Start » Filter Reference » Computer Vision » Hough Transform » DetectMultipleCircles

DetectMultipleCircles

Advanced

Module: FoundationBasic

Finds circles of a given radius in the input image using Hough Transform.

Applications

Detection of circular or close-to-circular objects like holes, pins, pills, particles.
Name Type Range Description
Input value
 inImage Image Input image
Input value
 inRoi Region* Input region of interest
Input value
 inRadius Real 0.0 - Circles' radius
Input value
 inMaxOverlap Real 0.0 - 1.0 Maximum accepted overlapping coefficient
Input value
 inMinScore Real 0.0 - Minimum matching score
Input value
 inEdgeThreshold Real Minimum accepted edge magnitude
Output value
 outCircles HoughCircleArray Found circles
Diagnostic input
 diagGradientMagnitudeImage Image Visualized gradients magnitude of an input image
Diagnostic input
 diagScoreImage Image Calculated score for each pixel of an input image

Description

The operation detects circular objects of given radius (in pixels) in the inImage using the Hough Transform approach. The output array is ordered from best matching to worst matching results.

The parameter inMaxOverlap defines how much the detected circles can overlap. The value of 0 means no overlapping is allowed, and also that each circle must be fully contained in the search ROI, whereas the value of 1 allows full overlapping.

Hints

  • Connect an input image to the inImage input.
  • Define the expected circle radius on the inRadius input. Use the Ruler tool on an image preview if you are not sure.
  • Set inEdgeThreshold to define the minimum strength of edges that will be taken into account. Verify this value with the diagGradientMagnitudeImage output.
  • Experimentally set the inMinScore value, whose meaning is more or less "the number of pixels voting for a particular object location".

Examples

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

DetectMultipleCircles performed on the sample image.

Hardware Acceleration

This operation supports automatic parallelization for multicore and multiprocessor systems.

Complexity Level

This filter is available on Advanced Complexity Level.

Filter Group

This filter is member of DetectCircles filter group.

See Also

  • DetectLines – Finds lines in an image using Hough Transform.
  • DetectPaths – Finds a specified shape in an image using Hough Transform.
  • DetectSegments – Finds segments in an image using Hough Transform.