MATLAB: Dimension issue when recreating bmp image using imshow()

Question

Hi, I am trying to read a 3*5 24-bit bmp image, divide the channels and recreate the original image from the divided channels. While recreating the image, I used the following code:

reconstruct = red + green + blue;
recons = cast(reconstruct,'uint8');
recon = zeros(width_dec, height_dec, 3,'uint8');
u= 1;
for row = height_dec:-1:1
  for column = 1:1:width_dec
      recon(row,column,3) = recons(u,:);
      fprintf('%d\t',u);
      recon(row,column,2) = recons(u+1,:);
      fprintf('%d\t',u+1);
      recon(row,column,1) = recons(u+2,:);
      fprintf('%d\t\n',u+2);
      u = u+3;
  end
end
    % CHECKING THE RECONSTRUCTED IMAGE
figure;
imshow(recon);

When I tried running the code, the dimensions of the reconstructed image changed to 5*5. Actual width of the image is 3 pixels. But in the reconstructed image, the remaining width of 2 pixel is appended with black colour. Why is it happening? Could I get some help regarding this issue?

Thanks in advance.

Answer 1

I'm sure that replacing the loops by reshape and/or permute would simplify the code (see Stephen's comment). But the actual problem of your code is, that you have swapped the 1st and 2nd dimension of recon:

recon = zeros(width_dec, height_dec, 3,'uint8');
for row = height_dec:-1:1
  for column = 1:1:width_dec
    recon(row, column, 3) = recons(u,:);
    ...
  end
end

You meant either:

      recon(column, row, 3) = recons(u,:);

or alternatively:

recon = zeros(height_dec, width_dec, 3, 'uint8');