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to ON PATROL ISSUE 2
Issues Surrounding Cameras
Topics:
WHEN
SHOULD I USE COLOUR?
COLOUR CAMERAS IN OUTSIDE APPLICATIONS
FORMAT SIZE
CAMERA RESOLUTION
What camera should I use to guarantee
that my security system is the best it can be for the buck spent?
Understanding that this question is one that
is asked by thousands of professionals each day might help you feel better if
you are a closet worrier.
Overall there three or four questions that
surface about which camera to use under what circumstance. These
questions range from; colour versus black & white (b/w); what format size
is best for my application; how much resolution is enough and what features do
I need in my camera to promote the best response possible?
WHEN SHOULD I
USE COLOUR?
Colour is always feasible and is highly
recommended in most cases. This is because of the increased capabilities
for identification, human response during interaction and decreased time and
fatigue factors.
Identification is almost self explanatory.
The objective of the video or live viewing is to be able to pick an
individual or object out of a crowd and be certain of their identification
based upon their overall looks (i.e.: skin tone, hair colour and style,
clothing, paint or covering colour, etc.). Obviously, a colour system
has a distinct advantage over a b/w system in this application.
Human Response during viewing is not
as self explanatory. What you need to consider is that the human eye is
designed to respond to colour and not b/w. This human flaw will
actually interfere with the controllers ability to detect and respond to
subtle actions or changes within a b/w scene.
Because the human eye trains on specific
points within a scene, and because b/w images are made up of subtle contrast
changes between bright and dark, it is very easy for a person to miss small
actions or scene changes on a b/w screen. Colour screens on the other
hand promote minor changes in contrast as actual colours versus mere light
or dark changes, thus giving the eye something that it recognises.
Time and Fatigue factors come into
play for those situations when system integration is not possible.
That is, a controller must sit for extended periods of time watching a fixed
scene. The average IQ person has the ability to watch a fixed b/w
scene for an average 45 - 60 minutes before losing comprehension of what they
are looking at (based upon a fixed, non involvement scene).
With a colour image the average IQ person
can watch a fixed scene for an average of one and a half to two hours before
losing comprehension of what they are looking at.
If nothing else, the above statement is a
strong argument for system integration as well as colour
imagery.
Bottom line, the twenty to thirty percent
additional cost of colour versus b/w is traded off by long term results.
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COLOUR
CAMERAS IN OUTSIDE APPLICATIONS
Colour in outside applications will depend
upon many different factors. However, the primary ones are: how big is
your budget?, how much light do you have? and what is the temperature of that
light?
With the advances of colour camera technology
today, the factor that distinguishes whether or not you use colour outside has
finally come down to cost.
There are standard off the shelf colour
cameras that produce an image in as little as three lux (.3 fc) that are quite
inexpensive, and at the same time, we now have special designed colour cameras
that will produce an excellent colour image in as little as 0.0003 fc at costs
ranging between ?????????.
It's amazing what is being done! I just
finished looking at a real time, excellent colour image produced by a camera
in moonlight conditions and I was blown away.
The colour temperature of the light you have
at night will be another determining factor in your system design. Most
outdoor lighting is either cold (void of colour) or tinted to a specific range
(yellow based sodium). This presents the obvious problem of actual
colour production in proper co-ordination.
Unfortunately, the temperature problem is
usually thought of after the fact and people are disappointed by the results
of their efforts. Nothing worse than installing an entire system to find
that all your night images have a strong yellow tint without the proper
identification capabilities. Designer beware! If it looks tinted
to your eye at night, it will took tinted to the camera as well.
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FORMAT SIZE
Format size simply refers to what size camera
should I use in my design? I've heard so much about the two thirds inch
versus the half inch, the one third versus the quarter inch. What size
is best? Is there a difference?
Absolutely there is a difference. To
understand the differences in format size and the implications of those differences you must do two things. First
understand the definition of
format size and second look into our recent past history.
The definition of format size is that it
refers to the actual size of the usable portion of the imager (CCD chip or
tube) as measured diagonally. Simply put, if the size of imager is one
quarter of an inch, the camera is a 1/4" formatted camera.
Now for history...In the old days, we were deep
into the use of tube cameras. For the most part we concentrated on two
basic format sizes, the one inch and the two thirds inch. The one inch
tube camera, having a larger image base offered better resolution (image
quality as related by horizontal scan lines) and a slightly better sensitivity
(ability to produce an image in lower light levels) than its two thirds inch
counter part. In addition, the one inch camera was by nature larger, and
more expensive than the two thirds camera.
Consequently, we use the one inch as an
unwritten standard for outside and the two thirds inch camera
inside. Outside we had longer views with telephoto or zoom lenses with
less light. The added sensitivity and resolution were very important for
good night vision Inside our images were usually closer and produced
through fixed lenses with fixed, bright light. It made it easy and we
became spoiled by obvious decisions.
With the introduction of the Charged Coupled
Devise (Chinese Confusion Devise or CCD or Chip) suddenly all bets were
off. In the beginning the mind set of the tube was so ingrained that we
continued to believe that the two thirds inch formatted camera would always
out perform the half inch.
Consequently, the obvious result was that more
two thirds inch cameras were installed outside the one half inch. The
crazy part about it all was that there was a certain amount of truth to the
mind set.
Today however, we have improved the
electronics behind our chips. Improved to the extent that we now have
quarter inch cameras that out perform the two thirds inch cameras.
The bottom line on all this new technology has
actually been held back, to some degree, by the lens manufacturer's ability to
keep up with new, smaller format lenses. It seems that as soon as a lens
manufacturer is finally able to come up with a complete line or selection of
lenses for a new smaller formatted camera, the camera manufacturers introduce
the next drop.
The bottom line. I like to wait six
months or one year before I jump into a new smaller format in my outside or
lower light situations. This gives everyone time to work out the bugs
and make sure that it will do what it is designed to do. It also gives
the next generation time to hit the shelf. Don't however, mistake this
statement for sit and wait. If you find a camera that meets the ticket
according to its specification sheet, test it out. If it works in your
application, then use it.
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CAMERA
RESOLUTION
Resolution by itself has become the
controversy of the nineties. First what is it and why does it seem to
rear its ugly head in so many conversations at the trade show bars.
Resolution is a term used to describe image quality.
The better resolution the sharper the image. B/w cameras as a norm have
a higher resolution than colour cameras. Yet colour images appear to be
better than black and white. Why? Go back to the colour section and look
up eye. Tube cameras as a norm ran as much as two hundred horizontal
lines of resolution better than their chip counterparts. Yet chip
cameras produce an image that appears better. Why? Chip cameras
have a higher dynamic range and so produce an image with a broader definition
between white and black.
In the past we referred to the resolution of
an image based upon the number of horizontal lines the camera produced to
paint the image on the screen. The more lines the tighter the image, the
better. Somewhere between the introduction of the first chip cameras and
today, resolution became a mute point and various new definitions and formulas
were introduced to explain the camera's resolution. Bottom line, if a
camera has three hundred horizontal rows of pixels within the usable portion
of its CCD, it has a horizontal resolution of 300 lines.
I about fell over laughing last year when an
engineer introduced a new resolution rating call "perceived
resolution". The way this worked (minus the complicated and nonessential
formula) was that a camera with three hundred horizontal lines of
resolution could have a perceived resolution of five hundred lines. That
is, "I know it's three hundred lines, but it produces an image that looks
as good a five hundred lines of resolution". Buyer Beware!
At the end of the day, resolution is a mute
point in most indoor applications and many outdoor applications.
Especially when you consider that the average video recorder has a play back
resolution of four hundred and fifty horizontal lines or less. If you
are relying on play back of your images for your information, who cares if the
camera resolution exceeds five hundred lines.
In those cases where you are required to
extend the image, such as viewing a person or object through a long telephoto
or zoom lens, the choice of camera that you use will be a camera that provides
a higher resolution. In normal cases however, most cameras with four
hundred plus lines of horizontal resolution will work just fine and provide
excellent imagery.
Incidentally, if you have been told that using
SVHS tape recorders will increase your playback resolution by one hundred
lines or more while using a standard b/w or colour camera, you have been
misinformed. The technology of SVHS requires the use of X -Y cabling and
recording to produce any significant increase in playback resolution. In
addition, if you are using b/w cameras, you gain absolutely nothing with
SVHS. Again, buyer beware!
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AUTHOR: Charlie Pierce is President of
L.T.C. Training Centre and L.R.C. Electronics Company in Davenport - United
States. Charlie is a world authority in CCTV design and application
techniques, installation and field service. He has been training technical and
non-technical personnel since 1971 and holds many honoured positions with the
US Security Industry.