Cryptography Reference
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(a) Empty pre-spatial decomposition
(b) One level pre-spatial decomposition
(c) Two level pre-spatial decomposition
Fig. 3.18. Three examples of pre- and post-spatial decompositions [22, 23].
These artifacts are particularly visible after a few levels of temporal filtering.
One remedy for this is by using the original frames as the low-pass frames.
It essentially skips the update step in the lifting scheme. The disadvantage of
this method is that it lowers the coding e ciency.
Another tool available in the VidWav software is leaky motion compensa-
tion. It is caused when high quality images are used for motion compensation,
drift errors occur when the decoder does not receive all the high quality im-
age information. The low quality image motion compensation suffers coding
e ciency loss. The leaky motion compensation is an in between compromise
and is typically used for low spatial sub-bands. When encoding these sub-
bands, the difference between the high quality reference and the low quality
interpolated reference is attenuated by a leaky factor. This leaky factor is
adjustable.
Some other tools available in the VidWav software are the mode-based
temporal filtering where each macroblock uses either the low quality reference
or the high quality reference to make the prediction. Another tool is the AVC
base-layer. When used, the wavelet scheme is applied only to the enhancement
layer [22, 23].
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