close_edges_length🔗
Short description🔗
close_edges_length — Close edge gaps using the edge amplitude image.
Signature🔗
close_edges_length( region Edges, image Gradient, out region ClosedEdges, integer MinAmplitude, integer MaxGapLength )
Description🔗
close_edges_length closes gaps in the output of an edge
detector, and thus tries to produce complete object contours. This
operator expects as input the edges (Edges) and amplitude
image (Gradient) returned by typical edge operators,
such as edges_image or sobel_amp.
Contours are closed in two steps: First, one pixel wide gaps in the
input contours are closed, and isolated points are eliminated. After
this, open contours are extended by up to MaxGapLength
points by adding edge points until either the contour is closed or
no more significant edge points can be found. A gradient is
regarded as significant if it is larger than
MinAmplitude. The neighboring points examined as
possible new edge points are the point in the direction of the
contour and its two adjacent points in an 8-neighborhood. For each
of these points, the sum of its gradient and the maximum gradient of
that points three possible neighbors is calculated
(look ahead of length 1). The point with the maximum
sum is then chosen as the new edge point.
Attention🔗
Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.
Execution information🔗
Execution information
-
Multithreading type: reentrant (runs in parallel with non-exclusive operators).
-
Multithreading scope: global (may be called from any thread).
Parameters🔗
Edges (input_object) region(-array) → object
Region containing one pixel thick edges.
Gradient (input_object) singlechannelimage → object (byte / uint2)
Edge amplitude (gradient) image.
ClosedEdges (output_object) region(-array) → object
Region containing closed edges.
MinAmplitude (input_control) integer → (integer)
Minimum edge amplitude.
Default: 16
Suggested values: 5, 8, 10, 12, 16, 20, 25, 30, 40, 50
Value range: 0 ≤ MinAmplitude ≤ 255
Minimum increment: 1
Recommended increment: 1
MaxGapLength (input_control) integer → (integer)
Maximal number of points by which edges are extended.
Default: 3
Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 30, 40, 50, 70, 100
Value range: 1 ≤ MaxGapLength ≤ 127
Minimum increment: 1
Recommended increment: 1
Example🔗
(C)
sobel_amp(Image,&EdgeAmp,"sum_abs",5)\;
threshold(EdgeAmp,&EdgeRegion,40.0,255.0)\;
skeleton(EdgeRegion,&ThinEdge)\;
close_edges_length(ThinEdge,EdgeAmp,&CloseEdges,15,3)\;
Result🔗
close_edges_length returns 2 (H_MSG_TRUE) if all parameters are
correct. If the input is empty the behavior can be set via
set_system('no_object_result',<Result>). If
necessary, an exception is raised.
Combinations with other operators🔗
References🔗
M. Üsbeck: “Untersuchungen zur echtzeitfähigen Segmentierung”; Studienarbeit, Bayerisches Forschungszentrum für Wissensbasierte Systeme (FORWISS), Erlangen, 1993.
Module🔗
Foundation