Image Processing Reference
Figure 32-4 Wipes with macroblock grids.
Wipes are less harsh on the compression process. If the edge is softened, it will increase the
amount of picture area that is changing. When you create a soft-edged wipe, try to ensure
that it spans as few macroblocks as possible. Figure 32-4 shows some wipe transitions
and draws macroblock grids over them to indicate the area of change.
A diagonal wipe affects more macroblocks than a perpendicular wipe. These blocks
are guaranteed to change from frame to frame. Other blocks may also be changing due to
the moving pictures being wiped.
Using Video That Has Already Been Compressed
Recompressing footage that has already been compressed with a lossy codec leads to
the introduction of some very nasty artifacts. For a start, unwrapping a compressed video
clip may yield some blocky effects that are a result of the macroblock-compression process