prewitt_amp ( Image : ImageEdgeAmp : : )

Detect edges (amplitude) using the Prewitt operator.

prewitt_amp 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:

  A =
        1       1       1
        0       0       0
       -1      -1      -1

  B =
        1       0      -1
        1       0      -1
        1       0      -1  
The result image contains the maximum response of the masks A and B.


Parameters

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

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


Example
read_image(:Image:'fabrik':) >
prewitt_amp(Image:Prewitt::) >
threshold__(Prewitt:Edges:128,255:).

Result

prewitt_amp 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

threshold__, grey_skeleton__, nonmax_suppression_amp, close_edges1, close_edges2


Alternatives

sobel_amp, kirsch_amp, frei_amp, robinson_amp, roberts__


See also

bandpass__, laplace_of_gauss



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