This marks the final installment of our 3-part series on megapixel
technology. In Part 1, we took a look at the overall cost of megapixel video
based on the three types of surveillance, general surveillance, forensic and
high detail and their comparative costs on a pixel-per-foot basis. In Part 2, we
looked at an apples-to-apples comparison of deploying a megapixel video system
instead of a low resolution (4CIF) system and how in many applications,
megapixel can be much more affordable.
PTZ Pros and Cons
In Part 3, we tackle the pros and cons of digital pan/tilt/zoom (PTZ) systems
vs. mechanical PTZ systems. First, let's talk about some basic 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 megapixel. 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 megapixel cameras
with digital pan/tilt/zoom. Megapixel 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, megapixel 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 megapixel 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/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 pan/tilt/zooming, you can always go back to recorded video and look
at other areas with no loss of detail. Additionally, since most megapixel
cameras do not have moving parts, maintenance requirements are minimized.
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
megapixel approach is a worthwhile solution. Weigh your needs to decide which
video solution is more applicable to your security needs.
HIGH-end Video Server Module board W1860
