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In television broadcasting, VIT signals (vertical interval test signals) are a group of test signals inserted in the composite video signal. These signals are used to weight [1] the transmission characteristics of the system between the test generator and the output of the demodulator, where the system includes the microwave links, or TVROs as well as the TV transmitters and the transposers. There are both ATSC and EBU standards for VIT. (Because analogue television is being phased out globally, VIT standards are considered superseded.)
In a composite video signal (CVS) there are two types of blanking: horizontal and vertical. Horizontal blanking is between lines and vertical blanking is between fields (half frames). In a poorly tuned TV receiver the horizontal blanking can be seen at the right or left of the image and the vertical blanking can be seen at the top or bottom of the image. VIT signals are inserted in the vertical blanking.
In each field vertical blanking is about 1612 μs in System B (also G and H; analogue system in most of Europe) and 1333 μs in System M (analogue TV system in USA). This duration is equal to 25 lines in system B and 21 lines in system M. [2] Although 7.5 lines are used for synchronization of the image, the remaining lines can be used for other purposes. [3] Two of these lines in each field are reserved for test signals. Since there are two fields in each frame (image), the number of lines reserved for test signals is four per frame.
In both systems, line numbers 17 and 18 are assigned for VIT signals in each field. (These line numbers are used just for the first field. For second field, they correspond to line 280 and 281 in system M, and line 330 and 331 in system B.)
Usually the following test signals are used:
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
The National Television System Committee (NTSC) developed the analog television format encoding system that was introduced in North America in 1954 and stayed in use until digital conversion. It is one of three major analog format television standards, the others being PAL and SECAM. All the countries using NTSC are currently in the process of conversion, or have already converted to the ATSC standard, or to DVB, ISDB or DTMB.
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields per second, and associated with CCIR analogue broadcast television systems B, D, G, H, I or K. The articles on analog broadcast television systems further describe frame rates, image resolution, and audio modulation.
SECAM, also written SÉCAM, is an analog color television system first used in France. It was one of three major analog color television standards, the others being PAL and NTSC. This page primarily discusses the SECAM colour encoding system. The articles on broadcast television systems and analog television further describe frame rates, image resolution, and audio modulation. SECAM video is composite video because the luminance and chrominance are transmitted together as one signal.
Composite video is an analog video signal format that carries standard-definition video as a single channel. Video information is encoded on one channel, unlike the higher-quality S-Video and the even higher-quality component video. In all of these video formats, audio is carried on a separate connection.
Genlock is a common technique where the video output of one source is used to synchronize other picture sources together. The aim in video applications is to ensure the coincidence of signals in time at a combining or switching point. When video instruments are synchronized in this way, they are said to be generator-locked, or genlocked.
Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.
Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is transmitted or stored as three separate signals. Component video can be contrasted with composite video in which all the video information is combined into a single signal that is used in analog television. Like composite, component-video cables do not carry audio and are often paired with audio cables.
SMPTE color bars are a television test pattern used where the NTSC video standard is utilized, including countries in North America. The Society of Motion Picture and Television Engineers (SMPTE) refers to the pattern as Engineering Guideline (EG) 1-1990. Its components are a known standard. Comparing it as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly.
Broadcast television systems are the encoding or formatting standards for the transmission and reception of terrestrial television signals.
A television transmitter is a transmitter that is used for terrestrial (over-the-air) television broadcasting. It is an electronic device that radiates radio waves that carry a video signal representing moving images, along with a synchronized audio channel, which is received by television receivers belonging to a public audience, which display the image on a screen. A television transmitter, together with the broadcast studio which originates the content, is called a television station. Television transmitters must be licensed by governments, and are restricted to a certain frequency channel and power level. They transmit on frequency channels in the VHF and UHF bands. Since radio waves of these frequencies travel by line of sight, they are limited by the horizon to reception distances of 40–60 miles depending on the height of transmitter station.
A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses or sync words. Generators of composite video signals will also include a colorburst signal as part of the output.
MUSE, commercially know as Hi-Vision was a Japanese analog HDTV system, with design efforts going back to 1979.
C-MAC is the television technology variant approved by the European Broadcasting Union (EBU) for satellite transmissions. The digital information is modulated using 2-4PSK, a variation of quadrature PSK where only two of the phaser angles (±90°) are used.
Differential gain is a kind of linearity distortion which affects the color saturation in TV broadcasting.
The following outline is provided as an overview of and topical guide to television broadcasting:
Differential phase is a kind of linearity distortion which affects the color hue in TV broadcasting.
This glossary defines terms that are used in the document "Defining Video Quality Requirements: A Guide for Public Safety", developed by the Video Quality in Public Safety (VQIPS) Working Group. It contains terminology and explanations of concepts relevant to the video industry. The purpose of the glossary is to inform the reader of commonly used vocabulary terms in the video domain. This glossary was compiled from various industry sources.
Color television as introduced in North America in 1954 is best described as being 'colored' television. The system used the existing black and white signal but with the addition of a component intended only for television receivers designed to show color. By careful application this 'colored' signal was ignored by ordinary TV sets and had negligible effect on the appearance of the black and white image. This meant that color programs were viewable on the many existing black and white receivers which fulfilled a requirement for 'compatibility' desired by the television industry. Once the so-called 'composite' video signal containing the color component had been generated it could be handled just as if it were a black and white signal, eliminating the need to replace much of the existing TV infrastructure. Colorplexer was the RCA name for the equipment that created this 'composite' color signal from three separate images each created in the primary colors, Red, Green and Blue supplied by a color video camera. This process was by the standards of the day quite complex and demanded accurate control of all the various parameters involved if an acceptable color image was to be achieved. The simplification afforded by this 'head end' approach became evident and contributed to the gradual acceptance of color programming over the following decades.
Composite artifact colors is a designation commonly used to address several graphic modes of some 1970s and 1980s home computers. With some machines, when connected to an NTSC TV or monitor over composite video outputs, the video signal encoding allowed for extra colors to be displayed, by manipulating the pixel position on screen, not being limited by each machine's hardware color palette.