dc_code.m

用离散余弦变换实现JPEG编码

%jpeg直流系数HUFFMAN编码
function b = dcencode(x)
% x == 0 的情况不查表编码
if x == 0
   b = [0 0];
   return 
else
   %数值范围分类
   c = floor(log2(abs(x)))+1;
end

% Hoffman table
%   码长 编码
tbl = [2 0 0 0 0 0 0 0 0 0
       3 0 1 0 0 0 0 0 0 0
       3 0 1 1 0 0 0 0 0 0
       3 1 0 0 0 0 0 0 0 0
       3 1 0 1 0 0 0 0 0 0
       3 1 1 0 0 0 0 0 0 0
       4 1 1 1 0 0 0 0 0 0
       5 1 1 1 1 0 0 0 0 0
       6 1 1 1 1 1 0 0 0 0
       7 1 1 1 1 1 1 0 0 0
       8 1 1 1 1 1 1 1 0 0
       9 1 1 1 1 1 1 1 1 0];
%前缀码查表获得 
b = tbl( c+1 ,2:tbl(c+1,1)+1 );
%将输入值转换成二进制数作为尾码
tmp = x_int2bin(x);
%确定输出原码还是补码
if x > 0 
   b = [ b tmp(1:c) ];
elseif x < 0
   b = [ b ones(1,c)-tmp(1:c) ];
end