coordinates of intersaction between vector and a pixel in an image

Hey

i have an a black/white image with a simpel shape, where i already run an edge detection on, i drawed an horizontal vector on the image.

How can i get the coordinates of all the intersection points, between my vector line and the white edge of the shape ?

any help will be appreciated. Thanks

Answer 1

[Image Analyst]

Are you looking for something like this demo:

% Code to have user draw line across a binary image and
% find intersection points.

% Take out the next two lines if you're transferring this to your program.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables.

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;

% Check that user has the Image Processing Toolbox installed.
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

grayImage = uint8(mat2gray(peaks(400)));
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
subplot(2, 1, 1);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize);
% 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') 

% Initialize

button = 1;
while button ~= 2
  % Get which action the user wants to do.
  button = menu('Choose an action', 'Find Intersection', 'Exit');
  if button == 2
    % Bail out because they clicked Exit.
    break;
  end
  % Make caption the instructions.
  subplot(2, 1, 1);
  cla reset;
  imshow(grayImage, []);
  axis on;
  title('Left-click first point.  Right click last point.', 'FontSize', fontSize);
  % Ask user to plot a line.
  [x, y, profile] = improfile();
  % Plot line.
  hold on;
  plot(x, y, 'r-', 'LineWidth', 2);
  % Restore caption.
  title('Binary Image', 'FontSize', fontSize);
  % Calculate distance
  distanceInPixels = sqrt((x(1)-x(end))^2 + (y(1)-y(end))^2);
  % Plot it.
  subplot(2,1,2);
  plot(profile, 'LineWidth', 2);
  grid on;
  
  % Initialize
  caption = sprintf('Intensity Profile Along Line\nThe distance = %f pixels', ...
    distanceInPixels);
  title(caption, 'FontSize', fontSize);
  ylabel('Gray Level', 'FontSize', fontSize);
  xlabel('Pixels Along Line', 'FontSize', fontSize);
  ylim([0 1.5]);
  
  % Find intersection points.
  dif = diff(profile);
  
  % Find where it goes from 0 to 1, and dif == 1;
  nonZeroElements = find(dif > 0);
  % Plot them
  subplot(2, 1, 1); % Go back to the image.
  hold on;
  plot(x(nonZeroElements), y(nonZeroElements),...
    'ro', 'MarkerSize', 10);

  % Find where it goes from 1 to 0, and dif == -1;
  nonZeroElements2 = find(dif < 0);
  % Plot them
  subplot(2, 1, 1); % Go back to the image.
  hold on;
  plot(x(nonZeroElements2), y(nonZeroElements2),...
    'ro', 'MarkerSize', 10);
end

Answer 2

[Matt J]

If it is black and white image bw and you want to find the column number of the first white pixel in each row, you could do

[~,col]=max(bw,[],2);

If you want to find the last white pixel in each row, you could do, similarly

[~,col]=max(fliplr(bw),[],2);
  col=size(bw,2)+1-col;