Measurement of heart rate from long-distance videos via projection of rotated orthogonal bases in POS

Remote photoplethysmography (rPPG) has long been an active research topic. Existing rPPG approaches achieve high accuracy of heart rate extraction, as long as the user is relatively close to the camera (typically, less than 1 meter distance). This article investigates the performance of existing rPPG approaches under the long-distance recording conditions and proposes a novel Projection of Rotated Orthogonal Bases in POS (ProPOS) algorithm for heart rate extraction. A set of orthogonal projection bases is generated around the original plain of POS algorithm. The raw measurement traces are projected on these bases and the final output signal is obtained by a designed SNR selection criterion. The long-distance rPPG (LD-rPPG) dataset is established for long-distance rPPG research by varying the recording distance from 3 m-30 m. Extensive experiments are performed in comparison with existing approaches. Experiments show that videos recorded by HikVision DS-V108 and Logitech C920 cameras contain a certain amount of physiological signal whereas the videos recorded by HikVision DS-U102D and Mercury cameras contain little physiological signal. Using zoom lenses is beneficial to improve the rPPG measurement accuracy under long-distance conditions.