Rgb2gray error

Good evening everyone,

I'm trying to read all images in a folder and convert them in gray scale with rgb2gray with this code (my images are not gray scale , there are RGB)

Filelist= dir('Clipboard*.png');
nfiles = length(Filelist);
for i=1:size(Filelist,1)
    t=imread(Filelist(i).name);
    I(:,:,i)=rgb2gray(t);
end

And after calculate the ssd between all the images :

N=((size(I(:,:,1),1)*size(I(:,:,1),2)).^2);
SSD=zeros(size(Filelist,1),size(Filelist,1));
for i=1:1:nfiles
     for j=1:1:nfiles
         SSD(i,j)=sum(sum(((I(:,:,i)-I(:,:,j)).^2)/(261501241)));
     end
end
imagesc(SSD);

but i have this error:

Error using rgb2gray>parse_inputs (line 80)
MAP must be a m x 3 array.

Error in rgb2gray (line 52)
isRGB = parse_inputs(X);

Error in test21 (line 32)
    I(:,:,i)=rgb2gray(t);

Answer 1

[Image Analyst]

Convert to gray scale:

Filelist= dir('Clipboard*.png');
numberOfFiles = length(Filelist);
for k = 1 : numberOfFiles % Don't use i (the imaginary variable).
    thisImage = imread(Filelist(k).name);
    [rows, columns, numberOfColorChannels] = size(thisImage);
    if k == 1
        % Instantiate I with the size of the first image.
        I = zeros(rows, columns, numberOfFiles, class(thisImage));
    end
    if numberOfColorChannels > 1
        % It's color.  Need to convert to gray scale before putting it into the 3D image as the k'th slice.
        I(:,:, k) = rgb2gray(thisImage);
    else
        % Already grayscale.  No need to convert.  Just put in directly as the k'th slice.
        I(:,:, k) = thisImage;
    end
end

[Benjamin Lemoine]

Thank you vey much