hough_line_trans_dir — Compute the Hough transform for lines using local gradient direction.
hough_line_trans_dir calculates the Hough transform for
lines in those regions passed in the domain of
To do so, the angles and the lengths of the lines' normal vectors are
registered in the parameter space (the so-called Hough or accumulator
In contrast to
hough_line_trans, additionally the edge direction in
ImageDir (e.g., returned by
edges_image) is taken into account. This results in a more efficient
computation and in a reduction of the noise in the Hough space.
DirectionUncertainty describes how much the edge
direction of the individual points within a line is allowed to vary. For
DirectionUncertainty = 10 a horizontal
line (i.e., edge direction = 0 degrees) may contain points with an edge
direction between -10 and +10 degrees. The higher
DirectionUncertainty is chosen, the higher the computation time
will be. For
DirectionUncertainty = 180
hough_line_trans_dir shows the same behavior as
hough_line_trans, i.e., the edge direction is ignored.
DirectionUncertainty should be chosen at least as high as the
step width of the edge direction stored in
ImageDir. The minimum
step width is 2 degrees (defined by the image type 'direction').
The result is stored in a newly generated UINT2-Image
HoughImage), where the x-axis (i.e., columns) represents the
angle between the normal vector and the x-axis of the original image, and the
y-axis (i.e., rows) represents the distance of the line from the origin.
The angle ranges from -90 to 180 degrees and will be stored with a
resolution of 1 /
AngleResolution, which means that one pixel
in x-direction is equivalent to 1 /
and that the
HoughImage has a width of
+ 1 pixels. The height of the
HoughImage corresponds to the
distance between the lower right corner of the surrounding rectangle
of the input region and the origin.
The local maxima in the result image are equivalent to the parameter values of the lines in the original image.
Image containing the edge direction. The edges must be described by the image domain.
Uncertainty of the edge direction (in degrees).
Default value: 2
Typical range of values:
Minimum increment: 2
Resolution in the angle area (in 1/degrees).
Default value: 4
List of values: 1, 2, 4, 8
hough_line_trans_dir returns the value 2 (H_MSG_TRUE)
if the input is not empty.
The behavior in case of empty input is set via the operator
If necessary an exception is raised.