Which of the following method is correct for finding the image compression ratio in matlab

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Renjith V Ravi 2017-3-10

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编辑： ahcen aliouat 2022-1-28

I am using Huffman coding for image compression.Here I have mentioned three methods for finding the compression ratio.

      clear all
      clc
      %Read the input image
      Ao=imread('Lena.bmp');
      Ao = imresize(Ao,[256 256]);
      in = imfinfo('Lena.bmp')
      % figure,
      subplot(221)
      imshow(Ao);
      title('input image')
      A=double(Ao);
      % 
      % A=[10 2 3 4;5 6 7 8];
      % display(A);
      e=A;
      tic
      %Perform prediction error
      for i = 1:size(A,1)
          for j = 2:size(A,2)
              e(i,j)=e(i,j)-A(i,j-1);
          end
      end
      display(e);
      %Huffman coding
      C=reshape(e,[],1);
      [D1,x]=hist(C,min(min(e)):max(max(e)));
      sym=x(D1>0);
      prob=D1(D1>0)/numel(e);
      [dict,avglen] = huffmandict(sym,prob);
      compressed = huffmanenco(C,dict);
      imwrite(uint8(compressed),'comp.bmp')
      cmprsd = imfinfo('comp.bmp');
%Three methods for finding the compression ratio
      Compression_Ratio_1 =  in.FileSize/length(compressed)
      Compression_Ratio_2 = (in.Width*in.Height*in.BitDepth/8)/cmprsd.FileSize
      Compression_Ratio_3 = (in.Width*in.Height*in.BitDepth/8)/length(compressed)

Kindly help me to identify which among the 3 is correct for finding the compression ratio.

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Answer 1

ahcen aliouat 2022-1-28

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https://ww2.mathworks.cn/matlabcentral/answers/329083-which-of-the-following-method-is-correct-for-finding-the-image-compression-ratio-in-matlab#answer_883965

编辑：ahcen aliouat 2022-1-28

Hello,

I think the third is the correct. W*H*BitDepth will give you the number of bits needed for the uncompressed image, divided by the number of bits of the compressd image (compressed) gives you the exact compression Ratio.