Image compression huffman coding

Question

lavanya vs 2019-4-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459170-image-compression-huffman-coding

回答： Saherish Pathan 2022-1-10

%clearing all variableas and screen
clear all;
close all;
clc;
%Reading image
a=imread('jpeg-image-compression-1-638.JPG');
figure,imshow(a)
%converting an image to grayscale
I=rgb2gray(a);
%size of the image
[m,n]=size(I);
Totalcount=m*n;
%variables using to find the probability
cnt=1;
sigma=0;
%computing the cumulative probability.
for i=0:255
k=I==i;
count(cnt)=sum(k(:))
%pro array is having the probabilities
pro(cnt)=count(cnt)/Totalcount;
sigma=sigma+pro(cnt);
cumpro(cnt)=sigma;
cnt=cnt+1;
end;
%Symbols for an image
symbols = [0:255];
%Huffman code Dictionary
dict = huffmandict(symbols,pro);
%function which converts array to vector
vec_size = 1;
for p = 1:m
for q = 1:n
newvec(vec_size) = I(p,q);
vec_size = vec_size+1;
end
end
%Huffman Encodig
hcode = huffmanenco(newvec,dict);
%Huffman Decoding
dhsig1 = huffmandeco(hcode,dict);
%convertign dhsig1 double to dhsig uint8
dhsig = uint8(dhsig1);
%vector to array conversion
dec_row=sqrt(length(dhsig));
dec_col=dec_row;
%variables using to convert vector 2 array
arr_row = 1;
arr_col = 1;
vec_si = 1;
for x = 1:m
for y = 1:n
back(x,y)=dhsig(vec_si);
arr_col = arr_col+1;
vec_si = vec_si + 1;
end
arr_row = arr_row+1;
end
%converting image from grayscale to rgb
[deco, map] = gray2ind(back,256);
RGB = ind2rgb(deco,map);
imwrite(RGB,'decoded.JPG');
%end of the huffman coding

This code works fine but the image decoded is grey in colour. I cannot find anything wrong in it please help

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nor saziana ariani sazali 2021-6-24

Hi, walter..can i know step for storing huffman dictionary after encoding using huffman?

Walter Roberson 2021-7-11

https://en.wikipedia.org/wiki/Canonical_Huffman_code

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Answer 1

Saherish Pathan 2022-1-10

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459170-image-compression-huffman-coding#answer_871850

clear all;

close all;

clc;

%Reading image

a=imread('jpeg-image-compression-1-638.JPG');

figure,imshow(a)

%converting an image to grayscale

I=rgb2gray(a);

%size of the image

[m,n]=size(I);

Totalcount=m*n;

%variables using to find the probability

cnt=1;

sigma=0;

%computing the cumulative probability.

for i=0:255

k=I==i;

count(cnt)=sum(k(:))

%pro array is having the probabilities

pro(cnt)=count(cnt)/Totalcount;

sigma=sigma+pro(cnt);

cumpro(cnt)=sigma;

cnt=cnt+1;

end;

%Symbols for an image

symbols = [0:255];

%Huffman code Dictionary

dict = huffmandict(symbols,pro);

%function which converts array to vector

vec_size = 1;

for p = 1:m

for q = 1:n

newvec(vec_size) = I(p,q);

vec_size = vec_size+1;

end

%Huffman Encodig

hcode = huffmanenco(newvec,dict);

%Huffman Decoding

dhsig1 = huffmandeco(hcode,dict);

%convertign dhsig1 double to dhsig uint8

dhsig = uint8(dhsig1);

%vector to array conversion

dec_row=sqrt(length(dhsig));

dec_col=dec_row;

%variables using to convert vector 2 array

arr_row = 1;

arr_col = 1;

vec_si = 1;

for x = 1:m

for y = 1:n

back(x,y)=dhsig(vec_si);

arr_col = arr_col+1;

vec_si = vec_si + 1;

end

arr_row = arr_row+1;

end

%converting image from grayscale to rgb

[deco, map] = gray2ind(back,256);

RGB = ind2rgb(deco,map);

imwrite(RGB,'decoded.JPG');

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Answer 2

Abdel Rahman Bekawi 2020-1-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459170-image-compression-huffman-coding#answer_409710

编辑：Abdel Rahman Bekawi 2020-1-12

在 MATLAB Online 中打开

well done, your code is great!

however, the thing that makes this logical error is that your map channels are equal to each other, hence you will get grayed scale image as well, so to overcome this issue, I recommend you work with indexed images.

% try the following 
[indexed, colormap] = rgb2ind(rgbimage, number_of_colors);
% do all the processing on this indexed format and then at the end 
RGB = ind2rgb(back, colormap);
% by this you should get a compressed colored image 

I hope this helps!

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hamza munawar 2020-8-31

have anyone done the huffman encoding on a 2D image in matlab???

Walter Roberson 2020-8-31

Yes, people have done that. Just reshape the image into a vector, and Huffman encode that. If you save or transmit the encoded image, remember to store the dictionary and the image size so that you can reconstruct afterwards.

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