The boundary-line extraction of binary patterns and aerial photographs by a computer are studied and also discussed the extraction of the line with a certain direction.
Usually, boundary definition is a sharp jump of the scene density, therefore, such a jump can be detected by differential operations such as the Laplacian (ð
2f (
x, y)/ð
x2+ð
2f (
x, y)/ð
y2).
If
f (
x, y) transforms
F (
wx, wy), then the Laplacian transforms to-(w
2x+w
2y).
F (
wx,
wy), so that one can accomplish the differential operation by the use of (
w2x+
w2y) filter in the Fourier domain.
On the other hand, if a pattern has straight lines with various directions, the frequency spectrum arrises perpendicular to the coressponding original ones. Therefore, one can extract the line coressponding to certain specific direction by a dirctional filter.
Cooley's FFT (Fast Fourier Transform) algorithm is extended to two dimensions and applied to these problems.
The computer simulation with a directional filter and a differential filter are effective as to binary patterns, however concering aerial photographs, the results are not so well as the case of binary patterns, but the road patterns in the picture can be detected.
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