How can I find the droplet contact angle of the image using hough transform to determine the boundaries? The code gives me droplet contact angle 0. But I want to calculate the angle the contact surface makes with the bubble.

Irgb = imread('hydrophobe1.jpg'); Igray = rgb2gray(Irgb); BW = edge(Igray,'canny'); [H,theta,rho] = hough(BW);

figure; imshow(imadjust(mat2gray(H)),[],... 'XData',theta,... 'YData',rho,... 'initialmagnification','fit'); colormap(gca,hot);

P = houghpeaks(H,5,'threshold',ceil(.7*max(H(:))));

lines = houghlines(BW,theta,rho,P,'Fillgap',5,'Minlength',7); figure, imshow(Igray), 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(xy(1,1),xy(1,2),'x','linewidth',2,'color','green');
    plot(xy(2,1),xy(2,2),'x','linewidth',2,'color','red');
    len = norm(lines(k).point1 - lines(k).point2);
    if (len > max_len)
        max_len = len;
        xy_long = xy;
    end
end
plot(xy_long(:,1),xy_long(:,2),'Linewidth',2,'Color','Red');

x1 = xy_long(1); x2 = xy_long(2); x3 = xy(1); x4 = xy(2);

y1 = xy_long(3); y2 = xy_long(4); y3 = xy(3); y4 = xy(4);

theta1 = atan((y1-y2)/(x1-x2)) theta2 = atan((y3-y4)/(x3-x4)) ThetaFinal = abs((theta1-theta2)*(180/pi)

[Image Analyst]

What is the difference in your mind between the "contact angle" (which you say your code computes) and the "angle the contact surface makes with the bubble" (which you say you need)??? Please attach diagram with lines and angles indicated on it. Read this too.