Fig. 1. 是The main steps for respiration monitoring with infrared thermal imaging

Fig. 2. IR thermography for monitoring respiration （a） the features of nostril with exhalation, （c） the features of nostril with inhalation

Fig. 3. Illustration of respiration signal of subject in normal and second-hand smoke environment （a） time series respiration signal, （b） the frequency spectrum of respiration signal

Fig. 4. Comparison of respiratory signals’ sample entropy with subject in normal and second-hand smoke environments