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Analogue and IP CCTV Image Quality
 

It is essential that when a system is established then the image quality offered must be good enough for the purpose intended. If the system is installed to prevent and detect crime then the system must reflect that and offer an output quality that can identify an offender or the scene of the crime.

Police Guidelines for analogue CCTV cameras, not guarantees: (Use smaller heights when possible)

Type / Quality of view Height    This is based on and analogue camera...
Identification 1.33m 1.6m man = 120% screen height
Recognition 3.2m 1.6m man = 50% screen height
Detection 16m 1.6m man = 10% screen height
Monitoring 32m 1.6m man = 5% screen height
Decide if the camera output is intended to monitor, detect, recognise or identify an intruder, this can be expressed as the proportion of the target to be viewed (%).

You can see from the table below that multi-mega-pixel cameras offer far greater resolution and fewer cameras are needed compared with old analogue cameras to provide the images quality required.

 

Comment

Quality

Lines

Notice

Detect

Recognise

Identify

Typical recording quality for analogue cameras

CIF

288

13%

26%

130%

312%

Highest quality analogue camera

PAL

576

5%

10%

50%

120%

1.3
Mega-pixel IP camera

MEGA

960

3%

7%

33%

78%

3.0
Mega-Pixel IP camera

QXGA

1536

2%

4%

20%

48%

Monitor

An observer can observe the number, direction and speed of movement of people whose presence is known to them, i.e. they do not have to be searched for. Subject matter should fill no less than 5% of the screen.

Detection

Following an alert an observer can, after a search, ascertain with a high degree of certainty whether or not a person is visible in the pictures displayed to them. Subject matter should fill no less than 10% of the screen.

Recognition

Viewers can say with a high degree of certainty whether or not the individual shown is the same as someone they have seen before. Subject matter should fill no less than 50% of the screen.

Identification

Picture quality and detail should be sufficient to enable the identity of a subject to be established beyond reasonable doubt. Subject matter should be no less than 120% of the screen.
 
D1 / 4CIF Analogue Recording Resolution
The digital video recorders DVRs we install are capable of recording at 25fps per camera at 4CIF resolution from existing analogue cameras and also support IP multi-mega-pixel cameras.
Obviously DVR and project cost is a big consideration, but typically entry level or budget DVR’s available that offer 20fps per camera do this at the cost of video image size and can typically only offer CIF 352 x 288 resolution, which will give disappointing results and may not be fit for purpose.

The DVR units we install are of very high quality and will record using MPEG4 video encoding at 25 fps per camera at 4CIF 704 x 576 which is basically near to DVD quality recording of your video images and the video playback will be as good as your CCTV operators will see on the monitors.

To get the best quality images for evidence purposes from analogue cameras you will need 25fps (frames per second), which is basically real time recording per camera channel and at 4CIF 704 x 576 resolution.

 

 

 
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