Heart rate estimation network from facial videos using spatiotemporal feature image.

Remote health monitoring has become quite inevitable after SARS-CoV-2 pandemic and continues to be accepted as a measure of healthcare in future too. However, contact-less measurement of vital sign, like Heart Rate(HR) is quite difficult to measure because, the amplitude of physiological signal is very weak and can be easily degraded due to noise. The various sources of noise are head movements, variation in illumination or acquisition devices. In this paper, a video-based noise-less cardiopulmonary measurement is proposed. 3D videos are converted to 2D Spatio-Temporal Images (STI), which suppresses noise while preserving temporal information of Remote Photoplethysmography(rPPG) signal. The proposed model projects a new motion representation to CNN derived using wavelets, which enables estimation of HR under heterogeneous lighting condition and continuous motion. STI is formed by the concatenation of feature vectors obtained after wavelet decomposition of subsequent frames. STI is provided as input to CNN for mapping the corresponding HR values. The proposed approach utilizes the ability of CNN to visualize patterns. Proposed approach yields better results in terms of estimation of HR on four benchmark dataset such as MAHNOB-HCI, MMSE-HR, UBFC-rPPG and VIPL-HR.