Measuring the Effective Resolution of Head-mounted Displays

Why does everything in my VR headset look so pixelated? It’s supposed to be using a 2160×1200 screen, but my 1080p desktop monitor looks so much sharper!

This is yet another fundamental question about VR that pops up over and over again, and like the others I have addressed previously, it leads to interesting deeper observations. So, why do current-generation head-mounted displays appear so low-resolution?

Here’s the short answer: In VR headsets, the screen is blown up to cover a much larger area of the user’s field of vision than in desktop settings. What counts is not the total number of pixels, and especially not the display’s resolution in pixels per inch, but the resolution of the projected virtual image in pixels per degree, as measured from the viewer’s eyes. A 20″ desktop screen, when viewed from a typical distance of 30″, covers 37° of the viewer’s field of vision, diagonally. The screen (or screens) inside a modern VR headset cover a much larger area. For example, I measured the per-eye field of view of the HTC Vive as around 110°x113° under ideal conditions, or around 130° diagonally (it’s complicated), or three and a half times as much as that of the 20″ desktop monitor. Because a smaller number of pixels (1080×1200 per eye) is spread out over a much larger area, each pixel appears much bigger to the viewer.

Now for the long answer.

Continue reading

Accommodation and Vergence in Head-mounted Displays

Why do virtual objects close to my face appear blurry when wearing a VR headset? My vision is fine!

And why does the real world look strange immediately after a long VR session?

These are another two (relates ones) of those frequently-asked questions about VR and head-mounted displays (HMDs) that I promised to address a while back.

Here’s the short answer: In all currently-available HMDs, the screens creating the virtual imagery are at a fixed optical distance from the user. But our eyes have evolved to automatically adjust their optical focus based on the perceived distance to objects, virtual or real, that they are looking at. So when a virtual object appears to be mere inches in front of the user’s face, but the screens showing images of that object are — optically — several meters away, the user’s eyes will focus on the wrong distance, and as a result, the virtual object will appear blurry (the same happens, albeit less pronounced, when a virtual object appears to be very far away). This effect is called accommodation-vergence conflict, and besides being a nuisance, it can also cause eye strain or headaches during prolonged VR sessions, and can cause vision problems for a short while after such sessions.

Now for the long answer.

Continue reading

A HoloArticle

Here is an update on my quest to stay on top of all things “holo:” HoloLamp and RealView “Live Holography.” While the two have really nothing to do with each other, both claim the “holo” label with varying degrees of legitimacy, and happened to pop up recently.


At its core, HoloLamp is a projection mapping system somewhat similar to the AR Sandbox, i.e., a combination of a set of cameras scanning a projection surface and a viewer’s face, and a projector drawing a perspective-correct image, from the viewer’s point of view, onto said projection surface. The point of HoloLamp is to project images of virtual 3D objects onto arbitrary surfaces, to achieve effects like the Millenium Falcon’s holographic chess board in Star Wars: A New Hope. Let’s see how it works, and how it falls short of this goal.

Creating convincing virtual three-dimensional objects via projection is a core technology of virtual reality, specifically the technology that is driving CAVEs and other screen-based VR displays. To create this illusion, a display system needs to know two things: the exact position of the projection surface in 3D space, and the position of the viewer’s eyes in the same 3D space. Together, these two provide just the information needed to set up the correct perspective projection. In CAVEs et al., the position of the screen(s) is fixed and precisely measured during installation, and the viewer’s eye positions are provided via real-time head tracking.

As one goal of HoloLamp is portability, it cannot rely on pre-installation and manual calibration. Instead, HoloLamp scans and creates a 3D model of the projection surface when turned on (or asked to do so, I guess). It does this by projecting a sequence of patterns, and observing the perspective distortion of those patterns with a camera looking in the projection direction. This is a solid and well-known technology called structured-light 3D scanning, and can be seen in action at the beginning of this HoloLamp video clip. To extract eye positions, HoloLamp uses an additional set of cameras looking upwards to identify and track the viewer’s face, probably using off-the-shelf face tracking algorithms such as the Viola-Jones filter. Based on that, the software can project 3D objects using one or more projection matrices, depending on whether the projection surface is planar or not. The result looks very convincing when shot through a regular video camera:

Continue reading

Optical Properties of Current VR HMDs

With the first commercial version of the Oculus Rift (Rift CV1) now trickling out of warehouses, and Rift DK2, HTC Vive DK1, and Vive Pre already being in developers’ hands, it’s time for a more detailed comparison between these head-mounted displays (HMDs). In this article, I will look at these HMDs’ lenses and optics in the most objective way I can, using a calibrated fish-eye camera (see Figures 1, 2, and 3).

Figure 1: Picture from a fisheye camera, showing a checkerboard calibration target displayed on a 30" LCD monitor.

Figure 1: Picture from a fisheye camera, showing a checkerboard calibration target displayed on a 30″ LCD monitor.

Figure 2: Same picture as Figure 1, after rectification. The purple lines were drawn into the picture by hand to show the picture's linearity after rectification.

Figure 2: Same picture as Figure 1, after rectification. The purple lines were drawn into the picture by hand to show the picture’s linearity after rectification.

Figure 3: Rectified picture from Figure 2, re-projected into stereographic projection to simplify measuring angles.

Figure 3: Rectified picture from Figure 2, re-projected into stereographic projection to simplify measuring angles. Concentric purple circles indicate 5-degree increments away from the projection center point.

Continue reading

Head-mounted Displays and Lenses

“It can’t be comfortable or healthy to stare at a screen a few inches in front of your eyes.”

The popularity of Google Cardboard, and the upcoming commercial releases of the Oculus Rift, HTC Vive, and other modern head-mounted displays (HMDs) have raised interest in virtual reality and VR devices in parts of the population who have never been exposed to, or had reason to care about, VR before. Together with the fact that VR, as a medium, is fundamentally different from other media with which it often gets lumped in, such as 3D cinema or 3D TV, this leads to a number of common misunderstandings and frequently-asked questions. Therefore, I am planning to write a series of articles addressing these questions one at a time.

First up: How is it possible to see anything on a screen that is only a few inches in front of one’s face?

Short answer: In HMDs, there are lenses between the screens (or screen halves) and the viewer’s eyes to solve exactly this problem. These lenses project the screens out to a distance where they can be viewed comfortably (for example, in the Oculus Rift CV1, the screens are rumored to be projected to a distance of two meters). This also means that, if you need glasses or contact lenses to clearly see objects several meters away, you will need to wear your glasses or lenses in VR.

Now for the long answer. Continue reading

On the road for VR: Redwood City, California

Last Friday I made a trek down to the San Francisco peninsula, to visit and chat with a couple of other VR folks: Cyberith, SVVR, and AltspaceVR. In the process, I also had the chance to try a couple of VR devices I hadn’t seen before.

Cyberith Virtualizer

Virtual locomotion, and its nasty side effect, simulator sickness, are a pretty persistent problem and timely topic with the arrival of consumer VR just around the corner. Many enthusiasts want to use VR to explore large virtual worlds, as in taking a stroll through the frozen tundra of Skyrim or the irradiated wasteland of Fallout, but as it turns out, that’s one of the hardest things to do right in VR.

Figure 1: Cyberith Virtualizer, driven by an experienced user (Tuncay Cakmak). Yes, you can jump and run, with some practice.

Continue reading

On the Road for VR: Augmented World Expo 2015, Part I: VR

I attended the Augmented World Expo (AWE) once before, in 2013 when I took along an Augmented Reality Sandbox. This time, AWE partnered with UploadVR to include a significant VR subsection. I’m going to split my coverage, focusing on that VR component here, while covering the AR offering in another post.

eMagin 2k×2k VR HMD

eMagin’s (yet to be named) new head-mounted display was the primary reason I went to AWE in the first place. I had seen it announced here and there, but I was skeptical it would be able to provide the advertised field of view of 80°×80°. Unlike Oculus Rift, HTC/Valve Vive, or other post-renaissance HMDs, eMagin’s is based on OLED  microdisplays (unsurprisingly, with microdisplay manufacture being eMagin’s core business). Previous microdisplay-based HMDs, including eMagin’s own Z800 3DVisor, were very limited in the FoV department, usually topping out around 40°. Magnifying a display that measures around 1cm2 to a large solid angle requires much more complex optics than doing the same for a screen that’s several inches across.

Figure 1: eMagin’s unnamed 2k x 2k, 80×80 degree FoV, VR HMD with flip-up optics.

Continue reading

On the road for VR: Silicon Valley Virtual Reality Conference & Expo

Yesterday, I attended the second annual Silicon Valley Virtual Reality Conference & Expo in San Jose’s convention center. This year’s event was more than three times bigger than last year’s, with around 1,400 attendees and a large number of exhibitors.

Unfortunately, I did not have as much time as I would have liked to visit and try all the exhibits. There was a printing problem at the registration desk in the morning, and as a result the keynote and first panel were pushed back by 45 minutes, overlapping the expo time; additionally, I had to spend some time preparing for and participating in my own panel on “VR Input” from 3pm-4pm.

The panel was great: we had Richard Marks from Sony (Playstation Move, Project Morpheus), Danny Woodall from Sixense (STEM), Yasser Malaika from Valve (HTC Vive, Lighthouse), Tristan Dai from Noitom (Perception Neuron), and Jason Jerald as moderator. There was lively discussion of questions posed by Jason and the audience. Here’s a recording of the entire panel:

One correction: when I said I had been following Tactical Haptics‘ progress for 2.5 years, I meant to say 1.5 years, since the first SVVR meet-up I attended. Brainfart. Continue reading

On the road for VR: Microsoft HoloLens at Build 2015, San Francisco

I have briefly mentioned HoloLens, Microsoft’s upcoming see-through Augmented Reality headset, in a previous post, but today I got the chance to try it for myself at Microsoft’s “Build 2015” developers’ conference. Before we get into the nitty-gritty, a disclosure: Microsoft invited me to attend Build 2015, meaning they waived my registration fee, and they gave me, like all other attendees, a free HP Spectre x360 notebook (from which I’m typing right now because my vintage 2008 MacBook Pro finally kicked the bucket). On the downside, I had to take Amtrak and Bart to downtown San Francisco twice, because I wasn’t able to get a one-on-one demo slot on the first day, and got today’s 10am slot after some finagling and calling in of favors. I guess that makes us even. 😛

So, on to the big question: is HoloLens real? Given Microsoft’s track record with product announcements (see 2009’s Project Natal trailer and especially the infamous Milo “demo”), there was some well-deserved skepticism regarding the HoloLens teaser released in January, and even the on-stage demo that was part of the Build 2015 keynote:

The short answer is: yes, it’s real, but… Continue reading

Messing around with 3D video

We had a couple of visitors from Intel this morning, who wanted to see how we use the CAVE to visualize and analyze Big Datatm. But I also wanted to show them some aspects of our 3D video / remote collaboration / tele-presence work, and since I had just recently implemented a new multi-camera calibration procedure for depth cameras (more on that in a future post), and the alignment between the three Kinects in the IDAV VR lab’s capture space is now better than it has ever been (including my previous 3D Video Capture With Three Kinects video), I figured I’d try something I hadn”t done before, namely remotely interacting with myself (see Figure 1).

Figure 1: How to properly pat yourself on the back using time-delayed 3D video.

Continue reading