www.gusucode.com > 图像压缩编码码matlab实现 > 图像压缩编码码matlab实现/JSjpeg/jpegdecode.m

    function x = jpegdecode(y)
%jpegdecode函数，jpegencode的解码程序
error(nargchk(1, 1, nargin));      %检查输入参数
m = [16 11 10 16 24 40 51 61       %JPEG量化步长矩阵
     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 98 112 110 103 99];
 order = [1 9 2 3 10 17 25 18 11 4 5 12 19 26 33 ...        %变换系数排列次序
       41 34 27 20 13 6 7 14 21 28 35 42 49 57 50 ...
       43 36 29 22 15 8 16 23 30 37 44 51 58 59 52 ...
       45 38 31 24 32 39 46 53 60 61 54 47 40 48 55 62 63 56 64];
rev = order;          %计算逆序
for k = 1:length(order)
    rev(k) = find(order == k);
end
% ff = max(rev(:)+1;
m = double(y.quality)/100*m;
xb = double(y.numblocks);          %得到图像块数
sz = double(y.size);
xn = sz(1);
xm = sz(2);
x = huffdecode(y.huffman, y.info);    %huffman1解码
x = double(x) - 128;
eob = max(x(:));
z = zeros(64, xb);
k = 1;
for j = 1: xb
    for i = 1: 64
        if x(k) == eob
            k = k + 1;
            break;
        else
            z(i, j) = x(k);
            k = k + 1;
        end
    end
end
z = z(rev, :);               %恢复次序
x = col2im(z, [8, 8], [xm, xn], 'distinct');       %重新排列成图像
x = blkproc(x, [8, 8], 'x.*P1', m);                %逆量化
t = dctmtx(8);
x = blkproc(x, [8, 8], 'P1*x*P2', t', t);          %DCT逆变换
x = uint8(x + 128);                                %进行位移