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04/29/2008

Blob Tool | Blob Stats

 

Perimeter

The perimeter is an 'iffy' sort of measurement - it often changes dramatically with image resolution.  Given that you want to use perimeter anyway, here are some notes on how Lispix measures it.

The blob perimeter is measured as the sum of the distance between the centers of the outer edges of the pixels (connect the *'s in diagram below).

           .            .           .

This is more accurate than counting pixels or edges. (and between the two in magnitude).

  Note on perimeter length from Joseph Barba, Kin S. Chan and Joan Gil,

 

 

     For polygons with uniformly distributed slopes, the length is over estimated by 1.055.

      Perimeter estimator - +2.5% for squares, -5.3% for circles.