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Camera
Demos and Sample Video
Part 1:
Recording speed
Video
recording capacity and its after the
fact usability is
governed by one main factor among
all others:
recording speed. Recording speed in
short determines how much data is
gathered and how quickly it is
gathered. The slower a recorder
records, the longer a time period
can be stored in the same amount of
storage space (such as an 80G drive).
When you capture less data, there is
less data to store. So by slowing
down your record rate, you increase
a given unit's ability to archive
more data, and thus get a longer
length of total time from the same
amount of hard drive space. However, taken to
extremes, slow record rates can be
so slow that the desired information
is missed in between recording
intervals (such as very fast and
slight hand movements or cars that
speed through entrances). Spy Centre
Security recommends
security level video recording to be
5 frames per second or better
for most situations.
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1 frame per second
1 fps, 30
sec clip, 1.5 MB |
1
frame per second video
is a very slow recording
rate usually only used when
a system is trying to get
the maximum amount of
archive possible, or when
periodic snapshots is all
that is necessary.
|
5 frames per second
5 fps, 30 sec clip,
4.5 MB |
5 frames per
second
video is standard security
recording. It is a good mix
of speed and storage
capacity. |
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15 frames per second
15 fps,
30 sec. clip,
12.5 MB |
15 frames per
second
video is considered high
speed video and is the
maximum usually used for
most generic recording. It
offers extreme fluidity of
movement, but does tend to
take up lots of storage
space. |
30 frames per second
30 fps,
30 sec. clip, 25 MB |
30 frames per
second
video is considered
real-time recording. It is
usually only used in
situations where slight hand
movements are being
recorded, or when trying to
capture license plates.
Real-time recording
typically requires extremely large amounts of storage
capacity. |
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Part 2:
Image size
The next main factor that affects the total
storage ability of a DVR is the size or resolution at which the
video is recorded. The larger the image that is recorded, the
more each individual clip takes up on the hard drive. However,
small pictures may not contain enough image resolution to
clearly display fine details. For example, facial recognition or
license plate recognition
might be difficult on a video clip recorded at 320 x 240
resolution. Although many DVRs have the ability to digitally
zoom an image after the fact from the video playback archive, this
effect tends to distort the picture as it gets bigger and
bigger, rendering most fine detail blurry and
undecipherable. It is always better to record your
information at a higher resolution initially, as opposed to
trying to digitally zoom in to it after it is already
recorded. The
last thing to note is that a 640 x 480 resolution picture is
actually 4 times the size of a 320 x 240 picture because
both the length and the width of the picture are doubled. All things
being equal, this means that a 320 x 240 resolution archive
will
be about 4 times the the archive length (in days) of the same footage
that was recorded at 640 x 480 resolution. Generally speaking, Spy Centre Security
recommends
640 x 480 resolution recording for most security
situations.
|
320 x 240
archive length x4
vs.
standard archive
320 x 240, 56k |
320 x 240 recording
resolution is typically used
when maximum record length
is desired. 320 x 240 mode
offers the smallest usable
video size which yields the
largest useable
recording archive, but tends to
suffer when it comes to fine
detail. This resolution is
best used for general
coverage shots, wide shots
where fine detail isn't
necessary, or when trying to
truly maximize storage
space.
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640 x 480
standard archive length
for security video
640 x 480, 188k |
640 x 480 recording
resolution is considered
standard security video
recording. It is a good mix
of recording resolution and
archive storage capacity.
This is possibly the most
common DVR/NVR recording
size used in the industry
today. |
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720 x 480
archive length x 0.9
vs.
standard archive
720 x 480, 210 k |
720 x 480 is a newer
recording resolution this is
slightly "wide screened". It
is typically used when your
end export media is DVD
format or if your monitor is
a widescreen monitor. This
is a fairly typical size for
DVD media. More and more
DVRs and NVRs are offering
this particular recording
size and it is becoming more
of an industry standard for
recommended recording
resolution. |
1600 x 1200
archive length x 0.12
vs.
standard archive
1600 x 1200, 487 k
** click on the picture,
then the magnifying glass to see
the full
image size |
1600 x 1200 recording
resolution is 2 mega-pixel
recording. This recording
resolution is typically used
in NVR recordings or very,
very high resolution DVR
recordings. Since the
picture generated at this
resolution is so large, most
DVRs or NVRs run at
comparatively slower
recording rates than their 640
x 480 counterparts. High
speed recording at this
resolution requires
extremely large amounts of
storage space. |
Part
3:
Lens size
and camera field of view
The lens size
quite simply determines your field of view. Field of view
directly affects the usability of playback video. Most of
the time, security camera coverage shots consist of three "typical
types" of shots: facial recognition, license plate
recognition, and wide general coverage shots. Facial
recognition and license plate shots need to have the desired
object fill at least 50% of the shot or more to capture
the detail necessary to identify the object properly. That
generally means that the field of view needs to be about 4
to 8 feet wide to yield useable detail. Wide
shots are not really concerned about fine detail so much as
viewing width. Typically the widest shot possible is the goal.
Taken to extremes, wide-angle shots have next to no
recognizable detail and are mostly just monitoring general
movement. Trying to pull a face or a license plate out of a wide angle
shot at a long distance is all but impossible. After-the-fact digital zooms will distort the picture and destroy any
detail their may be. The first step in determining the
appropriate lens size is to determining the viewing distance
(or focal length) to the desired object. Most standard fixed
lens bullets and domes have an approximately 4.0 mm lens by
default.
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30 foot distance
typical general
coverage
This is
a fairly typical distance for wide angle
shots of showrooms, small retail sales
floors and office coverage. The standard
lens on most bullets and domes (3.6 mm -
4.3 mm) is usually sufficient for
general coverage shots, providing a
usable width as well as usable detail in
the shot. License or facial recognition
at this distance requires 12+ mm lenses
minimum to be appropriate. |
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50
foot distance
typical
parking lot coverage
This is
a fairly typical distance for wide angle
shots in parking lots or larger office
and retail sales floors. At this
distance 6 to 12 mm lenses are required
for the general wide angle shots to
provide a usable width as well as usable
detail in the shot. License or facial
recognition at this distance requires
20+ mm lenses minimum to be appropriate. |
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120
foot distance
typical
license plate recognition
This is
a fairly typical distance for long range
license plate recognition for parking
lot entrances. Most situations at this
distance require 90+mm lenses to see
license plates clearly. Wide angle shots
of parking lots or warehouses at such a
long range distance typically require 25+ mm
lenses. |
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Camera field of view width
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Distance to target object in feet |
|
Lens |
10 |
15 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
110 |
150 |
200 |
300 |
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3.6 mm |
10 ft |
14 ft |
19 ft |
29 ft |
38 ft |
47 ft |
* |
* |
* |
* |
* |
* |
* |
* |
* |
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6.0 mm |
** |
** |
9 ft |
12 ft |
18 ft |
24 ft |
30 ft |
* |
* |
* |
* |
* |
* |
* |
* |
|
12.0 mm |
** |
** |
** |
9 ft |
12 ft |
15 ft |
18 ft |
21 ft |
24 ft |
27 ft |
30 ft |
33 ft |
* |
* |
* |
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25.0 mm |
** |
** |
** |
** |
** |
** |
** |
** |
** |
9 ft |
15 ft |
18 ft
|
21 ft |
29 ft |
43 ft |
*
Field of
view at this distance and lens size is
too wide for most applications
** Field of
view at this distance and lens size is too
narrow for most applications |
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Part
4:
Lighting and
the camera scene
Scene lighting is
the last major component in video usability. In short, if
the lighting is too low for a given camera, it cannot "see"
the scene properly. This effect results in an all black
image that is wasted and unusable. Many different types of
cameras exist and each is geared towards one main type of
ambient lighting situation. Extreme cases require the
ability to see an absolute darkness and require special
types of cameras. For example, a small storage closet with a
safe inside, or a server room with no overhead lights would
require an infrared camera to record much of anything. In
general, using a camera with the lowest possible light
rating is the most desirable.
There is one main exception to
this rule of thumb though: license plate recognition in low
light or darkness. License plates are designed to be
reflective so they can be seen at night when car
headlights make them "light up".
Infrared cameras work because they illuminate the scene with
a type of light the human eye generally cannot see, however
the image sensor of the camera can. Unless the camera in
question is a very special type of infrared,
this results in the
camera projecting light out on to the plate, the light
reflecting back at the camera, and thus causing the license
plate to appear as a big white blob.
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LUX and low
lighting chart |
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Ambient
Condition |
Illumination
|
Range
Details |
|
Foot candles |
LUX |
Sunlight
Full Daylight
Overcast Day
Very Dark Day
Twilight
Deep Twilight |
10,000
1,000
100
10
1
.1 |
107,527
10,752.7
1,075.3
107.53
10.75
1.08 |
Daylight
Range |
Full Moon
Quarter Moon
Starlight
Overcast Night |
.01
.001
.0001
.00001 |
.108
.0108
.0011
.0001 |
Low Light
Level Range |
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