Challenge: How to interact with MATLAB figure using mouse events?

Hi MATLAB Lovers..

Suppose I have a 2D empty matrix of 50x50 as A=zeros(50);

I use Figure1=imagesc(A); to plot this matrix.

What I want is the following:

1. When a user click on any pixel on Figure1, it automatically changes its value form zero to one.

2. MATLAB automatically update the matrix A.

Whoever answer this, deserves to be called: MATLAB NERD.

Thank you so much.

Answer 1

[Massimo Zanetti]

Also, try this simple version. You can update 5 pixels here, however choose the number in the for loop.

I=zeros(20,20);
h=image(I);
for k=1:5
    p=ginput(1);
    I(round(p(1,2)),round(p(1,1)))=100;
    set(h,'CData',I);
    drawnow;
end

[Tamim]

Thank you so much Massimo Zanetti, you are an actual Nerd ;)

[Mohamed Nedal]

Hello, please if I want to do this for a FITS-image file, How can I do that? The FITS file is an array with No. of rows represents frequency and the No. of columns represents time and the value inside each cell represent the intensity of a signal at (f,t). I tried your code but there's no "CData" in the file.

[Walter Roberson]

The I variable should be set to the data in the file, provided that it is real-valued. If it is not real valued then you may need to use the real() or the abs() values

Answer 2

[Walter Roberson]

Create an image object using image() or imshow(). Set the ButtonDownFcn callback to a routine. In the callback, get() the axes CurrentPoint property . round() to get the coordinates. Flip the bit at that location. set() the CData property of the image object to the updated image.

[Walter Roberson]

Get the axes CurrentPoint property, not the figure CurrentPoint

I=zeros(5);
x=1:5;
imagesc(x,x,I,'ButtonDownFcn',@lineCallback); 

function lineCallback(ImageHandle, Structure1)
    CursorLocation = get(ancestor(ImageHandle,'axes'), 'CurrentPoint');
    disp(CursorLocation);
    x = CursorLocation(1,1);
    y = CursorLocation(1,2);
      curCData = get(ImageHandle, 'CData');   %get the current version
      col = round(x);    %x is COLUMN!
      row = round(y);    %y is ROW!
      col = min(max(1, col), size(curCData,2));  %in case it was out of range
      row = min(max(1, row), size(curCData,1));  %in case it was out of range
      curCData(row, col) = ~curCData(row, col);  %flip the bit
      set(ImageHandle, curCData);   %send the change to the graphics
      drawnow();      %render it
  end

Answer 3

[Tamim]

Many thanks Walter for your answer. As I was not aware of it, last night I spent the time learning about ButtonDownFunc as a CallBackFun. It's absolutely a brilliant idea, and give more flexibility to execute more functions.

The problem I'm facing in this particular example is that, when I use "get(gcf,'CurrntPoint')" the returned numbers are out of range of the figure axis!! You said, I have to use "round() and then flip the bit! Could you please elaborate more on that?

Many thanks again for your response.

P.S.This is the code I used:

clc; 
I=zeros(5);
x=1:5;
imagesc(x,x,I,'ButtonDownFcn',@lineCallback); 

function lineCallback(Figure1,Structure1)
    CursorLocation=get(gcf,'CurrentPoint');
    disp(CursorLocation); 
end

Regards,