CCTV and imaging technology common
questions
- How do I retrieve video images from a digital CCTV System?
This depends on the system, but the primary aim is to retrieve
the video in its native format whenever possible. Listed below are
the typical options for exporting video data.
- Burning onto DVD or CD
- Transfer to memory card such as Compact
Flash®
- Via a USB port onto external hard
drive
- Via a network connection
- Through the removal of the system’s hard
disk drive/s
- By removing the actual digital CCTV
recorder
- How readily is digital video evidence accepted in court?
Video recordings are admissible as evidence and the digital
storage of these has not altered this. It is of course the courts’
decision whether to accept or decline any evidence, though digital
video evidence is routinely accepted in court. It is important to
maintain an audit trail while any video evidence is in police
custody. Check HOSDB publication no. 58/07 - Digital Imaging
Procedure for further information.
- I have poor quality CCTV images. How can image enhancement
help?
Image enhancement can sometimes uncover information within the
image that is not initially evident. Unfortunately most CCTV images
generally have low information content so any improvement is only
marginal at best.
However the following simple enhancement techniques could be
beneficial.
- Adjusting the brightness and contrast
levels
- Applying sharpening or edge enhancing
filters
- Increasing the colour
saturation
- Removing noise
More sophisticated image enhancement systems are available, but
again their effect is limited on low quality images.
- Is digital CCTV better than analogue CCTV ?
It could be, but requires greater thought in the design and
set-up.
- The main potential advantages of digital video are:
- Higher image quality;
- Easy export and duplication of video data;
- Addition of detailed metadata (e.g. time, date camera label
etc.);
- More convenient storage options.
However the reality is that:
- Image quality is often low due to poor data compression methods
and poor initial setup.
- Processes for exporting video data are
complicated and generally specific to each
manufacturer.
- Metadata use is unstructured and varies
between manufacturers.
- Systems are often set to maximise storage
by high compression rates and low image resolution, which reduces
the quality of stored video data.
As with any system, digital CCTV systems need to be correctly
specified, installed and properly maintained to gain the maximum
benefit.
- What constitutes master evidence for digital CCTV?
While the original recording such as the system’s hard disk
drives may be seized as master evidence, it is more usual for the
original image files to be copied to WORM (Write Once Read Many)
media such as non-rewriteable CDs or DVDs. It is from these that
working copies can be created. Check HOSDB publication
no. 58/07 - Digital Imaging Procedure for more
information.
- What should I look for when purchasing a digital CCTV
System?
Clearly identify your requirements and budget. The main areas to
consider are:
- Quality – are the stored pictures good enough? (ie high
resolution)
- Storage – are the pictures compressed and stored appropriately?
(ideally low compression)
- Export – can the pictures be easily exported from the
system?
- Playback – can the images be easily reviewed by authorised
third parties?
The HOSDB v4.0 publication 55/06 includes specific advice
on digital systems.
Video data from your CCTV system may be
required to assist with police investigations. To facilitate this,
the Home Office have issued a guidance document 'UK Police
Requirements for Digital CCTV Systems' (HOSDB publication number
09/05). This provides advice on how best to make your video data
accessible to police officers.