[M4IF Technotes] About Quarter sample mode interpolation

[Xue Xuhong]

hi, all
in  ISO/IEC 14496‑2:1999/Amd.1:2000(E),
subclause 7.6.2.2 Quarter sample mode interpolation(P207), it is described as following,
[
In quarter sample mode interpolation, for each block of size MxN in the reference VOP which position is defined by the decoded motion vector for the block to be predicted, a reference block of size (M+1)x(N+1) biased in the direction of the half or quarter sample position is read from the reconstructed and padded reference VOP. Then, this reference block is symmetrically extended at the block boundaries by three samples using block boundary mirroring according to Figure V2 - 17.
Figure V2 - 17 -- block boundary mirroring
]
Does Figure V2 - 17 provide an method to do quarter sample interpolation, I can not understand, would anyone please say some words on it? 
Thank you.
Best Regards,
Xue xuhong