detect_edge_segments🔗
Short description🔗
detect_edge_segments — Detect straight edge segments.
Signature🔗
detect_edge_segments( image Image, integer SobelSize, integer MinAmplitude, integer MaxDistance, integer MinLength, out line.begin.y BeginRow, out line.begin.x BeginCol, out line.end.y EndRow, out line.end.x EndCol )
Description🔗
detect_edge_segments detects straight edge segments in the gray
image Image. The extracted edge segments are returned as
line segments with start point (BeginRow,BeginCol)
and end point (EndRow,EndCol). Edge detection
is based on the Sobel filter, using 'sum_abs' as parameter and
SobelSize as the filter mask size (see
sobel_amp). Only pixels with a filter response larger
than MinAmplitude are used as candidates for edge points.
These thresholded edge points are thinned and split into straight
segments. Due to technical reasons, edge points in which several
edges meet are lost. Therefore, detect_edge_segments usually
does not return closed object contours. The parameter
MaxDistance controls the maximum allowed distance of an
edge point to its approximating line. For efficiency reasons, the
sum of the absolute values of the coordinate differences is used
instead of the Euclidean distance. MinLength controls
the minimum length of the line segments. Lines shorter than
MinLength are not returned.
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).
-
Automatically parallelized on tuple level.
Parameters🔗
Image (input_object) (multichannel-)image(-array) → object (byte)
Input image.
SobelSize (input_control) integer → (integer)
Mask size of the Sobel operator.
Default: 5
List of values: 3, 5, 7, 9, 11, 13
MinAmplitude (input_control) integer → (integer)
Minimum edge strength.
Default: 32
Suggested values: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110
Value range: 1 ≤ MinAmplitude ≤ 255
Minimum increment: 1
Recommended increment: 1
MaxDistance (input_control) integer → (integer)
Maximum distance of the approximating line to its original edge.
Default: 3
Suggested values: 2, 3, 4, 5, 6, 7, 8
Value range: 0 ≤ MaxDistance
Minimum increment: 1
Recommended increment: 1
MinLength (input_control) integer → (integer)
Minimum length of to resulting line segments.
Default: 10
Suggested values: 3, 5, 7, 9, 11, 13, 16, 20
Value range: 1 ≤ MinLength
Minimum increment: 1
Recommended increment: 1
BeginRow (output_control) line.begin.y-array → (integer)
Row coordinate of the line segments’ start points.
BeginCol (output_control) line.begin.x-array → (integer)
Column coordinate of the line segments’ start points.
EndRow (output_control) line.end.y-array → (integer)
Row coordinate of the line segments’ end points.
EndCol (output_control) line.end.x-array → (integer)
Column coordinate of the line segments’ end points.
Example🔗
(C)
Htuple SobelSize,MinAmplitude,MaxDistance,MinLength\;
Htuple RowBegin,ColBegin,RowEnd,ColEnd\;
create_tuple(&SobelSize,1)\;
set_i(SobelSize,5,0)\;
create_tuple(&MinAmplitude,1)\;
set_i(MinAmplitude,32,0)\;
create_tuple(&MaxDistance,1)\;
set_i(MaxDistance,3,0)\;
create_tuple(&MinLength,1)\;
set_i(MinLength,10,0)\;
T_detect_edge_segments(Image,SobelSize,MinAmplitude,MaxDistance,MinLength,
&RowBegin,&ColBegin,&RowEnd,&ColEnd)\;
Result🔗
detect_edge_segments 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🔗
Combinations
Possible predecessors
Possible successors
partition_lines, line_position, line_orientation
Alternatives
Module🔗
Foundation