Getting points with ginput from image and plotting simultaneously each selected point

I am trying to select an unlimited number of points from an image ([x,y] = ginput), and each time I select a point I want to plot it, so I can have a real time reference of each point I get.

I have tried with this code, but I don't get it to work.

Here is the code I use:

I = imread('cameraman.tif'); % example
imshow(I);
axis on;
button = 1;
i = 1;
n = 1;

while button(i) == 1
   [x,y, button] = ginput(1)
   x_n(n) = x(i); % save all points you continue getting
   x_n(n) = y(i);
   hold on
   plot(x(i),y(i),'r')
   drawnow
   n=n+1;
end

I have read some answers where they use for loops with a limited number of points to be selected, but I must have an unlimited number of points, that's why I use as loop condition the pressed button.

Thank you for any help in advance.

[Walter Roberson]

When the user finally clicks a button other than 1, do you want to plot the final point, or do you want to consider that to immediately terminate without entering the point the user is at?

[Alfonso]

Each time the user clicks the button with value 1 it means the user selected a new point, so it must plot the point before the user continues selecting more points.

When the user clicks a button different to 1, this means the user has finished, so the while loop breaks.

Answer 1

[Walter Roberson]

n = 0;
while true
   [x, y, button] = ginput(1);
   if isempty(x) || button(1) == 1; break; end
   n = n+1;
   x_n(n) = x(1); % save all points you continue getting
   y_n(n) = y(1);
   hold on
   plot(x(1), y(1), 'r')
   drawnow
end

[Alfonso]

Hello Walter, thanks for answering,

I have tried your code with an image and it doesn't seem to work. After the first click ginput stops and does not admit more points, also this first point clicked does not plot.

[Walter Roberson]

n = 0;
while true
   [x, y, button] = ginput(1);
   if isempty(x) || button(1) ~= 1; break; end
   n = n+1;
   x_n(n) = x(1); % save all points you continue getting
   x_n(n) = y(1);
   hold on
   plot(x(1), y(1), 'r')
   drawnow
end

[Alfonso]

Thank you for your help, works perfectly.

[Tim K]

Thanks for this code, works perfectly, after 50+ datatips caused a graphics crash.

I've just manually entered 390 points and then spotted the typo.

x_n(n) = x(1); % save all points you continue getting
y_n(n) = y(1);

[Walter Roberson]

Tim K, you are right, I did have a typo.

[LO]

is the typo the index for x and y = 1 ?

would x and y alone be Ok ? it seems to work but haven't tested large numbers

[Walter Roberson]

I think the typo got corrected already ? I do not remember now.

The index for x and y should be 1, since you ginput(1) .