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ScanExactlyNEdges

Header:	FIL.h
Namespace:	fil
Module:	MetrologyBasic

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

Applications: Very fast object detection (or presence verification) when the expected number of edges is clearly defined.

Syntax

void fil::ScanExactlyNEdges
(
	const fil::Image& inImage,
	const ScanMap& inScanMap,
	const EdgeScanParams& inEdgeScanParams,
	int inEdgeCount,
	fil::Selection::Type inEdgeSelection,
	float inMinDistance,
	ftl::Optional<float> inMaxDistance,
	ftl::Optional<const fil::LocalBlindness&> inLocalBlindness,
	ftl::Conditional<ftl::Array<fil::Edge1D> >& outEdges,
	ftl::Conditional<ftl::Array<fil::Gap1D> >& outGaps,
	ftl::Optional<fil::Profile&> outBrightnessProfile = ftl::NIL,
	ftl::Optional<fil::Profile&> outResponseProfile = ftl::NIL
)

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Input image
inScanMap	const ScanMap&			Data precomputed with CreateScanMap
inEdgeScanParams	const EdgeScanParams&		EdgeScanParams ( ProfileInterpolation: Quadratic4 SmoothingStdDev: 0.6f MinMagnitude: 5.0f EdgeTransition: BrightToDark )	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
outBrightnessProfile	Optional<Profile&>		NIL	Extracted image profile
outResponseProfile	Optional<Profile&>		NIL	Profile of the edge (derivative) operator response

Optional Outputs

The computation of following outputs can be switched off by passing value ftl::NIL to these parameters: outBrightnessProfile, outResponseProfile.

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 outResponseProfile 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

Read more about Local Coordinate Systems in Machine Vision Guide: Local Coordinate Systems.

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.