Dedicated exposure control for remote photoplethysmography

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.