How should I solve the "output argument not assigned" problem(GUI function)?

Hello, everyone. I want to turn a image into binary image, and to determine the threshold gray level according to the resulted binary image. So I design a function, in which a GUI will pop out showing the current threshold value and the binarized image. You can modify the threshold and see the new binarized image imediately. After several modifying, if you think the binarized image is OK, you click the OK button and the function returns the current threshold. All of these GUI functionality is realized by callback functions.

But when I call that function, the error message says:

    ??? Output argument "threshold_value" (and maybe others) not assigned during call to

the main function is

    raw_image = imread('beauty.jpg');
    raw_image = rgb2gray(raw_image);
    max(raw_image(:));
    raw_image = im2double(raw_image);
    max(raw_image(:));
    threshold_value = get_threshold_value(raw_image)

The function I designed is:

    function threshold_value = get_threshold_value(raw_image)
    % This function is used to get the wanted threshold value, by saying wanted
    % I mean the threshold judged by the user, and the value can binarize the
    % image appropriately.

    %%initialization
    current_value = 0.5;
    step_value = 0.05;
    % preprocessed_image = rgb2gray(raw_image);
    preprocessed_image = im2double(raw_image);

    binary_image = [];

    ......

        function ok_button_callback(source, eventdata)
            threshold_value = current_value;
            close(handle_new_figure)
        end

    end

[The Pirate]

The threshold_value is assigned in the callback function. But is I assign threshold_value as the default value outside the callback function. I will get the default value immediately in the main function, no matter what you have modified the threshold function.

Can you help me with this?

[per isakson]

"??? Output argument "threshold_value" (and maybe others) not assigned " I guess, the nested function isn't called during the execution of get_threshold_value.

Put a breakpoint at the line, threshold_value=current_value;, and run the function, get_threshold_value, to find out.

Answer 1

[Stephen23]

function threshold_value = get_threshold_value(raw_image)
threshold_value = [];
figure_handle = figure(...);
...
waitfor(figure_handle)
end

The waitfor lets the function return the threshold_value value when the figure is closed. Here is a minimum working example:

function out = myfun(x)
out = [];
h = uicontrol('callback',@foo);
    function foo(~,~)
        out = x;
    end
waitfor(h)
end

And tested:

>> myfun(4) % clicked the button
ans =
     4
>> myfun(4) % no click
ans =
     []

[The Pirate]

@Stephen Cobeldick, It works! Thank you very much!