ALGORITHMS FOR PROCESSING CONNECTED COMPONENTS WITH GRAY VALUES - Fundamentals of Three-Dimensional Digital Image Processing - page 202

+/ 8

? -

8

? +

Fig. 6.6. The starting point condition of Algorithm 6.4.

tion of the tracing , and the sign and the amount of the curvature at the
voxel P satisfy a given condition.

Algorithm 6.4 (Ridge line extraction tracing type).

[STEP 1] Scan the whole of an input image by the raster scan and start
the procedure at the next voxel after the current voxel if it has not been
traced yet.
Go to [STEP 3] , if all adjacent voxel pairs in the 26-neighborhood of a
voxel P satisfy the starting condition.
Go to [STEP 2] , if 12 of 13 adjacent voxel pairs satisfy the starting
condition.
Terminate tracing when the scan finishes.
[STEP 2] Select as tracing direction the direction toward one of the voxels
of the adjacent voxel pair that does not fulfill the starting point condition
from the trace starting point. Then start the actual tracing procedure.
Go to [STEP 4] ,ifthe tracing procedure terminates.
[STEP 3] If there exists a voxel P that satisfies the continuity condition
among voxels adjacent to a starting point, begin the tracing procedure in
the direction connecting the above voxel P and the starting point.
Go to [STEP 4] ,ifthe tracing procedure terminates.
Go to [STEP 2] unless the direction satisfying the continuity condition
exists.
[STEP 4] Go back to the starting point and begin tracing procedure again,
along the tracing direction rotated by 180 degrees (in the direction oppo-
site to the previous one).

[ Tracing procedure ] Prepare an image F W (work area; all voxels are initialized

by 0 ) of the same size as an input image.
[STEP I] Move a current voxel by one voxel in the direction of tracing. If
the continuity condition is satisfied at the current voxel after the above
one-voxel shift, then write value 1 into the voxel of the image

F W corre-

sponding to the current voxel and repeat [STEP I] .