50
Adaptive interpolation
offers the best image quality. The technique involves using only one of
the two consecutive fields and using interpolation to create the other field of lines to form a full
image.
Blending
involves merging two consecutive fields and displaying them as one image so that all
fields are present. The image is then filtered to smooth out the motion artifacts or ‘comb effect’
caused by the fact that the two fields were captured at slightly different times. The blending
technique is not as processor intensive as adaptive interpolation.
5.6
Video decoder
A video decoder decodes digital video and audio coming from a video encoder or a network
camera into analog signals, which can then be used by analog monitors, such as regular TV sets,
and video switches. A typical case could be in a retail environment where the user may want to
have traditional monitors in public spaces to demonstrate that video surveillance is used.
Another common application for video decoders is to use them in an analog-to-digital-to-analog
configuration for transporting video over long distances. The quality of digital video is not affected
by the distance traveled, which is not the case when sending analog signals over long distances.
The only downside may be some level of latency, from 100 ms to a few seconds, depending on the
distance and the quality of the network between the end points.
Figure 5.6a An encoder and decoder can be used to transport video over long distances, from an analog camera to
an analog monitor.
A video decoder has the ability to decode and display video from many cameras sequentially;
that is, decoding and showing video from one camera for some seconds before changing to
another and so on.
AXIS 292
Network Video Decode
r
VIDEO
ON/OFF
POWER
STAT
U
S
NETWOR
K
VID
EO
Axis video
encoder
Axis video
decoder
Analog camera
Analog monitor
AU
DIO
I/O
IN
OU
T
1
2
3
4
5
6
CHAPTER 5 - VIDEO ENCODERS
