HOW IN-DISPLAY FINGERPRINT SENSOR WORKS?
An in-display fingerprint sensor uses optical fingerprint sensor to capture the data, which is embedded under the display. Vivo X21 and the Xiaomi Mi 8 use synaptic Clear ID sensor for high resolution finger scanning. THE Clear ID sensor, is a CMOS chip is support by only OLED and AMOLED Display.
Fingerprint will get captured using reflected light, so when you touch the display, display lights up to illuminate the fingerprint and the sensor captures a high-resolution scan of fingerprint through reflected light from the gap between the pixels. To ensure that the fingerprint dat is being read accurately by the sensor, we need to hold it for while, this is done so that the sensor will recognize the fingerprint.
The fingerprint matching process is done by the help of Synaptic Quantum Matcher Software, and the host sensor used for illuminate the area and activate the scanner.