How can I decompress a DCT compressed image?

Hi, I was wondering how could I be able to decompress the image I've compressed in dct. I understand the decompression steps of images, but I don't know how to implement it in matlab. Much information would be appreciated

 if true
    % code
  end      if true
        % code
      end  if true
    im = imread('lena.ppm');
figure, imshow(im);
%a = imresize(im, [256 400]);
I = rgb2gray(im);
F = dct2(I);
figure, imshow(F * 0.01);
ff = idct2(F);
figure, imshow(ff/255);
[r,c] = size(I); %take size of image and as rows and columns
DF = zeros(r,c); %create vectors which store intermediate values
DFF = DF;
IDF = DF;
IDFF = DF;
depth = 4;% decides how many bits to keep after dct
N = 8; %block size
for i = 1 : N : r %iterate through rows then columns and columns
    for j = 1 : N : c
        f = I(i:i+N-1, j:j+N-1); %take values and put into f
        df = dct2(f);
        DF(i:i+N-1,j:j+N-1) = df; %DCT of blocks
        dff = idct2(df);
        DFF(i:i+N-1, j:j+N-1)= dff; %inverse DCT of blocks

        df(N:-1:depth+1,:) = 0;
        df(:,N:-1:depth+1) = 0;
        IDF(i:i+N-1,j:j+N-1) = df;%DCT of blocks with depth considered
        dff = idct2(df);
        IDFF(i:i+N-1,j:j+N-1) = dff; %inverse DCT of blocks with depth considered
    end
end
figure, imshow(DF / 255);
figure, imshow(DFF);
A = DFF / 255;
figure, imshow(A);
imwrite(A,'abc1.jpeg');
B = IDFF / 255;
imwrite(B,'abc2.jpeg');
figure, imshow(B);
compression_ratio = numel(N)/numel(depth);
  end