skelcurv.c File Reference

curvilinear binary skeleton guided by a priority image More...

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Detailed Description

curvilinear binary skeleton guided by a priority image

Usage: skelcurv in.pgm prio connex [inhibit] out.pgm

Description: Curvilinear binary skeleton guided by a priority image. The lowest values of the priority image correspond to the highest priority.

The parameter prio is either an image (byte or int32_t or float or double), or a numerical code indicating that a distance map will be used as a priority image; the possible choices are:

• 0: approximate euclidean distance
• 1: approximate quadratic euclidean distance
• 2: chamfer distance
• 3: exact quadratic euclidean distance
• 4: 4-distance in 2d
• 8: 8-distance in 2d
• 6: 6-distance in 3d
• 18: 18-distance in 3d
• 26: 26-distance in 3d
• 5: breadth-first and directional strategy

The parameter connex indicates the connectivity of the binary object. Possible choices are 4, 8 in 2d and 6, 26 in 3d.

If the parameter inhibit is given and is a binary image name, then the points of this image will be left unchanged.

Let X be the set corresponding to the input image in.pgm. Let P be the function corresponding to the priority image. Let I be the set corresponding to the inhibit image, if given, or the empty set otherwise. The algorithm is the following:

C = null image
Repeat until stability
  choose a point x in X \ I, simple for X, such that C[x] == 0 
    and such that P[x] is minimal
  X = X \ {x}
  for all y in gamma(x)
    if T(y) > 1 then C[y] = 1
Result: X

where T(y) refers to the connectivity number of y, that is, (informally) the number of connected components of gamma(y) inter (X \ {y}).

References:
[BC07] G. Bertrand and M. Couprie: "Transformations topologiques discretes", in Géométrie discrète et images numériques, D. Coeurjolly and A. Montanvert and J.M. Chassery, pp. 187-209, Hermès, 2007.

Types supported: byte 2d, byte 3d

Category: topobin

Author:

Michel Couprie