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 -1The result image contains the maximum response of the masks A and B.
Image (input_object) |
image(-array) -> object : byte |
Input image. |
ImageEdgeAmp (output_object) |
image(-array) -> object : byte |
Edge amplitude (gradient magnitude) image. |
read_image(:Image:'fabrik':) > frei_amp(Image:Frei_amp::) > threshold__(Frei_amp:Edges:128,255:).
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.
gauss__, sigma__, median, smooth__
sobel_amp, kirsch_amp, prewitt_amp, robinson_amp, roberts__