IMAQ Simple Edge VI

NI Vision 2019 for LabVIEW Help

Edition Date: March 2019

Part Number: 370281AG-01

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Requires: NI Vision Development Module

Finds step edges along an array of pixel coordinates. This VI can return the first, both the first and the last, or all the edges found.

Details

Supported Image Types

8-bit unsigned grayscale 16-bit unsigned grayscale 16-bit signed grayscale floating point grayscale

IMAQ Simple Edge

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Threshold Parameters is a cluster containing information used to determine whether a change in pixel value is considered as an edge. This cluster contains the following parameters:

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Level Type chooses between looking for peaks (positive-going bumps) and valleys (negative-going bumps).

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Threshold Level can be 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 can be either absolute or relative. This parameter determines the difference in threshold level between a rising and a falling edge, enabling accurate detection in noisy images.

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Image Src is a reference to the source image.

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Pixel Coordinates is an array containing the coordinates of the pixels to inspect. You can obtain the pixel coordinates from an ROI descriptor using the IMAQ ROIProfile VI.

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Process determines the type of search. Choose from the following values:

Get First Edge (0)

Returns the first edge.

Get First + Last Edge (1)

Returns the first and last edge.

Get All Edges (2)

(Default) Returns all edges found along the search path(s).

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error in (no error) describes the error status before this VI or function runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. This VI or function runs normally only if no error occurred before this VI or function runs. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node.

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status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.

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code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.

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source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

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Sub-Pixel Accuracy determines the accuracy required for the location of the edge coordinates. Setting this control to FALSE enables fast edge detection. A subpixel localization of the edges is obtained when this control is TRUE. The subpixel result is computed using a local quadratic interpolation. The default is FALSE.

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Edges Coordinates returns the coordinates of the detected edges. If the Sub-Pixel Accuracy control is set to TRUE, the result is given with subpixel accuracy.

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Number of Edges specifies the number of edges found.

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error out contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out indicator on the front panel and select Explain Error from the shortcut menu for more information about the error.

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status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.

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code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.

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source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

Details

Use the 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.

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