OpenCV: DCT and IDCT

float data[] = { 1, 2, 3, 4, 5, 6, 7, 8 };

CvMat a, b, c;
a = cvMat(2,4,CV_32FC1,data);
b = cvMat(2,4,CV_32FC1,data); // or initialize b,c
c = cvMat(2,4,CV_32FC1,data);

cvDCT(&a, &b, CV_DXT_FORWARD);
cvDCT(&b, &c, CV_DXT_INVERSE);

original matrix:
1 2 3 4
5 6 7 8

after DCT:
12.728 -3.154 0.000 -0.224
-5.657 0.000 0.000 0.000

after IDCT:
1 2 3 4
5 6 7 8