Dedicated Exposure Control for Remote Photoplethysmography

Abstract

This paper aims to show that control of exposure time during video capture will improve the accuracy of remote photoplethysmography (rPPG). We propose a purpose specific exposure control algorithm for use in heart rate estimation via rPPG applicable for any controllable camera. Our novel algorithm works by selecting exposure that acheives maximum Signal-to-Noise Ratio (SNR) before distortion will occur. We performed experiments to test the accuracy of non-contact PPG extracted simultaneously from two identical cameras positioned together but with different exposure time controls. Our purpose specific algorithm in camera A controlled exposure time to maximise rPPG SNR ratio while camera B remained set at one of a range of values. Exposure time set by our novel algorithm out-performed camera B with a lower mean absolute error relative to a standard pulse oximeter. A significant improvement to heart rate estimation performance using a research camera can be made with specific control of exposure time. The improvements in performance demonstrated here are an important step in taking rPPG out of a lab environment and into less controlled circumstances such clinical settings and emergency rescue scenarios.

Non-Contact SpO2 Prediction System Based on a Digital Camera

“…Colour-based techniques using cameras in a variety of forms (such as digital cameras, thermal cameras, IR cameras, Webcams, drone and Kinect), sometimes called imaging photoplethysmography (iPPG), have been widely used in healthcare for monitoring applications, especially to evaluate vital signs, including heart rate (HR) [14][15][16][17], heart rate variability (HRV) [18][19][20], breathing rate (BR) [21][22][23] and blood pressure (BP) [24][25][26]. The principle of iPPG is the non-contact monitoring of human cardiac synchronous variations by detecting optical features passing through or reflecting from the epidermis captured by a camera sensor.…”