representing DCT(discrete cosine transform) quantized block into circle block.

i've s gray scale image and thn i've divided it into overlapping blocks. starting from the first block i've applied dct on it and now want to reduce it into for circle blocks C1,C2,C3 and C4.

i dont know how to reduce the 8x8 matrix into C1,C2,C3 and C4.

   http://imageshack.us/photo/my-images/51/circleblock.jpg/

Denote r as the radius of the circle block, so we can get the area:

 c_area=pi * r^2
 and
 m_area=4 * r^2
 where c _ area, m _ area is the area of the circle block and matrix,
 respectively.

we can get p _ ratio = pi * r^2/4*r^2 = 0.79, which implies that the circle block can represent most of the elements of the matrix, and discards only a few of them.

can anybody help me how this can be done?