Pgmmorphconv User Manual(0) Pgmmorphconv User Manual(0)
pgmmorphconv - perform morphological convolutions: dilation, erosion
pgmmorphconv [ -erode | -dilate | -open | -close ] templatefile [pgm-
Minimum unique abbreviation of option is acceptable. You may use dou-
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name from
This program is part of Netpbm(1).
pgmmorphconv performs morphological convolutions on a PGM image: dila-
tion and erosion.
pgmmorphconv performs a "topological" convolution. For each pixel of
the input, pgmmorphconv generates an output pixel in the same position.
To determine the intensity of the output pixel, pgmmorphconv lays the
template image over the input image such that the middle pixel of the
template is over the input pixel in question. pgmmorphconv looks at
the input pixels underneath each white pixel in the template. For a
dilation, the maximum intensity of all those pixels is the intensity of
the output pixel. For an erosion, it is the minimum.
Thus, the dilation effect is that bright areas of the input get bigger
and dark areas smaller. The erosion effect is the opposite. The sim-
plest template image would be one with a white pixel in the middle and
the rest black. This would produce an output image identical to the
input. Another simple template image is a fully white square. This
causes bright or dark areas to expand in all directions. A template
image that is white on the left side and black on the right would smear
the image to the right.
The template file named by templatefile contains the template image as
a PBM image. It must have an odd number of rows and an odd number of
columns, so there is a definite middle pixel. It must contain at least
one white pixel.
This is similar to the continuous convolution done by pnmconvol, except
that with pnmconvol the output intensity is a weighted average of
nearby input pixels instead of a minimum or maximum.
This convolution changes the three Minkowski integrals in a predefined
way, and can be used to filter an image to enhance certain features, to
ease their automatic recognition.
The options -erode and -dilate obviously produce an erosion or dila-
The -open option causes pgmmorphconv to perform first an erode and then
a dilate operation. The -close option causes a dilate first and then
an erode. If you specify none of these options, it is the same as
pgmminkowski(1) pnmconvolz(1) pgm(1)
Luuk van Dijk, 2001.
Based on work which is Copyright (C) 1989, 1991 by Jef Poskanzer.
netpbm documentation 29 October 2002 Pgmmorphconv User Manual(0)
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