chesscornerfilter

 CHESSCORNERFILTER filters Harris corners for chessboard corners.
 
 CHESSCORNERFILTER takes as input the image, the sobel edge image and
 the Harris corner points and outputs of the corner points that passed
 the filter the number of those points and the peak directions for each 
 of the points. The peak direction is used by the grid extraction (refer 
 to Bachelor Thesis by Abdallah Kassir 2009).
   
 The details of the filter are applied in the function VALIDCORNER
 
 USAGE:
     [crnrs,nocrnrs,peaklocs]=chesscornerfilter(img,imgedge,crnrpts,debug)
 
 INPUTS:
     img: original grayscale image
 
     imgedge: Sobel edge image
 
     crnrpts: output of GETCRNRPTS
 
 OUTPUTS:
     crnrs: 2xN array of corners that passed the filter
 
     nocrnrs: number of corners found
 
     peaklocs: required by GETGRID

0001 function [crnrs,nocrnrs,peaklocs]=chesscornerfilter(img,imgedge,crnrpts,debug)
0002 % CHESSCORNERFILTER filters Harris corners for chessboard corners.
0003 %
0004 % CHESSCORNERFILTER takes as input the image, the sobel edge image and
0005 % the Harris corner points and outputs of the corner points that passed
0006 % the filter the number of those points and the peak directions for each
0007 % of the points. The peak direction is used by the grid extraction (refer
0008 % to Bachelor Thesis by Abdallah Kassir 2009).
0009 %
0010 % The details of the filter are applied in the function VALIDCORNER
0011 %
0012 % USAGE:
0013 %     [crnrs,nocrnrs,peaklocs]=chesscornerfilter(img,imgedge,crnrpts,debug)
0014 %
0015 % INPUTS:
0016 %     img: original grayscale image
0017 %
0018 %     imgedge: Sobel edge image
0019 %
0020 %     crnrpts: output of GETCRNRPTS
0021 %
0022 % OUTPUTS:
0023 %     crnrs: 2xN array of corners that passed the filter
0024 %
0025 %     nocrnrs: number of corners found
0026 %
0027 %     peaklocs: required by GETGRID
0028 
0029 if ~exist('debug','var') || isempty(debug)
0030     debug=0;
0031 end
0032 
0033 % comment the line to allow debugging
0034 debug=0;
0035 
0036 % get sweepmatrices, precalculation of these matrices allows for much
0037 % faster program execution
0038 [sweepmatx,sweepmaty]=sweepmatrix(img);
0039 
0040 % set output values
0041 nocrnrs=0;
0042 crnrs=[];
0043 peaklocs=[];
0044 
0045 i=0;
0046 
0047 % loop over all points
0048 for indx=1:size(crnrpts,2)
0049     x=crnrpts(1,indx);
0050     y=crnrpts(2,indx);
0051     
0052     % extract appropriate window size
0053     win=getwin(img,[x;y],crnrpts);
0054     
0055     % check window size
0056     if win<3
0057         continue;
0058     end
0059     imgcrop=img(x-win:x+win,y-win:y+win);
0060     imgedgecrop=imgedge(x-win:x+win,y-win:y+win);
0061     sweepmatxcrop=sweepmatx(1:round(1.3*win),:);
0062     sweepmatycrop=sweepmaty(1:round(1.3*win),:);
0063     
0064     % apply filter
0065     [valid,plocs]=validcorner(imgcrop,imgedgecrop,sweepmatxcrop,sweepmatycrop);
0066     if valid
0067         i=i+1;
0068         crnrs(1,i)=x;
0069         crnrs(2,i)=y;
0070         nocrnrs=nocrnrs+1;
0071         peaklocs(:,i)=plocs;
0072 %     elseif x==129
0073 %         close all;
0074 %         imshow(imgcrop,[]);
0075 %         keyboard;
0076     end
0077 end
0078 
0079 % debugging
0080 if debug
0081     close all;
0082     figure;imshow(img);hold on;
0083     plot(crnrpts(2,:),crnrpts(1,:),'+');
0084     plot(crnrs(2,:),crnrs(1,:),'o','color','red');
0085     pause;
0086 end