FindMultiLine

Locates multiple straight-line edges within an image region. FindMultiLine forms a one-dimensional projection of the image region by summing pixel values on radial line segments scanned in the positive y-direction relative to the region's local coordinate system. Edge transitions are extracted from the projected image data.

FindMultiLine Inputs

Parameter

Description

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.

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.

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; creates an Interactive Graphics Mode that can be transformed and rotated. With this parameter selected, by pressing the Maximize Region button on the property sheet's Job Edit toolbar, the region will automatically be stretched 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.
Width	The dimension along the region's x-axis.
Height	The dimension along the region's y-axis.
Angle	The orientation, in fixture coordinates.
Curve	The angular deviation between the region's x-axis and the opposing boundary line.

Note: The Fixture and Region parameters must be defined within the bounds of the image; otherwise, the function will return #ERR.

Number to Find

Specifies the maximum number of edges the function will return (1 to sensor's image width, minus 1; default = 3). The maximum number of edges that may be detected is one less than the width of the image for the particular In-Sight camera capturing the image (i.e., an ISC 8402 camera's maximum would be 1599, or one less than the vision system's 1600 x 1200 image resolution).

Threshold B2W

Specifies the minimum acceptable black-to-white edge contrast score (0 to 100; default = 25). FindMultiLine will reject any black-to-white edges whose contrast score falls below Threshold B2W. Edge contrast is normalized by the greyscale histogram of the scan region.

Threshold W2B

Specifies the minimum acceptable white-to-black edge contrast score (0 to 100 default = 25). FindMultiLine will reject any white-to-black edges whose contrast score falls below Threshold W2B. Edge contrast is normalized by the greyscale histogram of the scan region.

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.

Note: 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.

Find By

Specifies the edge selection technique the function will use to select an edge, amongst multiple edge candidates.

0 = best score (default)	Specifies that the edge with the highest score receives the highest consideration.
1 = first edge	Specifies that the first edge detected receives the highest consideration.
2 = last edge	Specifies that the last edge detected receives the highest consideration.

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: Setting this parameter to a value greater than 0 will reduce 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 FindMultiLine graphical overlays on top of the image.

0 = hide all (default)	All graphics will be hidden, except when the cell containing the FindMultiLine function is the active cell in the spreadsheet.
1 = result graphics only	The found line edges will be displayed at all times.
2 = input and result graphics	Both the input image region and the found line edges will be displayed at all times.
3 = show all: input, result, and chart	The input image region, the found line edges, and the edges' response chart will be displayed at all times. Note: The edge response chart is a dockable window. For more information, see the Spreadsheet Editor – Charts topic.

FindMultiLine Outputs

Returns

An Edge data structure containing multiple straight-line edge segments, or #ERR if any of the input parameters are invalid.

Results

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

One Edges Vision Data Access Functions is automatically inserted into the spreadsheet to create the result table:

NFound

GetNFound(Edges)

NFound is the number of edges found.

Additional data elements can be accessed using Edges Vision Data Access Functions.