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ScanExactlyNStripes

Header:	AVL.h
Namespace:	avl
Module:	MetrologyBasic

Locates a specified number of multiple pairs of opposite edges across a given path.

Applications: Very fast detection (or presence verification) of multiple pairs of opposite edges.

Syntax

void avl::ScanExactlyNStripes
(
	const avl::Image& inImage,
	const ScanMap& inScanMap,
	const StripeScanParams& inStripeScanParams,
	int inStripeCount,
	avl::Selection::Type inStripeSelection,
	float inMinGapWidth,
	atl::Optional<float> inMaxGapWidth,
	atl::Optional<const avl::LocalBlindness&> inLocalBlindness,
	atl::Conditional<atl::Array<avl::Stripe1D> >& outStripes,
	atl::Conditional<atl::Array<avl::Gap1D> >& outGaps,
	atl::Optional<avl::Profile&> outBrightnessProfile = atl::NIL,
	atl::Optional<avl::Profile&> outResponseProfile = atl::NIL
)

Parameters

Name	Type	Range	Default	Description
inImage	const Image&			Input image
inScanMap	const ScanMap&			Data precomputed with CreateScanMap
inStripeScanParams	const StripeScanParams&		StripeScanParams ( ProfileInterpolation: Quadratic4 SmoothingStdDev: 0.6f MinMagnitude: 5.0f MaxInnerEdgeMagnitude: Nil StripePolarity: Dark MinStripeWidth: 0.0f MaxStripeWidth: Nil )	Parameters controlling the stripe extraction process
inStripeCount	int	0 -	1	Number of stripes to be found
inStripeSelection	Selection::Type		Selection::Best	Selection mode of the resulting stripes
inMinGapWidth	float	0.0 -	0.0f	Minimal distance between consecutive stripes
inMaxGapWidth	Optional<float>	0.0 -	NIL	Maximal distance between consecutive stripes
inLocalBlindness	Optional<const LocalBlindness&>		NIL	Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
outStripes	Conditional<Array<Stripe1D> >&			Found stripes
outGaps	Conditional<Array<Gap1D> >&			Distances between consecutive stripes
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 atl::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 inStripeCount consecutive stripes (i.e. pairs of opposite-polarity edges running across the path). If no subset (of inStripeCount elements) of detected edge pairs meets the requirements of inStripeScanParams.stripePolarity, inStripeScanParams.minMagnitude, inStripeScanParams.minStripeWidth and inMinGapWidth 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 inStripeCount to the number of stripes that are to be found (the N number).
Define inStripeScanParams.StripePolarity to detect a particular stripe type, and only that type.
If the expected number of stripes cannot be found, try decreasing inStripeScanParams.MinMagnitude. Verify this with the values on the outResponseProfile output.
If consecutive edges are closer than 6 pixels apart, change inStripeScanParams.ProfileInterpolation to Quadratic3.
Adjust inMinGapWidth (in pixels) to filter out false stripes that appear in proximity to other stripes.
Adjust inStripeScanParams.inMinStripeWidth and inStripeScanParams.inMaxStripeWidth (in pixels) to increase reliability.

Examples

ScanExactlyNStripes locates the edge pairs using a scan map representing the scan path above (inStripeCount = 2, inStripeScanParams.stripePolarity = Dark).

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.