Figure showing how the optimal threshold for each image type was found. Each image type (IRIS 1400, Original AIA 304 Å RFit AIA 304 Å Deep Filter AIA 304 Å) is binarised at a range of intensity thresholds between 0.1 and 30 DN s⁻¹. For each 0.1 DN s⁻¹ step in this range, the binarised images are correlated with the pre-binarised IRIS 2796 images for the entirety of the evaluation dataset. The resulting correlation coefficients are calculated and then plotted. The threshold for each image type can then be found and are indicated by the dotted lines in the figure.