Hi,
- The ‘MinLength’ Argument to the ‘houghlines’ function determines the number of lines that will be given as output and stored in ‘lines’ Variable. This may vary from image to image.
- You could do a basic comparison on the ‘x’ and ‘y’ values of the end points of the lines to select which two lines to plot in the final output.
Here is the output that I got for this code.
clear all;
clc
a= imread('Figure.jpeg'); % Image A read
imshow(a) ; % Show image
%% Processing
grey = rgb2gray (a);
bwa = im2bw (grey, 175/255);
se = strel('diamond',1) ;
%% Detect Edges
bwb = edge(bwa,'canny');
%% Hough Transform
[H,theta,rho] = hough(bwb);
figure
imshow(imadjust(rescale(H)),[],...
'XData',theta,...
'YData',rho,...
'InitialMagnification','fit');
xlabel('\theta (degrees)')
ylabel('\rho')
axis on
axis normal
hold on
colormap(gca,hot);
%% Find Peaks
P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
%% Superimpose Peaks on image of transform to identify peaks
x = theta(P(:,2));
y = rho(P(:,1));
plot(x,y,'s','color','black');
%% Finde lines within Image
lines = houghlines(bwb,theta,rho,P,'FillGap',5,'MinLength',75);
%% Final plot
figure, imshow(bwb), hold on
% here lines(1) and lines(2) are the desired lines
max_len = 0;
midpt(1,:) = (lines(1).point1 + lines(2).point1)/2;
midpt(2,:) = (lines(1).point2 + lines(2).point2)/2;
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');
plot (midpt(1,1),midpt(1,2),'o','linewidth',2,'color','blue');
plot (midpt(2,1),midpt(2,2),'o','linewidth',2,'color','blue');
plot (midpt(:,1),midpt(:,2),'linewidth',2,'color','blue');
hold on
end
You could eliminate the third line by choosing the two lines that mark the road from the 'lines' variable. In this case they are the first two elements of the 'lines' variable
