kirsch_dir ( Image : ImageEdgeAmp, ImageEdgeDir : : )

Detect edges (amplitude and direction) using the Kirsch operator.

kirsch_dir calculates an approximation of the first derivative of the image data and is used as an edge detector. The filter is based on the following filter masks: -3 -3 5 -3 5 5 5 5 5 5 5 -3 -3 0 5 -3 0 5 -3 0 -3 5 0 -3 -3 -3 5 -3 -3 -3 -3 -3 -3 -3 -3 -3 5 -3 -3 -3 -3 -3 -3 -3 -3 -3 -3 -3 5 0 -3 5 0 -3 -3 0 -3 -3 0 5 5 -3 -3 5 5 -3 5 5 5 -3 5 5 The result image contains the maximum response of all masks. The edge directions are returned in ImageEdgeDir, and are stored as x / 2. They correspond to the direction of the mask yielding the maximum response.


Parameters

Image (input_object)
image(-array) -> object : byte
Input image.

ImageEdgeAmp (output_object)
image(-array) -> object : byte
Edge amplitude (gradient magnitude) image.

ImageEdgeDir (output_object)
image(-array) -> object : direction
Edge direction image.


Example
read_image(:Image:'fabrik':) >
kirsch_dir(Image:Kirsch_dirA,Kirsch_dirD::) >
threshold__(Kirsch_dirA:Res:128,255:).

Result

kirsch_dir always returns TRUE. If the input is empty the behaviour can be set via set_system(::'no_object_result',<Result>:). If necessary, an exception is raised.


Possible Predecessors

gauss__, sigma__, median, smooth__


Possible Successors

hysteresis_threshold__, threshold__, grey_skeleton__, nonmax_suppression_dir, close_edges1, close_edges2


Alternatives

edges__, sobel_dir, robinson_dir, prewitt_dir, frei_dir


See also

bandpass__, laplace_of_gauss



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