about elgendi method in ppg

[epsilon-deltta]

I wanted to know about that elgendi process in more detail. but, that paper[1] only handled electrocardiogram (ECG), impedance cardiogram (ICG), electromyogram (EMG), electrodermal activity (EDA), and continuous, noninvasive arterial blood pressure (BP).
there is no ppg preprocessing. could u explain this? (how elgendi method in ppg works)

[1] Nabian, Mohsen, et al. "An open-source feature extraction tool for the analysis of peripheral physiological data." IEEE Journal of Translational Engineering in Health and Medicine 6 (2018): 1-11.

[epsilon-deltta]

i got that