Under-display Camera Technology Is Upcoming! Is the “True Full Screen” Good or Not?
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Under-display Camera Technology Is Upcoming! Is the “True Full Screen” Good or Not?

The Debate on True & False Full Screen

The concept of “full screen” came into being in 2016. Then, the full screen was referred to smartphones with an aspect ratio of 18:9 or longer screens. Since the beginning of the“full screen” era, the screen-to-body ratio has become a key parameter in the competition. The higher the screen-to-body ratio, the more stunning the vision a smartphone can offer, the more overwhelming the visual effect of “all I can see is the screen” will be.

Many factors affect the screen-to-body ratio, such as the top and bottom of the screen for the antenna, the black matrix area for both sides of the screen, the position of the receiver, speaker, light sensor, proximity sensor, and much more.

Apart from the above factors, the front camera is the “killer,” which affects the extremely high screen-to-body ratio of smartphones. Mobile phone manufacturers and related production chains put in a lot of effort to eliminate the annoying element that requires a hole and affects the integrity of the screen.

Take MEIZU 16 Series smartphones as an example. They adopt the smaller image sensor to integrate the lens with much narrower bezel on the top, successfully making smartphones with ultra-slim bezels. Smartphones like Xiaomi Mi Mix 1/2/2s that have an ultra-thin top bezel, but the front camera at the bottom requires you to turn the screen upside down to take a selfie. The more common practice is to use a specially designed screen with a cut-out slot on the top of the screen to accommodate the camera, such as a notch display, waterdrop notch display, teardrop notch display. Later came the Huawei nova 4Honor 20Honor View 20, Samsung Galaxy A8s/S10 Series that have a hole on the top to accommodate the camera.

Since these solutions don’t do away with the front camera, which takes up part of the effective display area, users refer to the corresponding screens as “false full screens.”

Up till now, smartphones that accord with the definition of “true fullscreen” are those that use a pop-up or revolving camera, sliding, or double-screen design.

It is a pity that such a solution leads to higher costs, problems of built-up dust, and durability of the mechanical structure. What’s worse, it even means sacrificing the valuable internal space of the smartphone, limiting the battery capacity and weight, resulting in shorter battery life and worse tactile experience. 

Thoughts about the Hole-punch Display

Among all smartphones with “false full screens,” undoubtedly, the hole-punch display caters to most users, because the hole can be anywhere on the top of the screen.

Regretfully, no matter the screen is made of AMOLED or LCD, the camera is exposed as a hole, which affects the visual effect when the screen is on. Moreover, the system and Apps need to be optimized accordingly, or the icon and content will be blocked.

The camera part of the LCD hole-punch screen can’t display any content because it needs to perforate the backlit layer, allowing the light from outside to pass the glass and LCD panel to reach the image sensor for taking photos. 

Even though the particular “blind hole” won’t destroy the LCD panel, users will still have to face a black hole.

Comparison: The “through-hole” and “blind hole” of LCD hole-punch display 

Here comes the problem. AMOLED screens can generate light itself without the backlit layer. If an AMOLED display is perforated in reference to the “blind hole” technology, the display won’t be damaged. 

Then, is it possible to meet the needs of light transmission and normal display at the same time? Thereby, the custom “under-screen camera” technology intended for the AMOLED screen has emerged. 

Please refer to the under-screen camera technology above.

Different names

On June 3rd, the head of OPPO and Xiaomi unveiled their smartphone prototypes with the under-screen camera successively. The difference is that Xiaomi named the technology as “Xiaomi invisible screen,” while OPPO named it as “transparent full view display.” They are similar to the current fingerprint recognition technology. The front camera area won’t affect the display effect and operation.

When the front camera is turned on via the App, the corresponding area of the screen will be transparent instantly, which allows the hidden camera to capture scenes. 

The schematic of the under-screen camera (Only for your reference)

Opportunities for AMOLED screens

As we all know, apart from the image sensor, focusing technology, AI Beauty algorithms, the amount of light passing through the aperture diaphragm is also critical to the selfie taken by the front camera. Both the aperture size and light transmittance of the optical lens affect the amount of light. In the past, the front camera of the smartphone is under a piece of glass, which won’t affect the image effect.

However, the under-screen camera means the lens placed under the protective glass and the display panel. Therefore, the light needs to pass through more layers. Meanwhile, the light will refract, scatter, etc., which reduces the amount of light reaching the camera. 

The reason why the above mentioned “hole-punch” display can’t conceal the camera in most cases is to pursue the maximum light transmittance by clearing all obstacles. For example, neither the backlit panel of the LCD screen nor the display panel of the AMOLED screen can present the image for such a reason. 

However, both Xiaomi’s invisible screen and OPPO’s “transparent full view screen” are based on the AMOLED, a self-luminous material. In comparison with LCD, the AMOLED display is thinner, which means an advantage for light transmittance. 

Theoretically, as long as the AMOLED display is thin enough, the light transmittance will reach a specific value, which allows a sufficient amount of light to pass through the panel while hiding the camera. 

However, due to the limit of the current technology, the AMOLED display isn’t as thin to make the under-screen camera function normally. Thus, there’s no choice but punching a hole on the screen. 

Similar solutions to the full screen

According to Xiaomi’s official description of the “invisible screen,” the position of the front camera is a little “transparent screen,” which features low reflectivity and high light transmittance. 

The “transparent screen” can display contents normally, and become a piece of glass when you’re taking photos. When the camera is turned on, the screen and camera lens coordinate with each other, letting in enough light to reach the image sensor, realizing better image resolution than the “blind hole” technology for the LCD panel. 

The “transparent full view screen” advocated by OPPO is similar to the “invisible screen,” which involves the combination of two screens. A “transparent screen” covers the front camera. 

In comparison with Xiaomi’s description, OPPO’s description of the “transparent screen” is more accurate. It is not a piece of transparent glass as you think, but the “transparent material” with higher light transmittance through the redesigned pixel structure of the front camera area. In other words, it is an AMOLED display that can turn transparent. 

As we all know, the exclusive AMOLED panel for smartphones consists of three layers, including the traditional cathode material, organic light-emitting material, and traditional anode material. 

To ensure the thermal stability, the anode material at the bottom must be yellow, with ultra-low light transmittance, which leads to the “opacity” of normal AMOLED panels. In other words, to make the AMOLED panels transparent, the anode material at the bottom should be replaced.

The “transparent screens” by Xiaomi and OPPO are AMOLED screen with specially designed anode material which has high light transmittance. It allows the light fro the outside to pass through the screen and the part of the AMOLED panel to reach the image sensor inside the camera and thereby improve the image quality. 

When the camera is not in use, the small part of the “transparent screen” can display contents normally, harmonizing with the AMOLED screen on the whole.

An incurable sequela for the moment

Although the AMOLED panel whose anode material has been replaced looks transparent, still, its light transmittance isn’t comparable with the truly transparent glass. 

In other words, the under-screen camera can’t produce the same image effect as the non-under-screen ones. It’s because of the reduction of optical performance. The selfie will be slightly tinted and fuzzy. 

Meanwhile, there are issues of chromatic aberration and low resolution of this part of the AMOLED panel that can turn transparent. The problems are even more prominent when the screen displays images in light colors. 

Therefore, a dark wallpaper is used in the engineering prototype with an under-screen camera as a disguise.

Currently, the “under-screen camera” can be optimized through both the software and hardware.   

As for the hardware, the larger aperture, image sensor, single pixel size of the front camera can be used to increase further the amount of light entering the camera. 

In terms of the software, the brightness and details of the image can be improved through AI algorithms, white balance, HDR, in combination with the defogging algorithm to get rid of the fogging due to the under-screen camera and further enhance the clarity of the image.

Anyway, the under-screen camera can’t produce as descent selfies as the traditional front cameras. 

The emergence of the under-screen camera technology realizes the “true fullscreen” without changing the original shape. It also gets rid of the constraints of the complicated mechanical structure. What’s more, it won’t increase the weight of the smartphone or affect battery life. All in all, it is a perfect solution to the full screen. 

Although the technology results in lower display effect and image quality, there are more approaches than difficulties. 

As better anode material, image sensor, AI algorithms are being developed, the “true fullscreen” smartphones will eventually be prevalent. Let’s look forward to it!

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