This program is part of Netpbm(1).
pgmminkowski computes the 3 Minkowski integrals of a PGM image.
The Minkowski integrals mathematically characterize the shapes in the image and hence are the basis of
"morphological image analysis."
Hadwiger's theorem has it that these integrals are the only motion-invariant, additive and conditionally
continuous functions of a two-dimensional image, which means that they are preserved under certain kinds
of deformations of the image. On top of that, they are very easy and quickly calculated. This makes
them of interest for certain kinds of pattern recognition.
Basically, the Minkowski integrals are the area, total perimeter length, and the Euler characteristic of
the image, where these metrics apply to the foreground image, not the rectangular PGM image itself. The
foreground image consists of all the pixels in the image that are white. For a grayscale image, there is
some threshold of intensity applied to categorize pixels into black and white, and the Minkowski
integrals are calculated as a function of this threshold value. The total surface area refers to the
number of white pixels in the PGM and the perimeter is the sum of perimeters of each closed white region
in the PGM.
For a grayscale image, these numbers are a function of the threshold of what you want to call black or
white. pgmminkowski reports these numbers as a function of the threshold for all possible threshold
values. Since the total surface area can increase only as a function of the threshold, it is a
reparameterization of the threshold. It turns out that if you consider the other two functions, the
boundary length and the Euler characteristic, as a function of the first one, the surface, you get two
functions that are a fingerprint of the picture. This fingerprint is e.g. sufficient to recognize the
difference between pictures of different crystal lattices under a scanning tunnelling electron
microscope.
For more information about Minkowski integrals, see e.g.
• J.S. Kole, K. Michielsen, and H. De Raedt, "Morphological Image Analysis of Quantum Motion in
Billiards", Phys. Rev. E 63, 016201-1 - 016201-7 (2001)
• K. Michielsen and H. De Raedt, "Integral-Geometry Morphological Image Analysis", Phys. Rep. 347,
461-538 (2001).
The output is suitable for direct use as a datafile in gnuplot.
In addition to the three Minkowski integrals, pgmminkowski also lists the horizontal and vertical edge
counts.