Table Of Contents

Simple Edge (G Dataflow)

Last Modified: June 25, 2019

Finds step edges along an array of pixel coordinates.

This node can return the first, both the first and the last, or all the edges found.

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image in

Reference to the source image.

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pixel coordinates

Array containing the coordinates of the pixels to inspect.

You can obtain the pixel coordinates from an ROI descriptor using the ROI Profile node.

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threshold parameters

Cluster containing information used to determine whether a change in pixel value is considered as an edge.

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level type

Control that chooses between looking for peaks, or positive-going bumps, and valleys, or negative-going bumps.

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threshold level

Control that is either absolute or relative.

Absolute threshold is based on the pixel values. Relative threshold is expressed as a percentage of the pixel-value range found along the path defined by the pixel coordinates.

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hysteresis

Difference in threshold level between a rising and a falling edge, enabling accurate detection in noisy images.

Hysteresis can be either absolute or relative.

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process

Type of search.

Name Description
get first edge Returns the first edge.
get first + last edge Returns the first and last edge.
get all edges (Default) Returns all edges found along the search path(s).
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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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subpixel accuracy?

Boolean that specifies the accuracy required for the location of the edge coordinates.

Setting this control to FALSE enables fast edge detection. The subpixel result is computed using a local quadratic interpolation.

TRUE Obtains a subpixel localization of the edges.
FALSE Does not obtain a subpixel localization of the edges.

Default: FALSE

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image out

Reference to the source image.

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edges coordinates

Cordinates of the detected edges.

If the subpixel accuracy? control is set to TRUE, the result is given with subpixel accuracy.

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number of edges

Number of edges found.

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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.

Threshold Level

Use threshold parameters to determine whether a change in the pixel values is considered an edge. The main criterion is a threshold level on the pixel values. This threshold value can be either relative or absolute. Relative threshold level is specified as a percentage of the pixel range found in the pixel path. Absolute value is based directly on the pixel grayscale intensity. You can compute the location of the edges with subpixel accuracy.

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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