FindSegment

Locates a pair of Edge within an image region and computes the arc distance between them. FindSegment forms a one-dimensional projection of the image region by summing pixel values in the x-direction of the region. Edge transitions are extracted from the projected image data. The arc segment over which the edge-to-edge distance is computed is derived from the region used to extract the edges.

Inputs

Parameter

Description

Image

This parameter must reference a spreadsheet cell that contains an Image data structure. By default, this parameter references cell A0 , containing the AcquireImage function. This parameter can also reference other Image data structures, such as those returned by the Image Vision Data Access functions or Coordinate Transforms Functions.

Fixture

Defines the Region of Interest (ROI) relative to a Fixture input or the output of the image coordinate system for the Vision Tools function. Setting the ROI relative to a Fixture ensures that if the Fixture is rotated or translated, the ROI is rotated or translated in relation to the Fixture.

Note: 2D projections use real world units but fixturing with 2D tools requires input in pixel values. When using a 2D projection from a 3D point cloud as a Fixture, convert the real world units to pixel values using the TransWorldToPixel function.

The default setting is (0,0,0), the top leftmost corner of the image.

X	The X-offset, in image coordinates.
Y	The Y-offset, in image coordinates.
Theta	The rotation from the image X-axis, in the image coordinate system. (+/-360 degrees clockwise)

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.

X	The X-offset of the origin, in fixture coordinates.
Y	The Y-offset of the origin, in fixture coordinates.
Height	The dimension along the X-axis of the region.
Width	The dimension along the Y-axis of the region.
Angle	The orientation, in fixture coordinates.
Curve	The angular deviation between the x-axis and the opposing boundary line of the region.

Note: The Fixture and Region parameters must be defined within the bounds of the image. Otherwise, the function returns #ERR.

Segment Color

Specifies the color of the segment to be located. FindSegment will only report only edge pairs of the specified polarity.

0 = black (default)	Specifies black or white-to-black followed by black-to-white polarity.
1 = white	Specifies white or black-to-white followed by white-to-black polarity.

Find By

Specifies the edge selection technique.

0 = widest segment (default)	Finds the two edges farthest apart from which a segment of the specified Segment Color can be identified.
1 = strongest edges	Finds the two edges with the strongest response scores from which a segment of the specified Segment Color can be identified.
2 = widest contiguous segment	Finds the two edges from which a segment of the specified Segment Color can be identified without any other edges in between them.
3 = narrowest segment	Finds the two edges nearest each other from which a segment of the specified Segment Color can be identified.

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 rejects any edge whose contrast score falls below this value.

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)

0 = OFF	Do not normalize the score.
1 = ON (default)	Normalize the score.

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.

Angle Range

Specifies the tolerance of the function to edge rotation (0 to 10; default = 0). The function still finds edges that are outside of the specified range, but the accuracy may not be as high.

Note: Setting this parameter to a value greater than 0 reduces the speed of the function.

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.

Show

Specifies the display mode for FindSegment graphical overlays on top of the image.

0 = hide all (default)	All graphics are hidden, except when the cell containing the FindSegment function is the active cell in the spreadsheet.
1 = result graphics only	The two edges that define the edge segment are displayed at all times.
2 = input and result graphics	Both the input image region and the two edges are displayed at all times.
3 = show all: input, result, and chart	The input image region, the two edges, and the response chart of the edges are displayed at all times.

Outputs

Returns

An Edges data structure containing a matched pair of straight-line edges, or #ERR if any of the input parameters are invalid.

Results

When FindSegment is initially inserted into a cell, a result table is created in the spreadsheet.

Two Edges Vision Data Access functions are automatically inserted into the spreadsheet to create the result table:

Label	Function	Description
Distance	PairDistance(Edges, 0, 1)	The segment distance.
Score	GetScore(Edges, 0)	The contrast score of the segment.

Additional data elements can be accessed using Edges Vision Data Access functions