Mega pixel Surveillance Technology - Part 2

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In this part, we tackle the pros and cons of digital pan/tilt/zoom (PTZ) systems vs. mechanical PTZ systems. First, let's talk about some basics of pan, tilt and zoom.

Mechanical PTZ cameras consist of motors, slip rings, gears and/or belts and wheels to drive the camera into position. Traditionally, they were controlled by proprietary keyboards but recent advancements in our industry have allowed these same cameras to be controlled by software interfaces. These devices are available as integrated units, most commonly in the form of domes, or you can purchase the camera separately and mount it on a pan-tilt motor.

The amount of zoom, e.g. 25X, depends on the ratio of the telephoto setting to the wide angle setting. So, a lens that goes from 4mm to 100mm will have a 25x zoom. A lens that goes from 50mm to 150mm will only provide 3X zoom but will be much better at zooming in farther away because of the 150mm telephoto setting. However that same set-up will not have as wide of a field of view. The lower of the numbers (the 50 in a 50mm-150mm lens) is what you use to know how "wide" your field of view is. The lower the number, the wider angle the lens is. So, in this model, the 50-150mm is more of a telephoto lens, and the 4-100mm gives a wide angle view of the scene.

Mechanical PTZ

Today, most mechanical PTZ cameras employ low resolution cameras, typically around 704 x 480 or 1/3 of a mega pixel. In order to get high-detail (80 pixels/foot) with that camera, you would need to zoom into an area that is no wider than 8 feet (2.4 meters). If you zoomed out all the way you would now be spreading those pixels out over a very wide area and would lose almost all detail.

If your goal is to give security staff the ability to monitor general activity, and then zoom in over a long distance with good detail, then mechanical PTZ cameras with high zoom telephoto lenses are the way to go but there are a few things you should consider.

First, mechanical PTZ cameras should be thought of as "either/or". Because of the nature of lens options, you either get wide area coverage with low resolution or you get high resolution in a very narrow area. You really cannot get both. This means if you are "zoomed in," you will miss everything else that the camera is not zoomed in on. Alternatively if you are "zoomed out," you won't have the detail you need. If you are recording "zoomed out" mechanical PTZ images you can always "digitally zoom" after the fact, but the real world isn't like "CSI", and the results aren't pretty. This limitation places a great deal of responsibility on the guard controlling the camera, especially if there are simultaneous incidents in which case the guard must decide which is more important.

The second thing to consider is the cost of 24/7 guards dedicated to controlling the cameras which can be a substantial amount of money. Next, if you are controlling these mechanical cameras over a TCP/IP network, there can be a long delay between when you tell a camera to PTZ and when it actually responds. Finally, mechanical PTZ cameras have a number of moving parts which are susceptible to wear and tear, and will eventually require periodic maintenance and repair.

Digital PTZ

The other approach many people are opting for is to use mega pixel cameras with digital pan/tilt/zoom. Mega pixel cameras, which are commonly offered as IP cameras, are ideal for applications where you don't have the resources to have 24/7 live monitoring of the cameras and therefore, have to rely on the forensic value of recorded video. When combined with the right lens, mega pixel network cameras ensure that you will always have enough detail to go back after the fact and have forensic evidence like license plate numbers and facial detail to determine what happened.

If you opt for the mega pixel network camera approach, the only thing you have to do is make sure you have selected the proper resolution camera and lens to provide with you the desired detail (pixels/foot). Once configured, you can digitally pan/tilt/zoom around live images without affecting what is recorded, or you can come back in an investigation process and digitally pan/tilt/zoom on recorded video. In fact, thanks to advances in hardware and increasing use of IP communications, multiple people can connect to the same camera at the same time and independently pan/tilt/zoom around. Regardless of where someone may be digitally panning, tilting or zooming, you can always go back to recorded video and look at other areas with no loss of detail. Additionally, since most mega pixel cameras do not have moving parts, maintenance requirements are minimised.

In conclusion, if you aren't looking for both detail and situational awareness at the same time, then traditional mechanical PTZ cameras are a good fit. If you may need both the scene view and the detailed view at the same time, and if you can't allot the funds to staff guards to control your cameras, the mega pixel approach is a worthwhile solution. Weigh your needs to decide which video solution is more applicable to your security needs.