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Extracts a pixel-precise region of continuous edges. Faster, yet less accurate version.


void avl::DetectEdges_AsRegion_Mask
	const avl::Image& inImage,
	atl::Optional<const avl::Region&> inRoi,
	avl::EdgeMaskFilter::Type inEdgeMaskFilter,
	float inEdgeThreshold,
	float inEdgeHysteresis,
	float inMaxJoiningDistance,
	const int inMinBlobArea,
	avl::Region& outEdgeRegion,
	avl::Image& diagGradientMagnitudeImage


Name Type Range Default Description
inImage const Image& Image from which edges will be extracted
inRoi Optional<const Region&> NIL Region of the image from which edges will be extracted
inEdgeMaskFilter EdgeMaskFilter::Type Type of edge filter used for computing gradients
inEdgeThreshold float 0.0 - 35.0f Sufficient edge strength; edges of that strength will always be detected
inEdgeHysteresis float 0.0 - 15.0f Value by which the edge threshold is decreased for edge points neighboring with sufficiently strong edges
inMaxJoiningDistance float 0.0 - 0.0f Maximal distance between edges that can be joined
inMinBlobArea const int 0 - 1 Minimal area of an edge blob
outEdgeRegion Region& Region of the found edges
diagGradientMagnitudeImage Image& Visualization of the gradient magnitude


The operation extracts edges from the inRoi region in the inImage image and stores the result in the outEdgeRegion region. The extraction process is the same as in DetectEdges_AsPaths_Mask, the only difference being the data type of the result. This filter returns a region rather than array of subpixel-precise paths computed by DetectEdges_AsPaths_Mask.

The extraction process starts from gradient computing, what is done using chosen non-recursive filter with fixed size mask.

On the so computed gradient image threshold with hysteresis (as in ThresholdImage_Hysteresis) is performed with inEdgeThreshold and inEdgeHysteresis parameters. After this step only gradients which are strong enough are present. The resulting edge region can be much too thick, thus it has to be thinned. To achieve this, the non-maximum suppression is used. Every pixel with at least one of its neighbors having larger gradient is no longer considered to be an edge pixel (only neighbors in the direction of pixel's gradient matter).


DetectEdges_AsRegion_Mask performed on the sample image with inEdgeMaskFilter = Sobel, inEdgeThreshold = 20, inEdgeHysteresis = 5.


For more information about local coordinate systems please refer to the following article.

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

See Also

  • DetectEdges_AsPaths_Mask – Extracts subpixel-precise paths that represent continuous edges. Faster, yet less accurate version.