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ScanExactlyNEdges

Locates a specified number of the strongest transitions between dark and bright pixels along a given path.

Header:	AVL.h

Syntax

void avl::ScanExactlyNEdges
(
	const avl::Image& inImage,
	const ScanMap& inScanMap,
	const EdgeScanParams& inEdgeScanParams,
	int inEdgeCount,
	avl::Selection::Type inEdgeSelection,
	float inMinDistance,
	atl::Optional<float> inMaxDistance,
	atl::Optional<const avl::LocalBlindness&> inLocalBlindness,
	atl::Conditional<atl::Array<avl::Edge1D> >& outEdges,
	atl::Conditional<atl::Array<avl::Gap1D> >& outGaps,
	avl::Profile& diagBrightnessProfile,
	avl::Profile& diagResponseProfile
)

void ScanExactlyNEdges
(
	Image inImage,
	ScanMap inScanMap,
	EdgeScanParams inEdgeScanParams,
	int inEdgeCount,
	Selection inEdgeSelection,
	float inMinDistance,
	float? inMaxDistance,
	LocalBlindness? inLocalBlindness,
	out Edge1D[] outEdges,
	out Gap1D[] outGaps,
	out Profile diagBrightnessProfile,
	out Profile diagResponseProfile
)

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Input image
inScanMap	const ScanMap&			Data precomputed with CreateScanMap
inEdgeScanParams	const EdgeScanParams&			Parameters controlling the edge extraction process
inEdgeCount	int	0 -	1	Number of edges to be found
inEdgeSelection	Selection::Type		Selection::Best	Selection mode of the resulting edges
inMinDistance	float	0.0 -	0.0f	Minimal distance between consecutive edges
inMaxDistance	Optional<float>	0.0 -	NIL	Maximal distance between consecutive edges
inLocalBlindness	Optional<const LocalBlindness&>		NIL	Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
outEdges	Conditional<Array<Edge1D> >&			Found edges
outGaps	Conditional<Array<Gap1D> >&			Gaps between consecutive edges
diagBrightnessProfile	Profile&			Extracted image profile
diagResponseProfile	Profile&			Profile of the edge (derivative) operator response

Description

The operation scans the image using inScanMap previously generated from a scan path and finds a set of inEdgeCount image edges perpendicular to the path. If no subset (of inEdgeCount elements) of detected edges meets the requirements of inEdgeScanParams.minMagnitude, inMinDistance, inEdgeScanParams.edgeTransition then the outputs are set to NIL.

Note that in case of a scan path which is closed, the parameters controlling the distances between consecutive found objects do not control the distance between the first and the last of the found objects (counting from the beginning of the scan path).

Hints

Set inEdgeCount to the number of edges that are to be found (the N number).
Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
If the expected number of edges cannot be found, try decreasing inEdgeScanParams.MinMagnitude. Verify this with the values on the diagResponseProfile output.
If consecutive edges are closer than 6 pixels apart, change inEdgeScanParams.ProfileInterpolation to Quadratic3.
Adjust inMinDistance (in pixels) to filter out false edges that appear in proximity to other edges.

Examples

ScanExactlyNEdges locates the edges using a scan map representing the scan path above (inEdgeCount = 61).

Remarks

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

This filter is a part of the 1D Edge Detection toolset. For a comprehensive introduction to this technique please refer to 1D Edge Detection and 1D Edge Detection - Subpixel Precision chapters of our Machine Vision Guide.