边缘检测_算子_数字图像处理

% EDGELINK - Link edge points in an image into lists % % Usage: [edgelist edgeim] = edgelink(im, minlength, location) % % Arguments: im - Binary edge image, it is assumed that edges % have been thinned. % minlength - Minimum edge length of interest % location - Optional complex valued image holding subpixel % locations of edge points. For any pixel the % real part holds the subpixel row coordinate of % that edge point and the imaginary part holds % the column coordinate. See NONMAXSUP. If % this argument is supplied the edgelists will % be formed from the subpixel coordinates, % otherwise the the integer pixel coordinates of % points in 'im' are used. % % Returns: edgelist - a cell array of edge lists in row,column coords in % the form % { [r1 c1 [r1 c1 etc } % r2 c2 ... % ... % rN cN] ....] % % edgeim - Image with pixels labeled with edge number. % % % This function links edge points together into chains. Where an edge % diverges at a junction the function simply tracks one of the branches. % The other branch is eventually processed as another edge. These `broken % branches' can be remerged by MERGESEG after a call to LINESEG. % % See also: DRAWEDGELIST, LINESEG, MAXLINEDEV, MERGESEG, DRAWSEG, NONMAXSUP % Acknowledgement: % This code is inspired by David Lowe's Link.c function from the Vista image % processing library developed at the University of British Columbia % http://www.cs.ubc.ca/nest/lci/vista/vista.html % Copyright (c) 2001-2005 Peter Kovesi % School of Computer Science & Software Engineering % The University of Western Australia % http://www.csse.uwa.edu.au/ % % Permission is hereby granted, free of charge, to any person obtaining a copy % of this software and associated documentation files (the "Software"), to deal % in the Software without restriction, subject to the following conditions: % % The above copyright notice and this permission notice shall be included in % all copies or substantial portions of the Software. % % The Software is provided "as is", without warranty of any kind. % February 2001 - Original version % September 2004 - Revised to allow subpixel edge data to be used function [edgelist, edgeim] = edgelink(im, minlength, location) global EDGEIM; % Some global variables to avoid passing (and % copying) of arguments, this improves speed. global ROWS; global COLS; elist = {}; EDGEIM = im ~= 0; % make sure image is binary. % EDGEIM = bwmorph(EDGEIM,'thin',Inf); % make sure edges are thinned. % show(EDGEIM,1) EDGEIM = double(EDGEIM); [ROWS, COLS] = size(EDGEIM); edgeNo = 1; % Perform raster scan through image looking for edge points. When a % point is found trackedge is called to find the rest of the edge % points. As it finds the points the edge image pixels are labeled % with the -ve of their edge No for r = 1:ROWS for c = 1:COLS if EDGEIM(r,c) == 1 edgepoints = trackedge(r,c, edgeNo, minlength); if ~isempty(edgepoints) edgelist{edgeNo} = edgepoints; edgeNo = edgeNo + 1; end end end end edgeim = -EDGEIM; % Finally negate image to make edge encodings +ve. % If subpixel edge locations are supplied upgrade the integer precision % edgelists that were constructed with data from 'location'. if nargin == 3 for I = 1:length(edgelist) ind = sub2ind(size(im),edgelist{I}(:,1),edgelist{I}(:,2)); edgelist{I}(:,1) = real(location(ind))'; edgelist{I}(:,2) = imag(location(ind))'; end end % show(edgeim,2), colormap(flag); %---------------------------------------------------------------------- % TRACKEDGE % % Function to track all the edge points associated with a start point. From % a given starting point it tracks in one direction, storing the coords of % the edge points in an array and labelling the pixels in the edge image % with the -ve of their edge number. When no more connected points are % found the function returns to the start point and tracks in the opposite % direction. Finally a check for the overall number of edge points found is % made and the edge is ignored if it is too short. % % Note that when a junction is encountered along an edge the function % simply tracks one of the branches. The other branch is eventually % processed as another edge. These `broken branches' can be remerged by % MERGESEG. % % Usage: edgepoints = trackedge(rstart, cstart, edgeNo, minlength) % % Arguments: rstart, cstart - row and column No of starting point % edgeNo - the current edge number % minlength - minimum length of edge to accept % % Returns: edgepoints - Nx2 array of row and col values for % each edge point. % An empty array is returned if the edge % is less than minlength long. function edgepoints = trackedge(rstart, cstart, edgeNo, minlength) global EDGEIM; global ROWS; global COLS; edgepoints = [rstart cstart]; % Start a new list for this edge. EDGEIM(rstart,cstart) = -edgeNo; % Edge points in the image are % encoded by -ve of their edgeNo. [thereIsAPoint, r, c] = nextpoint(rstart,cstart); % Find next connected % edge point. while thereIsAPoint edgepoints = [edgepoints % Add point to point list r c ]; EDGEIM(r,c) = -edgeNo; % Update edge image [thereIsAPoint, r, c] = nextpoint(r,c); end edgepoints = flipud(edgepoints); % Reverse order of points % Now track from original point in the opposite direction [thereIsAPoint, r, c] = nextpoint(rstart,cstart); while thereIsAPoint edgepoints = [edgepoints r c ]; EDGEIM(r,c) = -edgeNo; [thereIsAPoint, r, c] = nextpoint(r,c); end % Reject short edges Npoints = size(edgepoints,1); if Npoints < minlength for i = 1:Npoints % Clear pixels in the edge image EDGEIM(edgepoints(i,1), edgepoints(i,2)) = 0; end edgepoints = []; % Return empty array end %---------------------------------------------------------------------- % % NEXTPOINT % % Function finds a point that is 8 connected to an existing edge point % function [thereIsAPoint, nextr, nextc] = nextpoint(rp,cp); global EDGEIM; global ROWS; global COLS; % row and column offsets for the eight neighbours of a point % starting with those that are 4-connected. roff = [1 0 -1 0 1 1 -1 -1]; coff = [0 1 0 -1 1 -1 -1 1]; r = rp+roff; c = cp+coff; % Search through neighbours and return first connected edge point for i = 1:8 if r(i) >= 1 & r(i) <= ROWS & c(i) >= 1 & c(i) <= COLS if EDGEIM(r(i),c(i)) == 1 nextr = r(i); nextc = c(i); thereIsAPoint = 1; return; % break out and return with the data end end end % If we get here there was no connecting next point. nextr = 0; nextc = 0; thereIsAPoint = 0;