CircleSegmentor is a multistage tool to identify and separate circular objects in the image. The following steps are invoked to locate circular objects:

• Edges (high gradient areas) in the image are located using a Sobel filter, possibly combined with the Canny algorithm

• A RANSAC search is performed, identifying possible circles with a given diameter or diameter range

• A PolygonMatch search follows, locating the circles with subpixel accuracy

• [Optional]  A secondary PolygonMatch is run, where the user can add other identifying polygons using a Polygon Wizard

Setup

Reference - Reference system selection

ROI

• Use whole picture - do not use the ROI polygons
• Vector/Contents - the ROI consists of the interior of all polygons defined

Gradients

Gradient definition

• Pick gradient positions with Canny - If checked, the Canny algorithm from OpenCV is used to find edges.

  • Canny threshold1/2 - the larger value is used to find initial edges, the smaller is used in linking them.

  • Canny aperture size - Sobel aperture for Canny

• Sobel smooth count - if Canny is not used, an internal Sobel algorithm is used to find edges. This offers additional smoothing of the image.

• Prune gradients closer than - if Canny is not used, the number of large gradients may become large. Gradients can be pruned within a neighbourhood if they differ in size but not angle:

  • Less than (%) - remove neighbour gradients smaller than this

  • Within angle (deg) - and with approximately the same direction

• Gradient min - ignore gradients smaller than this value

• Gradient max - ignore gradients larger than this value

• Image decimation - decimate image in both X and Y before the analysis

• Gradient decimation - decimate number of found gradients prior to RANSAC

Gradient visualization

• Reduce length by (factor) - visualisation of gradients in the image

Search settings

• Nominal diameter - Size of circles to search for

• Range (+/-) - Size range

• Min distance - Do not report circles closer than this

• Max RANSAC - Max number of RANSAC tests

• Max angle (deg) - An accepted gradient must point toward the circle center with max this angle error

• Min quality count - Number of accepted gradients to identify a circle

Polygon match

There are two polygon match stages in CircleSegmentor. By default stage 1 (Circle match) is active, while stage 2 (Additional match) is disabled. Stage two is intended to differentiate circles based on other marks or identifiers.

Circle match

Run circle polygon match - if disabled, neither polygon match step is run. Useful to evaluate the gradient/RANSAC steps.

Tracelines

• Use Traceline Count - selects to specify the traceline count
  • Count - number of trace lines
  • Step length - distance between traceline
    • Ref coord
    • Pixels
• Start point - position of starting point on trace line given in reference coordinates
• End point - position of end point on trace line given in reference coordinates
  • Inverted the sign of start and stop point will change the direction of the trace comb
• Trace step (pixels) - normally 1 - given in pixels
• Line width (pixels) - 0 - trace line is not averaged - a higher value will average 2N+1 pixels perpendicular to the trace comb

Edge detection

• Smooth base - 3 is normally a good value
• Smooth counter - 1 default - given i pixels
  • The smoothing increasing with higher values
• Differentiation
  • 0 - give threshold
  • 1 - 1. order differentiation - the derivative - default normally used
  • 2 - 2. order differentiation
• Threshold - the threshold or sensitivity of the edge detector - a lower value increases the sensitivity
  • % activates adaptive - threshold is set to N % of maximum values of edges
  • Minimum treshold define minimum value of threshold to accept when adaptive treshold is active
• Polarity - All transitions | Light to dark | Dark to light
• Mode - Peak | Threshold
• Edge choice - First | Largest | Last | Nearest | First then nearest | Largest then nearest
  • Largest is default and normally the best choice

Polygon match

• Parameters to adjust

  • Translation, scale - default

  • Translation - translation only, most useful when diameter is known

• Max repeat count - the number of iterations to fit the polygons

  • 2 is default but higher values will normally increase the accuracy

  • Lower values will save image processing time

• Stop if result deteriorates - if the polygonmatch seems to fail, do not process further

  • Match count/RMS/RMS factor - determines which result to evaluate

  • Hysteresis (%) - allow a small drop in performance

  • RMS factor - weight for RMS if both RMS and match count is used to measure the match

• Abort if fit % is less than - stops matching process if less than % edge points is located

• Keep best points (%) - the percentage of edge points used in iteration

  • 95% is default

• Perform final fit with distance constraints - default on - added to be able to investigate polygon matching in detail

  • Final fit max distance - can be given in pixels or reference coordinates

Diameters

• Use diameter steps (otherwise use nominal diameter, Gradients page) - if checked, run a series of matches with increasing diameter. Useful to find circles with varying size.

• Min diameter - start at this value

• Max diameter - end at this value

• Step - with these steps in between

Circle distance

• Min distance - do not report circles closer than this (also called kill radius)

Constraints

• Min fit percentage - percentage of edge points within range

• Max RMS - mean edge point inaccuracy

• Max movement - distance from original position

• Max offset X (abs) - X distance from original position

• Max offset Y (abs) - Y distance from original position

• Min intensity - min intensity within the circle

• Max intensity - max intensity within the circle

Additional match

The secondary polygon match stage is run centered at each accepted match from the Circle match stage. After a succesful stage 1, the tool lets you import an image around any of the original matches. Here you can use the polygon wizard to draw polygons matching interesting features within or outside the found circle.

Run additional polygon match  - disabled by default

Polygons

Tracelines

• Use Traceline Count - selects to specify the traceline count
  • Count - number of trace lines
  • Step length - distance between traceline
    • Ref coord
    • Pixels
• Start point - position of starting point on trace line given in reference coordinates
• End point - position of end point on trace line given in reference coordinates
  • Inverted the sign of start and stop point will change the direction of the trace comb
• Trace step (pixels) - normally 1 - given in pixels
• Line width (pixels) - 0 - trace line is not averaged - a higher value will average 2N+1 pixels perpendicular to the trace comb

Edge detection

• Smooth base - 3 is normally a good value
• Smooth counter - 1 default - given i pixels
  • The smoothing increasing with higher values
• Differentiation
  • 0 - give threshold
  • 1 - 1. order differentiation - the derivative - default normally used
  • 2 - 2. order differentiation
• Threshold - the threshold or sensitivity of the edge detector - a lower value increases the sensitivity
  • % activates adaptive - threshold is set to N % of maximum values of edges
  • Minimum treshold define minimum value of threshold to accept when adaptive treshold is active
• Polarity - All transitions | Light to dark | Dark to light
• Mode - Peak | Threshold
• Edge choice - First | Largest | Last | Nearest | First then nearest | Largest then nearest
  • Largest is default and normally the best choice

Initial values

• Copy values from circle match - a convenient way to pick default traceline settings

Polygon match

• Parameters to adjust

  • Translation, rotation, scale - default

  • Translation, rotation - translation and rotation only, most useful when diameter is known

• Max repeat count - the number of iterations to fit the polygons

  • 2 is default but higher values will normally increase the accuracy

  • Lower values will save image processing time

• Stop if result deteriorates - if the polygonmatch seems to fail, do not process further

  • Match count/RMS/RMS factor - determines which result to evaluate

  • Hysteresis (%) - allow a small drop in performance

  • RMS factor - weight for RMS if both RMS and match count is used to measure the match

• Abort if fit % is less than - stops matching process if less than % edge points is located

• Keep best points (%) - the percentage of edge points used in iteration

  • 95% is default

• Perform final fit with distance constraints - default on - added to be able to investigate polygon matching in detail

  • Final fit max distance - can be given in pixels or reference coordinates

Rotation

• Rotate template to find match - find the polygons in any position

• From/To/Step angle - default is to search the full circle [0..360> in steps of 30 degrees

Result updates

• Update match center, offset and movement - this will cause the position of the found circle to be reported from polygon additional match. Default is to use the position from Circle match.

Constraints

• Min fit percentage - percentage of edge points within range

• Max RMS - mean edge point inaccuracy

• Max movement - distance from original position

• Max offset X (abs) - X distance from original position

• Max offset Y (abs) - Y distance from original position

Advanced