Image Processing Reference
In-Depth Information
Solution?
1. Apply a dropout compensator.
2. Create an RF-shielded room (expensive).
3. Re-orient your antenna to receive from a different transmitter.
4. Hand-retouch if really necessary.
5. Live with it.
36.4.11
Aliasing
This happens when the interlacing interferes with the presentation of moving objects on
the screen. It is most obvious with near horizontal edges moving vertically, and it appears
suddenly during a pan.
The artifact will be most obvious on NTSC versions of 24-fps movies because of the
pulldown effect. Where it is evident in the output from a playback device, using progres-
sive scanning instead of interlaced presentation should cure it. Figure 36-12 shows what
might happen during a pan.
Figure 36-12 Aliasing during a pan.
Solution?
1. Carefully de-interlace or inverse-telecine the footage.
2. You may be able to reconstruct the broken frames by taking fields or parts of them
from the adjacent frames. This could become quite laborious, and whether it is
worth the effort depends on the value of the footage.
3. Manually cut and paste parts of frames that get through the inverse telecine pass.
36.4.12
Moiré Patterns
This happens when some repeating pattern in the image almost lines up with the scan
lines or pixel grid in the display. It is virtually impossible to remove, but applying some
selective blurring may help to disguise it. The example in Figure 36-13 is made by over-
laying two fine gratings, each alternating from black to white on every line, and slightly
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