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The THIN function returns the "skeleton" of a bi-level image. The skeleton of an object in an image is a set of lines that reflect the shape of the object. The set of skeletal pixels can be considered to be the medial axis of the object. For a much more extensive discussion of skeletons and thinning algorithms, see Algorithms for Graphics and Image Processing , Theo Pavlidis, Computer Science Press, 1982. The THIN function is adapted from Algorithm 9.1 (the classical thinning algorithm).
On input, the bi-level image is a rectangular array in which pixels that compose the object have a nonzero value. All other pixels are zero. The result is a byte type image in which skeletal pixels are set to 2 and all other pixels are zero.
The following commands display the "thinned" edges of a Sobel filtered image:
OPENR, 1, FILEPATH('people.dat', SUBDIR = ['examples','data'])
;
Open a file for reading.
A = BYTARR(192, 192) ; Create a byte array in which to store the image.
READU, 1, A ; Read first 192 by 192 image.
TVSCL, THIN(SOBEL(A) GT 75), 1 ; Apply the Sobel filter, threshold the image at value 75, and display the thinned edges.