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% CANNY - Canny边缘检测 
% 代码使用了由 Fleck 提出的修改 (IEEE PAMI No. 3, Vol. 14. March 1992. pp 337-345) 
% 
% 使用： 
%      [gradient or] = canny(im, sigma) 
% 
% Arguments:   im       - 要处理的图像 
%              sigma    - 高斯平滑滤波器的标准偏移，典型值为1 
%		       scaling  - 缩小输入图像的比例因子 
%		       vert     - 竖直梯度分量 
%		       horz     - 水平梯度分量 
% 
% Returns:     gradient - 边界增强图像 (梯度幅值) 
%              or       - 定位图像 (in degrees 0-180, positive 
%                         anti-clockwise) 
% 
% 同时参见:  NONMAXSUP, HYSTHRESH 
 
% Author:  
% Peter Kovesi    
% Department of Computer Science & Software Engineering 
% The University of Western Australia 
% pk@cs.uwa.edu.au  www.cs.uwa.edu.au/~pk 
% 
% April 1999    Original version 
% January 2003  Error in calculation of d2 corrected 
% March 2003	Modified to accept scaling factor and vertical/horizontal 
%		        gradient bias (Libor Masek) 
 
function [gradient, or] = canny(im, sigma, scaling, vert, horz) 
 
xscaling = vert; 
yscaling = horz; 
 
hsize = [6*sigma+1, 6*sigma+1];   % The filter size. 
 
gaussian = fspecial('gaussian',hsize,sigma); 
im = filter2(gaussian,im);        % Smoothed image. 
 
im = imresize(im, scaling); 
 
[rows, cols] = size(im); 
 
h =  [  im(:,2:cols)  zeros(rows,1) ] - [  zeros(rows,1)  im(:,1:cols-1)  ]; 
v =  [  im(2:rows,:); zeros(1,cols) ] - [  zeros(1,cols); im(1:rows-1,:)  ]; 
d1 = [  im(2:rows,2:cols) zeros(rows-1,1); zeros(1,cols) ] - ... 
                               [ zeros(1,cols); zeros(rows-1,1) im(1:rows-1,1:cols-1)  ]; 
d2 = [  zeros(1,cols); im(1:rows-1,2:cols) zeros(rows-1,1);  ] - ... 
                               [ zeros(rows-1,1) im(2:rows,1:cols-1); zeros(1,cols)   ]; 
 
X = ( h + (d1 + d2)/2.0 ) * xscaling; 
Y = ( v + (d1 - d2)/2.0 ) * yscaling; 
 
gradient = sqrt(X.*X + Y.*Y); % Gradient amplitude. 
 
or = atan2(-Y, X);            % Angles -pi to + pi. 
neg = or<0;                   % Map angles to 0-pi. 
or = or.*~neg + (or+pi).*neg;  
or = or*180/pi;               % Convert to degrees.