Problem with rgb2gray function ?

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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!
  2 Comments
VYSHAKH V NAIR
VYSHAKH V NAIR on 1 Jun 2017
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
Image Analyst on 1 Jun 2017
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.

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Accepted Answer

Sabarinathan Vadivelu
Sabarinathan Vadivelu on 23 Jan 2013
Check with your input image. It was gray image.
  2 Comments
Jenny
Jenny on 23 Jan 2013
You were right! Thank you very much!
VIKAS  PATEL
VIKAS PATEL on 29 May 2015
yes, I was having the same problem and it helped me. Thank you so much.

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More Answers (2)

Image Analyst
Image Analyst on 23 Jan 2013
Edited: Image Analyst on 10 Mar 2017
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
  6 Comments
linsong zhan
linsong zhan on 9 Mar 2017
Thanks for your short codes. It helps me for my project.
Asma Shahid
Asma Shahid on 13 Apr 2017
Thank you so much for your help.This code is very helping.

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Anis Abboud
Anis Abboud on 28 Nov 2014
Shorter version:
if size(I, 3) > 1
I = rgb2gray(I);
end

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