VR is gradually applied to various fields such as film and television, games, shopping, and social networking. Like smartphones, VR will have a huge impact on people's lifestyles. However, most people may not have a clear understanding of VR at present. Therefore, this article introduces some basic VR experience elements from the perspective of consumers, clarifies some confusing concepts, and helps more people to understand VR as a "high-tech". .
First, the VR concept
1.1 VR concept
The Chinese name of VR is virtual reality, which uses computers and various sensing technologies to enable people to perform various activities in a simulated real-world environment. The device we experience VR is VR head display. Currently, the VR head display on the market can be in three categories:
PC/host VR
Mobile VR
VR machine
The PC/host VR needs to be connected to a PC or a host to work. The performance is relatively powerful, with location tracking and somatosensory interaction. Mobile VR needs to be plugged into the mobile phone, and is limited by the mobile phone, so the performance is not as good as the former. The VR all-in-one is a stand-alone VR device that can be worn directly.
1.2 VR new experience
VR can provide the same visual, auditory, tactile and other sensory experiences as the real world. For example, when watching the VR live broadcast of Faye Wong concert, we can look around the 360-degree live environment, you can enjoy watching the songs on the stage, or you can turn your head and wave around with the fans around you. It feels like you are at the concert. Among them, it is full of immersion.
VR provides an interactive experience that is consistent with human behavior. For example, in the game, we may be like Harry Potter, while casting a magic wand to cast magic, while watching NBA live broadcasts may be played with other audiences, all interactions are as natural as in real life, A gesture, a look, can be our input control method!
1.3 The difference between VR and 3D movies
The stereoscopic display principle of VR and 3D movies is based on the parallax of the left and right eyes of the human body, but the implementation is slightly different. The common practice of 3D movies is to add different polarized lights to the images corresponding to the left and right eyes, and then overlap them through the screen. Played out, the naked eye viewing is blurred, and the polarized glasses corresponding to the left and right eyes are worn and then viewed, so that the left eye sees the left eye image and the right eye sees the right eye image. The VR approach is relatively straightforward, which is to provide two sets of images with parallax for the left and right eyes. Although they all have stereoscopic effects, the biggest difference between VR and 3D movies is that VR provides an immersive experience that makes people feel like they are there.
3D movie: left and right eye image overlay VR: left and right eye image display
3D Movie: Stereo Effect VR Immersion: Stereo Effect + Panorama
1.4 VR integration into life
Some people may think that VR is very "sci-fi", it is a very distant thing, no, VR is slowly integrating into our daily life. Spring Festival Evening, NBA, Star (Wang Fei) concerts and other current events, entertainment activities have been broadcast live using VR, YouTube, Tencent video, Youku and other video platforms have been providing VR panoramic video, as well as VR games, Taobao BUY + VR shopping, As well as walking away from the VR tour (Google Earth). In fact, all aspects of our lives have seen the shadow of VR.
Second, the VR experience and its related elements
Those who have experienced VR should know that although VR is very attractive, the current VR experience is not enough to meet our requirements. The first is visually unclear, and then it is easy to cause dizziness and nausea. Below we introduce the VR experience and its related elements.
2.1 picture experience elements
2.1.1 clarity
In general, video resolution is an indicator of how we measure video clarity. Taking video resolution as an example, first we give the common video resolution that everyone is familiar with, as shown in the following table:
However, two common video and VR panoramic video of the same resolution, their viewing effect is not the same. Assume that under the conditions supported by the display, the normal 4K video source is 4K displayed on the display. In the 4K panoramic video, the picture will be restored to a space sphere. When people look inside the space ball, they can only see part of the sphere within the field of view, so the display can only display part of the 4K panoramic video. For example, the VR live broadcast of Faye Wong's concert is 4K, but the clarity of viewing is much lower than that of 4K, so many people complain that they don't see the face of the day.
In addition, the definition is also related to the display. On the one hand, high-definition video requires a high-resolution display to support, the higher the resolution of the display, the better the clarity of viewing. On the other hand, the distance between the person and the display can also affect whether the viewing is clear. For example, the ordinary 2K TV, our viewing distance is about 2-3 meters or more, it will be very clear, but if we are close to half a meter to watch, it will be unclear. In VR, the screen is about 5-10cm away from the human eye. After optical magnification of the lens, it will probably be imaged at 25-50cm in front. Imagine seeing 2K TV in half a meter. It may be particles and jagged!
From a physiological point of view, this is actually related to human vision. The number of pixels that the human eye can see in a one-degree view is called PPD (Pixels Per Degree). Generally speaking, the larger the PPD, the higher the viewing resolution, and the clarity when the PPD reaches 60 (the retina limit of the human eye). highest. Taking 4K (3840*1920) VR panoramic video as an example, the horizontal PPD is about 11 (3840/360=10.67), far below 60, while the PPD for viewing standard SD video is about 11, so from the perspective of PPD Look, the current 4K VR panoramic video and standard definition video are almost the same.
But don't worry, the experience of VR panoramic video will be greatly improved soon, because in the VR panoramic video production, the professional-level panoramic camera can already generate 8K panoramic video source, and the display will be upgraded to 4K in 2017.
So why does 8K panoramic video require a 4K display? We know that 8K TV is ideal for watching 8K video, but not in VR panoramic video. The horizontal PPD of 8K panoramic video is about 22 (7680/360=21.33). We estimate it with the most basic 90-degree FoV requirement. The single-eye horizontal pixel number is 21.33*90=1920, that is, the screen resolution needs to reach one eye 1920*. 1920, binocular 3840*1920, which requires 4K screen. In the same way, you can get a 4K resolution video that requires 2K resolution. If you use the Vive and Rift 110 degree FoV, the results will be slightly biased, but in general, the binocular 2K head is suitable for watching 4K VR panoramic video, and the binocular 4K head is suitable for 8K VR panoramic video.
2.1.2 vertigo
When experiencing VR, the picture often changes, and people are usually still, and it is easy to feel dizzy at this time, similar to the situation of motion sickness and seasickness. In this case, the changing picture is transmitted to the brain through the human visual system. The brain believes that the picture change is caused by some movements in the body, and the ear vestibular organs that control the balance and coordination of the body do not feedback the body to the brain. Motion information, so the brain feels the inconsistency of visual information and exercise, which may lead to dizziness, nausea or vomiting, commonly known as motion sickness. Motion sickness is also related to the individual's physique, just as some people are prone to motion sickness and some people are naturally not dizzy.
People with natural VR can overcome VR motion sickness through the exercise of the day after tomorrow, and the equipment manufacturers will help us reduce the impact of motion sickness from the perspective of equipment. After research, one of the main causes of VR vertigo is MTP (MoTIon To Photons) delay, which refers to the time from the beginning to the display of the corresponding picture. MTP delay is too large to cause dizziness, it is currently recognized that MTP delay less than 20ms can significantly reduce the occurrence of motion sickness. In order to reduce the MTP delay, on the one hand, it is necessary to improve the rendering performance of the GPU. On the other hand, the refresh rate of the display screen needs to be increased to above 75 Hz. At present, the Vive and the Rift both achieve a screen refresh rate of 90 Hz. So don't worry too much about dizziness.
2.1.3 fluency
Another benefit of increasing the refresh rate is to make the picture smoother. When it comes to the refresh rate, everyone will naturally think of the frame rate. Refresh rate and frame rate are different concepts, but they affect the fluency of the VR experience.
Ordinary movies are generally 24FPS frame rate, it seems to be smooth enough, and Ang Lee's "Midfield War" has 120FPS, more smooth, it is said that only five cinemas in the world can play! This is because high frame rate video requires a high refresh rate display to match, for example, a 60 Hz display is used to play 120 FPS video, then the display will display one picture every other frame, and the person sees the effect of 60 FPS, so refresh The rate is the upper limit of the speed of the picture change. In turn, using the 60HZ display to play 30FPS video, the display will display each frame twice, and the person sees 30 frames in this second, so the frame rate represents the picture when the display supports it. Actual fluency.
The film uses the persistence characteristics of the human eye to form a smooth picture. A series of static pictures are played at 24 frames per second, which can fool the brain to produce a dynamic feeling. However, in some large games, 24FPS is not enough. For example, CS and LOL games may require 60FPS or more to feel smooth. The film or digital sensor used for filming also has visual residuals like the human eye. Taking 24FPS as an example, each frame of the movie records the motion track image of all objects in 1/24 seconds, so the human eye feels smooth. Very comfortable. The picture of the game is rendered by the GPU. Each frame of the game corresponds to an instant image. Even objects that move very fast will be rendered clearly and do not conform to the viewing habits of the human eye. Therefore, it feels contradictory and not Smooth.
This situation will be more prominent in VR, and a smooth picture may cause dizziness, so VR requires a high refresh rate display, while a high-performance GPU to ensure a stable, relatively high frame rate.
2.2 Interactive experience elements
Why do everyone think that the cheap VR box experience is not good? One of the big reasons is that because of its low interaction, the interaction can be simply understood as our feedback to the VR system's input and VR system. Good interaction can bring a stronger sense of immersion. Imagine playing "Resident Evil 7" in PSVR, using your own hand to take weapons to attack zombies than to use the handle to control, is it more sense? Interactions include location tracking, input control, and feedback.
2.2.1 Tracking system
If a person moves and rotates in the VR, and the picture does not change accordingly, then it will feel unnatural, so it needs to be tracked. There are three groups in the direction of our movement, from front to back, left and right, and the direction of the head is also three groups. Look at the left and right, look up and down, and look around, so there are a total of 6 degrees of freedom. It is 6DoF (Degree of Freedom). Ordinary VR boxes can only track the rotation of the head, only 3DoF. Of course, more natural and better is the tracking of 6DoF.
With the CES show in January 2017, the inside-out tracking has become the standard for VR boxes and VR all-in-ones. Corresponding to outside-in tracking, the Vive/Rift/PSVR tracking system is outside-in. The so-called outside-in is the need to place some tracking devices in the external space of the headset, such as Vive's two lighthouse base stations. The inside-out integrates the tracking system inside the head display, and no need to install other devices. They are two different ways of tracking, each with its own advantages and disadvantages.
2.2.2 Input Control and Feedback
A good VR experience requires a good input control and feedback system. For example, gesture recognition allows us to control the hands of virtual avatars more naturally. Expression recognition can greatly facilitate us to share our mood in VR. In addition, human vision, hearing, touch, smell, and taste can be directly related to VR immersion. Stereoscopic and stereo sound effects have been achieved, and feedback techniques for touch, smell and taste are accelerating. In VR, "This is a tasteful video" is no longer a ridicule.
Third, the network needs of a good VR experience
With good VR devices, we also need a good network to support the VR application experience. For example, when we watch a panoramic video through VR, if the network bandwidth is not enough, it will happen, and the serious situation may cause physical discomfort. Also, when playing VR online games, if the network delay is large, the game will lose if it is light, but it will cause dizziness and nausea. Therefore, the quality of the VR experience is also affected by the network. Next, let the general family introduce the network that is needed for a good VR experience.
3.1 Network Requirements for a Good VR Experience
If it is mainly to watch VR video, then it needs a relatively large bandwidth. According to iLab's "White Paper for Carrier Network Requirements for VR Services", it takes about 25Mbps for 4K panoramic video. It takes about 100Mbps for 8K panoramic video. The specific calculation formula is: the number of pixels per frame (7680 * 3840) * color depth (8bit) * the number of frames per second (30fps) * YUV420 sampling rate (3 / 2) * compression ratio of H264 (1/165) * experience Value (1.5).
In order to improve our viewing experience, the VR panoramic video will be gradually upgraded to 8K in 2017, so it is recommended to calculate the bandwidth requirements of 8K panoramic video. In addition, the number of VR terminals in a family needs to be considered. The average number of households in China is about 3, so an average family may have 1-3 VR terminals, so a 100-300 Mbps bandwidth package is recommended.
If it is mainly to play VR games, the demand for bandwidth is not as high as that of VR panoramic video, but the requirements for network delay are relatively high. When playing VR online games, the network is mainly responsible for transmitting some control data. In order to reduce the occurrence of motion sickness, it is necessary to ensure that the network delay + device processing delay is less than 20ms. The processing delay of the device includes the refresh period of the screen 11.1ms, the sampling time of the sensor is 1ms, and the rendering time of the graphics card (about a few milliseconds), so the time for network transmission is not much. It is recommended to use the optical package.
Considering a combination, it is now possible to recommend a home fiber bandwidth of 100-300 Mbps.
3.2 VR's network demand is still improving
First, the current VR is still in the early stage of development or the entry experience stage. In the next 1-2 years, there will be a big experience improvement, including higher resolution, higher frame rate, larger field of view, and basically no dizziness. . Second, social elements are constantly being integrated into VR applications, playing VR chats, playing multiplayer online VR games, and more. So a good VR experience in the next few years will require a higher home bandwidth and a lower latency network.
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