SrPPG: Semi-Supervised Adversarial Learning for Remote Photoplethysmography with Noisy Data

Remote Photoplethysmography (rPPG) systems offer contactless, low-cost, and ubiquitous heart rate (HR) monitoring by leveraging the skin-tissue blood volumetric variation-induced reflection. However, collecting large-scale time-synchronized rPPG data is costly and impedes the development of generalized end-to-end deep learning (DL) rPPG models to perform under diverse scenarios. We formulate the rPPG estimation as a generative task of recovering time-series PPG from facial videos and propose SrPPG, a novel semi-supervised adversarial learning framework using heterogeneous, asynchronous, and noisy rPPG data. More specifically, we develop a novel encoder-decoder architecture, where rPPG features are learned from video in a self-supervised manner (encoder) to reconstruct the time-series PPG (decoder/generator) with physics-inspired novel temporal consistency regularization. The generated PPG is scrutinized against the real rPPG signals by a frequency-class conditioned discriminator, forming a generative adversarial network. Thus, SrPPG generates samples without point-wise supervision, alleviating the need for time-synchronized data collection. We experiment and validate SrPPG by amassing three public datasets in heterogeneous settings. SrPPG outperforms both supervised and self-supervised state-of-the-art methods in HR estimation across all datasets without any time-synchronous rPPG data. We also perform extensive experiments to study the optimal generative setting (architecture, joint optimization) and provide insight into the SrPPG behavior.