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GRADIENT

Section: User Commands (1)
Updated: 16 Mar 1998
Index

NAME

gradient, sobel, prewitt, roberts, grad - gradient likeoperators

SYNTAX

gradient [-angle] [-magnitude] [-pseudo]
          [-xscale <xscale>] [-yscale <yscale>]
          [-title  <title>] [-verbose]
          <inimage> <outimage> <xconvfile> <yconvfile>

sobel [-angle] [-magnitude] [-pseudo]
[-title <title>] <inimage> <outimage>

prewitt [-angle] [-magnitude] [-pseudo]
[-title <title>] <inimage> <outimage>

roberts [-angle] [-magnitude] [-pseudo]
[-title <title>] <inimage> <outimage>

grad [-angle] [-magnitude] [-pseudo]
[-title <title>] <inimage> <outimage>

DESCRIPTION

gradientperforms a gradient operator on the input imageinimageand writes the result to outimage.

The convolution kernels are specified by xconvfileandyconvfile.

sobel,roberts,prewittand graduse standardconvolution kernels (see below).

OPTIONS

-magnitude

Combine horizontal and vertical contributions by addingthe absolute values.
magnitude = |convx| + |convy|

-angel

Combine horizontal and vertical contributions by calculatingthe gradient angle.
angle = atan(convy/convx)

-pseudo

Combine horizontal and vertical contributions by combiningthe magnitude and angle into a pseudo image.
pseudo = pseudo combination of magnitude and angle

The pseudo comination of magnitude and pseudo:
mag level = magnitude / 32;
  Level  First Length
      0      0      4
      1      4     12
      2     16     20
      3     36     28
      4     64     36
      5    100     44
      6    144     52
      7    196     60
pseudo = first[level] + angle/256*length[level]

The pseudo-image may be displayed with a "gradient"color-table.

-xscale xscale

Scale magnitude data. Default is xscale=0, which givesautoscaling.
xpix = (xconv. result) * xscale

-yscale yscale

Scale magnitude data. Default is yscale=0, which givesautoscaling.
ypix = (yconv. result) * yscale;

-title title

Set title of output image to title.

-verbose

Write a message if the convolution sum is less than 0 orgreater than 255.

STANDARD CONVOLUTION KERNELS

sobel:

            -1 0 1                 -1 -2 -1
xconv =    -2 0 2        yconv =   0  0  0
            -1 0 1                  1  2  1

prewitt

            -1 0 1                 -1 -1 -1
xconv =    -1 0 1        yconv =   0  0  0
            -1 0 1                  1  1  1

roberts

            1  0                  0  1
xconv =                 yconv =
            0 -1                 -1  0

grad

           -1  1                 -1  0
xconv =                 yconv =
            0  0                  1  0

AUTHOR

Otto Milvang

ID

$Id: gradient_op.c,v 1.34 1997/06/11 09:44:52 svein Exp $

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