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Box Camera Terminology
- Most modern security cameras have built-in AWB. Video that is captured in fluorescent light will look a lot different that images captured using HID lighting. Sometimes colors become washed out, or look like a different color altogether. A security camera can overcome this problem and adjust the video utilizing AWB in its DSP
. This technology analyzes the video in black and white to determine what is truly white and what is truly black. From that analysis, the true color of the objects in the video can be determined. The camera then makes adjustments to the video and sends it on to the DVR for recording or viewing.
- C Mount and CS Mount type lenses comprise a standard for video lenses that attach to a camera via a threaded collar. The difference between the two is determined by their flange back distance which is the distance between the back of the lens and the imaging sensor of the camera. CS Mount lenses have a flange back distance of 12.5mm vs. 17.526mm for C Mount lenses. All box security cameras offered on our site will accept C or CS Mount lenses.
- All surveillance cameras utilize an image sensor to convert light into electrical signals. There are basically two kinds of image sensors, CMOS
and CCD. Most security cameras use a CCD or Charged Coupled Device. Neither type of image sensor is categorically superior to the other, as they both have their strength and weaknesses. A major benefit of CCD vs CMOS
is that they typically perform better in photographic, scientific and industrial applications which require exacting imaging standards. These types of cameras are typically larger due to the CCDs inability to integrate any image processing circuitry onto the chip itself. A typical surveillance camera configuration consists of a CCD imaging chip, multiple supporting chips, and a lens.
- As with CCD
, it is common to find security cameras with CMOS or Complementary Metal Oxide Semiconductor image sensors. A major benefit of using CMOS vs CCD
image sensors is that many of the image processing functions of the camera can be built into the CMOS chip itself. This allows for more compact circuitry and smaller camera size. In theory, a security camera could consist of a lens and one CMOS image sensor. This is due to the capability of including all image processing circuitry on the CMOS chip. However, in most applications, manufacturers that utilize CMOS also add other image processing components.
- All day/night surveillance cameras are designed to provide the best possible images in daylight and low-light conditions. During the day, infrared light entering the camera can cause the images to be discolored or distorted. At night any extra light that the camera can gather, whether infrared or not can be used to improve LUX
rating of the camera. That being said, the security camera must filter the infrared light out during the day, while allowing it into the camera at night or in low-light situations. Normal day/night surveillance cameras achieve this using software built into the camera. This is a somewhat "quick and dirty" method as the camera has to determine what wavelengths of infrared are undesireable. A True Day/Night camera uses a much more precise method of filtering out infrared light. A physical filter called an ICR Cut Filter
that is tuned to a certain range of infrared light is positioned in front of the image sensor during the day. At night, it is mechanically moved out of the light path using a motor or actuator thus allowing the infrared light to enter the camera. This is the preferred method.
- In low light conditions or when viewing a scene that is illuminated using infrared, the main problem is noise. Light can scatter and infrared from the camera can illuminate dust and other particles in the air. This is particularly problematic when using the camera to detect motion. All the excess "movement" caused by noise triggers false motion events and eats up hard disk space. A feature of some of the more advanced surveillance cameras is DNR or Digital Noise Reduction. The security camera uses a DSP or Digital Signal Processor along with an algorithm to detect the noise in the video and digitally remove it. This smooths out the video and make motion detection more accurate.
- After the image sensor in the camera collects the image and converts it to an electrical signal, the DSP or Digital Signal Processor takes over. The DSP not only converts the electrical signal to a digital image, but it also performs any image manipulation that the camera is designed to perform. For example, the DSP would perform any AWB
functions or WDR
Field of View
- The Field of View or FOV of a camera lens is measured in degrees. As the focal length
of a lens is increased, the field of view decreases and vice versa. It is important when choosing a lens for your security cameras that you keep in mind that when a "zoom" lens is used, that the field of view will be very narrow. In contrast, when you want a wide angle lens in order to capture as much of an angle as possible, the focal length will be very short. The chart below demonstrates some FOV angles associated with some common focal lengths
- The most basic type of surveillance camera lens is the Fixed Lens. This lens has a "Fixed" focal length, so the field of view is predetermined. These types of security camera lenses typically come in 2.5, 4, 6, 8, and 12 mm focal lengths. The chart above demonstrates the various FOV
angles associated with some common focal lengths.
- The focal length of a security camera lens can be described simply as the distance from the primary magnifying lens to the image sensor. Imagine you are looking through a magnifying glass. As you move the lens away from your eye, the images gets bigger. The same thing happens inside a security camera lens. a lens that has a long focal length is farther away from the image sensor than a lens with a short focal length. Conversely, a surveillance camera lens with a longer focal length will have a more narrow FOV or Field of View
than a lens with a shorter focal length. The image below illustrates the basic concept of focal length.
ICR Cut Filter
- In a True Day/Night
Surveillance Camera, this is the filter that is used to "cut" out any infrared light in a scene. Infrared light scatters easily and can cause discoloration and/or distortion in the surveillance camera footage. Normal Day/Night
Security Cameras do not use a Cut Filter. Instead, they use software to digitally remove infrared interference from the image.
- An important factor to consider when choosing the right surveillance camera is the range of lighting conditions that it is designed to operate in. Obviously, most cameras will work fine in normal lighting, but, just like the human eye, the darker it gets, the less the camera sees. The minimum lighting level is measured in LUX. LUX is a measure of light intensity as percieved by the human eye. So, when a security camera is "rated" at .01 LUX, the minimum illumination level it can produce an image is .01 LUX. The chart below demonstrates some common lighting situations and their associated LUX levels.
- Many modern cameras use an OSD or On-Screen Display in order to access any functions that the camera may have built in. Almost all PTZ Surveillance Cameras, WDR
Security Cameras, True Day/Night
Security Cameras will have functionality that can only be accesst via the OSD. The OSD can be accessed via the RS485 connection if available, or by pressing buttons on the camera itself. Once activated, the OSD will be displayed on a monitor attached to the camera and allows the user to access the functions of the camera.
- With box surveillance cameras, in order to mount them outdoors, some type of housing is needed. Since these types of security cameras are not weatherproof, normally a standard CCTV Weatherproof Outdoor Housing is used to protect the camera from the elements. In some extremely cold or extremely hot environments a housing with a heater and blower are needed to prevent fogging of the lens. There are even some security camera outdoor housings with small windshield wipers built in to prevent any substances from building up on the window of the housing.
- A varifocal lens is a lens that has a manually VARI
length. Simply put, this type of lens acts like a manual zoom lens. This allows you to adjust the FOV
of the lens and widen or tighten the lens as needed to get the view you need. Varifocal lenses come in various sizes. Some standard sizes are 2.8-12, 3.5-8, 5-100 and 6-60mm.
- Some lighting situations are difficult to record due to extreme lighting conditions. For example, on a bright sunny day a truck backs up to your loading dock to unload. The back of the truck is dark. In this case, the camera doesn't know whether you intend for it to record the sunny dock or the dark back of the truck. So, it picks one. Either you can't see into the truck, or you are blinded by the bright sunny day. A WDR or Wide Dynamic Range surveillance camera is the answer to this type of security surveillance scenario. A WDR security camera takes two shots of the scene for each frame of video. One frame is optimized for bright scenes, and the other is optimized for dark scenes. the surveillance camera's DSP
then puts them together into one frame that shows both the dark and light areas of the scene clearly. The image below demonstrates a WDR surveillance camera in action.