viewer&#39;s  425  eyes using polarized glasses, shutter glasses, or some other method as previously described. The disparity distance DD between corresponding objects in the left and right images  440 L,  440 R, such as the images of the tree may be perceived by the viewer  425  as a disparity angle Φ D  between the line of sight to the object from the viewer&#39;s left and right eyes. The value of the disparity angle Φ D  perceived by the viewer  425  may be given by the formula
 
Φ D   =A  TAN(DD/VD)  (5)
 
where DD is the disparity distance between corresponding objects in the left and right images  440 L,  440 R and VD is a viewing distance from the viewer  425  to the display screen  420 .
 
     Since Φ D  must be limited to a small angle (such that TAN Φ D =Φ D ), the maximum allowable disparity distance may be defined as
 
DDmax=Φ Dmax ×VD,
 
where Φ Dmax  is the maximum allowable angular disparity.
 
     Although the viewing distance VD may not be known at the time a stereographic recording is made, the viewing distance VD may be presumed to be, to at least some extent, proportional to the size of the display screen  420 . For example the Society for Motion Picture and Television Engineers (SMPTE) recommends that, for optimal viewing, the width of a home theater display should subtend an angle of 30 degrees at the viewer&#39;s eyes, corresponding to a viewing distance of 1.87 times the width of the display screen. The viewing distance in homes and theaters is commonly greater than the recommended distance, and may range from 2.0 to 5.0 times the screen width. 
     Since the viewing distance VD may be assumed to be a multiple of the screen width W, the maximum disparity distance between the corresponding images in a stereographic display may be expressed as a fraction of the display width, as follows 
                       DD   ⁢   max     W     =       Φ   Dmax     ×   K             (   6   )               
where K is the ratio of the viewing distance to the screen width. For example, assuming a viewing distance of 2.3 times the screen width, a maximum disparity angle of 15 arc minutes may be converted to a maximum disparity distance of 1% of the screen width.
 
     Referring now to  FIG. 5 , a stereographic camera system may include a camera platform  550  coupled to a controller  560 . The camera platform  550  may include a left camera  510 L and a right camera  510 R, each of which has an associated lens  512 L,  512 R. The camera platform may include an IOD mechanism  552  to adjust an interocular distance between the left camera  510 L and the right camera  510 R. The camera platform may include a ⊖ mechanism  554  to adjust a convergence angle between the left camera  510 L and the right camera  510 R. Both the IOD mechanism  552  and the ⊖ mechanism  554  may include one or more movable platforms or stages coupled to motors or other actuators. The IOD mechanism  552  and the ⊖ mechanism  554  may be adapted to set the interocular distance and the convergence angle, respectively, in response to data received from the controller  560 . Within this patent, the term “data” is intended to include digital data, commands, instructions, digital signals, analog signals, optical signals and any other data that may be used to communicate the value of a parameter such as interocular distance or convergence angle. 
     The camera platform  550  may include a focus mechanism  556  to synchronously adjust and set the focus distance of the lenses  512 L,  512 R. The focus mechanism  556  may include a mechanical, electronic, electrical, or electro-mechanical linkage between the lenses  512 L,  512 R to simultaneously adjust the focus distance of both lenses to the same value. The focus mechanism  556  may include a motor or other actuator adapted to set the focus distance in response to data received from the controller  560 . The focus mechanism  556  may be manually controlled by an operator such as a cameraman or assistant cameraman (commonly called a “focus puller”). When manually controlled, the focus mechanism  556  may include an encoder, potentiometer, or other sensor to provide data indicating the focus distance to the controller  560 . The focus mechanism  556  may be adapted to operate under manual control and/or in response to data received from the controller  560 . 
     The camera platform  550  may include a zoom mechanism  558  to synchronously adjust and set the focal length of the lenses  512 L,  512 R. The zoom mechanism  558  may include a mechanical, electronic, electrical, or electro-mechanical linkage between the lenses  512 L,  512 R to simultaneously adjust the focal length of both lenses to the same value. The zoom mechanism  558  may include a motor or other actuator adapted to set the focal length in response to data received from the controller  560 . The zoom mechanism  558  may be manually controlled by an operator such as a cameraman or assistant cameraman. When manually controlled, the zoom mechanism  558  may include an encoder, potentiometer, or other sensor to provide data indicating the focal length to the controller  560 . The zoom mechanism  558  may be adapted to operate either under manual control or in response to data received from the controller  560 . 
     The controller  560  may receive data from a distance measurement device  565 . The distance measurement device may provide data indicating the distance to a nearest foreground object and/or the distance to a furthest background object. The distance measuring device  565  may be as simple as a tape measure or other manual measuring device used by an operator who then provides the distance data to the controller using a keyboard or other data entry device (not shown). The distance measuring device  565  may be a laser range finder, an acoustic rangefinder, an optical rangefinder, or other range finding device that may interface with the controller  560  via a dedicated connection or via a network. 
     The distance measuring device  565  may not be a separate device, but may be the camera platform  550  operating under control of an operator and/or the controller  560 . To measure distance, the convergence angle between the cameras  510 L,  510 R may be adjusted, automatically or under control of an operator, such that the images captured by the cameras  510 L,  510 R converge at a foreground object or a background object. The convergence distance to the foreground or background object may then be calculated from the interocular distance and convergence angle between the cameras  510 L and  510 R using the formulas given above. To provide maximum accuracy when the camera platform is used to measure distance, the interocular distance may be temporarily set to a maximum value. 
     The controller  560  may be coupled to an operator interface  562 . The controller  560  may receive data from the operator interface  562  indicating a focus-convergence offset, as described above. The controller  560  may receive data from the operator interface  562  indicating a maximum allowable disparity. The controller  560  may also receive data from the operator interface  562  indicating the focus distance and focal length of the lenses  512 L,  512 R. 
     The operator interface  562  may be partially or wholly incorporated into the camera platform  550 . The operator interface  562  may be close to the camera platform  550  or partially or wholly remote from the camera platform  550  For example, the focus mechanism  556  and/or the zoom mechanism  558  may be manually controlled by one or more operators such as a cameraman and/or an assistant cameraman. In this case, the focus mechanism  556  and/or the zoom mechanism  558  may provide data to the controller  560  indicating the manually-set focus distance and/or focal length. Similarly, control actuators to set the focus-convergence offset and/or the maximum allowable disparity may be located on the camera platform for operation by the cameraman and/or the assistant cameraman. 
     The operator interface  562  may be partially or wholly incorporated into the controller  560 . For example, in situations where the focus-convergence offset and/or the maximum allowable disparity are fixed during the recording of a scene, the focus convergence offset and/or the maximum allowable disparity may be manually provided to the controller using a keyboard or other data entry device. In situations where one or both of the focus-convergence offset and/or the maximum allowable disparity will be varied during the recording of a scene, the focus-convergence offset and/or the maximum allowable disparity may be controlled using, for example, arrows keys on a keyboard or one or more continuous control devices such as a potentiometer, joystick or mouse. 
     The controller  560  may interface with the camera platform  550 . The controller  560  may be integrated into the camera platform  550 . The controller may provide data to and/or receive data from the focus mechanism  556  and the zoom mechanism  558  indicating the focus distance and focal length, respectively, of the lenses  512 L,  512 R. The controller  560  may provide data to the IOD mechanism  552  and the ⊖ mechanism  554  to set the interocular distance and the convergence angle, respectively, between the cameras  510 L,  510 R. The controller  560  may provide data to the IOD mechanism  552  and the ⊖ mechanism  554  based on the focus distance and focal length of the lenses  512 L,  512 R, the focus-convergence offset, the maximum allowable disparity, and the distance to the nearest foreground object and/or the distance to the furthest background object. The controller  560  may provide data to the IOD mechanism  552  to set the interocular distance such that the largest disparity in the recorded image does not exceed the maximum allowable disparity value. 
     The controller  560  may be coupled to the camera platform  550  and the operator interface  562  via a network which may be a local area network; via one or more buses such as a USB bus, a PCI bus, a PCI Express bus, or other parallel or serial data bus; or via one or more direct wired or wireless connections. The controller  560  may be coupled to the camera platform  550  and the operator interface  562  via a combination of one or more of direct connections, network connections, and bus connections. 
       FIG. 6  is a block diagram of a computing device  660  that may be suitable for the controller  560 . As used herein, a computing device refers to any device with a processor, memory and a storage device that may execute instructions including, but not limited to, personal computers, server computers, computing tablets, set top boxes, video game systems, personal video recorders, telephones, personal digital assistants (PDAs), portable computers, and laptop computers. The computing device  660  may include hardware, firmware, and/or software adapted to perform the processes subsequently described herein. The computing device may include a processor  664  coupled to memory  666  and a storage device  668 . 
     The storage device  668  may store instructions which, when executed by the computing device  660 , cause the computing device to provide the features and functionality of the controller  560 . As used herein, a storage device is a device that allows for reading from and/or writing to a storage medium. Storage devices include hard disk drives, DVD drives, flash memory devices, and others. Each storage device may accept a storage media. These storage media include, for example, magnetic media such as hard disks, floppy disks and tape; optical media such as compact disks (CD-ROM and CD-RW) and digital versatile disks (DVD and DVD±RW); flash memory cards; and other storage media. 
     The computing device  660  may include or interface with a display device  670  and one or more input devices such a keyboard  672 . The computing device  660  may also include a network interface unit  674  to interface with one or more networks  676 . The network interface unit  674  may interface with the network  676  via a wired or wireless connection. The network  676  may be the Internet or any other private or public network. 
     The computing device  660  may receive distance data from a distance measuring device  665 . The computing device  660  may be coupled to the distance measuring device  665  by a dedicated wired or wireless connection or via a network. The computing device  660  may receive distance data from the distance measuring device  665  via an operator (not shown) who may enter the distance data using an input device such as the keyboard  672 . 
     The computing device  660  may also include a camera interface unit  678  to interface with a camera platform  650 , and/or a camera operator interface  662 . The camera interface unit  678  may include a combination of circuits, firmware, and software to interface with the camera platform  650 , and/or the camera operator interface  662 . The camera interface unit  678  may be coupled to the camera platform  650 , and/or the camera operator interface  662  via a network which may be a local area network; via one or more buses such as a USB bus, a PCI bus, a PCI Express bus, or other parallel or serial data bus; or via one or more direct wired or wireless connections. The camera interface unit  678  may be coupled to the camera platform  650 , and/or the camera operator interface  662  via a combination of one or more of direct connections, network connections, and bus connections. 
     The processes, functionality and features of the computing device  660  may be embodied in whole or in part in software which may be in the form of firmware, an application program, an applet (e.g., a Java applet), a browser plug-in, a COM object, a dynamic linked library (DLL), a script, one or more subroutines, or an operating system component or service. The computing device  660  may run one or more software programs as previously described and may run an operating system, including, for example, versions of the Linux, Unix, MS-DOS, Microsoft Windows, Palm OS, Solaris, Symbian, and Apple Mac OS X operating systems. The hardware and software and their functions may be distributed such that some functions are performed by the processor  664  and others by other devices. 
     Description of Processes 
       FIG. 7  is a flow chart of an exemplary process  780  for recording stereographic images using a stereographic camera system such as the stereographic camera  500 . Specifically,  FIG. 7  is a flow chart of a process for recording scenes without foreground objects, such as the scene  105 , and scenes with both foreground and background objects, such as the scene  205 . The flow chart has both a start  781  and an end  798  for any single shot, but the process  780  is continuous in nature and the actions within the process may be performed continuously and in near-real time during the recording of the shot. Additionally, the process  780  may be repeated, as indicated by the dashed line  799 , for each shot that is recorded. 
     Within this patent, the phrase “near-real time” means in real time except for processing delays that are very short compared with temporal events in the scene being recorded. 
     At  782 , a distance to at least one object in the scene may be determined. When the scene contains background objects, an extreme object distance (EOD), or the distance to an object within the scene that is the furthest from the stereographic camera, may be determined. When the scene contain foreground objects, a minimum object distance (MOD), or the distance to the object closest to the stereographic camera, may also be determined. The EOD and the MOD may be determined by a tape measure or other manual measuring device used by an operator who then enters the distance data into the stereographic camera system using a keyboard or other data entry device. The EOD and the MOD may be determined by a laser range finder, an acoustic rangefinder, an optical rangefinder, or other range finding device that may interface with the stereographic camera system via a dedicated connection or via a network. The EOD and the MOD may be determined using the stereographic camera system itself as a range finding device, as previously described. 
     When recording scenes where the stereographic camera remains fixed with respect the background, the EOD and the MOD may be determined once prior to the start of recording. The EOD and the MOD may then be considered as a constant during the recording period in which the scene is recorded. 
     When recording scenes where the stereographic camera and portions of the scene move with respect to each other during the recording period, the EOD and the MOD may be determined continuously and in real-time using a laser range finder, optical range finder, acoustic range finder, or other range-finding apparatus coupled to the stereographic camera. 
     At  783 , the stereographic camera system may receive inputs indicating a maximum allowable disparity, a focal distance-convergence distance offset, a focus distance of lenses in the stereographic camera, and a focal length or zoom value of the lenses. The inputs may be received, for example, from an operator interface such as the operator interface  562 . The maximum allowable disparity, the focal distance-convergence distance offset, a focus distance, and the focal length may be set by one or more operators such as a cameraman, assistant cameraman, or director. The focal length may commonly be set by an operator such as the assistant cameraman. However, the distance to a primary scene object may be measured in real time using a laser, acoustic, optical, or other range-finding device and the focal length may be automatically set in response to the real-time measurement such that the camera lenses are focused on the primary scene object. 
     The inputs indicating the maximum allowable disparity, the focal distance-convergence distance offset, the focus distance and the focal length may be received in the form of manually-entered data, analog or digital signals, or data received via a network. 
     At  784 , the convergence distance CD may be calculated based on the focus distance and the focus distance-convergence distance offset inputs. The convergence distance may be calculated using either formula (3) or formula (4) as described above. 
     A first interocular distance IOD EOD  may be calculated at  785 . IOD EOD  may be calculated based on the EOD as determined at  782 , the maximum allowable disparity input and focal length input received at  783 , and the convergence distance calculated at  784 . IOD EOD  may be calculated using the formula
 
IOD EOD =(EOD×CD×MD× W )/[(EOD−CD)×FL]  (7)
 
wherein
         IOD EOD =an interocular distance based on EOD   W=a width of an image sensor within each camera   FL=the focal of the lenses   EOD=the extreme object distance   MD=the maximum disparity as a fraction of the width of the scene recorded by the stereographic camera   CD=the convergence distance.       

     A  786 , a determination may be made if a foreground object is present in the scene. When a foreground object is not present in the scene, the IOD of the stereographic camera may to be set to IOD EOD  at  787 . 
     When a determination is made at  786  that a foreground object is present, a second interocular distance IOD MOD  may be calculated at  791 . IOD MOD  may be calculated based on the minimum object distance as determined at  782 , the maximum allowable disparity input and focal length input received at  783 , and the convergence distance calculated at  784 . IOD MOD  may be calculated using the formula
 
IOD MOD =(MOD×CD×MD× W )/[(CD−MOD)×FL]  (8)
 
wherein
         IOD MOD =an interocular distance based on MOD   W=a width of an image sensor within each camera   FL=the focal length of the lenses   MOD=the extreme object distance   MD=the maximum disparity as a fraction of the width of the scene recorded by the stereographic camera   CD=the convergence distance.       

     At  792 , the IOD of the stereographic camera may be set to the minimum of IOD EOD  and IOD MOD . Setting the IOD of the stereographic camera to the minimum of IOD EOD  and IOD MOD  ensures that the disparity in the stereographic image does not exceed the maximum disparity from  783 . 
     At  788 , the convergence angle ⊖ may be calculated and set. The convergence angle ⊖ may be calculated from the convergence distance CD from  784  and the interocular distance IOD set at either  787  or  792  using formula (1) as described above. 
     The convergence distance CD, the interocular distance IOD, and the convergence angle ⊖ may be calculated by a controller, such as the controller  560 , which may be a computing device such as the computing device  660 . The IOD and the convergence angle ⊖ may be set by a camera platform, such as the camera platform  550 , in response to data provided by the controller. 
     At  794 , a determination may be made if the recording of the scene has been completed. If the recording is ongoing, the process  780  may repeat continuously and in near real-time from  786  if the MOD is constant during the scene. The process  780  may repeat continuously and in near real-time from  784  (as indicated by the dashed line) if the MOD varies during the scene. When the recording of a scene has been completed, the process  780  may finish at  798 . Subsequently, the process  780  may start again from  782  to record the next scene. 
     Closing Comments 
     Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and procedures disclosed or claimed. Although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. With regard to flowcharts, additional and fewer steps may be taken, and the steps as shown may be combined or further refined to achieve the methods described herein. Acts, elements and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments. 
     As used herein, “plurality” means two or more. As used herein, a “set” of items may include one or more of such items. As used herein, whether in the written description or the claims, the terms “comprising”, “including”, “carrying”, “having”, “containing”, “involving”, and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of”, respectively, are closed or semi-closed transitional phrases with respect to claims. Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. As used herein, “and/or” means that the listed items are alternatives, but the alternatives also include any combination of the listed items.