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Computes the length of the input region perimeter.

Name Type Description
inRegion Region Input region
outPerimeterLength Real


The operation computes the perimeter length of a region shape. Because regions are pixel-precise, the literal computation of the length of the region contour would lead to the overestimation of the diagonal edges. Therefore, the filter employs the following equation to approximate the result:


  • sides denotes the number of pixel sides adjacent to the region background
  • vertices is the number of turns to right during clockwise walk along the pixel sides of the region boundary
  • a, b are constants defined as follows:

To compute the actual contour of the region, one can use RegionContours filter.


RegionPerimeterLength run on the sample region (circular region of radius 100) computes outPerimeterLength = 627.382, while the actual perimeter of the perfect circle of radius 100 is 628.318 .

Complexity Level

This filter is available on Basic Complexity Level.

See Also

  • RegionContours – Computes an array of closed paths corresponding to the contours of the input region.
  • RegionDiameter – Computes the longest segment connecting two pixels contained in region and its length.