A guide for chief security officers, directors and managers on how to maximize the effectiveness of surveillance solution by selecting the right combination of cameras for the task.
A guide for chief security officers, directors and managers on how to maximize the effectiveness of surveillance solution by selecting the right combination of cameras for the task.
Scanning
Cameras can vary by type of scanning. Network cameras use progressive or noninterlaced scanning in which all the lines of each frame are drawn in sequence. In contrast, analog cameras use interlacing where only the odd lines, then the even lines of each frame (each image now called a field), are drawn alternately. In the past, there were legitimate questions about the image quality digital delivered; today network cameras offer image quality superior to that of analog cameras. One reason is progressive scan; end users gain a very clear picture when looking at a video a frame at a time.
Progressive Scan Advantages
? Higher vertical resolution than interlaced video with the same frame rate.
? Absence of visual artifacts associated with interlaced video of the same line rate, such as interline twitter.
? No necessity in intentional blurring (sometimes referred to as anti-aliasing) of video to reduce interline twitter and eye strain.
? Offers much better results for scaling to higher resolutions than equivalent interlaced video. Scaling works well with full frames, therefore interlaced video must be deinterlaced before it is scaled. Deinterlacing can result in severe "combing" artifacts.
? Frames have no interlaced artifacts and can be used as still photos. The one disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate. There are cameras that, as a package of the camera, lens and motorized gear, can do more things than fixed versions.
One example is pan, tilt and zoom or PTZ. There are myriad situations in which a PTZ camera – analog or megapixel – is the only viable choice.
Presets and Speed Moving through Positions
Presets are a series of positions that a camera can be programmed to automatically go through during the course of a tour, shift or day to help ensure that a specific area is covered or when a video surveillance system is integrated with an alarm or access control system. The camera can be programmed to go to an appropriate pre-set position when a certain event occurs, for example, when a door is opened.
How quickly the PTZ camera changes positions is another consideration. For example, a camera may move up to 280 degrees per second when moving into a preset position but up to 100 degrees per second when security personnel or an officer controls the device manually. Speed domes, which have the ability to quickly move through a series of positions, are an alternative, especially when there are many points to monitor with a single camera or if the threat is particularly fast moving.
In preset mode, positioning accuracy from one view to another is critical. Poor positioning accuracy results in a camera not pointing to the scene an operator selected for a stop on the tour. In regard to forensics, this can create useless evidence when suspicious activity needs to be reviewed.
An optical zoom makes far objects appear closer by using a series of adjustments to an optical lens. Many cameras also have digital zoom: Instead of zooming manually through the optics, an operator can enlarge the pixels. But there is a limit to the latter in terms of blurry displays.
Magnifying pixels does not help make surveillance images more usable. Digital zoom is only useful as long as it is uncovering dark pixels collected by the camera. With megapixel cameras, it's likely to collect more pixels than a standard security monitor can display, so an operator sees the image at less resolution than the camera. In such a situation, digital zoom can bring more data to the monitor. But any further and digital zooming does not add any more information but more blur.