Under the epidemic situation of COVID-19, the portable health screening device can effectively assist relevant departments in epidemic control. Some respiratory infectious diseases such as COVID-19 have hidden symptoms, and the first symptom in many cases is not fever, but shortness of breath. For these infectious diseases, leveraging these symptoms to find infected people can stop the virus from spreading again and allow infected people to get timely treatment. At present, the single health portrait such as body temperature constructed by the existing screening technology has great limitations such as low detection rate and high missing rate.
The breathing state assessment is not mentioned as much as the body temperature in epidemic control. Respiration is one of the most significant characteristics of human vital signs. Among all the characteristics of respiration, respiratory rate and breathing patterns are particularly important. Studies illustrate that their changes are one of the earliest and major signs of many serious illnesses. So far, diverse studies have demonstrated that thermal imaging can be used to analyze the respiratory rate and breathing patterns [1] [2] . Hu et al. used thermal and visible imaging to achieving the noncontact and nonobtrusive measurements of breathing rate and pattern [3] . Therefore, we developed a remote respiratory infectious screening system based on portable thermal camera to help fight the current epidemic caused by SARS-CoV-2. The structure of our screening system is shown in Fig. 1 . It has the advantages of portability, low cost and easy operation. Through the 15-second detection window, this system can accurately determine body temperature and respiration state of people wearing masks, thus giving the screening result.
The main contributions of this demonstration are three-arXiv:2004.01479v1 [cs.CY] 3 Apr 2020 fold. First, we combine the face recognition technology with portable thermal camera to accomplish the nostril recognition of facial thermal images. Subsequently, the temperature information and respiration state is successfully obtained by applying image analysis algorithms to facial thermal images. Finally, based on the existing equipment conditions, we have implemented a non-contact and efficient measurement system for health screening on respiratory infections.
In our demonstration, we use a FLIR one thermal camera connected to an Android phone to collect thermal video, and use the application we developed to achieve real-time health screening of respiratory infections. The pipeline for our screening system is shown in Fig. 2 . Three modules are inserted in our developed application, which are thermal image collection module, health indicator calculation module and health assessment module. The detailed descriptions of these three modules are presented below: 1) Thermal image collection module: this module is mainly composed of hardware devices, which consists of an Android smartphone and a FLIR one thermal camera. The system can be put into use simply by connecting the camera to the phone and installing the application we developed. In this demonstration, a thermal camera is aimed at the face of a participant wearing a mask to obtain a corresponding facial thermal video.
2) Health indicator calculation module: this module is mainly responsible for extracrting features of temperature and respiration data from the thermal videos. When human body performs continuous periodic breathing activities, continuous heat exchange occurs between the nostril and the air, and periodic temperature fluctuations occur in the respiratory tract. Therefore, respiration data can be obtained by analyzing the periodic changes in the temperature around the nostril. After using a series of algorithms to deal with the collected temperature data, the accurate health indicator can be obtained.
In this system, we extract respiratory rate and one of the four common breathing patterns (Eupnea, Bradypnea, Tachypnea and Apnea) according to the obtained nostril signals. Body temperature is achieved through forehead signals.
3) Health assessment module: this module includes health screening and abnormal alert. Health screening is accomplished through a comprehensive analysis of body temperature, respiratory rate and breathing pattern. The algorithm is based on Hu's research [3] . Besides, an alert would be provided when abnormal health conditions are found.
In our experiments, participants wearing masks only need to stay hold in front of the thermal camera for 15 seconds to complete the health screening. The result shows that the system can efficiently extract the temperature and respiration data of participants, and give an accurate assessment of health conditions. During the whole non-contact screening process, slight movement of participants can be accepted. This system may have great application prospects in many scenarios such as community, campus and hospital which can be used to perform preliminary check for respiratory infections and give abnormal alerts.