FindCircle
Locates a single circular edge within an annular (shaped like a circle or ring) image region. FindCircle forms one-dimensional projections of the image region by summing pixel values on concentric circles, scanned in the direction of increasing radius. Edge transitions are extracted from the projected image data.
FindCircle Inputs
Syntax: FindCircle(Image,Fixture.Row,Fixture.Columm,Fixture.Theta,Annulus.X,Annulus.Y,Annulus.Inner Radius,Annulus.Outer Radius,Polarity,Find By,Accept Thresh,Normalize Score,Edge Width,Show)
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Specifies a reference to a spreadsheet cell that contains an Image data structure; by default, this parameter references A0, the cell containing the AcquireImage Image data structure. This parameter can also reference other Image data structures, such as those returned by the Vision Tool Image functions or Coordinate Transforms Functions. |
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Defines the Region of Interest (ROI) relative to a Fixture input or the output of a Vision Tool function's image coordinate system. Setting the ROI relative to a Fixture ensures that if the Fixture is rotated or translated, the ROI will be rotated or translated in relation to the Fixture. For more information, see Fixture and Vision Tools. The default setting is (0,0,0), the top leftmost corner of the image.
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Also known as the Region of Interest (ROI), specifies the region of the image that undergoes analysis; creates an annular image region that can be translated and rotated. With this parameter selected, by pressing the Maximize Region button on the property sheet's toolbar, the region will automatically be stretched to cover the entire image.
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Note: The Fixture
and Annulus parameters must be defined
within the bounds of the image; otherwise, the function will return #ERR.
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Specifies the polarity of the edge to be located, relative to the scan direction of the Region; the function will only report edges of the specified polarity.
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Specifies the edge selection technique the function will use to select an edge, amongst multiple edge candidates.
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Specifies the minimum acceptable edge contrast (0 to 100; default = 25). The contrast value is normalized from the greyscale histogram within the Region to a scale of 0 to 100. The function will reject any edge whose contrast score falls below this value. |
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Specifies whether the edge scores will be normalized by the greyscale histogram of the Region. When Normalize Score is enabled, raw edge scores are normalized by the maximum contrast found within the image region using the following formula: Score = (Raw Edge Score) x (100/Max Contrast) Where Raw Edge Score is the grey level difference across the edge and Max Contrast is the difference between the maximum and minimum grey level (0 to 255) within the image region. When Normalize Score is disabled, low contrast edges will score lower than high contrast edges. The following formula is used: Score = (Raw Edge Score) x (100/255)
Tip: This parameter is useful for finding edges in a low contrast region. If the edges to be detected are expected to be only high contrast, disable this parameter.
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Specifies the pixel distance (1 to 50; default = 3) over which an edge transition takes place. Edge Width is used to filter the image before edges are extracted. |
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Specifies the display mode for FindCircle graphical overlays on top of the image.
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FindCircle Outputs
Returns |
An Edges data structure containing a single circular edge, or #ERR if any of the input parameters are invalid. |
Results |
When FindCircle is initially inserted into a cell, a result table is created in the spreadsheet. |
FindCircle Vision Data Access Functions
The following Vision Data Access functions are automatically inserted into the spreadsheet to create the result table. For more information, see Edges.
CentRow |
GetRow(Edges, 0, 0) |
The center row. |
CentCol |
GetCol(Edges, 0, 0) |
The center column. |
Radius |
GetRadius(Edges, 0) |
The radius. |
Score |
GetScore(Edges, 0) |
The edge contrast score. Score is positive for black-to-white transitions, and negative for white-to-black transitions. |