Fig. 1
A representative example of Eulerian Video Magnification image processing of a gray seal (Halichoerus grypus) infrared video. Ai. In the raw infrared video without magnification, there is no visible temporal variation in thermal signatures, as demonstrated by the spatiotemporal slices (Aii.). Aiii. Signal intensity did not vary over time nor was there a peak frequency intensity. Bi. When the infrared video was magnified 40 × with a 0.1–3.5 Hz passband, there was substantial variation in signal intensity through time (Bii.). Biii. The frequency domain had a clear peak at 0.63 Hz which is assumed to be RR, and 0.63 Hz = 38 breaths per minute (brpm). The ‘true’ RR was 40 brpm. To ensure the narrow passband is not dominated by the RR peak, the narrow passband will be chosen to exclude 0.63 Hz. Ci. The infrared video was magnified 40 × with a 1–2 Hz passband, resulting in variation across spatiotemporal slices (Cii.), the frequency domain had an obvious peak at 1.64 Hz which is assumed to be HR (Ciii.), and 1.64 Hz = 98.4 beats per minute (bpm). The ‘true’ HR via stethoscope was 104 bpm