Form factor in CellProfiler

Hi, I have some questions on the “form factor” measurement in cellprofiler. I’m aware that form factor for a circular object =1, whereas a more elongated object will have form factor <1. What about when form factor >1? what does that say about the shape of the object?
And I noticed that in some published papers (eg https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2826413/#pone.0009367-Koopman1), form factor is defined as (perimeter2/4πarea) in comparison to cellprofiler, form factor is defined as ( 4π*Area/Perimeter2), why would this definition differ in different analysis?

Thank you in advance

Hi @Sue1,

The two you mention are different scales for a similar measurement. Perimeter^2/4piarea is typically called “form factor”, while the area / perimeter version can sometimes be called “roundness”. It’s mostly a change in units, with the latter a circle starts at 1 and increases as the shape becomes more irregular. This page has more details.

I’m not sure how an object could have a form factor above 1, perhaps it’s label is split across multiple non-touching objects? If you’ve encountered that in a CellProfiler pipeline, it’d be helpful if you could send a copy of the image in question and the pipeline you’ve used. Thanks

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