huffman encoding for image

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Nidhi Kumari
Nidhi Kumari 2018-10-9
评论： Walter Roberson 2018-10-26
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
Nidhi Kumari 2018-10-10
But how to make them same?
KALYAN ACHARJYA
KALYAN ACHARJYA 2018-10-10
@Nidhi
I have updated the answer, please check here

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采纳的回答

OCDER
OCDER 2018-10-10
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
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
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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