Heart rate estimation with monochrome cameras. (a) RGB signals captured from the subject’s forehead in a normal ambient lighting condition. Pulse signal determined from RGB signals using the POS method. (b) Effect of region of interest (ROI) on HR estimation accuracy. Skin. Seg. means skin segmentation. !forehead means excluding forehead. (c) Effect of detection latency (amount of time spent capturing data before estimating HR) on HR estimation accuracy. (d) Effect of ROI resolution on HR estimation accuracy. The ROI resolution (i.e., forehead resolution) captured by a 5 MP monochrome camera at 1 m, 2 m, and 3 m is displayed.