A while ago, there was a hot search related to “anti-peep film”. The general idea is: when a traffic star is photographed in public, the content of the conversation on the mobile phone can be seen clearly.
What’s even more funny is that some people in the comments suggested to buy a privacy screen, but another comment said that this is already a privacy screen (that is, a privacy film is attached)——
Wait, what the heck is a privacy film? Does it really prevent others from seeing our phone screens?
Privacy film: stick one on the screen
Miniature “Blinds”
In fact, in today’s widespread use of smartphones, all your personal information, whether it is work and family details, or privacy such as chat records and love life, and even information such as ID cards and bank cards, may be stored in a small piece of information. displayed on the screen. Once the mobile phone screen is stared at by people with ulterior motives nearby, I am afraid it will bring big trouble.
Therefore, in order to make the screen of the mobile phone more secure, a simple solution is to spend tens of yuan and put a privacy film on it, so that strangers on both sides of the mobile phone cannot easily see the displayed content.
Figure丨Pixabay
Why does the mobile phone privacy film have such an effect? The secret lies in its structure.
This layer of film looks transparent on the outside, but it is actually equivalent to a miniature “louver” . In the fine grating structure of tens of hundreds of microns, which is thinner than a human hair, there is a row of “small fences” that block light .
Figure丨posts.careerengine.us
As can be seen from the above figure, if the human eye is viewing within a small angle range ( such as 30 degrees ) directly in front of the mobile phone, the light emitted by the mobile phone screen can be received normally, while for the viewer on the side of the mobile phone screen Said that because of the occlusion of the “small fence” array, the mobile phone screen seems to be “black” . Relying on this simple and direct way, the privacy screen can protect the personal privacy of mobile phone users to a great extent.
Of course, the size of the “viewable angle” is not a fixed value, it is related to the width, height and spacing of these “small fences”, which can be designed artificially.
Designing the size of the ” viewing angle ” is not easy. Since mobile phone users often look obliquely when viewing the screen, for example, when taking pictures, they raise or lower the mobile phone. At this time, the viewing angles of the user and bystanders are actually similar. Therefore, if the angle is set small , the chances of others peeking at the screen content will be small, but it may also prevent you from normal viewing. But it’s also easier for others to peek at.
How to do it? The designer of mobile phone privacy film can only strike a balance between the two, so that the “viewable angle” is in a compromise size , but sometimes it still cannot meet the needs, resulting in “the things that should be seen cannot be seen” or “What should not be seen is seen”.
A hint of an anti-peep angle丨@王方伟/zhihu
Also, everything has two sides. While blocking peeping, the “louver” structure on the privacy film will inevitably block some of the light when you are viewing the screen from the front, resulting in negative results such as decreased screen brightness or increased power consumption.
A reverse brain hole:
Turn your phone into a “naked eye 3D” effect
Putting a privacy film is naturally to prevent your screen from being peeped. However, there are still times when we will do the opposite, not only do not stop the “enthusiastic viewers” who are looking at the screen sideways, but also specially send them the image content , so that they “have to watch it if they don’t want to” .
How to do it? As long as another film is pasted on the mobile phone or computer screen, there are still many small fences in the film, but the design is slightly different, as shown in the following figure-
Figure丨Wikipedia
The result is that looking at the screen from two different angles will see the red and green parts of the screen at different locations.
If the angle is set smaller, the red and green areas just correspond to the left and right eyes of a person . One of the important reasons why we usually look at things is three-dimensional and three-dimensional, because the left and right eyes are slightly different, and the images of the same object viewed will also be different.
When we superimpose the left eye picture and the right eye picture on the screen as the red area and the green area, respectively, and then project the two groups of pictures to the left and right eyes through this layer of film, the viewer’s brain will associate the left and right eye pictures with each other. Combined, the effect of naked-eye three-dimensional display can be achieved. A 2D mobile phone can be used as a 3D mobile phone by attaching such a layer of film to the screen of the mobile phone and adding special binocular format image and video files .
If the angle is set larger, through this layer of film, two viewers at different angles can see the content of different parts of the screen, which can achieve “one screen for two purposes”, and two people “do their own thing” , For example, on a screen, one person is watching a movie, and the other is typing and chatting.
Continue to the brain hole: if you put the privacy film
What about wearing it on human eyes?
Let’s open our minds and think about a possibility——
Putting a layer of film on the screen of the mobile phone, whether it is anti-peeping or three-dimensional display, is actually equivalent to putting “a pair of glasses” on the screen of the mobile phone, and glasses can originally be worn on the human eye, so if the What happens to this “privacy film glasses” when worn on the human eye ?
I want to talk about the polarization of light here. Light is a kind of electromagnetic wave. When it propagates in the same direction with the same brightness, it will vibrate in different directions, that is, the polarization direction is different, and the light of different polarization directions is the same in appearance. After special detection of polarized light Only when the polarizer is used will it “show its original shape”. Polarized glasses can be used for both 3D display and anti-peeping.
The kind of 3D movies we usually watch in theaters with glasses, such as “Avatar”, “The Avengers” and “Spider-Man”, use such a method. The screen display contains light with two different polarization directions, such as Left-handed circularly polarized light and right-handed circularly polarized light, the left eye picture and the right eye picture are displayed with two kinds of light respectively, and the left and right eye polarized lenses on the glasses will filter the polarized light in the corresponding direction respectively, thus realizing binocular parallax. 3D display.
When preventing peeking, a composite image will be displayed on the screen of the mobile phone, which contains both the hidden image displayed by polarized light in one direction and the noise interference displayed by polarized light in the other direction. If you don’t wear special glasses, the result of the mixture of the two is “white flowers”, and if the user wears polarized glasses corresponding to the polarized light in the first direction, the hidden image can be “filtered” out, and you can still watch it normally. The screen of the mobile phone, and people without glasses around them can only “hurry up, stare blankly, there is no way”. Of course, the disadvantage of this anti-peeping method is that it is not very convenient to wear special glasses every time when using a mobile phone.
A hidden image display device using polarized light丨The author was photographed in Shenzhen Huaqiangbei Museum
In fact, a similar principle can also explain the stunt of seeing through mahjong tiles and playing cards in many “God of Gamblers” movies – the polarizer can extract the originally hidden pattern by allowing only polarized light in a specific direction to pass through, cheating in the game .
Figure 丨 Screenshot of the movie “God of Gamblers”
Well, the brain hole is over, back to reality.
“Anti-screen peeping” is indeed an increasingly important issue in our daily life. Fortunately, technology is advancing with each passing day. I believe that to solve the problem of privacy protection of mobile phone screens or other screen content, there will be many other ingenious technical means. However, the most important thing is that users themselves should pay attention to their surroundings when using mobile phones in public. .
Author: Jiao Shuming
Editor: Malt Young
Source of cover image: The movie “God of Gamblers”
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