FindCurve
Locates a single circular arc edge segment within a curved image region. FindCurve forms a one-dimensional projection of the image region by summing pixel values on concentric arc segments scanned in the positive x-direction relative to the region's local coordinate system. Edge transitions are extracted from the projected image data.
FindCurve Inputs
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Image |
This parameter must reference a spreadsheet cell that contains an Image data structure; by default, this parameter references A0, the cell containing the AcquireImage data structure. This parameter can also reference other Image data structures, such as those returned by the Image Vision Data Access Functions or Coordinate Transforms Functions. |
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Fixture |
Defines the Region of Interest (ROI) relative to a Fixture input or the output of a Vision Tools 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. The default setting is (0,0,0), the top leftmost corner of the image.
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Region |
Also known as the Region of Interest (ROI), specifies the region of the image that undergoes analysis. Double-click on the Region parameter to create an Interactive Graphics Mode that you can transform and rotate. Select this parameter and press the Maximize Region button on the Job Edit toolbar of the property sheet to automatically stretch the region to cover the entire image.
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Note: The Fixture and Region parameters must be defined
within the bounds of the image; otherwise, the function will return #ERR.
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Polarity |
Specifies the polarity of the edge to be located, relative to the scan direction of the Edge Region; the function will only report edges of the specified polarity.
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Find By |
Specifies the edge selection technique the function will use to select an edge, amongst multiple edge candidates.
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Accept Thresh |
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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Normalize Score |
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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Angle Range |
Specifies the function's tolerance to edge rotation (0 to 10; default = 0). The function will still find edges that are outside of the specified range, but the accuracy may not be as high. Note:
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Edge Width |
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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Show |
Specifies the display mode for FindCurve graphical overlays on top of the image.
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FindCurve Outputs
Returns |
An Edge data structure containing a single curved edge segment, or #ERR if any of the input parameters are invalid. |
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Results |
When FindCurve is initially inserted into a cell, a result table is created in the spreadsheet. The following Edges Vision Data Access Functions are automatically inserted into the spreadsheet to create the result table:
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