Digital Signal Processing Reference
In-Depth Information
6
VIDEO DEINTERLACING
CHAPTER OUTLINE
6.1 Basic Deinterlacing Techniques 40
6.2 Motion-Adaptive Deinterlacing: The Basics
43
6.3 Logic Requirements 45
6.4 Cadence Detection 47
6.4.1 Another feature that is becoming standard in advanced deinterlacers
47
6.5 Conclusion
48
In the days of CRT the video sent to the TV was interlaced (the
meaning of which will be discussed later) and the TV monitor on
which it was displayed worked perfectly for that format. However,
most TVs and monitors are now LCD or Plasma, and these have
no ability to interpret interlaced video.
Video deinterlacing techniques were developed to address the
problem of legacy interlaced video that was required by old
analog televisions.
First we need to understand interlaced video (see
Figure 6.1
).
Consider a video frame that is coming in at 30 fps. One way to
represent this would be to break it up into two fields
one field
would consist of all the odd numbered rows and one field would
consist of all the even numbered rows. Of course, since one frame
is now two fields, these would have to be transmitted twice as fast,
i.e. at 60 fields per second. This is interlaced video
e
essentially
a succession of 50/60 fields per second, where each field carries
only half of the rows that are displayed in each frame of video.
If this sounds convoluted
e
it is. It was done to support the
older analog TVs which were based on CRTs. The electron gun
needed time to switch back after “painting” row one and so we
needed to skip row two and present it with row three. The detailed
operation of a CRT screen is not important for digital video
processing. What is important is that we have to deal with this
“interlaced” video.
Interlaced video is not suitable for the majority of our moni-
tors today, which paint individual pixels within a single video
frame (referred to as progressive).
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