frei_amp ( Image : ImageEdgeAmp : : )

Detect edges (amplitude) using the Frei-Chen operator.

frei_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       sqrt(2)        1
         0          0           0
        -1      -sqrt(2)       -1

  B =
         1          0          -1
       sqrt(2)      0       -sqrt(2) 
         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':) >
frei_amp(Image:Frei_amp::) >
threshold__(Frei_amp:Edges:128,255:).

Result

frei_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__


Alternatives

sobel_amp, kirsch_amp, prewitt_amp, robinson_amp, roberts__


See also

bandpass__, laplace_of_gauss



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