How to update values across functions in a GUI

I'm currently working on a program for image processing. The window has two displays: one for the full size of the images in coming, and one for a zoomed-in portion the photo. I have a text display with two buttons which control a bias for the zoom.

(EDIT: It may help to say that I am grabbing these images from IP Cam, so anytime you go to the web address, the current image from the camera is grabbed. By doing this with a while loop repeatedly, a low frame rate feed is created)

Currently, I have to stop the feed, change the bias, and then start the feed again to see the changes. How can I make it so I can change the value and have it update live? Here is the code for the feed:

% --- Executes on button press in previewButton2.
function previewButton2_Callback(hObject, eventdata, handles)
% hObject    handle to previewButton2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of previewButton2

%this code is for the right-hand button
button_state2 = get(hObject,'Value');
if button_state2 == get(hObject,'Max')
    %display('down');
    handles.button2 = 1;
    while handles.button2 > 0
        %read image from URL
        image = imread(handles.IPshot{1},'jpg');
        %rotate if requested
        switch handles.rotateImg
            case 'left'
                image = imrotate(image,-90);
            case 'right'
                image = imrotate(image,90);
            case 'down'
                image = imrotate(image,-180);
        end
        %run full picture simultaneously if requested
        isChecked = get(handles.runSimul,'Value');
        if isChecked
            axes(handles.previewFrame);
            imagesc(image); axis image;
        end
        %crop the photos as they come
        [sizeX, sizeY] = size(image);
        cropX = ((sizeX/2)-handles.bias):((sizeX/2)+handles.bias);
        cropY = ((sizeY/2)-handles.bias):((sizeY/2)+handles.bias);
        colormap(gray);
        axes(handles.previewFrame2);
        imagesc(image(cropX,cropY)); axis image;
        %see if it's time to stop
        button_state2 = get(hObject,'Value');
        if button_state2 == get(hObject,'Min')
            handles.button2 = 0;
        end
    end

elseif button_state2 == get(hObject,'Min')
  %display('up');
end

Here is the code for the update buttons:

% --- Executes on button press in minusButton.
function minusButton_Callback(hObject, eventdata, handles)
% hObject    handle to minusButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles.bias = handles.bias-1;
set(handles.zoomText, 'String', num2str(handles.bias));
% Update handles structure
guidata(hObject, handles);

% --- Executes on button press in plusButton.
function plusButton_Callback(hObject, eventdata, handles)
% hObject    handle to plusButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
handles.bias = handles.bias+1;
set(handles.zoomText, 'String', num2str(handles.bias));
% Update handles structure
guidata(hObject, handles);

Please let me know if I need to post other details, this is my first time posting.

Thanks, Richard

[José-Luis]

Would something like evalin() work? You can pass data to the caller that way.

Answer 1

[Image Analyst]

Unless special actions are taken, all variables in a function are local. You can make the variables global by declaring them global. Functions where the variable is declared global will see it and other functions won't see it. Other options for sharing variables are shown in the FAQ: http://matlab.wikia.com/wiki/FAQ?title=FAQ&cb=2205#How_can_I_share_data_between_callback_functions_in_my_GUI.28s.29.3F