Welcome to the
"Technical Section"
Doktor Jons

Guide to Closed Circuit TV (CCTV)

So would you like to play "Spot the CCTV Camera?". Eagle eyed visitors may recognise the profusion of street furniture, surrounding a single heritage dome camera keeping watch over part  of Londons' prestigious Oxford Street shopping area.

If you need to handle
multiple images ....

Quad Display Multiplexers

The next logical step up from a PIP unit, is the Quad Display Multiplexer.

As its name suggests, this device will split a screen into four quarters, and insert a complete compressed image into each quadrant. The picture quality does vary depending on the manufacturers choice of internal components and design, but a good high resolution unit, can provide an amazingly useful, and indeed flexible piece of kit.

One particular varient is known as the ‘Duo-Quad’, which again splits the screen into four equal quadrants, but will accept eight cameras that can be displayed as two seperate ‘pages’ , each of four images.

As you would expect, any of the cameras may be ‘pulled up’ full screen, either manually or by external alarm input. In addition, some better quality units will also incorporate a basic form of motion detection, so if movement is sensed in a particular quadrant, again that picture will instantly expand to fill the monitor screen. It is also normal for this type of device to allow some basic form of captioning, to identify individual cameras, although not all models provide this feature.

The units are particularly useful for providing ‘group displays’ of sector cameras on a control room monitor, or as an entry level method of reducing the number of monitors required to provide security in commercial premises; other applications include use as a scientific research tool, particularly where a number of cameras are set up to provide comparative angles of the same target, which can then be filmed in real time for later analysis.

As with the PIP units, any recordings made will generally not allow the individual quads to be brought up full screen on replay, although the odd one or two units that do offer this facility, do so with a particularly poor picture quality. This is because when the image is compressed down to a specific pixel density, any attempt to reconstiitute this display full screen, means that although the pixel count stays the same, the individual pixels become intrusively larger (i.e. they are four times bigger than when compressed).

If full screen replay from recording is required, then a four channel recording multiplexer should be used.
One particular benefit of using a Quad is that although the top end models are quite sophisticated units, they are almost always very simple to operate, and in particular provide (untrained security) staff (such as receptionists), the ability to easily monitor a reasonably comprehensive CCTV System. That said. recording in quad format is rarely recommended. as the replay quality is generally inadequate for security purposes.

Display Multiplexers >>

The unique "TRUSTED" National CCTV Improvement Campaign

IMPORTANT: No material may be reproduced, copied or redistributed from this site,
without the express written consent of doktorjon.co.uk

All the detailed information on this site is provided in good faith; and as such, Doktor Jon
does not accept responsibility for any consequential loss, injury or disadvantage
resulting from any individual or organisation acting on the details contained herein.

© doktorjon.co.uk 2004 - 2008

Homepage...:...Gateway...:...Technical Gateway....:....Quickfind Index....:....Equipment Directory
Site Index...:...About this site....:....CCTV Helpdesk....:.... The Forum ....:....Contact Doktor Jon