How do I measure the angle of a line in my image using the Image Processing Toolbox in MATLAB?

I have an image with a few line objects. I would like to know if the Image Processing Toolbox has the capability to recognize these line objects from the figure and give me an estimate of their orientation.

Answer 1

[MathWorks Support Team]

To recognize line objects in your figure window, you may use the HOUGH Transform. Information about the HOUGH transform may be found at the following location:

 

 <http://www.mathworks.com/help/toolbox/images/ref/hough.html>

As a simple example, run the following code on the attached file "test.jpg":

 

% read the image into MATLAB and convert it to grayscale
I = imread('test.jpg');
Igray = rgb2gray(I);
figure, imshow(I);

% We can see that the image is noisy. We will clean it up with a few
% morphological operations
Ibw = im2bw(Igray,graythresh(Igray)); 
se = strel('line',3,90);
cleanI = imdilate(~Ibw,se);
figure, imshow(cleanI);

% Perform a Hough Transform on the image 
% The Hough Transform identifies lines in an image 
[H,theta,rho] = hough(cleanI);
peaks  = houghpeaks(H,10);
lines = houghlines(Ibw,theta,rho,peaks);
figure, imshow(cleanI)

% Highlight (by changing color) the lines found by MATLAB
hold on
for k = 1:numel(lines)
    x1 = lines(k).point1(1);
    y1 = lines(k).point1(2);
    x2 = lines(k).point2(1);
    y2 = lines(k).point2(2);
    plot([x1 x2],[y1 y2],'Color','g','LineWidth', 2)
end
hold off

% Identify the angles of the lines. 
% The following command shows the angle of the 2nd line found by the Hough
% Transform
lines(1).theta
lines(2).theta