Video Cameras Information

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Selecting video cameras Video cameras record live-action scenes that are available for viewing via a stored or transmitted video feed. This allows the user to create a permanent and detailed chronicle of events. Original video cameras—invented in the late 19th Century—created a "motion picture." This term is still apt today, as video cameras record dozens of pictures (or frames) a second that when viewed in succession, clearly distinguish the translation of an object or person over time. Most cameras also record audio in sync with their video capture.

Video Camera Operation

Cameras function by capturing light from the visible spectrum as well others parts of the electromagnetic spectrum. This is controlled by only allowing light into the recording chamber through a hollow tube called the aperture. This light is then focused onto the recording device by the use of a lens. Light entering the aperture is controlled by a shutter, usually within the lens mechanism; it controls the length of exposure. High-end film video cameras may utilize a rotary shutter to expose negatives accurately. Digital cameras can offer a faster shutter speed, since there are no moving parts. This is known as an electronic shutter, and if paired with external automation such as a motion detector, it operates better than film cameras.

Monochrome vs. Color: Monochrome video capture is photography that depicts images in the same hue (greyscale), rather than the authentic colors of the object recorded. Monochrome tends to produce sharper, higher-resolution images. Color images rely on the interpolation (or the average light intensity from nearby, filtered neighboring pixels) of light to produce an estimated color. Monochrome image sensors do not need a filter applied, so each pixel has an accurate greyscale measurement based upon light intensity in each pixel. This also means that color image sensors have less sensitivity to light, so monochrome recording may be better for low-light situations.

Image credit: Photonics.com

Imaging Technology

Older model video cameras use photographic film to record the light spectrum on a plastic strip covered with light-sensitive silver-halide salts. Light that is exposed to the aperture is redirected to the film to create a latent image. The film stock is rolled at a rapid speed so the same image may appear to be depicted on consecutive frames, but when viewed at length and at an equally rapid speed (called 'frame rate'), they actually portray an object in motion. Originally this rapid viewing rate was responsible for the first color films, as each frame would have a red or green filter to it, which the viewer would individually interpret because of the eye's sensitivity to these colors. Later, methods to remove the silver emulsion on both sides of the film and replace it with red and green dyes led to more vivid, color motion pictures.

To reproduce the images captured on film stock, the film roll must be unwound and passed in front of a light. When the frame is alit, the images captured on the film stock are projected away from the film stock. Even with less-than-modern video cassette players, this was the method used to transmit videos to screens and monitors. Video collected by image sensors recreates scenes by digitally recreating them sequentially.

Images credits: Wikimedia; eHow

Newer model video capture devices have done away with the analog film prevalent in the 20th Century. Modern devices capture images digitally, via the means of an image sensor. Image sensors turn visible light into electronic signals with information to determine the signal's organization when the picture is recreated. Digital cameras utilize an electronic shutter in most instances, since there is no need to keep a film from accidental exposure. The image captured is arranged in a grid pattern on the sensor, with each grid square called a pixel. Image sensors cannot recognize the color of light, only the level of light (or, more accurately, the number of photons in each pixel). To determine color, a filter is placed over each pixel that will only allow red, blue, or green photons to pass into the pixel. The most common type of filter is the Bayer filter, featured below. A pixel row is aligned with either a red and green, or blue and green alternating pattern. When the pixel patterns are viewed as a two-pixel by two-pixel square, the camera averages the four colors to create an estimate of the correct color. Any inaccuracy is measured as interpolation. These types of cameras use CCD, CMOS, or CID image sensing technology.

Images credit: Cambridge in Colour

CCD

Charge coupled devices (CCDs) are light-sensitive silicon chips that detect electrons excited by incoming light. They contain micro circuitry that transfers a detected signal along a row of discrete picture elements or pixels, scanning the image very rapidly. CCD cameras use two-dimensional CCD arrays with millions of pixels.

CMOS

Complementary metal oxide semiconductor (CMOS) image sensors operate at lower voltages than charged coupled devices (CCDs), reducing power consumption for portable applications. Analog and digital processing functions can be integrated readily onto a CMOS chip, reducing system package size and overall cost. With CMOS, each active pixel sensor cell has its own buffer amplifier and can be addressed and read individually. Commonly used cells have four transistors and a photo sensing element. Each cell has a transfer gate that separates the photo sensor from a capacitive floating diffusion and a reset gate between the floating diffusion and the power supply. Each cell also has a source-follower transistor to buffer the floating diffusion from readout-line capacitance, and a row-select gate to connect the cell to the readout line. All of the pixels in a column connect to a common sense-amplifier.

CID

Charge injection devices (CIDs) are photosensitive image sensors that are often implemented with large-scale integration technologies. CIDs can be randomly addressed, read non-destructively, and sub-scanned in a small region. CIDs are also less susceptible to charge overflows from bright pixels. To capture incident light, the pixel structure is contiguous with the maximum surface. This technique is also useful for sub-pixel measurements. CID cameras tend to be the least common type of camera.

CCD vs. CMOS

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Two of the more common types of image sensors, CCD and CMOS, use different methods to electronically archive images, as explained above. While CCDs were more popular during the early years of image sensor technology, developments in lithography have provided CMOS image sensors with an industry resurgence. Both CCD and CMOS offer high-quality recording. CMOS imagers offer more features on each sensor, lower power use, and a smaller footprint. In theory, CMOS imaging should be cheaper due to their ease of manufacture, but because of its additional production and development to create parity with a CCD device, CMOS imagers are often more expensive than CCD imagers. CCD imagers are less susceptible to noise, consume extremely more power than similarly-capable CMOS imagers, and offer more pixels. Their advanced development means that they are often implemented in less-expensive, low-power devices like cell phone and simple security cameras. CMOS imaging is often reserved for high-performance professional and industry camera-types.

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Digital vs. Film

There is an ongoing debate about the superiority of digital or film recording. This depends largely upon the application today, though it is suspected that digital video recording may make film videography obsolete eventually. In truth, there is no "better" medium, only a more suitable one.

For both digital and photochemical recording, the resolution of the images is largely dependent upon the quality of the camera lens, but other attributes affect picture quality as well. For digital cameras, they are the number of pixels used, the effect of the image filter, and the processing algorithm used to interpret sensor pixels to image pixels. For film, the area of the film used to record (35 mm, medium/large format) and the exposure determines the image resolution. Noise has a greater adverse effect on digital images than grain (parts of a film negative that were not properly exposed) does on filmed images.

Film creates a first-generation, authentic image. It is much easier to modify a digital file than a film roll. For the use of security or authentic expression, film is the preferable medium. Digital cameras are typically more expensive than comparable photochemical models, but it does not cost anything to develop digital recordings. It is much less expensive to archive digital files for future use, but considering the rapidly developing nature of computer technology, some digital formats may face obsoletion. Film, on the other hand, has existed for more than 150 years, and the already-extensive catalog of photochemical film archives ensures film's foreseeable future.

Video Camera Input

Video Quality

Lens

Regardless of the image capture method of the camera, the lens remains the most critical component regarding high-quality video capture. Lenses are meant to refine optical aberrations that occur when recording video, and there is a wide variety of camera lenses for various recording scenarios. Lenses come in several standard uses and mounting styles.

CS/C/S mount lenses

Image credit: Bosch Security; Wikipedia

C-mount lenses have a flange-back distance of 17.5 mm and are required for C-mount cameras. By comparison, CS-mount lenses have a flange-back distance of 12.5 mm. Because of their shorter back focal distance, CS-mount lenses cannot be used with C-mount cameras. C-mount features a diameter of 1" and a 32-thread per inch mounting thread.
CS-mount cameras can use both C-mount and CS-mount lenses; however, C-mount lenses require either a 5 mm adapter or adjustments to the CS-mount camera. Because of their shorter back focal distance, CS-mount lenses can be used only with CS-mount cameras. CS-mount features a diameter of 1" and a 32-thread per inch mounting thread.
S-mount is a smaller mounting configuration used in devices such as PC cameras and board-mounted cameras. S-mounts use a M12 x 0.5 threads.
An F-mount lens utilizes a bayonet-style mount standardized by Nikon.

f mount lens technical drawing

F lens mount dimensions

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Resolution

Resolution is the quality of the image when viewed. For digital cameras, resolution depends upon the number of pixels (horizontally and vertically). At a standard size, more pixels sharpen details on a photograph, but when enlarged the pixels become apparent in an effect called pixelization. This is similar to grain on film. Digital camera resolution is commonly measured in megapixels (MPx), with each mega representing one million square pixels. High-definition is regarded as a resolution of 1,280 x 720 pixels or more.

Film cameras tend to have a higher resolution than comparable digital cameras. Film cameras can have the equivalent of 50 megapixels or more if the camera uses medium or large format film. Film resolution is also dependent upon the exposure and the quality of grain the film uses.

Frame Rate

Measured in frames per second, this is the number of image captures. The human eye is capable of differentiating between 10 to 12 separate images per second; anything more and the rapidly changing images creates the illusion of movement. Frame rate of individual cameras is very much reliant upon the playback method and territory, or the specific application of the camera, both of which are covered in depth below.

Shutter Speed

This is responsible for the duration that light reaches the image sensor or film. It directly controls the exposure rate along with the aperture. Slower shutter speeds result in blurred motion capture.

Sensitivity

How well a camera captures images in low-light situations is measured in lux. It is a number that represents how sensitive a camera is, and a lower number lux sees better in less light. Color and monochrome cameras measure LUX differently.

Video Playback

No matter the event captured on camera, the video must be relayed to an audience. This can be done by the use of storage devices, such as VHS cassettes or data storage devices, or by electronic frequency transmissions.

Analog Television Systems

The National Television System Committee (NTSC) established protocols for wireless, analog television in the USA in 1941. NTSC has a lower resolution than PAL or SECAM, but has a faster frame rate to reduce flicker. NTSC broadcasts often results in reflections and multi-path signals being received. As such, color distortion in NTSC broadcasts is common. This can be diminished with directional antennas and tuners, but is always prevalent. Despite its defects, NTSC is the simplest analog signal to transmit and receive.
PAL stands for 'phase alternating line' and was developed to specifically compensate for the shortcomings of NTSC, notably color shifting due to poor broadcasting. The color information of a PAL transmission has its color signal reversed on every second line, which automatically corrects phase inaccuracies by not displaying them. Phase errors result in saturation changes, the average of which is less noticeable to the human eye than a poorer refresh rate, which is diminished by this color interpretation method. Variations of PAL have been produced to help refresh rates, as well as to track and fix phase inaccuracies better over long distances and rough terrain (such as in South America). The variations are largely compatible, but sound and color signals may be distorted. Other variations are reserved either for strictly broadcast, or strictly personal audio/video recording.
SECAM is based on PAL, but uses a different color processing source. SECAM was developed in France, and stands for 'Sequential Couleur Á Memoire'. Instead of color information being transmitted all at once, in SECAM the color differences are transmitted separately and in alternating fashion. The receiver must be able to remember the previous wave's color information so all colors can be displayed at once. This standard was developed and widely adopted for political reasons, and offers no particular advantage over PAL. Variations have been developed solely for VHS recording (ME), as well as for particular territories. Unlike PAL, these variations are not even slightly compatible amongst each other.

The map below indicates which countries observe each video standard.

Image credit: Wikimedia

Digital Television Systems

The Advanced Television Systems Committee (ATSC) developed a high-standard transmission signal to relay terrestrial digital video. This provides a resolution enhancement six times better than NTSC, though it is capable of transmitting NTSC video feeds as well. This quality enhancement led to the development of high-definition television (HDTV). In North America, permanent transitions from broadcast NTSC to ATSC have already begun.
DTMB(Digital Terrestrial Multimedia Broadcast) was developed in China to replace analog broadcasts beginning in 2008. DTMB has a clear depiction whether received on a mobile or fixed antenna, a notable upgrade of ATSC. DTMB is transmitted in encrypted signals, which allows for better frequency estimations and the broadcasting of analog, digital, and multimedia signals.
DVB-T(Digital Video Broadcast - Terrestrial) is a European based standard for the broadcast of highly-developed video feeds. The data is split in a large number of slow digital streams to adjacent carrier frequencies. Within countries, two broadcasts can be transmitted on the same frequency with the same information, provided they are time-aligned at the transmitter. This allows a higher number of programs to be transmitted compared to a multi-frequency network.
ISDB. This is a Japanese-invented standard for the transmission of digital television and radio. Integrated Services Digital Broadcasting is responsible for data transmission as well, enabling interactive programming. This type of transmission is called "hi-vision." Main differences of ISDB include the transmission of video through unused TV frequencies (even for radio), and the advent of rights management protection, which embeds data into programming to mechanically enforce copyrights.

Image credit: Wikimedia

Satellite Broadcasting

Using a telecommunications relay satellite, video feeds are transmitted to receivers positioned on the Earth, be it a parabolic satellite dish or a satellite tuner. This allows video to be transmitted to very remote locations, and also allows for the transference of data information. Satellite transmissions are similar to broadcast transmissions as they both use microwaves to provide video feeds. Broadcast transmissions can be reflected by mountains or the Earth's curvature, so satellite transmissions reduce the amount of obstacles that can interfere with the radio waves.

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Mobile Reception

Both digital and analog radio transmissions can be received on mobile display devices, like portable TVs, cell phones, and tablet computers. This is also true for transmissions using a satellite relay. In this instance, the compressed video information is interpreted by the device and then displayed. Most digital television broadcasts must be simultaneously transmitted in a different frequency and bandwidth range.

Wired Video

By providing videos via radio waves that are transmitted by wired connections, companies are able to offer subscription video content to customers. This is much more exclusive than over-the-air broadcast options, and in some jurisdictions is not subject to media restrictions. This type of video can be streamed directly to TVs or monitors.

Subscription-Based Video

Since the advent of digital television, video services are available in conjunction with internet subscriptions via the use of an Ethernet cable. Ethernet is a local area network (LAN) protocol that uses a bus or star typology and supports data transfer rates of 10 Mbps. Typically, a programming box or similar device is required to decipher the transferred electronic signals into the appropriate video/audio signals. To handle simultaneous demands, Ethernet uses carrier-sense multiple access/collision detection (CSMA/CD) to monitor network traffic.

Using coaxial cables to receive video broadcasts is becoming less popular, but is still prevalent. This method offers considerably less reviewing options, and does not support data transfer.

Source-to-Display Video

Instances that will use security cameras often have a closed circuit with a direct connection to a display. These videos are not publicly available or broadcast, though they may be recorded. The camera exchanges and transmits the feed instantly to the monitor. This method of video recording is also used for webcasts, where a camera is connected to an internet connection and the scene captured is available for viewers worldwide. This type of monitoring can be done wirelessly, but is more commonly hard-linked.

Stored Video

Options to store video as compressed files is a common way to create an exchangeable, mass produced chronicle. These devices require a separate machine to decode and provide the video feed directly to a monitor or through an output video cable. Some hardware video-storage formats such as VHS, Betamax, and DVD, are subject to the analog broadcast standards mentioned above (PAL, NTSC, SECAM), as well as regional restrictions emplaced by film distribution companies. Other video storage devices and formats, like data sticks (which will contain files like MPEG-2 or AVCHD) and Blu-ray Discs, are not subject to these international codecs and solely require a computer or player to display video.

Video Camera Features

Camera Mounting

Camera positioning is accomplished by the use of various types of mounts. Extendable and adjustable arms are common so cameras can be repositioned. Brackets are reserved for the most utilitarian of designs. Stands, such as unipods and tripods, offer a stable base while making the camera accessible to operators. Finally, many cameras come with the option of handheld or shoulder-mounted operation.

Security cameras are often mounted to a wall or ceiling by an adjustable arm bracket with standard hardware, providing pan and tilt functions. This eases their installation and increases their effectiveness. Security cameras can be mounted inconspicuously to record individuals surreptitiously, or prominently to deter misbehavior.

Industrial and scientific-based cameras are sometimes placed within a housing to protect the device from hostile environments. Industrial cameras are usually mounted with brackets or a separate type of mount that limits the device's movements. They also may provide resistance to mechanical vibration, which is common in manufacturing settings. Scientific cameras utilize whatever mount best suits the research, which may mean atypical placement. These mounts may apply by temporary means, may be exceptionally small, or the camera may not be mounted at all. Scientific cameras need the highest degree of flexibility among mounting options.

Entertainment cameras are valued for their aesthetic picture quality, and are almost always mounted on a stand of some type since they are attended. The stand may include wheels to provide object tracking, a suspension system to keep objects in focus, and other conveniences for the camera operator. Entertainment cameras also have unique mounts produced for them to capture irregular camera angles, or may have entire vehicles dedicated to their operation.

Camera jib; Tripod; Stainless steel bracket

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Camera Options

These specifications are often optional on video cameras, but depending upon the use they will enhance video quality.

Anti-Blooming: Saturation occurs when the light that is sensed exceeds a pixel's capacity to emit electrons. Excessive charge can bleed into adjacent pixels and cause bright spots or streaks to appear on the image, a condition known as blooming. Anti-blooming gates remove excessive charge and can significantly reduce blooming, but often at the cost of reduced sensitivity.	Anti-blooming before/after Image credit: Astrosurf
Auto-Lens: Auto-lens operation is a mode in which the lens iris automatically adjusts to maintain a predetermined level of light on the image pickup device. Cameras with auto-lens mode may also provide automatic lens focusing.
Board Mount: Camera optics are mounted directly on a printed circuit board (PCB). Often, PCBs are components of larger devices.
Cooled Sensor: Sensors are actively cooled by a Peltier element or other method. Cooling reduces "dark current" noise and improves sensitivity.	Image credit: Apstas
Dome: Cameras are enclosed in a protective dome made from materials such as acrylic or polycarbonate. Typically, these materials are optically-corrected for accurate image capture. This can create a tamper-proof housing common for security use.	Image credit: Jarrett Security
Gain Control: Automatic gain control (AGC) uses electronic circuitry to increase video signals in low-light conditions. This can introduce noise and, subsequently, graininess in the picture. Typically, AGC is disabled and specifications are presented with this feature turned off.
Gamma Correction: Gamma is the nonlinear relationship between the video signal level and the subsequent image element brightness. Gamma correction compensates for this nonlinearity in order to render the image true in color while providing intensity to the original object.
High Definition: High definition is a video standard that has higher picture sharpness, larger picture, more colors, and higher quality sound than regular video standards. The low-end threshold for HD video is considered 1,280 x 720 pixels.
High-Speed Camera: High-speed cameras record images at a higher frame rate than a typical camera. After recording, the images can be played back in slow-motion for close study of actions that may be ephemeral. This is particularly helpful for scientific study, but also has a wide variety of uses. Almost all modern high-speed cameras are digital in design and capable of recording over 1000 frames per second. Too many frames per second sacrifices area coverage while also producing a large, unwieldy file.	Image credit: Tony Rogers
Low-Light Camera: These are meant to be used in dark situations where an otherwise suitable camera will not reach an exposure level capable of capturing an image. The cameras contain image sensors that are exceptionally perceptive of subtle light sources.
Machine Vision Sensors: Machine vision sensors have the capability to analyze events captured by its camera, and alert operators or make decisions based on the information collected. These are also called smart cameras. If they are not uniform machines, the camera is typically linked to a computer interface via a FireWire, USB, or Ethernet connection.
Outdoor Rated: Outdoor-rated devices are designed to withstand outdoor temperature variations, rain, snow, and other weather conditions.
Pan/Tilt: These devices have integral or optional mounting features enabling side-to-side (pan) and up-and-down (tilt) controllable motion.
Progressive Scan: This is a CCD design that allows acquisition of both even and odd fields at the same time. Each pixel contains information from one complete frame. This technology allows high resolution without the use of a mechanical shutter. Progressive scan cameras are used for image acquisition of rapidly moving objects and accurate dimensional measurements.
Radiation Hardened: Devices are designed to withstand high levels of radiation. These cameras can be used in nuclear facility applications, or in scientific research that will expose the device to radiation.	Image credit: Thermo Scientific
Underwater Rated: Devices are designed to work when completely submerged in water. This feature can be added with an aftermarket housing.	Image credit: JW Fisers
Zoom: Cameras are designed with a feature that allows the device to closely focus on distant objects. Optical zooms offer better resolution than digital zooms.
3D Recording: The camera has the capability of recording images in three distinct directional planes. This is helpful for recording the depth of an object.	Image credit: Automation World

Video Camera Applications

Video cameras are very versatile, and as such, hundreds of styles with different features are available depending upon the application. Common industries served include broadcast/entertainment, industrial, scientific, and security.

Broadcast/entertainment

These types of cameras are useful for recording feature films, television shows and commercials, news broadcasts, sports events, web casts, and other types of motion capture that is meant for high-quality distribution. These cameras are characterized by a standardized frame rate to make their replay mechanisms compatible for use in a particular market's entertainment devices. These types of cameras almost always use film stock instead of digital frame rendering because of the lack of image noise when displayed at large dimensions. The most common film stock is 35 mm film. These types of cameras are sometimes used for unique recording and replay experiences, like for 3D films or IMAX theaters. These cameras will also have a sound recording unit, whether integral or part of a double-system recording.

Industrial

Industrial cameras are meant for troubleshooting, accident detection and investigation, counting, color mark recognition, flaw detection, and remote monitoring. The video quality of industrial-employed cameras is usually unimportant, provided it can accurately record and depict motion imaging. In fact, due to the environment of their use, some features may be purposefully left out to reduce costs. These types of cameras are usually of the digital quality. Common uses include; cameras mounted on plumbing snakes; those used to monitor conditions in a toxic environment; providing a digital readout or analysis of products on an assembly line; and those mounted on the bumper of cars that provide an in-dash feed of the car's reverse clearance. Line scan cameras can be helpful in quality assurance monitoring. Line scan cameras capture data in a single row of pixels, rather than in a a full display. This is helpful for monitoring a stream of moving materials, like on an assembly line.

Scientific

Cameras meant for scientific research and studies usually have some proprietary feature not incorporated into other camera styles in order to aid in a specific function of the research. This could include low-light settings, submersible components, extremely high frame rates, clean-room compatibility, recordings of different light spectrums, miniature sizes, or resistance to chemicals and wear. These cameras can be used to research everything from space exploration to molecular biology. These cameras usually have high connectivity, so the image feeds can be relayed to multiple recording devices, transmitters, or computers. Scientific cameras can often do away with a synced audio feed in order to cut down their adverse expense.

Security

Security cameras are prevalent in many urban areas, as well as locations where valuable goods may be kept. These types of cameras are designed to provide remote surveillance. These cameras are meant to protect both individuals and property from trespass. By centralizing multiple security feeds, a trained security officer can provide an ubiquitous guard, which is often an enough to discourage potential criminals. These cameras are also used to provide a reliable chronicle of events, which can be used to identify and prosecute alleged criminals. Security cameras are commonly produced with a tamperproof or protective housing. These cameras are also available with extremely small footprints or disguises to aid in espionage or covert surveillance. Audio feeds are optional with this type of camera, but some cameras placed in pugnacious locations can automatically detect gunshots and alert authorities.