Inverse DCT the 8x8 matrix as:
only (x, y) = 255 * 64,
other 63 elements are 0
(0,0) | (1,0) | (2,0) | (3,0) | (4,0) | (5,0) | (6,0) | (7,0) |
(0,1) | (1,1) | (2,1) | (3,1) | (4,1) | (5,1) | (6,1) | (7,1) |
(0,2) | (1,2) | (2,2) | (3,2) | (4,2) | (5,2) | (6,2) | (7,2) |
(0,3) | (1,3) | (2,3) | (3,3) | (4,3) | (5,3) | (6,3) | (7,3) |
(0,4) | (1,4) | (2,4) | (3,4) | (4,4) | (5,4) | (6,4) | (7,4) |
(0,5) | (1,5) | (2,5) | (3,5) | (4,5) | (5,5) | (6,5) | (7,5) |
(0,6) | (1,6) | (2,6) | (3,6) | (4,6) | (5,6) | (6,6) | (7,6) |
(0,7) | (1,7) | (2,7) | (3,7) | (4,7) | (5,7) | (6,7) | (7,7) |