Potatoes were purchased directly from a packinghouse (Patatas
Aguilar, S.A., Valencia, Spain) which carries out the grading and
sorting processes either manually or mechanically. During the process
inside the packinghouse, the potatoes were mechanically
cleaned and washed to remove all dirt and clay clouds and then
transferred in front of workers to pick up sprouted, infected, damaged
and all undesirable tubers. In this study, rather than sampling
the potatoes randomly we intentionally selected tubers of various
sizes and shapes as a training/learning set to cover as much as possible
the full spectrum in potato size and regularity. Indeed, establishing
discrimination boundaries using shape information usually
requires inspection and grading by an experienced human expert.
The tubers were first classified manually by a professional inspector
into regular and misshapen (irregular) tubers. The judgement of
a good shape or a misshapen potato was performed from a viewpoint
of the regularity of the tuber shape. The irregular potatoes
could include any potato suffering from serious cuts, misshapen
or with the presence of secondary-grown tubers called bead-like
tubers or secondary tubers. Fig