houghlines() - Image Processing

lines = houghlines(BW,theta,rho,peaks) extracts
line segments in the image BW associated with
particular bins in a Hough transform. theta and rho are
vectors returned by function hough. peaks is
a matrix returned by the houghpeaks function that
contains the row and column coordinates of the Hough transform bins
to use in searching for line segments. The return value lines is
a structure array whose length equals the number of merged line segments
found.examplelines = houghlines(___,Name,Value,...) extracts
line segments in the image BW, where named parameters
affect the operation.Code Generation support:
Yes.MATLAB® Function Block support: No.

Syntax

lines = houghlines(BW,theta,rho,peaks) examplelines = houghlines(___,Name,Value,...) example

Example

Find Line Segments and Highlight longest segmentOpen This Example
Read image into workspace.I  = imread('circuit.tif');
Rotate the image.rotI = imrotate(I,33,'crop');
Create a binary image.BW = edge(rotI,'canny');
Create the Hough transform using the binary image.[H,T,R] = hough(BW);
imshow(H,[],'XData',T,'YData',R,...
            'InitialMagnification','fit');
xlabel('\theta'), ylabel('\rho');
axis on, axis normal, hold on;

Find peaks in the Hough transform of the image.P  = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
x = T(P(:,2)); y = R(P(:,1));
plot(x,y,'s','color','white');

Find lines and plot them.lines = houghlines(BW,T,R,P,'FillGap',5,'MinLength',7);
figure, imshow(rotI), 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 by coloring it cyan.plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','cyan');

Output / Return Value

Limitations

Alternatives / See Also

Reference