A Comparison of Bounding Box and Landmark Detection Methods for
  Video-Based Heart Rate Estimation
Laurence Liang
Remote Photoplethysmography (rPPG) uses the cyclic variation of skin tone on
a person's forehead region to estimate that person's heart rate. This paper
compares two methods: a bounding box-based method and a
landmark-detection-based method to estimate heart rate, and discovered that the
landmark-based approach has a smaller variance in terms of model results with a
standard deviation that is more than 4 times smaller (4.171 compared to
18.720).