points_lepetit — Detect points of interest using the Lepetit operator.
points_lepetit extracts points of interest like corners or
blob-like structures from
Image is first
smoothed with a median of size 3x3. Then, all the gray values on a circle
Radius around an interest point candidate
(m) are examined. The absolute differences of two diagonally
opposed gray values (m1,m2) on the circle to the central pixel
m is computed. At least one of these differences has to be
MinCheckNeighborDiff. All diagonally opposed pixels
on the circle must fulfill that condition. To suppress detection of
points at edges that have a small curvature (aliasing), it is possible
CheckNeighbor further differences of circle point
neighbors of m1 and m2 to the center, that as well
fulfill the above criteria. By computing all gray value differences of
the circle points to the center, a mean gray value difference is
determined. That value has to be larger than
allows to restrict the results to points with high contrast. By computing
the score of all eight neighbors of m, it is possible to fit a quadratic
equation to that. The maxima of that equation determines a subpixel
accurate interest point position. By setting the parameter
to 'interpolation' (default) or 'none', it is possible to turn that refinement
step on or off. The resulting points are returned in
Column. The operator
points_lepetit can especially be
used for very fast interest point extraction. The results are however
less robust than points extracted by
points_harris for example.
Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.
→object (byte / uint2)
Radius of the circle.
Default value: 3
Suggested values: 3, 5, 6, 7, 8, 9, 10, 15
Number of checked neighbors on the circle.
Default value: 1
Suggested values: 1, 2, 3, 5
Threshold of grayvalue difference to each circle point.
Default value: 15
Suggested values: 10, 15, 20, 25, 30, 35, 40, 45, 60, 80
Threshold of grayvalue difference to all circle points.
Default value: 30
Suggested values: 5, 10, 15, 20, 25, 30
Subpixel accuracy of point coordinates.
Default value: 'interpolation'
List of values: 'interpolation', 'none'
→(integer / real)
Row-coordinates of the detected points.
→(integer / real)
Column-coordinates of the detected points.