“Because of this
we thought it would be appropriate to carry out independent objective tests on
these new cameras,” says consultant and regular SE&N contributor, Les
Simmonds.
“For the next three
months we will publish objective test results in SE&N for one new
technology camera each month. The tests and evaluations will be carried out on
what we consider to be three of the most interesting new technology CCTV
cameras,” Simmonds explains. “Others may follow later.”
According to
Simmonds, most CCTV camera evaluations are very basic and subjective so the
actual true performance of the camera may still remain a mystery.
“Television
professionals in the industry always use a recognised standard; it may be
objective measurements by testing to a published technical standard or
subjective measurement/assessment systems learned over many years, or, to a
published standard.
“In the past I
have mentioned that you should test cameras under your conditions and lighting.
What I didn’t expect was some in the industry would carry out this type of
basic subjective test under conditions which would not allow for reasonable
camera assessment,” Simmonds says.
“In a number of
cases we know of low quality monitors and lenses have totally masked the good
or bad performance of a camera. For example, it’s not much use evaluating a 520
TV line colour camera on a 300 TV line colour monitor and/or with a low quality
lens which is struggling to pass 350 TV line resolution and may also suffer
from flair. But believe me, it happens!”
Simmonds says
that recently his company made independent comment on a CCTV/Security
specification which specified two cameras as suitable for that project.
“We had
previously tested both cameras for a client and found one satisfactory and the
other a very poor performer. In that case only the satisfactory camera was
specified. Why would the consultant specify two such diverse performing cameras
for the same project?”
Simmonds says
that the SE&N CCTV camera tests will be carried out using the world
recognised European Standard EN 61146-1 Video Cameras (PAL/SECAM/NTSC) –
Methods of measurement – Part 1: Non-broadcast single-sensor camera is the best
known single-sensor objective testing procedure which has a common sense and
accurate approach.
“For many years,
ITU-R BT.500 has provided standards for subjective picture quality measurement.
Over the last few years this has been extended to deal with the changing
measurement requirements for compressed systems. Several measurement techniques
are described within this standard, two of which are basically described below.
“The first,
referred to as “The double-stimulus impairment scale method (the EBU method)”
provides a measurement that can be represented within a five-grade impairment
scale,” Simmonds says.
“The second and alternative measurement referred
to as ‘The double stimulus continuous quality scale method’ (DSCQS). It
replaces the five-grade scale above with voting on the quality of both the
reference image sequence and the test image sequence. The difference between
the two represents the impairment.”
