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ScanExactlyNStripes


Module: MetrologyBasic

Locates a specified number of multiple pairs of opposite edges across a given path (without a scan map).

Applications

Very fast detection (or presence verification) of multiple pairs of opposite edges.
Name Type Range Description
inImage Image Input image
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
inSamplingParams SamplingParams Parameters controlling the sampling process
inStripeScanParams StripeScanParams Parameters controlling the stripe extraction process
inStripeCount Integer 0 - Number of stripes to be found
inStripeSelection Selection Selection mode of the resulting stripes
inMinGapWidth Real 0.0 - Minimal distance between consecutive stripes
inMaxGapWidth Real* 0.0 - Maximal distance between consecutive stripes
inLocalBlindness LocalBlindness* Defines conditions in which weaker edges can be detected in the vicinity of stronger edges
outStripes Stripe1DArray? Found stripes
outGaps Gap1DArray? Distances between consecutive stripes
outAlignedScanPath Path Transformed input path
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 contributes to a single value of the extracted profile
diagSamplingStep Real Used distance between consecutive sampling points on the scan path

Description

The operation scans the image along inScanPath 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.

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 inStripeCount to the number of stripes that are to be found (the N number).
  • Create inScanPath which is more or less perpendicular to the stripes you want to detect. It should be long enough to anticipate all possible stripe locations.
  • Define inStripeScanParams.StripePolarity to detect a particular stripe 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 inStripeScanParams.SmoothingStdDev.
  • If the expected number of stripes cannot be found, try decreasing inStripeScanParams.MinMagnitude. Verify this with the values on the diagResponseProfile 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

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

ScanExactlyNStripes locates the edge pairs across inScanPath (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.

Complexity Level

This filter is available on Basic Complexity Level.

Filter Group

This filter is member of ScanStripes filter group.

See Also

  • ScanSingleStripe – Locates the strongest pair of edges across a given path (without a scan map).
  • ScanMultipleStripes – Locates multiple pairs of edges across a given path (without a scan map).
  • ScanExactlyNStripes – Locates a specified number of multiple pairs of opposite edges across a given path.