why do i get error when i try to use rgb2gray function in gui?

i tried to make a GUI which converts a rgb image to grayscale image.

this is my code:

clc

clear all

ext='*.jpeg';

folder='C:\Users\SAGARIKA\Desktop\butter\butterfly2';

image = uigetfile([folder '\' ext])

old_image = fullfile(folder,image)

copyfile(old_image,['C:\Users\SAGARIKA\Desktop\butter\' image]);

imshow(old_image);

I = rgb2gray(old_image);

i got the following error:

Error using rgb2gray>parse_inputs (line 81)

MAP must be a m x 3 array.

Error in rgb2gray (line 35)

X = parse_inputs(varargin{:});

Error in que (line 9)

I = rgb2gray(old_image);

>>

[sagarika tewary]

thanks a lot. it worked

Answer 1

[Geoff Hayes]

sagarika - first, do not name local variables as image as this conflicts with the built-in MATLAB function with the same name (see image for details).

Now, look at the line of code that is generating the error

 I = rgb2gray(old_image);

where old_image is the path (to) and the filename of the image that you wish to convert. According to rgb2gray, the input to this function is either a true-colour (RGB) image specified as a 3D array, or it is a mx3 map. In either case, it isn't a string.

I think that what you want to do instead is something like

 myImage = imread(old_image);
 imshow(myImage);
 myImageAsGray = rgb2gray(myImage);

Note that the confusion may be because imshow does allow you to pass in the path and filename of the image you wish to load. Unfortunately, rgb2gray behaves differently.

[Image Analyst]

rgb2gray() will throw an error if you pass it a grayscale image, so to avoid potential problems, I'd make it more robust like this:

[rows, columns, numberOfColorChannels] = size(myImage);
if numberOfColorChannels > 1
    myImageAsGray = rgb2gray(myImage);
end

Or you could popup a warning message with uiwait(warndlg()) if you want to warn the user and get instructions on what to do.

Answer 2

[Jo]

I have this code :

I1 = gpuArray(reshape(linspace(0,1,20),[5 4])); %performs the conversion on a GPU.
W = gather (I1);
[I1,map] = imread(fullname);
imshow(I1,map)
myImageAsGray = rgb2gray(map)
%graycomatrix ignores pixel pairs if either of the pixels contains a NaN,
%replaces positive Infs with the value NumLevels,
%replaces negative Infs with the value 1. 
%ignores border pixels, if the corresponding neighbor pixel falls outside the image boundaries
graycomatrix(I1, 'offset', [0 1], 'Symmetric', true)
graycomatrix(I1, 'offset', [0 1], 'Symmetric', false) 
graycomatrix(I1, 'offset', [0 -1], 'Symmetric', false)
imshow(myImageAsGray)
imagesc(myImageAsGray)

and the same critical issue!

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 CoC>pushbutton10_Callback (line 634)
myImageAsGray = rgb2gray(map)

I'm able to see the image in grayscale without problem,but with this error message! I tried to add the code that you suggested but the error message is the same.

[Image Analyst]

Please attach your image with the paperclip icon.