while photoplethysmography commonly requires some form of contact with the human skin (e.g., ear, finger), remote photoplethysmography allows to determine physiological processes such as blood flow without skin contact. this is achieved by using face video to analyze subtle momentary changes in the subject's skin color which are not detectable to the human eye. such camera-based measurement of blood oxygen levels provides a contactless alternative to conventional photoplethysmography. for instance, it can be used to monitor the heart rate of newborn babies.