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Module: MetrologyBasic

Locates the strongest transition between dark and bright pixels along a given path (without a scan map).


Very fast detection of an object (e.g. horizontal displacement of a bottle) and simple measurements (e.g. liquid level in a bottle).
Name Type Range Description
Input value inImage Image Input image
Input value inScanPath Path Path along which the scan is performed
Input value inScanPathAlignment CoordinateSystem2D* Adjusts the scan path to the position of the inspected object
Input value inScanWidth Integer 1 - Width of the scan field in pixels
Input value inSamplingParams SamplingParams Parameters controlling the sampling process
Input value inEdgeScanParams EdgeScanParams Parameters controlling the edge extraction process
Input value inEdgeSelection Selection Selection mode of the resulting edge
Input value inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
Output value outEdge Edge1D? Found edge
Output value outAlignedScanPath Path Transformed input path
Output value outBrightnessProfile Profile Extracted image profile
Output value outResponseProfile Profile Profile of the edge (derivative) operator response
Diagnostic input diagSamplingPoints PathArray Array of paths each one containing the sampling points that contributes to a single value of the extracted profile
Diagnostic input diagSamplingStep Real Used distance between consecutive sampling points on the scan path


The operation scans the image along inScanPath and locates the strongest edge perpendicular to the path. If the strongest edge is weaker than inEdgeScanParams.minMagnitude 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.


  • Connect an input image to the inImage input.
  • Create inScanPath which is more or less perpendicular to the edge 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 no edge is 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.


Description of usage of this filter can be found in examples and tutorial: Cap (Easy), Cap (Advanced), Parallel Enumeration, Bottle Inspector Part 2: Measuring Liquid Level, Bottle Inspector Part 3: Foam Detection.

ScanSingleEdge locates the strongest edge across inScanPath.


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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of ScanEdges filter group.

See Also

  • ScanMultipleEdges – Locates multiple transitions between dark and bright pixels along a given path (without a scan map).
  • ScanExactlyNEdges – Locates a specified number of the strongest transitions between dark and bright pixels along a given path (without a scan map).
  • ScanSingleEdge – Locates the strongest transition between dark and bright pixels along a given path (without a scan map).