MATLAB: Image pixel info on

figureimage analysis

Hello.

I have 2 different images (image1, image2). I want to place the mouse (or click with it) on image1 (to get the (x,y) of that pixel), and to view the pixel value of image2 on that (x,y) location (the one I choose on image1).

how can that be done?

thanks.

Best Answer

Hi Nirit, you can use the WindwoButtonMotionFunction of the Figure, your image 1 is in. Here is a quick example:

function m_easy_mouse_handling_example()
%example data
a = [1,1,1;2,2,2;3,3,3];
b = [10,12,14;16,18,20; 22 24 26];
%show the two figures
h_fig1 = figure()
h_ax1 = axes('Parent',h_fig1);
h_im1 = imagesc(a,'Parent',h_ax1);
h_fig2 = figure()
h_ax2 = axes('Parent',h_fig2);
h_im2 = imagesc(b,'Parent',h_ax2);
%set function which is used when mouse is over figure 1 (h_fig1)
set(h_fig1,'WindowButtonMotionFcn', @MouseMoveFcn)
function MouseMoveFcn(varargin)
    try
     mouse_pos = get(h_ax1, 'CurrentPoint');
     ii = round(mouse_pos(1,1));
     jj = round(mouse_pos(1,2));
       %show value of image 2 in command line
       disp(num2str(b(jj,ii)))  %please check, if order of dimensions is correct
      catch
          %catch error, if you are outside the image (to do)
      end
  end

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MATLAB: Unknown axes in GUI

When calling plot or axes you can optionally specify a "parent" or "container", where the axes or plot object gets created in. The container is the handle object to the object where the new object will be created in. If you don't specify the container, it will be created in the "current figure" or "current axes". This can be literally anything you created or selected with your mouse before.

If you call plot and no current axes or figure exists, it will create the missing figure window, create an axes object inside it and then creates the plot into the axes.

See this example which creates some figures and uses a button in one window to plot something in another window (also attached):

function example_436887
% Create thee new figure windows
h_fig1 = figure;
h_fig2 = figure;
h_fig3 = figure;
% Create axes manually
h_ax2 = axes(h_fig2); % axes(container,...)
h_ax3 = axes(h_fig3);
% Plot something in h_ax2 which is in h_fig2
plot(h_ax2,1:10,rand(1,10))
% Modify Size of h_fig1 and disable menu bar and toolbar
h_fig1.Position(3) = 350;
h_fig1.Position(4) = 100;
set(h_fig1,'MenuBar','none',...
    'ToolBar','none');
% Create a Button in h_fig1
button_plot  = uicontrol(h_fig1, ... % use h_fig1 as parent container
    'Style','pushbutton',...
    'String','Call Plot in Figure specified as h_fig3', ...
    'Position',[20,20,300,25],...
    'Callback',@button_plot_Callback);
function button_plot_Callback(source,eventdata) 
% Plot something in h_ax3:


    plot(h_ax3,1:10,rand(1,10)); % plot into parent container h_ax3

end % function button_plot_Callback


end % function example_436887

When pushing the button to plot inside h_fig1, the target container needs to be specified. If you change the Callback-Function from this:

function button_plot_Callback(source,eventdata) 
% Plot something in h_ax3:
    plot(h_ax3,1:10,rand(1,10)); % plot into parent container h_ax3
end % function button_plot_Callback

to this:

function button_plot_Callback(source,eventdata) 
% Plot something in h_ax3:
    plot(1:10,rand(1,10)); % plot into current axes/figure
end % function button_plot_Callback

The error you described occurs, as the plot command creates an axes in the current figure (which is the figure with the button) because there is no axes to plot into.

MATLAB: Impoly no longer animates the tracing line after placing other animated line objects

JK from the Matlab Support Team provided a solution. Before the origButtonMotionCB definition above, he suggested adding the following code:

if isempty(get(hFig, 'WindowButtonMotionFcn'))
set(hFig, 'WindowButtonMotionFcn',@(~,~) deal());
end

He provided two reasons why the "impoly" function was not showing the animated lines:

================================

1. The "impoly" function uses the figure's "WindowButtonMotionFcn" callback to handle animating the line as you move the mouse around. Right now, the "WindowButtonUpFcn" gets rid of any existing callbacks in "WindoButtonMotionFcn". Although this allows for "hline" to stop moving when the mouse is released, it also removes the "impoly" function's callback as you release the mouse.

2. The "CurrentPoint" property is used to determine where the mouse is located in the axes data space. However, this property is only ever updated on mouse clicks or when the figure's WindowButtonMotionFcn is not empty. Because of this, the animation for "impoly" will work only if "WindowButtonMotionFcn" is not empty. Setting the "WindowButtonMotionFcn" to something that is not empty but still doesn't really do anything (e.g. deal()) could resolve this issue.

To deal with these issues, the following work around will work if using "drawpolygon" as opposed to "impoly".

The modified code avoids setting an empty callback in WindowButtonMotionFcn during drawing.

================================

The solution does work for drawpolygon and drawpolyline. It still does not work for impoly. But I should probably update my application anyway... :-)

Mega thanks to JK at Matlab Support for the solution!

Best Answer

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MATLAB: Impoly no longer animates the tracing line after placing other animated line objects

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