Figure 11: Proper spatial pooling is imperative for revealing the signal of interest. (a) A frame from the face video (Figure 1) with white Gaussian noise (σ = 0.1 pixel) added. On the right are inten- sity traces over time for the pixel marked blue on the input frame, where (b) shows the trace obtained when the (noisy) sequence is processed with the same spatial filter used to process the original face sequence, a separable binomial filter of size 20, and (c) shows the trace when using a filter tuned according to the estimated radius in Eq. 15, a binomial filter of size 80. The pulse signal is not visi- ble in (b), as the noise level is higher than the power of the signal, while in (c) the pulse is clearly visible (the periodic peaks about one second apart in the trace).