vmskel(1)

PROGRAM
vmskel - Computes the skeletonization of a binary byte image

SYNTAX

vmskel

-i  input image filename

-o  output image filename

[-V]
    Gives the version for vmskel

[-U]
    Gives the usage for vmskel

[-P]
    Prompts for command line options

[-A [file1]]
    Creates the answer file called vmskel.ans or file1

[-a [file1]]
    Uses vmskel.ans or file1 as the answer file

DESCRIPTION
vmskel Computes the skeleton of a binary byte image using a fixed disk as the structuring element.

From a general scientific perspective, the word MORPHOLOGY refers to the study of form and structure.

The morphological approach is generally based upon the analysis of a two valued image in terms of some predetermined geometric shape known as a structuring element. Essentially, the manner in which the structuring element fits into the image is studied.

The morphological operations can be employed for many purposes, including edge detection, segmentation, and enhancement of images.

BASIC OPERATIONS :

Most morphological operations can be defined in terms of two basic operations, EROSION (i.e. vmerode) and DILATION (i.e. vmdilate)

SKELETON
The skeleton or medial axis algorithm thins by creating an archetypal stick figure that internally locates the central axis of the figure. The skeleton of a set S in the Euclidean plane is defined in the following manner:

    For each x in S, let D(x) denote the largest disk centered at x such that, D(x) is a subset of S. Then x is in the skeleton of S, if there does not exist a disk Ds, not necessarily centered at x, such that Ds properly contains D(x), and Ds is contained in S.

There are several ways to define a digital version of Euclidean disks; we will use square disks. This method is used in the book referenced at the end of this description.

This method does not guarantee a continuous skeleton, but does guarantee a thin skeleton.
Also, the skeleton of a square, rectangle, etc. can be substantly different from the classic result obtained in continuous morphology.

ADVICE:

    For this skeleton function, all grey levels different from 0 are considered "white" or equivalent to 255. Therefore, the image is not required to be binary, however, it is strongly advisable to use vthresh on grey level images before using any morphological function.

These algorithms were obtained from:

    "Morphological Methods in Image and Signal Processing"
    Charles R. Giardina
    Edward R. Dougherty
    Prentice Hall, Englewood Cliffs, New Jersey 07632

REQUIRED ARGUMENTS

-i  type: infile
    desc: input image filename

-o  type: outfile
    desc: output image filename

OPTIONAL ARGUMENTS
none

EXAMPLES

vmskel -i image1 -o image2
Computes the skeletonisation of a byte binary image (image1). The result is stored in image2.

SEE ALSO
intro(1), verror(3), vgparms(3), vutils(3), lvmskel(3) vmdilate(1), lvmdilate(3), vmerode(1), lvmerode(3), vmopen(1), lvmopen(3), vmclose(1), lvmclose(3), vxor(1), lvxor(3)

RESTRICTIONS
vmskel accepts only BYTE images, and it is strongly advisable to use vthresh to binarize the image before eroding it.

COPYRIGHT
Copyright 1991, University of New Mexico. All rights reserved.