Vision

Head-mounted Displays (HMDs) are the most important and basic devices of VR. It can directly deceive your eyes and brain and make you think you are immersed in another real space. Maybe the current ‘Virtual Reality headsets’ gives you the impression that the design is kind of cumbersome, but in fact, HMD combines multiple vision technologies to achieve the best experience.

Pixels and displays technology, refresh rate, and latency must be considered of course, which are the basic factors that affect vision. Compared to 2D imaging, VR has higher requirements for these technologies. Achieving these may require better recording equipment, renderers, or internet speeds. While when specific focusing on VR visual technology, the key technologies can be divided into three points, optics, head tracking, and eye-tracking.

Optics refers to the stretching of flat images to fill your field of vision completely, in which way HMD can create an immersive feeling of inhabiting a virtual world. Experimentation shows that the field of view (FOV) should be between 90 and 100 to present the virtual world naturally. The lens of the HDM fills flat images to every corner of our line of sight, so the quality of the lenses used has a direct impact on the image clarity. (Virtual Reality Society, 2017)

Head tracking is used to confirm the user’s head position and convert the head position effect into visual information. In this way, our field of vision will change with the movement of the head, and the speed of this transformation is also critical to the immersive experience of VR. Currently, HMD mainly considers two kinds of movements and corresponding two speeds, as shown in figure. (WebVR concepts,” n.d.) One is using an infrared laser and an external sensor to track the linear movement position of the head, which x is to the left and right, y is up and down, and z is towards and away from the position sensor. The other is adding a multi-axis accelerometer on a chip, which could be used to calculate the acceleration of the HMD movement to determine the rotation of the head.

The third is eye tracking. As the name implies, it is a technology that tracks where your eyes are currently located and can change that information into visible data. With this technology, your HMD may change the depth of the field of vision on-screen to simulate natural vision. (Virtual Reality Society, 2017) In this way, your gaze could affect the virtual character or can be used to quickly select certain items. Of course, the importance of eye tracking is more than that. As the sayings, “the eyes may be the windows to the soul”, the gaze points are also important data for the VR experience. The maturity of eye-tracking technology means that the device can know what you want to see and what you need to see clearly, so it can perform partial high-definition rendering to improve the user experience.

Currently, HMD equipment has rapid iterations, which makes imaging more high-definition and lower vertigo, but there are still some obvious problems that need to be solved. For example, when worn for a long time, the eyes will suffer from fatigue and dryness, which is caused by high brightness of the screen and eye focal length is fixed for a long time. Besides, current HMD is relatively bulky. Therefore, if you wear it for a long time, your head and neck will have obvious fatigue.