I want to display RGB channels separately and I wrote below code and executed it. Why it shows an error like "Index exceeds matrix dimensions. Error in clusteredit (line 21) green = imIDX(:,:,2); % Green channel" . Please tell me how to tackle this

clear all;
     newImageRGB = imread('p2_left_norm_1.bmp'); 
     figure;
     imshow(newImageRGB);
     title('Original image');
     grayImage = rgb2gray(newImageRGB);
     figure;
     imshow(grayImage); 
     title('grayscale image');
     afterWiener = wiener2(grayImage,[6 6]);
     figure;
     imshow(afterWiener);
     title('Wiener filter');
      imData=reshape(afterWiener,[],1);
    imData=im2double(imData);
    [IDX mn]=kmeans(imData,3);
    imIDX=reshape(IDX,size(afterWiener));

red = imIDX(:,:,1); % Red channel
green = imIDX(:,:,2); % Green channel
blue = imIDX(:,:,3); % Blue channel
a = zeros(size(imIDX, 1), size(imIDX, 2));
just_red = cat(3, red, a, a);
just_green = cat(3, a, green, a);
just_blue = cat(3, a, a, blue);
back_to_original_img = cat(3, red, green, blue);
figure, imshow(just_red), title('Red channel')
figure, imshow(just_green), title('Green channel')
figure, imshow(just_blue), title('Blue channel')

[KSSV]

Your imIDX is a 2D matrix, and you are treating it as 3D, that's why error popping out.