def scan64(block):
    """Apply zigzag scan for one 8x8 block."""

    indexes = [
            0,   1,  8, 16,  9,  2,  3, 10,
            17, 24, 32, 25, 18, 11,  4,  5,
            12, 19, 26, 33, 40, 48, 41, 34,
            27, 20, 13,  6,  7, 14, 21, 28,
            35, 42, 49, 56, 57, 50, 43, 36,
            29, 22, 15, 23, 30, 37, 44, 51,
            58, 59, 52, 45, 38, 31, 39, 46,
            53, 60, 61, 54, 47, 55, 62, 63]

    return block.flatten()[indexes]