While running very quickly, the Inflection Method unfortunately only works for highly populated plates, as shown below.
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Densely populated plate: 4th order polynomial is a good fit. Optimal sensitivity: 0.9284
Using this sensitivity setting returns a count of 1205. It failed to detect 24 colonies and detected 39 false positives, but most of the false positives can addressed by cropping the edge of the petri dish out of the detection zone.
Sparsely populated plate: not 4th order polynomial. Optimal sensitivity: Cannot be determined using this method.
Sparsely populated plate