Huffman coding and decoding for image(JPEG, BMP)

Question

Manisha Mehra 2011-2-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2158-huffman-coding-and-decoding-for-image-jpeg-bmp

评论： Harshil Patel 2020-4-28

I have to implement huffman encoding and decoding for a '.bmp' image without using the inbuilt matlab function like huffmandict, huffmanenco and huffmandeco.

Can anybody help me by sending me the source code?

Moreover, I have done the encoding part but I am not able to do the decoding. I have no idea as how to reconstruct the image through decoding.

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Walter Roberson 2015-6-23

That is possible. You need to store the code dictionary as well as the encoding. With 256 different symbols possible, unless at least half of them are never used, you can be sure that some of the encodings will be at least 8 bits, the original length. When the probabilities are about equally distributed each of the symbols would come out as 8 bits, so saving nothing for the encoded part. But you need to save the dictionary as well and that takes room.

Huffman encoding is a lossless encoding, so you need to have as much "information" stored in the encoded version as in the unencoded version. It doesn't begin to save space on the encoding until some of the symbols are at least twice as probable as some of the others or at least half the potential symbols are never unused, which are situations that would allow it to save 1 bit per occurrence. Those bits saved have to add up to the size of the saved dictionary before you get any net savings on the storage.

Efficient storage of the dictionary takes some thought since each of the entries is a variable number of bits -- the bit pattern and the symbol it decodes to. And remember to account for the end-of-stream marker or some other method of indicating where the end of the stream of bits is, since it will not generally be at a byte boundary so you can't tell by end-of-file.

Jasmina Vanasiwala 2016-12-12

I have to implement huffman encoding and decoding for a 'jpeg' image using C or C++. Please anyone help me by sending the source code?

Walter Roberson 2016-12-12

this is a resource for MATLAB questions not C or C++
there are already a lot of public sources for that task including libjpeg
if we send you source then you would not have implemented it. Would we get the academic credit or would you?

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Answer 1

Paulo Silva 2011-2-28

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https://ww2.mathworks.cn/matlabcentral/answers/2158-huffman-coding-and-decoding-for-image-jpeg-bmp#answer_3374

There are good examples on the matworks file exchange, for example this presentation with source code and good explanation

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Manisha Mehra 2011-3-1

Thanks..

It worked awesome.

fateh 2014-11-9

how could i run this example

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Answer 2

Falak 2012-5-4

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2158-huffman-coding-and-decoding-for-image-jpeg-bmp#answer_46713

在 MATLAB Online 中打开

Try this one... just change to your required image

%Author Name:Falak Shah
%Target: To huffman encode and decode user entered string
%--------------------------------------------------------------------------
string=input('enter the string in inverted commas');         %input string
symbol=[];                                %initialise variables
count=[];
j=1;
%------------------------------------------loop to separate symbols and how many times they occur
for i=1:length(string)                   
  flag=0;    
  flag=ismember(symbol,string(i));      %symbols
      if sum(flag)==0
      symbol(j) = string(i);
      k=ismember(string,string(i));
      c=sum(k);                         %no of times it occurs  
      count(j) = c;
      j=j+1;
      end 
end    
ent=0;
total=sum(count);                         %total no of symbols
prob=[];                                         
%-----------------------------------------for loop to find probability and
%entropy
for i=1:1:size((count)');                   
prob(i)=count(i)/total;
ent=ent-prob(i)*log2(prob(i));            
end
var=0;
%-----------------------------------------function to create dictionary
[dict avglen]=huffmandict(symbol,prob);    
% print the dictionary.
         temp = dict;
         for i = 1:length(temp)
         temp{i,2} = num2str(temp{i,2});
         var=var+(length(dict{i,2})-avglen)^2;  %variance calculation
         end
         temp
%-----------------------------------------encoder  and decoder functions           
sig_encoded=huffmanenco(string,dict)
deco=huffmandeco(sig_encoded,dict);
equal = isequal(string,deco)
%-----------------------------------------decoded string and output
%variables
str ='';
for i=1:length(deco)    
str= strcat(str,deco(i));
end
str
ent
avglen
var

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satyendra kumar 2019-3-23

在 MATLAB Online 中打开

they not work properly.....how can solve it?

%Target: To huffman encode and decode user entered string
%--------------------------------------------------------------------------
filename = input('enter the image file name', 's');
string = imread('cameraman.tif');
string = string(:);
symbol=[];                                %initialise variables
count=[];
j=1;
%------------------------------------------loop to separate symbols and how many times they occur
for i=1:length(string)                   
  flag=0;    
  flag=ismember(symbol,string(i));      %symbols
      if sum(flag)==0
      symbol(j) = string(i);
      k=ismember(string,string(i));
      c=sum(k);                         %no of times it occurs  
      count(j) = c;
      j=j+1;
      end 
end    
ent=0;
total=sum(count);                         %total no of symbols
prob=[];                                         
%-----------------------------------------for loop to find probability and
%entropy
for i=1:1:size((count)');                   
prob(i)=count(i)/total;
ent=ent-prob(i)*log2(prob(i));            
end
var=0;
%-----------------------------------------function to create dictionary
[dict avglen]=huffmandict(symbol,prob);    
% print the dictionary.
         temp = dict;
         for i = 1:length(temp)
         temp{i,2} = num2str(temp{i,2});
         var=var+(length(dict{i,2})-avglen)^2;  %variance calculation
         end
         temp
%-----------------------------------------encoder  and decoder functions           
sig_encoded=huffmanenco(string,dict)
deco=huffmandeco(sig_encoded,dict);
equal = isequal(string,deco)
%-----------------------------------------decoded string and output
%variables
str ='';
for i=1:length(deco)    
str= strcat(str,deco(i));
end
str
ent
avglen
var

Walter Roberson 2019-3-23

What leads you to say that it does not work?

Harshil Patel 2020-4-28

I ran the code in matlab 2020a, and it generated some otput with some values for str, ent, avglen and var for an image input. So, how do I know if it's correct?

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Answer 3

slama najla 2012-5-19

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https://ww2.mathworks.cn/matlabcentral/answers/2158-huffman-coding-and-decoding-for-image-jpeg-bmp#answer_48365

Hello please is that you can help me? is that you can send me your registration code files before you get the picture compressed as I encounter the same problem as let go of compressed image is a very superior picture framer and my original remark that the fault is in the recording files. thank you in advance