Robust and Remote Photoplethysmography Based on Smartphone Imaging of the Human Palm

• Published in: IEEE transactions on instrumentation and measurement Vol. 72; p. 1
• Main Authors: Lian, Chao, Yang, Yiming, Yu, Xiaodong, Sun, Hui, Zhao, Yuliang, Zhang, Guanglie, Li, Wen J.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Arrhythmia; Cameras; Cardiac arrhythmia; Electrocardiography; Faces; Fast Fourier transformations; Fourier transforms; Heart rate; Heart rate measurement; Image color analysis; Luminous intensity; non-contact; photoplethysmography; rPPG; Signal to noise ratio; Skin; Smartphones; Video data; video surveillance
• DOI: 10.1109/TIM.2023.3264041
• ISSN: 0018-9456

Arrhythmia is a marked symptom of many cardiovascular diseases (CVDs). Fast and accurate measurement of heart rate (HR) can lead to prompt detection of arrhythmia, which could be potentially life-threatening. However, it remains a challenge to robustly and remotely measure HR due to the typically changing ambient conditions surrounding human subjects. In this study, we propose a method to accurately measure human HR by simply using a smartphone camera. We use three special approaches for HR estimation. Firstly, we fuse the raw data by subtracting G channel from R channel to enhance the heartbeat signal from video data. Secondly, instead of the entire palm, we select a region of interest (ROI) from the palm for heart rate detection based on signal-to-noise ratio (SNR) maps, which reduces the proportion of the weak signal area. Thirdly, after applying Fast Fourier Transform (FFT) analyses of the time-series data from the video, we set an interval threshold based on the heart rate range to accurately determine heart rate. With a reference HR value measured by electrocardiography (ECG), the detection rate of the proposed method is 95.84% (overall result from 30 test subjects) when used for measurement at an ambient light intensity of 150 lux within a distance of 4.5 meters. The method's strong adaptability to changing ambient conditions and ease of implementation makes it applicable to many scenarios, such as homes of the elderly, classrooms, and other public spaces.