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ScanExactlyNRidges


Locates a specified number of the strongest dark or bright pixel peak 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
inRidgeScanParams RidgeScanParams Parameters controlling the ridge extraction process
inRidgeCount Integer 0 - Number of ridges to be found
inRidgeSelection Selection Selection mode of the resulting ridges
inMinDistance Real 0.0 - Minimal distance between consecutive ridges
inMaxDistance Real* 0.0 - Maximal distance between consecutive ridges
inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
outRidges Ridge1DArray? Found ridges
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 ridge 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

Applications

Very fast detection (or presence verification) of thin structures like scratches or scale marks.

Description

The operation scans the image along inScanPath 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.

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).

Hints

  • Connect an input image to the inImage input.
  • Set inRidgeCount to the number of ridges that are to be found (the N number).
  • Create inScanPath which is more or less perpendicular to the ridges you want to detect. It should be long enough to anticipate all possible ridge locations.
  • Define inEdgeScanParams.RidgePolarity to detect a particular ridge 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 inRidgeScanParams.SmoothingStdDev.
  • 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.

Examples

Description of usage of this filter can be found in examples and tutorial: Inset Distances.

ScanMultipleRidges locates the ridges across inScanPath.

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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of ScanRidges filter group.

See Also

  • 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.