An icing process of a single supercooled-water droplet is focused in the present study. A stationary icing as well as an icing of a moving droplet gives us great insights into the development of an ice-prevention system for engineering purpose. For academic purpose, it gives experimental findings in a two-phase flow. To understand the icing process, we applied a luminescent imaging technique. It uses a temperature-sensitive luminophore and a temperature-insensitive luminophore to create the luminescent water. The luminescent outputs from these luminophores are simultaneously captured by a high-speed color camera. By simply taking a ratio, the temperature distribution can be extracted. In this paper, this imaging system is shown with its temperature characterization. An icing process of a stationary droplet is shown in this paper. Also, a current status of an icing process of a moving droplet is shown.