Abstract
Many camera-based remote photoplethysmography (PPG) applications require sensing in near infrared (NIR). The performance of PPG systems benefits from multi-wavelength processing. The illumination source in such system is explored in this paper. We demonstrate that multiple narrow-band LEDs have inferior color homogeneity compared to broadband light sources. Therefore, we consider the broadband option based on phosphor material excited by LEDs. A first prototype was realized and its details are discussed. It was tested within a remote-PPG monitoring scenario in darkness and the full system demonstrates robust pulse-rate measurement. Given its accuracy in pulse rate extraction, the proposed illumination principle is considered a valuable asset for large-scale NIR-PPG applications as it enables multi-wavelength processing, lightweight set-ups with relatively low-power infrared light sources.
Highlights
Camera-based remote photoplethysmography enables contactless measurement of the cardiac pulse by detecting the pulse-induced subtle color changes from the human skin surface [1]
Since we cannot incorporate two different light sources in the same video recording for a synchronous comparison, we have to compare to the results obtained in a different study with the incandescent light source and such comparison will be on a qualitative level
From preliminary experiments on the prototyped light source, we found that, when the distance between the light source and test subject is reduced to 0.5 m, a realistic scenario for many applications in particular driver monitoring and home care, only 12 LEDs are required at a total power consumption of 8 W
Summary
Camera-based remote photoplethysmography (remote-PPG) enables contactless measurement of the cardiac pulse by detecting the pulse-induced subtle color changes from the human skin surface [1]. It is desired for low-acute settings or free-living applications, such as baby/elderly care at home [4] and driver monitoring [5] in automotive For automotive, it requires the complete remote-PPG solution, including camera and light source, to be energy efficient, lightweight (for integration), and cost-effective (for large-scale deployment). Various PPG-extraction algorithms [6,7,8,9,10,11,12,13] proposed to address motion challenges profit from the fundamental use of multi-wavelength measurements It enables the measurement of other physiological variables in addition to the pulse rate and it can potentially extend the scope of vital signs monitoring, such as blood oxygen saturation which requires simultaneous measurement of at least two infrared wavelengths
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