VisionWorks Toolkit Reference

December 18, 2015 | 1.2 Release

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Optical Flow PyrLK Extensions

Adds various extensions to the Optical Flow PyrLK vision function.

This section describes different extensions to the standard Optical Flow Pyramid (LK) vision function.

Supported Input Formats

In addition to standard formats for the Optical Flow PyrLK primitive, VisionWorks supports the following input array formats:

For NVX_TYPE_POINT2F type lost points will be marked as (-1, -1) value.

Input Tracking Status

The primitive uses tracking_status information for input points (VX_TYPE_KEYPOINT, NVX_TYPE_KEYPOINTF) and updates only points with non-zero tracking_status. The points with tracking_status == 0 gets copied to the output array as is.

The VisionWorks corner detectors (FastCorners, HarrisCorners, FAST Track, Harris Track) initialize the tracking_status field of detected points to 1.

If the input keypoints are provided from user code, the tracking_status field must be explicitly initialized to non-zero value.

For NVX_TYPE_POINT2F type points, the outside of the image border are considered lost and are copied to the output array as is.

Window Dimension Limitation

The supported range for the window_dimension parameter is limited to [3; max_dimension_value]. The maximum supported value can be obtained via vxQueryContext with VX_CONTEXT_ATTRIBUTE_OPTICAL_FLOW_WINDOW_MAXIMUM_DIMENSION.