Create a slider in GUI?

Hi,

I'm experimenting with GUIDE and was wondering how to create a slider that allows the user to fix the threshold value from 0 - 255 of an image.

    % --- Executes on slider movement.
    function slider1_Callback(hObject, eventdata, handles)
    % hObject    handle to slider1 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)

    % Hints: get(hObject,'Value') returns position of slider
    %        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
    global grayImage;
    thresholdValue = uint8(get(handles.sldThreshold, 'Value'));
    binaryImage= grayImage > thresholdValue; 
    axes(handles.axes2);

[Walter Roberson]

what does get(handles.slider1, 'Max') return?

[kelly123]

It returns:

Undefined variable "handles" or function "handles.slider1".

[Varian Adisuryo]

same here. I have the same eror. what should I do?

Answer 1

[Image Analyst]

After the call to axes() in slider1_Callback, you need to call

imshow(binaryImage);

[kelly123]

I did insert that line earlier as I was tinkering around and it still hadn't worked. Is there anything else I could be missing?

This is the error I get:

Reference to non-existent field 'sldThreshold'.

Error in FinalProject>slider1_Callback (line 253) thresholdValue = uint8(get(handles.sldThreshold, 'Value'));

Error in gui_mainfcn (line 95) feval(varargin{:});

Error in FinalProject (line 42) gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)FinalProject('slider1_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating uicontrol Callback

Reference to non-existent field 'sldThreshold'.

Error in FinalProject>slider1_Callback (line 253) thresholdValue = uint8(get(handles.sldThreshold, 'Value'));

Error in gui_mainfcn (line 95) feval(varargin{:});

Error in FinalProject (line 42) gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)FinalProject('slider1_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating uicontrol Callback

[Image Analyst]

In GUIDE, you need to make the tag property of the slider "sldThreshold".

Or else (less preferred), change sldThreshold to slider1.

[kelly123]

Thank you. I changed sldThreshold to slider1, and received no errors when I ran the program. However, when I move my slider, axes2 does not change.

To see what was happening, I changed my call to axes ( handles . axes2 ) to axes1. Then, when I moved my slider, the loaded image disappeared and was replaced with a blank white axes on axes1.

[Image Analyst]

You don't have spaces around the dots, do you? So it's handles.axes2, not handles . axes2, right? And what do you expect to see happening? You're not doing anything with the binary image you create. Like I said originally, if you want to see the binary image you'll need to call

imshow(binaryImage);

[Image Analyst]

What is the value of thresholdValue?

[kelly123]

I'm not sure if I set one? Can you give me an example?

[Image Analyst]

After you do this:

thresholdValue = uint8(get(handles.slider1, 'Value'));

put in these lines:

sliderValue = get(handles.slider1, 'Value')
message = sprintf('\nThe slider value = %f\nThe threshold value = %f', sliderValue , thresholdValue);
uiwait(helpdlg(message));

[Varian Adisuryo]

I just did what you told, but when I run it the slider doesn't show and it become like this: Warning: slider control can not have a Value outside of Min/Max range Control will not be rendered until all of its parameter values are valid

what should I do? please help. I've been struggling with this slider for 3 days :(

[Adam]

You can set the min, max and value all in a single set command if you want e.g.

set( handles.slider1, 'Min', 0, 'Max', 10, 'Value', 5 )

to make sure that the value is always within the min to max range and avoid getting that warning. The warning is pretty self-explanatory though from the point of view of knowing what is wrong.