compute hough space for vertical lines in matlab

To compute Hough space for vertical lines in Matlab, you can follow the steps below:

1. Read the input image using the imread function

main.m
img = imread('input_image.jpg');
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2. Convert the image to grayscale using the rgb2gray function

main.m
gray_img = rgb2gray(img);
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3. Apply edge detection on the grayscale image using the edge function

main.m
edge_img = edge(gray_img, 'canny');
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4. Compute Hough Transform on the edge image using the hough function. For detecting vertical lines, you can set the 'Theta' parameter to a vector of angles containing only 90 degrees (vertical lines).

main.m
[H, theta, rho] = hough(edge_img, 'Theta', [90]);
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5. Display the Hough space using the imshow and the imagesc functions

main.m
imshow(H,[],'XData',theta,'YData',rho,'InitialMagnification','fit');
xlabel('\theta'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(hot);
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The above lines of code display the Hough space with theta values on x-axis, rho values on y-axis, and the magnitude of the peaks representing the number of pixels that lie on a straight line in the original image.

Note: The Hough Transform technique is sensitive to noisy edges in the input image, so it is always better to pre-process the image by removing the noise before applying Hough Transform.