How to get onclick coordinate pixel value and location from an image?

Hey frndz, I am new in Matlab. Since 3months ago I am using matlab. Within these 3 months I just learned some matrix manipulation functionm addition, string handling etc. So I need all of your help. Please please help me............... How to get onclick coordinate pixel value and location from an image? Actually I want to get some location(x,y) and corresponding pixel value after clicking on image. how can I do this????????

[Xylo]

please help me as soon as possible...........

Answer 1

[David Young]

Use ginput

If you want to record multiple points, you can use something like the function that follows. You can easily modify it to display dots rather than lines between the points - check the documentation for the plot function.

function pts = readPoints(image, n)
%readPoints   Read manually-defined points from image
%   POINTS = READPOINTS(IMAGE) displays the image in the current figure,
%   then records the position of each click of button 1 of the mouse in the
%   figure, and stops when another button is clicked. The track of points
%   is drawn as it goes along. The result is a 2 x NPOINTS matrix; each
%   column is [X; Y] for one point.
% 
%   POINTS = READPOINTS(IMAGE, N) reads up to N points only.

if nargin < 2
    n = Inf;
    pts = zeros(2, 0);
else
    pts = zeros(2, n);
end

imshow(image);     % display image
xold = 0;
yold = 0;
k = 0;
hold on;           % and keep it there while we plot

while 1
    [xi, yi, but] = ginput(1);      % get a point
    if ~isequal(but, 1)             % stop if not button 1
        break
    end
    k = k + 1;
    pts(1,k) = xi;
    pts(2,k) = yi;

      if xold
          plot([xold xi], [yold yi], 'go-');  % draw as we go
      else
          plot(xi, yi, 'go');         % first point on its own
      end

      if isequal(k, n)
          break
      end
      xold = xi;
      yold = yi;
  end

hold off;
if k < size(pts,2)
    pts = pts(:, 1:k);
end

end

[Xylo]

thank u for response. I have already used this function. but this function use a two-axis cross line, which i dnt want to use. and another thing is that this function does not allow to put a sign/symbol(for understnding that i have clicked on this point) on that particular point.

Actually I want to get multiple location's cordinate value and their intensity also. just like this photo(for example):

in this uploaded photo black dots are the clicked point and after clicking i want to get corresponding location and pixel vale. thank u.

[David Young]

I'm not sure how to get rid of the cross-line cursor (what would you replace it with?) I'm editing a function I use for multiple points into the answer above.

[Xylo]

thank you David Young........ your code is working fine............... and about to get rid of the cross-line cursr I will handle it later. lot of thanks to u..

[Hari]

May I know where the values are getting stored?

[Image Analyst]

In xi and yi in the line of code that says this:

[xi, yi, but] = ginput(1);      % get a point

That's asking the user for a single points. Then he stores that point into a list of multiple points with these lines of code:

    pts(1,k) = xi;
    pts(2,k) = yi;

[Kaveh Vejdani]

The question remained unanswered. xi and yi are only the coordinates. Where is the pixel value captured?

[Mrutyunjaya Hiremath]

pixels = impixel(image, pts(1,:), pts(2,:));

Answer 2

[Image Analyst]

If you don't need the value in your code but just want to interactive view the x,y and RGB as you mouse over the image, you can use impixelinfo().

[Xylo]

No, not at all. I need values as well as location.............

Answer 3

[Alberto Zafra Navarro]

According to ChatGPT is easier to do:

function pts = readPoints(image, n)
%readPoints   Read manually-defined points from image
%   POINTS = READPOINTS(IMAGE, N) reads up to N points only.
imshow(image);     % display image
[x,y] = ginput(n);
pts = [x y];
end