  The new trend of full-screen devices encourages us to position a camera
behind a screen. Removing the bezel and centralizing the camera under the
screen brings larger display-to-body ratio and enhances eye contact in video
chat, but also causes image degradation. In this paper, we focus on a
newly-defined Under-Display Camera (UDC), as a novel real-world single image
restoration problem. First, we take a 4k Transparent OLED (T-OLED) and a phone
Pentile OLED (P-OLED) and analyze their optical systems to understand the
degradation. Second, we design a Monitor-Camera Imaging System (MCIS) for
easier real pair data acquisition, and a model-based data synthesizing pipeline
to generate Point Spread Function (PSF) and UDC data only from display pattern
and camera measurements. Finally, we resolve the complicated degradation using
deconvolution-based pipeline and learning-based methods. Our model demonstrates
a real-time high-quality restoration. The presented methods and results reveal
the promising research values and directions of UDC.
