vmoredge(1)

PROGRAM
vmoredge - Morphological Edge Extraction for Binary Byte Images

SYNTAX

vmoredge

-i  input image

-k  input kernel

-o  output image

[-V]
    Gives the version for vmoredge

[-U]
    Gives the usage for vmoredge

[-P]
    Prompts for command line options

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

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

DESCRIPTION
vmoredge computes an edge extraction in an image by using morphological operations.

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.

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

MORPHOLOGICAL METHOD FOR EDGE DETECTION:

    In image processing, the term edge is not as well defined as the term boundary. It has the intuitive meaning of boundary, but an edge need not be rigorously specified. Indeed an image can have numerous "edges", each one defined by the methodology from which it was derived.

    The purpose of an edge-detection methodology is to compress the image, more than giving a specific mathematical entity.

    The method used to extract an approximation of the true Euclidean boundary of a set A, is to apply the morphological fundamental operations:
    MOREDGE(A,B) = D(A,B) - A

    The thickness of that approximation results from the thickness of the structuring element B.

    This edge can be called external edge.

    It is advisable to use a kernel whose center is located on (0,0) and is not on the border of the kernel itself. If the center is not on the border, the extracted edges will not be continuous. If we take, for example, the square kernel 2x2 with all values set to one and the origin or center located at (0,0), the resulting edge will not be desirable. This is because (0,0) is on the border of the kernel, so the dilation operation will not dilate the region in all directions. When the morphological subtraction is processed, the upper border of the regions will not be detected.
    A 3x3 square kernel with all values set to one and the center located at (0,0) will give a correct edge map image. The extracted edges will have a thickness of one.

The structuring element must be a morphological kernel (created by vmcustom). This kernel is nothing but an image file with two variables, ispare1 and ispare2 that define the origin of the structuring element (refer to vmcustom and lvmcustom).

This algorithm was 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

-k  type: infile
    desc: input kernel

-o  type: outfile
    desc: output image

OPTIONAL ARGUMENTS
none

EXAMPLES

vmoredge -i image1 -k kernel -o image2
Extract the edges of an image by computing the difference between the original image and the dilation by the input kernel.

SEE ALSO
intro(1), verror(3), vgparms(3), vutils(3), lvmoredge(3) vmcustom(1), lvmcustom(3), lvmdilate(3), vmdilate(1)

RESTRICTIONS
vmoredge accepts only Two Valued BYTE images, so it is strongly advisable to use vthresh before using vmoredge.

The structuring element is an image file, nevertheless, it should always be created by vmcustom.

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