Types and choice of security cameras (II)

By: Mark S. Wilson.

Dome cameras are a good choice for video surveillance systems to respond to any basic need. When installation requires the extra power and flexibility of a pan/tilt/zoom camera, the dome housing is necessary to allow the camera an unobstructed view no matter where you look, and some end users see value in the dome housing, although when using a fixed camera for wall or ceiling applications the dome can provide a nicer appearance. Of course, wearing a dome, often smoked, means that the bad guy doesn't know if the camera is pointing or not at him.

Whether PTZ or fixed dome cameras are part of a legacy installation or when purchasing new equipment, security executives should consider the environment in which the camera will work. Some have vandal-resistant and reinforced domes, which can be important when installing a camera in an area that can be reached with a baseball bat or weapon. Other cameras may require a separate housing for vandal protection. Putting automatic tracking in a camera compartment can speed up reaction time when a dome PTZ camera follows a subject. Special housings may also be needed if a camera will be installed on the outside.

In certain climates, a heater is needed and, for certain areas, a hidden fan. Sunshades can also play a substantial role for some outdoor applications. Depending on the type of business or industry of the end user, housings are offered that protect from water or dust damage, such as housings with pressurized seal.

What about the lenses?
The lens is the second most important choice in a security video system after the camera. One of the reasons lenses are sometimes taken for granted is that many video cameras, particularly the popular domes, come with an already built-in lens.

Still, Helen has mentioned to Terry that they both need to clearly describe what exactly they want the camera to see.

To determine which is the right lens, the duo must think about how far and how wide the angle each camera should see. So why think of a lens when some cameras come with one? We had already said it, Terry already knows that low-end solutions often include the camera and lens. But in crucial applications, other more suitable solutions include an integrator's selection of a lens for each camera based on the scenario and lighting of the view.

There's also the look of megapixel lenses for HD or megapixel cameras. Without the right lens, a megapixel camera might not produce the high-resolution images that correspond to the camera's sensor capability. The decisive point of the lens: When selecting a megapixel lens make sure that the resolution power in megapixels extends throughout the entire field of view of the lens, not just the center. Some lenses, often lower in price, produce a resolution of megapixels only in the center of the lens; in the periphery, the resolution can be much lower.

On the wall of the meeting room, Terry and Helen began to answer some key questions:

1. What is the lighting in the installation area (indoors and outdoors)?
2. Do you just want to see activity in one area or do you want to specifically identify something or someone?
3. How far will the person or object to be identified be?

Even if they cost a little more, varifocal lenses are flexible in most situations except where objects are at a great distance. Motorized and telephoto zoom lenses work with fixed cameras and, of course, with PTZ. They have a greater scope in which to look at a specific part of the total image and are often used for special scenarios and applications. End users, including Terry and Helen, typically have basic rules about varifocal lenses for their fixed cameras.

Aspherical lens, standard; manual iris, automatic
Aspherical lenses — high-end but not necessarily high-priced — have highly polished, computer-designed convex surfaces that allow more light to enter than standard lenses and better retain image focus from center to edge. The technology has a smaller size, can correct chromatic aberration and reduce the f-stop number (speed) of the lens for greater light transmission.

The iris of a lens is like the iris in the human eye; it opens and closes in response to light. The irises in manual iris lenses are programmed with a fixed f-stop aperture and are best where the illumination is relatively constant. Automatic iris lenses have an electronically controlled iris that opens and closes when the light changes to maintain an image with a constant video level.

Focal length: lens and camera together
Focal length, measured in millimeters, is the distance from the center of a lens to the sensor. The longer the focal length, the narrower the angle of view; the shorter the focal length, the greater the angle of view. To calculate the field of view or focal length of the lens of a security video camera, Terry and Helen must know some parameters of the installation. Among those parameters:

- Camera distance - maximum distance from camera to lens
- Camera installation height
- Field of view – height
- Field of view: width
- Camera sensor format

Lighting
Lighting can also have an impact on the type and location of security video cameras. Undoubtedly, on the outside, day/night cameras have a role to play. However, there are unique lighting issues related to megapixel cameras. For example, when it comes to getting full resolution for higher-priced megapixel cameras, with no higher levels of illumination than there is naturally in a scenario, the camera will not produce the optimal resolution. As far as lux lighting levels are concerned, they usually refer to the sensor light, not the ambient lighting in a given scenario.

Frame rate also affects low-light performance. The higher the exposure, the better the image a low-light sensor can produce. But there's a balance when it comes to moving images. Helen has suggested to Terry that they go beyond some commercial brochures that only show scenes without movement when it comes to setting low-light performance.

By the way, frame rate is also an issue with megapixel cameras. Many of these cameras can only produce 12-15 frames per second. This may prove insufficient for situations involving small, quick moves, such as dealers delivering cards at a casino table or counting money inside a bank.

Image cropping, people counting, object tracking, detection of improper alterations, and modification of the exposure of parts of a video image are also possible. Some surveillance cameras include metadata about what is shown in the video, offer the time and date when the video was recorded, and perform facial and license plate recognition, to point out a few features.

Of course, how smart a camera should be based on each individual application. However, having intelligence in the camera—that is, at the edge—makes it possible to set up quickly without relying much on network resources. Cameras should not have great intelligence inside, however, intelligence can also reside in encoders in the case of analog, storage devices and through analysis software in video management systems.

Storage, command and control in the camera
With the move to more features at the end, storage has also taken a leap, right inside the camera. Some cameras now boast useful and inexpensive SD memories. In general, digital and network video recorders still play a storage role at the end of the image, of course. In between, there are compression-decompression (codec) options: MPEG-4 is 50% more efficient than MJEG, and H.264 is even more efficient, although it may not work as well with megapixel cameras. By the way, most megapixel cameras use MJPG, especially at higher resolutions.

There is also a balancing act between the codec being used, the processing capacity and the need for storage. In general, H.264 needs more processing power but less storage capacity. This is useful when you realize that megapixel cameras—by their very nature—generate more data than lower-resolution cameras.

Network Video Management Systems
At the command and control end, there are software-based video management systems (VMS) but, as far as cameras are concerned, VMS must support all the features of the selected camera. Typically, brand-leading VMS solutions can support only a subseries of features that are common to all IP or megapixel cameras.

Take the leap
There are cost implementations when moving from analog video to network video, as well as cost consequences when moving from IP video to megapixel and HD cameras. But the benefits are also evident. On the wall of Terry and Helen's office are two simple equations:

- Camera reduction = cost savings
- Increased resolution = loss prevention

While analog is less expensive in small installations with fewer than 30 cameras, for example, a strategy of coexistence of analog and digital cameras is a solid maneuver. In addition, the use of megapixel cameras can reduce the total number of cameras needed. An overview of this strategy is described in the first of this series of detailed technical reports.

That report also covers the impact on infrastructure including switching to CAT 5 or 6, corporate network sharing of data, bandwidth, and compression and decompression methods.

Infinova has a wide variety of technology that emphasizes the coexistence strategy that can gradually and intelligently jump from analog video to IP. There are fixed analog cameras and fixed minidomes, PTZ domes and PTZ cameras, and cameras with IR lighting. There are fixed IP cameras and fixed minidomes, as well as domes and PTZ cameras.

* Mark Wilson is infinova's vice president of marketing.