Simplified layout of the experiment.

<p>Video of subject’s palm and electrocardiogram were simultaneously recorded. Green illumination of the palm was switched to the NIR and vice versa in a frame-to-frame regime.</p

Influence of the skin-glass contact on the PPG amplitude measured at green and NIR wavelengths.

<p>(a) Average PPG amplitude measured in “hot” spots in the contact experiment (Gl) and in respective spots in the contactless experiment (NC). Here Gr and NIR stand for green (525 nm) and NIR (810 nm) illumination, respectively. (b) Ratio of the mean amplitude measured in the glass-contact to that in the contactless experiment for both wavelengths. The individual measurements are shown by circles, whereas the bars represent mean values for the whole data sets.</p

Spatial and amplitude correlation of changes induced by the skin-glass contact at green and NIR illumination.

<p>(a) The shift between the centers of the “hot” spots in the amplitude maps found at green and NIR illumination for all studied subjects. (b) Scatter plot of the PPG-amplitude increase due to the contact calculated at green and NIR illumination.</p