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gridextractor.m
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%Extracts the grid for the grid defined on
%http://www.vision.ee.ethz.ch/~cwengert/calibration_toolbox.php
%
%Input: im The image to process
% show 0 to not display any information graphically
% minArea The minimum area a grid dot occupies
% maxArea The minimum area a grid dot occupies
%Output: success 1 if everything went ok
% stats The processed blobs of this image
% id0 The index of the main bar
% id1 The index of the second main bar
% searchPoints The potential grid points
%
%
%Christian Wengert
%Computer Vision Laboratory
%ETH Zurich
%Sternwartstrasse 7
%CH-8092 Zurich
%www.vision.ee.ethz.ch/cwengert
function [success, stats, cnt, id0, id1, searchPoints] = gridextractor(im, show, minArea, maxArea)
%crop image
if(nargin==1)
show=0;
end
success = 0;
stats = [];
cnt = 0;
searchPoints = [];
%Indices for main bars
idx = [];
ids = [];
id0 = -1;
id1 = -1;
x_ = [];
X_ = [];
%Show the image
if(show)
if(isfloat(im))
imshow(im/255.0),hold on
else
imshow(im),hold on
end
end
%Get the size of the image
[h,w,bpp] = size(im);
if(h<=0 & w<=0)
return
end
if(bpp==3)
img = rgb2gray(im);
else
img = im;
end
%used to filter for ellipticity
minEllipticity = 1.95;
maxEllipticity = 8;
minSolidity = 0.80;
%Used to filter by closeness to border->to close to border cannot be
%correct
borderRect = [0+50, 0+50, w-50, h-50];
x0 = w/2;
y0 = h/2;
imc = im;
for i=1:w
for j=1:h
r = sqrt((x0-i)*(x0-i) + (y0-j)*(y0-j));
if(r>160)
imc(j,i) = 0;
end
end
end
%Rather median filter
imb = medfilt2(img,[3 3]);
%Threshold
h1 = fspecial('gaussian',100, 15);
imf= (imfilter(im, h1));
imt = ( imclose(medfilt2(im<imf,[3 3]), ones(5))) ;
%Label
iml = bwlabel(imt,8);
%Extract features
stats=regionprops(iml,'Centroid','Area','Orientation','MajorAxisLength','MinorAxisLength','ConvexHull','BoundingBox','Solidity');
%Extract values and put them into vectors, just makes it easier
areas = [stats.Area];
pts = [stats.Centroid];
ptsx = pts(1:2:end);
ptsy = pts(2:2:end);
majors = [stats.MajorAxisLength];
minors = [stats.MinorAxisLength];
solidity = [stats.Solidity];
%Now get the two major things
cnt = 0;
for i=1:length(stats)
%Filter on closeness to border
if(stats(i).Centroid(1)>borderRect(1) & stats(i).Centroid(1)<borderRect(3) & stats(i).Centroid(2) > borderRect(2) & stats(i).Centroid(2) <borderRect(4))
%Filter area
if(areas(i)>minArea & areas(i)<maxArea & solidity(i) > minSolidity)
idx = [idx;i];
%Filter on ellipticity
if((majors(i)/minors(i))>minEllipticity & (majors(i)/minors(i))<maxEllipticity )
if(show)
plot(stats(i).Centroid(1),stats(i).Centroid(2),'r+')
end
ids = [ids;i];
cnt = cnt+1;
%Delete it from searchPoints, serves as an ellipticity
%filter!
idx(end) = [];
end
end
end
end
%Show area filtered blobs
if(show)
for i=1:length(idx)
plot(stats(idx(i)).Centroid(1),stats(idx(i)).Centroid(2),'go')
end
end
try
%Extract the main bars
if(cnt==2)
if(areas(ids(1))>areas(ids(2)))
id0 = ids(1); id1 = ids(2);
else
id0 = ids(2); id1 = ids(1);
end
%Test angle between main lines
dir0 = (stats(id1).Centroid-stats(id0).Centroid);
dir0 = dir0/norm(dir0);
%get the orientation of main bar
orientation = stats(id0).Orientation;
y = tand(orientation);
dir90 = [-1,y];
dir90 = dir90/norm(dir90);
%Check angle
theta = acos((dir0*dir90')/(norm(dir0)*norm(dir90)))/pi*180;
if(theta<70 | theta>110)
disp('gridextractor:: Could not find both main bars, bar-count = 1. ')
stats = [];
searchPoints = [];
success = 0;
cnt = 0;
id0 = 0;
id1 = 0;
else
searchPoints = [areas(idx);...
ptsx(idx);...
ptsy(idx)];
success = 1;
if(show)
text(stats(id0).Centroid(1)+5,stats(id0).Centroid(2)+5,'0','Color','m');
text(stats(id1).Centroid(1)+5,stats(id1).Centroid(2)+5,'1','Color','m');
end
end
elseif(cnt>2)
disp('gridextractor:: Found too many possible candidates, trying to choose the correct ones')
%get the two blobs that are closest to each other!
a = [];
xb = [];
%Sort by Area
for i=1:length(ids)
xb = [xb, [stats(ids(i)).Centroid(1);stats(ids(i)).Centroid(2)]];
if(xb(1,i) > 50 | xb(1,i) < (w-50) | xb(2,i) > 50 | xb(2,i) < (h-50))
a = [a;stats(ids(i)).Area];
else
a = [a;-1];
end
end
[a,ixxx] = sort(a);
%Take the two biggest ones
id0 = ids(ixxx(end));
id1 = ids(ixxx(end-1));
%Directions
dir0 = (stats(id1).Centroid-stats(id0).Centroid);
dir0 = dir0/norm(dir0);
%get the orientation of main bar
orientation = stats(id0).Orientation;
y = tand(orientation);
dir90 = [-1,y];
dir90 = dir90/norm(dir90);
%Check angle
theta = acos((dir0*dir90')/(norm(dir0)*norm(dir90)))/pi*180;
if(theta<80 | theta>100)
id1 = ids(ixxx(end-2));
%Test again
dir0 = (stats(id1).Centroid-stats(id0).Centroid);
dir0 = dir0/norm(dir0);
%get the orientation of main bar
orientation = stats(id0).Orientation;
y = tand(orientation);
dir90 = [-1,y];
dir90 = dir90/norm(dir90);
%Check angle
theta = acos((dir0*dir90')/(norm(dir0)*norm(dir90)))/pi*180;
if(theta<80 | theta>100)
disp('gridextractor:: Could not find both main bars, bar-count = 1. ')
stats = [];
searchPoints = [];
success = 0;
cnt = 0;
id0 = 0;
id1 = 0;
end
end
if(show)
text(stats(id0).Centroid(1)+5,stats(id0).Centroid(2)+5,'0','Color','y');
text(stats(id1).Centroid(1)+5,stats(id1).Centroid(2)+5,'1','Color','y');
end
cnt = 2;
success = 1;
searchPoints = [areas(idx);...
ptsx(idx);...
ptsy(idx)];
else
disp('gridextractor:: Could not find both main bars, bar-count = 1. ')
stats = [];
searchPoints = [];
success = 0;
cnt = 0;
id0 = 0;
id1 = 0;
end
catch
disp('gridextractor:: Problems extracting the main bars. Please verify whether it is visible in this image.')
s = lasterror;
disp(['gridextractor:: ' s.message ' in function ' s.stack.name ' in ' s.stack.file ' @line ' num2str(s.stack.line)])
stats = [];
searchPoints = [];
success = 0;
cnt = 0;
id0 = 0;
id1 = 0;
end