(a) Representative BF TEM image of an image used for validation with its (b) hand tracing and (c) postprocessed U-Net output overlaid in yellow. Boundaries are dilated for clarity. Grain size distributions obtained from the validation data via (d) hand tracings and (e) U-Net measurements. Log-normal fits are shown as solid curves. Insets: Corresponding normal Q–Q plot for the logs of the reduced diameters with a normal distribution shown as a solid line.