The calculation of F1 Score, Precision, and Recall considers "the characters in both images are the same" as a positive case. Threshold is determined by finding the maximum value on the F1 Score curve.
Cluster_2 represents the approximate optimal clustering solution obtained by tuning the eps value in DBSCAN clustering algorithm with min_samples set to 2, and evaluating the similarity between the obtained clusters and the true distribution using the random_adjust_score.
Cluster_Free represents the approximate optimal solution obtained by tuning the max_eps and min_samples values in the OPTICS clustering algorithm, and evaluating the similarity between the obtained clusters and the true distribution using the random_adjust_score.