Box plot shows S/N obtained with all the reference libraries created with the correlation method using the optimized zone, identified in the x-axis by the respective N and R values (in the format N_R). The horizontal lines indicate the best S/N achieved with the ADI-PCA full-frame (red dashed line) and optimized zones (orange line), and the single RSDI (green dashed line) and optimized zones (blue line). The maximum S/N value is 9.1, achieved with N=40 and R=50.