How does Xiaomi Mix 4 CUP Flexible Screen Solution Work?
Xiaomi MIX 4 phone was officially released on August 10, the phone is Xiaomi’s first CUP full-screen technology, the front camera hidden under the screen, to achieve no open-hole true full-screen. Officially, the research and development of this technology, the amount of investment up to 500 million yuan, took 2 years to complete.
Xiaomi said the mission of the MIX series is to explore, from the first generation of MIX led the whole industry into the “full screen”, has tried COF package, sliding design, shaped screen, cutout screen, wrap-around screen, and many other options. This time, Xiaomi MIX 4 is equipped with the third-generation CUP flexible screen, which enhances the sense of unity of the screen to an unprecedented degree while ensuring the front camera and display quality.
So, how is it achieved? Today Xiaomi published an official article to further introduce this third-generation process of Xiaomi Mix 4 CUP flexible screen solution.
We once released the Xiaomi transparent TV in 2020, which has considerable transparency by rearranging the pixels and optimizing the substrate material. The CUP screen only needs to apply the same basic principles to increase the light transmittance of the screen panel to allow the camera to be hidden under the screen.
Flexible OLED screens already have some transparency of their own, a characteristic that is at the heart of what drives under-screen fingerprinting and under-screen light sensitivity. But this transparency alone is not enough for the camera.
To make it easier for light to pass through the screen and reach the front camera sensor, Xiaomi Mi Mix 4 first had to move the TFT circuitry below the pixels, which mainly blocks light, out of the CUP area so that it can use the pixel gap to pass light. We can see that the CUP area is like an “eye” and the “pupil” in the middle is the light-transmitting area.
To increase the light transmission, the gap between the pixels needs to be enlarged, so the individual sub-pixels need to be reduced accordingly. After the reduction, the RGB ratio of the pixels is still the same to ensure the display effect, and the pixel shape needs to be modified to be round to reduce the diffraction phenomenon when light passes through the screen.
After reducing the pixel area and removing the TFT driver circuit, the lead circuit between the pixels was changed to Indium Tin Oxide (ITO), a transparent wire that further increases light transmission. Also to reduce diffraction, the path of the alignment was changed to a wavy shape. In this way, Xiaomi has given the screen significant transparency, allowing the CUP area to reach 5 times the transparency of the normal display area.
But no one can defy the laws of physics, and even after all this, you can’t make diffraction disappear completely or make the screen 100% transparent, so the under-screen front camera still needs to use software algorithms to optimize the screen and compensate for the reduced amount of incoming light.
On the production line, Xiaomi Mi MIX 4 calibrates the color temperature of the under-screen camera one by one to make the screen and sensor hardware match. And after the user takes a photo, the algorithm performs multi-frame HDR, noise reduction, and defogging in the RAW domain. Xiaomi Mi Mix 4 uses a neural network to train a de-diffraction model to reduce diffraction traces caused by point light sources in the image, followed by a series of detail enhancement, color enhancement, and local brightening algorithms. The final result is a usable level of front camera photography in the MIX 4.
Xiaomi Mi MIX 4 Review – Suggested Reading.
The CUP flexible screen of Xiaomi MIX 4 has taken years of research and development, more than sixty national patents, and all the efforts just to achieve the future of smartphone screens and create a flawless vision.