Calculate angles from extracted leaf veins - matlab

Question

I'm trying to calculate the angles that exist between leaf veins in matlab. What I've thought is to detect the lines (veins) using Hough and then calculate the angles. But the result I get when I try to detect the lines is a little strange.
Here is the code:
[H,theta,rho] = hough(vein);
P = houghpeaks(H,4);
x = theta(P(:,2));
y = rho(P(:,1));
%lines = houghlines(BW,theta,rho,P,'FillGap',2,'MinLength',4);
lines = houghlines(BW,theta,rho,P);
figure, imshow(vein), 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
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','red');
Any ideas?

Answer 1

I suppose you just mixed the names of the matrices.
In your code, there is vein matrix and BW matrix.
You are using:
vein here: [H,theta,rho] = hough(vein);
BW here: lines = houghlines(BW,theta,rho,P);
I added the line BW = vein;, and the result is much less strange:
vein = imbinarize(rgb2gray(imread('https://i.stack.imgur.com/cuwb0.jpg'))); %Read image, and convert to binary
BW = vein; %Copy vein to BW
[H,theta,rho] = hough(vein);
P = houghpeaks(H,4);
x = theta(P(:,2));
y = rho(P(:,1));
%lines = houghlines(BW,theta,rho,P,'FillGap',2,'MinLength',4);
lines = houghlines(BW,theta,rho,P);
figure, imshow(vein), 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
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','red');
Result: