dcencode.asv

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 的特殊情况编码
if x == 0
   b = [0 0];
   return 
else
   %数值范围分类
   c = floor(log2(abs(x)))+1;
end

% Hoffman table
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];
 
b = tbl(c+1,2:tbl(c+1,1)+1);

tmp=int2bin(x,c);  
% tmp is 1 by c+1 vector containing sign-mag
% representation of x, first bit is sign bit.

if tmp(1)==0, % if x > 0
   b=[b tmp(2:c+1)];
elseif tmp(1)==1, % if x < 0
   b=[b ones(1,c)-tmp(2:c+1)];
end