% read image, find edges and Hough transform
I = imread('pillows.jpg');
I = imread('chip.tif');
BW = edge(I,'canny'); % extract edges
[H,theta,rho] = hough(BW,'RhoResolution',0.5,'ThetaResolution',0.5);

% display the original image
subplot(2,1,1);
%imshow(RGB);
imshow(I);

% display the hough matrix
subplot(2,1,2);
imshow(imadjust(mat2gray(H)),'XData',theta,'YData',rho,...
      'InitialMagnification','fit');
title('Hough transform of gantrycrane.png');
xlabel('\theta'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(gray(256));


% find peaks in Hough Transform
P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
hold on;
x = theta(P(:,2)); 
y = rho(P(:,1));
plot(x,y,'s','color','red');

% find the lines
lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',7);

% plot lines on image
figure, imshow(I), hold on
max_len = 0;
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');

   % Plot beginnings and ends of lines
   plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
   plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');

   % Determine the endpoints of the longest line segment 
   len = norm(lines(k).point1 - lines(k).point2);
   if ( len > max_len)
      max_len = len;
      xy_long = xy;
   end
end

% highlight the longest line segment
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','cyan');