Problem with rgb2gray function ?

I've made a GUI with GUIDE which makes a RGB image into binary image. I have the following code in one part of the program :

fileName = uigetfile('*.jpg');
imshow(fileName); 
I        = imread(fileName);    
Iinitial = I;
Igray    = rgb2gray(Iinitial);
I        = imcomplement(I);
Igray    = rgb2gray(I);

And it gives me that following error:

??? Error using ==> rgb2gray>parse_inputs at 82
MAP must be a m x 3 array.

Error in ==> rgb2gray at 35
X = parse_inputs(varargin{:});

Error in ==> lets_see>pushbutton1_Callback at 97
Igray    = rgb2gray(Iinitial);

Error in ==> gui_mainfcn at 96
        feval(varargin{:});

Error in ==> lets_see at 42
    gui_mainfcn(gui_State, varargin{:});

Error in ==>
@(hObject,eventdata)lets_see('pushbutton1_Callback',hObject,eventdata,guidata(hObject))

??? Error while evaluating uicontrol Callback

I cannot find the problem and fix it. If somebody knows, please help. Thanks!

[VYSHAKH V NAIR]

may be this is because you are choosing a gray scale image as input.and trying again to convert it to gray scale.

[Image Analyst]

Yes, and that's what my solution below checks for. It checks how many color channels there are and only calls rgb2gray() if it's a color image.

Answer 1

[Sabarinathan Vadivelu]

Check with your input image. It was gray image.

[Jenny]

You were right! Thank you very much!

[VIKAS PATEL]

yes, I was having the same problem and it helped me. Thank you so much.

Answer 2

[Image Analyst]

You can only call rgb2gray() on a color image. Calling rgb2gray() on an image that is already gray scale will throw an error. Add this code to make sure the conversion is done ONLY on RGB images:

% Get the number of rows and columns, 
% and, most importantly, the number of color channels.
[rows, columns, numberOfColorChannels] = size(Iinitial);
if numberOfColorChannels > 1
    % It's a true color RGB image.  We need to convert to gray scale.
    Igray = rgb2gray(Iinitial);
else
    % It's already gray scale.  No need to convert.
    Igray = Iinitial;
end

[Jenny]

Perfect! This was really useful. Thanks a lot!

[James]

I found this code very useful, thank you!

[Manoj Kumar]

Thanks for your code. It helped me

[aimi shaharuddin]

thank you! helps me a lot

[linsong zhan]

Thanks for your short codes. It helps me for my project.

[Asma Shahid]

Thank you so much for your help.This code is very helping.

Answer 3

[Anis Abboud]

Shorter version:

if size(I, 3) > 1
  I = rgb2gray(I);
end