**Appendix A. Ambiguous Organ Classes**

This section illustrates examples of ambiguous frames due to lacking a clearly defined transition between tissue classes.

(**e**) (**f**)

**Figure A1.** Examples of images with similar imaging features, which are lacking a hard definable border for a classification label. (**a**–**c**) contain images that represent the transition area from stomach to the Barrett's esophagus, which all contain features, like gastric folds, and (**a**,**b**) also include a view into the stomach. (**d**–**f**) contain representations seen around the transition from Barrett's esophagus to healthy squamous tissue, which all contain visual features from the Barrett's esophagus and squamous tissue. (**a**) Cardia of the stomach labeled as 'Stomach'. (**b**) Image captured after the esophageal sphincter labeled as 'transition Z-line'. (**c**) Contracted Barrett's esophagus labeled as 'Barrett'. (**d**) Barrett's esophagus with healthy squamous tissue falling into the field of view labeled as 'Barrett'. (**e**) Transition zone between Barrett's esophagus and healthy squamous tissue, labeled as 'transition squamous. (**f**) Mostly squamous tissue, with Barrett's esophagus in the background, labeled as 'squamous'.
