Using getpts to get selected points

I'm trying to use `getpts` to get the location of the selected points by the user.

I used it as follows:

    [X,Y] = getpts(imread('xyz.jpg'));

But, got the following error:

    Error using getpts (line 46)
    First argument is not a valid handle.

    Error in program (line 7)
    [X,Y] = getpts(imread('xyz.jpg'));

Why is that?

Thanks.

Answer 1

[Geoff Hayes]

Hi med-sweng,

According to the documentation for getpts, the valid inputs to this function are a figure (fig), the axes specified by the handle ax, or the current figure handle (gcf). In your example, you are passing the result of imread('xyz.jpg') which is a matrix containing the image data and so is not a "valid handle" as per the error message. You may need to do something like the following instead:

[I] = imread('xyz.jpg');  % read the image into the matrix
imshow(I);                % display the image 
[x,y] = getpts;           % get the points from the current image

You don't need to pass anything to getpts as the current figure handle will be used. (An alternative may be to do [x,y] = getpts(imshow(I)) ;

Hope that this helps!

Geoff