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Learn More: Information Index
We have provided information below to help you know more about our products, services, and for your own personal enlightenment!
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 AGC (Automatic Gain Control)
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Automatic Gain Control. An electronic system found in many types of devices. Its purpose is to control the gain of a system in order to maintain adequate performance over a range of input signal levels. Also a circuit for automatically controlling amplifier gain in order to maintain a constant output voltage with a varying input voltage within a predetermined range of input-to-output variation.
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Aliasing |
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Phenomenon of interference which occurs when a signal being sampled contains frequencies that are higher than half the sampling frequency. Typically can be seen as ragged edges on horizontal lines.
In statistics, signal processing, and related disciplines, aliasing is an effect that causes different continuous signals to become indistinguishable (or aliases of one another) when sampled. When this happens, the original signal cannot be uniquely reconstructed from the sampled signal. Aliasing can take place either in time, temporal aliasing, or in space, spatial aliasing.
Aliasing is a major concern in the analog-to-digital conversion of video and audio signals: improper sampling of the analog signal will cause high-frequency components to be aliased with genuine low-frequency ones, and be incorrectly reconstructed as such during the subsequent digital-to-analog conversion. To prevent this problem, the signals must be appropriately filtered before sampling.
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Analog Video |
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Analog video is a video signal transferred by analog signal. It contains the luminance (brightness) and chrominance (color) of the image, which may be carried in separate channels, as in component video (YPbPr) and S-Video, or combined in one channel, as in composite video and RF connector.
Analog video is used in both consumer and professional applications. However, digital signal formats with higher quality have been adopted, including serial digital interface (SDI), Firewire (IEEE1394), DVI and HDMI.
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AWB (Automatic White Balance) |
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Normally our eyes compensate for lighting conditions with different color temperatures. A digital camera needs to find a reference point which represents white. It will then calculate all the other colors based on this white point. For instance, if a halogen light illuminates a white wall, the wall will have a yellow cast, while in fact it should be white. So if the camera knows the wall is supposed to be white, it will then compensate all the other colors in the scene accordingly.
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Most digital cameras feature automatic white balance whereby the camera looks at the overall color of the image and calculates the best-fit white balance. However these systems are often fooled especially if the scene is dominated by one color, say green, or if there is no natural white present in the scene as show in this example. |
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The auto white balance was unable to find a white reference, resulting in dull and artificial colors. |
The auto white balance got it right this time in a very similar scene because it could use the clouds as its white reference. |
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Most digital cameras also allow you to choose a white balance manually, typically sunlight, cloudy, fluorescent, incandescent etc. Prosumer and SLR digital cameras allow you to define your own white balance reference. Before making the actual shot, you can focus at an area in the scene which should be white or neutral gray, or at a white or gray target card. The camera will then use this reference when making the actual shot. |
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Blanking |
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The time during a raster scan retrace when the video signal is suppressed.
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BLC (Back Light Compensation) |
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If an excessive light is behind the center object, it is necessary to prevent the center object from becoming too dark. The cameras equipped with automatic back light compensation usually increase contrast locally in the center of the field of view to help avoid silhouetting.
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C-Mount |
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A Threaded mounting standard with flange back of 17.526mm, 1 inch in diameter, with 32 threads per inch.
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CCD (Charged Coupled Device) |
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A device which converts light into electrical energy in a CCD camera. A CCD consists of a two-dimensional matrix of many thousands of individual photosensitive elements. The camera optics focus the scene onto the matrix and each element generates a charge which varies with the intensity of the light it receives.
These charges are passed out, one by one, row by row, from a single connection to form a continuous analogue signal. This charge/discharge process is continuously repeated, normally at field rate (see also Progressive scan).
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CCD Iris |
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A special operating mode of the electronic shutter of a CCD camera. The shutter timing is automatically adjusted to maintain, as far as possible, the same video signal level from the camera irrespective of scene illumination. Allows the use of a fixed iris lens under variable lighting conditions.
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CCD Size |
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CCD sensor size, field of view, working distance, resolution and lens magnification are closely related characteristics of the camera. By using a smaller size CCD sensor, the field of view of the camera is decreased when using same lens. With smaller size CCD sensor, smaller details may be resolved from the same working distance.
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CCIR |
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CCIR stands for Committee Consultatif International Radiotelecommunique. This is the committee that recommended the standards for B/W television accepted by most of Europe, Australia and others. This is why when we refer to equipment that complies with the B/W TV standards we call it CCIR compatible.
European norm with 625 lines per frame. The vertical reading (field) frequency is 50 Hz.
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Color CCD Cameras |
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Digital color cameras generally use a Bayer mask over the CCD. Each square of four pixels has one filtered red, one blue, and two green (the human eye is more sensitive to green than either red or blue). The result of this is that luminance information is collected at every pixel, but the color resolution is lower than the luminance resolution.
Better color separation can be reached by three-CCD devices (3CCD) and a dichroic beam splitter prism, that splits the image into red, green and blue components. Each of the three CCDs is arranged to respond to a particular color. Some semi-professional digital video camcorders (and all professionals) use this technique.
Since a very-high-resolution CCD chips are very expensive, a 3CCD high-resolution still camera would be beyond the price range even of many professional photographers. There are some high-end still cameras that use a rotating color filter to achieve both color-fidelity and high-resolution. These multi-shot cameras are rare and can only photograph objects that are not moving.
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Color Coding |
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The transmission of color TV signal had to be solved in a way compatible with existing monochrome systems. That's why the color information is decomposed to its luminance Y and two color carrying signals R-Y and B-Y. All R, G and B image components in RGB color model.
Both color R-Y and B-Y components are modulated to the luminance Y signal. The color carrier frequency (used for demodulating) is read out from short color synchronizing impulse, «burst», presented during horizontal retrace. That's why color signal can be watched in monochrome TV (as b/w image, of course) and vice versa.
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Color Models |
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The purpose of a color model (also color space) is to facilitate the specification of colors in some standard, generally accepted way. In essence, a color model is specification of a 3-D coordinate system and a subspace within that system where each color is represented by a single point.
Monochrome (grayscale) The image information is represented only by means of intensity (brightness) of various bit depths: from 1-bit (black and white), over 8-bit (usual, 256 values of gray) to 10- or 12-bit. RGB An additive color format with Red, Green, and Blue base colors. Used for most display devices. All the three color components (R-G-B) may be expressed with a different bit depths: 3-3-2 (8-bit), 5-5-5 (15-bit), 5-6-5 (16-bit), 8-8-8 (24-bit). YUV, YIQ Color model used in commercial color TV broadcasting. The Y stands for intensity (luminance, brightness) and thus provides all the information required by the monochrome television. The other two components carry the color (chrominance) information. Various bit depths are possible again. HSI, HSB The color information is represented by Hue, Saturation, and Intensity (Brightness). CMY, CMYK Subtractive color model with Cyan, Magenta, Yellow (or also blacK) base colors. Used in the press industry.
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Compact PCI Bus |
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A PCI-based specification designed to address the needs of industrial users who need the PCI functionality in a more rugged package. Compact PCI offers high reliability, compact size, passive bacplane design, optimized cooling, and other features needed in industrial environment.
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Composite Video Signal |
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The combined picture signal, including vertical and horizontal blanking and synchronizing signals.
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CS-Mount |
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Similar to C-mount, but with 12.5 mm flange back. CS mount cameras can be converted to C-mount by using a 5 mm spacer element.
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Digital Zoom |
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Digital zoom is a method of decreasing (narrowing) the apparent angle of view of a digital photographic or video image. Digital zoom is accomplished by cropping an image down to a centered area with the same aspect ratio as the original, and usually also interpolating the result back up to the pixel dimensions of the original. It is accomplished electronically, without any adjustment of the camera's optics, and no optical resolution is gained in the process.
Because interpolation disturbs the original pixel layout of the image, as captured by the camera's image sensor, it is usually considered detrimental to image quality. The results of digital zoom are, however, sometimes superior to the results of manual cropping and resizing (interpolation) in post-production. This is because the camera may apply its interpolation before performing lossy image compression, thereby preserving small details that would otherwise be lost. For cameras that save images in a raw format, however, resizing in post-production will yield results equal or superior to digital zoom.
Some digital cameras rely entirely on digital zoom, lacking a real zoom lens, as on most camera phones. Other cameras do have a real zoom lens, but apply digital zoom automatically once its longest focal length has been reached. Professional cameras generally do not feature digital zoom.
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DMA (Direct Memory Access) |
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DMA is a feature of modern computers, that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards, and sound cards. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel.
Without DMA, using programmed input/output (PIO) mode, the CPU typically has to be occupied for the entire time it's performing a transfer. With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done. This is especially useful in real-time computing applications where not stalling behind concurrent operations is critical.
This is a method by which data can be transferred from a device (e.g. frame grabber) to the computer memory and vice versa without processor intervention. As a result, the processor is free for other tasks and the data transfer is faster.
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Donpisha |
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Donpisha means «immediate» in Japanese. A Donpisha shutter can be triggered to operate at a particular point in time and is used to shoot moving objects without a time delay. A fixed-position camera fitted with a Donpisha shutter can capture flicker-free images of fast moving objects.
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Dual Channel Operation |
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The major disadvantage of conventional CCD image sensors designed for interlaced scan video systems lies in their low vertical resolution (see Scanning). To reach both high vertical and dynamic resolution, one needs progressive scan CCD camera. A way to grab both odd and even fields at the same time is to use a dual channel camera (for example SONY XC-7500/8500CE or compatible).
Such a camera is equipped with two video outputs, each of them providing conventional interlaced image (this is allowed thanks to newly developed CCD design - the chip contains two horizontal shift registers, one outputting odd, the other even lines to accordant video output).
While one of the registers provide just odd and the other just even field data every 1/60 or 1/50 sec, the outputting image signal of both video outputs is compatible to common EIA or CCIR standards. However using appropriate frame grabber, they can be formed to one full frame (i.e. 625 or 525 lines) high resolution image (see image bellow). Thanks to the fact, that both fields were read at the same time (during a single exposure), no motion blur will be caused.
Following pictures of Sherlock Holmes may help you understand, how two outputs of a dual-channel camera can be mixed to acquire full frame image.
Original image |
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Video out 1
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Video out 2
(even field) |
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Video out 1 + 2
(mixed in frame grabber) |
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Dummy Bits |
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While the pixel clock timing differs from camera to camera, after providing image, sync and other necessary information, some output pixels with no meaningful information have to be added to the video signal to fill up horizontal line timing specified by a video norm. Such a «padding» pixels are called dummy bits.
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Effective Pixels |
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Those pixels in the CCD chip, which actually provide relevant image information to output video signal (i.e. total number of pixels minus optical black).
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EIA (RS170) |
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EIA stands for Electronics Industry Association, an association that created the standard for B/W television in the USA, Canada and Japan, where it is often referred to as RS-170, it being the recommendation code of the EIA proposal.
One image frame consists of 525 lines, vertical reading frequency is 59.9 Hz.
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Electronic Shutter |
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Employing an electronic shutter, the camera CCD integration time (exposure) can be controlled to less than 1/60 or 1/50 sec to reduce smear when capturing fast moving objects. All light sensitive sensors can be simultaneously erased (while darkened shift registers are not affected). Effective time of exposure (the time between erasing the sensor and start of the read out process) can thus be freely controlled by the camera electronics.
Note: Unless using a progressive scan camera, one shutter grabs just one half an image (one field). It means that in case of composing full frame image, both odd and even fields will be shifted each other (the odd field of real image is captured at a different point of time than the even field is).
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Ethernet |
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Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.
Ethernet has been standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, has become the most widespread wired LAN technology. It has been in use from the 1990s to the present, largely replacing competing LAN standards such as coaxial cable Ethernet, token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, has been used instead of Ethernet for many home and small office networks and in addition to Ethernet in larger installations.
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Ethernet (Crossover Cable) |
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An Ethernet crossover cable is a type of network cable used to connect computing devices together directly where they would normally be connected via a network switch, hub or router. For example, one would use a crossover cable to directly connect two personal computers via their network adapters.
Overview
The 10BASE-T and 100BASE-TX Ethernet standards use one wire pair for transmission in each direction. The Tx+ line from each device connects to the tip conductor and the Tx- line is connected to the ring. This requires that the transmit pair of each device be connected to the receive pair of the device on the other end. When a terminal device is connected to a switch or hub, this crossover is done internally in the latter. A standard straight through cable is used for this purpose where each pin of the connector on one end is connected to the corresponding pin on the other connector.
One terminal device may be connected directly to another without the use of a switch or hub, but in that case the crossover must be done externally in the cable. Since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. This is a crossover cable. A crossover cable must also be used to connect two internally crossed devices (e.g., two hubs) as the internal crossovers cancel each other out. This can also be accomplished by using a straight through cable in series with a modular crossover adapter.
Because the only difference between the TIA/EIA-568-B T568A and T568B pin/pair assignments are that pairs 2 and 3 are swapped, a crossover cable may be envisioned as a cable with one connector following T568A and the other T568B. Such a cable will work for 10BASE-T or 100BASE-TX. 1000BASE-T4 (Gigabit crossover) which uses all four pairs requires the other two pairs (1 and 4) to be swapped and also requires the solid/striped within each of those two pairs to be swapped.
Crossover cable pinouts
Two pairs crossed, two pairs uncrossed
10baseT/100baseTX crossover ( shown as T568A )
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Connection 1 pair
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Connection 2 pair
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Connection 1
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Connection 2
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Pins on plug face (jack is reversed)
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1
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3
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2
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white/green stripe
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white/orange stripe
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2
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3
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2
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green solid
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orange solid
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3
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2
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3
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white/orange stripe
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white/green stripe
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4
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1
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1
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blue solid
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blue solid
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5
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1
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1
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white/blue stripe
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white/blue stripe
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6
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2
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3
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orange solid
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green solid
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7
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4
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4
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white/brown stripe
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white/brown stripe
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8
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4
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4
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brown solid
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brown solid
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Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 (pins 4, 5, 7 and 8) remain un-crossed.
When a crossover cable is used to connect two routers or switches, some units, especially older ones, will work with two-pairs-crossed cables or four-pairs-crossed cables, but not both. Prudent technicians keep both kinds of crossover cables on hand.
Gigabit crossover
All four pairs crossed
10base-T/100base-TX/1000base-TX/T4 crossover (shown as T568B)
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Pin
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Connection 1 pair
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Connection 2 pair
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Connection 1
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Connection 2
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Pins on plug face (jack is reversed)
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1
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2
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3
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white/orange stripe
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white/green stripe
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2
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2
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3
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orange solid
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green solid
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3
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3
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2
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white/green stripe
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white/orange stripe
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4
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1
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4
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blue solid
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white/brown stripe
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5
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1
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4
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white/blue stripe
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brown solid
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6
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3
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2
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green solid
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orange solid
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7
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4
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1
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white/brown stripe
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blue solid
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8
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4
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1
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brown solid
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white/blue stripe
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It really does not matter if your Ethernet cables are wired as T568A or T568B, just so long as both ends follow the same wiring format. In other words it is just as valid to make a four-pair crossover using T568A, or a two pair crossover using T568B, as it is to wire them the way shown here.
Typical commercially available "pre-wired" cables can, (and often do), follow either format depending on who made them.
What this means is that you may discover that one manufacturer's cables are wired one way and another's the other way, yet both are "correct" and will work.
In either case, T568A or T568B, a normal (un-crossed) cable will have both ends wired according to the layout in the first connections column.
Other networking technologies
Other technologies use different pairs to transmit data, so crossover cables for them have different configurations to swap the transmit and receive pairs:
- Twisted pair Token ring uses T568B pairs 1 and 3 (the same as T568A pairs 1 and 2), so a crossover cable to connect two Token Ring interfaces must swap these pairs, connecting pins 4, 5, 3, and 6 to 3, 6, 4, and 5 respectively.
- A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2 respectively.
- A 56K DDS cable uses T568B pairs 02 and 04, so a crossover cable for these devices swaps those pairs (pins 01, 02, 07, and 08 are connected to 07, 08, 01, and 02 respectively).
Automatic crossover NICs
Almost all newer Ethernet network interface cards (NICs), switches and hubs automatically apply an internal crossover when necessary. This feature is known by various vendor-specific terms, e.g., Netgear calls it Auto uplink and trade, and other common vendor terms include Auto-MDI/MDI-X, Universal Cable Recognition and Auto Sensing. This eliminates the need for crossover cables, obsoletes the uplink/normal ports and manual selector switches found on many older hubs and switches, and greatly reduces installation errors, especially by non-technical users.
Automatic MDI/MDI-X capability is specified in the 1000BASE-T standard, so straight-through cables will work in almost all cases. But it is optional, so a crossover cable is needed if neither of the connected devices supports it, or the function has been disabled. Unlike the crossover cable described above, with only pairs 2 and 3 swapped, a 1000BASE-T crossover cable also has pairs 1 and 4 swapped.
Networks created using crossover cables
Example crossover network configuration
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192.168.0.1 |
192.168.0.2 |
| Subnet Mask |
255.255.255.0 |
| Default gateway |
192.168.0.2 |
192.168.0.1 |
A two-computer network, sometimes called a peer-to-peer network, can be created using a crossover Ethernet cable. Like any other network, each computer needs to be assigned a unique IP address. The other machine, in turn, can act as the default gateway (or router), mirroring the same address.
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Ethernet (Power Over Ethernet) |
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Power over Ethernet or PoE technology describes a system to transmit electrical power, along with data, to remote devices over standard twisted-pair cable in an Ethernet network. This technology is useful for powering IP telephones, wireless LAN access points, webcams, Ethernet hubs, embedded computers, and other appliances where it would be inconvenient, expensive (mains wiring must often be done by qualified and\or licensed electricians for legal or insurance reasons) or infeasible to supply power separately. The technology is somewhat comparable to POTS telephones, which also receive power and data (although analog) through the same cable. It works with an unmodified Ethernet cabling infrastructure.
There are several general terms used to describe this feature. The terms Power over Ethernet (PoE), Power over LAN (PoL), and Inline Power are synonymous terms used to describe the powering of attached devices via Ethernet ports.
There are several PoE implementations, including ad-hoc techniques, but supplying power over Ethernet according to the IEEE standard is strongly recommended.
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Field |
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One of the two equal but vertically separated parts into which a common video (interlaced) frame is divided in an interlaced system of scanning. The odd field consists of 1-3-5... lines, the even one of 2-4-6... lines.
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FIT CCD (Frame Interline Transfer) |
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The areas for exposing and storing are arranged in two big sections. The whole CCD surface (light sensitive and darkened shift registers) has about twice the size of the IT sensor. For a FIT sensor, the shifting registers are light sensitive. Within 500 µs, all charges are pushed into the darkened shift register by the transport register. From here, the charges are forwarded into the vertical read out register and are eventually read out serially within at a rate of less than 64 µs per line. If an IT CCD is grossly over-exposed, it is possible for charges to leak from the sensing elements into the adjacent registers (see Vertical Smear). In the sensor this is avoided by very rapidly transferring the contents of the vertical registers into a separate storage area, fabricated as part of the CCD. Read-out then continues at the normal rate. A FIT CCD is a complex and therefore expensive semiconductor structure, but offers high performance.
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Flange Back |
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The distance between a lens flange surface and the surface of a CCD chip. The flange back value is mount standard specific.
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Focal Length Calculator |
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This calculator requires the use of Javascript
enabled and capable browsers. This calculator finds the maximum lens
focal length and the appropriate minimum field of view, based on data
entered for the CCD
size, the distance from the lens to the object, and the maximum size of
the target object to be imaged. Select the CCD size from the options in
the drop box or select CUSTOM. If CUSTOM is selected, enter the numeric
value for the custom CCD size in millimeters. The standard default is
1/4 inch and the custom default is 10mm. Enter the numeric value for
the distance from the lens to the target object and select the
designation for distance from the drop box. The combined defaults yield
10 meters. Enter the numeric value for the maximum size of the target
object also select the designation for the size, from the drop box. The
default is again, 10 meters. All calculations take place at each entry.
You may however, click Calculate to update if needed. You may click
Clear Values to begin again. The result is displayed as a very accurate
rendering of the maximum focal length, in millimeters, and the minimum
field of view in degrees.
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Focus |
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The point at which rays of light converge for any given point on the object in the image. Also called the focal point. Auto focus The ability of an imaging system to control the focus of the lens to obtain the sharpest image on the detector.
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Frame |
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The total area, occupied by the television picture, which is scanned while the picture signal is not blanked. In conventional interlaced systems, the frame consists of two fields.
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Frame Grabber |
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Computer card that samples and digitizes analog video signals so that the information may be processed, stored, or operated on by the computer. It is also called image acquisition or image capture board.
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Gain |
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An increase in voltage or power, usually expressed in decibels.
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HAD CCD |
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Abbreviation of Hole Accumulated Diode . A semiconductor structure developed for Sony third-generation CCDs. It permits a considerable increase in pixel count and improves overload and vertical smear characteristics.
Hyper HAD A further development of the HAD structure in which individual micro lenses are positioned over each photosensitive element.
IT sensor without lenses:
IT sensor with on-chip lenses:
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Image Characteristics |
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Color hue A color attribute associated with the dominant wavelength in a mixture of light waves. It represents the dominant color as perceived by an observer (e.g. red, yellow,...). Saturation Saturation refers to the relative purity or the amount of white light mixed with a hue. The pure spectrum colors are fully saturated. The white, black and gray colors have zero saturation. Brightness The attribute of visual perception in accordance with which area appear to emit more or less light. Contrast The difference of light intensity between two adjacent regions in the image. Contrast is usually expressed as the difference between the lightest ad darkest portion of the image.
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Image Resolution |
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Image resolution describes the detail an image holds. The term applies equally to digital images, film images, and other types of images. Higher resolution means more image detail. The resolution of digital images can be described in many different ways.
Pixel resolution
The term resolution is often used as a pixel count in digital imaging, even though American, Japanese, and international standards specify that it should not be so used, at least in the digital camera field. An image of N pixels high by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as resolution, the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 640 by 480. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.
Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).
Spatial resolution
The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in pixels per inch (ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image.
The spatial resolution of computer monitors is generally 72 to 100 lines per inch, corresponding to pixel resolutions of 72 to 100 ppi.
In Geospatial Information Systems (GIS), Spatial Resolution commonly refers to the Ground Sample Distance (GSD) of an image. Or in other words, how much of the earth's surface a single pixel covers.
Spectral resolution
Color images distinguish light of different spectrum. Multi-spectral images resolve even finer differences of spectrum or wavelength than is needed to reproduce color. That is, they can have higher spectral resolution.
Temporal resolution
Movie cameras and high-speed cameras can resolve events at different points in time. The time resolution used for movies is usually 15 to 30 frames per second (fps), while high-speed cameras may resolve 100 to 1000 fps, or even more.
Radiometric resolution
Radiometric resolution determines how finely a system can represent or distinguish differences of intensity, and is usually expressed as a number of levels or a number of bits, for example 8 bits or 256 levels which is typical of computer image files. The higher the radiometric resolution, the better subtle differences of intensity or reflectivity can be represented, at least in theory. In practice, the effective radiometric resolution is typically limited by the noise level, rather than by the number of bits of representation.
Resolution in various media
- DVDs are 720 by 480 (NTSC) pixels or 720 by 576 (PAL) pixels
- High definition television is 1920 by 1080 pixels or 1280 by 720 pixels
- 35 mm film is scanned for release on DVD at 1080 or 2000 lines as of 2005.
- 35 mm original camera negative motion picture film can resolve up to 6,000 lines.
- 35 mm projection positive motion picture film has about 2,000 lines which results from the analogue printing from the camera negative of an interpositive, and possibly an internegative, then a projection positive.
- Sequences from newer films are scanned at 2,000, 4,000 or even 8,000 columns (line measured the other directions), called 2K, 4K and 8K, for quality visual effects editing on computers.
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Industrial PCI Bus |
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Another industrial solution for PCI-based systems.
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Infrared (Night Vision) |
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Infrared is used in night-vision equipment when there is insufficient visible light to see an object. In infrared photography, infrared filters are used to capture the near-infrared spectrum. Digital cameras often use infrared blockers. Cheaper digital cameras and some camera phones which do not have appropriate filters can "see" near-infrared, appearing as a bright white colour (try pointing a TV remote at your digital camera). This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image. There is also a technique called 'T-ray' imaging, which is imaging using far infrared or terahertz radiation. Lack of bright sources makes terahertz photography technically more challenging than most other infrared imaging techniques. Recently T-ray imaging has been of considerable interest due to a number of new developments such as terahertz time-domain spectroscopy.
Simple infrared sensors were used by British, American and German forces in the Second World War as night vision aids for snipers.
Smoke is more transparent to infrared than to visible light, so firefighters use infrared imaging equipment when working in smoke-filled areas.
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Infrared (Thermography) |
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Infrared thermography is a non-contact, non-destructive test method that utilizes a thermal imager to detect, display and record thermal patterns and temperatures across the surface of an object. Infrared thermography may be applied to any situation where knowledge of thermal profiles and temperatures will provide meaningful data about a system, object or process. Thermography is widely used in industry for predictive maintenance, condition assessment, quality assurance, and forensic investigations of electrical, mechanical and structural systems. Other applications include, but are not limited to: law enforcement, firefighting, search and rescue, and medical and veterinary sciences.
Aside from test equipment, training is the most important investment a company will make in an infrared inspection program. Advances in technology have provided infrared equipment that is user-friendly; however, infrared thermography is not a "simply point and shoot" technology. In addition to understanding the object or system being inspected, thermographers must also understand common error sources that can influence observed thermal data. Typically,infrared training courses should cover the topics of infrared theory, heat transfer concepts, equipment selection and operation, how to eliminate or overcome common error sources, and specific applications. Training courses from independent training companies are preferred since they are not biased toward a single brand or type of equipment.
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Iris |
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An aperture of adjustable size, normally forming part of the camera lens, which is used to control the amount of light reaching the CCD. Iris control may be either manual or automatic, depending on the application / type of camera.
Auto iris lens A lens that are able to adjust the amount of light reaching the imager automatically, by changing its iris aperture.
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IT CCD: Interline Transfer |
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The sensor is divided into areas for exposing and areas for storing. In the IT CCD these two components are ordered in the shape of stripes. Via a link between the sensor surface and the vertical shift register, the created electrical charge is taken over in parallel by the darkened shift register cell (storing area). This process takes 2.5 µs. Now the electrical charge in the vertical shift registers is pushed line by line into the horizontal shift register (read out register). From there it is read out serially according to the frequency defined by the video norm. The registers are shielded from incident light so that the read-out is performed without corruption.
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Jitter |
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Small, rapid variations in a waveform due to mechanical disturbances or to changes in the characteristic of components. They are caused by variations in supply voltages, imperfect synchronizing signals, circuits,etc.
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LCD (Liquid Crystal Display) |
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A liquid crystal display (commonly abbreviated LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices.
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Lens |
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A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical), that they serve to converge or diverge the transmitted rays of an object, thus forming a real or virtual image of that object. Often used in groups for light control and focusing.
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Lens Mount |
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A lens mount is an interface —mechanical and often also electrical —between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the single lens reflex type or any movie camera of 16 mm or higher gauge. A lens mount is also found on a lens accessory like a teleconverter or an extension tube, which goes in between a lens and a camera.
There are several standards for mounting lenses to a camera, and those few are listed below:
C-Mount
CS-Mount
NF-Mount
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Mbps: Megabit per second |
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A megabit per second (abbreviated as Mbps, Mbit/s, or mbps) is a unit of data transfer rates equal to 1,000,000 bits per second (this equals 1,000 kilobits per second). Because there are 8 bits in a byte, a transfer speed of 8 megabits per second (8 Mbps) is equivalent to 1,000,000 bytes per second (approximately 976 KiB/s).
Usage Examples
The bandwidth of consumer broadband internet services is often rated in Mbps.
Data streams representing compressed video are often measured in Mbit/s:
- 2 Mbit/s — VHS quality
- 8 Mbit/s — DVD quality
- 55 Mbit/s — HDTV quality
More specific examples found on standard Comcast digital streams (transmitted in MPEG2 format):
- 2-3 Mbit/s — a low-definition digital channel with a very clean signal
- 5-6 Mbit/s — a low-definition digital channel with a digitized ("dirty") analog signal (or just an analog channel)
- 8-12 Mbit/s — a medium to high-definition digital channel with DVD quality data (equivalent to HBO-HD)
- 18-20 Mbit/s — a high-definition digital channel at 1080i (equivalent to Discovery HD)
Another example, Network cards and cables are typically available in 10/100/1000 Mbit/s. This means they can support a transfer rate of 10 or 100 or 1000 Mbit/s.
Interface and device speeds
| Interface |
Megabits per second
[Mbit/s] |
Megabytes per second
[MB/s] |
| USB, Low speed |
1.5 Mbit/s |
0.18 MB/s |
| USB, Full speed |
12 Mbit/s |
1.5 MB/s |
| USB, Hi speed |
480 Mbit/s |
60 MB/s |
| Firewire 400 (IEEE 1394) |
400 Mbit/s |
50 MB/s |
| Firewire 800 (IEEE 1394b) |
800 Mbit/s |
100 MB/s |
| CD-ROM, 1x |
1.2 Mbit/s |
0.15 MB/s |
| CD-ROM, 52x |
62.4 Mbit/s |
7.8 MB/s |
| DVD-ROM, 1x |
11.1 Mbit/s |
1.3 MB/s |
| DVD-ROM, 16x |
177.3 Mbit/s |
21.1 MB/s |
| BD-ROM, 1x |
54.0 Mbit/s |
6.75 MB/s |
| SATA II |
2400 Mbit/s |
300 MB/s |
| SATA III |
8000 Mbit/s |
1000 MB/s |
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Minimum Illumination |
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Minimum amount of light (in luxes) that is needed to generate reasonable image signal in accordant CCD chip.
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Monochrome |
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Monochrome comes from the two Greek words mono (ěoíď, meaning "only"), and chroma (÷ńůěá, meaning "surface" or "the color of the skin"). A monochromatic object has a single color.
In physics, the word is used more generally to refer to electromagnetic radiation of a single wavelength. In the physical sense, no real source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration. Even sources such as lasers have some narrow range of wavelengths (known as the linewidth or bandwidth of the source) within which they operate.
For an image, the term monochrome is usually taken to mean the same as black-and-white or, more likely, grayscale, but may also be used to refer to other combinations containing only two colors, such as green-and-white or green-and-black. It may also refer to sepia or cyanotype images. In computing, monochrome has two meanings:
it may mean having only one color which is either on or off,
allowing shades of that color, although the latter is more correctly known as grayscale.
A monochrome computer display is able to display only a single color, often green, amber, red or white, and often also shades of that color.
The monochromatic scheme should be used with caution when designing a space. Certain monochromatic color concepts will appear rather monotonous, and some variety in the intensities, textures and forms should be used to give life to the interior.
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Motion JPEG (M-JPEG) |
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Motion JPEG (M-JPEG) is an informal name for multimedia formats where each video frame or interlaced field of a digital video sequence is separately compressed as a JPEG image. It is often used in mobile appliances such as digital cameras.
M-JPEG is frequently used in non-linear video editing systems. Reproduction of this format at full speed requires fast JPEG decoding capability.
M-JPEG is also commonly used by IP based video cameras via HTTP streams by using the multipart/x-mixed-replace content type. This separates each image into individual HTTP replies on a specified marker. Mozilla based browsers like Netscape and Firefox have native support for viewing these streams whereas Internet Explorer does not.
The PlayStation game console has integrated M-JPEG decompression hardware in order to play in-game FMV sequences. Nintendo's Wii game console can play M-JPEG-encoded videos off an SD card using its Photo Channel. The SanDisk Sansa digital audio player plays short M-JPEG videos.
Motion JPEG uses intraframe coding technology that is very similar in technology to the I-frame part of video coding standards such as MPEG-1 and MPEG-2, but does not use interframe prediction. The lack of use of interframe prediction results in a loss of compression capability, but eases video editing, since simple edits can be performed at any frame when all frames are I-frames. Video coding formats such as MPEG-2 can also be used in such an I-frame only fashion to provide similar compression capability and similar ease of editing features.
Using only intraframe coding technology also makes the degree of compression capability independent of the amount of motion in the scene, since temporal prediction is not being used. (Using temporal prediction can ordinarily substantially improve video compression capability, but makes the compression performance dependent on how well the motion compensation performs for the scene content.) Because of this, it is used in surveillance cameras which only take one frame per second, in which time there could be large amounts of change.
For Quicktime formats, Apple have defined two types of coding: MJPEG-A and MJPEG-B. MJPEG-B no longer retains valid JPEG Interchange Files within it, hence it is not possible to take a frame into a JPEG file without slightly modifying the headers.
The bitrate falls between uncompressed formats (like RGB, compression 1:1, and YCbCr, compression 1:1.5 to 1:2.5) and MPEG (1:100). Data rates in the range of 29 Mbit/s are very high quality, but also result in comparatively large file sizes.
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Multiplexer (MUX) |
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A multiplexer or mux (occasionally the term muldex is also found, for a combination multiplexer-demultiplexer) is a device that selects one of many data-sources and outputs that source into a single channel.
A demultiplexer (or demux) is a device taking a single input that selects one of many data-output-lines and connects the single input to the selected output line. A multiplexer is often used with a complementary demultiplexer on the receiving end.
In electronics, multiplexers function as multiple-input, single-output switches. A multiplexer has multiple inputs and a selector that connects a specific input to the single output. The schematic symbol for a multiplexer is an isosceles trapezoid with the longer parallel side containing the input pins and the short parallel side containing the output pin. The schematic on the right shows a 2-to-1 multiplexer on the left and an equivalent switch on the right. The sel wire connects the desired input to the output.
In digital signal processing (DSP), the multiplexer takes several separate digital data streams and combines them together into one data stream of a higher data rate. This allows multiple data streams to be carried from one place to another over one physical link, which saves cost.
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Nanometers (nm) |
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The metre or meter (symbol: m) is the fundamental unit of length in the International System of Units (SI). The metre was originally defined by a prototype object meant to represent 1⁄10 000 000 the distance between the poles and the Equator. Today, it is defined as 1⁄299 792 458 of a light-second.
Because it is the base unit of length in the SI, all SI units which involve length (such as area or speed) are defined relative to the metre. Additionally, due to the metre being the only SI base unit used to measure a vector (i.e. displacement), all vector units are defined relative to the metre. However, decimal multiples and submultiples of the metre— such as kilometre (1000 metres) and centimetre (0.01 metres)— can be formed by adding SI prefixes to metre (see the table below).
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NF-Mount |
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Mount standard with flange back of 12 mm developed by Sony. The lens mount can also be converted into a C-mount.
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Noise (Video) |
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Noise in analog video and television is perceived as a random dot pattern that is superimposed on the picture as a result of electronic noise and radiated electromagnetic noise picked up by the receiver's antenna – it is the "snow" that is seen with poor analog television reception or on VHS tapes.
When there is no transmission, the "snow" is mostly due to thermal noise from the device itself, stray electromagnetic fields from other electric devices, and cosmic background radiation that are being interpreted as a luminance signal.
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Non-Composite Video Signal |
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A signal containing visual information and horizontal and vertical blanking but not sync.
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NTSC |
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NTSC (National Television Standards Committee) is a standard used in North America and Japan. It has the ability to display up to 525 lines of resolution.
Used for color coding in systems based on EIA (RS170) video norm. Because the accessible bandwidth for color information is too narrow, just one signal should be used for color coding. Nevertheless transmission of two R-Y and B-Y components is necessary. The modulation is thus performed as a quadrature modulation - one component is modulated by amplitude, the other by phase of the color carrying signal.
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Optical Black |
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Number of pixels presented in the CCD chip but not in video output. These pixels (which lie by the chip borders) are optically overshadowed, i.e. no light can affect them.
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PAL |
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PAL (Phase Alternating Line), a standard used almost everywhere else in the world, has the ability to display 625 lines of resolution.
A modification of NTSC system used with the CCIR video norm. As the phase of the color carrier is 180 ° shifted every image line, the PAL (Phase Alternated Lines) system is not so sensitive to the color signal phase distortion. On the other hand it needs more complicated technical equipment. It also provides lower vertical resolution than NTSC system.
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Partial Scanning |
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In the partial scanning mode, the camera reads out only a limited number of lines, not the entire CCD sensor. The vertical resolution is thus decreased, but the output frame rate is accordingly increased. The partial scanning mode is used in applications requiring a high speed camera output, when resolution is not a critical parameter.
The following image shows an example of partial scanning chip. Besides the effective lines (containing a real video information), one has to count with the vertical blanking period same for all scanning modes.
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PCI Bus |
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PCI local bus is a standard used in today's computers for high speed component-to-component connection. It offers features like bus mastering, DMA, data bursting, scale ability, plug&play support. Thanks to its high performance (up to 132 MB/s throughput), the modern frame grabbers can offer real-time transfer of video data to the main and video memory.
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Pixel |
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Short for Picture Element . A pixel is the smallest area of a television picture capable of being delineated by an electrical signal passed through the system of part thereof. The number of picture elements (pixels) in a complete picture, and their geometric characteristics of vertical height and horizontal width, provide information on the total amount of detail which the raster can display and on the sharpness of the detail, respectively.
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Pixel Binning |
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Pixel binning technology used by some CCD cameras lies in combining adjacent pixels with the goal of faster output when needed. For example when pixels are vertically combined to pairs, two times higher frame rate may be archived (with 1/2 vertical resolution).
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Point-to-Multipoint |
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Point-to-multipoint communication is a term that is used in the telecommunications field which refers to communication which is accomplished via a specific and distinct type of multipoint connection, providing multiple paths from a single location to multiple locations.
Point-to-multipoint is often abbreviated as P2MP or PTMP.
Point-to-multipoint telecommunications is most typically used in wireless Internet and IP Telephony via gigahertz radio frequencies. P2MP systems have been designed both as single and bi-directional systems. A central antenna or antenna array broadcasts to several receiving antennae and the system uses a form of Time-division Multiplexing to allow for the back-channel traffic.
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Restart/Reset |
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The Restart/Reset function is a feature of some CCD cameras, that enables to start new image integration at any time (specified by external reset pulse) and only those pictures at the specified timing to be recorded in the picture memory. The major difference from a trigger shutter mode is that Restart/Reset function is not a shutter mode, the integration time is fixed: 1/60 or 1/50 sec, depending on the video norm.
The common mode of the Restart/Reset function causes a new integration start after supplying the reset pulse (the pulse resets internal vertical sync timing of the camera). While one field reading time (1/60 or 1/50 sec) is needed for the charge integration, irrelevant signal is output during this interval. Shooting information accumulated within the first field after the reset is output in the second field and so on (in frame integration interlace mode 1/30 or 1/25 sec the Restart/Reset requires two vertical sync pulses for integration, meaningful signal is output since the third field).
An other kind of the Restart/Reset function (which requires further internal setting in the camera) assures the slow speed shutter operation. In this mode, the first external trigger pulse resets the camera vertical sync timing. The camera is kept on standby for a prolonged period of time after this, integrating new image. Nothing but noise is output from the camera now. The second trigger pulse ends image integration; all the signals integrated since the previous reset are taken out as standard video within next two fields. This operation may be used for capturing dark objects.
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RS-232 |
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In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24.
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RS-422 |
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American national standard ANSI/TIA/EIA-422-B (formerly RS-422) and its international equivalent ITU-T Recommendation V.11 (also known as X.27), are technical standards that specify the "electrical characteristics of the balanced voltage digital interface circuit". It provides for data transmission, using balanced or differential signaling, with unidirectional/non-reversible, terminated or non-terminated transmission lines, point to point, or multi-drop. In contrast to RS-485 (which is multi-point instead of multi-drop) EIA-422/V.11 does not allow multiple drivers but only multiple receivers.
The current title of the ANSI standard is TIA-422 Electrical Characteristics of Balanced Voltage Differential Interface Circuits and is now in revision B, published in May 1994, and was reaffirmed by the Telecommunications Industry Association in 2005.
Several key advantages offered by this standard include the differential receiver, a differential driver and data rates as high as 10 megabaud at 12 metres (40 ft). The specification itself does not set an upper limit on data rate, but rather shows how signal rate degrades with cable length. The figure plotting this stops at 10 Mbit/s.
EIA-422 only specifies the electrical signaling characteristics of a single balanced signal. Protocols and pin assignments are defined in other specifications. The mechanical connections for this interface are specified by EIA-530 (DB-25 connector) or EIA-449 (DC-37 connector), however devices exist which have 4 screw-posts to implement the transmit and receive pair only. The maximum cable length is 1200 m. Maximum data rates are 10 Mbit/s at 12 m or 100 kbit/s at 1200 m. EIA-422 cannot implement a truly multi-point communications network (such as with EIA-485), however one driver can be connected to up to ten receivers.
A common use of EIA-422 is for RS-232 extenders. In video editing studios it is used to link control signals for all video and audio players/recorders to a central control board. Also, an RS-232-compatible variant of RS-422 using a mini-DIN-8 connector was widely used on Macintosh hardware until it was replaced by Intel's Universal Serial Bus on the iMac in 1998.
EIA-422 can interoperate with interfaces designed to MIL-STD-188-114B, but they are not identical. EIA-422 uses a nominal 0 to 5 Volt signal while MIL-STD-188-114B uses a signal symmetric about 0 V. However the tolerance for common mode voltage in both specifications allows them to interoperate. Care must be taken with the termination network.
EIA-423 is a similar specification for unbalanced signaling.
When used in relation to communciations wiring, RS-422 wiring refers to cable made of 2 sets of twisted pair, often with each pair being shielded, and a ground wire. While a double pair cable may be practical for many RS-422 applications, the RS-422 specification only defines one signal path and does not assign any function to it. Any complete cable assembly (i.e. with connectors) should be labeled with the specification that defined the signal function and mechanical layout of the connector, such as RS-449.
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S-Video |
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Separate video, abbreviated S-Video and also known as Y/C (or erroneously, S-VHS and "super video") is an analog video signal that carries the video data as two separate signals (brightness and color), unlike composite video which carries the entire set of signals in one package. S-Video works in 480i or 576i resolution.
The luminance (Y; greyscale) signal and modulated chrominance (C; colour) information are carried on separate synchronized signal/ground pairs.
In composite video, the luminance signal is low-pass filtered to prevent crosstalk between high-frequency luminance information and the color subcarrier. S-Video separates the two, and detrimental low-pass filtering is unnecessary. This increases bandwidth for the luminance information, and also subdues the color crosstalk problem. The infamous dot crawl is eliminated. This means that S-Video leaves more information from the original video intact, thus having a much-improved image reproduction compared to composite video.
Due to the separation of the video into brightness and colour components, S-Video is sometimes considered a type of component video signal, although it is also the most inferior of them, quality-wise, being far surpassed by the more complex component video schemes (like RGB). What differentiates S-Video from these higher component video schemes is that S-Video carries the colour information as one signal. This means that the colours have to be encoded in some way, and as such NTSC, PAL and SECAM signals are all decidedly different through S-Video. Thus, for full compatibility the used devices not only have to be S-Video compatible but also compatible in terms of colour encoding.
Y/C signal comparison between composite (a) and S-video (b).
Connector
Today, S-Video signals are generally connected using 4 pin mini-DIN connectors using a 75 ohm termination impedance. Apart from the impedance requirement, these cables are equivalent to regular mini-DIN cables (like Apple's ADB); these cables can be used for S-Video transfer if no other cable is available, but picture quality may not be as good.
The mini-DIN pins, being weak, sometimes bend. This can result in the loss of color, or other corruption (or loss) in the signal. A bent pin can be forced back into shape, but this carries the risk of further damage, or even the pin breaking off.
Before the mini-DIN plug became standard, S-Video signals were often carried through different types of plugs. For example, the Commodore 64 home computer of the 1980s, one of the first widely available devices to feature S-Video output, used an 8-pin DIN connector on the computer end and a pair of RCA plugs on the monitor end. The S-Video connector is the most common video-out connector on laptop computers, however many devices with S-Video outputs also have composite outputs.
S-Video can be transferred through SCART connections as well. However, it was not part of the original SCART standard, and not every SCART-compatible device supports it for this reason. Also, S-Video and RGB are mutually exclusive through SCART, due to the S-Video implementation using the pins allocated for RGB. Most SCART-equipped televisions or VCRs (and almost all of the older ones) do not actually support S-Video, resulting in a black-and-white picture if attempted to use, as only the luminance signal portion is used. Black-and-white picture in itself can also be a sign of incompatible colour encoding, for example NTSC material viewed through a PAL-only device.
A hack exists to possibly attain color on devices that do not support S-Video through SCART. This is done via joining the pins 15 and 20 in the SCART connector (either directly or using a 470pF capacitor), and may not yield optimal results.
*Key* - 1: GND: Ground (Y) - 2: GND: Ground (C) - 3: Y: Intensity (Luminance) - 4: C: Color (Chrominance)
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SECAM |
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SECAM (Sequential Color Memory) is used sparingly around the world and can be found in France, parts of Greece, Eastern Europe, Russia, Africa and a few other parts of the world. However, any SECAM country can display PAL tapes in full color, but not all PAL countries can display all SECAM tapes in color. Only if they are true SECAM and not MESECAM can those VCR's display SECAM.
Technical Details:
Just as the other color standards adopted for broadcast usage over the world, SECAM is a compatible standard, which means that monochrome television receivers predating its introduction are still able to show the programs, although only in black and white. Because of this compatibility requirement, color standards add a second signal to the basic monochrome signal, and this signal carries the color information, called chrominance or C in short, while the black and white information is called the luminance (Y in short). Old TV receivers only see the luminance, while color receivers process both signals.
Additionally, for compatibility, it is required to use no more bandwidth than the monochrome signal alone; the color signal has to be somehow inserted into the monochrome signal, without disturbing it. This insertion is possible because the spectrum of the monochrome TV signal is not continuous, hence empty space exists which can be utilized. This lack of continuity results from the discrete nature of the signal, which is divided into frames and lines. Analogue color systems differ by the way in which empty space is used. In all cases, the color signal is inserted at the end of the spectrum of the monochrome signal.
In order to be able to separate the color signal from the monochrome one in the receiver, a fixed frequency sub carrier has to be used, this sub carrier being modulated by the color signal.
The color space is three dimensional by the nature of the human vision, so after subtracting the luminance, which is carried by the base signal, the color sub carrier still has to carry a two dimensional signal. Typically the red (R) and the blue (B) information are carried because their signal difference with luminance (R-Y and B-Y) is stronger than that of green (G-Y).
SECAM differs from the other color systems by the way the R-Y and B-Y signals are carried.
First, SECAM uses frequency modulation to encode chrominance information on the sub carrier.
Second, instead of transmitting the red and blue information together, it only sends one of them at a time, and uses the information about the other color from the preceding line. It uses a delay line, an analog memory device, for storing one line of color information. This justifies the "Sequential, With Memory" name.
Because SECAM transmits only one color at a time, it is free of the color artifacts present in NTSC and PAL and resulting from the combined transmission of both signals.
This means that the vertical color resolution is halved relative to NTSC. It is however not halved compared to PAL. Although PAL does not eliminate half of vertical color information during encoding, it combines color information from adjacent lines at the decoding stage, in order to compensate for "color sub carrier phase errors" occurring during the transmission of the Amplitude-Modulated color sub carrier. This is normally done using a delay line borrowed from SECAM (the result is called PAL DL or PAL Delay-Line, sometimes interpreted as DeLuxe), but can be accomplished "visually" in cheap TV sets (PAL standard). Because the FM modulation of SECAM's color sub carrier is insensitive to phase (or amplitude) errors, phase errors do not cause loss of color saturation in SECAM, although they do in PAL. In NTSC, such errors cause color shifts.
The color difference signals in SECAM are actually calculated in the YDbDr color space, which is a scaled version of the YUV color space. This encoding is better suited to the transmission of only one signal at a time.
FM modulation of the color information allows SECAM to be free of the dot crawl problem commonly encountered with the other analog standards and first widely noticed with Laserdiscs. Dot crawl can be removed from PAL and NTSC-encoded signals using a comb filter. Such filters are usually only included in high-end displays. Dot crawl patterns (animated checkerboard) are easily visible along vertical lines in DVD menus displayed even by expensive (eg. plasma) displays if these displays are connected to a signal source (DVD player) using a composite PAL or NTSC connection rather than, for example, RGB.
The idea of reducing the vertical color resolution comes from Henri de France, who observed that color information is approximately identical for two successive lines. Because the color information was designed to be a cheap, backwards compatible addition to the monochrome signal, the color signal has a lower bandwidth than the luminance signal, and hence lower horizontal resolution. Fortunately, the human visual system is similar in design: it perceives changes in luminance at a higher resolution than changes in chrominance, so this asymmetry has minimal visual impact. It was therefore also logical to reduce the vertical color resolution.
DVD and other digital television formats have continued to exploit this visual artifact, sub sampling color both horizontally and vertically. Hence, paradoxically, VHS NTSC videos and especially NTSC Laserdiscs can have a greater vertical color resolution than DVD.
A similar paradox applies to the vertical resolution in television in general: reducing the bandwidth of the video signal will preserve the vertical resolution, even if the image loses sharpness and is smudged in the horizontal direction. Hence, video could be sharper vertically than horizontally. However, because of the interlacing, vertical resolution is effectively not as great as the number of scan lines. Additionally, transmitting an image with too much vertical detail will cause annoying flicker on television screens, as small details will only appear on a single line, and hence be refreshed at half the frequency. Computer-generated text and inserts have to be carefully low-pass filtered to prevent this.
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Structure of a CCD Chip |
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The structure of a basic CCD has the disadvantage that the charge on individual sensors is corrupted by changes in illumination during the read out process. Today's CCD sensors are developed with two different structures with two different ways of read out process and with slightly different features.
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Syncronization Types |
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Every CCD camera should be equipped with an internal circuit generating its internal timing. This information is used for synchronizing the read-out process from CCD chip and (in case of composite video signal) than provided to output. Except the internal sync, some cameras can accept sync information from an external device (for example from a frame grabber) as well. Such external sync signal is used to control a PLL/VCO, which provides the internal clock cycle. There are several types of sync signal:
HD/VD (horizontal drive/vertical drive) signals The camera determines whether to operate in interlace or non interlace modes from the phase relation between HD and VD (see Scanning system) VBS (composite video signal) The camera is synchronized by supplying a composite video signal (for example from another image sensor) SYNC (composite sync signal) Synchronization is performed by means of composite sync input signal. Pixel synchronous acquisition A pixel clock is a timing signal used to divide the incoming line of video into pixels. It should be used (in addition to the H/V sync signals) when 100% exact pixel mapping into the memory is needed, e.g. in metrology. The resulting precise acquisition thus significantly reduces the pixel jitter to an acceptable level. Master The device that provides the synchronization information to other devices involved in the acquisition process to synchronize them is called a master. Slave Similarly the other devices, that use the synchronization (generated by a master) to adapt their timing, are called slaves.
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TCP/IP (Internet protocol suite) |
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The Internet protocol suite is the set of communications protocols that implements the protocol stack on which the Internet and many commercial networks run. It is part of the TCP/IP protocol suite, which is named after two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were also the first two networking protocols defined. A review of TCP/IP is given under that heading. Note that today's TCP/IP networking represents a synthesis of two developments that began in the 1970's, namely LAN's (Local Area Networks) and the Internet, both of which have revolutionized computing.
The Internet protocol suite — like many protocol suites — can be viewed as a set of layers. Each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the upper layer protocols based on using services from some lower layers. Upper layers are logically closer to the user and deal with more abstract data, relying on lower layer protocols to translate data into forms that can eventually be physically transmitted. The original TCP/IP reference model consists of 4 layers, but has evolved into a 5-layer model.
The OSI model describes a fixed, seven-layer stack for networking protocols. Comparisons between the OSI model and TCP/IP can give further insight into the significance of the components of the IP suite. The OSI model with its increased numbers of layers provides for more flexibility. Both the OSI and the TCP/IP models are 'standards' and application developers will often implement solutions without strict adherence to proposed 'division' of labour within the standard whilst providing for functionality within the application suite. This separation of 'practice' from theory often leads to confusion.
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Telnet |
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TELNET (TELetype NETwork) is a network protocol used on the Internet or local area network (LAN) connections. It was developed in 1969 beginning with RFC#0015 and standardized as IETF STD 8, one of the first Internet standards.
The term telnet also refers to software which implements the client part of the protocol. TELNET clients have been available on most Unix systems for many years and are available for virtually all platforms. Most network equipment and OSs with a TCP/IP stack support some kind of TELNET service server for their remote configuration (including ones based on Windows NT). Recently, SSH has begun to dominate remote access for Unix-based machines.
"To telnet" is also used as a verb meaning to establish or use a TELNET or other interactive TCP connection, as in, "To change your password, telnet to the server and run the passwd command".
Most often, a user will be telneting to a unix-like server system or a simple network device such as a switch. For example, a user might "telnet in from home to check his mail at school". In doing so, he would be using a telnet client to connect from his computer to one of his servers. Once the connection is established, he would then log in with his account information and execute operating system commands remotely on that computer, such as ls or cd.
On many systems, the client may also be used to make interactive raw-TCP sessions.
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Thermography |
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Thermography, thermal imaging, or thermal video, is a type of infrared imaging. Thermographic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 900–14,000 nanometers or 0.9–14 µm) and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black body radiation law, thermography makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, therefore thermography allows one to see variations in temperature (hence the name). When viewed by thermographic camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily visible against the environment, day or night. As a result, thermography's extensive use can historically be ascribed to the military and security services.
Thermal imaging photography finds many other uses. For example, firefighters use it to see through smoke, find persons, and localize the base of a fire. With thermal imaging, power lines maintenance technicians locate overheating joints and parts, a telltale sign of their failure, to eliminate potential hazards. Where thermal insulation becomes faulty, building construction technicians can see heat leaks to improve the efficiencies of cooling or heating air-conditioning. Thermal imaging cameras are also installed in some luxury cars to aid the driver, the first being the 2000 Cadillac DeVille. Some physiological activities, particularly responses, in human beings and other warm-blooded animals can also be monitored with thermographic imaging.
The appearance and operation of a modern thermographic camera is often similar to a camcorder. Enabling the user to see in the infrared spectrum is a function so useful that ability to record their output is often optional. A recording module is therefore not always built-in.
Instead of CCD sensors, most thermal imaging cameras use CMOS Focal Plane Array (FPA). The most common types are InSb, InGaAs, QWIP FPA. The newest technologies are using low cost and uncooled microbolometers FPA sensors. Their resolution is considerably lower than of optical cameras, mostly 160x120 or 320x240 pixels, up to 640x512 for the most expensive models. Thermographic cameras are much more expensive than their visible-spectrum counterparts, and higher-end models are often export-restricted. Older bolometers or more sensitive models as InSB require cryogenic cooling, usually by a miniature Stirling cycle refrigerator or liquid nitrogen.
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Trigger |
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The term «trigger» is sometimes used also in meaning of a trigger shutter (a shutter mode with random timing or even with random shutter speed). Such a randomness is controlled by the trigger signal mentioned above.
Trigger is a special signal provided to a camera (or other device) to ignite some needed operation - most frequently to reset its timing, turn on a flash or a strobe etc.
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TTL (Transistor Transistor Logic) |
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Transistor Transistor Logic, a digital signal using 0 V to 0.4 V to represent logical «0» and 3 V to 5 V to represent logical «1».
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TVL: TV Lines |
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In video, lines are a measurement of display resolution or image resolution. While the EIA standard for RS-170 video is 525 horizontal lines, this is not the same lines. The NTSC standard for RS-170 has a resolution of 480 TV Lines.
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Units |
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Below you can find description of some of the units frequently used in the camera/frame grabber technology.
Vp-p: Volts peak-to-peak. The amplitude (voltage) difference between the most positive and the most negative excursions (peaks) of an electrical signal. A full video signal measures one volt peak-to-peak, 1 Vp-p.
lux: The SI measurement of light intensity taken at the surface which the light source is illuminating. The measure of the total lumens falling upon a unit of area (1 lumen per square meter).
dB: Decibel. Logarithmic measure of relative power levels, applied e.g. to signal-to-noise ratio. Thus S/N ratio = 10·log(signal/noise) dB .
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VD/VBS/EXT Sync, Gen. Lock, AC Line Lock |
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Q: What is VD sync., VBS Sync., EXT sync., Gen. lock and AC line lock?
A: There are different ways to do synchronization among cameras.
General lock is the best way to fully synchronize two cameras for most dedicated application such as broadcasting studio. It will synchronize Vertical, Horizontal, Even/Odd field, and Color burst frequency and Phase.
VD sync. is the most simple way to synchronize two cameras by vertical drive frequency to ensure video can be processed by plan old switcher or quad machine to display several image sources on the same monitor. VD signal is usually constructed by a pulse on the repeat rate of 20/16.7ms ( 50/60 Hz) and with pulse width of 1~ 3 ms.
VBS stands for video and color burst signal. It means the camera will synchronize an external composite color video signal. Although it is read as VBS sync. it is actually doing H sync. and V sync. only , and does not do color burst synchronization.
External sync. is almost the same as VBS sync. A camera can be synchronized by video signal supplied by another camera. An External sync camera will take an incoming VBS video, and extract the vertical and horizontal sync. signal for sync. purpose.
Many our cameras have VD sync. or VBS/External sync. feature but because surveillance cameras never need Gen lock, CCTV cameras scarcely have general lock feature. In Mintron, there is only one OEM model has Gen lock feature that is not open for distribution channel.
AC line lock is an old technology for synchronizing camera by AC 50/60 Hz power line current. AC 24 volts power is widely used for fire-fighting alarm system in most of the buildings and is very easy to get. Therefore, it is widely used in north American. Because old style switcher and quad system have no digital memory, synchronization among cameras is necessary to maintain stable picture. The trade off for AC line lock is camera synching to ac 50/60 hertz. The timing relation between color sub carrier and horizontal /vertical signal will be disengaged and cause bad color rendering ( color phase draft )Therefore, all user that enjoying AC line lock will unavoidably scarify good color rendering. Fortunately, modern quad, 16-channel multiplexer and DVR have internal memory to overcome this difficulty and need no sync. signal so AC line lock might be obsolete couple years later.
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Vertical Smear |
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Vertical smear is a phenomenon peculiar to some types of CCD camera which occurs when a bright object or light source is shot with the camera. This phenomenon is observed on the monitor as a vertical streak above and below the object or light source.
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Video Norm |
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Reading out from a CCD sensor is regulated by a video norm that defines the timing and the level of the transmission. There are two different norms (both strongly related to an interlacing technique).
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Video Signal Forming |
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The charge accumulated in the CCD sensor is used to form resulting video signal by camera electronics. Resulting waveform should correspond to according video norm. Waveform Shape of a signal wave, its time behavior.
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Video Signal Types |
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Color video signals are composed of luminance and chroma (color) information. Composite signals carry both parts on a single line (wire), whereas component signals (Y/C, RGB) carry the video information separately on more lines. Breaking up the signal components generally improves signal fidelity, especially when recording or balancing color.
Composite A single video signal including luminance, color and sync information. The signal is usually coded in accordance with EIA or CCIR video norm, using NTSC or PAL color coding. S-video (Y/C) Luminance (brightness) and color information are transmitted as two separate signals. RGB signal Three color image components, Red, Green, and Blue are transmitted as separate signals.
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Video Standards |
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Country |
Color System |
| Afghanistan |
SECAM & PAL |
| Alaska |
NTSC |
| Albania |
PAL |
| Algeria |
PAL |
| Andorra |
PAL |
| Angola |
PAL |
| Antarctica |
NTSC |
| Antigua & Barbuda |
NTSC |
| Argentina |
PAL |
| Armenia |
SECAM (Vertical) |
| Aruba |
NTSC |
| Australia |
PAL |
| Austria |
PAL |
| Azerbaijan |
SECAM (Vertical) |
| Azores |
PAL |
Country |
Color System |
| Bahamas |
NTSC |
| Bahrain |
PAL |
| Bangladesh |
PAL |
| Barbados |
NTSC |
| Belgium |
PAL |
| Belize |
NTSC |
| Benin |
SECAM (Vertical) |
| Bermuda island |
NTSC |
| Bhutan |
- |
| Bolivia |
NTSC |
| Bosnia |
PAL |
| Botswana |
SECAM (Vertical) |
| Brazil |
PAL |
| British Indian Ocean Territory |
NTSC |
| Brunei |
PAL |
| Bulgaria |
SECAM (Vertical) |
| Burkina Faso |
SECAM (Vertical) |
| Burma |
NTSC |
| Burundi |
SECAM (Vertical) |
| Byelarus |
SECAM (Vertical) |
Country |
Color System |
| Cayman Island |
NTSC |
| Camaroon |
PAL |
| Canada |
NTSC |
| Canary Island |
Pal |
| Cape Verde |
- |
| Central African Republic |
SECAM (Vertical) |
| Chad |
SECAM (Vertical) |
| Chile |
NTSC |
| China (Peoples Rep.) |
PAL |
| Columbia |
NTSC |
| Comoros |
- |
| Congo |
SECAM (Vertical) |
| Cook Island |
PAL |
| Costa Rica |
NTSC |
| Crete |
PAL |
| Croatia |
PAL |
| Cuba |
NTSC |
| Cyprus |
PAL |
| Czech |
SECAM (Vertical) |
Country |
Color System |
| Denmark |
PAL |
| Djibouti |
SECAM (Vertical) |
| Dominica |
NTSC |
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| Ecuador |
NTSC |
| Eqypt |
PAL |
| El Salvador |
NTSC |
| Equatorial Guinea |
SECAM (Vertical) |
| Estonia |
SECAM & PAL |
| Ethiopia |
PAL |
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| Falkland Islands |
PAL |
| Faroe Island |
PAL |
| Fiji |
PAL |
| Finland |
PAL |
| France |
SECAM (Vertical) |
Country |
Color System |
| Gabon |
SECAM (Vertical) |
| Gambia |
PAL |
| Georgia |
SECAM (Vertical) |
| Germany |
PAL |
| Ghana |
PAL |
| Gibralta |
PAL |
| Gilbert Islands |
- |
| Greece |
SECAM (Vertical) |
| Greenland |
PAL |
| Greenland US Airforce Base |
NTSC |
| Grenada |
NTSC |
| Guadeloupe |
SECAM (Vertical) |
| Guam |
NTSC |
| Guatemala |
NTSC |
| Guinea |
PAL |
| Guinea Bissau |
- |
| Guyana |
NTSC |
| Guyana (French) |
SECAM (Vertical) |
Country |
Color System |
| Haiti |
NTSC |
| Hawaii |
NTSC |
| Honduras |
NTSC |
| Hong Kong |
PAL |
| Hungary |
PAL |
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| Iceland |
PAL |
| India |
PAL |
| Indonesia |
PAL |
| Iran |
SECAM (Vertical) |
| Iraq |
SECAM (Vertical) |
| Ireland |
PAL |
| Israel |
PAL |
| Italy |
PAL |
| Ivory Coast |
SECAM (Vertical) |
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| Jamaica |
NTSC |
| Japan |
NTSC |
| Johnston Island |
NTSC |
| Jordan |
PAL |
Country |
Color System |
| Kampuchea |
PAL |
| Kazakhstan |
SECAM (Vertical) |
| Kenya |
PAL |
| Korea (North) |
PAL & NTSC |
| Korea (South) |
NTSC |
| Kuwait |
PAL |
| Kyrgyzstan |
SECAM (Vertical) |
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| Laos |
PAL |
| Latvia |
SECAM (Vertical) |
| Lebanon |
SECAM (Vertical) |
| Lesotho |
PAL |
| Liberia |
PAL |
| Libya |
PAL |
| Lithuania |
SECAM (Vertical) |
| Luxembourg |
SECAM & PAL |
Country |
Color System |
| Macao |
PAL |
| Macedonia |
PAL |
| Madagascar |
SECAM (Vertical) |
| Madaira |
PAL |
| Malawi |
PAL |
| Malaysia |
PAL |
| Maldives |
PAL |
| Mali |
SECAM (Vertical) |
| Malta |
PAL |
| Marshall Islands |
NTSC |
| Martinique |
SECAM (Vertical) |
| Mauritania |
SECAM (Vertical) |
| Mauritius |
SECAM (Vertical) |
| Mayotte |
SECAM (Vertical) |
| Mexico |
NTSC |
| Micronesia |
NTSC |
| Midway Island |
NTSC |
| Moldava |
SECAM (Vertical) |
| Monaco |
SECAM & PAL |
| Mongolia |
SECAM (Vertical) |
| Montserrat |
NTSC |
| Morocco |
SECAM (Vertical) |
| Mozambique |
PAL |
| Mynmar |
NTSC |
Country |
Color System |
| Nambia |
PAL |
| Nepal |
PAL |
| Netherlands |
PAL |
| Netherlands Antilles |
NTSC |
| New Caledonia |
SECAM (Vertical) |
| New Zealand |
PAL |
| Nicaragua |
NTSC |
| Niger |
SECAM (Vertical) |
| Nigeria |
PAL |
| Norfolk Island |
PAL |
| Northern Marina Islands |
NTSC |
| Norway |
PAL |
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| Okinawa |
NTSC |
| Oman |
PAL |
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| Pakistan |
PAL |
| Palau |
NTSC |
| Panama |
NTSC |
| Papua New Guinea |
PAL |
| Paraguay |
PAL |
| Peru |
NTSC |
| Philippines |
NTSC |
| Poland |
PAL |
| Polynesia (French) |
SECAM (Vertical) |
| Portugal |
PAL |
| Puerto Rico |
NTSC |
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| Quatar |
PAL |
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| Reunion |
SECAM (Vertical) |
| Romania |
PAL |
| Russia |
SECAM (Vertical) |
| Rwanda |
- |
Country |
Color System |
| Salomon Islands |
- |
| Samoa (American) |
NTSC |
| Samoa (Western) |
PAL |
| Sao Tome |
PAL |
| Saudi Arabia |
SECAM & PAL |
| Senegal |
SECAM (Vertical) |
| Seychelles Island |
PAL |
| Sierra Leone |
PAL |
| Singapore |
PAL |
| Slovakia |
SECAM & PAL |
| Slovenia |
PAL |
| Somalia |
PAL |
| South Africa |
PAL |
| Spain |
PAL |
| Sri Lanka |
PAL |
| St. Grenadines |
NTSC |
| St. Lucia |
NTSC |
| St. Marino |
PAL |
| St. Pierre Miquelon |
SECAM (Vertical) |
| St. Vincent |
NTSC |
| St. Kitts |
NTSC |
| Sudan |
PAL |
| Swaziland |
PAL |
| Sweden |
PAL |
| Switzerland |
PAL |
| Syria |
PAL |
Country |
Color System |
| Tahiti |
SECAM (Vertical) |
| Taiwan |
NTSC |
| Tajikistan |
SECAM (Vertical) |
| Tanzania |
PAL |
| Thailand |
PAL |
| Togo |
SECAM (Vertical) |
| Tonga |
NTSC |
| Trinidad & Tabago |
NTSC |
| Tunesia |
SECAM (Vertical) |
| Turkey |
PAL |
| Turkmenistan |
SECAM (Vertical) |
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| Uganda |
PAL |
| Ukraine |
SECAM (Vertical) |
| United Arab Emirates |
PAL |
| United Kingdom |
PAL |
| Uruguay |
PAL |
| USA |
NTSC |
| Uzbekistan |
SECAM (Vertical) |
Country |
Color System |
| Vanuatu |
- |
| Venezuela |
NTSC |
| Vietnam |
SECAM & NTSC |
| Virgin Island (American) |
NTSC |
| Virgin Island (British) |
NTSC |
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| Wallis & Futuna |
SECAM (Vertical) |
| Western Sahara |
- |
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| Yemen |
SECAM & NTSC |
| Yugoslavia |
PAL |
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| Zaire |
SECAM (Vertical) |
| Zambia |
PAL |
| Zanzibar |
PAL |
| Zimbabwe |
PAL |
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White Balance |
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A function enabling adjustment of the image colors to make the white objects really appear as white. Thus one can avoid color shifts caused e.g. by different illuminating conditions.
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Zoom Lens |
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A compound lens which remains in focus as the image size is varied continuously. May be motorized or manually operated.
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