Table Of Contents

Extract Contour (G Dataflow)

Last Modified: June 25, 2019

Extracts a single, best contour from an image.

If the input image is calibrated, the contour will be learned with calibration.

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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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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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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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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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image in

Reference to the source image.

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contour image in

Reference to the destination image.

If this input is connected, the contour image will be the image extracted from the ROI bounding box.

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ROI descriptor

Descriptor that defines the region within which to search for contours.

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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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search direction

Direction in which the ROI is examined.

Name Value Description
rect left to right 0

(Default) Searches the ROI from left to right.

rect right to left 1

Searches the ROI from right to left.

rect top to bottom 2

Searches the ROI from top to bottom.

rect bottom to top 3

Searches the ROI from bottom to top.

annulus inner to outer 4

Searches the ROI from the inner radius to the outer radius. The inner radius is the radius of the inner circle defining one edge of the circular strip. The outer radius is the radius of the outer circle defining the second edge of the circular strip.

annulus outer to inner 5

Searches the ROI from the outer radius to the inner radius. The inner radius is the radius of the inner circle defining one edge of the circular strip. The outer radius is the radius of the outer circle defining the second edge of the circular strip.

annulus start angle to end angle 6

Searches the ROI from start angle to end angle. The start angle is the first angle of the circular strip and is measured counterclockwise from the x-axis of a coordinate system centered on the center of the circle or annulus. The end angle is the second angle of the circular strip and is measured counterclockwise from the x-axis of a coordinate system centered on the center of the circle or annulus.

annulus end angle to start angle 7

Searches the ROI from end angle to start angle. The start angle is the first angle of the circular strip and is measured counterclockwise from the x-axis of a coordinate system centered on the center of the circle or annulus. The end angle is the second angle of the circular strip and is measured counterclockwise from the x-axis of a coordinate system centered on the center of the circle or annulus.

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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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contour selection

Extracted contour based on the selected property.

Name Description
closest to search start (Default) Selects the curve closest to the ROI.
maximum length Selects the longest curve.
strongest mean gradient change Selects the curve with the highest edge strength averaged from each point on the curve.
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curve connection options

Option that specifies how to connect curves.

Select a maximum of 1 constraint of each type.

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match constraints

Criteria to use to consider two curves part of a contour.

Name Value Description
distance (pixel) 0

Specifies the distance, in pixels, within which the end points of two curves must lie in order to be considered part of a contour.

angle difference (degrees) 1

Specifies the range, in degrees, within which the difference between the angle of two curves, measured at the end points, must lie in order for the two curves to be considered part of a contour. This value can range from 0 to 180.

connectivity distance (pixel) 2

Specifies the distance, in pixels, within which a line extended from the end point of a curve must pass the end point of another curve in order for the two curves to be considered part of a contour.

gradient difference (degrees) 3

Specifies the range, in degrees, within which the gradient angles of two curves, measured at the end points, must lie in order for the two curves to be considered part of a contour. This value can range from 0 to 180.

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Min

Minimum value of the range for a given match constraint.

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Max

Maximum value of the range for a given match constraint.

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image out

Reference to the source image.

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contour image out

Reference to the image containing a contour.

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contour points

All points found on the contour.

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x

X-coordinate of the point.

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y

Y-coordinate of the point.

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source image points

All points found on the contour in the source image.

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x

X-coordinate of the point.

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y

Y-coordinate of the point.

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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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