MATLAB: Line detection in an image

image processingImage Processing Toolbox

My image is a square. What i want here is: select 4 points on the upper horizontal boundary in the square and along those 4 points draw a straight line. (eventually, repeat this for all 4 sides). What functions should i use?

When selecting points i can use ginput(4) i guess, but i doubt houghline is the function for drawing straight line along selected points? Any suggestions?

Best Answer

To plot the line in the overlay, you can use line()

line([x1 x2], [y1 y2], 'Color', 'r');

To "burn" the line into the image, you can either use normal indexing if the line is along rows and columns

grayImage(row1:row2, col) = 255; % or whatever intensity you want

or you can use imline() if the points are not in the same row or column, as the attached demo illustrates.

Related Solutions

MATLAB: How to draw a line from the centre of the image to its border

Did you try the line() function? That will plot in the overlay. If you want the line burned into the image use the imline() function's createMask() method.

% Demo to write a line into the overlay of an image,
% and then to burn the overlay into the image.
%----- Initializing steps -----
% Clean up
clc;
clear all;
close all;
workspace; % Display the workspace panel.
hasIPT = license('test', 'image_toolbox');
if ~hasIPT
  % User does not have the toolbox installed.
  message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
  reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
  if strcmpi(reply, 'No')
    % User said No, so exit.
    return;
  end
end
% Display images to prepare for the demo.
monochromeImage = imread('pout.tif');
subplot(2, 2, 1);
imshow(monochromeImage);
title('Original Image');
subplot(2, 2, 2);
imshow(monochromeImage);
title('Original Image with line in overlay');
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
set(gcf,'name','Image Analysis Demo','numbertitle','off') 
%----- Burn line into image -----
burnedImage = imread('pout.tif');
% Create line mask, h, as an ROI object over the image.
hLine = imline(gca,[10 100],[10 100]); % Second argument defines line endpoints.
% Create a binary image ("mask") from the ROI object.
binaryImage2 = hLine.createMask();
% Display the line mask.
subplot(2, 2, 3);
imshow(binaryImage2);
title('Binary mask of the line');
% Burn line into image by setting it to 255 wherever the mask is true.
burnedImage(binaryImage2) = 255;
% Display the image with the "burned in" line.
subplot(2, 2, 4);
imshow(burnedImage);
title('New image with line burned into image');

MATLAB: Find the euclidean distance

I wouldn't use ginput() or pdist(). I'd use the function improfile() in the Image Processing Toolbox. It's a lot easier to use than imdistline(). Here's a snippet:

% Display sample image.
grayImage = imread('moon.tif');
imshow(grayImage);
title('Left click, then right click');
% Have user draw the line.
[x, y, grayLevels] = improfile();
% Re-Draw the line in the overlay (which normally vanishes)
line([x(1), x(end)], [y(1), y(end)]);
% Compute the distance between the endpoints.
dist = sqrt((x(end)-x(1))^2 + (y(end)-y(1))^2)

Best Answer

Related Solutions

MATLAB: How to draw a line from the centre of the image to its border

MATLAB: Find the euclidean distance

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