VA implementation requires digitized video accessible by a suitable image processing resource. There are three predominant architectures in use:
- Analog Cameras connected to frame grabbers installed in a PC.
- IP Cameras connected via Ethernet to a PC.
- Self contained "Smart Cameras", Video Analytics on the Edge (VAE).
In both the Analog Camera/Frame Grabber and IP Camera systems, the VA intelligence is located in the PC. The sole function of the camera system is to collect and deliver suitable digitized video to the Video Analytics in the PC. All decisions are made in the PC.
The VAE system, on the other hand, is a fundamentally different architecture. The VAE "camera" does both the video collection and the VA processing/event detection. A PC is not directly involved on a real time basis and in principle; a PC may not even be connected. However, in most applications it performs the Human Machine Interface (HMI), system management functions, and event archival.
Table 1 summarizes some of the key strengths and weaknesses of the three predominate VA architectures, as discussed in the next sections.
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Table 1: Comparison of video analytics architecture
Analog cameras and frame grabbers
The Analog Camera/Frame Grabber/Computer system shown in Figure 1 has the advantage of mature technology and cost effectiveness. There are a wide variety of analog cameras available, of every conceivable configuration. Frame grabber cards are also a mature technology; while they typically require a slot in the PC, multiple channel units per card are available. While coax cable is required to connect the camera to the frame grabber, it is relatively inexpensive and fairly long lengths (up to 1500ft, depending upon the cable type) can be accommodated without repeaters. Longer cable lengths result in high frequency losses--translating to loss of resolution or focus. The cables between the camera and frame grabber are typically unique and will have to be installed. In addition to the video coax cable, each camera requires its own power wiring. If any camera controls are desired (focus, zoom, aperture, pan/tilt); this will necessitate yet another cable. Potentially, there are three special purpose cables required.
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Figure 1: Analog cameras with frame grabber in analytics PC
Each camera/cable/frame grabber port is a standalone system--communication bandwidth is not shared. When another camera is added, the frame rate up through the frame grabber to PC interface is not affected. Since all VA processing takes place in the PC, PC processor power and resources are shared. VA can be quite processor intensive, resulting in an aggregate total frame rate from all connected cameras that can be serviced by the PC. If more cameras are added, or additional or a more processor intensive VA are installed, the PC will either have to be upgraded or the system restructured to add additional PCs. If less than the aggregate maximum frame rate is installed, the PC is oversized.
Analog cameras are inherently limited to NTSC/PAL resolutions, which are about 0.4 megapixel, approximately VGA. This is problematic in today's world; CMOS sensors approaching 10 megapixels are readily available. Higher sensor resolution makes possible either better image quality, or wider fields of view. These capabilities are not easily obtained in the analog camera world.
While Analog cameras alone appear quite cost effective, to the camera cost needs to be added the cost of a frame grabber channel per camera and the special purpose coax cable. Especially if cabling and installation is considered, the analog camera may no longer be cost effective.
Next: IP cameras