Vandal Dome Camera Terminology
- A surveillance camera's image sensor collects the light that is reflected off of objects. That is how it "sees". In recorded footage, color is very important. You want to be able to identify the color of a car or the color of clothing in order to catch a criminal. Colors can look very different in flourescent lighting and in incandescent lighting. To overcome this, many modern surveillance cameras use AWB or Auto White Balance. This function takes place in the DSP
of the camera and performs color correction. It does this by analyzing the scene in black and white and determining what is truly black and what is truly white. Based on this information, the camera can extrapolate all other colors in the spectrum with surprising accuracy.
- Often, an object being viewed by a security camera is lit very strongly from behind. This can make the object dark and unrecognizable. A security camera can overcome this by utilizing BLC or BackLight Compensation. This technology is a function of the DSP
of the camera. The DSP
analyzes the image and recognizes that the brightest portion of the image is backlighting. The DSP
adjusts the view so that the darker portions of the image are lightened up so that they can be seen. In extreme cases, BLC is not sufficient to overcome this scenario and a WDR
camera must be used.
- All digital cameras contain an image sensor. In comparison with the human eye, this would be the retina. Light is collected on the image sensor and converted to an electrical signal. The two most common types of image sensors are CCD and CMOS
. CCD stands for Charged Coupled Device. A CCD is normally used in scientific, industrial, and photography applications due to its high quality image. The disadvantage to using a CCD is that it requires multiple supporting chips to achieve a high quality image. This places restrictions on how small a manufacturer can make a surveillance camera.
- Complementary Metal Oxide Semiconductors or CMOS chips have historically been used in lower quality cameras due to their lower quality images and less expensive manufacturing processes. However, in recent years, CMOS technology has improved to the point that it meets and often exceeds the imaging quality of CCD
type image sensors. The major benefit of CMOS is that the chip can be manufactured with all supporting circuitry included on the chip. This allows manufacturers to product smaller cameras.
- There are many times when a surveillance camera is used in an environment where there is low light at night. In order to achieve the best images regardless of lighting levels, a day/night surveillance camera is used. A day/night camera takes advantage of an image sensor to be able to see light that is outside our normal range of vision, i.e. infrared. During the day, infrared light must not be allowed to enter the camera as it can cause image distortion. But during periods of low light, infrared light can be used to help enhance the camera's ability to see. There are two methods of achieving this. A standard day/night camera uses its DSP
to digitally filter out the infrared during the day, and not in low light. A TRUE day/night camera uses a physical filter that is placed in front of the image sensor during the day to fileter out the infrared light. In low light, the filter is mechanically removed using a motor or actuator to allow the infrared into the camera.
- Any time an image processor collects light from a scene, there is a chance that image noise will be created. Dust particles, electronic interference, and other environmental factors can add noise to a scene. This is especially problematic when a security camera is being used in a surveillance system to record only when there is motion. In order to overcome this, some cameras implement DNR or Digital Noise Reduction. This uses an algoritm, or formula to determine which pixels in the scene are noise, and which pixels are the image you want to capture. These types of surveillance cameras contain advanced DSP
s to be able to perform this image manipulation.
- All surveillance cameras use a DSP or Digital Signal Processor to perform image manipulation. Whether the camera is a day/night
surveillance camera, a WDR
security camera, or does any sort of DNR
, the DSP is used to process the image before it is sent to the DVR.
Field of View
- A security camera's field of view or FOV is determined by the focal length
of the lens. A long focal length lens will result in a "tight" shot and a short focal length will result in a "wide" shot. "Wide" or "tight" refers to the angle of view of the shot. There is both a horizontal and vertical FOV. The horizontal is the side-to-side angle and the vertical is the up-down angle. The chart below demonstrates the relationship between focal length and angle of view or FOV.
- The fixed lens is the most common type of lens used in security cameras.. This lens has a "Fixed" focal length, so the field of view
is predetermined. The chart above demonstrates the various FOV
angles associated with some common focal lengths. If a camera will be installed in a location where a fixed lens will not obtain the optimum FOV
, the a Varifocal Lens
should be used.
- Security camera lenses are measured in milimeters. The milimeters correspond to the distance between the primary lens and the image sensor. Focal length determines the FOV
of a scene and directly impacts the distance that can be seen via the security camera. 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.
- A camera's greatest vulnerability is its lens. The lens must be able to see the scene, but at the same time be protected. Most, if not all vandal resistant dome security camera uses a Lexan® dome to cover the lens. Lexan® is a trademark name for a high-impact polycarbonate resin thermoplastic. This type of plastic is extremely durable and EXTREMELY
- No matter what type of camera you choose to install in a particular location, withouth adequate lighting it will not be able to "see". Each camera is "rated" for a certain minimum light level or LUX. The LUX rating of a camera is defined as the minimum amount of lighting needed for the camera to produce a usable image. Using the chart below, you can see that a camera that is rated at .001 LUX would be appropriate for areas where the lighting never falls below the amount of light that would occur during a quarter moon on a clear night.
- Most cameras that feature advanced functions such as WDR
, or any advanced image processing will have an OSD. OSD stands for On-Screen Display, and provides a means by which the user can access the settings of the camera. This menu is displayed on the surveillance monitor and is activated either by buttons on the camera, or through an RS-485
- The most common type of surveillance cameras are fixed cameras. This means that, once you mount them and aim them, they don't move. A PTZ or Pan Tilt Zoom security camera, however, can be moved and zoomed in and out to allow you to cover a greater area and get better detail. This type of surveillance camera can be set to automatically move in a pre-defined pattern. It can also be controlled manuall via the DVR or with a PTZ Controller unit. Most PTZ cameras are controlled via RS-485
. Some of the more advanced PTZ security cameras can be set up to follow moving objects automatically.
- RS-485 is an industry standard that describes a communication method used to control devices. This method is used in video surveillance systems to control a security camera's OSD
, and to control PTZ
cameras. The control cable consists of one pair of wires A (-) and B (+). Each device on the RS485 control lines must be addressed differently. When a communication is sent to control a device, the address of the device and the command are sent. The device that matches the address will be the only one to respond to the command. This allows multiple devices to be controlled over the same pair of wires if they are wired in parallel. RS-485 has a distance limitation of approximately 4000 feet (1200 meters).
- Security cameras use one of two different types of lens. Varifocal or VARI
length lenses have an adjustable focal length to allow you widen or tighten the FOV
of the lens. A varifocal lens is especially important if you need to adjust the FOV of the camera to get a shot that cannot be obtained using a fixed lens
- In some lighting conditions, the bright areas are so bright and the dark areas are so dark that the camera cannot utilize BLC
to adjust itself to view the scene properly. In this case, a special function called WDR
or Wide Dynamic Range
is used. Using this method, the camera takes two shots of the scene for each frame of video. One shot is adjusted so that the bright areas are seen clearly and the other shot is optimized for the dark areas. The DSP
of the camera then combines the two images to produce an image where the light and dark areas are both clear. The image below demonstrates the WDR function.