Abstract:
For implementing an anthropomorphic visual telepresence system with high resolution and low loop latency a sequential color video loop is provided. A sequential color camera sequentially captures color images, each captured image consisting of a portion of a single color component, and provides information as separate color information relating to portions of the sequentially sensed color images. The information is transmitted as separate color information. A sequential color display receives the transmitted information and displays sequentially each color image within the received information. Synchronization means synchronize the sequence and color of corresponding portions of images comprising a single color in said display with the portions of the images sensed by said camera.

Description:
This application is a continuation of U.S. patent application Ser. No. 09/383,070 filed Aug. 26, 1999 now abandoned. 

   FIELD OF THE INVENTION 
   The present invention relates to visual telepresence systems. More particularly, the present invention relates to an anthropomorphic visual telepresence system having a high resolution and a low loop latency. 
   BACKGROUND OF THE INVENTION 
   The concept of telepresence has been in the public domain since the early 1960s, when Ivan Sutherland demonstrated its basic principles. Two major components of a visual telepresence system are a head mounted display (HMD) and its associated high speed servomechanism on which video cameras are mounted. Two other important components of a visual telepresence system are a head tracker and a communications system linking the HMD with the high-speed servomechanism. When an operator, wearing the HMD, moves her head in any direction, the head tracker senses that movement, sends the appropriate position data to the high-speed servomechanism, which thereby tracks in real-time or in near real-time the operator&#39;s head movements. Images from the video cameras mounted on the high-speed servomechanism are transmitted through the communications system to a display positioned in front of the eyes of the operator; for example, such a display forms part of the HMD. As a result, the operator is given a visual impression similar to that from a same location as the remote cameras. 
   In order to describe this concept more accurately, the term anthropomorphic is often used, whereby a human-shaped configuration is implied. Many systems have been referred to as telepresence systems, for example a camera mounted on a pan and tilt servomechanism controlled by a joystick and in communication with a conventional monitor. This necessitates the use of the term anthropomorphic to provide a more accurate description of human-shaped telepresence wherein the camera is tracking in real-time or near real-time the head and/or eye movement of an operator, and the images thereby gathered by the camera are displayed directly in front of the eyes of the operator. 
   The use of anthropomorphic visual telepresence is highly advantageous for the operation of remote controlled vehicles. With current advancements in robotic technology the use of remote systems is steadily increasing, especially for performing tasks in hazardous environments where the lives of people are at risk. Hazardous environments are found, for example, in nuclear installations where radiation is a significant concern; in the production and handling of chemicals and explosives; in mining; and in underwater operations such as offshore oil exploration. Further applications include emergency, search and rescue operations, as well as space applications, such as controlling robots and/or vehicles located in the environment of space, while remaining in the safer location of a spacecraft or other human-tended spaceborne habitat. The operator of the remote controlled vehicle is located in a safe place, from which he or she controls the vehicle using other human-machine interface components such as a joystick, while the HMD gives him or her the visual impression of being physically located at a same location as the cameras, which are controlled by the movement of his or her head. 
   Generally, a telepresence system attempts to recreate an environment for an operator of a remote system. The better the environmental factors are recreated, the more natural the resulting control process is. Of course, because the environmental factors are recreated, the “simulation” is often implemented with safety in mind. For example, radiation levels are not usually simulated other than by showing gauges of sensors within the remote system. In some instances, some environmental factors are altered for providing useful feedback. For example, temperature is raised and lowered to indicate temperature changes, but the simulated temperatures are scaled for operator comfort and safety. 
   The human visual system is marvelous. From birth, our brain learns to process visual data. The visual data is real-time visual data (for the most part). To clarify, what is seen in a person&#39;s hand is felt in their hand at the same time and in the same place. The latency between seeing, feeling and manipulating is truly negligible. This is particularly true of the often occurring situation where a person rotates their head and/or eyes to center an object of interest into the so-called foveal area of the human visual system, from the peripheral area where it was previously located. In such a situation, the brain almost instantly processes new retinal information, and the object of interest is perceived without noticeable delay. Unfortunately, with anthropomorphic visual telepresence systems, this is not so. A small latency of more than a few tens of milliseconds is very noticeable. The brain of an operator of an anthropomorphic visual telepresence system having such a latency is not used to dealing with such a delay. Hence, psycho-physiological discomfort results. Of course, when the latency is negligible these reactions do not occur or are greatly lessened since the brain is operating in its normal mode of operation. It is also clear to those skilled in the art of visual telepresence that latency or time delay between a movement of the HMD worn by the operator, and return of corresponding video images reflecting appropriate movement of the high-speed servomechanism, is a very critical parameter, and that the degree of susceptibility to such latency varies among subjects. 
   Of course, a similar problem exists with image resolution. The human eye captures images at a high resolution. This resolution is actually variable across the retina, from its maximum in the so-called foveal region to its minimum in the peripheral region. For stationary images, the human brain assembles these images and enhances resolution or accepts the limited resolution presented; however, for moving images, the quantisation—dividing the image into individual points—at a low resolution results in choppy or discretised movement, as opposed to being relatively smooth and continuous as provided by the human visual system. For example, if each square inch of an image is displayed as a single dot, from a location close to the display, a baseball would appear less round and its motion would appear to jump an inch at a time. This also results in psycho-physiological discomfort, such as headaches and nausea, when experienced continuously for extended periods of time. Therefore, it is clear to those skilled in the art of visual telepresence that the resolution of displayed images is of primary importance. It is also well known to those skilled in the art of visual telepresence that video image transmission using analog radio frequency techniques is significantly less robust than video image transmission using digital radio frequency techniques. When using analog video image transmission, frequent interference-induced loss of horizontal and/or vertical synchronization signals may occur. This is significantly reduced when using digitised video image transmission. Loss of synchronization also contributes to psycho-physiological discomfort of an operator wearing the HMD. Therefore, it is often desirable to use digitised video transmission. Unfortunately, this results in a significant increase of the required radio frequency bandwidth for transmission of the video signal. Digital signal compression and decompression, also referred to as CODEC, reduces the required bandwidth but results in added loop latency due to the image processing performed. In situations requiring the use of digitised video image transmission, an anthropomorphic visual telepresence architecture either uses a high transmission bandwidth or suffers the added latency resulting from using the CODEC. 
   With regards to resolution for applications where colour is required, the implementation of field sequential colour imaging is very successful. In field sequential colour imaging, a colour image is composed of a succession of primary colour components—typically red, green and blue—of the desired image. Several patents have been issued for sequential colour cameras. Similarly, many patents have been issued for sequential colour displays. The field of sequential colour displays is generally a more recent field than that of sequential colour cameras. 
   It is well known to those skilled in the art of colour image displays that sequential colour displays, when using a sufficiently fast sequential rate so that the human brain will imperceptibly fuse the primary colour images into full colour images, achieve a much higher effective resolution than the more conventionally used composite displays, for which it is implied that the information of all colours is displayed simultaneously instead of sequentially. This is due to the fact that in composite colour displays, a technique must be used in which the available display surface must be subdivided into several primary color groups often referred to as red green blue triads, thus leading to a resolution loss. With sequential colour displays, all of the display&#39;s resolution is available for each primary color, as the display&#39;s surface does not have to be allocated among the three primary colors. 
   U.S. Pat. No. 5,684,498 issued Nov. 4, 1997 to Welch et al. describes the use of standard composite colour cameras in conjunction with a sequential colour display forming part of a HMD. This approach leads to colour fringing whenever the HMD is in motion at an appreciable rate. The method described by Welch suppresses colour fringing based on data from rate sensors measuring the motion of the HMD. This method suffers from the inherent inaccuracies of the rate sensors in detection of an acceleration of a head on which the HMD is mounted. Therefore, the image shifting implemented to suppress colour fringing imperfectly corrects for the colour fringing. The method taught by Welch does not achieve a maximum resolution because it uses a composite colour source at its input. Furthermore, the conversion of the composite colour signal into a field sequential colour signal results in additional loop latency. 
   It is, therefore, an object of this invention to provide an anthropomorphic visual telepresence system having a high resolution and a low loop latency. 
   It is further an object of this invention to provide an anthropomorphic visual telepresence system enabling, when desired, the use of digital video compression and decompression techniques, while maintaining loop latency within acceptable limits. 
   SUMMARY OF THE INVENTION 
   In accordance with the invention there is provided a sequential colour anthropomorphic visual telepresence system comprising:
     a sequential colour camera for sequentially capturing colour images, each captured image consisting of a portion of a single colour component, and for providing information as separate colour information relating to portions of the sequentially sensed colour images;   transmission means for transmitting an electrical signal including the information as separate colour information;   a sequential colour display for receiving the transmitted signal and for displaying sequentially each colour image within the received information; and,   synchronization means for synchronizing the sequence and colour of corresponding portions of images comprising a single colour in said display with the portions of the images sensed by said camera.   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of this invention will now be described in conjunction with the attached drawings, in which: 
       FIG. 1  illustrates a visual telepresence system; 
       FIG. 2  illustrates a composite colour video loop according to the prior art; 
       FIG. 3  illustrates a colour video loop according to the prior art comprising a composite colour camera and a sequential colour display; 
       FIG. 4  illustrates a field sequential colour video loop according to the invention; 
       FIG. 5  illustrates a frame sequential colour video loop according to the invention; 
       FIG. 6  illustrates a field sequential colour video loop with digital image compression and decompression according to the invention; 
       FIG. 7  illustrates a frame sequential colour video loop with digital image compression and decompression according to the invention; 
       FIG. 8  illustrates a sequential colour video loop with timing means according to the invention. 
   

   In the figures “sc” refers to sequential colour, “t” refers to time duration, “msec” refers to milliseconds, “f” refers to frequency, “Hz” refers to Hertz (cycles per second), and NTSC, PAL, and SECAM refer to commonly known television signal standards. Using interlacing a full image, referred to as a “frame”, is composed of a successive presentation of two half images, referred to as a “field”. Each “field” commonly consists of odd or even numbered image lines of a “frame”, respectively. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a basic visual telepresence system  100 , with three axes of rotation used to emulate human neck movement. Two major components of the visual telepresence system  100  are a head mounted display (HMD)  102 , and its associated high speed servomechanism  104  on which video cameras  106  are mounted. Other important components of the visual telepresence system  100  are a head tracker  108  and a communication system  110  that links the HMD  108  with the high speed servomechanism  104 . When an operator, wearing the HMD  102  moves her head in any direction, the head tracker  108  senses that movement and sends appropriate position data to the high speed servomechanism  104 , which thereby tracks in real-time or in near real-time the operator&#39;s head movements. Images from the video cameras  106  mounted on the high-speed servomechanism  104  are transmitted through the communications system  110  to a display  112  positioned in front of the eyes of the operator; for example, such a display forms part of the HMD  102 . In some applications two video cameras  106  are provided at a same distance as the human eyes. Images gathered by the two video cameras are simultaneously displayed in front of each of the operator&#39;s eyes, respectively, creating a stereo-visional impression of three dimensional space imaged by the cameras. 
   Prior art visual telepresence systems, as shown in  FIG. 2 , use a composite colour video loop  200 . A composite colour camera  202  is linked by a communication link  203  to a composite colour display  204 . In composite colour video, all primary colours of a colour image are gathered simultaneously. Timing diagram  206  shows the timing of interlaced image fields comprising the odd and even numbered lines of an image separately sensed, transmitted and displayed. Table  208  shows the timing and frequencies for commonly available prior art video systems. In composite colour video a severe reduction in resolution occurs, due to the general arrangement of imaging sensors within, for example, a sensor array in red, green and blue triads. Using this method, the reduction in resolution for a coloured image can potentially attain a factor of three along one axis, in comparison to the resolution offered by a black and white or gray scale image for which the sensor&#39;s available pixels have not been shared among primary colour triads. This problem is further exacerbated with many of the display technologies often used in HMDs, due to the relatively low fill factor, or percentage of the surface serving in the display of an image, attainable with such technologies, along with the same triad arrangement situation previously described for composite colour cameras, which also adversely affects the resolution of such composite colour displays. 
   With regards to resolution for applications where colour is required, the implementation of sequential colour imaging is very successful. In field sequential colour imaging, a colour image is composed of a succession of primary colour components—red, green and blue—of the desired image. Using a display based on this same sequential colour technique the human retina and brain naturally integrate these colour components, if the rate at which the primary colour components are presented is sufficiently high, and a single colour image is perceived. The actual frequency of sequential colour imaging at which the retina and brain naturally integrate the colour components depends on the individual, brightness of the image and interlacing. When required, sensors sensitive to wavelengths outside the visible spectrum, for example infrared, are used. The sensed images are then converted into images comprising the primary colours of the visible spectrum for displaying. 
     FIG. 3  shows a visual telepresence system  300  according to Welch. A composite colour camera  302  is linked by a communication link  304  to colour separation means  306  in the form of a colour separator. The separated colour images consisting of three primary colour images are then converted into sequential colour images using parallel to serial conversion means  308  in the form of a parallel to serial converter which is linked by a communication link  310  to a sequential colour display  312 . Timing diagram  320  shows the timing of interlaced image fields  322  produced by the composite colour camera  302  and the timing of the sequential colour image fields  324  after the conversion. The timing diagram  320  indicates the latency  326  resulting from colour separation and parallel to serial conversion. Table  330  shows the timing, frequencies and latency for commonly available prior art video systems. As is evident to those of skill in the art, the first primary colour image displayed has a minimum latency of 0 seconds. The second primary colour image has a minimum latency of ⅓ of the interval between composite images; for NTSC, this is 1/180 th  of a second. The third primary colour image has a minimum latency of ⅔ of the interval between composite images; for NTSC, this is 2/180 th  of a second. 
   It is an object of this invention to provide an anthropomorphic visual telepresence system having a high resolution and a low loop latency. To achieve a maximum resolution in a visual telepresence system, it is necessary to use a sequential colour camera as well as a sequential colour display. Specific means for synchronization (and sequence alignment) between camera and display is implemented in order to minimize loop latency. The anthropomorphic visual telepresence system according to this invention is highly advantageous in applications where significant concentration of an operator on a remote controlled vehicle is required. It eliminates or significantly reduces the main sources of an operator&#39;s psycho-physiological discomfort and allows the use of such a system for longer time periods or the use of such a system for critical operations. 
     FIG. 4  shows an anthropomorphic visual telepresence system  400  according to the invention. A field sequential colour camera  402  is linked by a communication link  403  to a field sequential display  404 . The field sequential colour camera  402  operates on the same basic principles as field sequential colour cameras described in prior art, excepting that an output therefrom is a field sequential colour signal. The communication link  403  is often a cable—for example, in environments such as nuclear facilities—but is sometimes a wireless communications link—for example, in space and underwater applications. The field sequential colour display  404  is for accepting a field sequential colour signal and for displaying said colour signal with little latency from receipt thereof. Timing diagram  420  shows the timing of sequential colour image fields produced by the field sequential colour camera  402 , transmitted by the communication link  403  and displayed by the field sequential display  404 . The sequential colour image fields are separately sensed, transmitted and displayed. The display of information relating to a single sequential colour image field occurs before receipt of information relating to the next sequential colour image field. In embodiment “A”  422  alternating fields cover the three primary colours in succession for the odd image line numbers field, and then repeated for the even image line numbers field. In embodiment “B”  424  the alternating fields cover in succession the odd and even image line number fields for one primary colour and then the process is repeated for the other two primary colours. In embodiment “C”  426  both, the field—odd/even image line numbers—and the primary colour at each new field, are alternated. The timing diagram  420  also shows a synchronization signal or flag  428  at the beginning of the image field sequence. The synchronization signal  428  ensures synchronization and sequence alignment of the alternating fields. The field sequential colour camera  420  adds the synchronization signal  428  at the beginning of the image field sequence, which is then transmitted to the field sequential colour display  404  for synchronization and colour sequence alignment. Without this synchronization signal  428 , display technologies, even those using the inherent formatting of the incoming signal such as cathode ray tubes, have a possibility of sequence misalignment. For example a red camera image is displayed as a green display image. The synchronization signal  428  also helps to avoid data buffering, which results in additional loop latency. One synchronization signal  428  is sufficient, as long as the field sequential colour display  404  is for receiving a synchronization signal  428  at the relative position of this flag within the sequence. There are numerous other locations than the one shown in  FIG. 4  for positioning the synchronization signal  428  within the image field sequence. Table  430  shows the timing, frequencies and latency for the present invention—a custom built system. Timing and frequencies of prior art video systems are shown for comparison. 
     FIG. 5  shows embodiment “D”  522  of an anthropomorphic visual telepresence system  500  according to the invention. A frame sequential colour camera  502  is linked by a communication link  503  to a frame sequential display  504 . The frame sequential colour camera  502  operates on the same basic principles as frame sequential colour cameras described in prior art, excepting that an output therefrom is a frame sequential colour signal. The communication link  503  is often a cable but is sometimes a wireless communications. The field sequential colour display  504  is for accepting a frame sequential colour signal and for displaying said colour signal with minimal latency from receipt thereof. Timing diagram  520  shows the timing of sequential colour image frames produced by the frame sequential colour camera  502 , transmitted by the communication link  503  and displayed by the frame sequential display  504 . The sequential colour image frames are separately sensed, transmitted and displayed. The display of information relating to a single sequential colour image frame occurs before receipt of information relating to the next sequential colour image frame. Table  530  shows the timing, frequencies and latency for the present invention, Timing and frequencies of prior art video systems are shown for comparison. 
   When the transmission time is negligible, the minimum latency in the embodiments “A”, “B”, “C” and “D” approaches zero (see tables  430  and  530 ). 
     FIG. 6  shows embodiments “E”, “F” and “G”  600  corresponding to embodiments “A”, “B” and “C” of an anthropomorphic visual telepresence system according to the invention. The system comprises a field sequential colour camera  602 , a communication link  603 , digital image compression means  604  in the form of a digital image compressor, a digital data link  605 , digital image decompression means  606  in the form of a digital image extractor for decompressing the compressed digital data, a communication link  607 , and a field sequential colour display  608 . The field sequential colour camera  602  operates on the same basic principles as field sequential colour cameras described in prior art, excepting that an output therefrom is a field sequential colour signal. The digital image compressor  604  is preferably in the form of dedicated hardware, firmware and software components implementing the compression portion of a CODEC so as to efficiently compress the data received from the field sequential colour camera  602  via the communication link  603  and thereby to maintain loop latency within reasonable limits. The digital data link  605  is often a cable but is sometimes a wireless communications. The digital image extractor is for extracting data compressed by the digital compressor, and is preferably in the form of dedicated hardware, firmware and software implementing the decompression portion of a CODEC so as to efficiently execute in reverse the algorithm used at the compression stage to restitute the original, uncompressed image, sometimes with some level of resulting image degradation in comparison to its original counterpart. Timing diagram  620  shows a timing graph  622  of sequential colour image fields from the field sequential colour camera  602 , a timing graph  624  of compressed digital data provided by the digital image compression means  604 , and a timing graph  626  of digital image data provided by the digital image decompression means  606  to the display  608 . The timing diagram  620  also indicates a delay for compression  628  and decompression  629 . The upper bound for the compression and decompression delay is preferably shorter than the duration of a field  640 . Table  630  shows the timing, frequencies and latency for the present invention with timing and frequencies of prior art video systems for comparison. 
     FIG. 7  shows an embodiment “H”  700  corresponding to embodiment “D” of the anthropomorphic visual telepresence system according to the invention. The system comprises a frame sequential colour camera  702 , a communication link  703 , digital image compression means  704  in the form of a digital image compressor, a digital data link  705 , digital image decompression means  706  in the form of a digital image extractor, a communication link  707  and a frame sequential colour display  708 . The frame sequential colour camera  702  operates on the same basic principles as frame sequential colour cameras described in prior art, excepting that an output therefrom is a frame sequential colour signal. The digital image compressor  704  is preferably in the form of dedicated hardware, firmware and software components implementing the compression portion of a CODEC so as to efficiently compress the data received from the frame sequential colour camera  702  via the communication link  703  and thereby to maintain loop latency within reasonable limits. The digital data link  705  is often a cable but is sometimes a wireless communications link. The digital image extractor is for extracting data compressed by the digital compressor, and is preferably in the form of dedicated hardware, firmware and software implementing the decompression portion of a CODEC so as to efficiently execute in reverse the algorithm used at the compression stage to restitute the original, uncompressed image, sometimes with some level of resulting image degradation in comparison to its original counterpart. Timing diagram  720  shows a timing graph  722  of sequential colour image fields from the field sequential colour camera  702 , a timing graph  724  of compressed digital data provided by the digital image compression means  704 , and a timing graph  726  of digital image data provided by the digital image decompression means  706  to the display  708 . The timing diagram  720  also indicates the delay for compression  728  and decompression  729 . The upper bound for the compression and decompression delay is preferably shorter than the duration of a single primary colour image or image portion when interlacing is used  740 . Table  730  shows the timing, frequencies and latency for the present and prior art video systems for comparison. 
   The use of anthropomorphic visual telepresence systems as described in  FIGS. 6 and 7  is highly advantageous in applications where a remote controlled vehicle is exposed to high levels of radiation, for example solar wind and cosmic rays in space applications or radiation in nuclear facilities, which hold the potential for at least indirectly distorting analog signal transmission. 
     FIG. 8  shows another embodiment of an anthropomorphic visual telepresence system  800  according to the invention. A field or frame sequential colour camera  802  is linked by a communication link  803  to a field or frame sequential display  804 . Connected to the camera  802  and the display  804  are timing means  806  and  808  respectively. The timing information from the timing means  806  such as a Global Positioning System, GPS receiver, or other form of satellite-based global positioning system is embedded within a synchronization signal and transmitted via the communication link  803 . At the display  804 , this timing information is compared with timing information from timing means  808  in order to determine loop latency. This is beneficial in applications where the loop delay varies such as a highly mobile vehicle. For example, such a vehicle may require satellite communication links for the digital data link when located in some areas. In other areas, direct wireless communication is used. Because the digital data link path length is significantly different between direct communication links and those requiring satellites, such a timing marker is advantageous. Furthermore, it enables implementation of time delay correction algorithms to alter the displayed image in order to alleviate adverse psycho-physiological effects of latency in visual telepresence systems. Alternatively, a slow drift is used to vary timing from a first latency to a second latency when latency resulting from the digital data link is substantially varied between image frames. 
   In an alternative embodiment, each image is encoded with further data corresponding to sensor input. For example, vehicle speed is encoded into each image in a same location and in a fashion that is intelligible to an operator of the visual telepresence system. Encoding data in this fashion is well known. For example, video cameras as are commonly available often allow superposition of date or time information onto an image frame. Similarly, speed information could be superimposed onto images of a telepresence system. 
   Of course, numerous other embodiments may be envisaged without departing from the spirit and scope of the claimed invention.