Patent Publication Number: US-2011050852-A1

Title: Stereo telestration for robotic surgery

Description:
FIELD 
     The embodiments of the invention relate generally to telestration systems. More particularly, the embodiments of the invention relate to telestration mentoring systems for robotic surgery. 
     BACKGROUND 
     A telestrator is a device that allows its operator to draw a freehand sketch over a motion picture image. The act of drawing a freehand sketch over a motion picture image is often referred to as telestration. The freehand sketch may be referred to as a telestration image. Telestrators have been used to annotate televised weather reports and televised sporting events. 
     Telestration systems are often used in television broadcasts of football games to make a point to a television audience regarding one or more plays during the game. A sports commentator may draw sketches of objects, such as X and O, circles or lines, that is overlaid and displayed on still or moving video images of the play on the television monitor. Typically, the telestration image is displayed on a single television monitor in a mono-visual (“mono-view”) format and viewed by both eyes of the television viewer. The mono-view provided by the single television monitor is limited to two dimensional images. 
     BRIEF SUMMARY 
     The embodiments of the invention are summarized by the claims that follow below. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a block diagram of a robotic surgery system including a stereo viewer and a stereo telestration system to provide annotated stereo images to a surgeon. 
         FIG. 2A  is a block diagram of a first system to provide a stereo telestration image overlay in both left and right video channels to provide three-dimensional images in a stereo viewer. 
         FIG. 2B  is a block diagram of a second system to provide a stereo telestration image overlay in both left and right video channels to provide three-dimensional images in a stereo viewer. 
         FIG. 3  is a perspective view of a robotic surgical master control console including the stereo viewer. 
         FIG. 4  illustrates the stereo viewer of the master control console of  FIG. 3  with a stereo telestration image overlay in both left and right monitors to provide three-dimensional images of the surgical site and the telestration images. 
         FIG. 5A  illustrates a block diagram of a digital composite video mixer to mix a surgical site video signal and a telestration video signal together. 
         FIG. 5B  illustrates a block diagram of a digital component video mixer to mix a surgical site video signal and a telestration video signal together. 
         FIG. 5C  illustrates a block diagram of an analog video mixer to mix an analog surgical site video signal and an analog telestration video signal together. 
         FIG. 6A  illustrates left and right annotated surgical site images. 
         FIG. 6B  illustrates a three dimensional coordinate system for the stereo images of a background object and the stereo telestration images. 
         FIG. 6C  illustrates a stereo window of left and right images in the stereo viewer to show the horizontal offset between the left telestration image and the right telestration image to achieve fusing and the same depth. 
         FIG. 7  is a block diagram of an exemplary endoscopic camera. 
         FIG. 8  is a magnified perspective view of the exemplary endoscopic camera and the plane of a tissue or objection. 
         FIGS. 9A-9C  are diagrams to illustrate the generation of a disparity map. 
         FIG. 10  is side perspective stereo view illustrating differences in a telestration mark generated at an apparent constant depth and a telestration mark generated with an apparent depth continuum to appear painted onto a surface. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the embodiments of the invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one skilled in the art that the embodiments of the invention may be practiced without these specific details. In other instances well known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the invention. 
     One application for telestration systems is robotic surgery. In robotic surgery, two monitors are used to provide a stereo-visual (“stereo-view”) and a three-dimensional image to a pair of eyes. The three-dimensional image is important for depth perception of the surgical site and viewing the robotic surgical tools perform surgery on a patient within the surgical site. 
     A mono-visual image in a single monitor to a single eye is less desirable in robotic surgery. Similarly, while a stereo image of the surgical site is desirable, a mono-visual telestration image in only one monitor of the pair of monitors is less desirable during robotic surgery. With only a mono-visual telestration image, a surgeon may be confused, as one eye sees one half of a stereo image without the telestration image. Moreover, it may be hard on the surgeon&#39;s eyes and brain to view a mono-visual telestration image for extended periods and cause fatigue during surgery which is undesirable. 
     A video frame or a frame of pixel data may be used interchangeably with image herein. However, at a viewing device, an image is what is perceived by a user when viewing the video frame or pixel frame of data on the viewing device. A stereo image with a pair of images (e.g., a left image and a right image) has left and right video frames or left and right frames of pixel data. A mono-visual image or mono-image has one of a left image or a right image and one of a left or right video frame or a left or right frame of pixel data. 
     The embodiments of the invention include a method, apparatus, and system for stereo telestration for robotic surgery. 
     Robotic Surgical System 
     Referring now to  FIG. 1 , a block diagram of a robotic surgery system  100  is illustrated to perform minimally invasive robotic surgical procedures using a stereo telestration system. Robotic surgery generally involves the use of a robot manipulator that has multiple robotic manipulator arms. One or more of the robotic manipulator arms often support a surgical tool which may be articulated (such as jaws, scissors, graspers, needle holders, micro dissectors, staple appliers, tackers, suction/irrigation tools, clip appliers, or the like) or non-articulated (such as cutting blades, cautery probes, irrigators, catheters, suction orifices, or the like). At least one of the robotic manipulator arms  153  (e.g., the center robotic manipulator arm  153 ) is used to support a stereo or three dimensional surgical image capture device  110  such as a stereo endoscope (which may be any of a variety of structures such as a stereo laparoscope, arthroscope, hysteroscope, or the like), or, optionally, some other stereo imaging modality (such as ultrasound, fluoroscopy, magnetic resonance imaging, or the like). Robotic surgery may be used to perform a wide variety of surgical procedures, including but not limited to open surgery, neurosurgical procedures (such as stereotaxy), endoscopic procedures (such as laparoscopy, arthroscopy, thoracoscopy), and the like. 
     A user or operator O (generally a surgeon) performs a minimally invasive surgical procedure on patient P by manipulating input devices at a master control console  150 . A computer  151  of the console  150  directs movement of robotically controlled endoscopic surgical instruments  101 A- 101 B and  110 , by means of one or more feedback/control cables  159 , effecting movement of the instruments using a robotic surgical manipulator  152 . The robotic surgical manipulator  152  may also be referred to as robotic patient-side cart system or simply as a cart. The robotic surgical manipulator  152  has one or more robotic arms  153 . Typically, the robotic surgical manipulator  152  includes at least three robotic manipulator arms  153  supported by linkages  156 , 156 ′, with a central arm  153  supporting an endoscopic camera  110  and the robotic arms  153  to left and right of center supporting tissue manipulation tools  101 A- 101 B. 
     Generally, the robotic arms  153  of robotic surgical manipulator  152  include a positioning portion and a driven portion. The positioning portion of the robotic surgical manipulator  152  remains in a fixed configuration during surgery while manipulating tissue. The driven portion of the robotic surgical manipulator  152  is actively articulated under the direction of the operator O generating control signals at the surgeon&#39;s console  150  during surgery. The actively driven portion of the arms  153  is herein referred to as an end effector  158 . The positioning portion of the robotic arms  153  that are in a fixed configuration during surgery may be referred to as positioning linkage and/or “set-up joint”  156 ,  156 ′. 
     An assistant A may assist in pre-positioning of the robotic surgical manipulator  152  relative to patient P as well as swapping tools or instruments  101  for alternative tool structures, and the like, while viewing the internal surgical site via an assistant&#39;s display  154 . 
     The image of the internal surgical site shown to A by the assistant&#39;s display  154  is provided by a left or right channel  176  of the stereo endoscopic camera  110  supported by the robotic surgical manipulator  152 . In contrast, both left and right channels of the stereo endoscopic camera  110  are provided to the operator O in a stereo display  164  at the surgeon&#39;s console  150 , one channel for each eye. 
     Stereo Telestration 
     A teacher, instructor, or other person, referred to generally as mentor M, may be on site or at a remote location and use a telestrator to generate telestration and provide comments and instructions to the operator O regarding the robotic surgical procedure in the surgical site of the patient P. In this manner an expert on the robotic surgical procedure, such as mentor M, may guide a less experienced operating surgeon O. 
     A typical telestration system provides mono-view images. The robotic surgical system has a stereo viewer which displays a three dimensional image of the surgical site to the surgeon O. If the telestration image is displayed in only one eye, confusion can result since the other eye is seeing the other image of the stereo pair without the telestration image overlay. To support stereo telestration from the mentor M, the robotic surgical system  100  includes a stereo telestration system  160  coupled between the console  150  and remote located telestration equipment  161 . The remote located telestration equipment  161  may be located remotely in the same room as the patient and surgeon or in a different room, a different hospital, or a different city, country, continent or other differing location. 
     The stereo telestration system  160  processes left and right channels of stereo video signals and optionally, full duplex audio signals for audio/video communication. The stereo telestration system  160  receives stereo images of the surgical site (“stereo surgical images”) from the stereo endoscopic camera  110  over the stereo video communication link  170 . A mono-view of telestration images (“mono telestration images”) is generated by a telestrator or telestration generator  162  (such as a drawing tablet  262  and drawing pen  263  illustrated in  FIG. 2B  for example) and coupled into the stereo telestration system  160  over the communication link  172 . The telestration generator  162  digitizes a telestration mark or telestration graphic into a digital telestration graphic image for communication over the link  172 . 
     The stereo telestration system  160  overlays the mono telestration images onto the stereo surgical images of the surgical site generated by the stereo endoscopic camera  110  to form annotated stereo surgical images. The telestration system  160  couples the annotated stereo surgical images into the stereo display  164  of the console  150  over the stereo video communication link  175  for viewing by the operator O. The telestration system  160  may also couple the annotated stereo surgical images over a video communication link  176  to a stereo viewer at a remote location for viewing by the person generating the telestration. Alternatively, a single left or right channel of the annotated stereo surgical images may be coupled by the telestration system  160  over the video communication link  176  to a single video monitor  165 A at a remote location for viewing by the person generating the telestration. 
     While the telestration system  160  generates video images, it may optionally provide a full duplex audio communication channel between the operator O and the person generating the telestration. Alternatively, a wireless or wired telephone system, such as cellular telephone system, internet protocol telephone system, or plain old telephone system may be used to provide the full duplex audio communication channel. 
     The remote located telestration equipment  161  may include a video monitor  165 A, a telestration generator, a microphone  180 , a speaker  181 , and an audio processor  182  coupled together as shown. Telestration images are generated by the telestration generating device  162  that is coupled to the stereo telestration system  160  over the communication link  172 . A telestration generating device may also be referred to herein as a telestrator or a telestration generator. 
     In the case of a mono-view monitor, the video monitor  165 A receives either the left or right channel of the annotated stereo surgical images over the video communication link  176  for viewing by the mentor M at the remote location. In the case of a stereo viewer for the mentor M, the stereo viewer receives both of the left and right channels of the annotated stereo surgical images over the video communication link  176  at the remote location so that the mentor M may view stereo images similar to the stereo viewer  164  in the console  150 . That is, the communication link  176  may carry either one or both of a left or right channel of annotated surgical images. 
     As discussed previously, the stereo telestration system  160  may overlay a mono telestration image onto stereo images of the surgical site (referred to as “stereo surgical images”) generated by the stereo endoscopic camera  110  to form annotated stereo surgical images. However in an alternate embodiment of the invention, the mono telestration image is not immediately overlayed onto the stereo surgical images. Instead, the mentor M privately previews his telestration graphics overlayed onto the surgical site images on the monitor  165 A, 165 B before the telestration graphics are overlayed onto the surgical site images displayed at the stereo viewer  164  to the operator O. That is, the mentor M views the annotated surgical images before the telestration goes “live” on the stereo viewer for the operator O to see. 
     As previously discussed, the telestration system  160  may optionally provide a full duplex audio communication channel  184  between the operator O and the mentor M. To support full duplex communication, the remote located telestration equipment  161  may include a microphone  180 , a speaker  181 , and an audio processor  182  coupled to the communication channel  184 . The console may also include a microphone  180 , a speaker  181 , and an audio processor  186  coupled to the channel  184  to support full duplex communication. 
     If cables cannot be used to reach the remote located telestration equipment  161 , modems, transceivers, or other communication devices  191 , 192  may be used to form data/audio/video communication channels  172 , 176 , 184  over a communication network  190 . In one embodiment of the invention, the communication network  190  is a wide area network such as the internet and the communication devices  191 , 192  are wide area network routers. For the audio channel, hands-free telephones may be used at each end to communication between remote locations over the plain old telephone system (POTS) of communication. 
     Referring now to  FIG. 3 , a perspective view of the robotic surgical master control console  150  is illustrated. The master control console  150  of the robotic surgical system  100  may include the computer  151 , a binocular or stereo viewer  312 , an arm support  314 , a pair of control input wrists and control input arms in a workspace  316 , foot pedals  318  (including foot pedals  318 A- 318 B), and a viewing sensor  320 . The master control console  150  may further include the telestration system  160  for providing the telestration images overlaid on the surgical site images. The master control console  150  may also include an audio processor or transceiver  317  coupled to a speaker  320  and a microphone  315  for a bi-directional voice communication system to provide full duplex voice communication between the operating surgeon O and the mentor M. The audio processor or transceiver  317  may couple to or be a part of the telestration system  160  in embodiments of the invention. 
     The stereo viewer  312  has two displays where stereo three-dimensional images of the telestration and surgical site may be viewed to perform minimally invasive surgery. When using the master control console, the operator O typically sits in a chair, moves his or her head into alignment with the stereo viewer  312  to view the three-dimensional annotated images of the surgical site. To ensure that the operator is viewing the surgical site when controlling the robotic surgical tools  101 , the master control console  150  may include the viewing sensor  320  disposed adjacent the binocular display  312 . When the system operator aligns his or her eyes with the binocular eye pieces of the display  312  to view a stereoscopic image of the telestration and surgical worksite, the operator&#39;s head sets off the viewing sensor  320  to enable the control of the robotic surgical tools  101 . When the operator&#39;s head is removed the area of the display  312 , the viewing sensor  320  can disable or stop generating new control signals in response to movements of the touch sensitive handles in order to hold the state of the robotic surgical tools. 
     The arm support  314  can be used to rest the elbows or forearms of the operator O (typically a surgeon) while gripping touch sensitive handles of the control input wrists, one in each hand, in the workspace  316  to generate control signals. The touch sensitive handles are positioned in the workspace  316  disposed beyond the arm support  314  and below the viewer  312 . This allows the touch sensitive handles to be moved easily in the control space  316  in both position and orientation to generate control signals. Additionally, the operator O can use his feet to control the foot-pedals  318  to change the configuration of the surgical system and generate additional control signals to control the robotic surgical instruments. 
     The computer  151  may include one or microprocessors  302  to execute instructions and a storage device  304  to store software with executable instructions that may be used to generate control signals to control the robotic surgical system  100 . The computer  151  with its microprocessors  302  interprets movements and actuation of the touch sensitive handles (and other inputs from the operator O or other personnel) to generate control signals to control the robotic surgical instruments  101  in the surgical worksite. In one embodiment of the invention, the computer  151  and the stereo viewer  312  map the surgical worksite into the controller workspace  316  so it feels and appears to the operator that the touch sensitive handles are working over the surgical worksite. 
     Referring now to  FIG. 4 , a perspective view of the stereo viewer  312  of the master control console  150  is illustrated. To provide a three-dimensional perspective, the viewer  312  includes stereo images for each eye including a left image  400 L and a right image  400 R of the surgical site including any robotic surgical tools  400  respectively in a left viewfinder  401 L and a right viewfinder  401 R. The images  400 L and  400 R in the viewfinders may be provided by a left display device  402 L and a right display device  402 R, respectively. The display devices  402 L, 402 R may optionally be pairs of cathode ray tube (CRT) monitors, liquid crystal displays (LCDs), or other type of image display devices (e.g., plasma, digital light projection, etc.). In the preferred embodiment of the invention, the images are provided in color by a pair of color display devices  402 L, 402 R; such as color CRTs or color LCDs. 
     In the stereo viewer, three dimensional telestration images may be provided to a surgeon by overlaying them onto the three dimensional image of the surgical site. In a right viewfinder  401 R, a right telestration image (RTI)  410 R is merged into or overlaid on the right image  400 R being displayed by the display device  402 R. In a left viewfinder  401 L, a left telestration image (LTI)  410 L is merged into or overlaid on the left image  400 L of the surgical site provided by the display device  402 L. In this manner, a stereo telestration image may be displayed to provide instructions to the operator O in the control of the robotic surgical tools in the surgical site. 
     Referring now to  FIGS. 2A-2B , embodiments of stereo telestration imaging systems are illustrated. In  FIG. 2A , a first embodiment of the stereo telestration imaging system includes the stereo endoscopic camera  110 , the telestration system  160 , remote telestration equipment  161 A, and the stereo viewer  164 . 
     As discussed previously, the remote telestration equipment  161 A includes a telestration generator  162 A and a single video monitor  165 A for the mentor M to view a mono view of the annotated surgical site generated by the telestration system  160 . The remote telestration equipment  161 A may further include a part of a full duplex audio communication system such as a telephone or speaker phone described previously with reference to  FIG. 1 . 
     The telestration generator  162 A may include a drawing tablet  262  and a drawing pen  263 , to generate the mono view telestration images for overlay onto the stereo images of the surgical site. The drawing tablet  262  and drawing pen  263  may also be referred to herein as a digitizing tablet and digitizing pen as they digitize a sketched drawing into a digital telestration graphic image. The telestration generator  162 A may also include a keyboard  264 . The telestration generator  162 A may additionally or in the alternative include one or more elements of the telestration generator  162 B described in greater detail below. 
     As discussed previously for one embodiment of the invention, a mentor M may preview the telestration graphics that are to overlayed onto the surgical site images on the monitor  165 A, 165 B before the telestration graphics are overlayed onto the surgical site images displayed at the stereo viewer  164  to the operator O. Additionally, a mono-view telestration image may be generated for multiple video frames until an erase command is issued to the drawing tablet. That is, as the sketch is made on the drawing tablet, the mono view telestration images show the growth of the sketch until completion, which is then shown in a steady state until erased. 
     The stereo endoscopic camera  110  includes an endoscope  202  for insertion into a patient, a camera head  204 , a left image forming device (e.g., a charge coupled device (CCD))  206 L, a right image forming device  206 R, a left camera control unit (CCU)  208 L, and a right camera control unit (CCU)  208 R coupled together as shown. The stereo endoscopic camera  110  generates a left video channel  211 L and a right video channel  211 R of frames of images of the surgical site. To initially synchronize left and right frames of data, a lock reference signal is coupled between the left and right camera control units  208 L, 208 R. In one embodiment of the invention, the right camera control unit generates the lock signal that is coupled to the left camera control unit to synchronize the left view channel to the right video channel. However in another embodiment of the invention, the left camera control unit generates the lock reference signal and the right video channel synchronizes to the left video channel. 
     The stereo display  164  includes a left monitor  230 L and a right monitor  230 R. As discussed previously with reference to  FIG. 4 , the viewfinders or monitors  230 L, 230 R may be provided by a left display device  402 L and a right display device  402 R, respectively. In the preferred embodiment of the invention, the stereo images are provided in color by a pair of color display devices  402 L, 402 R. 
     Additional details of a stereo endoscopic camera and a stereo display may be found in U.S. Pat. No. 5,577,991 entitled “Three Dimensional Vision Endoscope with Position Adjustment Means for Imaging Device and Visual Field Mask” filed on Jul. 7, 1995 by Akui et al; U.S. Pat. No. 6,139,490 entitled “Stereoscopic Endoscope with Virtual Reality Viewing” filed on Nov. 10, 1997 by Breidenthal et al; and U.S. Pat. No. 6,720,988 entitled “Stereo Imaging System and Method for use in Telerobotic Systems” filed on Aug. 20, 1999 by Gere et al.; all of which are incorporated herein by reference. Stereo images of a surgical site may be captured by other types of endoscopic devices and cameras with different structures. For example, a single optical channel may be used with a pair of spatially offset sensors to capture stereo images of the surgical site. 
     The telestration device or system  160  for the left video channel includes a left video combiner  210 L and a left synchronizer/noise reducer/enhancer device  214 L coupled to a VSD board  218 ; while the right channel includes a right video combiner  210 R and a left synchronizer/noise reducer/enhancer device  214 L coupled to the VSD board  218 . The telestration device or system  160  may further include left and right power transformers  240 L- 240 R coupled to an isolation transformer  242  to receive power. 
     The left video combiner  210 L combines the telestration graphics or images with the left video images of the surgical site on the left video channel  211 L. The right video combiner  210 R combines the telestration graphics or images with the right video images of the surgical site on the right video channel  211 R. For the respective left and right video channels, the left and right synchronizer/noise reducer/enhancer devices  214 L- 214 R perform analog-to digital conversion as necessary, plus electronic noise reduction and image enhancement/sharpening in order to improve (“sweeten”) the left and right images. Synchronization may also be provided by the devices  214 L- 214 R however is not strictly necessary since the camera control units (CCUS) are already synchronized. The VSD board  218  performs interlaced-to-progressive video scan conversion; electronic image-shifting to correct endoscope and camera optical misalignment as is described further in U.S. Pat. No. 6,720,988 by Gere et al. (previously incorporated by reference); and control graphic overlay for the respective left and right video channels. 
     The left and right video combiners  210 L, 210 R may combine video signals in various ways depending upon the type of video signals being provided. In one embodiment of the invention, the stereo video signals of the surgical site provided on the left and right video channels  211 L, 211 R are analog video signals. In another embodiment of the invention, the stereo video signals of the surgical site provided on the left and right video channels  211 L, 211 R are digital video signals. Similarly, the mono telestration video signals on the link  172  are analog video signals in one embodiment of the invention and are digital video signals in another embodiment of the invention. Depending upon whether analog, digital, or mixed analog and digital video signals are used, various mixing techniques may be employed to mix the stereo surgical site video signals with the telestration video signals to form the stereo annotated surgical site video signals. Additionally, depending upon the format of the video signals (composite video or component video and their respective video formats e.g., RGB, S-Video or Y/C, YUV, YIQ, YCrCb), the type of mixing techniques used may vary to mix the stereo surgical site video signals and the telestration video signals together. In any case, an alpha synchronizing signal may be provided that can be used to overlay the graphic telestration images onto the video signal of the surgical site. 
     Mixing two digital video sources may be simply performed by using a multiplexer to switch between sources or by soft keying by implementing full alpha mixing. In  FIG. 5A , two digital composite video signals each having their own alpha channel are mixed together. The digital video signal of the surgical site is coupled into the mixer  500 A as one source and the digital video signal of the telestration image is coupled into the mixer  500 A as a second source. After subtracting out the digital value of the black level at the subtractors  502 A- 502 B, the sources are keyed by their respective alpha signals alpha_ 0  and alpha_ 1  by the keying device (e.g., multiplier)  504 A- 504 B and then added together at the summer or adder  506 . The result from the summer  506  is then rounded and limited by a rounding/limiting device  508  to an appropriate number of bits of digital video. The black level is then added back into the digital video signal at the adder or summer  510  to generate the annotated surgical site video signal as the resultant output from the mixer  500 A. 
     For RGB component digital video signals, the mixing may be somewhat similar for each component signal. In  FIG. 5B , an RGB component digital video signal is provided for the surgical site video signal (Surgical Site R_ 1 , G_ 1 , and B_ 1 ) and the telestration video signal (Telestration R_ 1 , G_ 1 , and B_ 1 ) and coupled into the video mixer  500 B. The resultant output from the video mixer  500 B are the RGB components of the annotated surgical site video signal (Annotated Surgical Site R_out, G_out, and B_out). With the component video signals, the black level is typically zero by convention and therefore of little concern and this can be simplified from that of mixer  500 A. For each component signal, the sources are keyed by their respective alpha signals alpha_ 0  and alpha_ 1  by the keying devices (e.g., multipliers)  504 A- 504 B to synchronize when the signals are to be added. The synchronized signals are then added together at the summer or adders  506 A- 506 C for each respective component signal. The result from each of the summers  506 A- 506 C is then rounded and limited by the rounding/limiting devices  508 A- 508 C to an appropriate number of bits of digital video to generate each respective RGB component of the annotated surgical site video signal (Annotated Surgical Site R_out, G_out, and B_out). 
       FIG. 5C  illustrates a simple analog video mixer  500 C consisting of an analog multiplexer  520  that is responsive to a keying signal coupled to its select terminal. The multiplexer  520  selects to output a video signal from two input video signals. The multiplexer selects between the surgical video signal coupled to one input terminal and the telestration video signal coupled to a second input terminal. 
     In response to the keying signal, the multiplexer  520  can generate the annotated surgical site video signal. The keying signal is generated in response to a level of the input telestration video signal. In one embodiment, the luminance level of the telestration video signal may be used as the keying signal. With the luminance of telestration video signal above a predetermined level, the telestration video signal is selected to be output from the multiplexer  520 . With the luminance level of the telestration video signal below the predetermined level, the surgical site video signal is selected to be output from the multiplexer  520 . In this manner, the Annotated surgical site video signal can be generated by the mixer  500 C. 
     If mixed analog and digital video signals are provided, the analog video signal may be converted into a digital video signal and mixed according to digital mixing techniques. Alternatively, the digital video signal may be used to key the analog video signal to select a monochrome image in the analog mixing technique or the digital video signal may be converted to an analog video signal and mixed according to analog mixing techniques. 
     The right video combiner  210 R may be a master video combiner feeding through the telestration graphics or images to a slave video combiner, the left video combiner  210 L, over a communication link  272 . In this case, the right video combiner  210 R receives control/data signals and the telestration images on the communication link  172  (at COMM IN input) from the remote telestration generator  162 A. The COMM-OUT output of the right video combiner  210 R is coupled to the COMM-IN input of the left video combiner  210 L by means of the communication link  272 . Alternatively, the left video combiner may be the master combiner and the right video combiner may be the slave combiner. 
     The remote telestration device  162 A may couple to the telestration system  160  through the communication link  172  over the communication system  190  by means of the communication devices  191 , 192 . 
     The telestration images on the communication link  172  are in a digital data format in a preferred embodiment of the invention. The communication link  172  may use a standard RS-232 digital communication protocol as the telestration data may be simple X and Y coordinates which are not of high bandwidth. 
     As discussed previously, the right video combiner  210 R may be coupled to the left video combiner  210 L by way of the communication link  272 . The communication link  272  may be another RS-232 link, for example. In this case, the right video combiner  210 R simply relays the control/data signals and the telestration images on the communication link  172  to the left video combiner  210 L over the communication link  272 . 
     As discussed previously, the remote telestration equipment  161 A includes the single video monitor  165 A for a mono view of the annotated surgical site generated by the telestration system  160 . The video monitor  165 A couples to either a left annotated video channel  212 L or a right annotated video channel  212 R of the annotated surgical images to generate the mono view. The video monitor  165 A may couple to either the left annotated video channel  212 L or the right annotated video channel  212 R over the communication system  190  by means of the communication devices  191 , 192 . 
     Referring now to  FIG. 2B , a second embodiment of the stereo telestration imaging system is illustrated. The stereo telestration imaging system includes the stereo endoscopic camera  110 , the telestration system  160 , remote telestration equipment  161 B, and the stereo viewer  164 . The stereo telestration imaging system of  FIG. 2B , while substantially similar to that of  FIG. 2A , differs in the remote telestration equipment  161 B (e.g., includes a stereo viewer  165 B instead of a monitor  165 A) and how it may be connected. 
     As previously discussed, the annotated stereo surgical images from the telestration system  160  may be coupled over the video communication link  176  to a stereo viewer  165 B at a remote location for viewing by the person generating the telestration, such as the mentor M. In this case, the stereo viewer  165 B may couple to the left and right video channels  220 L, 220 R to receive the stereo annotated surgical images and display them in the left display L and the right display R for viewing by the left and right eyes, respectively. Alternatively, the stereo viewer  165 B may couple to the left and right video channels elsewhere in the telestration system  160  after the telestration images are mixed with the surgical site images, such as at left and right video channels  212 L, 212 R after the devices  210 L, 210 R or the left and right video channels  216 L, 216 R after the devices  214 L, 214 R. In any case, the remote stereo viewer may couple to the telestration system  160  through the video link  176  over the communication system  190  by means of the communication devices  191 , 192 . 
     As mentioned previously, the remote telestration equipment  161  may be connected differently. Instead of the left and right video combiners being connected to the telestrator device in a master-slave configuration, they may be coupled in parallel to it. In this case, both of the left and right video combiners  210 L, 210 R receive control/data signals and the telestration data signals over the communication link  172  (at the COMM-IN inputs) from the remote telestration generator  162 B. If for some reason analog video signals are used, the communication link  172  may be split in two. If digital signals are used, the digital signal can be readily fanned out into two signals as illustrated and coupled into each communication input of the left and right video combiners  210 L, 210 R. The remote telestration generator  162 B may couple to the telestration system  160  through the communication link  172  over the communication system  190  by means of the communication devices  191 , 192 . 
     The telestration generator  162 B may include a computer  265 , a keyboard  264 , and an input device  266  (such as a mouse, for example) to generate the mono view telestration images for overlay onto the stereo images of the surgical site. The telestration generator  162 B may additionally, or in the alternative, include one or more elements of the telestration generator  162 A, such as the drawing tablet  262  and the drawing pen  263  described in greater detail above. 
     In yet another embodiment of the invention, the stereo telestration imaging system of  FIG. 2B  is modified to include a three-dimensional input device  266  as part of the remote telestration equipment  161 B with the stereo viewer  165 B. The three-dimensional input device  266  may be a three-D mouse or a duplicate of the three-D input control devices at the master console  150 . In this manner, a mentoring surgeon M could view a three dimensional surgical site and draw one or more telestration marks at a depth he/she desires by means of the three-dimensional input device without need of any depth perception correction. 
     While  FIGS. 2A-2B  illustrate separate functional blocks for the telestration device or system  160 , such as the left video combiner  210 L and the right video combiner  210 R, a plurality of the functional blocks may be incorporated into one integral electronic system, one integrated printed circuit board, or one integrated circuit, such as the VSD board  218  for example. 
     Depth Perception Correction for Stereo Telestration 
     In typical telestration systems, a telestration graphic image is typically placed in the foreground while the image being telestrated or sketched on is placed in the background. The telestration graphic image may be a pure opaque overlay so that background objects may be visible. This implies that the depth of the telestration graphic is no deeper than the depth of the background object in order to preserve a foreground/background illusion. 
     In stereo telestration, the telestration image is displayed to both left and right eyes as is discussed above. 
     By simply mixing the stereo surgical site with a mono-view telestration image, there may be a perceived difference in depth between the surgical site image and the telestration image in the annotated stereo surgical site image. Moreover, the left and right telestration images derived from the mono view of the telestration image may not fuse into a stereo or three dimensional image. In some cases, this may not matter and no depth perception correction is needed. However if a mono-view telestration image is used to generate stereo telestration, it is desirable to correct for the differences in depth perception between the surgical site image and the telestration image in most applications. That is, it is desirable to fuse the left and right telestration images together in the stereo viewer at the same apparent depth of the surgical site stereo image when using a mono-view telestration image. 
     Note that typically the telestration images are placed at a depth less than or equal to the surgical site image and not greater, if the surgical site image is the background. Placing the telestration images at a depth equal to the dept of the surgical site image is particularly useful when a mono view telestration image is generated by the mentor from a mono view. However, if the mentor has a stereo view and can directly generate a stereo image of the telestration graphics, placing the telestration images at a depth equal to the depth of the surgical site is less important. In which case, stereo image of the telestration graphics can be placed at a depth less than the depth of the surgical image because both mentor and operator viewing stereo telestration images can agree on the interpretation of the telestration graphic. 
     Referring now to  FIG. 6A , a left image  602 L and a right image  602 R of an annotated stereo surgical site image is illustrated. The right image  602 R includes a right telestration image  610 R in the surgical site around the needle  605 . Simply mixing the mono telestration image drawn with respect to the right channel may result in a left telestration image  610 L offset within the surgical site from the needle  605  as illustrated in  FIG. 6A . In this case, the telestration graphic is positioned at a depth other than the foreground depth and it cannot uniquely identify any particular point to an operator O. 
     Referring now to  FIG. 6B , it is desirable to adjust the perceived depth of the stereo telestration image  612 A or  612 B to the perceived depth of the object of interest  611 . The telestration image is adjusted to the same depth of the background object so that the stereo telestration image may uniquely identify a background location. In one case, the horizontal position of one half of the stereo pair of images is adjusted further away from the other so as to move the stereo telestration image  612 A down towards the perceived depth of the object of interest  611 . In another case, the horizontal position of one half of the stereo pair of images is adjusted closer to the other so as to move the stereo telestration image  612 A up above the perceived depth of the object of interest  611 . 
     Referring now to  FIG. 6C , a stereo window  620  of the annotated stereo surgical site is illustrated having a left image  621 L and a right image  621 R that may be viewed in the stereo viewer. The images in the stereo window may be moved in depth with respect to the plane of the stereo window by adjusting the stereo base or horizontal offset of the images. 
     Assuming the right channel was used by the mentor to generate a right telestration image  612 R around the right image  611 R of the object of interest, the left telestration image  612 L 1  or  612 L 2  is horizontally adjusted to fuse and form a stereo telestration image at the perceived depth of the stereo image  611  of the object of interest. The horizontal separation distance  625  between the left telestration image  612 L 1  or  612 R and the right telestration image  612 R may also be referred to herein as the horizontal offset or stereo base. 
     To move the stereo telestration image  612 A down towards the perceived depth of the object of interest  611 , the horizontal position of the left telestration image  612 L 2  in the left image  621 L is adjusted further away from the right telestration image  612 R to a position of the left telestration image  612 L 1 , for example, to fuse and form the stereo telestration image at the perceived depth of the stereo image  611  of the object of interest. That is, the horizontal separation or horizontal offset is increased. Alternatively, to move the stereo telestration image  612 B up towards the perceived depth of the object of interest  611 , the horizontal position of the left telestration image  612 L 1  in the left image  621 L is adjusted closer to the right telestration image  612 R to a position of the left telestration image  612 L 2 , for example, to fuse and form the stereo telestration image at the perceived depth of the stereo image  611  of the object of interest. That is, the horizontal separation or horizontal offset is decreased. 
     In an alternate embodiment of the invention, the left or right image of the surgical site associated with the non-view channel is adjusted horizontally to move the perceived depth of the surgical image deeper in the stereo window or shallower in the stereo window. In yet another embodiment of the invention, the left and right telestration images are both adjusted horizontally to move close together or farther apart so as to adjust the perceived depth in the stereo window. In yet another embodiment of the invention, the left and right surgical site images are both adjusted horizontally to move close together or farther apart so as to adjust the perceived depth in the stereo window. Moving the left and right images further apart in the stereo window, increasing the horizontal offset, moves the stereo image farther away, increasing the perceived depth of the stereo image. Moving the left and right images closer together in the stereo window, decreasing the horizontal offset, moves the stereo image closer, reducing the perceived depth of the stereo image. 
     In the case of a mono-view being provided to the mentor, for the operator O to view a telestration image on the stereo viewer so that it is fusible with the left and right images of the surgical site, the telestration image associated with the video channel not viewed by the mentor is positionally adjusted. For example, in  FIG. 2A  the right channel  212 R of the annotated surgical site video signal is viewed by the mentor M over the video monitor  165 A. The mentor generates the telestration graphic images relative to the right video channel  211 R images of the surgical site video signal so that it appears at the correct position therein. 
     The left video channel  211 L images of the surgical site video signal may not viewed by the Mentor M and may be referred to as the “non-viewed channel”. In which case, the position of the telestration image associated with the non-viewed channel, left video channel  211 L of the surgical site, is positionally adjusted. For example, in  FIG. 6  the position of the left telestration image  610 L is adjusted to correct for the offset so that it is similarly positioned around the needle  605  as illustrated in the right image  602 R. 
     The telestration images for the non-viewed channel are positionally (i.e., horizontally assuming parallel camera and viewer/eyes) adjusted so that telestration images and the surgical site images are fusible and appear at the same depth, as located by the mentor. The telestration images for the non-viewed channel may be automatically adjusted in position by the stereo telestration video system or it may be manually performed. 
     For the surgeon O to adjust the horizontal offset of the left and right images, the robotic surgery system  100  may further include a control input  187 , such as a control knob, at the console  150 . The control input may generate one or more control signals onto one or more control lines  186  to control the stereo telestration system  160 . Alternately, the control input may mechanically or electromechanically control the stereo endoscopic camera  110  through one or more control lines  159 . 
     For manual adjustment, a manual control input such as a control knob in the console  150  may be provided to allow the surgeon O in some embodiments of the invention to adjust the horizontal position of at least one of the left or right telestration images until they are fusible together. 
     The control knob may be used to generate an electronic control signal to control the mixing of the telestration image with the surgical site image for one channel. In this case, the electronic control signal may alter the alpha signal in a digital mixer or the keying signal in an analog mixer, as to where the telestration image is to be overlaid onto the surgical site image. Alternatively, the electronic control signal may cause a horizontal shift in the position of the digital pixel data of the telestration image in the video signal on one channel with respect to the surgical site image. In some embodiments of the invention, the control knob may be used to mechanically or electro-mechanically (e.g., by electric motor control) control the left or right channels of the endoscopic camera  110  to move a left or right image of the surgical site to be properly located under the telestration image. 
     In other embodiments of the invention, the robotic surgery system  100  may further include a control input  187 ′, such as a control knob, that may be manipulated by the mentor M at the remote telestration equipment  161  to generate an electronic control signal transmitted to the telestration system  160 . The control input  187 ′ may generate one or more control signals onto one or more control lines  186 ′ to control the stereo telestration system  160  as further described herein. Alternately, the control input may mechanically or electromechanically control the stereo endoscopic camera  110  as further described herein through the one or more control lines  186 ′. If local cabling is unavailable, the control signals for the one or more control lines  186 ′ may be communicated over the communication link  190  by means of the communication devices  191 , 192 . 
     Referring now to  FIG. 7 , a block diagram of an exemplary endoscopic camera  110  is illustrated. The exemplary endoscopic camera  110  includes a left observation optical system  702 L and a right observation optical system  702 R in the endoscope  202 . The exemplary endoscopic camera  110  further includes a first mirror  711 L and a second mirror  712 L and one or more image formation lenses  703 L- 704 L in the left channel and a first mirror  711 R and a second mirror  712 R and one or more image formation lenses  703 R- 704 R in the right channel as part of the camera head  204 . 
     The exemplary endoscopic camera  110  further includes a focusing arrangement. The lenses  704 L and  704 R may be adjusted in position by a position adjustment mechanism  724  to focus left and right images into the left and right cameras  206 L, 206 R, respectively. The position adjustment mechanism  724  may be moved by an electric motor  784  through an appropriate transmission coupled there-between. A position sensor  785  may be coupled to the position adjustment mechanism  724 , the motor  784  or the transmission coupled there-between to obtain a measure of focus position. The motor  784  is controlled by means of a focus controller  786  that is typically connected to an input device at the console. 
     The left and right cameras  206 L, 206 R couple to the camera head  204  to receive the respective left and right images of the surgical site to provide a stereo image thereof. The cameras  206 L, 206 R in one embodiment of the invention are charge coupled devices to generate a digital video signal. The exemplary endoscopic camera  110  further includes the left and right camera control units  208 L, 208 R coupled to the left and right cameras  206 L, 206 R. 
     In one embodiment of the invention, the left and right cameras  206 L, 206 R are movable about the respective optical axes  750 L, 750 R of the camera head  204  by position adjustment mechanisms  706 L, 705 R. That is, the position adjustment mechanisms  706 L, 705 R adjust the relative positions of the cameras  206 L, 206 R with respect to the left and right optical systems. In this manner, the position adjustment mechanisms  706 L, 705 R can be used to manually adjust the horizontal position of the left or right cameras  206 L- 206 R by a control knob  187 , 187 ′ to move a left or right image of the surgical site so that it is properly located under the telestration image. 
     In another embodiment of the invention, the mirror  712 L and the and one or more image formation lenses  703 L- 704 L in the left channel are movable by a position adjustment mechanism  714 L while the mirror  712 R and the one or more image formation lenses  703 R- 704 R in the right channel are movable by a position adjustment mechanism  714 R. In this manner, the position adjustment mechanisms  714 L, 714 R may move the left or right optical axes  750 L, 750 R of the camera head  204  under the left and right cameras  206 L, 206 R by a control knob  187 , 187 ′ to move a left or right image of the surgical site so that it is properly located under the telestration image. 
     As discussed previously, the control knob for adjusting the position of the left or right telestration image may also be manipulated by the mentor M at the remote telestration equipment instead of the operator O at the console. The control knob  187 ′ of the remote telestration equipment under control of the mentor M generates an electronic control signal transmitted to the telestration system  160  over communication link  190  through the communication devices  191 - 192 . In this case, the mentor M views both left and right channels of the stereo pair of images such as illustrated in  FIG. 2B . This allows the mentoring surgeon M to view the same stereo pair of images as the operating surgeon O. 
     Closing one eye (or using some functionally similar technology such as a shutter on the left or right video image), the mentoring surgeon M “marks” one half or side (i.e., one of the left or right channel) of the stereo pair with a telestration marking instrument. The telestration system duplicates the mark in the other half or side of the stereo pair displays both to the operating surgeon O and mentor M. The mentoring surgeon M then uses the control knob  187 ′ of the remote telestration equipment  161  to adjust the horizontal offset of the second mark (with respect to the first mark) until the stereo representation of the mark appears to be at the correct depth with respect to whatever the mentoring surgeon M determines is appropriate. 
     The control knob  187 , 187 ′ may be a generic control input device, which could be replaced with some other input device capable of representing a continuum of choices in the horizontal offset of the telestration image. 
     The automatic positional adjustment of the telestration image in the non-viewed channel uses a plurality of values for the position of the endoscopic camera in relationship to the surgical site, such as a plurality of distances between the endoscopic camera and the tissue at a plurality of points of the surgical site and a plurality of angles between lines from the endoscopic camera to the points in the tissue and line segments between the respective points. 
       FIG. 8  illustrates a first distance  801 A between the end of the endoscopic camera  110  and a first point P 1  on a plane of tissue  800 . The first distance  801 A represents the depth of the object of interest in the stereo field of view at the first point P 1 , with P 1  being in the tissue plane and along the centerline C of the endoscopic camera  110 .  FIG. 8  further illustrates a second point P 2  and a third point P 3  on the tissue  800  with respective distances  801 B- 801 C between a line of sight of the range finder  805  and the plane of the tissue  800 . Additionally one may define angles  802 A- 802 D representing the angles between the various line-of-sight line segments  801 A- 801 C and the line segments between the points P 1 -P 3  as illustrated. 
     As previously discussed, a plurality of points P on the tissue  800  with respective angles  802  and distances  801  may be used to determine the horizontal offset. If one angle  802 A, 802 D between the camera and the tissue is known, at least two distances ( 801 A, 801 B or  801 A, 801 C) between at least three points (P 1 ,P 2 , and P 3 ) may be used to determine the orientation of the tissue plane  800  and hence the horizontal offset at any point on that plane. Otherwise, at least three distances ( 801 A, 801 B, 801 C) between the camera and the tissue to at least three points (P 1 ,P 2 ,P 3 ) may be used to determine the horizontal offset. 
     Several sensing or computing modalities may be used to determine or estimate the distance  801  that represents the depth of the object of interest in the stereo field. The sensing techniques may use hardware, software, or a combination thereof. 
     In one embodiment of the invention, one or more range finders  805  similar to that used in auto-focus cameras may be used to determine the distances  801 A- 801 C. In another embodiment of the invention, the distances  801 A- 801 C may be computed from the position sensed by the focus sensor  785  associated with the focus motor  784  of the focusing arrangement of the endoscopic camera. 
     The one or more angles  802 A- 802 C between the endoscopic camera  110  and the respective one or more points P 1 -P 3  on the tissue plane  800  may be determined by using a plurality of range finders  805 . Alternatively, the one or more angles may be determined by using a scanning range finder that scans in a circle around an axis on the tissue plane  800 . Without a range finder, angles may be determined using known tool tip locations in the surgical site acquired during an initialization sequence, for example. Such an initialization sequence may ask the operator O to provide the location of the tissue plane to the electronics system by touching it with the system&#39;s surgical instruments, which may be positionally encoded to supply joint angles. As is appreciated by those in the art, one may deduce the position of the instrument tips relative to the endoscopic camera tip if all joints are encoded and the kinematics are known. 
     In yet another embodiment of the invention, image processing is used in that left and right images of the tissue in a surgical site are captured or registered as digital pixels into respective left and right digital arrays similar to the one array illustrated in FIG. 13 of U.S. Pat. No. 6,720,988. A three dimensional model of the left and right images are further formed similar to that described and illustrated in FIGS. 15 and 16 of U.S. Pat. No. 6,720,988. The depth of the central feature in the three-dimensional model at point 128 in FIG. 16 of U.S. Pat. No. 6,720,988 may be used to represent the distance  801 A, for example. 
     Other image processing methods may be used to compare the left and right images of the tissue in a surgical site to determine a measure for the distance  801 , such as spatial correlation, where the spatial delay provides an indication of the desired horizontal offset (“the crucial number”) between the left and right telestration images to fuse them together at an appropriate depth. 
     In another embodiment of the invention, a depth map may be generated by software to judge the depth of a surgical site and render the telestration images at that depth. A depth map may be constructed by several ways known in the field of computer vision depth estimation including generating a depth map from the stereo images of the surgical site using left and right image correlation. Alternately, a depth map could be generated by a scanning range sensor, or similar raster depth measurement instrument, attached or otherwise registered to the endoscope tip. 
     In yet another embodiment of the invention, a disparity map may be used to indicate how a pixel in the left eye should be associated with a pixel in the right eye. In a number of computer vision depth estimation algorithms, a depth map is formed by first creating a disparity map. With a disparity map, a depth map need not be created as the disparity map may be used directly to generate a stereo telestration graphic at desired depths. In some cases, a disparity map is created from a pure depth map (such as from a scanning range finder for example) to generate the stereo telestration mark. 
     Referring now to  FIGS. 9A-9C , ignoring well known issues of occlusion for the purpose of simplification, diagrams illustrating the generation of a disparity map are now described. In  FIG. 9A , the endoscopic camera  110  scans the surgical site  900  within its field of view using the its left and right image forming devices  206 L, 206 R. A feature A  902  in the surgical site  900  is received and scanned by different areas and pixels of the left and right image forming devices  206 L, 206 R. 
       FIG. 9B  illustrates left pixels of an exemplary left image  906 L and right pixels of an exemplary right image  906 R in the field of view of surgical site including the feature A  902  scanned in  FIG. 9A . The exemplary left image  906 L includes a matrix of a plurality of left pixels LP 0 , 0  through LPM,N on N left scan lines  910 L. The exemplary right image  906 R includes a matrix of a plurality of right pixels RP 0 , 0  through RPM,N on N right scan lines  910 R. 
     The feature A  902  scans into the left and right images  906 L, 906 R at different horizontal pixel locations along respective scan lines  910 L-A and  910 R-A. From an edge (e.g., the left edge) of the left image, a left horizontal distance d 1  along the scan line  910 L-A can be determined to the scanned location of the feature A  902 . From a similar edge (e.g., the left edge) of the right image, a right horizontal distance d r  along the scan line  910 R-A can be determined to the scanned location of the feature A  902 . 
     Ignoring issues of occlusion, the disparity DP of the feature A  902  between right and left images may be determined by the equation DP=d r −d l . Similarly, a disparity DP x,y  for each pixel along scan lines in the right image  906 R may be determined in comparison with pixels in corresponding scan lines in the left image  906 L to form a disparity map. Alternatively, a disparity DP x,y  for each pixel along scan lines in the left image  906 L may be determined in comparison with pixels in corresponding scan lines in the right image  906 R to form a disparity map. Typically a mixture of feature-based matching and interpolation is employed to provide a DP x,y  for every single point in one image, relative to the other image, where interpolation is useful to match points with which no feature is clearly associated. 
     Referring now to  FIG. 9C , a matrix  950  of disparities DP x,y  for each pixel in one image (right or left) forms the disparity map between right and left images. DP 0 , 0  represents the disparity for one of the left pixel LPX 0 , 0  or right pixel RPX 0 , 0 . Similarly, DPm,n represents the disparity for one of the left pixel LPXm,n or right pixel RPXm,n. Assuming that the left image is the base image, the disparity map for the right image and its pixels RPX 0 , 0  through RPXm,n is to be determined such as by the equation DP x,y =drRPX x,y −dlLPX x,y . 
     A depth map is related to the disparity map by elementary geometric relationships. Given the optics of the viewer and/or endoscope, a depth map can be deduced from the disparity map. With the depth map and pixels of the left image  906 L as the base image, most of the right image  906 R may be generated, but for right-eye scenes that are occluded in the left eye. 
     While the horizontal offset between the left and right telestration images may be used to set a depth of the stereo telestration image, a two-dimensional (“depth-less”) telestration mark or image may be “painted” onto a surgical site over a continuum of depths. That is, a telestration mark, drawing, or image may be drawn on top of one (e.g., the left) image of the stereo pair, and the artificial disparity in the other image (e.g., the right) of the stereo pair is created at a variety of depths, including different depths for different parts of the telestration mark. Digital image processing techniques may be applied to generate a continuum of depths for the stereo telestration image. 
     Referring now  FIG. 10 , a side perspective view of a surgical site to illustrate differences between a telestration mark having an apparent constant depth and a telestration mark having a depth continuum generated by a disparity map, such as the disparity map matrix  950 , between left and right images of the surgical site. 
     A surface  1000  of tissue for example in a surgical site is captured by a camera from above the tissue and viewed in stereo by a stereo viewer. The surface  1000  is uneven having varying surface characteristics that are viewed at differing depths in the field of vision of the stereo viewer. 
     A mentor M generates a mono-view of a telestration mark  1002 A using a two dimensional input device. The mono view telestration is transformed into a stereo view of left and right telestration images that are fused together and overlayed over the surface  1000  in the surgical site using a single horizontal offset value. Alternatively, the mentor M may generate a stereo view of the telestration mark using a three dimensional input device but it is constrained to be above the surface  1000 . In either case, the telestration mark  1002 A may appear to be hovering at an apparent constant depth over the varying surface  1000 . 
     Instead of generating the telestration mark  1002 A at a constant depth, a “painted” telestration mark  1002 B may be generated that appears to be painted onto the varying surface  1000  over its depth continuum. The constant depth telestration mark  1002 A may be generated using a single horizontal offset value and a mono-view telestration image as previously discussed with reference to  FIGS. 6B-6C . In contrast, the “painted” telestration mark  1002 B may be generated using the pixels of the mono-view telestration image and a disparity map with disparities for each pixel. 
     For example, assume the mono-view of the telestration image is directly coupled to the left image for viewing by a left eye of the operator. The disparity map is applied to the pixels of the left image to transform them into pixels for the right image. The transformed pixels of the right image are viewed by the right eye of the operator. As the disparity map was generated using each pixel, the right image can be generated on a pixel-by-pixel basis so that when viewed by a stereo viewer, the mark  1002 B appears to be painted on top of the surface  1000 . 
     Visual feedback may be provided to show the difference between the placements of the constant depth telestration mark  1002 A and the painted telestration mark  1002 B. For example, the constant depth telestration mark  1002 A may be viewed as a red color image in the stereo viewer and the “painted” telestration mark  1002 B may be viewed as a blue color image on the surface  1000  in the stereo viewer. 
     As discussed previously, the horizontal offset between the left and right telestration images may be a function of one or more distances  801 A- 801 C and one or more angles  802 A- 802 C. Regardless of how the distances and angles are determined, it is desirable to determine the amount of horizontal offset between the left and right telestration images to represent a point in space as points in a stereo pair, such that the left and right telestration images fuse together and the operator O perceives the point as being at the appropriate depth, which in some cases is at the same apparent depth as the object of interest in the stereo pair image. It is advantageous to adjust the position of the telestration image so that the operator O can view a three-dimensional image on a stereo viewer with a telestration overlay, without being confused or distracted by a non-fused stereo telestration image. 
     While certain exemplary embodiments of the invention have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the embodiments of the invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. For example, elements of one embodiment of the invention may be swapped for or combined with elements of another embodiment of the invention. As a further example, the control knob  187 , 187 ′ to control the position of a left or right telestration image may be one or more of control buttons, keys, wheels, track ball, or other control input device. Rather, the embodiments of the invention should be construed according to the claims that follow below.