function x_idct=myidct_good(X)
%確定矩陣大小
[N,N]=size(X);
%求T矩陣
Tpq=zeros(N,N);
Tpq(1,:)=1/sqrt(N);
p=1:N-1;
q=0:N-1;
Tpq(p+1,q+1)=sqrt(2/N)*cos(p'*(2*q+1)*pi/(2*N));

%由T'*X*T得到DCT反變換的結果
x_idct=Tpq'*X*Tpq;