Reducing the effects of parallax in camera-based pulse-oximetry

Abstract

Camera-based pulse-oximetry enables contactless estimation of peripheral oxygen saturation (SpO 2 ). Because of the lack of readily available and affordable single-optics multi-spectral cameras, custom-made multi-camera setups with different optical filters are currently mostly used. The introduced parallax by these cameras could however jeopardise the SpO 2 algorithm assumptions, especially during subject movement. In this paper we investigate the effect of parallax quantitatively by creating a large dataset consisting of 150 videos with three different parallax settings and with realistic and challenging motion scenarios. We estimate oxygen saturation values with a previously used global frame registration method and with a newly proposed adaptive local registration method to further reduce the parallax-induced image misalignment. We found that the amount of parallax has an important effect on the accuracy of the SpO 2 measurement during movement and that the proposed local image registration reduces the error by more than a factor of 2 for the most common motion scenarios during screening. Extrapolation of the results suggests that the error during the most challenging motion scenario can be reduced to approximately 2 percent when using a parallax-free single-optics camera. This study provides important insights on the possible applications and use cases of remote pulse-oximetry with current affordable and readily available cameras.