Table Of Contents

Extract Curves (G Dataflow)

Last Modified: October 26, 2017

Finds curves in an image.

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image in

Reference to the source image.

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ROI descriptor

Region of the image from which to extract curves.

This region must be a single rectangle or rotated rectangle contour. By default, the node returns the curves for the entire image.

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Global Rectangle

Coordinates of the bounding rectangle.

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Contours

Individual shapes that define an ROI.

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ID

Object specifying if contour is the external or internal edge of an ROI.

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Type

Shape type of the contour.

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Coordinates

Relative position of the contour.

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curve extraction options

Cluster containing information about how curves are extracted from the image.

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Extraction Mode

Input that specifies how the node identifies curves in the image.

Name Value Description
Normal 0

(Default) Select if you want the node to make no assumptions about the uniformity of objects in the image or the image background.

Uniform Regions 1

Select if you want the node to assume that either the objects in the image or the image background consist of uniform pixel values. This allows the node to more accurately calculate the external curves of the objects.

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Edge Threshold

Minimum contrast a seed point must have for it to begin a curve.

Valid values range from 1 to 255.

Default: 75

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Edge Filter Size

Width of the edge filter that the node uses to identify curves in the image.

Name Value Description
Fine 0

Sets to fine edge filter size.

Normal 1

(Default) Sets to normal edge filter size.

Contour Tracing 2

Sets to contour tracing edge filter size, which provides the best results for contour extraction but increases the time required to process the image.

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Min Length

Length, in pixels, of the smallest curve that you want the node to identify.

The node ignores any curves that have a length less than this value.

Default: 25

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Row Search Step Size

Distance, in the y direction, between the image rows that the algorithm inspects for curve seed points.

Valid values range from 1 to 255.

Default: 15

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Col Search Step Size

Distance, in the x direction, between the image columns that the algorithm inspects for curve seed points.

Valid values range from 1 to 255.

Default: 15

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Max Endpoint Gap

Maximum gap, in pixels, between the endpoints of a curve that the node identifies as a closed curve.

If the gap is larger than this value, the node identifies the curve as an open curve.

Default: 10

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Closed

Boolean value that specifies only closed curves are identified in the image.

TRUE Identifies only closed curves.
FALSE Identifies both open and closed curves.

Default: FALSE

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Subpixel

Boolean value that specifies if curve points are detected with subpixel accuracy.

TRUE Curve points are detected with subpixel accuracy.
FALSE Curve points are not detected with subpixel accuracy.

Default: FALSE

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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image out

Reference to the source image.

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curves

Array describing the curves found in the image.

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points

Location of every point detected on the curve.

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closed?

Boolean that specifies the distance between the endpoints of the curve are less than or equal to or greater than max endpoint gap.

TRUE Distance between the endpoints of the curve are less than or equal to max endpoint gap.
FALSE Distance between the endpoints of the curve are greater than max endpoint gap.
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curve length

Length of the curve.

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min edge strength

Llowest edge strength detected on the curve.

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max edge strength

Highest edge strength detected on the curve.

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average edge strength

Average of all edge strengths detected on the curve.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application


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