why hough transform detects more lines while there is only one line?

%% Hough Transform


    I4 = imbinarize(I4);
    BW2 = imcomplement(I4);
    
    
    [H,theta,rho] = hough(BW2,'RhoResolution',1.8);
    figure(2);
    imshow(imadjust(rescale(H)),'XData',theta,...
       'YData',rho,...
       'InitialMagnification','fit');
    axis on
    axis normal 
    hold on
    colormap(gca,hot)
    
    
    P = houghpeaks(H,40,'threshold',ceil(0.05*max(H(:))));
    x = theta(P(:,2));
    y = rho(P(:,1));
    lines = houghlines(BW2,theta,rho,P,'FillGap',3,'MinLength',36);
    
    figure(1);subplot(2,2,4);
    imshow(I4), 
    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');
    end

Answer 1

[Matt J]

Because your line is actually not a line, but rather a tube with non-zero thickness, there are multiple thinner lines that will fit inside it. The number that are found depend on the boundaries of your rho and theta bins.

You can use clusterdata or uniquetol to group the redundant line tip detections into single points.