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188 9 Directional Filtering Transform
t
1
,t
2
= 1,2,··· ,N/2, where θ is the angle of prediction direction and the vertical
axis in Figure 9.9.
For the modes H
0
−H
2
, the horizontal filtering is performed first, followed by
the vertical lifting and unidirectional prediction (see Figure 9.10). With the adap-
tive lifting order, BDF provides us with an evenly distributed set of modes covering
the whole plane. If the image block exhibits a strong vertical correlation, lifting in
the vertical dimension is performed first, and vice versa. Therefore, the directional
correlation can be fully exploited.
As previously mentioned, we take one-level lifting as an example. The hierarchi-
cal structure can be obtained by iteratively performing two dimensional lifting ...