huffman encoding for image

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Nidhi Kumari 2018-10-9

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423107-huffman-encoding-for-image

评论： Walter Roberson 2018-10-26

采纳的回答： OCDER

在 MATLAB Online 中打开

for the code-

A=imread('xyz.jpg');
A1=rgb2gray(A);
A = A1(:);
[symbols,p]=hist(A,double(unique(A)))
p=p/sum(p)
symbols=symbols/sum(symbols)
[dict,avglen]=huffmandict(symbols,p)
comp=huffmanenco(A,dict)

i am getting error-

Error using huffmandict (line 164)
Source symbols repeat
Error in new (line 7)
[dict,avglen]=huffmandict(symbols,p)

suggest necessary changes

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Nidhi Kumari 2018-10-10

But how to make them same?

KALYAN ACHARJYA 2018-10-10

@Nidhi

I have updated the answer, please check here

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采纳的回答

OCDER 2018-10-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423107-huffman-encoding-for-image#answer_340760

在 MATLAB Online 中打开

I haven't used huffmandict before, but based on the document and the error message you have, I suspect your inputs are wrong.

https://www.mathworks.com/help/comm/ref/huffmandict.html

Double check your inputs to huffmandict. Make sure symbols are unique values, and p are the probability of each value. That means:

[symbols, p] = hist(A,double(unique(A)))  should be
[p, symbols] = hist(A,double(unique(A)))  because the 1st output of hist is the frequency (probability)
                                          and the second output is the unique bin (unique symbol)

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Walter Roberson 2018-10-26

编辑：Walter Roberson 2018-10-26

在 MATLAB Online 中打开

Do you have the Image Processing Toolbox?

https://www.mathworks.com/matlabcentral/answers/54439-list-of-builtin-demo-images

If you use

imshow('peppers.png')

then does an image show up?

As of R2018b that particular image was moved to the Deep Learning Toolbox (formerly known as Neural Network Toolbox), and a new image test.jpg was added to that directory.

But since peppers.png was present for quite a number of releases, use that. In my test on peppers.png, the decoding took about 4.3 seconds.

function huff
a = imread('xyz.jpg');
imshow(a);
A1=rgb2gray(a);
imhist(A1);
[M, N]=size(A1);
A = A1(:);
count = 0:255;
p = imhist(A1) / numel(A1);
tic; [dict,avglen]=huffmandict(count,p); toc % build the Huffman dictionary
tic; comp= huffmanenco(A,dict); toc        %encode your original image with the dictionary you just built
compression_ratio= (512*512*8)/length(comp);   %computing the compression ratio
display(compression_ratio)
%%DECODING
tic; Im = huffmandeco(comp,dict); toc % Decode the code
I11=uint8(Im);
decomp=reshape(I11,M,N);
imshow(decomp);

Walter Roberson 2018-10-26

You are using a version of MATLAB no later than R2017b: I can tell because is_a_valid_code was removed from huffmandeco as of R2018a.

Looking at the amount of memory you have, I suspect you are running R2015b or earlier with a 32 bit MATLAB.

When I test with peppers.png on R2017b on my system, the decoding took about 53 seconds.

Walter Roberson 2018-10-26

I have a memory of having reported an inefficiency to MATLAB having to do with is_a_valid_code, that it was being called far too often. However, I do not seem to find that in my case list, so perhaps I reported it years ago on a different license.

Anyhow: upgrading to R2018a or later would probably speed up quite a bit.

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