All in a spin?

That said, domes also have one potentially major disadvantage. The basic problem is that they don't come with a ready-made, built-in and 'obvious' lighting solution which will automatically allow the units to perform well at night. Faced with this perplexing dilemma, all-too-many dome users are being asked to accept the fact that poorer performance in darkness is a mere inevitability. As a result, the security of their sites is being put at risk.

Certainly, lamps – or light sources – cannot be fitted into dome cameras because of the obvious size issues and associated problems with overheating and internal reflection. In contrast, the traditional pan, tilt and zoom (PTZ) camera set-up can have powerful infrared lamps mounted on its sides to sweep around and illuminate whichever area the camera is focused upon.

There are a number of other factors which serve to reduce the night-time performance of some dome cameras. First, tinted dome covers reduce light pick-up by blocking out a percentage of whatever light's available. In addition, the combined camera/lens combination may not be as sensitive or effective as models specifically designed for low light performance. Many domes are based on smaller CCDs with integral lenses, yet these don't provide the most sensitive low light performance. End result? Users are forced to work with a surveillance system which offers great visual appeal and flexibility during the day, but provides reduced performance and low light capability during the more vulnerable hours of darkness.

Due to the many advantages to be had with domes it's all-too-easy to disregard the down side, but to do so increases the risk of security failures.

The performance of any given dome camera at night can be significantly improved through the correct use of infrared (IR). What the end user really wants to know, though, is what techniques might be applied to ensure reliable and accurate surveillance functions under both daytime and night-time conditions.

Basic solutions: fixed domes
Dome cameras can be divided into two categories: fixed and fully-functional. Fixed domes are often vandal-resistant and used for short range surveillance purposes. As the unit is fixed, the low light issues involved are similar to those of other standard cameras. In low light or zero lux conditions, fixed domes will require additional lighting. Typically, IR provides the best, most practical and cost-effective solution.

Be warned!!!! Many dome systems are sold with smoked domes which can reduce the IR that reaches the camera by as much as 70%, thus further degrading the low light performance. Bear this in mind when considering the claimed low light performance of the camera. Increased IR illumination levels may be required to compensate for the domes' IR attenuation.

Many dome systems are sold with smoked domes which can reduce the IR that reaches the camera by as much as 70%, thus further degrading the low light performance. Increased IR illumination levels may be required to compensate for the domes’ IR attenuation

A good tip for maximising low light performance would be to use clear domes. To ensure full coverage of the scene, the IR illumination must be matched to the field of view of the camera/lens combination. Narrow beam illumination should be used to match narrow field of camera view, wide beam illumination to match a wider field of view. Failure to match camera field of view and IR beam can dramatically reduce system performance. Make sure that you match the cameras' field of view with that of the infrared.

Advanced solutions: fully-functional domes
The big challenge with fully-functional dome cameras lies in the aforementioned inability to mount IR illuminators on the moving part of the dome. There are three basic solutions, one of which involves providing up to 360 degrees of IR coverage so that, no matter where the camera moves, there's sufficient IR illumination to enable the camera to view the scene effectively.

However, as figure 1 illustrates this may require a high level of investment to achieve, since full 360 degree coverage would require the location of approximately eight 45 degree spread Uniflood IR lamps. Domes mounted on the corner of a building may only require 270 degrees IR coverage, while those dome cameras mounted on walls might only require 180 degrees IR coverage.

The second solution would involve specific target illumination. This is a method of providing illumination in and around the scene to illuminate specific areas of risk rather than the whole area being viewed by the dome camera. The technique, which involves the strategic positioning of IR illuminators to light up specific areas, matches the illumination to the vulnerable areas within the scene. These can be gates, doorways and/or pathways where intruders are likely to enter, or anywhere the security manager perceives there is an exposure to risk.

During the full 360 degree rotation of the dome camera, there may be only two or three specific targets to be viewed. IR units may be mounted on and around the camera pole to continuously illuminate these targets, allowing the camera to monitor all key areas of the scene (figure 2).

The third solution centres on local area illumination. Consider locating the IR illumination above or near the specific target. Once again, the clever matching of the camera angle of view and that of the IR illumination is essential for maximum system performance. Approach with care, as the angle of illumination and camera field of view are critical to success. However, if you successfully match the field of view, then local area illumination is a viable alternative to locating illumination with the dome (figure 3).

For both specific target illumination and local area illumination it may be possible to trigger the IR on/off via a pre-set on the dome. In addition, a PIR detector may be used to activate the IR lamp upon detection. A good tip here is that using dome pre-sets or PIRs to activate specific target or local area illumination will eventually reduce the running costs of the system.

The big challenge with fully-functional dome cameras lies in the inability to mount IR illuminators on the moving part of the dome. There are three basic solutions – one of which involves providing up to 360 degrees of IR coverage so that, no matter where

Looking into frame integration
Some dome cameras include frame integration techniques to attempt to overcome the problems of obtaining clear images in dark scenes. A slow shutter speed is used to capture enough light in dark areas of the overall scene.

One important point to think about here is that this may be acceptable only in a limited number of applications because of the inability of these systems to work with moving objects. If an intruder moves through these areas during the dome's 'tour', he or she will only be recorded as a blur and vital information and detail will be missed. The net result is a large – and potentially serious – gap in the surveillance system's total coverage.

Always remember, then, that frame integration will naturally tend to miss vital information and elements of detail, particularly when it comes to moving scenes.

IR... and video motion detection

However, a person walking through a dark scene is unlikely to cause any pixel changes if there's insufficient illumination to detect pixel change – thereby defeating the system altogether. End users have to bear in mind the fact that IR illumination will dramatically increase the effectiveness of video motion detection systems and intelligent video analysis systems.

Ultimately, the designers of CCTV systems need to consider some fundamental issues involved in achieving effective 24/7 pictures using dome cameras, particularly under low light conditions. Without sufficient light there can be no picture. Smoked and semi-smoked dome covers dramatically reduce the night-time performance of dome camera systems and, because of their size, dome cameras often use smaller camera chips and integrated lenses – both of which may reduce their low light operational capabilities.