How Resolution and Scene Width Affect CCTV Image Quality
Channel: Guru Tim
Date: 2014-09-08

http://catchcriminals.com.au
Thanks Ammar for asking this question, which is one of the most important and yet commonly misunderstood fundamentals of video surveillance and consequently why much of the news stories asking for help catching criminals is useless.

What clarity and resolution is required for a good CCTV image.

This question has many part to answer it in full but as a broad brush answer (more detail in the manual) we first need to determine what the CCTV camera is needed for. Maybe a silly sounding question but most cameras that are shown on TV have not first considered this and instead have just installed it to give an overview (not that they realised that was what they were getting).

A surveillance camera needs to do one of 3 core things. Allow you to:

Identify a person you don't know
Recognise a person you do know
Observe a persons behaviour
The first is what most people are expecting to achieve but the third is what they typically have.
You can have a camera setup to ID people and also observe behaviour further away but the reverse is not true.
There is a science to calculating the right lens and camera resolution but we are not going to cover that right now. The key things you need to be aware of, as explained in this video are there is a direct relationship between the scene width (field of view or FOV), the camera resolution (pixel density) and which of the above three you will achieve at a given distance.

To summarize it, if want to identify a person at 10 metres from a camera, assuming good lighting and the camera is not mounted too high, you could have a 1080p (2MP) camera with a FOV at the 10m point of 5m wide.

If we now drop the resolution to 720p, the FOV needs to be reduced to 3m wide (approximately)

Infact based on this, you have a rule of thumb for these 2 resolutions. At any distance you want to ID a person, if you have a maximum scene 5m for 1080p or 3m for 720p you will get a good result. So even if the person was 20 metres away, so long as you apply this rule of thumb, you will get a great clarity image that the police will actually be able to use. Of course there are many other factors that need to be considered but this one rule is a big step in the right direction.

The IP Video Design tool used in this tutorial can be found at http://bit.ly/JVSGh