detect_edge_segmentsT_detect_edge_segmentsDetectEdgeSegmentsDetectEdgeSegments (Operator)

Name

detect_edge_segmentsT_detect_edge_segmentsDetectEdgeSegmentsDetectEdgeSegments — Detect straight edge segments.

Signature

detect_edge_segments(Image : : SobelSize, MinAmplitude, MaxDistance, MinLength : BeginRow, BeginCol, EndRow, EndCol)

Description

detect_edge_segmentsdetect_edge_segmentsDetectEdgeSegmentsDetectEdgeSegmentsDetectEdgeSegments detects straight edge segments in the gray image ImageImageImageImageimage. The extracted edge segments are returned as line segments with start point (BeginRowBeginRowBeginRowBeginRowbeginRow,BeginColBeginColBeginColBeginColbeginCol) and end point (EndRowEndRowEndRowEndRowendRow,EndColEndColEndColEndColendCol). Edge detection is based on the Sobel filter, using 'sum_abs' as parameter and SobelSizeSobelSizeSobelSizeSobelSizesobelSize as the filter mask size (see sobel_ampsobel_ampSobelAmpSobelAmpSobelAmp). Only pixels with a filter response larger than MinAmplitudeMinAmplitudeMinAmplitudeMinAmplitudeminAmplitude 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_segmentsdetect_edge_segmentsDetectEdgeSegmentsDetectEdgeSegmentsDetectEdgeSegments usually does not return closed object contours. The parameter MaxDistanceMaxDistanceMaxDistanceMaxDistancemaxDistance 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. MinLengthMinLengthMinLengthMinLengthminLength controls the minimum length of the line segments. Lines shorter than MinLengthMinLengthMinLengthMinLengthminLength 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

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

ImageImageImageImageimage (input_object) (multichannel-)image(-array) → object (byte)

Input image.

SobelSizeSobelSizeSobelSizeSobelSizesobelSize (input_control) integer → (integer)

Mask size of the Sobel operator.

Default value: 5

List of values: 3, 5, 7, 9, 11, 13

MinAmplitudeMinAmplitudeMinAmplitudeMinAmplitudeminAmplitude (input_control) integer → (integer)

Minimum edge strength.

Default value: 32

Suggested values: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110

Typical range of values: 1 ≤ MinAmplitude MinAmplitude MinAmplitude MinAmplitude minAmplitude ≤ 255

Minimum increment: 1

Recommended increment: 1

Restriction: MinAmplitude >= 0

MaxDistanceMaxDistanceMaxDistanceMaxDistancemaxDistance (input_control) integer → (integer)

Maximum distance of the approximating line to its original edge.

Default value: 3

Suggested values: 2, 3, 4, 5, 6, 7, 8

Typical range of values: 1 ≤ MaxDistance MaxDistance MaxDistance MaxDistance maxDistance ≤ 30

Minimum increment: 1

Recommended increment: 1

Restriction: MaxDistance >= 0

MinLengthMinLengthMinLengthMinLengthminLength (input_control) integer → (integer)

Minimum length of to resulting line segments.

Default value: 10

Suggested values: 3, 5, 7, 9, 11, 13, 16, 20

Typical range of values: 1 ≤ MinLength MinLength MinLength MinLength minLength ≤ 500

Minimum increment: 1

Recommended increment: 1

Restriction: MinLength >= 0

BeginRowBeginRowBeginRowBeginRowbeginRow (output_control) line.begin.y-array → (integer)

Row coordinate of the line segments' start points.

BeginColBeginColBeginColBeginColbeginCol (output_control) line.begin.x-array → (integer)

Column coordinate of the line segments' start points.

EndRowEndRowEndRowEndRowendRow (output_control) line.end.y-array → (integer)

Row coordinate of the line segments' end points.

EndColEndColEndColEndColendCol (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_segmentsdetect_edge_segmentsDetectEdgeSegmentsDetectEdgeSegmentsDetectEdgeSegments 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>)set_system("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>). If necessary, an exception is raised.

Possible Predecessors

sigma_imagesigma_imageSigmaImageSigmaImageSigmaImage, median_imagemedian_imageMedianImageMedianImageMedianImage

Possible Successors

partition_linespartition_linesPartitionLinesPartitionLinesPartitionLines, line_positionline_positionLinePositionLinePositionLinePosition, line_orientationline_orientationLineOrientationLineOrientationLineOrientation

Alternatives

sobel_ampsobel_ampSobelAmpSobelAmpSobelAmp, thresholdthresholdThresholdThresholdThreshold, skeletonskeletonSkeletonSkeletonSkeleton

Module

Foundation

Operators