Network camera types
Network
cameras can be classified in terms of whether they are designed for
indoor use only or for indoor and outdoor use. Outdoor network cameras
often have an auto iris lens to regulate the amount of light the image
sensor is exposed to. An outdoor camera will also require an external,
protective housing unless the camera design already incorporates a
protective enclosure. Housings are also available for indoor cameras
that require protection from harsh environments such as dust and
humidity, and from vandalism or tampering. In some camera designs,
vandal and tamper-proof features are already built-in and no external
housing is required. Network cameras, whether for indoor or outdoor use,
can be further categorized into fixed, fixed dome, PTZ, and PTZ dome
network cameras.
Fixed network cameras
A
fixed network camera, which may come with a fixed or varifocal lens, is a
camera that has a fixed field of view (normal/telephoto/wide-angle)
once it is mounted. A fixed camera is the traditional camera type where
the camera and the direction in which it is pointing are clearly
visible. This type of camera represents the best choice in applications
where it is advantageous to make the camera very visible. A fixed camera
usually enables its lens to be changed. Fixed cameras can be installed
in housings designed for indoor or outdoor installation.
Fixed dome network cameras
A
fixed dome network camera, also called a mini dome, essentially involves
a fixed camera that is pre-installed in a small dome housing. The
camera can be directed to point in any direction. Its main benefit lies
in its discreet, non-obtrusive design, as well as in the fact that it is
hard to see in which direction the camera is pointing. The camera is
also tamper resistant. One of the limitations of a fixed dome camera is
that it rarely comes with an exchangeable lens, and even if it is
exchangeable, the choice of lenses is limited by the space inside the
dome housing. To compensate for this, a varifocal lens is often provided
to enable the camera’s field of view to be adjusted.
PTZ cameras and PTZ dome cameras
A
PTZ camera or a PTZ dome camera can manually or automatically pan, tilt
and zoom in and out of an area or object. All PTZ commands are sent over
the same network cable as for video transmission; no RS-485 wires need
to be installed as is the case with an analog PTZ camera. Some of the
features that can be incorporated in a PTZ camera or a PTZ dome camera
include:
- Electronic image stabilization (EIS). In outdoor installations, PTZ dome cameras with zoom factors above 20x are sensitive to vibrations and motion caused by traffic or wind. EIS helps reduce the affects of vibration in a video. In addition to getting more useful video, EIS will reduce the file size of the compressed image, thereby saving valuable storage space.
- 3D privacy masking. 3D privacy masking is supported in most Axis PTZ dome cameras and enables selected areas of a scene to be blocked or masked from viewing and recording. It allows masking to be maintained even as the camera’s field of view changes through panning, tilting and zooming as the masking moves with the camera’s coordinate system.
- Preset positions. Many PTZ cameras and PTZ dome cameras enable a number of preset positions, normally between 20 and 100, to be programmed. Once the preset positions have been set in the camera, it is very quick for the operator to go from one position to the next.
- E-flip. When a PTZ dome camera is mounted on a ceiling and is used to follow a person in, for example, a retail store, there will be situations when a person will pass just under the camera. When following through on the person, images would be seen upside down without the E-flip functionality. E-flip electronically rotates images 180 degrees in such cases. It is performed automatically and will not be noticed by an operator.
- Auto-flip. PTZ cameras, unlike PTZ dome cameras, do not normally have a full 360-degree continuous pan due to a mechanical stop that prevents the cameras from making a continuous circular movement. However, with the Auto-flip functionality, a PTZ network camera can instantly flip the camera head 180 degrees and continue to pan beyond its zero point. The camera can then continue to follow a passing person or object in any direction.
- Auto-tracking. Auto-tracking is an intelligent video functionality that will automatically detect a moving person or vehicle and follow it within the camera’s area of coverage. Autotracking is particularly beneficial in unmanned video surveillance situations where the occasional presence of people or vehicles requires special attention. The functionality cuts down substantially the cost of a surveillance system since fewer cameras are needed to cover a scene. It also increases the effectiveness of the solution since it allows a PTZ camera or PTZ dome camera to record areas of a scene with activity.
Although PTZ cameras and PTZ dome cameras may share similar functionalities, there are differences between them:
- PTZ network cameras do not have a full 360-degree continuous pan due to a mechanical stop. It means that the camera cannot follow a person walking continuously in a full circle around the camera. Exceptions are PTZ cameras that have the Auto-flip functionality.
- PTZ network cameras are not made for continuous automatic operation or so-called guard tours where the camera automatically moves from one preset position to the next.
Mechanical PTZ network cameras
Mechanical
PTZ cameras are mainly used indoors and in applications where an
operator is employed. The optical zoom on PTZ cameras typically ranges
from 10x to 26x. A PTZ camera can be mounted on a ceiling or wall.
Non-mechanical PTZ network cameras
A
non-mechanical PTZ network camera offers instant pan, tilt, zoom
capabilities with no moving parts, so there is no wear and tear. Using a
wide-angle lens, it offers a wider field of view than a mechanical PTZ
network camera.
A
non-mechanical PTZ camera uses a megapixel image sensor and allows an
operator to instantly zoom in on any part of a scene without any loss in
image resolution. This is achieved by presenting an overview image in
VGA resolution (640×480 pixels) even though the camera captures a much
higher resolution image. When the camera is instructed to zoom in on any
part of the overview image, the camera uses the original megapixel
resolution to provide a full 1:1 ratio in VGA resolution. The resulting
close-up image offers good details with maintained sharpness. With a
normal digital zoom, the zoomed-in image often loses detail and
sharpness. A non-mechanical PTZ camera is ideal for discreet,
wall-mounted installations.
PTZ dome network cameras
PTZ
dome network cameras can cover a wide area by enabling greater
flexibility in pan, tilt and zoom functions. They enable a 360-degree,
continuous pan, and a tilt of usually 180 degrees. PTZ dome cameras are
ideal for use in discreet installations due to their design, mounting
(particularly in drop-ceiling mounts), and difficulty in seeing the
camera’s viewing angle (dome coverings can be clear or smoked).
A
PTZ dome network camera also provides mechanical robustness for
continuous operation in guard tour mode, whereby the camera
automatically moves from one preset position to the next in a
per-determined order or at random. Normally up to 20 guard tours can be
set up and activated during different times of the day. In guard tour
mode, one PTZ dome network camera can cover an area where 10 fixed
network cameras would be needed. The main drawback is that only one
location can be monitored at any given time, leaving the other nine
positions unmonitored.
The
optical zoom of a PTZ dome typically ranges between 10x and 35x. A PTZ
dome is often used in situations where an operator is employed. This
type of camera is usually mounted on a ceiling if used indoors, or on a
pole or wall of a building in outdoor installations.
Day & Night network cameras
All
types of network cameras—fixed, fixed dome, PTZ, and PTZ dome—can offer
day and night functionality. A day and night camera is designed to be
used in outdoor installations or in indoor environments with poor
lighting.
A
day and night, color network camera delivers color images during the
day. As light diminishes below a certain level, the camera can
automatically switch to night mode to make use of near infrared (IR)
light to deliver high-quality, black and white images.
Near-infrared
light, which spans from 700 nanometers (nm) up to about 1000 nm, is
beyond what the human eye can see, but most camera sensors can detect it
and make use of it. During the day, a day and night camera uses an
IR-cut filter. IR light is filtered out so that it does not distort the
colors of images as the human eye sees them. When the camera is in night
(black and white) mode, the IR-cut filter is removed, allowing the
camera’s light sensitivity to reach down to 0.001 lux or lower.
Day
and night cameras are useful in environments that restrict the use of
artificial light. They include low-light video surveillance situations,
covert surveillance and discreet applications, for example, in a traffic
surveillance situation where bright lights would disturb drivers at
night.
An
IR illuminator that provides near-infrared light can also be used in
conjunction with a day and night camera to further enhance the camera’s
ability to produce high-quality video in low-light or nighttime
conditions.
Megapixel network cameras
Megapixel
network cameras, available in Axis’ fixed cameras and fixed dome
cameras, incorporate a megapixel image sensor to deliver images with one
million or more pixels. This is at least two times better pixel
resolution than what can be provided by analog cameras.
A
megapixel, fixed network camera can be used in one of two ways: it can
enable viewers to see greater details in a higher resolution image,
which would be helpful in identifying people and objects, or it can be
used to cover a larger part of a scene if the image resolution is kept
the same as a non-megapixel camera.
Megapixel
cameras today are normally less light sensitive than a non-megapixel
network camera. The higher-resolution video streams generated by a
megapixel camera also put higher demands on the network bandwidth and
storage space for recordings, although this can be mitigated by using
the H.264 video compression standard.