A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems; the word raster comes from the Latin word rastrum, derived from radere. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster, it is a systematic process of covering the area progressively, one line at a time. Although a great deal faster, it is similar in the most-general sense to how one's gaze travels when one reads lines of text. In a raster scan, an image is subdivided into a sequence of strips known as "scan lines"; each scan line can be transmitted in the form of an analog signal as it is read from the video source, as in television systems, or can be further divided into discrete pixels for processing in a computer system. This ordering of pixels by rows is known as raster scan order.
Analog television has discrete scan lines, but does not have discrete pixels – it instead varies the signal continuously over the scan line. Thus, while the number of scan lines is unambiguously defined, the horizontal resolution is more approximate, according to how the signal can change over the course of the scan line. In raster scanning, the beam sweeps horizontally left-to-right at a steady rate blanks and moves back to the left, where it turns back on and sweeps out the next line. During this time, the vertical position is steadily increasing, but much more – there is one vertical sweep per image frame, but one horizontal sweep per line of resolution, thus each scan line is sloped "downhill", with a slope of –1/horizontal resolution, while the sweep back to the left is faster than the forward scan, horizontal. The resulting tilt in the scan lines is small, is dwarfed in effect by screen convexity and other modest geometrical imperfections. There is a misconception that once a scan line is complete, a CRT display in effect jumps internally, by analogy with a typewriter or printer's paper advance or line feed, before creating the next scan line.
As discussed above, this does not happen: the vertical sweep continues at a steady rate over a scan line, creating a small tilt. Steady-rate sweep is done, instead of a stairstep of advancing every row, because steps are hard to implement technically, while steady-rate is much easier; the resulting tilt is compensated in most CRTs by the tilt and parallelogram adjustments, which impose a small vertical deflection as the beam sweeps across the screen. When properly adjusted, this deflection cancels the downward slope of the scanlines; the horizontal retrace, in turn, slants smoothly downward. In detail, scanning of CRTs is performed by magnetic deflection, by changing the current in the coils of the deflection yoke. Changing the deflection requires a voltage spike to be applied to the yoke, the deflection can only react as fast as the inductance and spike magnitude permit. Electronically, the inductance of the deflection yoke's vertical windings is high, thus the current in the yoke, therefore the vertical part of the magnetic deflection field, can change only slowly.
In fact, spikes do occur, both horizontally and vertically, the corresponding horizontal blanking interval and vertical blanking interval give the deflection currents settle time to retrace and settle to their new value. This happens during the blanking interval. In electronics, these movements of the beam are called "sweeps", the circuits that create the currents for the deflection yoke are called the sweep circuits; these create a sawtooth wave: steady movement across the screen a rapid move back to the other side, for the vertical sweep. Furthermore, wide-deflection-angle CRTs need horizontal sweeps with current that changes proportionally faster toward the center, because the center of the screen is closer to the deflection yoke than the edges. A linear change in current would swing the beams at a constant rate angularly. Computer printers create their images by raster scanning. Laser printers use a spinning polygonal mirror to scan across the photosensitive drum, paper movement provides the other scan axis.
Considering typical printer resolution, the "downhill" effect is minuscule. Inkjet printers have multiple nozzles in their printheads, so many of "scan lines" are written together, paper advance prepares for the next batch of scan lines. Transforming vector-based data into the form required by a display, or printer, requires a Raster Image Processor. Computer text is created from font files that describe the outlines of each printable character or symbol; these outlines have to be converted into what are little rasters, one per character, before being rendered as text, in effect merging their little rasters into that for the page. In detail, each line consists of: scanline, when beam is unblanked, moving to the right front porch, when beam is blanked, moving
Arnold Johannes Wilhelm Sommerfeld, was a German theoretical physicist who pioneered developments in atomic and quantum physics, educated and mentored a large number of students for the new era of theoretical physics. He served as doctoral supervisor for many Nobel Prize winners in chemistry, he introduced the 3rd quantum number. He introduced the fine-structure constant and pioneered X-ray wave theory. Sommerfeld studied mathematics and physical sciences at the Albertina University of his native city, Königsberg, East Prussia, his dissertation advisor was the mathematician Ferdinand von Lindemann, he benefited from classes with mathematicians Adolf Hurwitz and David Hilbert and physicist Emil Wiechert. His participation in the student fraternity Deutsche Burschenschaft resulted in a dueling scar on his face, he received his Ph. D. on 24 October 1891. After receiving his doctorate, Sommerfeld remained at Königsberg to work on his teaching diploma, he passed the national exam in 1892 and began a year of military service, done with the reserve regiment in Königsberg.
He completed his obligatory military service in September 1893, for the next eight years continued voluntary eight-week military service. With his turned up moustache, his physical build, his Prussian bearing, the fencing scar on his face, he gave the impression of being a colonel in the hussars. In October 1893, Sommerfeld went to the University of Göttingen, the center of mathematics in Germany. There, he became assistant to Theodor Liebisch, at the Mineralogical Institute, through a fortunate personal contact – Liebisch had been a professor at the University of Königsberg and a friend of the Sommerfeld family. In September 1894, Sommerfeld became Felix Klein's assistant, which included taking comprehensive notes during Klein's lectures and writing them up for the Mathematics Reading Room, as well as managing the reading room. Sommerfeld's Habilitationsschrift was completed under Klein, in 1895, which allowed Sommerfeld to become a Privatdozent at Göttingen; as a Privatdozent, Sommerfeld lectured on a wide range of mathematical and mathematical physics topics.
His lectures on partial differential equations were first offered at Göttingen, they evolved over his teaching career to become Volume VI of his textbook series Lectures on Theoretical Physics, under the title Partial Differential Equations in Physics. Lectures by Klein in 1895 and 1896 on rotating bodies led Klein and Sommerfeld to write a four-volume text Die Theorie des Kreisels – a 13-year collaboration, 1897–1910; the first two volumes were on theory, the latter two were on applications in geophysics and technology. The association Sommerfeld had with Klein influenced Sommerfeld's turn of mind to be applied mathematics and in the art of lecturing. While at Göttingen, Sommerfeld met daughter of Ernst Höpfner, curator at Göttingen. In October, 1897 Sommerfeld began the appointment to the Chair of Mathematics at the Bergakademie in Clausthal-Zellerfeld; this appointment provided enough income to marry Johanna. At Klein's request, Sommerfeld took on the position of editor of Volume V of Enzyklopädie der mathematischen Wissenschaften.
In 1900, Sommerfeld started his appointment to the Chair of Applied Mechanics at the Königliche Technische Hochschule Aachen as extraordinarius professor, arranged through Klein's efforts. At Aachen, he developed the theory of hydrodynamics, which would retain his interest for a long time. At the University of Munich, Sommerfeld's students Ludwig Hopf and Werner Heisenberg would write their Ph. D. theses on this topic. From 1906 Sommerfeld established himself as ordinarius professor of physics and director of the new Theoretical Physics Institute at the University of Munich, he was selected for these positions by Wilhelm Röntgen, Director of the Physics Institute at Munich, looked upon by Sommerfeld as being called to a "privileged sphere of action."Up until the late 19th century and early 20th century, experimental physics in Germany was considered as having a higher status within the community. However, in the early 20th century, such as Sommerfeld at Munich and Max Born at the University of Göttingen, with their early training in mathematics, turned this around so that mathematical physics, i.e. theoretical physics, became the prime mover, experimental physics was used to verify or advance theory.
After getting their doctorates with Sommerfeld, Wolfgang Pauli, Werner Heisenberg, Walter Heitler became Born's assistants and made significant contributions to the development of quantum mechanics, in rapid development. Over his 32 years of teaching at Munich, Sommerfeld taught general and specialized courses, as well as holding seminars and colloquia; the general courses were on mechanics, mechanics of deformable bodies, optics and statistical mechanics, partial differential equations in physics. They were held four hours per week, 13 weeks in the winter and 11 weeks in the summer, were for students who had taken experimental physics courses from Röntgen and by Wilhelm Wien. There was a two-hour weekly presentation for the discussion of problems; the specialized courses were of topical interest and based on Sommerfeld's research interests. The objective of these special lectures was to grap
In telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal. Digital data can be encoded and transmitted via FM by shifting the carrier's frequency among a predefined set of frequencies representing digits – for example one frequency can represent a binary 1 and a second can represent binary 0; this modulation technique is known as frequency-shift keying. FSK is used in modems such as fax modems, can be used to send Morse code. Radioteletype uses FSK. Frequency modulation is used for FM radio broadcasting, it is used in telemetry, seismic prospecting, monitoring newborns for seizures via EEG, two-way radio systems, music synthesis, magnetic tape-recording systems and some video-transmission systems.
In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation signal. For this reason, most music is broadcast over FM radio. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation; these methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. If the information to be transmitted is x m and the sinusoidal carrier is x c = A c cos , where fc is the carrier's base frequency, Ac is the carrier's amplitude, the modulator combines the carrier with the baseband data signal to get the transmitted signal: y = A c cos = A c cos = A c cos where f Δ = K f A m, K f being the sensitivity of the frequency modulator and A m being the amplitude of the modulating signal or baseband signal. In this equation, f is the instantaneous frequency of the oscillator and f Δ is the frequency deviation, which represents the maximum shift away from fc in one direction, assuming xm is limited to the range ±1.
While most of the energy of the signal is contained within fc ± fΔ, it can be shown by Fourier analysis that a wider range of frequencies is required to represent an FM signal. The frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are neglected in practical design problems. Mathematically, a baseband modulating signal may be approximated by a sinusoidal continuous wave signal with a frequency fm; this method is named as single-tone modulation. The integral of such a signal is: ∫ 0 t x m d τ = A m sin
405-line television system
The 405-line monochrome analogue television broadcasting system was the first electronic television system to be used in regular broadcasting. It was introduced with the BBC Television Service in 1936, suspended for the duration of World War II, remained in operation in the UK until 1985, it was used between 1961 and 1982 in Ireland, as well as from 1957 to 1973 for the Rediffusion Television cable service in Hong Kong. Sometimes called the Marconi-EMI system, it was developed in 1934 by the EMI Research Team led by Sir Isaac Shoenberg; the figure of 405 lines had been chosen following discussions over Sunday lunch at the home of Alan Blumlein. The system used interlacing. In the 405 system the scanning lines were broadcast in two complementary fields, 50 times per second, creating 25 frames per second; the actual image was 377 lines high and interlaced, with additional unused lines making the frame up to 405 lines to give the slow circuitry time to prepare for the next frame. At the time of its introduction the 405-line system was referred to as "high definition" - which it was, compared to earlier systems, although of lower definition than 625-line and standards.
In 1934 the British government set up a committee to advise on the future of TV broadcasting. The committee recommended; the recommendation was accepted and tenders were sought from industry. Two tenders were received: one from the Baird company offering a 240-line mechanical system, the other from EMI offering a 405-line all-electronic one; the Television Committee advised that they were unable to choose between the two systems and that both tenders should be accepted, the two systems to be run together for an experimental period. Broadcasting of the resulting BBC Television Service from its Alexandra Palace site began in November 1936, at first time-sharing broadcasts with the 240-line Baird system; this became the standard for all British TV broadcasts until the 1960s. It soon became apparent that television reception was possible well outside the original intended service area. In February 1938, engineers at the RCA Research Station, Long Island, New York, in the USA, were able to receive the BBC signal 5,000 km away, due to the signal being "bounced" back to earth from the ionosphere.
A few minutes of programming were recorded on 16mm movie film. This is now considered to be the only surviving example of live British television; the images recorded included two of the original three BBC announcers, Jasmine Bligh and Elizabeth Cowell, an excerpt from an unknown period costume drama, the BBC's station identification transmitted at the beginning and end of the day's programmes. The BBC temporarily ceased transmissions on 1 September 1939, the day of the German invasion of Poland, as war was imminent. After the BBC Television Service recommenced in 1946, distant reception reports were received from various parts of the world, including Italy, South Africa, the Middle East, North America and the Caribbean; the BBC lost its monopoly of the British television market in 1954, the following year the commercial network ITV, comprising a consortium of regional companies, was launched. In 1964, the BBC launched its BBC2 service on UHF using only a 625-line system, which older sets could not receive.
For several years BBC1 and ITV transmitted BBC2 the 625-line standard. The introduction of colour on BBC2 in 1967 necessitated an more complex dual-standard set to receive all three channels. In November 1969 BBC1 and ITV started broadcasting in 625-line PAL colour on UHF; as their programming was now produced using the new standard, the 405-line broadcasts served only as a rebroadcast in monochrome for people who did not have the newer receivers. Thereafter, receivers were of a simpler single standard design which could not receive the legacy 405-line transmissions. One reason for the long switchover period was the difficulty in matching the coverage level of the new UHF 625-line service with the high level of geographic coverage achieved with the 405-line VHF service; the last 405-line transmissions were seen on 4 January 1985 in Scotland. This left only the UHF PAL system in operation in the UK; the frequencies used by the 405-line system were left empty, but were sold off. Ireland's use of the 405-line system began in 1961, with the launch of Telefís Éireann, but only extended to two main transmitters and their five relays, serving the east and north of the country.
This was because many people in these areas had 405-line sets for receiving UK broadcasts from Wales or Northern Ireland. Telefís Éireann's primary standard was 625-line; the last 405-line relays, in County Donegal, were turned off in 1982.
CCIR System B
CCIR System B was the 625-line analog broadcast television system which at its peak was the system used in most countries. It is being replaced across part of Asia and Africa by digital broadcasting; the system was developed for VHF band. A frame is the total picture; the frame rate is the number of pictures displayed in one second. But each frame is scanned twice interleaving odd and lines; each scan is known as a field So field rate is twice the frame rate. In each frame there are 625 lines So line rate 625 • 25 = 15625 Hz; the video bandwidth is 5.0 MHz. The video signal modulates the carrier by Amplitude Modulation, but a portion of the lower side band is suppressed. This technique is known as vestigial side band modulation; the polarity of modulation is negative, meaning that an increase in the instantaneous brightness of the video signal results in a decrease in RF power and vice versa. The sync pulses result in maximum power from the transmitter; the primary audio signal is modulated by Frequency modulation with a preemphasis time constant of τ = 50 μs.
The deviation for a 1.0 kHz. AF signal is 50 kHz; the separation between the primary audio FM subcarrier and the video carrier is 5.5 MHz. The total RF bandwidth of System B was 6.5 MHz, allowing System B to be transmitted in the 7.0 MHz wide channels specified for television in the VHF bands with an ample 500 kHz guard zone between channels. In specs, other parameters such as vestigial sideband characteristics and gamma of display device are given. System B has variously been used with both the SECAM colour systems, it could have been used with a 625-line variant of the NTSC color system, but apart from possible technical tests in the 1950s, this has never been done officially. When used with PAL, the colour subcarrier is 4.43361875 MHz and the sidebands of the PAL signal have to be truncated on the high-frequency side at +570 kHz. On the low-frequency side, the full 1.3 MHz sideband is radiated. When used with SECAM, the'R' lines' carrier is at 4.40625 MHz deviating from +350±18 kHz to -506±25 kHz.
The'B' lines' carrier is at 4.250 MHz deviating +506±25 kHz to -350±18 kHz. Neither colour encoding system has any effect on the bandwidth of system B as a whole. Enhancements have been made to the specification of System B's audio capabilities over the years; the introduction of Zweiton in the 1970s allowed for stereo sound or twin monophonic audio tracks. This was implemented by adding a second FM audio subcarrier at +5.74 MHz. Alternatively, starting in the late 1980s and early 1990s it became possible to replace the second audio FM subcarrier with a digital signal carrying NICAM sound. Either of these extensions to audio capability have eaten into the guard band between channels. Zweiton uses an extra 150 kHz; the alternative NICAM system uses an extra 500 kHz, needs to be spaced further from the primary audio subcarrier, thus System B with NICAM has only 150 kHz guard zones between channels. System B was the first internationally accepted 625-line broadcasting standard in the world; the European 41-68 MHz Band I television allocation was agreed at the 1947 ITU conference in 1947, the first European channel plan was agreed in 1952 at the ITU conference in Stockholm.
The extension to VHF Band III was agreed in the 1950s. Since the System B specification has been used with different broadcast frequencies in many other countries. † Channel 1 was never used. § Not used in the former East Germany Transmitters were operational on the above channels in 1959. During the 1960s, channels 1 to 3 were deleted and channels E3 to E12 adopted, bringing East Germany into line with the channel allocations used in the West. Italian channel-spacings were erratic. System B is no longer in use in Italy, the switchover to DVB-T having been completed 4 July 2012. Note: Band I is no longer used for television in Italy. Note: Unusually for Europe, Band III is used for DVB-T in Italy. At digital switchover time, Italy took the opportunity to discontinue their erratic System B frequencies, the digital channels are regularly-spaced every 7.0 MHz from 177.5 MHz. Australia were unique in the world by their use of Band II for television broadcasting. ‡ Channels 3, 4 and 5 were scheduled to be cleared during 1993-96 to make way for FM radio stations in Band II.
This clearance action took much longer than was anticipated, as a result, many stations on channel 3 still remain, along with a few on 4 and 5. ♦ New channel allocations from 1993. ‡ Channels 10 and 11 were shifted up in frequency by 1 MHz to make room for channel 9A. The frequencies of existing stations did not change. Digital multiplexes on channels 10 and 11 are using the new channel boundaries. Australia are nearly unique in the world for their use of 7 MHz channel-spacing on UHF. † Added in the 1980s ‡ Added in the 1990s Note: the Band III frequencies are the same as Australia's. When the UHF bands came into use in the early 1960s, two variants of System B began to be used on those frequencies. In most countries, the channels on the UHF bands are
CCIR System H
CCIR System H is an analog broadcast television system used in Belgium, the Balkans and Malta on the UHF bands. Some of the important specs are listed below. A frame is the total picture; the frame rate is the number of pictures displayed in one second. But each frame is scanned twice interleaving odd and lines; each scan is known as a field So field rate is twice the frame rate. In each frame there are 625 lines So line rate 625 • 25 = 15625 Hz; the RF parameters of the transmitted signal are the same as those for System B, used on the 7.0 MHz wide channels of the VHF bands. The only difference to the RF spectrum of the signal is that the vestigial sideband is 500 kHz wider at 1.25 MHz. Due to this and the extra width of the channel allocations at UHF, the width of the guard band between the channels is 650 kHz. Many countries use a variant of system H, known as System G. System G is similar to system H but the lower side band is 500 kHz narrower; this makes poor use of the 8.0 MHz channels of the UHF bands by increasing the width of the guard-band by 500 kHz to 1.15 MHz.
The advantage is that the RF spectrum of system G is the same as system B, simplifying the band-switching circuitry in VHF/UHF televisions. Broadcast television systems Television transmitter Transposer World Analogue Television Standards and Waveforms Fernsehnormen aller Staaten und Gebiete der Welt
Analog high-definition television system
Analog high-definition television was an analog video broadcast television system developed in the 1930s to replace early experimental systems with as few as 12-lines. On 2 November 1936 the BBC began transmitting the world's first public regular analog high-definition television service from the Victorian Alexandra Palace in north London, it therefore claims to be the birthplace of television broadcasting. John Logie Baird, Philo T. Farnsworth, Vladimir Zworykin had each developed competing TV systems, but resolution was not the issue that separated their different technologies, it was patent interference lawsuits and deployment issues given the tumultuous financial climate of the late 1920s and 1930s. Most patents were expiring by the end of World War II leaving no worldwide standard for television; the standards introduced in the early 1950s stayed for over half a century. When Europe resumed TV transmissions after WWII most countries standardized on a 576i television system; the two exceptions were the British 405-line system, introduced in 1936, the French 819-line system.
During the 1940s René Barthélemy reached 1015-lines and 1042-lines. On November 20, 1948, François Mitterrand, the Secretary of State for Information, decreed a broadcast standard of 819-lines developed by Henri de France; this was arguably the world's first high-definition television system, and, by today's standards, it could be called 737i with a maximum theoretical resolution of 408×368-line pairs with a 4:3 aspect ratio. It was used only in France by TF1, in Monaco by Tele Monte Carlo. However, the theoretical picture quality far exceeded the capabilities of the equipment of its time, each 819-line channel occupied a wide 14 MHz of VHF bandwidth. By comparison, the modern 720p standard is 1280×720 pixels, of which the 4:3 portion would be 960×720 pixels, while PAL DVDs have a resolution of 720×576 pixels. Television channels were arranged as follows: Technical specifications of the broadcast television systems used with 819-lines. System E implementation provided good picture quality but with an uneconomical use of bandwidth.
Thus an unusually crisp "standard" definition image only needed half, or one-quarter the vision bandwidth of the 819-line system to give a "balanced" appearance, despite their lower overall resolution still seeming clear on the more affordable small-screen receivers used in the pre-color era. With the usual additions of sound carrier and vestigial sideband the result was a combined signal that demanded two to three times the bandwidth of more moderately specified standards when colour was added to them. System F was an adapted 819-line system used in Belgium and Luxembourg as an answer to this problem, with only half the vision bandwidth and half the sound carrier offset, it allowed French 819-line programming to squeeze into the 7 MHz VHF broadcast channels used in those neighbouring countries, albeit with a substantial loss of horizontal resolution. Use of System F was discontinued in Belgium in February 1968, in Luxembourg in September 1971. Despite some attempts to create a color SECAM version of the 819-line system, France abandoned it in favor of the Europe-wide standard of 625-lines, with the final 819-line transmissions from Paris in 1984.
TMC in Monaco were the last broadcasters to transmit 819-line television, closing down their System E transmitter in 1985. However, between 1976 and 1981 when French channel TF1 was switching area by area to the new analog 625-lines UHF network with SECAM color, some transmitters and gapfillers broadcast the 819-line signal in UHF; when switching to 625-lines, most gapfillers did not change UHF channel. They were switched to 625-lines in June 1981. Japan had the earliest working HDTV system, with design efforts going back to 1979; the country began broadcasting wideband analog high-definition video signals in the late 1980s using an interlaced resolution of 1035 or 1080-