frei_dirfrei_dirFreiDirFreiDirfrei_dir (Operator)

Name

frei_dirfrei_dirFreiDirFreiDirfrei_dir — Detect edges (amplitude and direction) using the Frei-Chen operator.

Signature

Description

frei_dirfrei_dirFreiDirFreiDirfrei_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:

The result image contains the maximum response of the masks A and B. The edge directions are returned in ImageEdgeDirImageEdgeDirImageEdgeDirimageEdgeDirimage_edge_dir, and are stored in 2-degree steps, i.e., an edge direction of x degrees in mathematically positive sense and with respect to the horizontal axis is stored as x / 2 in the edge direction image. Furthermore, the direction of the change of intensity is taken into account. Let denote the image gradient. Then the following edge directions are returned as r/2: Points with edge amplitude 0 are assigned the edge direction 255 (undefined direction).

Attention

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.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on tuple level.
• Automatically parallelized on channel level.
• Automatically parallelized on domain level.

Parameters

read_image(Image,'fabrik')
frei_dir(Image,Frei_dirA,Frei_dirD)
threshold(Frei_dirA,Res,128,255)

read_image(&Image,"fabrik");
frei_dir(Image,&Frei_dirA,&Frei_dirD);
threshold(Frei_dirA,&Res,128,255);

read_image(Image,'fabrik')
frei_dir(Image,Frei_dirA,Frei_dirD)
threshold(Frei_dirA,Res,128,255)

read_image(Image,'fabrik')
frei_dir(Image,Frei_dirA,Frei_dirD)
threshold(Frei_dirA,Res,128,255)

Result

frei_dirfrei_dirFreiDirFreiDirfrei_dir always returns 2 ( H_MSG_TRUE) . If the input is empty the behavior can be set via set_system('no_object_result',<Result>)set_system("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>)set_system("no_object_result",<Result>). If necessary, an exception is raised.

Possible Predecessors

binomial_filterbinomial_filterBinomialFilterBinomialFilterbinomial_filter, gauss_filtergauss_filterGaussFilterGaussFiltergauss_filter, sigma_imagesigma_imageSigmaImageSigmaImagesigma_image, median_imagemedian_imageMedianImageMedianImagemedian_image, smooth_imagesmooth_imageSmoothImageSmoothImagesmooth_image

Possible Successors

hysteresis_thresholdhysteresis_thresholdHysteresisThresholdHysteresisThresholdhysteresis_threshold, thresholdthresholdThresholdThresholdthreshold, gray_skeletongray_skeletonGraySkeletonGraySkeletongray_skeleton, nonmax_suppression_dirnonmax_suppression_dirNonmaxSuppressionDirNonmaxSuppressionDirnonmax_suppression_dir, close_edgesclose_edgesCloseEdgesCloseEdgesclose_edges, close_edges_lengthclose_edges_lengthCloseEdgesLengthCloseEdgesLengthclose_edges_length

Alternatives

edges_imageedges_imageEdgesImageEdgesImageedges_image, sobel_dirsobel_dirSobelDirSobelDirsobel_dir, robinson_dirrobinson_dirRobinsonDirRobinsonDirrobinson_dir, prewitt_dirprewitt_dirPrewittDirPrewittDirprewitt_dir, kirsch_dirkirsch_dirKirschDirKirschDirkirsch_dir

See also

bandpass_imagebandpass_imageBandpassImageBandpassImagebandpass_image, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGausslaplace_of_gauss

Module

Foundation