% -*- texinfo -*- % @deftypefn {Function File} {@var{bw} =} edge (@var{im}, @var{method}) % @deftypefnx{Function File} {@var{bw} =} edge (@var{im}, @var{method}, @var{arg1}, @var{arg2}) % @deftypefnx{Function File} {[@var{bw}, @var{thresh}] =} edge (...) % Detect edges in the given image using various methods. The first input @var{im} % is the gray scale image in which edges are to be detected. The second argument % controls which method is used for detecting the edges. The rest of the input % arguments depend on the selected method. The first output @var{bw} is a % @code{logical} image containing the edges. Most methods also returns an automatically % computed threshold as the second output. % % The @var{method} input argument can any of the following strings (the default % value is 'Sobel') % % @table @asis % @item 'Sobel' % Finds the edges in @var{im} using the Sobel approximation to the % derivatives. Edge points are defined as points where the length of % the gradient exceeds a threshold and is larger than it's neighbours % in either the horizontal or vertical direction. The threshold is passed to % the method in the third input argument @var{arg1}. If one is not given, a % threshold is automatically computed as 4*@math{M}, where @math{M} is the mean % of the gradient of the entire image. The optional 4th input argument controls % the direction in which the gradient is approximated. It can be either % 'horizontal', 'vertical', or 'both' (default). % % @item 'Prewitt' % Finds the edges in @var{im} using the Prewitt approximation to the % derivatives. This method works just like 'Sobel' except a different aproximation % the gradient is used. % % @item 'Roberts' % Finds the edges in @var{im} using the Roberts approximation to the % derivatives. Edge points are defined as points where the length of % the gradient exceeds a threshold and is larger than it's neighbours % in either the horizontal or vertical direction. The threshold is passed to % the method in the third input argument @var{arg1}. If one is not given, a % threshold is automatically computed as 6*@math{M}, where @math{M} is the mean % of the gradient of the entire image. The optional 4th input argument can be % either 'thinning' (default) or 'nothinning'. If it is 'thinning' a simple % thinning procedure is applied to the edge image such that the edges are only % one pixel wide. If @var{arg2} is 'nothinning', this procedure is not applied. % % @item 'Kirsch' % Finds the edges in @var{im} using the Kirsch approximation to the % derivatives. Edge points are defined as points where the length of % the gradient exceeds a threshold and is larger than it's neighbours % in either the horizontal or vertical direction. The threshold is passed to % the method in the third input argument @var{arg1}. If one is not given, a % threshold is automatically computed as @math{M}, where @math{M} is the mean % of the gradient of the entire image. The optional 4th input argument controls % the direction in which the gradient is approximated. It can be either % 'horizontal', 'vertical', or 'both' (default). % % @item 'LoG' % Finds edges in @var{im} by convolving with the Laplacian of Gaussian (LoG) % filter, and finding zero crossings. Only zero crossings where the % filter response is larger than an automatically computed threshold are retained. % The threshold is passed to the method in the third input argument @var{arg1}. % If one is not given, a threshold is automatically computed as 0.75*@math{M}, % where @math{M} is the mean of absolute value of LoG filter response. The % optional 4th input argument sets the spread of the LoG filter. By default % this value is 2. % % @item 'Zerocross' % Finds edges in the image @var{im} by convolving it with the user-supplied filter % @var{arg2} and finding zero crossings larger than the threshold @var{arg1}. If % @var{arg1} is [] a threshold is computed as the mean value of the absolute % filter response. % % @item 'Canny' % Finds edges using the Canny edge detector. The optional third input argument % @var{arg1} sets the thresholds used in the hysteresis thresholding. If % @var{arg1} is a two dimensional vector it's first element is used as the lower % threshold, while the second element is used as the high threshold. If, on the % other hand, @var{arg1} is a single scalar it is used as the high threshold, % while the lower threshold is 0.4*@var{arg1}. The optional 4th input argument % @var{arg2} is the spread of the low-pass Gaussian filter that is used to smooth % the input image prior to estimating gradients. By default this scale parameter % is 2. % % @item 'Lindeberg' % Finds edges using in @var{im} using the differential geometric single-scale edge % detector given by Tony Lindeberg. The optional third input argument @var{arg1} % is the scale (spread of Gaussian filter) at which the edges are computed. By % default this 2. % % @item 'Andy' % A.Adler's idea (c) 1999. Somewhat based on the canny method. The steps are % @enumerate % @item % Do a Sobel edge detection and to generate an image at % a high and low threshold. % @item % Edge extend all edges in the LT image by several pixels, % in the vertical, horizontal, and 45 degree directions. % Combine these into edge extended (EE) image. % @item % Dilate the EE image by 1 step. % @item % Select all EE features that are connected to features in % the HT image. % @end enumerate % % The parameters for the method is given in a vector: % @table @asis % @item params(1)==0 or 4 or 8 % Perform x connected dilatation (step 3). % @item params(2) % Dilatation coeficient (threshold) in step 3. % @item params(3) % Length of edge extention convolution (step 2). % @item params(4) % Coeficient of extention convolution in step 2. % @end table % defaults = [8, 1, 3, 3] % % @end table % % @seealso{fspecial, nonmax_supress} % @end deftypefn

- dilate % Perform a dilation morphological operation on a binary image.
- fspecial % Create spatial filters for image processing.
- imsmooth % Smooth the given image using several different algorithms.
- isgray % Returns true for an gray-scale intensity image. An variable is a gray scale image

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