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pgmmorphconv

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Updated: 29 March 2015
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Table Of Contents
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NAME

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pgmmorphconv - perform morphological convolutions: dilation, erosion
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SYNOPSIS

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pgmmorphconv
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[
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 -erode |
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 -dilate |
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 -open |
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 -close |
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 -gradient
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]
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templatefile
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[pgmfile]
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Minimum unique abbreviation of option is acceptable. You may use

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double hyphens instead of single hyphen to denote options.  You may use
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white space in place of the equals sign to separate an option name
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from its value.
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DESCRIPTION

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This program is part of Netpbm.

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pgmmorphconv performs morphological convolutions on a

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PGM image: dilation and erosion.
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pgmmorphconv performs a "topological" convolution. For each

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pixel of the input, pgmmorphconv generates an output pixel in
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the same position.  To determine the intensity of the output pixel,
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pgmmorphconv lays the template image over the input image such
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that the middle pixel of the template is over the input pixel in
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question.  pgmmorphconv looks at the input pixels underneath each
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white pixel in the template.  For a dilation, the maximum intensity of
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all those pixels is the intensity of the output pixel.  For an erosion,
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it is the minimum.
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Thus, the dilation effect is that bright areas of the input get bigger

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and dark areas smaller.  The erosion effect is the opposite.  The simplest
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template image would be one with a white pixel in the middle and the rest
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black.  This would produce an output image identical to the input.  Another
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simple template image is a fully white square.  This causes bright or dark
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areas to expand in all directions.  A template image that is white on the
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left side and black on the right would smear the image to the right.
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The template file named by templatefile contains the

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template image as a PBM image.  It must have an odd number of rows and
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an odd number of columns, so there is a definite middle pixel.  It
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must contain at least one white pixel.
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This is similar to the continuous convolution done by

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pnmconvol, except that with pnmconvol the output intensity is
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a weighted average of nearby input pixels instead of a minimum or maximum.
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This convolution changes the three Minkowski integrals in a predefined

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way, and can be used to filter an image to enhance certain features, to
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ease their automatic recognition.
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The options -erode and -dilate obviously produce an

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erosion or dilation, respectively.  

The -open option causes

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pgmmorphconv to perform first an erode and then a dilate
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operation.  The -close option causes a dilate first and then an
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erode.  If you specify none of these options, it is the same as
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-dilate.
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With -gradient, pgmmorphconv produces an image which is the

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difference between the eroded image and the dilated image.  -gradient
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was new in Netpbm 10.70 (March 2015).
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SEE ALSO

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  • pgmminkowski
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  • pnmconvol
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  • pgm
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    For more information about morphological convolutions, see e.g.

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      href="http://rugth30.phys.rug.nl/compphys0/2001.htm"> K. Michielsen and
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      H. De Raedt, "Integral-Geometry Morphological Image Analysis",
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      Phys. Rep. 347, 461-538 (2001).
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      J.S. Kole, K. Michielsen, and H. De Raedt,
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      "Morphological Image Analysis of Quantum Motion in Billiards",
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      Phys. Rev. E 63, 016201-1 - 016201-7 (2001)
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      AUTHORS

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      Luuk van Dijk, 2001.
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      Based on work which is Copyright (C) 1989, 1991 by Jef Poskanzer.

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      Table Of Contents

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      • SYNOPSIS
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      • DESCRIPTION
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      • SEE ALSO
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      • AUTHORS
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