How to extend hough lines over the image space

I need to extend lines over the image space. I used Hough transform to find vanishing lines, but i need to get lines longer and see where is vanishing points. How can i do it? Please help.

This is my code: clear; clc;

I = imread('22pp.jpg');

%rotI = imrotate(I,33,'crop'); bw_I = rgb2gray(I); BW = edge(bw_I,'canny');

figure, imshow(BW); %pause;

BW=edge(BW,'canny',(graythresh(I)*(0.3)),'horizontal');

figure, imshow(BW); %pause;

[H,T,R] = hough(BW); imshow(H,[],'XData',T,'YData',R,'InitialMagnification','fit'); xlabel('\theta'), ylabel('\rho'); axis on, axis normal, hold on; P = houghpeaks(H,15,'threshold',ceil(0.3*max(H(:)))); x = T(P(:,2)); y = R(P(:,1)); plot(x,y,'s','color','white'); % Find lines and plot them lines = houghlines(BW,T,R,P,'FillGap',200,'MinLength',200); figure, imshow(I), hold on

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

[Image Analyst]

Get the equations of the lines, and just plug in x = 1 and x = numberOfColumns. It will draw them. If the line would go off the top of off the bottom of the image, I believe the line will get clipped to the inside of the image.

[Lina Bielinyte]

I do not understand. Can you show it on my script?

[Image Analyst]

Perhaps, if you attach '22pp.jpg' and if I get time later today or this weekend.

[Lina Bielinyte]

Thank you

[Image Analyst]

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

rgbImage = imread('22pp.jpg');
subplot(2, 3, 1);
imshow(rgbImage);
title('Original Color Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 

rotI = imrotate(rgbImage,33,'crop');
bw_I = rgb2gray(rgbImage);
BW = edge(bw_I,'canny');
subplot(2, 3, 2);
imshow(BW);
title('Canny Edge Image #1', 'FontSize', fontSize, 'Interpreter', 'None');

BW=edge(BW,'canny',(graythresh(rgbImage)*(0.3)),'horizontal');

subplot(2, 3, 3);
imshow(BW);
title('Canny Edge Image #1', 'FontSize', fontSize, 'Interpreter', 'None');

[H,T,R] = hough(BW);
subplot(2, 3, 4);
imshow(H,[],'XData',T,'YData',R,'InitialMagnification','fit');
title('Hough Transform', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('\theta'),
ylabel('\rho');
axis on, axis normal, hold on;
P = houghpeaks(H,15,'threshold',ceil(0.3*max(H(:))));
x = T(P(:,2));
y = R(P(:,1));
plot(x,y,'s','color','white'); % Find lines and plot them
lines = houghlines(BW,T,R,P,'FillGap',200,'MinLength',200); 
subplot(2, 3, 5);
imshow(rgbImage)
title('Image with lines', 'FontSize', fontSize, 'Interpreter', 'None');
hold on
[rows, columns] = size(BW);

for k = 1:length(lines)
  xy = [lines(k).point1; lines(k).point2];
  % Get the equation of the line
  x1 = xy(1,1);
  y1 = xy(1,2);
  x2 = xy(2,1);
  y2 = xy(2,2);
  slope = (y2-y1)/(x2-x1);
  xLeft = 1; % x is on the left edge
  yLeft = slope * (xLeft - x1) + y1;
  xRight = columns; % x is on the reight edge.
  yRight = slope * (xRight - x1) + y1;
  plot([xLeft, xRight], [yLeft, yRight], 'LineWidth',2,'Color','green');  
  
  % Plot original points on the 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

[Sumi Anwar]

I tried the same. But I couldn't find the vanishing point. Can you please help me?