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

Name Type Range Description
inImage Image Input image to be measured
inScanPath Path Path along which the scan is performed
inScanPathAlignment CoordinateSystem2D* Adjusts the scan path to the position of the inspected object
inScanWidth Integer 1 - Width of the scan field in pixels
inImageInterpolation InterpolationMethod Interpolation method used in extraction of image pixel values
inEdgeScanParams EdgeScanParams Parameters controlling the edge extraction process
inEdgeCount Integer 0 - Number of edges to be found
inEdgeSelection Selection Selection mode of the resulting edges
inMinDistance Real 0.0 - Minimal distance between consecutive edges
inMaxDistance Real* 0.0 - Maximal distance between consecutive edges
inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
outEdges Edge1DArray? Found edges
outGaps Gap1DArray? Gaps between consecutive edges
outAlignedScanPath Path Path along which the scan is performed; in the image coordinate system
diagBrightnessProfile Profile Extracted image profile
diagResponseProfile Profile Profile of the edge (derivative) operator response
diagSamplingPoints PathArray Array of paths each one containing the sampling points that contributed to a single value of the extracted profile
diagSamplingStep Real Used distance between consecutive sampling points on the scan path


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


The operation scans the image along inScanPath 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.

The optional parameter inScanPathAlignment defines a transform to be performed on the inScanPath so that the actual scan path (outAlignedScanPath) is adjusted to the position of the object, typically detected by one of Template Matching filters.

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).


  • Connect an input image to the inImage input.
  • Set inEdgeCount to the number of edges that are to be found (the N number).
  • Create inScanPath which is more or less perpendicular to the edges you want to detect. It should be long enough to anticipate all possible edge locations.
  • Define inEdgeScanParams.EdgeTransition to detect a particular edge type, and only that type.
  • Use a local coordinate system connected to inScanPathAlignment to automatically adjust the measurement to variable object position (optional).
  • If the noise level is high, try increasing inScanWidth and/or inEdgeScanParams.SmoothingStdDev.
  • 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.


ScanExactlyNEdges locates the edges across inScanPath (inEdgeCount = 61).


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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of ScanEdges filter group.

See Also

  • ScanExactlyNEdges – Locates a specified number of the strongest transitions between dark and bright pixels along a given path.
  • ScanSingleEdge – Locates the strongest transition between dark and bright pixels along a given path.