Non-contact Measurement of Respiration Rate with Camera-based Photoplethysmography During Rest and Mental Stress

Cameras offer new possibilities in assessing human states like stress. This work addresses the measurement of respiration rate with several approaches. Data from a mental stress study (> 40 h recording time, 54 participants) were evaluated and color channel combinations were examined using a hemispherical surface grid search with mean absolute error MAE to optimize the approaches. The grid search converged towards the green channel in the baseline modulation approach
$(MAE= 2.53 rpm$
). However, best results were achieved with the frequency modulation approach
$(MAE=2.13$
rpm) with the color channel combination optimal for heart rate measurement. Respiration rate increased highly significant during stress (
$p < 0.001$
, Mann-Whitney U-test). Deliberate selection of the color channel combination is crucial for respiration rate measurement with cameras in order to assess human states or pathophysiological processes.