# Optical Flow (Optical Flow (HS)) (G Dataflow)

Computes the optical flow (velocity flow) information in two successive images using the Horn-Schunck algorithm.

## stopping criteria

Conditions that need to be met to stop the optical flow computation.

### type

Type of stopping criteria to use.

Choose one of the following criteria.

Name Description
Iterations Specifies that the computation should stop after the number of iterations in the max. iterations control.
Epsilon Specifies the computation should stop after the value of epsilon has been reached.
Both Specifies the computation should stop after the maximum iterations and Epsilon value have both been reached.

### max. iterations

Maximum iterations to run the optical flow computation.

### epsilon

Maximum difference allowed between the velocity information computed between two successive iterations.

## ROI descriptor

Descriptor that defines the region of interest (ROI) within which the optical flow is computed.

### global rectangle

Coordinates of the bounding rectangle.

### contours

Individual shapes that define an ROI.

#### ID

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

#### Type

Shape type of the contour.

#### Coordinates

Relative position of the contour.

## current frame

Reference to the current source image.

## previous frame

Reference to the previous source image.

## velocity component 1 in

Reference to the image that will contain the horizontal component or the magnitude component of the computed velocity at each pixel.

## velocity component 2 in

Reference to the image that will contain the vertical component or the phase component of the computed velocity at each pixel.

## smoothing parameter

Smoothing effect to apply to the velocity information in the image.

## 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

## velocity representation

Computed velocity information represented in Cartesian or polar coordinates.

## use previous

Boolean value which, when True, uses the information in velocity component 1 in and velocity component 2 in as the initial estimates of the velocity to compute the current velocity.

## current frame out

Duplicate of the input current frame.

## velocity component 1 out

Reference to the image that contains the horizontal component or the magnitude component of the computed velocity at each pixel.

## velocity component 2 out

Reference to the image that contains the vertical component or the phase component of the computed velocity at each pixel.

## 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