Stanford Workshop on Medical VR and AR

5 April 2018, there will be a public workshop on medical head-mounted displays in Stanford. The workshop is designed to support collaborations between the engineers who are developing VR and AR technologies and the surgeons and clinicians who are using these technologies to treat their patients.

The workshop features talks by researchers who are developing VR and AR technologies to advance healthcare and panel discussions with Stanford physicians who are using VR and AR applications for surgical planning and navigation and for alleviating pain and anxiety in their patients.

There will be an interactive demo session featuring research projects, clinical applications, and startup ventures.

Seating is limited, so if you wish to attend, we recommend that you register now at the website https://scien.stanford.edu/index.php/medicalvrar.

Computational Near-Eye Displays with Focus Cues

SCIEN has resumed at Stanford with the talk Computational Near-Eye Displays with Focus Cues by Gordon Wetzstein. This presentation is an overview of research at Stanford.

Inflection points in near-eye displays:

• 1838 Stereoscopes by Wheatstone, Brewster, …
• 1968 Ivan Sutherland
• 1995 Nintendo Virtual Boy
• 2012–2017 VR explosion

Currently, the big enablers are the smartphone components.

The main purpose of the lenses in near-eye displays is to set the virtual image further away because we cannot focus too close.

Stereoptics is binocular; the mechanism of vergence is cued by binocular disparity. Focus cues are monocular; the mechanism of accommodation is cued by retinal blur.

The big problem is the vergence-accommodation conflict..

Gaze-contingent focus. For non-presbyopes, the adaptive focus is like the real world, but it requires eye tracking. Presbyopes need a fixed focal plane with correction.

Light field displays are not yet well-developed. The idea is to project multiple different perspectives into different parts of the pupil. Example: tensor displays. Light field displays are limited by diffraction.

The next step is multifocal lenses: point spread function engineering.

The challenges for AR are

1. Design thin beam combiners using waveguides
2. Eye box vs. field of view trade-off
3. Eye tracking
4. Chromatic aberrations
5. Occlusions; difficulty: need to block real light

Breaking the barriers to true augmented reality

Today, when you run a job on a digital press, you just turn it on, load the stock, and start printing. An army of sensors and feedback loops work with mathematical models will set up the press. In the heydays of color printing, the situation was very different: skilled press operators would spend hours making ready the press, with only the use of a densitometer and their eyes. It took them years of experience to achieve their master status.

A big breakthrough came when in 1968 when Felix Brunner invented the print control strip, which made press make-ready more of a technical process instead of a magic ceremony. Felix Brunner lived in Corippo, Val Verzasca.

Corippo is a beautiful village but it had been abandoned—people like Michael Silacci of the Opus One Winery, whose grandparents had come to California and never went back. Corippo is still the smallest municipality in Switzerland, with a population of just 13.

Corippo is so stunning, in 1975 it became a protected heritage village. This was quite difficult because the village had become dilapidated. Switzerland raised the funds to transform it into a state-of-the-art modern village that would attract a sophisticated population like Felix Brunner. The challenge was to rebuild it to modern architectural standards without changing its atmosphere and look.

The architecture department at the ETH in Zurich build a 3D model of the entire village, then one by one they started rebuilding the interiors of the houses to the state-of-the-art. The department acquired an Evans and Sutherland Picture System and at each planning step, the commission walked through the virtual village to ascertain that nothing changed the spirit outdoors. For example, if a roof was raised, it was not allowed to cast new and unexpected shadows. If a window was changed, the character of the street was not allowed to change for a passerby, and the view had to feel original from any window.

Although the Picture System was limited to 35,000 polygons, the experience was truly impressive for the planners. If you have a chance to visit Corippo, you will be surprised by the realization. The system was such a breakthrough for urbanists, that Unesco used it for the restoration of Venice. I was also sufficiently impressed to sit down and implement an interactive 3D rendering system, although on the PDP-11with 56 KB of memory running RT-11, I could only display wireframes.

My next related experience was in 1993 when Canon had developed a wearable display and was looking for an acquirer of the rendering software. While the 1975 system for Corippo was rendering coarse polygons, by early 1990 it was possible to do ray tracing, although using an SGI RealityEngine for each eye. An application was to train astronauts for building a space station.

On the quest of finding an interested party for the software, I had the chance to visit almost all companies in the San Francisco Bay Area who were developing wearable displays. On one side, using ray tracing instead of rendering plain solid color polygons made the scene feel more natural, but the big advantage over the Picture System was to be immersed in the virtual scene instead of looking at a display.

There were still quite a few drawbacks. For one, the helmets felt like they were made of lead. The models were still crude because to follow the head movements, ideally, the refresh rate should have been 90 Hz, but even with simple scenes, the refresh rate was typically just 15 or 30 Hz. However, the worst perceptual problem was the lag, which disabled the physiological equilibrium system and caused motion sickness. Another positive development was the transition from the dials and joysticks of 1975 to gloves providing a haptic user interface.

People from my generation spent 13 years in school learning technical drawing, which allows us to visualize mentally a 3D scene from three orthographic projections or from an axonometric projection with perspective. However, in general, understanding a 3D scene from projections is difficult for most people. The value of an immersive display is that you can move your head and thus more easily decode the scene. Consequently, there is still a high interest in wearable displays.

Today, a decent smartphone with CPU, GPU, and DSP has sufficient computing power to do all the rendering necessary for a wearable display. The electronic is so light that it can be fit in a pair of big spectacles that are relatively comfortable to wear and are affordable for professionals to buy. Last year, Bernard Kress had predicted that 2017 would be the year of the wearable display, with dozens of brands and prices affordable by consumers. Why is it not happening?

On March 14, 2017, Prof. Christian Sandor of the Nara Institute of Science and Technology (NAIST) gave a talk with title Breaking the Barriers to True Augmented Reality at SCIEN in Stanford, where he suggested the problem might be that today's developers are not able to augment reality so that the viewer cannot tell what is real. He showed the example of Burnar, where flames are mixed with the user's hands and these users had to interrupt the experiment because their hands were feeling too hot.

True AR has the following two requirements:

1. undetectable modification of user's perception
2. goal: seamless blend of real and virtual world

On a line from manipulating atoms with controlled matter to manipulating perception with implanted AR, current systems should achieve surround AR (full light field display) or personalized AR (perceivable subset). In a full light-field display, the display functions as a window, but with the problem of matching accommodation and vergence. Personalized AR is a smarter approach because the human visual system is measured and only a subset of the light-field is generated, reducing the required display pixels by several orders of magnitude.

In many current systems, the part of the image generated from a computer model is just rendered as a semitransparent blue rendering, hence it is perceived as separate from the real world. True AR requires a seamless blend. The most difficult step is the alignment calibration with the single point active alignment method (SPAAM). The breakthrough from NAIST is that they need to perform SPAAM only once: after that, they use eye tracking for calibration.

The technology is hard to implement. The HoloLens has solved the latency problem, but Microsoft has invested thousands of man-years in developing the system. The optics are very difficult and there are only a few universities teaching it.

Designing and assessing near-eye displays to increase user inclusivity

Today Emily Cooper, Psychological and Brain Sciences Department at Dartmouth College, gave a talk on designing and assessing near-eye displays to increase user inclusivity. A near-eye display is a wearable display, for example, an augmented reality (AR) or a virtual reality (VR) display.

With most near-eye displays it is not possible or recommended to wear glasses. Some displays, like the HTV Vive, have available lenses to correct the accommodation. We do want to integrate flexible correction into near-eye displays. This can be achieved with a liquid polymer lens with a membrane that can be tuned.

In her lab, for the refraction self-test, the presenter uses an EyeNetra auto-refractometer, which is controlled with a smartphone.

The near-eye display correction is as good as with contact lenses, both in sharpness and in fusion correction. Therefore, it is not necessary to make users wear their correction glasses.

There are two factors determining the image quality of a near-eye display: accommodation and vergence. The problems with incorrect vergence are that users get tired after 20 minutes and the reaction time is slower when the vergence is incorrect.

The solution is to use tunable optics to match the user's visual shortcomings.

A different problem is presbyopia, which is a range reduction. For people older than 45 years, an uncorrected stereo display provides better image quality than correcting the accommodation. However, tunable optics provide better vergence for older people.

A harder problem are people with low vision, regardless of their age. In her lab, Emily Cooper investigated whether consumer-grade augmented reality displays are good enough to help users with low vision.

She used the HoloLens, in which the depth camera in the NIR domain is the key feature to address this problem. Her proposal is to overlay the depth information as a luminance map over the image so that near objects are light and far objects are dark. This allows the users to get by with their residual vision.

Instead of a luminance overlay, a color overlay also works. In this approach, the hue is changed on a segment from warm to cold colors in dependence of their distance. She also tried to encode depth with flicker but is does not work well.

With the HoloLens, it is possible to integrate OCR in the near-eye display and then read all text in the field of view using the 4 speakers in the HoloLens, making the sound come from the location where the text is written.

Progress in wearable displays

Yesterday afternoon, Bernard Kress, Partner Optical Architect at Microsoft Corp, in the HoloLens project, gave a talk at the Stanford Center for Image Systems Engineering (SCIEN) with the title "Human-centric optical design: a key for next generation AR and VR optics." Here is the abstract:

The ultimate wearable display is an information device that people can use all day. It should be as forgettable as a pair of glasses or a watch, but more useful than a smartphone. It should be small, light, low-power, high-resolution and have a large field of view (FOV). Oh, and one more thing, it should be able to switch from VR to AR.

These requirements pose challenges for hardware and, most importantly, optical design. In this talk, I will review existing AR and VR optical architectures and explain why it is difficult to create a small, light and high-resolution display that has a wide FOV. Because comfort is king, new optical designs for the next-generation AR and VR system should be guided by an understanding of the capabilities and limitations of the human visual system.

There are three kinds of wearable displays:

• Smart eyewear: extension of eyewear. Example: Google Glass
• Augmented reality (AR) and mixed reality (MR): extension of the computer. An MR display has a built-in 3d scanner to create a 3d model of the world
• Virtual reality (VR): extension of the gaming console

Bernard surveyed all avenues in wearable displays from their inception to the projections in the future. The speed of the presentation and the amount of material made it impossible to follow the talk unless you are an expert in the field. After the presentation, Bernard told me the size of his PowerPoint file is about 250 MB!

My takeaway was that the biggest issue in wearable displays is cost. So far, the optics engineers designed with cameras in mind and over-designed. The current breakthrough is that now the optics engineers start understanding the HVS, so they can design systems that are just as good as our MTF. Bernard claims that so far the industry has been mostly about hype but in 2017, products will take off and the new challenge is "show me the money."