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. 2021 Sep 20;21(18):6296. doi: 10.3390/s21186296

Figure 1.

Figure 1

Principle of remote photoplethysmography (rPPG) based on the dichromatic reflection model (DRM). The digital camera captures the specular and diffuse reflection from ambient light. The specular reflection contains surface information that does not relate to physiological signals, while the diffuse reflection is modulated by blood flow. The rPPG signal can be obtained from further signal processing.