Non-Contact Reflectance Photoplethysmography: Progress, Limitations, and Myths
Photoplethysmography (PPG) is a non-invasive method of measuring changes of blood volume in human tissue. The literature on non-contact reflectance PPG related to cardiovascular activity is extensively reviewed. We identify key factors limiting the performance of the PPG methods and reproducibility of the research as: a lack of publicly available datasets and incomplete description of data used in published experiments (missing details on video compression, lighting setup and subject's skin type), use of unreliable pulse oximeter devices for ground-truth reference and missing standard experimental protocols. Two experiments with 5 participants are presented showing that the quality of the reconstructed signal (1) is adversely affected by a reduction of spatial resolution that also amplifies the effects of H.264 video compression and (2) is improved by precise pixel-to-pixel stabilization.