ORIGIN PCA thresholds. The left image displays the field segmentation in 6 zones. The 6 plots show the corresponding histograms of the PCA test statistics for each zone. The red curves exhibit the Gaussian fit of the distribution. The computed thresholds are displayed as blue vertical lines. They identify the minimum value above which the spectrum triggers the PCA cleaning process. This value corresponds to the 10% upper quantile of the empirical distribution.