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Iterative Morphological Operations

The basic morphological functions are erosion, the removal of pixels from the periphery of a feature, or dilation, the adding of pixels to that periphery. Classical erosion removes any pixel that has a background neighbor (any of the eight neighbors that share an edge or corner). Conversely, classical dilation adds any pixel that touches a pixel in the feature. Of course, both of these operations change the size of features or structures and so they are most often used together. An opening is an erosion followed by a dilation, while a closing is a dilation followed by an erosion. These operations can smooth irregular borders, and fill in or remove isolated pixel noise and fine lines.

This interactive tutorial illustrates the use of iterative morphological operations on a binary image. In the tutorial, each function can be applied multiple times to add or remove more pixels. An opening of M iterations consists of M steps of erosion, followed by M steps of dilation, and vice versa.

The tutorial initializes with a randomly selected specimen appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of thresholded binary images, in addition to the initial randomly chosen one. The Operation buttons select Erosion, Dilation, Opening or Closing. The Iterations slider controls the number of times the selected operation is performed. The Neighborhood Threshold slider controls the conditional test based on the number of neighboring pixels that must be of the opposite color (black or white) for the pixel to change state. Setting this to 0 corresponds to classical morphological operations. The result of the selected operation and settings is shown in the Processed Image at the right.

Contributing Authors

John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.

Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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