Image Approximation (imshow) trouble -- I believe I'm doing Image Compression??

I have been asked to do the following (which I've done successfully):

Here is the beginning of what I entered, and I'm attaching a PDF for the rest.

I get confused when it gets to the second set of directions where I am to show an "image approximation". After all I've researched, again never have coded before, I cannot seem to enter anything correct because all I get is a white image. I used this help page to try to get me on the correct path: https://www.mathworks.com/help/matlab/math/image-compression-with-low-rank-svd.html but have had no luck. Here are the 2nd set of directions specifically that I'm struggling with. The math part of all the coding, I'm golden! It's the image part, and displaying that image where I'm getting the 1st image to display properly, but not the compressed/approximated images to come up as anything other than white.

Thank you!

[DGM]

As to why the image is white, it's probably because your floating-point images are improperly scaled for their class because of the manner in which you handled them or cast them.

https://www.mathworks.com/matlabcentral/answers/171253-how-can-convert-a-image-from-type-of-double-unit16-to-a-grayscale-image

https://www.mathworks.com/help/images/convert-image-data-between-classes.html

Answer 1

[Karl]

The code below builds on code given by Torsten in relation to a related question: https://mathworks.com/matlabcentral/answers/2084643-how-to-do-a-rank-1-approximation.

% Read test image, which has data type uint8.
im1 = imread('moon.tif');
imshow(im1)
title(['original image']);

% Set rank of approximation.
k = 10;
% Convert to and from type double.
% The svd() function used in rank_k_approximation()
% requires data of type single or double.
im2 = uint8(rank_k_approximation(double(im1), k));
imshow(im2)
title(['rank-',num2str(k),' approximation']);

function Ak = rank_k_approximation(A, k)
%RANK_K_APPROXIMATION Calculate rank-k approximation of matrix A.
%   The matrix A must be of type single or double
%   (required by the function svd).
  [U, S, V] = svd(A);
  Ak = zeros(size(A));
  for i=[1:k]
     Ak = Ak + S(i,i)*U(:,i)*V(:,i).';
  end
end

[Jessica]

Unfortunately, neither of these worked. I wonder if it's because the "free" version I have from the school is from 2006? I keep getting so many syntax errors. Yet, if I code here in the Community Board, everything pops up just fine :/

Thank you for trying to help! Much appreciated!

[Karl]

If you post the syntax errors that you're seeing, and the code that produced them, someone might be able to suggest changes for getting things to work with a MATLAB release from 2006.

In case it could be useful, MathWorks offers a free version of MATLAB Online:

https://mathworks.com/products/matlab-online/matlab-online-versions.html

[Jessica]

Thank you, my Professor helped me enough where I'm not going to fail anyways.