A calibration method for smartphone camera photophlethysmography

• Published in: Frontiers in digital health Vol. 5; p. 1301019
• Main Authors: Xuan, Yinan, Barry, Colin, Antipa, Nick, Wang, Edward Jay
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 2023
• Subjects: calibration; camera; hemoglobin; photoplethysmography; pulse oximetry; smartphone; pulse oximetry; smartphone; photoplethysmography; camera; calibration; hemoglobin
• ISSN: 2673-253X; 2673-253X
• DOI: 10.3389/fdgth.2023.1301019

Smartphone camera photoplethysmography (cPPG) enables non-invasive pulse oximetry and hemoglobin concentration measurements. However, the aesthetic-driven non-linearity in default image capture and preprocessing pipelines poses challenges for consistency and transferability of cPPG across devices. This work identifies two key parameters-tone mapping and sensor threshold-that significantly impact cPPG measurements. We propose a novel calibration method to linearize camera measurements, thus enhancing consistency and transferability of cPPG across devices. A benchtop calibration system is also presented, leveraging a microcontroller and LED setup to characterize these parameters for each phone model. Our validation studies demonstrate that, with appropriate calibration and camera settings, cPPG applications can achieve 74% higher accuracy than with default settings. Moreover, our calibration method proves effective across different smartphone models ( ), and calibrations performed on one phone can be applied to other smartphones of the same model ( ), enhancing consistency and scalability of cPPG applications.