Study on the influence of polarization characteristics of light on rPPG signal
Guangdianzi Jiguang/Journal of Optoelectronics Laser
Remote Photoplethysmography (rPPG) realizes heart rate measurement by capturing facial video and analyzing the periodic changes of the average gray level in the range of interest (ROI). Noise elimination is one of the key techniques in rPPG systems. Among all the noises, diffuse light on the skin surface is a recognized common noise. According to the principle of interaction between light and biological tissues, backscattered light without contact with subcutaneous artery should also be considered as noise, which is called 'shallow noise' in this paper. According to the author's literature research, there is no research paper on this noise and its elimination method in the rPPG research field. In this paper, the polarization characteristics of the imaging beam is systematically analyzed to improve the polarization based noise elimination technique, the results show that: (1) When the incident light is S- or P- wave, the polarization direction of the backscattered and incident light is different. In this case, the diffuse light and shallow noise cannot be completely eliminated by making the analyzer and polarizer orthogonal. The analyzer should be orthogonal to the imaging beam; (2) The polarization degree of the imaging beam is not evenly distributed. The polarization degree of the forehead is the highest, which can be used to optimize ROI selection. The results of this paper are helpful for rPPG systems based on polarization imaging to achieve better signal quality and improve the accuracy of heart rate measurement.
Open Access Status
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