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Lost DCT coefficients can be determined by interpolation among the corresponding
frequency coefficients of spatially adjacent blocks. Two things have to be noted
on interpolation. First, it can only be applied within intra-coded blocks, as
the inter-coded blocks contain prediction errors, which do not exhibit high
levels of correlation. Second, it is preferably applied to the DC and the
low-frequency AC coefficients, as the smoothness assumption is not valid for the
high frequency coefficients.
Motion vectors can be determined through interpolation. Various combinations of
reference motion vectors for the interpolation can be used. One is motion
vectors from the corresponding block of the previous frame, assuming rigid
motion for the video sequence. Another is the motion vectors corresponding to
the spatially adjacent blocks, assuming a monotonic distribution for the vector
field. Combinations of the above with averaging and medians are also
used.
Isaac Kokkinidis
1998-08-27