Recording
While a proportion of surveillance systems are continuously monitored, these are in the minority. The majority of systems are not actively monitored and, even when they are, in most cases, the images are still recorded.
The underlying principle to be considered in relation to the recording of images is that they may ultimately be required as evidence in criminal proceedings. Despite sometimes poor quality recordings, many spectacular successes have recently been achieved in the detection and conviction of serious offenders, thanks to the existence of recording material.
Analogue Recording
The preferred medium for recording and storing activity has been, and still is, VHS videotape, usually recorded on a
The extended recording facility is achieved by reducing the frequency of fields that are recorded, thereby extending the recording period of the tape. The number of fields is further reduced when the VCR is recording multiple cameras from, for example, a multiplexer.
VHS VCRs record around 300 TV lines horizontal resolution in monochrome and 240 TV lines in colour. The requirement to record higher resolution images has led to an increase in the use of
These are recommended where it is intended to record vehicle registration numbers or other fine points of detail.
VCRs have many moving parts which require regular service to maintain performance. For this reason, it is recommended that VCRs are serviced once a year.
Digital Recording
Increasing demand for higher quality, more flexibility and lower maintenance has encouraged manufacturers to develop recording equipment which more closely matches the needs of surveillance systems.
This new technology is based on digital processing and storage and, in most cases, produces higher quality images than analogue systems. Greatly increased storage capacity also allows higher picture refresh rates and selectable resolution modes. Camera inputs are multiplexed, stored on a hard disk and, periodically
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The Sony Guide to CCTV . Issue 3