MATLAB: I have image with black background and white lines. How to find co-ordinate (x,y) of end points of white lines on that image

Question

Answer 1

It looks to me like my code works, as long as you skeletonize your lines before finding branchpoints and endpoints. See code below and image below that it creates.

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;
%===============================================================================
% Read in a gray scale demo image.
folder = pwd;
baseFileName = 'image.png';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % File doesn't exist -- didn't find it there.  Check the search path for it.
  fullFileNameOnSearchPath = baseFileName; % No path this time.
  if ~exist(fullFileNameOnSearchPath, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Convert it to gray scale by taking only the green channel.
  grayImage = grayImage(:, :, 2); % Take green channel.
end
% Display the image.



subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 
% Unfortunately the image was saved as color so we need to get the circle only.
% Threshold the image at 128 to binarize it.
binaryImage = grayImage >= 128;
% Crop out the center part, getting rid of the 4 pixel wide border that's there for some reason.
binaryImage = binaryImage(4:end-4, 4:end-4);
% Make sure it's skeletonized to 8-connected, not 4-connected like it is originally
binaryImage = bwmorph(binaryImage, 'skel', inf);
% Display the image.
subplot(2, 2, 2);
imshow(binaryImage, []);
axis on;
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
branchpoints = bwmorph(binaryImage, 'branchpoints');
[rowsBP, columnsBP] = find(branchpoints)
% Display the image.
subplot(2, 2, 3);
imshow(branchpoints, []);
axis on;
title('Branchpoints Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Plot circles over the branchpoints because we can't see all of them due to subsampling for display on the monitor.
hold on;
for k = 1 : length(rowsBP);
  plot(columnsBP(k), rowsBP(k), 'ro', 'MarkerSize', 12, 'LineWidth', 2);
end
% You can find the endpoints where a single line hits the edge of the image using the 'endpoints' option instead of branchpoints.
endpoints = bwmorph(binaryImage, 'endpoints');
[rowsEP, columnsEP] = find(endpoints);
% Display the image.
subplot(2, 2, 4);
imshow(endpoints, []);
axis on;
title('Endpoints Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Plot circles over the endpoints because we can't see all of them due to subsampling for display on the monitor.
hold on;
for k = 1 : length(rowsEP);
  plot(columnsEP(k), rowsEP(k), 'ro', 'MarkerSize', 12, 'LineWidth', 2);
end
% Tell user we're done
message = sprintf('Done!');
uiwait(helpdlg(message));