The Role of Light and Reflection

A scene or target area to be viewed is illuminated by natural or artificial light sources. Natural sources include the sun, the moon (reflected sunlight), and starlight. Artificial sources include incandescent, sodium, metal-arc, mercury, fluorescent, IR, and other man-made lights.

The camera lens receives the light reflected from the scene. Depending on the scene to be viewed, the amount of light reflected from objects in the scene can vary from 5% or 10% to 80% or 90% of the light incident on the scene. Typical values of reflected light for normal scenes such as foliage, automobiles, personnel, and streets fall in the range of about 25-65%. Snow-covered scenes may reach 90%.

The amount of light received by the lens is a function of the brightness of the light source, the reflectivity of the scene, and the transmission characteristics of the intervening atmosphere. In outdoor applications, there is usually a considerable optical path from the source to the scene and back to the camera; therefore, the transmission through the atmosphere must be considered. When atmospheric conditions are clear, there is generally little or no attenuation of the reflected light from the scene. However, when there is precipitation (rain, snow, or sleet, or when fog intervenes) or in dusty, smoky, or sand-blown environments, this attenuation might be substantial and must be considered. Likewise, in hot climates, thermal effects (heat waves) and humidity can cause severe attenuation and/or distortion of the scene. Complete attenuation of the reflected light from the scene (zero visibility) can occur, in which case no scene image is formed.

Since most solid-state cameras operate in the visible and near-IR wavelength region, the general rule of thumb with respect to visibility is that if the human eye cannot see the scene, neither can the camera. Under this situation, no amount of increased lighting will help; however, if the visible light can be filtered out of the scene and only the IR portion used, scene visibility might be increased to some degree.

This problem can often be overcome by using a thermal IR imaging camera that works outside of the visible wavelength range. These thermal IR cameras produce a monochrome display with reduced image quality and are much more expensive than the charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) cameras. Figure 21.5 illustrates the relationship between the viewed scene and the scene image on the camera sensor.

The lens located on the camera forms an image of the scene and focuses it onto the sensor. Almost all video systems used in security systems have a 4 × 3 aspect ratio (4 units wide × 3 units high) for both the image sensor and the FOV. The width parameter is designated as h, and H, and the vertical as v, and V. Some cameras have a 16 × 9 units high-definition television (HDTV) format.

The Lens Function

The camera lens is analogous to the lens of the human eye (Figure 21.6) and collects the reflected radiation from the scene much like the lens of your eye or a film camera. The function of the lens is to collect reflected light from the scene and focus it into an image onto the CCTV camera sensor. A fraction of the light reaching the scene from the natural or artificial illumination source is reflected toward the camera and intercepted and collected by the camera lens. As a general rule, the larger the lens diameter, the more the light will be gathered, the brighter the image on the sensor, and the better the final image on the monitor. This is why larger aperture (diameter) lenses, having a higher optical throughput, are better (and more expensive) than smaller diameter lenses that collect less light. Under good lighting conditions—bright indoor lighting, outdoors under sunlight—the large-aperture lenses are not required and there is sufficient light to form a bright image on the sensor by using small-diameter lenses.

Most video applications use a fixed-focal-length (FFL) lens. The FFL lens, like the human eye lens, covers a constant angular FOV. The FFL lens images a scene with constant fixed magnification. A large variety of CCTV camera lenses are available with different focal lengths (FLs) that provide different FOVs. Wide-angle, medium-angle, and narrow-angle (telephoto) lenses produce different magnifications and FOVs. Zoom and varifocal lenses can be adjusted to have variable FLs and FOVs.

Most CCTV lenses have an iris diaphragm (as does the human eye) to adjust the open area of the lens and change the amount of light passing through it and reaching the sensor. Depending on the application, manual- or automatic-iris lenses are used.

In an automatic-iris CCTV lens, as in a human eye lens, the iris closes automatically when the illumination is too high and opens automatically when it is too low, maintaining the optimum illumination on the sensor at all times. Figure 21.7 shows representative samples of CCTV lenses, including FFL, varifocal, zoom, pinhole, and a large catadioptric lens for long-range outdoor use (which combines both mirror and glass optical elements).

The Transmission Function

Once the camera has generated an electrical video signal representing the scene image, the signal is transmitted to a remote security-monitoring site via some transmission means: coaxial cable, two-wire twisted-pair, LAN, WAN, intranet, Internet, fiber optics, or wireless techniques. The choice of transmission medium depends on factors such as distance, environment, and facility layout.

If the distance between the camera and the monitor is short (10-500 feet), coaxial cable, UTP, and fiber optics or wireless is used. For longer distances (500 feet to several thousand feet) or where there are electrical disturbances, fiber optic cable and UTP are preferred. For very long distances and in harsh environments (frequent lightning storms) or between separated buildings where no electrical grounding between buildings is in place, fiber optics is the choice. In applications where the camera and monitor are separated by roadways or where there is no right of way, wireless systems using RF, microwave, or optical transmission are used. For transmission over many miles or from city to city, the only choice is the digital or Internet IP camera that uses compression techniques and transmits over the Internet. Images from these Internet systems are not real time but sometimes come close to real time.

The Monitor Function

At the monitoring site, CRT or LCD, HD, or plasma monitor converts the video signal back into a visual image on the monitor face via electronic circuitry similar but inverse to that in the camera.

The final scene is produced by a scanning electron beam in the CRT in the video monitor. This beam activates the phosphor on the CRT, producing a representation of the original image onto the faceplate of the monitor. Alternatively, the video image is displayed point by point on an LCD or plasma screen. A permanent record of the monitor video image is made using a VCR tape or DVR hard disk magnetic recorder and a permanent hard copy is printed with a video printer.

The Recording Function

For decades, the VCR has been used to record monochrome and color video images. The real-time and TL VCR magnetic tape systems have been a reliable and efficient means for recording security scenes.

Beginning in the mid-1990s, the DVR was developed using a computer hard disk drive and digital electronics to provide video image recording. The availability of large memory disks (hundreds of megabytes) made these machines available for long-duration security recording. Significant advantages of the DVR over the VCR are the high reliability of the disk as compared with the cassette tape, its ability to perform high-speed searches (retrieval of images) anywhere on the disk, and absence of image deterioration after many copies are made.

Natural Light

During daytime, the amount of illumination and spectral distribution of light (color) reaching a scene depends on the time of day and atmospheric conditions. The color spectrum of the light reaching the scene is important if color CCTV is used. Direct sunlight produces the highest contrast scene, allowing maximum identification of objects. On a cloudy or overcast day, less light is received by the objects in the scene resulting in less contrast. To produce an optimum camera picture under the wide variation in light levels (daytime to nighttime), an automatic-iris camera system is required. Table 21.1 shows the light levels for outdoor illumination under bright sun, partial clouds, and overcast day down to overcast night.

Scene illumination is measured in foot-candles (fc) and can vary from 10,000 to 1 (or more). This exceeds the dynamic operating range of most camera sensors for producing a good-quality video image. After the sun has gone below the horizon and if the moon is overhead, reflected sunlight from the moon illuminates the scene and may be detected by a sensitive monochrome camera. Detection of information in a scene under this condition requires a very sensitive camera, since there is very little light reflected into the camera lens from the scene. As an extreme, when the moon is not overhead or is obscured by cloud cover, the only light received is ambient light from (1) local man-made lighting sources; (2) nightglow caused by distant ground lighting reflecting off particulate (pollution), clouds, and aerosols in the lower atmosphere; and (3) direct light caused by starlight. This is the most severe lighting condition and requires (1) ICCD, (2) monochrome camera with IR light-emitting diode (LED) illumination, or (3) thermal IR camera. Table 21.2 summarizes the light levels occurring under daylight and these LLL conditions and the operating ranges of typical cameras. The equivalent metric measure of light level (lux) compared with the fc is given. One fc is equivalent to approximately 9.3 lux.

Artificial Light

Artificial illumination is often used to augment outdoor lighting to obtain adequate video surveillance at night. The light sources used are tungsten, tungsten-halogen, metal-arc, mercury, sodium, xenon, IR lamps, and LED IR arrays. Figure 21.11 illustrates several examples of these lamps.

The type of lighting chosen depends on architectural requirements and the specific application. Often a particular lighting design is used for safety reasons so that personnel at the scene can see better and for improving the video picture. Tungsten and tungsten-halogen lamps have by far the most balanced color and are best for color cameras. The most efficient visual outdoor light types are the low- and high-pressure sodium-vapor lamps to which the human eye is most sensitive. These lamps, however, do not produce all colors (missing blue and green) and therefore are not good light sources for color cameras. Metal-arc lamps have excellent color rendition. Mercury-arc lamps provide good security illumination but do not produce the color red; therefore, they are not as good as the metal-arc lamps at producing excellent-quality color video images. Long-arc xenon lamps with excellent color rendition are often used in outdoor sports arenas and large parking areas.

LED IR illumination arrays mounted in monochrome video cameras or located near the camera are used to illuminate scenes when there is insufficient lighting. Since they only emit energy in the IR spectrum, they can only be used with monochrome cameras. They are used at short ranges (10-25 feet) with wide-angle lenses (50-75° FOV) or at medium long ranges (25-200 feet) with medium to narrow FOV lenses (5-20°).

Artificial indoor illumination is similar to outdoor illumination, with fluorescent lighting used extensively in addition to the high-pressure sodium, metal-arc, and mercury lamps. Since indoor lighting has a relatively constant light level, automatic-iris lenses are often unnecessary. However, if the CCTV camera views a scene near an outside window or a door where additional light comes in during the day, or if the indoor lighting changes between daytime and nighttime operation, then an automatic-iris lens or electronically shuttered camera is required. The illumination level from most indoor lighting is significantly lower by 100-1000 times than that of sunlight.

Target Size

In addition to the scene’s illumination level and the object’s contrast with respect to the scene background, the object’s apparent size, that is, its angular FOV as seen by the camera, influences a person’s ability to detect it. (Try to find a football referee with a striped shirt in a field of zebras.)

The requirements of a video system are a function of the application. These include: (1) detection of the object or movement in the scene; (2) determination of the object’s orientation; (3) recognition of the type of object in the scene, that is, adult or child, car or truck; or (4) identification of the object (Who is the person? Exactly what kind of truck is it?). Making these distinctions depends on the system’s resolution, contrast, and signal-to-noise ratio (S/N). In a typical scene, the average observer can detect a target about one-tenth of a degree in angle. This can be related to a standard video picture that has 525 horizontal lines (from the National Television System Committee; NTSC) and about 350 TV line vertical and 500 TV line horizontal resolution. Figure 21.12 and Table 21.3 summarize the number of lines required to detect, orient, recognize, or identify an object in a television picture. The number of TV lines required will increase for conditions of poor lighting, highly complex backgrounds, reduced contrast, or fast movement of the camera or target.

Reflectivity

The reflectivity of different materials varies greatly depending on its composition and surface texture. Table 21.4 gives some examples of materials and objects viewed by video cameras and their respective reflectivity.

Since the camera responds to the amount of light reflected from the scene, it is important to recognize that objects have a large range of reflectivity. The objects with the highest reflectivity produce the brightest images. To detect one object located within the area of another the objects must differ in reflectivity, color, or texture. Therefore, if a red box is in front of a green wall and both have the same reflectivity and texture, the box will not be seen on a monochrome video system. In this case, the total reflectivity in the visible spectrum is the same for the green wall and the red box. This is where the color camera shows its advantage over the monochrome camera.

The case of a color scene is more complex. While the reflectivity of the red box and the green wall may be the same as averaged over the entire visible spectrum from blue to red, the color camera can distinguish between green and red.

It is easier to identify a scene characteristic by a difference in color in a color scene than it is to identify it by a difference in gray scale (intensity) in a monochrome scene. For this reason, the target size required to make an identification in a color scene is generally less than it is to make the same identification in a monochrome scene.

Effects of Motion

A moving object in a video image is easier to detect, but more difficult to recognize than a stationary one provided that the camera can respond to it. LLL cameras produce sharp images for stationary scenes but smeared images for moving targets. This is caused by a phenomenon called “lag” or “smear.” Solid-state sensors (CCD, CMOS, and ICCD) do not exhibit smear or lag at normal light levels; therefore, they can produce sharp images of both stationary and moving scenes. Some image intensifiers exhibit smear when the scene moves fast or when there is a bright light in the FOV of the lens.

When the target in the scene moves very fast, the inherent camera scan rate (30 frames per second; fps) causes a blurred image of this moving target in the camera. This is analogous to the blurred image in a still photograph when the shutter speed is too slow for the action. There is no cure for this as long as the standard NTSC television scan rate (30 fps) is used. However, CCTV snapshots can be taken without any blurring using fast-shuttered CCD cameras. For special applications in which fast-moving targets must be imaged and tracked, higher scan rate cameras are available.

Scene Temperature

Scene temperature has no effect on the video image in a CCD, CMOS, or ICCD sensor. These sensors do not respond to temperature changes or temperature differences in the scene. On the other hand, IR thermal imaging cameras do respond to temperature differences and changes in temperature in the scene. Thermal imagers do not respond to visible light or the very near-IR radiation like that produced by IR LEDs. The sensitivity of IR thermal imagers is defined as the smallest change in temperature in the scene that can be detected by the thermal camera.

FFL Lens

Figure 21.13 illustrates three fixed FFL or fixed FOV lenses with narrow (telephoto), medium, and wide FOVs and the corresponding FOV obtained when used with a 1/3-inch camera sensor format.

Wide FOV (short FL) lenses permit viewing a very large scene (wide angle) with low magnification and therefore provide low resolution and low identification capabilities. Narrow FOV or telephoto lenses have high magnification with high resolution and high identification capabilities.

Zoom Lens

The zoom lens is more versatile and complex than the FFL lens. Its FL is variable from wide-angle to narrow-angle (telephoto) FOV (Figure 21.14).

The overall camera/lens FOV depends on the lens FL and the camera sensor size as shown in Figure 21.14. Zoom lenses consist of multiple lens groups that are moved within the lens barrel by means of an external zooming ring (manual or motorized), changing the lens FL and angular FOV without having to switch lenses or refocusing. Zoom FL ratios can range from 6:1 up to 50:1. Zoom lenses are usually large and used on pan/tilt mounts viewing over large areas and distances (25-500 feet).

Varifocal Lens

The varifocal lens is a variable FL lens used in applications where an FFL lens would be used. In general, they are smaller and cost much less than zoom lenses. Like the zoom lens, the varifocal lens is used because its FL (angular FOV) can be changed manually or automatically, using a motor, by rotating the barrel on the lens. This feature makes it convenient to adjust the FOV to a precise angle when installed on the camera. Typical varifocal lenses have FLs of 3-8, 5-12, and 8-50 mm. With just these three lenses, FLs from 3 to 50 mm (91-5° horizontal FOV) can be covered on a 1/3-inch format sensor. Unlike zoom lenses, varifocal lenses must be refocused each time the FL and the FOV are changed. They are not suitable for zoom or pan/tilt applications.

Panoramic—360° Lens

There has always been a need to see “all around,” i.e., an entire room or other location, seeing 360° with one panoramic camera and lens. In the past, 360° FOV camera viewing systems have only been achieved by using multiple cameras and lenses and combining the scenes on a split-screen monitor.

Panoramic lenses have been available for many years but have only recently been combined with digital electronics and sophisticated mathematical transformations to take advantage of their capabilities. Figure 21.15 shows two lenses having a 360° horizontal FOV and a 90° vertical FOV.

The panoramic lens collects light from the 360° panoramic scene and focuses it onto the camera sensor as a donut-shaped image. The electronics and mathematical algorithm convert this donut-shaped panoramic image into the rectangular (horizontal and vertical) format for normal monitor viewing.

Covert Pinhole Lens

This special security lens is used when the lens and CCTV camera must be hidden. The front lens element or aperture is small (from 1/16 to 5/16 of an inch in diameter). Although this is not the size of a pinhead, it nevertheless has been labeled as such. Figure 21.16 shows examples of straight and right-angle pinhole lenses used with C or CS mount cameras. The very small mini-pinhole lenses are used on the low-cost, small board cameras.

Special Lenses

Some special lenses useful in security applications include split-image, right-angle, relay, and fiber optic lenses (Figure 21.17).

The dual-split and tri-split lenses use only one camera to produce multiple scenes. These are useful for viewing the same scene with different magnifications or different scenes with the same or different magnifications. Using only one camera can reduce cost and increase reliability. These lenses are useful when two or three views are required and only one camera was installed.

The right-angle lens permits a camera using a wide-angle lens installed to view a scene that is perpendicular to the camera’s optical axis. There are no restrictions on the FLs, so they can be used in wide- or narrow-angle applications.

The flexible and rigid coherent fiber optic lenses are used to mount a camera several inches to several feet away from the front lens as might be required to view from the opposite side of a wall or in a hazardous environment. The function of the fiber optic bundle is to transfer the focused visual image from one location to another. This may be useful for (1) protecting the camera and (2) locating the lens in one environment (outdoors) and the camera in another (indoors).

The Scanning Process

Two methods used in the camera and monitor video scanning process are raster scanning and progressive scanning. In the past, analog video systems have all used the raster scanning technique; however, newer digital systems are now using progressive scanning. All cameras use some form of scanning to generate the video picture. A block diagram of the CCTV camera and a brief description of the analog raster scanning process and video signal are shown in Figures 21.8, 21.9, 21.18, and 21.19.

The camera sensor converts the optical image from the lens into an electrical signal. The camera electronics process the video signal and generate a composite video signal containing the picture information (luminance and color) and horizontal and vertical synchronizing pulses.

Signals are transmitted in what is called a frame of picture video, made up of two fields of information. Each field is transmitted in 1/60 of a second and the entire frame in 1/30 of a second, for a repetition rate of 30 fps. In the United States, this format is the Electronic Industries Association (EIA) standard called the NTSC system. The European standard uses 625 horizontal lines with a field taking 1/50 of a second and a frame 1/25 of a second and a repetition rate of 25 fps.

Solid-State Cameras

Video security cameras have gone through rapid technological changes during the last half of the 1980s to the present. For decades, the vidicon tube camera was the only security camera available. In the 1980s, the more sensitive and rugged silicon-diode tube camera was the best available. In the late 1980s, the invention and development of the digital CCD and later the CMOS cameras replaced the tube camera. This technology coincided with rapid advancement in DSP in cameras, the IP camera, and use of digital transmission of the video signal over LAN, WANs, and the Internet.

The two generic solid-state cameras that account for most security applications are the CCD and the CMOS.

The first generation of solid-state cameras available from most manufacturers had 2/3-inch (sensor diagonal) and 1/2-inch sensor formats. As the technology improved, smaller formats evolved. Most solid-state cameras in use today are available in three image sensor formats: 1/2, 1/3, and 1/4 inch. The 1/2-inch format produces higher resolution and sensitivity at a higher cost. The 1/2-inch and smaller formats permitted the use of smaller, less expensive lenses as compared with the larger formats. Many manufacturers now produce 1/3-inch and 1/4-inch format cameras with excellent resolution and light sensitivity. Solid-state sensor cameras are superior to their predecessors because of their (1) precise, repeatable pixel geometry, (2) low power requirements, (3) small size, (4) excellent color rendition and stability, and (5) ruggedness and long life expectancy. At present, solid-state cameras have settled into three main categories: (1) analog, (2) digital, and (3) Internet.

LLL-Intensified Camera

When a security application requires viewing during nighttime conditions where the available light is moonlight, starlight, or other residual reflected light and the surveillance must be covert (no active illumination like IR LEDs), LLL-ICCD cameras are used. The ICCD cameras have sensitivities between 100 and 1000 times higher than the best solid-state cameras. The increased sensitivity is obtained by the use of a light amplifier mounted in between the lens and the CCD sensor. LLL cameras cost between 10 and 20 times more than CCD cameras.

Thermal Imaging Camera

An alternative to the ICCD camera is the thermal IR camera. Visual cameras see only visible light energy from the blue end of the visible spectrum to the red end (approximately 400-700 nm). Some monochrome cameras see beyond the visible region into the near-IR region of the spectrum up to 1000 nm. This IR energy, however, is not thermal IR energy. Thermal IR cameras using thermal sensors respond to thermal energy in the 3-5 and 8-14 μm range. The IR sensors respond to the changes in heat (thermal) energy emitted by the targets in the scene. Thermal imaging cameras can operate in complete darkness, as they require no visible or IR illumination whatsoever. They are truly passive nighttime monochrome imaging sensors. They can detect humans and any other warm objects (animals, vehicle engines, ships, aircraft, warm/hot spots in buildings) or other objects against a scene background.

Panoramic—360° Camera

Powerful mathematical techniques combined with the unique 360° panoramic lens have made a 360° panoramic camera possible. In operation, the lens collects and focuses the 360° horizontal by up to 90° vertical scene (one-half of a sphere; a hemisphere) onto the camera sensor. The image takes the form of a “donut” on the sensor (Figure 21.20).

The camera/lens is located at the origin (0). The scene is represented by the surface of the hemisphere. As shown, a small part (slice) of the scene area (A, B, C, D) is “mapped” onto the sensor as a, b, c, d. In this way, the full scene is mapped onto the sensor. Direct presentation of the donut-ring video image onto the monitor does not result in a useful picture.

That is where the use of a powerful mathematical algorithm comes in. Digital processing in the computer using the algorithm transforms the donut-shaped image into the normal format seen on a monitor, that is, horizontal and vertical.

All of the 0-360° horizontal by 90° vertical images cannot be presented on a monitor in a useful way—there is just too much picture “squeezed” into the small screen area. This condition is solved by computer software by looking at only a section of the entire scene at any particular time.

The main attributes of the panoramic system include: (1) capturing a full 360° FOV, (2) the ability to digitally pan/tilt to anywhere in the scene and digitally zoom any scene area, (3) having no moving parts (no motors, etc., that can wear out), and (4) having multiple operators that can view any part of the scene in real time or at a later time.

The panoramic camera requires a high-resolution camera since so much scene information is contained in the image. Camera technology has progressed so that these digital cameras are available and can present a good image of a zoomed-in portion of the panoramic scene.

Hard-wired

There are several hard-wired means for transmitting a video signal: coaxial cable, UTP, LAN, WAN, intranet, Internet, and fiber optic cable.

Fiber optic cable is used for long distances and when there is interfering electrical noise. LANs and Internet connections are digital transmission techniques used in larger security systems and where the signal must be transmitted over existing computer networks or over long distances.

Wireless

In legacy analog video surveillance systems, it is often more economical or beneficial to transmit the real-time video signal without cable (wireless) from the camera to the monitor using an RF or IR atmospheric link. In digital video systems using digital transmission, the use of wireless networks (WiFi) permits routing the video and control signals to any remote location. In both the analog and the digital systems, some form of video scrambling or encryption is often used to remove the possibility of eavesdropping by unauthorized personnel outside the system. Three important applications for wireless transmission include: (1) covert and portable rapid deployment video installations, (2) building-to-building transmission over a roadway, and (3) parking lot light poles to building. The Federal Communications Commission (FCC) restricts some wireless transmitting devices using microwave frequencies or RF to government and law enforcement use but has given approval for many RF and microwave transmitters for general security use. These FCC-approved devices operate above the normal television frequency bands at approximately 920 MHz and 2.4 and 5.8 GHz. The atmospheric IR link is used when a high-security link is required. This link does not require an FCC approval and transmits a video image over a narrow beam of visible light or near-IR energy. The beam is very difficult to intercept (tap). Figure 21.22 illustrates some of the Wireless Transmission Techniques Available Today.

Fiber optics

Fiber optic transmission technology has advanced significantly in the last 5-10 years and represents a highly reliable, secure means of transmission. Fiber optic transmission holds several significant advantages over other hard-wired systems: (1) very long transmission paths up to many miles without any significant degradation in the video signal with monochrome or color; (2) immunity to external electrical disturbances from weather or electrical equipment; (3) very wide bandwidth, permitting one or more video, control, and audio signals to be multiplexed on a single fiber; and (4) resistance to tapping (eavesdropping) and therefore a very secure transmission means.

While the installation and termination of fiber optic cable requires a more skilled technician, it is well within the capability of qualified security installers. Many hard-wired installations requiring the optimum color and resolution rendition use fiber optic cable.

Standard

There are four basic switcher types: manual, sequential, homing, and alarming. Figure 21.23 shows how these are connected into the video security system.

The manual switcher connects one camera at a time to the monitor, recorder, or printer. The sequential switcher automatically switches the cameras in sequence to the output device. The operator can override the automatic sequence with the homing sequential switcher. The alarming switcher connects the alarmed camera to the output device automatically, when an alarm is received.

Microprocessor Controlled

When the security system requires many cameras in various locations with multiple monitors and other alarm input functions, a microprocessor-controlled switcher and keyboard is used to manage these additional requirements (Figure 21.24).

In large security systems, the switcher is microprocessor controlled and can switch hundreds of cameras to dozens of monitors, recorders, or video printers via an RS-232 or other communication control link. Numerous manufacturers make comprehensive keyboard-operated, computer-controlled consoles that integrate the functions of the switcher, pan/tilt pointing, automatic scanning, automatic preset pointing for pan/tilt systems, and many other functions. The power of the software-programmable console resides in its flexibility, expandability, and ability to accommodate a large variety of applications and changes in facility design. In place of a dedicated hardware system built for each specific application, this computer-controlled system can be configured via software for the application.

Monochrome

Until the late 1990s, the most popular monitor used in CCTV systems was the monochrome CRT monitor. It is still used and is available in sizes ranging from a 1-inch diagonal viewfinder to a large 27-inch diagonal CRT. By far, the most popular monochrome monitor size is the 9-inch diagonal that optimizes video viewing for a person seated about 3 feet away. A second reason for its popularity is that two of these monitors fit into the standard EIA 19-inch wide rack-mount panel. Figure 21.26b shows two 9-inch monitors in a dual rack-mounted version. A triple rack-mount version of a 5-inch diagonal monitor is used when space is at a premium. The triple rack-mounted monitor is popular, since three fit conveniently into the 19-inch EIA rack. The optimum viewing distance for the triple 5-inch diagonal monitor is about 1.5 feet.

Color

Color monitors are now in widespread use and range in size from a 3- to 27-inch diagonal and have required viewing distances and capabilities similar to those of monochrome monitors. Since color monitors require three different colored dots to produce one pixel of information on the monitor, they have lower horizontal resolution than monochrome monitors. Popular color monitor sizes are 13, 15, and 17 inch diagonal.

CRT, LCD, Plasma, HD, Displays

The video security picture is displayed on three basic types of monitor screens: (1) CRT, (2) LCD, and most recently, (3) the plasma display. The analog CRT has seen excellent service from the inception of video and continues as a strong contender providing a low-cost, reliable security monitor. The digital LCD monitor is growing in popularity because of its smaller size (smaller depth)—2-3 inches versus 12-20 inches for the CRT. The LCD is an all solid-state display that accepts the VGA computer signal. Most small (3-10 inch diagonal) and many large (10-17 inch diagonal) LCD monitors also accept an analog video input. The most recent monitor entry into the security market is the digital plasma display. This premium display excels in resolution and brightness and viewing angle and produces the highest quality image in the industry. It is also the most expensive. Screen sizes range from 20 to 42 inches diagonal. Overall depths are small and range in size from 3 to 4 inches. They are available in 4:3 and HDTV 16:9 format.

Audio/Video

Many monitors have built-in audio channel with speakers to produce audio and video simultaneously.

VCR

Magnetic storage media have been used universally to record the video image. The VCR uses the standard VHS cassette format. The 8-mm Sony format is used in portable surveillance equipment because of its smaller size. Super VHS and Hi-8 formats are used to obtain higher resolution. VCRs can be subdivided into two classes: real time and TL. The TL recorder has significantly different mechanical and electrical features permitting it to take snapshots of a scene at predetermined (user-selectable) intervals. It can also record in real time when activated by an alarm or other input command. Real-time recorders can record up to 6 hours in monochrome or color. TL VCRs are available for recording TL sequences up to 720 hours.

DVR

The DVR has emerged as the new generation of magnetic recorder of choice. A magnetic HD like those used in a microcomputer can store many thousands of images and many hours of video in digital form. The rapid implementation and success of the DVR has resulted from the availability of inexpensive digital magnetic memory storage devices and the advancements made in digital signal compression techniques. Present DVRs are available in single channel and 4 and 16 channels and may be cascaded to provide many more channels.

A significant feature of the DVR is the ability to access (retrieve) a particular frame or recorded time period anywhere on the disk in a fraction of a second. The digital technology also allows many generations (copies) of the stored video images to be made without any errors or degradation of the image.

Optical disk

When very large volumes of video images need to be recorded, an optical disk system is used. Optical disks have a much larger video image database capacity than magnetic disks given the same physical space they occupy. These disks can record hundreds of times longer than their magnetic counterparts.

Camera Housings

Indoor and outdoor camera housings protect cameras and lenses from dirt, dust, harmful chemicals, the environment, and vandalism. The most common housings are rectangular metal or plastic products, formed from high-impact indoor or outdoor plastic, painted steel, or stainless steel (Figure 21.29). Other shapes and types include cylindrical (tube), corner-mount, ceiling-mount, and dome housings.

Pan/Tilt Mounts

To extend the angle of coverage of a CCTV lens/camera system a motorized pan/tilt mechanism is often used. Figure 21.30 shows three generic outdoor pan/tilt types: top-mounted, side-mounted, and dome camera.

The pan/tilt motorized mounting platform permits the camera and lens to rotate horizontally (pan) or vertically (tilt) when it receives an electrical command from the central monitoring site. Thus, the camera lens is not limited by its inherent FOV and can view a much larger area of a scene. A camera mounted on a pan/tilt platform is usually provided with a zoom lens. The zoom lens varies the FOV in the pointing direction of the camera/lens from a command from the central security console. The combination of the pan/tilt and zoom lens provides the widest angular coverage for video surveillance. There is one disadvantage with the pan/tilt/zoom configuration compared with the fixed camera installation.

When the camera and lens are pointing in a particular direction via the pan/tilt platform, most of the other scene area the camera is designed to cover is not viewed. This dead area or dead time is unacceptable in many security applications; therefore, careful consideration should be given to the adequacy of their wide FOV pan/tilt design. Pan/tilt platforms range from small, indoor, lightweight units that only pan, up to large, outdoor, environmental designs carrying large cameras, zoom lenses, and large housings. Choosing the correct pan/tilt mechanism is important since it generally requires more service and maintenance than any other part of the video system.

VMD

Another important component in a video surveillance system is a VMD that produces an alarm signal based on a change in the video scene. The VMD can be built into the camera or be a separate component inserted between the camera and the monitor software in a computer. The VMD electronics, analog or digital, store the video frames, compare subsequent frames to the stored frames, and then determine whether the scene has changed. In operation, the VMD digital electronics decides whether the change is significant and whether to call it an alarm to alert the guard or some equipment, or declare it a false alarm.

Screen Splitter

The electronic or optical screen splitter takes a part of several camera scenes (two, three, or more), combines the scenes, and displays them on one monitor. The splitters do not compress the image. In an optical splitter, the image combining is implemented optically at the camera lens and requires no electronics. The electronic splitter/combiner is located between the camera output and the monitor input.