rgb2gray conversion in GUI

So I'm working on my semestrial work.I'm working on noise reduction filters and right now I'm working on GUI for theese filters. I allready have functional filter code and part of the code is conversion to grayscale. But when I put it together in GUI I've got an error message:

Error using rgb2gray>parse_inputs (line 77)
MAP must be a m x 3 array.

Error in rgb2gray (line 52)
[X, threeD] = parse_inputs(X);

Error in untitled>FILT_IMG_Callback (line 97)
A = rgb2gray (X);

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

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

Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)untitled('FILT_IMG_Callback',hObject,eventdata,guidata(hObject)) 
Error while evaluating UIControl Callback

I understand that image have to be in 3 dimenesion to be grayscaled but my image is allready in 3 dimensions. Any idea how to figure that out? Here's whole code:

function LOAD_IMG_Callback(hObject, eventdata, handles)
% hObject    handle to LOAD_IMG (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global X
X=uigetfile('*.*')
%filename=X;
%setappdata(0,'filename', filename);
X=imread(X);
axes(handles.axes1);
imshow(X);
%setappdata(0, 'A', X);

% --- Executes on button press in FILT_IMG.
function FILT_IMG_Callback(hObject, eventdata, handles)
% hObject    handle to FILT_IMG (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
global X
A = rgb2gray (X);
X = A;
axes(handles.axes1);
imshow(X);

[Rik]

Don't use global, you have a perfectly functional guidata struct to pass data between callbacks.

[Stephen23]

Do not use global variables. Use the appdata, or guidata.

[Tomas Pechac]

But when I don't use global how I'll pass image which is imported in first button to whole program? Because I need same image for every filter. Could you send me some examples?

[Adam]

https://uk.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

[Stephen23]

The documentation, which describes all ways to pass data between callbacks:

http://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

The wiki that explains this:

http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.28s.29.3F

And some of the many threads on this forum that answer your question:

http://www.mathworks.com/matlabcentral/answers/146215-pass-data-between-gui-s

http://www.mathworks.com/matlabcentral/answers/179265-how-to-pass-a-struct-between-callbacks-in-gui

Answer 1

[Image Analyst]

Don't have X be a global string, then pass it into uigetfile() and rewrite X with a totally different data type. Talk about bad programming practice! Try this:

% Have user browse for a file, from a specified "starting folder."
% For convenience in browsing, set a starting folder from which to browse.
startingFolder = 'C:\wherever you want';
if ~exist(startingFolder, 'dir')
  % If that folder doesn't exist, just start in the current folder.
  startingFolder = pwd;
end
% Get the name of the file that the user wants to use.
defaultFileName = fullfile(startingFolder, '*.*');
[baseFileName, folder] = uigetfile(defaultFileName, 'Select a file');
if baseFileName == 0
  % User clicked the Cancel button.
  return;
end
fullFileName = fullfile(folder, baseFileName)
rgbImage = imread(fullFileName);

% Get the dimensions of the image.  
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(rgbImage);
if numberOfColorChannels > 1
  % It's not really gray scale like we want - it's color.
  % Use weighted sum of ALL channels to create a gray scale image.
  grayImage = rgb2gray(grayImage); 
  % ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
  % which in a typical snapshot will be the least noisy channel.
  % grayImage = grayImage(:, :, 2); % Take green channel.
else
        grayImage = rgbImage; % It's not really RGB, it's gray already!
end