IMAQ Optical Flow (LKP) VI

NI Vision 2014 for LabVIEW Help

Edition Date: June 2014

Part Number: 370281W-01

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Owning Palette: Motion Estimation
Requires: NI Vision Development Module

Computes the change in location of a set of feature points between two successive image frames using the pyramid-based Lucas and Kanade algorithm.

IMAQ Optical Flow (LKP)

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Options specifies the options that are used to track the features between two successive frames.

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Level specifies the number of pyramid levels to use.

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Max. Iterations specifies the number of iterations to run the tracking algorithm at each level.

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Window Size specifies the region around each input feature point that is used to search for a match.

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Displacement Threshold specifies the minimum allowed displacement between the location of the tracked features from iteration to iteration. That is, if the position of a feature does not move more than the Displacement Threshold from its location on a previous iteration, the current location of the feature is finalized and it is not tracked anymore.

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Current Frame is a reference to the current source image.

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Previous Frame is a reference to the previous source image.

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Kernel specifies the coefficients of the filter that is used to smooth the image. The kernel coefficients must be symmetric.

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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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Feature Points In is an array of points that need to be tracked.

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X is the x-coordinate of the point.

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Y is the y-coordinate of the point.

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Current Frame Out (dup) is a duplicate of the input Current Frame.

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Distance Array returns the distance between Feature Points In and Feature Points Out.

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Feature Points Out is an array of points that represent the new locations of the input Feature Points.

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X is the x-coordinate of the point.

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Y is the y-coordinate of the point.

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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.

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