frei_dirfrei_dirFreiDirFreiDirfrei_dir (Operator)

Name

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

Signature

Description

frei_dirfrei_dirFreiDirFreiDirFreiDirfrei_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 ImageEdgeDirImageEdgeDirImageEdgeDirImageEdgeDirimageEdgeDirimage_edge_dir, and are stored in 2-degree steps, i.e., an edge direction of degrees in mathematically positive sense and with respect to the horizontal axis is stored as 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 : 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)

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

Result

frei_dirfrei_dirFreiDirFreiDirFreiDirfrei_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>)SetSystem("no_object_result",<Result>)set_system("no_object_result",<Result>). If necessary, an exception is raised.

Possible Predecessors

binomial_filterbinomial_filterBinomialFilterBinomialFilterBinomialFilterbinomial_filter, gauss_filtergauss_filterGaussFilterGaussFilterGaussFiltergauss_filter, sigma_imagesigma_imageSigmaImageSigmaImageSigmaImagesigma_image, median_imagemedian_imageMedianImageMedianImageMedianImagemedian_image, smooth_imagesmooth_imageSmoothImageSmoothImageSmoothImagesmooth_image

Possible Successors

hysteresis_thresholdhysteresis_thresholdHysteresisThresholdHysteresisThresholdHysteresisThresholdhysteresis_threshold, thresholdthresholdThresholdThresholdThresholdthreshold, gray_skeletongray_skeletonGraySkeletonGraySkeletonGraySkeletongray_skeleton, nonmax_suppression_dirnonmax_suppression_dirNonmaxSuppressionDirNonmaxSuppressionDirNonmaxSuppressionDirnonmax_suppression_dir, close_edgesclose_edgesCloseEdgesCloseEdgesCloseEdgesclose_edges, close_edges_lengthclose_edges_lengthCloseEdgesLengthCloseEdgesLengthCloseEdgesLengthclose_edges_length

Alternatives

edges_imageedges_imageEdgesImageEdgesImageEdgesImageedges_image, sobel_dirsobel_dirSobelDirSobelDirSobelDirsobel_dir, robinson_dirrobinson_dirRobinsonDirRobinsonDirRobinsonDirrobinson_dir, prewitt_dirprewitt_dirPrewittDirPrewittDirPrewittDirprewitt_dir, kirsch_dirkirsch_dirKirschDirKirschDirKirschDirkirsch_dir

See also

bandpass_imagebandpass_imageBandpassImageBandpassImageBandpassImagebandpass_image, laplace_of_gausslaplace_of_gaussLaplaceOfGaussLaplaceOfGaussLaplaceOfGausslaplace_of_gauss

Module

Foundation