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enable analog PTZ cameras to be controlled over long distances, even through the Internet. (In an
analog CCTV system, each PTZ camera would require separate and dedicated serial wiring from the
control board—with joystick and other control buttons—all the way to the camera.)
To control a specific PTZ camera, a driver must be uploaded to the video encoder. Many manufac-
turers of video encoders provide PTZ drivers for most analog PTZ cameras and PTZ dome cameras.
A PTZ driver can also be installed on the PC that runs the video management software program if
the video encoder’s serial port is set up as a serial server that simply passes on the commands.
Figure 5.4a An analog PTZ dome camera can be controlled via the video encoder’s serial port (e.g., RS-485), making
it possible to remotely control it over an IP network.
The most commonly used serial port for controlling PTZ functions is RS-485. One of the benefits
that RS-485 allows is the possibility to control multiple PTZ cameras using twisted pair cables in a
daisy chain connection from one dome camera to the next. The maximum distance of an RS-485
cable, without using a repeater, is 1,220 meters (4,000 feet) at baud rates up to 90 kbit/s.
5.5
Deinterlacing techniques
Video from analog cameras is designed to be viewed on analog monitors such as traditional TV
sets, which use a technique called interlaced scanning. With interlaced scanning, two consecu-
tive interlaced fields of lines are shown to form an image. When such video is shown on a
computer screen, which uses a different technique called progressive scanning, interlacing
effects (i.e., tearing or comb effect) from moving objects can be seen. In order to reduce the
unwanted interlacing effects, different deinterlacing techniques can be employed. In advanced
Axis video encoders, users can choose between two different deinterlacing techniques: adaptive
interpolation and blending.
Figure 5.5a At left, a close-up of an interlaced image shown on a computer screen; at right, the same interlaced
image with deinterlacing technique applied.
Coax
Cable
Video encoder
PC workstation
Analog dome
camera
Joystick
IP NETWORK
RS-485
twisted pair
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VIDEO ENCODERS - CHAPTER 5
