
vdistance(1)                 Khoros                  vdistance(1)

PROGRAM
     vdistance - Computes the distance from the boundary in a
     two_valued byte image.

SYNTAX
     vdistance

     -i             input image

     -o             output image

     [-V]           Gives the version for vdistance

     [-U]           Gives the usage for vdistance

     [-P]           Prompts for command line options

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

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

DESCRIPTION
     vdistance Computes the distance from the nearest boundary
     point.

     The distance transform uses the following iterative algo-
     rithm :

     U(m,n) : original image. This image contains only two gray
     levels, 0 for the background, and any other value for the
     objects.

     Uk(i,j): image after k iterations.

     U0(m,n)= U(m,n),  and for k= 1, 2, 3, ...

     Uk(m,n)= U0(m,n)+min{Uk-1(i,j);((i,j):dist(m,n;i,j)<= 1)},

          dist(m,n;i,j) is the distance between (m,n) and (i,j).

          dist(i,j-1;i,j) = dist(i,j+1;i,j) =dist(i-1,j;i,j)
          =dist(i+1,j;i,j) = 1.

          dist(i-1,j-1;i,j) = dist(i+1,j-1;i,j) =dist(i-
          1,j+1;i,j) =dist(i+1,j+1;i,j) = 2.

     The transform is completed when k equals the maximum thick-
     ness of the region. That is, when Uk+1 equals Uk.

     The distance image can be used to extract edges or the
     medial axis (form of skeleton).

     Set of functions that can be used with vdistance:

     vmedian     Customizes the medial axis from the distance
                 image.

     vthresh     Generates a binary image.

     ADVICE: For this routine, the image must be a byte binary
     image, with the gray-level value 0 for the background.
     It is advisable to use vthresh prior to using vdistance.

REQUIRED ARGUMENTS
     -i     type: infile
            desc: input image

     -o     type: outfile
            desc: output image

OPTIONAL ARGUMENTS
     none

EXAMPLES
     vdistance -i image1  -o image2
     Computes the distance from the nearest boundary point.
     For this routine, the image has to be a byte binary image,
     with the gray-level value 0 for the background. So it is
     strongly advisable to use vthresh previously to vdistance.

SEE ALSO
     intro(1), verror(3), vgparms(3), vutils(3), lvdistance(3)
     lvthresh(3), vthresh(1).

RESTRICTIONS
     vdistance works only on BYTE binary images which background
     value is zero.

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

Khoros                    Release: 1.0                          1

