jpegdoc.m

jpeg compresion withquantization matrices

function b = jpeg(file);
 
A = imread('hulic1.bmp'); %reads file into a matrix
A = rgb2gray(A);
B = imfinfo('hulic1.bmp') 
 
%convert to YCbCr
%if B.Format=='bmp'
%    A=rgb2ycbcr(A)
 
width=B.Width
height=B.Height
 
%urcenie poctu matic 8x8 zaokruhlenim nahor
W=ceil(width/8);
H=ceil(height/8);
 


%create a matrix of zeros and add the image to it k naplneniu out the 8x8
%matrices  (matrix will stay the same size if height and width are
%divisible by 8

I=zeros(H*8,W*8,'uint8');% uint8 vracia hodnoty z intervalu 0-255
I(1:height,1:width)=A(1:height,1:width);
 
imshow(I);

%rozdelenie cisel do WxH 8x8 matic
X=zeros(H,W,8,8);
for J=1:H
    for K=1:W
        for j=1:8
            for k=1:8
                X(J,K,j,k)=I((J-1)*8+j,(K-1)*8+k);
            end
        end
    end
end

%definovanie kvantizacnej matice
Q=[...
    16  11  10  16  24  40  51  61
    12  12  14  19  26  58  60  55
    14  13  16  24  40  57  69  56
    14  17  22  29  51  87  80  62
    18  22  37  56  68  109 103 77
    24  35  55  64  81  104 113 92
    49  64  78  87  103 121 120 101
    72  92  95  98  112 100 103 99];
 
b=[];
vprev=[];
vcurrent=[];
for J=1:H
    for K=1:W
        temp=zeros(8,8,'uint8');%vytvorenie docasnej matice
        temp(:,:)=X(J,K,:,:); %pridenie hodnot z aktualneho 8x8 sektoru
        temp=double(temp);    %convertuje cisla to double formatu(floating point)
        temp=temp-128;        %posunutie na prostriedok okolo nuly
        temp=dct2(temp);      %vykonava 2-D cosinusovu transformacnu funkciu
        temp=temp./Q;         %delenie quantizacnou maticou
        temp=round(temp);     %zaokruhlenie quantizacnej matice
        vcurrent= zigzag(temp);%convertovanie quantizacnej matice do 1-D vectoru
        vcurrent=shorten(vcurrent);%remove extra zeros from vector
        if J==1 && K==1
            b=[b vecenc(vcurrent)];
        else
            vcurrent(1)=vcurrent(1) - vprev(1);%take difference of first value
            b=[b vecenc(vcurrent)];
        end
        vprev=vcurrent;
    end
end
 
 
%b=[head(Q) b 1 1 1 1 1 1 1 1   1 0 0 1 1 0 1 1];%last two bytes:ff d9 denote EOF End of File
imshow(A);