Spliting an image into 4 blocks and apply a function to each block

I want to split an image into 4 blocks and apply a function to each block and display the result as one figure. My code is given below. But it gives the error " Error using horzcat. Dimensions of matrices being concatenated are not consistent". How to solve this and get my work done ?

    clc;    
    close all;
    workspace; 
    format longg;
    format compact;
    fontSize = 20;

    folder = fullfile(matlabroot, '\toolbox\images\imdemos');
    baseFileName = 'Photoshop_Resampled\ucid00059u.tif';

    rgbImage = imread(baseFileName);
     % Get the dimensions of the image.  numberOfColorBands should be = 3.
    [rows columns numberOfColorBands] = size(rgbImage);
    % Display the original color image.
    subplot(2, 3, 1);
    imshow(rgbImage, []);
    imgr = rgb2gray(rgbImage);

    title('Original Color Image', 'FontSize', fontSize);
    % Enlarge figure to full screen.
    set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
    % Get the rows and columns to split at,
    % Taking care to handle odd-size dimensions:
    col1 = 1;
    col2 = floor(columns/2);
    col3 = col2 + 1;
    row1 = 1;
    row2 = floor(rows/2);
    row3 = row2 + 1;

     lowerLeft = imcrop(imgr, [col1 row3 col2 row2]);
     subplot(2, 3, 2);
     imshow(lowerLeft);

    upperLeft = imcrop(imgr, [col1 row1 col2 row2]);
    subplot(2, 3, 2);
    imshow(upperLeft);

    upperRight = imcrop(imgr, [col3 row1 columns - col2 row2]);
    subplot(2, 3, 2);
    imshow(upperRight);

    lowerRight = imcrop(imgr, [col3 row3 columns - col2 rows - row2]);
    subplot(2, 3, 2);
    imshow(upperRight);

    blockArray = [upperLeft, lowerLeft,upperRight, lowerLeft];

   for i=1:length(blockArray)
    imIdx = 8;
    % RESAMPLING PARAMETERS

    resampleRatio = 1.1;

    N = 2;   % window size
    M = 16 % block size

   im  = baseFileName;
   [H,W,~] = size(imgr);

    for k = 1:length(resampleRatio)   
      r = resampleRatio(k);   

   img = double(blockArray(i));           

   % img = imresize(img,[M M],'bilinear');    
    pmap = emresampleN(img,N,'verbose');                  
    fmap = fft2c(pmap);

    %disp(fmap);

    % display p-map
    subplot(2, 3, 3);
    imshow(blockArray(i));

    figure;
    subplot(131)
    imshow(img,[])
    subplot(132)
    imshow(pmap,[])
    subplot(133)
    imshow(abs(rmcenter(fmap)),[]);

     end    
   end

Answer 1

[Guillaume]

I strongly suspect that your blockArray is meant to be a cell array, hence dthe line

blockArray = [upperLeft, lowerLeft,upperRight, lowerLeft];

should be

 blockArray = {upperLeft, lowerLeft,upperRight, lowerLeft};

It seems you also don't know how to index cell arrays. The line

img = double(blockArray(i));

should be

img = blockArray{i};

Finally, the line

[H,W,~] = size(imgr);

is completely pointless. You don't use H or W and in any case, you already know the size of imgr, it's [rows, columns, numberOfColorBands].

[NC]

Thank you very much, The problem was solved by your instructions.