frei_amp — 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.
Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.
Edge amplitude (gradient magnitude) image.
read_image(Image,'fabrik') frei_amp(Image,Frei_amp) threshold(Frei_amp,Edges,128,255)
frei_amp always returns 2 (H_MSG_TRUE). If the input is empty the behavior can be set via set_system('no_object_result',<Result>). If necessary, an exception is raised.
binomial_filter, gauss_filter, sigma_image, median_image, smooth_image
sobel_amp, kirsch_amp, prewitt_amp, robinson_amp, roberts