Continuous Real-Time Measurement Method for Heart Rate Monitoring Using Face Images

This paper investigates fundamental mechanisms of brightness changes in heart rate (HR) measurement from face images through three kinds of experiments; (i) measurement of light reflection from cheek covered with/without copper film, (ii) spectroscopy measurement of reflection light from face and (iii) simultaneous measurement of face images and laser speckle images. The brightness change of the face skin are found to be caused by both the green light absorption variation by the blood volume changes and the light reflection variation by pulsatory face movements. The Real-time Pulse Extraction Method (RPEM), designed to extract the variation of light absorption by removing motion noise, is corroborated for the robustness by comparing the RPEM with the pulse wave of the ear photoplethysmography. The RPEM is also applied to heart rate measurements of seven participants during office work under non-controlled condition in order to evaluate continuous real-time HR monitoring. RMSE = 6.7 bpm is achieved as an average result of seven participants in five days with the 44% of HR measured rate with respect to the number of reference HRs from the electrocardiogram during face is detected. The result indicates that the RPEM method enables HR monitoring in daily life.