# A Survey of Photoplethysmography and Imaging Photoplethysmography Quality Assessment Methods
## 4 SQI for cPPG
### Rule-Based
#### 4.1.1 Criteria Based on Signal Features
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Scale** & **Domain** & **Features** & **References** \\ \hline \multirow{8}{*}{Pulse} & & & Pulse amplitude & [44,45,68,69] \\ \cline{3-5}  & & Amplitude & Area under pulse & [44,45] \\ \cline{3-5}  & & & Mean, std of pulse waveform & [35,37] \\ \cline{3-5}  & Temporal & Temporal & Pulse width & [44,45] \\ \cline{3-5}  & & Temporal & Pulse rate & [36,70] \\ \cline{3-5}  & & & Ratio of maximum positive & \\ \cline{3-5}  & & Derivative & slope over minimum & [59] \\ \cline{3-5}  & & & negative slope & \\ \cline{3-5}  & Spectral & Entropy & [51] \\ \cline{3-5}  & & Principal frequencies and residual noise & [69] \\ \cline{3-5}  & & & Skewness & [37,50,51,57,69] \\ \cline{3-5}  & Statistical & & Kurtosis & [37,50,51,57,69] \\ \cline{3-5}  & & & IBI & [35,37,46,59,71] \\ \cline{3-5}  & & & Successive IBI & [59] \\ \cline{3-5}  & & & Inter-foot interval & [46] \\ \cline{3-5}  & & Amplitude difference between successive peaks (mean, std) & [35,37,44,45,46] \\ \cline{3-5}  & & Amplitude difference between successive feet & [46,69] \\ \cline{3-5}  & & Difference between pulse widths & [44,45] \\ \cline{3-5}  & & Difference between rising times & [44,45] \\ \hline \multirow{8}{*}{Temporal} & & Amplitude of the signal & [48,72] \\ \cline{3-5}  & & Difference between autocorrelation of PPG from red and infrared & [48] \\ \cline{3-5}  & & Ratio of oxygenated and deoxygenated blood measured & [48] \\ \cline{3-5}  & & Ratio between systolic and diastolic time & [35] \\ \cline{3-5}  & & Kurtosis & [58] \\ \cline{3-5}  & & Shannon entropy on signal amplitude distribution & [47,58] \\ \cline{3-5}  & & Shannon entropy on signal amplitude distribution & [47,58] \\ \cline{3-5}  & & Permutation and sample entropy & [73] \\ \cline{3-5}  & & Predictor (autoregressive model) coefficients fitted on 5 s signals & [66] \\ \hline \multirow{8}{*}{Signal} & & & Residual noise & [36] \\ \cline{3-5}  & & & Projected frequency modulation & [36] \\ \cline{3-5}  & & & difference between PR and IBI & [36] \\ \cline{3-5}  & & & Difference and amplitude of dominant & [74,75] \\ \cline{3-5}  & Spectral & & frequencies in PR range & [74] \\ \cline{3-5}  & & & Energy of non-dominant frequencies in & [74] \\ \cline{3-5}  & & & PR range & [75] \\ \cline{3-5}  & & & Variation of dominant frequencies with & [75] \\ \cline{3-5}  & & & time & [37] \\ \cline{3-5}  & & & Spectral entropy & [73] \\ \cline{3-5}  & & & Hjort parameters & [37] \\ \hline \multirow{8}{*}{Statistics} & & SNR & [47,51] \\ \cline{3-5}  & & Variance of the signal & [37] \\ \cline{3-5}  & & 2 first peaks of correlogram of the signal & [47] \\ \cline{3-5}  & & First peak amplitude and time and number of zero crossing of the auto-correlation of the & [72] \\ \cline{3-5}  & & signal & [73] \\ \cline{3-5}  & & Detrended Fluctuation Analysis, Fractal Dimension, and Higuchi Fractal Dimension & [73] \\ \hline \hline \end{tabular}  
* IBI = Inter-Beat Interval, PR = Pulse Rate, SNR = Signal to Noise Ratio, std = Standard Deviation.  
\end{table} 
Table 4: Enumeration of the different PPG signal features extracted for the assessment of its quality.