jpegdemo.m

这是一个JPEG程序

% JPEGdemo.m
% Prototype JPEG compression algorithm demostration
% This algorithm only demonstrate the basic 
% JPEG functionalities.
% It is not necessarily a faithful 
% implementation of JPEG.
% Its output will not be binary bit streams 
% either, but rather
% an integer stream of 0 and 1s
% Only gray scale picture is considered
clear all
clc
% Load data
disp('Enter ...')
disp('0 (default) - load a row x col image, or ')
disp('1 - Use text book 8 x 8 data (example 8.28)')
chos=input('Enter your choice: ');
q = 0.1;
if isempty(chos), chos=0; end % default choice
if chos==0, 
    x = imread('Cameraman.bmp');
    f=double(x);%(1+128:128+128,1+128:128+128);
    imshow(mat2gray(f))
    clear x
else
    %  variable f  is taken from the text book.
f=[139 144 149 153 155 155 155 155
144 151 153 156 159 156 156 156
150 155 160 163 158 156 156 156
159 161 162 160 160 159 159 159
159 160 161 162 162 155 155 155
161 161 161 161 160 157 157 157
162 162 161 163 162 157 157 157
162 162 161 161 163 158 158 158];
end
%echo on

% level shift by 128
if chos==0, f=f-128; elseif chos==1, f=f-128; end
%pause
drawnow
[mf,nf]=size(f); mb=mf/8; nb=nf/8;  
% size of f, # of blocks of f

% Step 1. 2D separable DCT on each 8x8 
% blocks 
if chos==0, 
    Ff=blkproc(f,[8 8],'dct');  
    % apply DCT to each column of each block of f
    Ff=blkproc(Ff',[8 8],'dct');
    % apply DCT to each row of each block of Ff
    Ff=round(Ff');
    % transpose back to proper orientation
elseif chos==1,
    Ff=blkproc(f,[8 8],'dct')
    % apply DCT to each column of each block of f
    Ff=blkproc(Ff',[8 8],'dct')
    % apply DCT to each row of each block of Ff
    Ff=round(Ff')
    % transpose back to proper orientation
end
%pause

% Perceptual scaler quantization
%
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]*q;
% this is the quantization matrix shown in figure 8.37 in the textbook
%pause
% Now perform rounding
if chos==0, 
    Fq=round(blkproc(Ff,[8 8],'divq',Q));
elseif chos==1,
    Fq=round(blkproc(Ff,[8 8],'divq',Q))
end
%pause
%echo off
% DPCM of DC component, scaned row-wise 
if mb*nb > 1,
   fdc=reshape(Fq(1:8:mf,1:8:nf)',mb*nb,1);   
   fdpcm=dpcm(fdc,1);
else
   fdpcm=Fq(1,1)-(-17);

end
dccof=[];
for i=1:mb*nb,
   dccof=[dccof jdcenc(fdpcm(i))];
end
if chos==1,
    disp(['Differential DC coefficient (' num2str(fdpcm) ') is encoded as: ']);
    disp(int2str(dccof));
end
%pause
%echo on

% Zig-Zag scanning of AC coefficients
z=[1   2   6   7  15  16  28  29
   3   5   8  14  17  27  30  43
   4   9  13  18  26  31  42  44
  10  12  19  25  32  41  45  54
  11  20  24  33  40  46  53  55
  21  23  34  39  47  52  56  61
  22  35  38  48  51  57  60  62
  36  37  49  50  58  59  63  64];
%pause
%echo off
acseq=[];
for i=1:mb
  for j=1:nb
    tmp(z)=Fq(8*(i-1)+1:8*i,8*(j-1)+1:8*j);
    % tmp is 1 by 64
    eobi=max(find(tmp~=0)); %end of block index
                    % eobi is labelled with 999    
    acseq=[acseq tmp(2:eobi) 999];
  end
end
accof=jacenc(acseq);
save acdcdata accof dccof
disp(['DC coefficient after Huffman coding has ' int2str(length(dccof)) ...
' bits']);
disp(['AC coefficient after Huffman coding has ' int2str(length(accof)) ...
' bits']);

disp(['Compression Rate   ' num2str((length(dccof)+length(accof))/(mb*nb*64)) '   Bits / pixel '])
disp(['Compression Ratio   ' num2str(8/((length(dccof)+length(accof))/(mb*nb*64))) ' : 1'])