“…In this way, the raw signals for each ROI are obtained: with i = 1,..., N, where N is the number of frames. We then proceed with the conditioning of the raw signals, which involves two steps: (i) raw r-PPG signals detrending [ 18 , 44 , 45 ] and (ii) smoothness prior approach (SPA) [ 10 , 15 , 46 , 47 , 48 , 49 ]. At this point, for each ROI, we obtain a three-dimensional signal in time, where the three RGB channels represent the three dimensions.…”