Published in, the on line companion to the MIT Press journal PRESENCE: Teleoperators and Virtual Environments, Date Posted: 2002 August 6

Steve Mann
University of Toronto
Department of Electrical and Computer Engineering
Toronto, Ontario, M5S 3G4

Mediated Reality with implementations for everyday life


Mixed Reality exists in many forms along a continuum from Augmented Reality (reality enhanced by graphics, such as Sutherland's work from more than 30 years ago) to more recent efforts at Augmented Virtuality (graphics enhanced by reality, graphics enhanced by video, etc.). Mixed Reality provides numerous ways to add together (mix) various proportions of real and virtual worlds. However, Mediated Reality is an even older tradition, introduced by Stratton more than 100 years ago. Stratton presented two important ideas:

  1. the idea of constructing special eyeglasses to modify how he saw the world; and
  2. the ecologically motivated approach to conducting his experiments within the domain of his own everyday personal life.
Stratton's seminal work has inspired a wide variety of devices that can be used to augment, deliberately diminish, or otherwise alter human visual perception. The first half of this paper presents some of the problems with the existing taxonomies (e.g. mixed reality) and distinctions (e.g. optical versus video see-through), that arise when we consider reality-modifying devices. The second half of the paper presents various new designs for reality-modifying devices, especially those used to modify only a portion of the visual reality stream, suitable for use in everyday life. These devices have the appearance of ordinary bifocal eyeglasses and reading glasses. Finally, a new kind of reality mediator that uses the eyeglass frames themselves as the mediating element is presented. This design makes it impossible for those other than the wearer, even upon very close inspection, to determine whether or not the eyeglasses contain a reality mediator. Such designs make possible livelong experiments and mediated reality experiences in personal everyday life, without the social stigma associated with obvious reality--modifying devices.


Virtual Reality, Mediated Reality, Mixed Reality, Modulated Reality, Modified Reality, Wearable Computing, Personal Imaging, Personal Technologies, Humanistic Intelligence, Intelligent Image Processing

1 Introduction

In 1989, Jaron Lanier, CEO of VPL, coined the term ``virtual reality'' to bring a wide variety of virtual projects under a single rubric [Steuer 92]. Tom Caudell coined the term ``augmented reality'' at Boeing in the early 1990s, while working together with David Mizell, researching ways to superimpose diagrams and markings to guide workers on a factory floor [Caudell 92] Augmented reality, involving superposition of computer graphics onto a view of the real world, was initially proposed and explored by Ivan Sutherland and his students at Harvard University and University of Utah, in the 1960s [Sutherland 68].

Steven Feiner defines augmented reality as follows:

Augmented reality refers to computer displays that add virtual information to a user's sensory perceptions. [Feiner 02]
One way to add virtual information to our visual field of view is to display the information on some kind of beamsplitter or other similar device, and thus use the human eye itself as the adder that achieves the superposition of the real and virtual information. Alternatively, the superposition can take place outside the eye, where the real plus virtual (added together by a video mixer) have been combined before being presented to the eye. The choice of which system to use depends on various factors such as whether or not the signals from the real world are available in electronic form. (The signals from the virtual world are assumed to already exist in electronic form since they are usually computationally generated.)

Reality mixers

When the real world, as well as the virtual world, is to be experienced electronically (e.g. by seeing the real world through a camera), the virtual world and real world are blended together using well-known methods. Such superposition of video signals is commonly used in broadcast television, for example, to overlay virtual information (closed captioning, title credits, weather information, etc.) from a computer onto a broadcast video signal from a television camera. This superposition is typically achieved by way of a device called a ``video mixer'' that adds two (or more) video signals.

Illusory transparency

Illusory transparency reconstructs rays of actual (real) light from the scene, with rays of synthetic (virtual) light from an electronic device, as shown, for example, in Figure 1 below:

Figure 1: Illusory transparency. A television camera is connected to a television, both being arranged to display, upon the television, that which it occludes.

Illusory transparency is an older concept than, as well as a generalization of, the notion of video see-through. Illusory transparency includes media that do not necessarily involve video. The concept of
illusory transparency continues to apply to systems that do not involve video. Examples of illusory transparency include computational see-through by way of laser EyeTap devices, as well as optical computing to produce a similar illusory transparency under computer program control. With optical computing, the concept of illusory transparency continues to provide a distinction between devices that can modify (not just add to) our visual perception and devices that cannot. Not all reality--modifying devices involve video, but many still involve the concept of illusory transparency.

It has been shown that the addition of video signals, in augmented reality, is fundamentally flawed because cameras operate approximately logarithmically and displays (including most head mounted displays) operate anti-logarithmically (Comparametric Equations, IEEE Trans. Image Proc., 9(8) August, 2000, pp1389-1406) Thus video mixers effectively perform something that is closer to multiplication than it is addition, because they operate on approximately the logarithms of the underlying true physical quantities of light. Accordingly, antihomomorphic filters have been proposed for augmented or mediated reality, wherein this undesirable effect is cancelled (Intelligent Image Processing, John Wiley and Sons, 2001) [Mann 01].

The concept of mixing real and virtual worlds exists in a wide variety of situations in the broadcast, entertainment, audiovisual, and computer graphics industries, and beyond. Therefore a taxonomy of the different mixtures of real and virtual information content [Milgram 94, Drascic96], with particular emphasis on a continuum from augmented reality to augmented virtuality, is useful. This taxonomy is especially useful in considering the way in which real and virtual are combined in head mounted displays [Milgram 99].

Reality mediators

Mixed reality covers a continuum between graphics enhanced by video and video enhanced by graphics [Tamura 02]. However, there are important categories of visual information processors that do not fit within this taxonomy or continuum.

One of the earliest and most important such examples was the eyeglasses George Stratton built and wore. His eyewear, made from two lenses of equal focal length, spaced two focal lengths apart, was basically an inverting telescope with unity magnification, so that he saw the world upside-down [Stratton 96, Stratton 97].

These eyeglasses, in many ways, actually diminished his perception of reality. His deliberately diminished perception of reality was neither graphics enhanced by video, nor was it video enhanced by graphics, nor any linear combination of these two. (Moreover it was an example of optical see-through that is not an example of registered illusory transparency, e.g. it problematizes the notion of the optical see-through concept because both the mediation zone, as well as the space around it, are examples of optical-only processing.)

Others followed in Stratton's footsteps by living their day-to-day lives (eating, swimming, cycling, etc.) through left-right reversing eyeglasses, prisms, and other optics [Kohler 64, Dolezal 82] that were neither examples of augmented reality nor augmented virtuality (and for which the optical see-through versus video see-through distinction fails to properly address important similarities and differences among various such devices).

Thus a more general concept than that of mixed reality is needed.

Because of the existence of a broad range of devices that modify human perception, mediated reality, a more general framework that includes the reality virtuality continuum, as well as devices for modifying as well as mixing these various aspects of reality and virtuality has been proposed [Mann 94, Mann 01].

Mediated Reality, therefore, refers to a general framework for artificial modification of human perception by way of devices for augmenting [Starner 97], deliberately diminishing, and more generally, for otherwise altering sensory input. This gives rise to the Reality, Virtuality, Mediality continuum depicted in Figure 2, as shown below:

Figure 2: (at left) Taxonomy of Reality, Virtuality, Mediality. The origin R denotes unmodified reality. A continuum across the Virtuality axis V includes reality augmented with graphics (Augmented Reality), as well as graphics augmented by reality (Augmented Virtuality). However, the taxonomy also includes modification of reality or virtuality or any combination of these. The modification is denoted by moving up the mediality axis. Further up this axis, for example, we can find mediated reality, mediated virtuality, or any combination of these. Further up and to the right we have virtual worlds that are responsive to a severely modified version of reality. (at right) Mediated reality generalizes the concepts of mixed reality, etc.. It includes the virtuality reality continuum (mixing) but also, in addition to additive effects, also includes multiplicatave effects (modulation) of (sometimes deliberately) diminished reality. Moreover, it considers, more generally, that reality may be modified in various ways. The mediated reality framework describes devices that deliberately modify reality, as well as devices that accidentally modify it.

Indeed, mediated reality has been shown to be useful in deliberately diminishing reality, such as by filtering out advertisements [Mann and Fung 02]. The HOLZER (Homographically Obliterating Labels by Zeroing, Enhancement or Replacement) system is a diminished reality system that filters out billboards and other advertising material, replacing them with blank spaces or other, more useful material [Mann and Niedzviecki 01]. Mediated reality relates to Feiner's distinction of virtual reality and augmented reality as follows: ``whereas virtual reality brashly aims to replace the real world, augmented reality respectfully supplements it.'' [Feiner 02] whereas mediated reality modifies it.

Computer Mediated Reality

Since the 1970s the author has been exploring electronically mediated environments using body--borne computers. These explorations in Computer Mediated Reality were an attempt at creating a new way of experiencing the perceptual world, using a variety of different kinds of sensors, transducers, and other body--borne devices controlled by a wearable computer [Mann 01]. Early on, the author recognized the utility of computer mediated perception, such as the ability to see in different spectral bands (Figure 3 below) and to share this computer mediated vision with remote experts in real time (Figure 4).

Figure 3: There was no doubt that Mediated Reality had practical uses. (at left) Author (looking down at the mop he is holding) wearing a thermal EyeTap wearable computer system for seeing heat. This device {\em modified} the author's visual perception of the world, and also allowed others to communicate with the author by modifying his visual perception. A bucket of 500 degree asphalt is present in the foreground. (at right) Thermal EyeTap principle of operation: Rays of thermal energy that would otherwise pass through the center of projection of the eye (EYE) are diverted by a specially made 45 degree ``hot mirror'' (DIVERTER) that reflects heat, into a heat sensor. This effectively locates the heat sensor at the center of projection of the eye (EYETAP POINT). A computer controlled light synthesizer (AREMAC) is controlled by a wearable computer to reconstruct rays of heat as rays of visible light that are each collinear with the corresponding ray of heat. The principal point on the diverter is equidistant to the center of the iris of the eye and the center of projection of the sensor (HEAT SENSOR). (This distance, denoted ``d'', is called the eyetap distance.) The light synthesizer (AREMAC) is also used to draw on the wearer's retina, under computer program control, to facilitate communication with (including annotation by) a remote roofing expert.

Figure 4: Practical application of collaborative Computer Mediated Reality: (leftmost) First person perspective as captured by the EyeTap device. Author's hands are visible grasping the mop. (left of middle) Mop and hot asphalt as viewed through wearer's right eye. (middle) After mopping hot asphalt onto the roof surface, a base sheet is rolled down (bucket of hot asphalt shows as white in the upper right area of the frame). (right of middle) The thermal EyeTap is useful for ``seeing through'' the top layers of felt or fiberglass, to determine heat flow underneath. (rightmost) The kettle (upper right of frame) shows up as white (approx. 500 degrees) whereas the propane cylinder (bottom of frame) and the propane hose supplying it show up as black, because the cylinder and hose are cold due to the expansion of the propane gas (Joule Thomson effect). The thermal EyeTap was also useful when the kettle caught on fire because of its ability to see through smoke. Kettle fires are easy to extinguish (simply by slamming the lid shut) if the kettle can be seen through the thick black smoke given off by the burning asphalt.

Such devices can be used to modify the visual perception of reality within certain mediation zones (e.g. only one eye rather than both eyes, or only a portion of that eye), giving rise to {\em partially mediated realitly}~\cite{intelligentimageprocessing}. Moreover these devices can also be worn with prescription eyeglass lenses, or even have prescription eyeglass lenses incorporated into the design. Prescription eyeglasses are themselves partial reality mediators, having a peripheral zone, a transition zone (frames or lens edges), and one or more {\em mediation zones} (one or more lenses, or lens zones as in bifocal, trifocal, etc., lenses).

Ecological origins of mediated reality

An important element of Stratton's work was that he wore the device in his ordinary everyday life. If performed on other subjects, such work might have far outstripped the ability of university ethics committees, the protocols required of ``informed consent'', and the tendency for many academics to work in labs, controlled spaces, and existing literature.

Unlike traditional scientific experiments that take place in a controlled lab-like setting (and therefore do not always translate well into the real world), Stratton's approach required a continuous rather than intermittent commitment. For example, he would remove the eyewear only to bathe or sleep, and he even kept his eyes closed during bathing, to ensure that no un-mediated light from the outside world could get into his eyes directly [Stratton 96, Stratton 97]. This work involved a commitment on his part, to devote his very existence -- his personal life -- to science.

Stratton captured a certain important human element in his broad seminal work, which laid the foundation for others to later do carefully controlled lab experiments within narrower academic disciplines. Moreover, his approach was one that broke down the boundaries between work and leisure activity, as well as the boundaries between the laboratory and the real world.

Similarly, it is desired to integrate computer mediated reality into daily life. The past 22 years of wearing computerized reality mediators in everyday life has provided the author with some insight into some of the sociological factors such as how others react to such devices~\cite{cyborg}. In particular, this has given rise to a desire to design and build reality mediators that do not have an unusual appearance.

Reality Mediators for everyday life

Typical virtual reality headsets, and other cumbersome devices are not well suited to ordinary everyday life because of the bulky constrained and tethered operation, as well as their unusual appearance.

Indeed, it is preferable that commonly used reality mediators, such as hearing aids and personal eyeglasses must have an unobtrusive (or hidden) appearance, or be designed to be sleek, slender, and fashionable. Figure 5 shows how miniaturization of components makes this evolution possible.

Figure 5: (at left) EyeTap devices, such as this infrared night vision computer system, when the components are visible, tend to have a frightening appearance, owing to the ``glass eye'' effect, in which optics, projected to the center of projection of a lens of the tapped eye are visible to others. Here we see the image of the infrared camera located in the center of the author's right eye. (at right) Author's recent (1996) reality mediator design with systems built into dark glasses tends to mitigate this undesirable social effect. The eyeglass lenses are also transparent in the infrared, allowing the night vision portion of the apparatus to take over in low light, without loss of gain. In the visible portion of the spectrum, a 10dB loss of sensitivity is incurred to conceal the color sensor elements and optics.

The author's wearable computer reality mediators have evolved from headsets of the 1970s, to eyeglasses with optics outside the glasses in the 1980s, to eyeglasses with the optics built inside the glasses in the 1990s [Mann 01] to eyeglasses with mediation zones built into the frames, lens edges, or the cut lines of bifocal lenses in the year 2000 (e.g. exit pupil and associated optics concealed by the transition regions). Reality mediators that have the capability to measure and resynthesize electromagnetic energy that would otherwise pass through the center of projection of a lens of an eye of a user, such as shown in Figures 3, 4, and 5, are referred to as EyeTap [Mann 01] devices. These devices divert at least a portion of eyeward bound light into a measurement system that measures how much light would have entered the eye in the absence of the device. Some eyetap devices use a focus control to reconstruct light in a depth plane that moves to follow subject matter of interest. Others reconstruct light in a wide range of depth planes, in some cases having infinite or near infinite depth of field.

Reality mediators for everyday life

Even a very small size optical element, when placed within the open area of an eyeglass lens, looks unusual. Thus eyeglasses having display optics embedded in an eyeglass lens, such as those made by Microoptical (, still appear unsual. In normal conversation, people tend to look one-another right in the eye, and therefore will notice even the slightest speck of dust on an eyeglass lens.

Therefore, the author has proposed that any intermediary elements to be installed in an eyeglass lens be installed in the transition zones, e.g. as transfer functions between peripheral vision and the eyeglass lens itself (e.g. in the frames), or as the transfer functions between different portions of a multifocal (bifocal, trifocal, etc.) eyeglass lens.

Consider first the implementation of a reality mediator as part of transfer function of the glass to glass transition region of bifocal eyeglasses.

In the case in which a monocular version of the apparatus is being used, the apparatus is built into one lens, and a dummy version of the diverter portion of the apparatus is positioned in the other lens for visual symmetry. It was found that such an arrangement tended to call less attention to itself than when only one diverter was used for a monocular implementation.

These diverters may be integrated into the lenses in such a manner to have the appearance of the lenses in ordinary bifocal eyeglasses.

Where the wearer does not require bifocal lenses, the cut line in the lens can still be made, such that transfer function simply defines a transition between two lenses of equal focal length.

Transition zone reality mediators: Reversal of the roles of eyeglass frames and eyeglass lenses

The size of the mediation zone that can be concealed in the cut-line of a bifocal eyeglass lens is somewhat limited.

The peripheral transfer function (e.g. at the edges of the glass, or the eyeglass frame boundaries) provides a more ideal location for a partial reality mediator, because the device can be concealed directly within the frames of the eyeglasses, as shown in Figure 6 below.

Reality mediator incorporated into the eyeglass frames:

Upon close inspection with the unaided eye, the eyeglasses have a normal appearance.

Using a magnifier, macro lens, etc., we can see the diverter when magnified in an extreme close-up.

Side view shows sleek and slender design, where apparatus can be hidden in hair, at back of wearer's head.

In view of such a concealment opportunity, the author envisioned a new kind of eyeglass design in which the frames would come right through the center of the visual field. With materials and assistance provided by Rapp optical, eyeglass frames were assembled using standard photochromic prescription lenses drilled in two places on the left eye, and four places on the right eye, to accommodate a break in the eyeglass frame along the right eye (the right lens being held on with two miniature bolts on either side of the break). The author then bonded fiber optic bundles concealed by the frames, to locate the camera and aremac in back of the device.

This research prototype proves the viability of using eyeglass frames as a mediating element. The frames being slender enough (e.g. two millimeters wide) do not appreciably interfere with normal vision, being close enough to the eye to be out of focus.

But even if the frames were wider, they can be made out of a see-through material, or they can be seen through by way of the illusory transparency afforded by the EyeTap principle [Mann 01]. Therefore, there is definite merit in seeing the world trough eyeglass frames.

In particular, the eyeglasses of Figure 6 were crude and simple. A more sophisticated design could use a plastic coating to completely conceal all the elements, so that even when examined under a microscope, evidence of the EyeTap would not be visible.

Conclusions and further research

Wearable Computer Mediated Reality was presented as a new framework for visual reality modification in everyday life. In particular, a new form of partial reality mediator having the appearance of a new kind of stylish eyeglasses, and suitable for use in ordinary life, was presented. In this design, the roles of eyeglass lenses and eyeglass frames are reversed. The eyeglass lenses become the decorative element, whereas the eyeglass frames become the element that the wearer sees through.


The author would like to thank Mel Rapp, of Toronto-based Rapp Optical, for assistance in recovering from an unfortunate incident that had involved the damage of the author's eyeglasses, and for providing the author much in the way of motivation to persevere through these difficult times.


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