gradient

Contents

• Name
• Syntax
• Description
• Options
• Standard convolution kernels
• See also
• Author
• Id

Name

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

Options

-magnitude

Combine horizontal and vertical contributions by adding the absolute values.

 magnitude = |convx| + |convy|

-angel

Combine horizontal and vertical contributions by calculating the gradient angle.

 angle = atan(convy/convx)

-pseudo

Combine horizontal and vertical contributions by combining the 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 gives autoscaling.

 xpix = (xconv. result) * xscale

-yscale yscale

Scale magnitude data. Default is yscale=0, which gives autoscaling.

 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 or greater 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

See also

Author

Id