# Performance Evaluation of rPPG Approaches with and without the Region-of-Interest Localization Step
## 3 Results
VK: Viola-Jones combined with ROI width reduction and Kanade–Lucas–Tomasi tracker; VK-Conaire: Viola-Jones combined with skin detector based on the maximization of mutual information and Kanade–Lucas–Tomasi tracker; VK-LMK: Viola-Jones combined with landmarks detection and Kanade–Lucas–Tomasi tracker; VK-RGBHCbCr: Viola-Jones combined with RGB–H–CbCr skin-color segmentation and Kanade–Lucas–Tomasi tracker; FVP: Full Video Pulse Extraction rPPG algorithm. Figure 2 shows the performance of studied approaches in combination with two rPPG algorithms (POS and 2 SR) in extracting rPPG signals from video recordings from PURE in terms of SNR. Black horizontal lines denote median SNR values, upper and bottom sides of the boxes the 25 th and 75 th percentiles, and whiskers extend to the values not considered as outliers, which are marked with black diamonds; green triangles denote mean SNR values. The largest SNR values are achieved for the resting scenario, followed by the head translation, the head rotation and the talking scenarios. For the resting and talking scenario, one-way ANOVA showed no statistically significant differences (at \(\alpha=0.05\)) of mean SNR values between all pairs of studied approaches (\(p=0.954\) and \(p=0.260\)). The boxplot of FVP and VK-RGBhCbCr SNR values exhibits the widest interquartile range for the resting and talking scenarios, respectively. For the head translation scenario, one-way ANOVA showed statistically significant differences in mean SNR values between FVP and (1) VK-POS (\(p=0.0013\)), (2) VK-2 SR (\(p=0.0004\)), (3) VK-L \begin{table}
\begin{tabular}{l l l l} \hline  & **VK** & **VK-LMK** & **VK-RGBhCbCr** & **VK-Conaire** \\ \hline PURE & 19,063 \(\pm\) 3581 & 9114 \(\pm\) 1591 & 13,407 \(\pm\) 5339 & 19,984 \(\pm\) 5252 \\ PBDTrPPG & 28,849 \(\pm\) 14,196 & 12,731 \(\pm\) 4498 & 19,514 \(\pm\) 16,015 & 19,128 \(\pm\) 9699 \\ LGI-PPGI-FVD & 38,060 \(\pm\) 13,863 & 14,962 \(\pm\) 7106 & 32,916 \(\pm\) 12,141 & 40,550 \(\pm\) 15,970 \\ \hline \end{tabular}
\end{table} 
Table 2: ROI sizes (in pixels) expressed as a mean \(\pm\) standard deviation for different image-processing front-ends and all studied data sets. VK: Viola-Jones combined with ROI width reduction and Kanade-Lucas–Tomasi tracker; VK-Conaire: Viola-Jones combined with skin detector based on the maximization of mutual information and Kanade–Lucas–Tomasi tracker; VK-LMK: Viola-Jones combined with landmarks detection and Kanade–Lucas–Tomasi tracker; VK-RGBhCbCr: Viola-Jones combined with RGB–H–CbCr skin-color segmentation and Kanade–Lucas–Tomasi tracker; FVP: Full Video Pulse Extraction rPPG algorithm. Figure 2: Performance of the studied approaches with and without ROI localization step in combination with two rPPG algorithms (POS and 2 SR) in terms of SNR for PURE. VK: Viola-Jones combined with ROI width reduction and Kanade-Lucas–Tomasi tracker; VK-Conaire: Viola-Jones combined with skin detector based on the maximization of mutual information and Kanade–Lucas–Tomasi tracker; VK-LMK: Viola-Jones combined with landmarks detection and Kanade-Lucas–Tomasi tracker; VK-RGBhCbCr: Viola-Jones combined with RGB-H-CbCr skin-color segmentation and Kanade-Lucas-Tomasi tracker; FVP: Full Video Pulse Extraction rPPG algorithm. VK-LMK-2 SR (\(p=0.0004\)), (5) VK-RGBHCbCR-POS (\(p=0.0023\)), (6) VK-RGBHCbCR-2 SR (\(p<0.0020\)). The boxplot of VK-Conaire-2 SR SNR values exhibits the widest interquartile range for this recording scenario. For the head rotation scenario, one-way ANOVA showed statistically significant differences in mean SNR values between VK-POS and VK-LMK-2 SR (\(p=0.0002\)), VK-POS and VK-Conaire-2 SR (\(p=0.0029\)), VK-2 SR and FVP (\(p=0.0427\)), VK-LMK-POS and VK-LMK-2 SR (\(p=0.0123\)), VK-LMK-2 SR and VK-RGBHCbCr-POS (\(p=0.0029\)), VK-LMK-2 SR and FV (\(p=0.0001\)), VK-RGBHCbCr-POS and VK-Conaire-2 SR (\(p=0.0267\)), and VK-Conaire-2 SR and FVP (\(p=0.0022\)). Similarly as in the previous recording scenario, the boxplot of VK-Conaire-2 SR SNR values exhibits the widest interquartile range.