fuzzy_measure_pos — Extract straight edges perpendicular to a rectangle or an annular arc.
fuzzy_measure_pos extracts straight edges which lie perpendicular to the major axis of a rectangle or an annular arc. In addition to measure_pos it uses fuzzy functions to evaluate and select the edges.
The algorithm works by averaging the gray values in “slices” perpendicular to the major axis of the rectangle or annular arc in order to obtain a one-dimensional edge profile. The sampling is done at subpixel positions in the image Image at integer row and column distances (in the coordinate frame of the rectangle) from the center of the rectangle. Since this involves some calculations which can be used repeatedly in several measurements, the operator gen_measure_rectangle2 is used to perform these calculations only once, thus increasing the speed of fuzzy_measure_pos significantly. Since there is a trade-off between accuracy and speed in the subpixel calculations of the gray values, and thus in the accuracy of the extracted edge positions, different interpolation schemes can be selected in gen_measure_rectangle2. (The interpolation only influences rectangles not aligned with the image axes and annular arcs.) The measure object generated with gen_measure_rectangle2 is passed in MeasureHandle.
After the one-dimensional edge profile has been calculated, subpixel edge locations are computed by convolving the profile with the derivatives of a Gaussian smoothing kernel of standard deviation Sigma. Salient edges can be selected with the parameter AmpThresh, which constitutes a threshold on the amplitude, i.e., the absolute value of the first derivative of the edge. Additionally, it is possible to select only positive edges, i.e., edges which constitute a dark-to-light transition in the direction of the major axis of the rectangle (Transition = 'positive'), only negative edges, i.e., light-to-dark transitions (Transition = 'negative'), or both types of edges (Transition = 'all'). Finally, it is possible to select which edge points are returned.
Having extracted subpixel edge locations, features of these edges are evaluated by a corresponding fuzzy function, which can be set by set_fuzzy_measure. Which edges are selected can be determined with the parameter FuzzyThresh, which constitutes a threshold on the weight over all fuzzy sets, i.e., the geometric mean of the weights of the defined sets.
The selected edges are returned as single points, which lie on the major axis of the rectangle or annular arc, in (RowEdge,ColumnEdge). The corresponding edge amplitudes are returned in Amplitude, the fuzzy scores in FuzzyScore. In addition, the distance between consecutive edge points is returned in Distance. Here, Distance[i] corresponds to the distance between Edge[i] and Edge[i+1], i.e., the tuple Distance contains one element less than the tuples RowEdge and ColumnEdge.
fuzzy_measure_pos only returns meaningful results if the assumptions that the edges are straight and perpendicular to the major axis of the rectangle are fulfilled. Thus, it should not be used to extract edges from curved objects, for example. Furthermore, the user should ensure that the rectangle is as close to perpendicular as possible to the edges in the image. Additionally, Sigma must not become larger than approx. 0.5 * Length1 (for Length1 see gen_measure_rectangle2).
It should be kept in mind that fuzzy_measure_pos ignores the domain of Image for efficiency reasons. If certain regions in the image should be excluded from the measurement a new measure object with appropriately modified parameters should be generated.
Measure object handle.
Sigma of Gaussian smoothing.
Default value: 1.0
Suggested values: 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 7.0, 10.0
Typical range of values: 0.4 ≤ Sigma ≤ 100 (lin)
Minimum increment: 0.01
Recommended increment: 0.1
Restriction: Sigma >= 0.4
Minimum edge amplitude.
Default value: 30.0
Suggested values: 5.0, 10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 90.0, 110.0
Typical range of values: 1 ≤ AmpThresh ≤ 255 (lin)
Minimum increment: 0.5
Recommended increment: 2
Minimum fuzzy value.
Default value: 0.5
Suggested values: 0.1, 0.3, 0.5, 0.6, 0.7, 0.9
Typical range of values: 0.0 ≤ FuzzyThresh ≤ 1.0 (lin)
Recommended increment: 0.1
Select light/dark or dark/light edges.
Default value: 'all'
List of values: 'all', 'negative', 'positive'
Row coordinate of the edge point.
Column coordinate of the edge point.
Edge amplitude of the edge (with sign).
Fuzzy evaluation of the edges.
Distance between consecutive edges.
If the parameter values are correct the operator fuzzy_measure_pos returns the value 2 (H_MSG_TRUE). Otherwise an exception is raised.
gen_measure_rectangle2, gen_measure_arc, set_fuzzy_measure
fuzzy_measure_pairing, fuzzy_measure_pairs, measure_pairs