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Locates a specified number of the strongest dark or bright pixel peak along a given path.



void avl::ScanExactlyNRidges
	const avl::Image& inImage,
	const ScanMap& inScanMap,
	const RidgeScanParams& inRidgeScanParams,
	int inRidgeCount,
	avl::Selection::Type inRidgeSelection,
	float inMinDistance,
	atl::Optional<float> inMaxDistance,
	atl::Optional<const avl::LocalBlindness&> inLocalBlindness,
	atl::Conditional<atl::Array<avl::Ridge1D> >& outRidges,
	atl::Conditional<atl::Array<avl::Gap1D> >& outGaps,
	avl::Profile& diagBrightnessProfile,
	avl::Profile& diagResponseProfile


Name Type Range Default Description
inImage const Image& Input image
inScanMap const ScanMap& Data precomputed with CreateScanMap
inRidgeScanParams const RidgeScanParams& Parameters controlling the ridge extraction process
inRidgeCount int 0 - 1 Number of ridges to be found
inRidgeSelection Selection::Type Selection::​Best Selection mode of the resulting ridges
inMinDistance float 0.0 - 0.0f Minimal distance between consecutive ridges
inMaxDistance Optional<float> 0.0 - NIL Maximal distance between consecutive ridges
inLocalBlindness Optional<const LocalBlindness&> NIL Defines conditions in which weaker ridges can be detected in the vicinity of stronger ridges
outRidges Conditional<Array<Ridge1D> >& Found ridges
outGaps Conditional<Array<Gap1D> >& Gaps between consecutive edges
diagBrightnessProfile Profile& Extracted image profile
diagResponseProfile Profile& Profile of the ridge operator response


The operation scans the image using inScanMap previously generated from a scan path and finds a set of inRidgeCount image ridges perpendicular to the path. If no subset (of inRidgeCount elements) of detected ridges meets the requirements of inRidgeScanParams.minMagnitude, inMinDistance, inRidgeScanParams.ridgePolarity 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).


  • Set inRidgeCount to the number of ridges that are to be found (the N number).
  • Define inEdgeScanParams.RidgePolarity to detect a particular ridge type, and only that type.
  • If the expected number of ridges cannot be found, try decreasing inRidgeScanParams.MinMagnitude. Verify this with the values on the diagResponseProfile output.
  • If consecutive ridges are very close to each other, change inEdgeScanParams.ProfileInterpolation to Quadratic3.
  • Adjust inMinDistance (in pixels) to filter out false ridges that appear in proximity to other ridges.


ScanMultipleRidges locates the ridges using a scan map representing the scan path above.


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.

See Also

  • CreateScanMap – Precomputes a data object that is required for fast 1D edge detection.
  • ScanExactlyNRidges – Locates a specified number of the strongest dark or bright pixel peak along a given path.
  • ScanSingleRidge – Locates the strongest dark or bright pixel peak along a given path.