Smile, You’re Onto CCTV Cameras
The security surveillance profession is chockablock with buzzwords rolling off the tongues of industry veterans and newbies alike. Storage. Compression. Encryption. IP-enabled. Analytics. Integration. Convergence. Remote administration. But when it comes down to it, the heart of video surveillance systems reside elsewhere.
Video security system practitioners employ the latest terminology that will entice their customer to say, “Yes, I want you install a CCTV system for me.” But the most important part of the CCTV system is hardly ever mentioned. Systems integrators who are not paying proper attention to the cameras they are installing are doing their clients — and themselves — a major disservice.
Keep in mind that DVRs, NVRs or whatever the storage medium du jour, only records what they receive and cannot discard images that are out of focus, too broad or too dark. Sure, some DVRs can make minor adjustments to an image, but essentially all a recording device can do is take the signal it receives, compress it and play it back when commanded.
Therefore, the viability and functionality of a video security system starts and ends with the camera equipment. Good cameras produce good images; images you can use to analyze a situation, assess a threat and turn over for evidence. An end user can pay for the best recording device available, but if the cameras do not provide quality, installers risk alienating a client who likely will feel they have wasted their money.
While most of the focus of the security industry as of late has been squarely on head-end equipment such as DVRs and NVRs, large strides have been made toward the improvement of image quality provided by CCTV cameras. When evaluating cameras and lenses, there are some key specifications you must consider, such as resolution, sensitivity and wide dynamic range.
Resolution Specs Provide Starting Point for Camera Evaluation
In a nutshell, resolution can be simply defined as “more is better.” If you have two analog cameras that seem to appear identical, and one has 380 TV lines (TVL) of resolution while the other has 470 TVL, you can expect two things. First, the 470-TVL camera will have the capability to produce a crisper image; secondly, the 470-TVL camera will be more expensive. Resolution depends on the number of pixels in the camera’s image sensor or CCD (charged-couple device) chip. If a camera manufacturer can put a higher number of pixels into the same size CCD chip, that camera will have more resolution.
Resolution traditionally has been broken down into two categories: vertical and horizontal. There is less emphasis put on the vertical resolution as most manufacturers achieve the same figure. Horizontal resolution, on the other hand, is a specification to which integrators should pay close attention.
For definition purposes, horizontal resolution is actually the number of vertical lines on the CCD chip. The more vertical lines, the higher the horizontal resolution value, and the better picture the camera provides. Resolution is the most common specification offered by manufacturers and is a good place to start when comparing products.
Sensitivity Indicates Least Light Level Needed for Usable Image
In most cases, a camera’s light sensitivity is measured in foot-candles or its lux rating. Sensitivity ratings are normally stated as the minimum lux levels a camera will generate an acceptable image. For instance, a camera with a lux rating of 0.1 will perform better in low light conditions compared to a camera with a 1.0 lux rating. So, the lower the lux rating, the more light sensitive the camera. A color camera will require more light for signal processing and, therefore, will typically have a higher lux rating than a black-and-white camera.
However, while the lux rating is important for camera selection, you must also factor in the f-stop of the lens. Lux level ratings (and the amount of light entering the camera) are inversely proportional to the aperture of the camera iris and so are stated at a specific f-stop (focal length divided by aperture). A camera with a lux rating of 1.0 at f1.4 will only have a lux rating of 2.0 at f2.0.
The f-stop is a number that indicates the aperture of the lens, or how much light can pass through the lens. The lower the number, the more light is allowed to pass through. In other words, if you are working in a low-light situation a lens with a low f-stop is preferred, as this will allow for more light to pass through and create more usable images. Gauging a camera’s lux rating and a lens’ f-stop is vital to consider when selecting a camera.
Additionally, you must consider what the camera in intended to survey. Not so much the objects, but rather what color the objects are likely to be. Cameras gather the lighting around objects from reflective light. In other words, the camera sees what is reflected from the object. Hence, dark hued objects require more illumination in order to be visible, compared to brightly colored objects.
To further explain, consider two cameras with the exact same specifications in the same lighting conditions: one camera is surveying a black object and the other, a white object. The white object will remain clear in the picture as the lighting levels are reduced, while the black object will become more difficult to see. Why? Because dark colors absorb light, while lighter colors reflect light.
Wide Dynamic Range Technology
Helps Overcome High Contrast All too often the best placement location for a camera is not one that provides the best lighting conditions. Situations arise where large bright areas will silhouette the desired object to be viewed. Surveillance cameras are beleaguered by dynamic range problems around the clock because of harsh reflections, glare, car headlights and direct sunlight.
Thankfully, wide dynamic range (WDR) technology has now provided the ability to record crisper images. A typical example is a camera that views an indoors setting with a window in the background. A regular camera would silhouette a person moving in front of the heavily lighted background. This can also result in the object being blurred out because the camera cannot process such a strong contrast in lighting.
WDR technology allows an image to be processed as individual pixels. This means cameras can process the glare in certain areas of the image and tone them down, while brightening up the images that are darkened due to this same brightness.
Camera Selection Is Based on the Type of Surveillance Application
While it is important to understand the technology and specifications of the cameras you are using, it is equally significant to make sure the camera you select will work for the intended application. For example, using a bullet (or lipstick) camera to cover a parking lot is basically useless, unless you just want to count cars. The technology and lens combination is not designed to support a focal length distance of more than 30 feet in most situations.
In fact, you could even go so far as to say that focal length, or depth of field, is the most important consideration when selecting cameras for a surveillance job. Basically, a fixed camera and lens can only focus on a fixed area. (Obviously, pan/tilt/zoom systems allow for more adjustments via the control system.)
Let’s take a typical parking lot as an example. Consider a fixed camera mounted on a pole that covers a parking lot entrance. Clearly, the preferred zone of focus is the immediate gate area where cars gain entry or exit the lot. However, by focusing on just this part of the image the objects that pass in front of the gate and beyond the gate, while both in view of the camera, will not be as sharply f
ocused as cars that pass directly through the gate (the main focal point).
The same is also true for indoor applications, such as hallways. In this situation, however, the depth of field is not as important because you are dealing with a smaller area, and the fixed focal length that is available with macro-focus lenses is acceptable.
In the world of CCTV there is a dizzying array of camera options; full body box cameras to bullet cameras to dome cameras, and covert cameras as well. Even IP cameras and integrated pan/tilt/zoom (p/t/z) devices each deserve their own article. With all the options out there it is important to make sure you are comparing similar products when determining equipment for a job.
If a camera company cannot provide comprehensive specifications for its product, then in all likelihood they could be trying to veil performance limitations. A camera with poor performance specifications can save money on the initial price, but eventually do more harm in the long run with images that don’t have the necessary clarity.
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