Broadcast Fundamentals

Broadcast Fundamentals

Sony Training Services

Version 4

28 October 2003Part 1 Table of Contents

iPart 1Table of Contents

Part 2The history of television2Multimedia timeline2Part 3Image perception & colour30The human eye30The concept of primary colours36Secondary and tertiary colours37Hue saturation and luminosity38The CIE space39Part 4The basic television signal42The problem of getting a picture from A to B42Interlaced raster scanning43Half lines44Synchronisation46Part 5The monochrome NTSC signal48The 405 line system48The 525 line monochrome system48Frame rate and structure48Line rate and structure49Bandwidth considerations49Part 6Colour and television52Using additive primary colours52A compatible monochrome signal52Adding colour53Combining R-Y & B-Y55Video signal spectra56Combining monochrome and colour57Part 7Colour NTSC television58Similarity to monochrome58Choice of subcarrier frequency.58Adding colour59The gamut62Vertical interval structure62Part 8PAL television64What is PAL?64The PAL signal65The PAL chroma signal65Choice of subcarrier frequency67Bruch blanking68The disadvantages of PAL71Part 9SECAM television72Part 10The video camera74Types of video camera74System cameras74Parts of a video camera75Video camera specifications77Part 11Lenses80Refraction80The block of glass81The prism81The convex lens82The concave lens84Chromatic aberration85Spherical aberration87Properties of the lens87The concave and convex mirrors89Lens types90Extenders and adaptors91Filters92Part 12Early image sensors94Selenium detectors94The Ionoscope94The Orthicon tube95The Image Orthicon tube95The Vidicon tube96Variations on the Vidicon design97Part 13Dichroic blocks99The purpose of a dichroic block99Mirrors and filters99Optical requirements of a dichroic block101Variation on a theme101Using dichroic blocks in projectors101Part 14CCD sensors104Advantages of CCD image sensors104The basics of a CCD105Using the CCD as a delay line106Using CCDs as image sensors109Back lit sensors112Problems with CCD image sensors114CCD image sensors with stores115HAD technology119HyperHAD121SuperHAD sensors121PowerHAD sensors121PowerHAD EX (Eagle) sensors122EX View HAD sensors123Single chip CCD designs123Noise reduction127The future of CCD sensors131Part 15The video tape recorder132A short history132The present day134Magnetic recording principles137The essentials of helical scan139Modern video recorder mechadeck design144Variation in tape path designs150Definition of a good tape path151The servo system152Analogue video tape recorder signal processing153Popular analogue video recording formats157Digital video tape recorders160Popular digital video tape formats162Part 16Betacam and varieties168Part 17The video disk recorder176History176Present day176RAID technology178Realising RAID systems185Part 18Television receivers & monitors194The basic principle194Input signals194Part 19Timecode196A short history196Timecode197Timecodes basic structure197Longitudinal timecode201Bi-phase mark coding206Adjusting the LTC head206Vertical Interval Timecode209Drop frame timecode214Which timecode am I using ?215Timecode use in video recorders216Typical VTR timecode controls216The future218Part 20SDI (serial digital interface)220Parallel digital television220Serial digital television229Serial digital audio230SDI235Video index235Part 21Video compression236Traditional analogue signals236Analogue to digital conversion236Compressing digital signals236Digital errors in transmission237Compensating for digital errors237The advantage of digital compression237Entropy and redundancy237The purpose of any compression scheme239Lossless and lossy compression239Inter-frame and Intra-frame240What is DCT?241The church organ241The Fourier transform242The Discrete Fourier Transform (DFT)244Discrete Cosine Transform (DCT) solution to judder246What does the result of DCT look like?247DCT in video248The mathematics of DCT as used for video250DCT in audio252Basis pictures252Why bother?252Huffmans three step process253The principle behind variable length codes257The results of discrete cosine transforms257Using bell curves for variable length coding257Decoding variable length codes259Disadvantages of variable length codes259Part 22The television station262The studio262The post production studio262The edit suite263The news studio263The outside broadcast vehicle263Part 23CCTV, security & surveillance266What is CCTV?266CCTV privacy & evidence266CCTV use267CCTV terminology269The typical CCTV chain273CCTV cameras276Reading CCTV camera specifications281CCTV lenses287CCTV switchers and control stations293CCTV over IP296Character and shape recognition296Part 24Numbers & equations298Decibels298Part 25Things to do300

Part 2 The history of television

Multimedia timelinePrehistoric

BC

45,000Neanderthal carvings on Wooly Mammoth tooth, discovered near Tata, Hungary.

30,000Ivory horse, oldest known animal carving, from mammoth ivory, discovered near Vogelherd, Germany.

28,000Cro-Magnon notation, possibly of phases of the moon, carved onto bone, discovered at Blanchard, France.

@ 10,000Engraved antler baton, with seal, salmon and plants portrayed, discovered at Montgaudier, France.

8,000 - 3100In Mesopotamia, tokens used for accounting and record-keeping

3500In Sumer, pictographs (cuneiforms) of accounts written on clay tablets.

3400 - 3100Inscription on Mesopotamian tokens overlap with pictography

2600Scribes employed in Egypt.

2400In India, engraved seals identify the writer.

2200Date of oldest existing document written on papyrus.

1500Phoenician alphabet.

1400Oldest record of writing in China, on bones.

1270Syrian scholar compiles an encyclopedia.

900China has an organized postal service for government use.

775Greeks develop a phonetic alphabet, written from left to right.

530In Greece, a library.

500Greek telegraph: trumpets, drums, shouting, beacon fires, smoke signals, mirrors.

500Persia has a form of pony express.

500Chinese scholars write on bamboo with reeds dipped in pigment.

400Chinese write on silk as well as wood, bamboo.

@ 300Alexandria library founded by Ptolomy. At its peak the library at Alexandria had about 700000 manuscripts and books and was a magnet for scolary from all over the world.

200Books written on parchment and vellum.

200Tipao gazettes are circulated to Chinese officials.

59 Julius Caesar orders postings of Acta Diurna.

48Alexandria library burnt during Julius Caesers siege of Alexandria.

AD

100Roman couriers carry government mail across the empire.

105T'sai Lun invents paper.

175Chinese classics are carved in stone which will later be used for rubbings.

180In China, an elementary zoetrope.

250Paper use spreads to central Asia.

350In Egypt, parchment book of Psalms bound in wood covers.

450Ink on seals is stamped on paper in China. This is true printing.

600Books printed in China.

700Sizing agents are used to improve paper quality.

751Paper manufactured outside of China, in Samarkand by Chinese captured in war.

765Picture books printed in Japan.

868The Diamond Sutra, a block-printed book in China.

875Amazed travelers to China see toilet paper.

950Paper use spreads west to Spain.

950Folded books appear in China in place of rolls.

950Bored women in a Chinese harem invent playing cards.

1000-1499

1000Mayas in Yucatan, Mexico, make writing paper from tree bark.

1035Japanese use waste paper to make new paper.

1049Pi Sheng fabricates movable type, using clay.

1116Chinese sew pages to make stitched books.

1140In Egypt, cloth is stripped from mummies to make paper.

1147Crusader taken prisoner returns with papermaking art, according to a legend.

1200European monasteries communicate by letter system.

1200University of Paris starts messenger service.

1241In Korea, metal type.

1282In Italy, watermarks are added to paper.

1298Marco Polo describes use of paper money in China.

1300Wooden type found in central Asia.

1305Taxis family begins private postal service in Europe.

1309Paper is used in England.

1392Koreans have a type foundry to produce bronze characters.

1423Europeans begin Chinese method of block printing.

1450A few newsletters begin circulating in Europe.

1451Johnannes Gutenberg uses a press to print an old German poem.

1452Metal plates are used in printing.

1453Gutenberg prints the 42-line Bible.

1464King of France establishes postal system.

1490Printing of books on paper becomes more common in Europe.

1495A paper mill is established in England.

1500 1599

1500Arithmetic + and - symbols are used in Europe.

1510By now approximately 35,000 books have been printed, some 10 million copies.

1520Spectacles balance on the noses of Europe's educated.

1533A postmaster in England.

1545Garamond designs his typeface.

1550Wallpaper brought to Europe from China by traders.

1560In Italy, the portable camera obscura allows precise tracing of an image.

1560Legalized, regulated private postal systems grow in Europe.

1556The pencil.

1600 1699

1609First regularly published newspaper appears in Germany.

1627France introduces registered mail.

1631A French newspaper carries classified ads.

1639In Boston, someone is appointed to deal with foreign mail.

1639First printing press in the American colonies.

1640Kirchner, a German Jesuit, builds a magic lantern.

1650Leipzig has a daily newspaper.

1653Parisians can put their postage-paid letters in mail boxes.

1659Londoners get the penny post.

1661Postal service within the colony of Virginia.

1673Mail is delivered on a route between New York and Boston.

1689Newspapers are printed, at first as unfolded "broadsides."

1696By now England has 100 paper mills.

1698Public library opens in Charleston, S.C.

1700 - 1799

1704A newspaper in Boston prints advertising.

1710German engraver Le Blon develops three-color printing.

1714Henry Mill receives patent in England for a typewriter.

1719Reaumur proposes using wood to make paper.

1725Scottish printer develops stereotyping system.

1727Schulze begins science of photochemistry.

1732In Philadelphia, Ben Franklin starts a circulating library.

1755Regular mail ship runs between England and the colonies.

1770The eraser.

1774Swedish chemist invents a future paper whitener.

1775Continental Congress authorizes Post Office; Ben Franklin first Postmaster General.

1780Steel pen points begin to replace quill feathers.

1784French book is made without rags, from vegetation.

1785Stagecoaches carry the mail between towns in U.S.

1790In England the hydraulic press is invented.

1792Mechanical semaphore signaler built in France.

1792In Britain, postal money orders.

1792Postal Act gives mail regularity throughout U.S.

1794First letter carriers appear on American city streets.

1794Panorama, forerunner of movie theaters, opens.

1794Signaling system connects Paris and Lille.

1798Senefelder in Germany invents lithography.

1799Robert in France invents a paper-making machine.

1800 - 1899

1800Paper can be made from vegetable fibers instead of rags.

1800Letter takes 20 days to reach Savannah from Portland, Maine.

1801Semaphore system built along the coast of France.

1801Joseph-Marie Jacquard invents a loom using punch cards.

1803Fourdrinier continuous web paper-making machine.

1804In Germany, lithography is invented.

1806Carbon paper.

1807Camera lucida improves image tracing.

1808 Turri of Italy builds a typewriter for a blind contessa.

1817Jons Berzelius discovered selenium, an element shown in later years to have photo-voltaic effects. The material was a bi-products of chemical processes carried out in a Swedish factory. At first he though the material was tellurium earth, but later found it to be a new element and named it selenium from the Greek word selene meaning moon.

1831Michael Faraday in Britain and Joseph Henry in the United States experiment with electromagnetism, providing the basis for research into electrical communication.

1844Samuel Morse publicly demonstrates the telegraph for the first time.

1862Italian physicist, Abbe Giovanni Caselli, is the first to send fixed images over a long distance, using a system he calls the "pantelegraph".

1873Two English telegraph engineers, May and Smith, experiment with selenium and light, giving inventors a way of transforming images into electrical signals.

1880George Carey builds a rudimentary system using dozens of tiny light-sensitive selenium cells.

1884In Germany, Paul Nipkow patents the first mechanical television scanning system, consisting of a disc with a spiral of holes. As the disc spins, the eye blurs all the points together to re-create the full picture.

1895Italian physicist Guglielmo Marconi develops radio telegraphy and transmits Morse code by wireless for the first time.

1897Karl Ferdinand Braun, a German physicist, invents the first cathode-ray tube, the basis of all modern television cameras and receivers.

1900 1909

1900

Kodak Brownie makes photography cheaper and simpler.

Pupin's loading coil reduces telephone voice distortion.

1901

Sale of phonograph disc made of hard resinous shellac

First electric typewriter, the Blickensderfer.

Marconi sends a radio signal across the Atlantic.

1902

Germany's Zeiss invents the four-element Tessar camera lens.

Etched zinc engravings start to replace hand-cut wood blocks.

U.S. Navy installs radio telephones aboard ships.

Photoelectric scanning can send and receive a picture.

Trans-Pacific telephone cable connects Canada and Australia.

1903

Technical improvements in radio, telegraph, phonograph, movies and printing.

London Daily Mirror illustrates only with photographs.

A telephone answering machine is invented.

Fleming invents the diode to improve radio communication.

Offset lithography becomes a commercial reality.

A photograph is transmitted by wire in Germany.

Hine photographs America's underclass.

The Great Train Robbery creates demand for fiction movies.

The comic book.

The double-sided phonograph disc.

1905

In Pittsburgh the first nickelodeon opens.

Photography, printing, and post combine in the year's craze, picture postcards.

In France, Pathe colors black and white films by machine.

In New Zealand, the postage meter is introduced.

The Yellow Pages.

The juke box; 24 choices.

1906

A program of voice and music is broadcast in the U.S.

Lee de Forest invents the three-element vacuum tube.

Dunwoody and Pickard build a crystal-and-cat's-whisker radio.

An animated cartoon film is produced.

Fessenden plays violin for startled ship wireless operators.

An experimental sound-on-film motion picture.

Strowger invents automatic dial telephone switching.

1907

Bell and Howell develop a film projection system.

Lumiere brothers invent still color photography process.

DeForest begins regular radio music broadcasts.

In Russia, Boris Rosing develops theory of television and transmits black-and-white silhouettes of simple shapes, using a mechanical mirror-drum apparatus as a camera and a cathode-ray tube as a receiver.

1908

Campbell-Swinton, a Scottish electrical engineer, publishes proposals about an all-electronic television system that uses a cathode-ray tube for both receiver and camera.

In U.S., Smith introduces true color motion pictures.

1909

Radio distress signal saves 1,700 lives after ships collide.

First broadcast talk; the subject: women's suffrage.

1910-1919

1910

Sweden's Elkstrom invents "flying spot" camera light beam.

1911

Efforts are made to bring sound to motion pictures.

Rotogravure aids magazine production of photos.

"Postal savings system" inaugurated.

1912

U.S. passes law to control radio stations.

Motorized movie cameras replace hand cranks.

Feedback and heterodyne systems usher in modern radio.

First mail carried by airplane.

1913

The portable phonograph is manufactured.

Type composing machines roll out of the factory.

1914

A better triode vacuum tube improves radio reception.

Radio message is sent to an airplane.

In Germany, the 35mm still camera, a Leica.

In the U.S., Goddard begins rocket experiments.

First transcontinental telephone call.

1915

Wireless radio service connects U.S. and Japan.

Radio-telephone carries speech across the Atlantic.

Birth of a Nation sets new movie standards.

The electric loudspeaker.

1916

David Sarnoff envisions radio as "a household utility."

Cameras get optical rangefinders.

Radios get tuners.

1917

Photocomposition begins.

Frank Conrad builds a radio station, later KDKA.

Condenser microphone aids broadcasting, recording.

1918

First regular airmail service: Washington, D.C. to New York.

1919

The Radio Corporation of America (RCA) is formed.

People can now dial telephone numbers themselves.

Shortwave radio is invented.

Flip-flop circuit invented; will help computers to count.

1920-1929

1920

The first broadcasting stations are opened.

First cross-country airmail flight in the U.S.

Sound recording is done electrically.

Post Office accepts the postage meter.

KDKA in Pittsburgh broadcasts first scheduled programs.

1921

Quartz crystals keep radio signals from wandering.

The word "robot" enters the language.

Western Union begins wirephoto service.

1922

A commercial is broadcast, $100 for ten minutes.

Technicolor introduces two-color process for movies.

Germany's UFA produces a film with an optical sound track.

First 3-D movie, requires spectacles with one red and one green lens.

Singers desert phonograph horn mouths for acoustic studios.

Nanook of the North, the first documentary.

1923

Vladimir Zworykin patents the "Iconoscope", an electronic camera tube. By the end of the year he has also produced a picture display tube, the "Kinescope".

People on one ship can talk to people on another.

Ribbon microphone becomes the studio standard.

A picture, broken into dots, is sent by wire.

16 mm nonflammable film makes its debut.

Kodak introduces home movie equipment.

Neon advertising signs.

The A.C. Nielsen Company is founded. Nielsen's market research is soon being used by companies deciding where to advertise on radio.

1924

John Logie Baird is the first to transmit a moving silhouette image, using a mechanical system based on Paul Nipkow's model.Low tech achievement: notebooks get spiral bindings.

The Eveready Hour is the first sponsored radio program.

At KDKA, Conrad sets up a short-wave radio transmitter.

Daily coast-to-coast air mail service.

Two and a half million radio sets in the U.S.

1925

John Logie Baird obtains the first actual television picture.

Vladimir Zworykin takes out the first patent for colour television.

The Leica 35 mm camera sets a new standard.

Commercial picture facsimile radio service across the U.S.

All-electric phonograph is built.

A moving image, the blades of a model windmill, is telecast.

From France, a wide-screen film.

1926

John Logie Baird gives the first successful public demonstration of mechanical television at his laboratory in London.

The National Broadcasting Company (NBC) is formed by Westinghouse, General Electric and RCA.

Commercial picture facsimile radio service across the Atlantic.

Some radios get automatic volume control, a mixed blessing.

The Book-of-the-Month Club.

In U.S., first 16mm movie is shot.

Goddard launches liquid-fuel rocket.

Permanent radio network, NBC, is formed.

Bell Telephone Labs transmit film by television.

1927

The British Broadcasting Corporation is founded.

Columbia Phonographic Broadcasting System, later CBS, is formed

Pictures of Herbert Hoover, U.S. Secretary of Commerce, are transmitted 200 miles from Washington D.C. to New York, in the world's first televised speech and first long-distance television transmission.

NBC begins two radio networks.

Farnsworth assembles a complete electronic TV system.

Jolson's "The Jazz Singer" is the first popular "talkie."

Movietone offers newsreels in sound.

U.S. Radio Act declares public ownership of the airwaves.

Technicolor.

Negative feedback makes hi-fi possible.

1928

Station W2XBS, RCA's first television station, is established in New York City, creating television's first star, Felix the Cat the original model of which is featured in Watching TV

Later in the year, the world's first television drama, The Queen's Messenger, is broadcast, using mechanical scanning

John Logie Baird transmits images of London to New York via shortwave.

The teletype machine makes its debut.

Television sets are put in three homes, programming begins.

Baird invents a video disc to record television.

In an experiment, television crosses the Atlantic.

In Schenectady, N.Y., the first scheduled television broadcasts.

Steamboat Willie introduces Mickey Mouse.

A motion picture is shown in color.

Times Square gets moving headlines in electric lights.

IBM adopts the 80-column punched card.

1929

In London, John Logie Baird opens the world's first television studio, but is still able to produce only crude and jerky images. However, because Baird's television pictures carry so little visual information, it is possible to broadcast them from ordinary medium-wave radio transmitters.

Experiments begin on electronic color television.

Telegraph ticker sends 500 characters per minute.

Ship passengers can phone relatives ashore.

Brokers watch stock prices on an automated electric board.

Something else new: the car radio.

In Germany, magnetic sound recording on plastic tape.

Air mail flown from Miami to South America.

Bell Lab transmits stills in color by mechanical scanning.

Zworykin demonstrates cathode-ray tube "kinescope" receiver, 60 scan lines.

1930-1939

1930

The first commercial is televised by Charles Jenkins, who is fined by the U.S. Federal Radio Commission.

The BBC begins regular television transmissions.

Photo flashbulbs replace dangerous flash powder.

"Golden Age" of radio begins in U.S.

Lowell Thomas begins first regular network newscast.

TVs based on British mechanical system roll off factory line.

Bush's differential analyzer introduces the computer.

AT&T tries the picture telephone.

1931

Owned jointly by CKAC and La Presse, Canada's first television station, VE9EC, starts broadcasting in Montreal. Ted Rogers, Sr. receives a licence to broadcast experimental television from his Toronto radio station. Also this year, RCA begins experimental electronic transmissions from the Empire State Building.

Commercial teletype service.

Electronic TV broadcasts in Los Angeles and Moscow.

Exposures meters go on sale to photographers.

NBC experimentally doubles transmission to 120-line screen.

1932

Parliament creates the Canadian Radio Broadcasting Commission, superseded by the CBC in 1936.

Disney adopts a three-color Technicolor process for cartoons.

Kodak introduces 8 mm film for home movies.

The "Times" of London uses its new Times Roman typeface.

Stereophonic sound in a motion picture, "Napoleon."

Zoom lens is invented, but a practical model is 21 years off.

The light meter.

NBC and CBS allow prices to be mentioned in commercials.

1933

Western Television Limited's mechanical television system is toured and demonstrated at Eaton's stores in Toronto, Montreal and Winnipeg.

Armstrong invents FM, but its real future is 20 years off.

Multiple-flash sports photography.

Singing telegrams.

Phonograph records go stereo.

1934

Drive-in movie theater opens in New Jersey.

Associated Press starts wirephoto service.

In Germany, a mobile television truck roams the streets.

In Scotland, teletypesetting sets type by phone line.

Three-color Technicolor used in live action film.

Communications Act of 1934 creates FCC.

Half of the homes in the U.S. have radios.

Mutual Radio Network begins operations.

1935

William Hoyt Peck of Peck Television of Canada uses a transmitter in Montreal during five weeks of experimental mechanical broadcasts. Germany opens the world's first three-day-a-week filmed television service. France begins broadcasting its first regular transmissions from the top of the Eiffel Tower.

German single lens reflex roll film camera synchronized for flash bulbs.

Also in Germany, audio tape recorders go on sale.

IBM's electric typewriter comes off the assembly line.

The Penguin paperback book sells for the price of 10 cigarettes.

All-electronic VHF television comes out of the lab.

Eastman-Kodak develops Kodachrome color film.

Nielsen's Audimeter tracks radio audiences.

1936

There are about 2,000 television sets in use around the world. The BBC starts the world's first public high-definition/electronic television service in London.

Berlin Olympics are televised closed circuit.

Bell Labs invents a voice recognition machine.

Kodachrome film sharpens color photography.

Co-axial cable connects New York to Philadelphia.

Alan Turing's "On Computable Numbers" describes a general purpose computer.

1937

Stibitz of Bell Labs invents the electrical digital calculator.

Pulse Code Modulation points the way to digital transmission.

NBC sends mobile TV truck onto New York streets.

A recording, the Hindenburg crash, is broadcast coast to coast.

Carlson invents the photocopier.

Snow White is the first feature-length cartoon.

1938

Allen B. DuMont forms the DuMont television network to compete with RCA. Also this year, DuMont manufactures the first all-electronic television set for sale to the North American public. One of these early DuMont television sets is featured in Watching TV.

Strobe lighting.

Baird demonstrates live TV in color.

Broadcasts can be taped and edited.

Two brothers named Biro invent the ballpoint pen in Argentina.

CBS "World News Roundup" ushers in modern newscasting.

DuMont markets electronic television receiver for the home.

Radio drama, War of the Worlds," causes national panic.

1939

Because of the outbreak of war, the BBC abruptly stops broadcasting in the middle of a Mickey Mouse cartoon on September 1, resuming at that same point when peace returns in 1945. The first major display of electronic television in Canada takes place at the Canadian National Exhibition in Toronto. Baseball is televised for the first time.

Mechanical scanning system abandoned.

New York World's Fair shows television to public.

Regular TV broadcasts begin in USA.

Air mail service across the Atlantic.

Many firsts: sports coverage, variety show, feature film, etc.

1940-1949

1940

Dr. Peter Goldmark of CBS introduces a 343-line colour television system for daily transmission, using a disc of three filters (red, green and blue), rotated in front of the camera tube.

Fantasia introduces stereo sound to American public.

1941

North America's current 525-line/30-pictures-a-second standard, known as the NTSC (National Television Standards Committee) standard, is adopted.

Stereo is installed in a Moscow movie theater.

FCC sets U.S. TV standards.

CBS and NBC start commercial transmission; WW II intervenes.

Goldmark at CBS experiments with electronic color TV.

Microwave transmission.

Zuse's Z3 is the first computer controlled by software.

1942

Atanasoff, Berry build the first electronic digital computer.

Kodacolor process produces the color print.

1943

Repeaters on phone lines quiet long distance call noise.

1944

Harvard's Mark I, first digital computer, put in service.

IBM offers a typewriter with proportional spacing.

NBC presents first U.S. network newscast, a curiosity.

1945

BBC returns regular transmission of television, at the exact same time of day at exactly the same point in the programme.

Clarke envisions geo-synchronous communication satellites.

It is estimated that 14,000 products are made from paper.

1946

NBC and CBS demonstrate rival colour systems. The world's first television broadcast via coaxial cable is transmitted from New York to Washington D.C.

Jukeboxes go into mass production.

Pennsylvania's ENIAC heralds the modern electronic computer.

Automobile radio telephones connect to telephone network.

French engineers build a phototypesetting machine.

1947

A permanent network linking four eastern U.S. stations is established by NBC. On June 3, Canadian General Electric engineers in Windsor receive the first official electronic television broadcast in Canada, transmitted from the new U.S. station WWDT in Detroit. This year also sees the development of the transistor, on which solid-state electronics are based.

Hungarian engineer in England invents holography.

The transistor is invented, will replace vacuum tubes.

The zoom lens covers baseball's world series for TV.

1948

Television manufacturing begins in Canada. The television audience increases by 4,000 percent this year, due to a jump in the number of cities with television stations and to the fact that one million homes in the U.S. now have television sets. The U.S. Federal Communications Commission puts a freeze on new television channel allocations until the problem of station-to-station interference is resolved.

The LP record arrives on a viny disk.

Shannon and Weaver of Bell Labs propound information theory.

Land's Polaroid camera prints pictures in a minute.

Hollywood switches to nonflammable film.

Public clamor for television begins; FCC freezes new licenses.

Airplane re-broadcasts TV signal across nine states.

1949

The first Emmy Awards are presented, and the Canadian government establishes an interim policy for television, announcing loans for CBC television development.

An RCA research team in the U.S. develops the Shadow Mask picture tube, permitting a fully electronic colour display.

Network TV in U.S.

RCA offers the 45 rpm record.

Community Antenna Television, forerunner to cable.

Whirlwind at MIT is the first real time computer.

Magnetic core computer memory is invented.

1950-1959

1950

Cable TV begins in the U.S., and warnings begin to be issued on the impact of violent programming on children.

European broadcasters fix a common picture standard of 625 lines. (By the 1970s, virtually all nations in the world used 625-line service, except for the U.S., Japan, and some others which adopted the 525-line U.S. standard.)

Over 100 television stations are in operation in the U.S.

Regular USA color television transmission.

Vidicon camera tube improves television picture.

Changeable typewriter typefaces in use.

A.C. Nielsen's Audimeters track viewer watching.

1951

The first colour television transmissions begin in the U.S. this year. Unfortunately, for technical reasons, the several million existing black-and-white receivers in America cannot pick up the colour programmes, even in black-and-white, and colour sets go blank during television's many hours of black-and-white broadcasting. The experiment is a failure and colour transmissions are stopped.

The U.S. sees its first coast-to-coast transmission in a broadcast of the Japanese Peace Conference in San Francisco.

One and a half million TV sets in U.S., a tenfold jump in one year.

Cinerama will briefly dazzle with a wide, curved screen and three projectors.

Computers are sold commercially.

Still camera get built-in flash units.

Coaxial cable reaches coast to coast.

1952

Cable TV systems begin in Canada. On September 6, CBC Television broadcasts from its Montreal station; on September 8, CBC broadcasts from the Toronto station.

The first political ads appear on U.S. television networks, when Democrats buy a half-hour slot for Adlai Stevenson. Stevenson is bombarded with hate mail for interfering with a broadcast of I Love Lucy. Eisenhower, Stevenson's political opponent, buys only 20-second commercial spots, and wins the election.

3-D movies offer thrills to the audience.

Bing Crosby's company, Crosby Enterprises, tests video recording.

Wide-screen Cinerama appears; other systems soon follow.

Sony offers a miniature transistor radio.

EDVAC takes computer technology a giant leap forward.

Univac projects the winner of the presidential election on CBS.

Telephone area codes.

Zenith proposes pay-TV system using punched cards.

Sony offers a miniature transistor radio.

1953

A microwave network connects CBC television stations in Montreal, Ottawa and Toronto.

The first private television stations begin operation in Sudbury and London.

Queen Elizabeth's coronation is televised.

CBC beats U.S. competitors to the punch by flying footage across the Atlantic.

In the USA TV Guide is launched.

NTSC colour standard adopted and the USA begins colour transmission again, this time successfully.

Japanese television goes on the air for the first time.

CATV system uses microwave to bring in distant signals.

1954

Magazines now routinely offer the homemaker tips on arranging living-room furniture for optimal television-viewing pleasure.

U.S.S.R. launches Sputnik.

Radio sets in the world now outnumber newspapers printed daily.

Regular colour TV broadcasts established.

Sporting events are broadcast live in colour.

Radio sets in the world now outnumber daily newspapers.

Transistor radios are sold.

1955

Tests begin to communicate via fiber optics.

Music is recorded on tape in stereo.

1956

Ampex Corporation demonstrates videotape recording, initially used only by television stations.

Henri de France develops the SECAM (sequential colour with memory) procedure. It is adopted in France, and the first SECAM colour transmission between Paris and London takes place in 1960.

Several Louisiana congressmen promote a bill to ban all television programmes that portray blacks and whites together in a sympathetic light.

Bell tests the picture phone.

First transatlantic telephone calls by cable.

1957

The Soviet Union launches the world's first Earth satellite, Sputnik.

Soviet Union's Sputnik sends signals from space.

FORTRAN becomes the first high-level language.

A surgical operation is televised.

First book to be entirely phototypeset is offset printed.

1958

The CBC's microwave network is extended from Victoria, B.C. to Halifax and Sydney, Nova Scotia, to become the longest television network in the world.

Pope Pius XII declares Saint Clare of Assisi the patron saint of television. Her placement on the television set is said to guarantee good reception.

Videotape delivers colour pictures.

Stereo recording is introduced.

Data moves over regular phone circuits.

Broadcast bounced off rocket, pre-satellite communication.

The laser is introduced.

Cable carries FM radio stations.

1959

CBC Radio-Canada Montreal producers go on strike.

Bonanza debuts, starring Canadian actor Lorne Greene.

Local announcements, weather data and local ads go on cable.

The microchip is invented.

Xerox manufactures a plain paper copier.

Bell Labs experiments with artificial intelligence.

French SECAM and German PAL systems introduced.

1960-1969

1960

The Nixon-Kennedy debates are televised, marking the first network use of the split screen. Kennedy performs better on television than Nixon, and it is believed that television helps Kennedy win the election.

Sony develops the first all-transistor television receiver, making televisions lighter and more portable.

Ninety percent of American homes now own television sets, and America becomes the world's first "television society". There are now about 100 million television sets in operation worldwide.

Echo I, a U.S. balloon in orbit, reflects radio signals to Earth.

In Rhode Island, an electronic, automated post office.

A movie gets Smell-O-Vision, but the public just sniffs.

Zenith tests subscription TV; unsuccessful.

1961

The Canadian Television Network (CTV), a privately owned network, begins operations.

The beginning of the Dodd hearings in the U.S., which examined the television industry's "rampant and opportunistic use of violence".

Boxing match test shows potential of pay-TV.

FCC approves FM stereo broadcasting; spurs FM development.

Bell Labs tests communication by light waves.

IBM introduces the "golf ball" typewriter.

Letraset makes headlines simple.

The time-sharing computer is developed.

1962

The Telstar television satellite is launched by the U.S., and starts relaying transatlantic television shortly after its launch. The first programme shows scenes of Paris.

A survey indicates that 90 percent of American households have television sets; 13 percent have more than one.

Cable companies import distant signals.

FCC requires UHF tuners on television sets.

The minicomputer arrives.

Comsat created to launch, operate global system.

1963

From Holland comes the audio cassette.

Zip codes introduced.

CBS and NBC TV newscasts expand to 30 minutes in color.

PDP-8 becomes the first popular minicomputer.

Polaroid camera instant photography adds color.

Communications satellite is placed in geo-synchronous orbit.

On November 22, regular television programming is suspended following news of the Kennedy assassination.

On November 24, live on television, Jack Ruby murders Lee Harvey Oswald, Kennedy's suspected assassin. Kennedy's funeral is televised the following day. 96 per cent of all American television sets are on for an average 31 hours out of 72 during this period watching, many say, simply to share in the crisis.

1964

The Beatles appear for the first time on Ed Sullivan Show.

Procter and Gamble, the largest American advertiser, refuses to advertise on any show that gives "offense, either directly or by inference, to any organized minority group, lodge or other organizations, institutions, residents of any State or section of the country or a commercial organization."

Olympic Games in Tokyo telecast live globally by satellite.

Touch Tone telephones and Picturephone service.

From Japan, the videotape recorder for home use.

Russian scientists bounce a signal off Jupiter.

Intelsat, international satellite organization, is formed.

1965

The Vietnam War becomes the first war to be televised, coinciding with CBS's first colour transmissions and the first Asia-America satellite link. Protesters against the war adopt the television-age slogan, The whole world is watching.

Sony introduces Betamax, a small home videorecorder.

Electronic phone exchange gives customers extra services.

Satellites begin domestic TV distribution in Soviet Union.

Computer time-sharing becomes popular.

Color news film.

Communications satellite Early Bird (Intelsat I) orbits above the Atlantic.

Kodak offers Super 8 film for home movies.

Cartridge audio tapes go on sale for a few years.

Most television broadcasts in the USA are in colour.

FCC rules bring structure to cable television.

Solid-state equipment spreads through the cable industry.

1966

Colour television signals are transmitted by Canadian stations for the first time.

Linotron can produce 1,000 characters per second.

Fiber optic cable multiplies communication channels.

Xerox sells the Telecopier, a fax machine.

1967

Sony introduces the first lightweight, portable and cheap video recorder, known as the "portapak". The portapak is almost as easy to operate as a tape-recorder and leads to an explosion in "do-it-yourself" television, revolutionizing the medium.

Also this year, the FCC orders that cigarette ads on television, on radio and in print, carry warnings about the health dangers of smoking.

Dolby introduces a system that eliminates audio hiss.

Computers get the light pen.

Pre-recorded movies on videotape sold for home TV sets.

Cordless telephones get some calls.

Approx. 200 million telephones in the world, half in U.S.

1968

Sony develops the Trinitron tube, revolutionizing the picture quality of colour television.

World television ownership nears 200 million, with 78 million sets in the U.S. alone. The U.S. television industry now has annual revenues of about $2 billion and derives heavy support from tobacco advertisers.

FCC approves non-Bell equipment attached to phone system.

The RAM microchip reaches the market.

1969

On July 20, 1969, the first television transmission from the moon is viewed by 600 million television viewers around the world.

Sesame Street debuts on American Public Television, and begins to revolutionize adult attitudes about what children are capable of learning.

Astronauts send live photographs from the moon.

1970-1979

1970

Postal Reform Bill makes U.S. Postal Service a government corporation.

In Germany, a videodisc is demonstrated.

U.S. Post Office and Western Union offer Mailgrams.

The computer floppy disc is an instant success.

1971

Canada's Anik I, the first domestic geo-synchronous communications satellite, is launched, capable of relaying 12 television programmes simultaneously.

India has a single television station in New Delhi, able to reach only 20 miles outside the city.

South Africa has no television at all.

Intel builds the microprocessor, "a computer on a chip."Wang 1200 is the first word processor.

1972

The Munich Olympics are broadcast live, drawing an estimated 450 million viewers worldwide. When Israeli athletes are kidnapped by Palestinian terrorists during the games, coverage of the games cuts back and forth between shots of the terrorists and footage of Olympic events.

The American-conceived Intelsat system is launched this year, becoming a network and controlling body for the world's communications satellite system.

HBO starts pay-TV service for cable.

Sony introduces 3/4 inch "U-Matic" cassette VCR.

New FCC rules lead to community access channels.

Polaroid camera can focus by itself.

Digital television comes out of the lab.

The BBC offers "Ceefax," two-way cable information system.

"Open Skies": Any U.S. firm can have communication satellites.

Landsat I, "eye-in-the-sky" satellite, is launched.

"Pong" starts the video game craze.

1973

Ninety-six countries now have regular television service.

Watergate unfolds on the air in the U.S. and ends the following year with Nixon's resignation.

U.S. producers sell nearly $200 million dollars worth of programmes overseas, more than the rest of the world combined.

The microcomputer is born in France.

IBM's Selectric typewriter is now "self-correcting."

The term Electronic News Gathering, or ENG is introduced.

"Teacher-in-the-Sky" satellite begins educational mission.

1975

A study indicates that the average American child during this decade will have spent 10,800 hours in school by the time he or she is 18, but will have seen an average 20,000 hours of television. Studies also estimate that, by the time he/she is 75, the average American male will have spent nine entire years of his life watching television; the average British male will have spent eight years watching.

The microcomputer, in kit form, reaches the U.S. home market.

Sony's Betamax and JVC's VHS battle for public acceptance.

"Thrilla' from Manila"; substantial original cable programming.

1976

The Olympics, broadcast from Montreal, draw an estimated 1 billion viewers worldwide.

Apple I compter introduced.

Ted Turner delivers programming nationwide by satellite.

Still cameras are controlled by microprocessors.

1977

South Africans see television for the first time on May 10, as test transmissions begin from the state-backed South Africa Broadcast Co. The Pretoria government has yielded to public pressure after years of banning television as being morally corrupting. Half the broadcasts are in English, half in Afrikaans.

Columbus, Ohio, residents try 2-way cable experiment, QUBE.

1978

Ninety-eight percent of American households have television sets, up from nine percent in 1950. Seventy-eight percent have colour televisions, up from 3.1 percent in 1964.

From Konica, the point-and-shoot camera.

PBS goes to satellite for delivery, abandoning telephone lines.

Electronic typewriters go on sale.

1979

There are now 300 million television sets in operation worldwide.

Flat-screen pocket televisions, with liquid crystal display screens, are patented by the Japanese firm Matsushita. The pocket television is no bigger than a paperback book.

Speech recognition machine has a vocabulary of 1,000 words.

From Holland comes the digital videodisc read by laser.

In Japan, first cellular phone network.

Computerized laser printing is a boon to Chinese printers.

1980-1989

1980

During the 1980s, in the U.S. and Germany, laws and policies are enacted to preserve a person's right to television in the event of financial setback. Later in the year, the U.S. Cable News Network (CNN) goes on the air in the U.S.

India launches its national television network.

Sony Walkman tape player starts a fad.

In France, a holographic film shows a gull flying.

Phototypesetting can be done by laser.

Intelsat V relays 12,000 phone calls, 2 color TV channels.

Public international electronic fax service, Intelpost, begins.

Atlanta gets first fiber optics system.

CNN 24-hour news channel started.

Addressable converters pinpoint individual homes.

1981

450,000 transistors fit on a silicon chip 1/4-inch square.

Hologram technology improves, now in video games.

The IBM PC.

The laptop computer is introduced.

The first mouse pointing device.

1982

From Japan, a camera with electronic picture storage, no film.

USA Today type set in regional plants by satellite command.

Kodak camera uses film on a disc cassette.

1983

Cellular phone network starts in U.S.

Lasers and plastics improve newspaper production.

Computer chip holds 288,000 bits of memory.

Time names the computer as "Man of the Year."

ZIP + 4, expanded 9-digit ZIP code is introduced.

AT&T forced to break up; 7 Baby Bells are born.

American videotext service starts; fails in three years.

1984

Trucks used for SNG transmission.

Experimental machine can translate Japanese into English.

Portable compact disc player arrives.

National Geographic puts a hologram on its cover.

A television set can be worn on the wrist.

Japanese introduce high quality facsmile.

Camera and tape deck combine in the camcorder.

Apple Macintosh, IBM PC AT.

The 32-bit microprocessor.

The one megabyte memory chip.

Conus relays news feeds for stations on Ku-Band satellites.

1985

Digital image processing for editing stills bit by bit.

CD-ROM can put 270,000 papers of text on a CD record.

Cellular telephones go into cars.

Synthetic text-to-speech computer pronounces 20,000 words.

Picture, broken into dots, can be transmitted and recreated.

USA TV networks begin satellite distribution to affiliates.

At Expo, a Sony TV screen measures 40x25 meters.

Sony builds a radio the size of a credit card.

In Japan, 3-D television; no spectacles needed.

Pay-per-view channels open for business.

1986

HBO scrambles its signals.

Cable shopping networks.

1987

Half of all U.S. homes with TV are on cable.

American government deregulates cable industry.

1988

Government brochure mailed to 107 million addresses.

1989

Tiananmen Square demonstrates power of media to inform the world.

Pacific Link fiber optic cable opens, can carry 40,000 phone calls.

1990- 2000

1990

Flyaway SNG aids foreign reportage.

IBM sells Selectric, a sign of the typewriter's passing.

Most 2-inch videotape machines are also gone.

Videodisc returns in a new laser form.

1991

During the Gulf War, CNN coverage of the conflict is so extensive and wide-ranging that it is commonly remarked, only half in jest, that Saddam Hussein is watching CNN for his military intelligence, instead of relying on his own information-gathering methods.

Beauty and the Beast, a cartoon, Oscar nominee as best picture.

Denver viewers can order movies at home from list of more than 1,000 titles.

Moviegoers astonished by computer morphing in Terminator 2.

Baby Bells get government permission to offer information services.

Collapse of Soviet anti-Gorbachev plot aided by global system called the Internet.

More than 4 billion cassette tape rentals in U.S. alone.

3 out of 4 U.S. homes own VCRs; fastest selling domestic appliance in history.

1992

Cable TV revenues reach $22 billion.

At least 50 U.S. cities have competing cable services.

After President Bush speaks, 25 million viewers try to phone in their opinions.

1993

A TV Guide poll finds that one in four Americans would not give up television even for a million dollars.

Dinosaurs roam the earth in Jurassic Park.

Unfounded rumors fly that cellphones cause brain cancer.

Demand begins for "V-chip" to block out violent television programs.

1 in 3 Americans does some work at home instead of driving to work.

1994

After 25 years, U.S. government privatizes Internet management.

Rolling Stones concert goes to 200 workstations worldwide on Internet "MBone."

To reduce Western influence, a dozen nations ban or restrict satellite dishes.

Prodigy bulletin board fields 12,000 messages in one after L.A. quake.

1995

CD-ROM disk can carry a full-length feature film. (CD-Video)

Sony demonstrates flat TV set.

DBS feeds are offered nationwide.

Denmark announces plan to put much of the nation on-line within 5 years.

Major U.S. dailies create national on-line newspaper network.

Lamar Alexander chooses the Internet to announce presidential candidacy.

There are over a billion television sets in operation around the world.2002

Bibliotheca Alexandrina is due to open on April 23. This is intended as the modern equivalent to the ancient Alexandria Library which burnt down about 1600 years ago with great loss of information and human understanding.

Part 3 Image perception & colour

The human eye

Evolutionary advantage

The human eye is a marvel of evolution and selective breeding. Mapping the evolutionary history of the eye is difficult but almost certainly started as in some ancient creature that possessed a group of especially light sensitive cells on the surface of its skin.

The advantage of being able to sense possible attack, the presence of possible food and a possible mate, must have been a very big advantage. The eye must have evolved quickly from one generation of creature to another.

It is perhaps easy to see how the light sensitive cells became better, and how the ability to see colour must have given creatures a clear advantage over those that could not. Even the ability to see a wide spectrum of colours must have helped creatures.

Exactly how the lens evolved is less clear. However the lens started its evolution is obviously gave those creatures that possessed them the ability to see with greater clarity. It is also not clear why certain evolutionary paths favoured the multi-lens compound eye, and why others favoured the single lens design.

Evolution has not been entirely favourable, especially to humans. The human eye is not perfect. It has a few drawbacks, most of which we have adapted to. Some of these shortcomings actually make it easier to design television, as we will see later.

What is the eye

Most of us have two working eyes. Sight in humans is more important than any of our other senses. If either or both of our eyes fails to work, it is one of the most disabling disabilities humans can have.

The eye grows from rudimentary skin cells before we are born. Neural connections are made directly to the brain early on in development, and what results is one of the most complex and wonderful structures in the human body.

The eyes structure

As far as broadcast video is concerned most of the complexity of the human eye is irrelevant. However there are a few features and facts about the eye that are interesting.

The human eye approximates to a sphere. In fact for somebody with perfect sight the back of the eye is very close to a perfect sphere.

The eye is filled with a jelly like fluid called the vitreous humor. This fluid keeps the eyeball in shape. The fact that its is clear means that light can pass through it from front to back.

The front of the eye is covered with a clear protective film called the conjunctiva. Behind this is another protective film called the cornea.

Just behind this is the iris, a muscular ring that allows the amount of light entering the eye to be regulated. In bright light the iris closes. The iris is tinted. There appears to be no reason why this is so, but this is what gives the eye its colour.

Between the cornea and the iris is a watery fluid called the aqueous humor. This keeps the front of the eye in shape.

Behind the iris is the lens. A marvel of evolution this organic structure focuses light to the back of the eyeball. The amazing thing about this lens is that its shape can be altered to change the focal length. The cillary muscle, a small muscle surrounding the lens, squashed it and allows the eye to focus on closer objects. When the muscle relaxes the eye focuses to infinity.

Figure 1The human eye

(Lens optics is discussed in a later chapter.)

As mentioned the back of the eye is almost spherical. It comprises a large structure called the retina.

The retina

The retina is a structure that senses light and colour, and sends this information to the brain. It is between 200 and 250 microns thick and comprises various layers.

The outermost layer is a pigment layer. This acts as the outer wall to the retina and as a light stop.

Inside this is the receptor cells. There are two types of receptor cells. One type are rod shaped, and the other fatter and are cone like. For this reason they are commonly referred to as rod and cones. Light hitting these cells starts a protein electro-chemical reaction in a material called rhodopsin. This reaction quickly passes along the length of the cells axion. The end of the axion connected to the axion of a nerve cell, called a bipolar cell, via a structure called a synapse. A synapse is not actually a connection, but a small gap across which a protein electro-chemical transfer takes place.

Figure 2The human retina

Once the transfer has taken place another protein electro-chemical reaction travels the length of the bipolar cell's axion to its body, and then out along another axion to another synapse.

This second synapse connects to another nerve cell called the ganglion cell. The signal passes down the ganglions axion using the same reaction mechanism. The ganglion cells axions pass across the inner surface of the eyeball and out through the nerve bundle, out of the eye. The bundle passes back into the head and directly to the brain.

Light therefore has to pass through the whole thickness of the retina before hitting the rods and cones.

Rods

Rod receptor cells have a broad sensitivity range. They are most sensitive to green, which is nearer the centre of the optical electro-magnetic spectrum.

Rod cells measure the brightness of the image, or put another way the black and white parts of the image.

Cones

Cone receptor cells have a narrow sensitivity range. There are three types of cone cell. The first is sensitive to about 440nm wavelength light (blue), the second to about 530 nm (green), and the third to about 560nm (red)

Cone cells are therefore responsible for seeing colour. Every colour is a mix of blue, green and red.

Receptor density across the retina

There are about 120,000,000 rod cells in the retina and about 7,000,000 cone cells.

About 64% of the cone cells are sensitive to red light, about 32% to green light and just 2% to blue light.

Most of the retina is the same, with an even concentration of rod and cone cells. However there are two areas of the retina where this even concentration is different, the fovea and the blind spot.

The fovea

The lens focuses the centre of the image to a point on the retina called the fovea. This area of the retina has a very dense concentration of receptor cells. Furthermore, all these cells are cones. There are no rod cells in the fovea. The fovea allows the eye to study the centre of an image or scene in great colour detail.

The blind spot

Because all the ganglion cell axions are on the inside of the retina they need to pass out of the eyeball at some point. It stands to reason therefore that wherever this point is there can be no receptor cells at all. This area is therefore known as the blind spot.

Interesting facts about the eye

The eye is far from perfect

Although the eye is a marvel of biological engineering it has a number of design flaws. The cornea, lens and vitreous humor are not absolutely clear. They all reduce the amount of light hitting the retina and colour it slightly.

The eyes image is bent out of shape and upside down

The image falling on the retina is reasonably well proportioned near to the fovea. However the nearer you get to the outer edge the more compressed and distorted the image becomes.

The lens also focuses the image upside down and back to front on the retina.

The brain corrects for imperfections

The brain corrects the image to remove colour casting from the cornea, lens and vitreous humor. It also corrects edge distortion giving us the impression of a flat correctly proportioned image.

Having two eyes allows us to measure distance

When focusing of close object, not only do the lenses squash to focus, but also the eyeballs turn towards each other. This can be used by the brain the measure how far away an object is.

You can see this happening by getting a friend to hold their finger up at arms length, and focus on it. Then ask them to keep focussing on the finger while slowly moving it closer to their face.

The eye gets board easily

The eye is very good as seeing change. If you stare at something long enough it will disappear. The brain eventually cancels the image out altogether. Thus the eye works best if it continually moves, scanning across edges and shapes continually updating what the brain receives.

Images can burn in to the retina

Linked to the last interesting fact, if you stare at something long enough it will appear to disappear but the image is burnt in. If you then look at something else the original image will appear in negative for a while.

The eye remembers

The protein electro-chemical reactions in the eyes cells that sense light and pass the signals back to the brain take a certain time to react and stop.

A flash is therefore stretched so that the eye effectively sees it for longer than it actually occurs. This effect is known as persistence of vision. Film and television rely heavily on persistence of vision to turn what is actually many still images flashing one after another, into what appears to be a constantly changing image.

The eye is good at seeing patterns

The eye can pick out patterns very well. This is a problem for television and digital imagery because lines and pixels tend to stand out.

For instance a digital photograph will appear to be not as good an image when compared to a conventional photograph of exactly the same resolution, because the digital photograph pixels have a pattern and the conventional photograph grains are random.

The eye is very sensitive to green

A third of the cone cells are sensitive to green. The rod cells, although intended for seeing the overall brightness of an image. are more sensitive to green.

This makes the eye sensitive to green and more sensitive to changes in the green part of the spectrum.

This has an important impact of the design of colour television.

The fovea is not good for dark vision

Rod receptor cells are more sensitive that cone receptor cells. Thus in dark conditions things appear to turn black and white.

It is best not to look at something directly in low light, but to look just to the side or above it. This will put the object on the retina where there are plenty of rod cells and you will be able to see it. (Incidentally, it may not be a good idea to look just below an object in dark conditions as you may put it into the blind spot, where you cant see it at all.)

The concept of primary colours

Any colour can be described as a combination of 3 primary colours. Children are often taught that the three primary colours are Red, Yellow and Blue. This is a perfectly reasonable assumption when learning painting and art. Mixing these colours allows children to make almost any colour they want.

Figure 4Childrens primary colours

Subtractive colour mixing

This concept is called subtractive colour mixing, because the overall colour gets darker the more paint you add to the mix.

Figure 5Subtractive primary colours

In reality Red Yellow and Blue are not the correct primary colours for subtractive colour mixing. The reason for this is that mixing Red , Blue and Yellow does not give Black, it makes Brown. True subtractive primaries should remove all colour and brightness when mixed together, i.e. Black.

The true subtractive primaries are Magenta, Yellow and Cyan. While these three colours might appear close to Red, Yellow and Blue as far as children are concerned, they are sufficiently different to go to Black when mixed together in equal proportions.

Additive colour mixing

The opposite of subtractive colour mixing is additive colour mixing. Additive primary colours are relevant to light. If three additive primary coloured lights are mixed in equal proportions the result is White light.

The three additive primary colours are Red, Blue and Green.

Figure 6Additive primary colours

Secondary and tertiary colours

Each set of primary colour has a set of secondary colours. If you mix any two of the primary colours in equal proportions you will get a secondary colour.

In fact the three subtractive primary colours are the secondary colours of the additive primary colours, and visa versa.

A tertiary colour is found by mixing equal proportions of three primary colours. There are only two tertiary colours, White and Black.

Hue saturation and luminosity

Colour can be described as a 3 dimensional shape. At the top is white. Half way down is a circle of all the colours at their full intensity. You can see all six primaries, both additive and subtractive around the edge of the circle. At the bottom is Black.

Figure 7Colour 3D shape (front & back)

This is a 3 dimensional space, therefore it is possible to pick any point at have any colour you want. The line running down the centre runs from White to Black through Grey.

Figure 8Colour 3D shape (top & bottom)

If you look at the shape from the top you will get a circle with all the colours around the edge and White in the middle. Look at the shape from the bottom and you will see Black in the middle.

Figure 9Hue saturation & luminosity

Hue

Hue is the colour. You can change the hue by rotating around the centre of the circle.

Saturation

Saturation can be called colour intensity. It is a measure of how far from the centre you are. Zero saturation is White, Grey or Black. Full saturation is somewhere on the edge of the circle.

Luminosity

Luminosity is how far up or down the shape you are. If you take any colour and force its luminosity up it will tend towards White, and visa-versa down to Black.

The CIE space

The common method for describing colour is the CIE colour space. This 2 dimensional representation is used for additive colour fields to define the ability of a video system to capture and display colour. As you can see the NTSC and PSL gamuts are well within the total range of natural colours.

Each corner of the gamut triangles for NTSC and PAL specify the primary colours. They are different for each standard.

Television cameras and displays have a long way to go before they are able to capture and display every colour available in nature.

Figure 11CIE colour space

Part 4 The basic television signal

The problem of getting a picture from A to B

A picture is a 2 dimensional object. It has height and width. A moving picture adds a third dimension, time, to the other two.

If we are to send a moving image from one place to another we need to change the image content into a serial signal.

Film frames

Film conveys a moving image as a series of frames. These are like 2 dimensional chunks of data appearing at once, one after another, so rapidly that it appears to be smooth.

The raster scan

A raster scan scans an image and turns it into a serial stream of data.

By combining films method of conveying frames with the raster scan method we could convey a moving image as a serial signal.

The basic raster frame

The normal raster scan, and the method used by all broadcast television standards, scans each line from left to right, and the each successive line from top to bottom. This is called a frame.

The definition of the signal itself is simple. The brighter the image is at that point on the line the higher the signals voltage.

Figure 12The raster scan

Lines and frame rate

We need to decide on a frame rate and the number of lines. We want the highest quality possible so it would be better to have as many lines as possible, and as many frames per second as possible. We would also want to ensure that each line had the highest quality (bandwidth) possible.

However the overall bandwidth of the signal is strictly limited by broadcast standards authorities, so we have to find a reasonable compromise between the number of frames per second, the number of lines, and the quality of each line.

An increase in either the number of lines, the number of frames per second, or the bandwidth of each line, will increase the signals overall bandwidth.

The blanking intervals

Horizontal blanking

Each raster line is normally referred to as the active line. This is where the line is traced out on the image. There is a short interval between one active line and the next. The scanning system uses this time to fly back to the beginning of the next line. The signal is cut for this period of time to prevent the flyback appearing on the television set. In the raster scanning system this interval is referred to as the horizontal flyback.

The interval is also called the line blanking interval or horizontal blanking interval.

Thus every video line consists of the active line period and the horizontal blanking interval which is used as a flyback period.

Vertical blanking

There is a longer interval between one entire scan and the next. During this time the scanning system moves back from the bottom right corner to the top left corner. Just as with the horizontal flyback interval the signal is cut, to prevent it appearing on the television screen. This is referred to as vertical flyback.

This is normally also called the vertical blanking interval.

Interlaced raster scanning

If a frame is raster scanned and the frame rate is the same as that of film i.e. 24 frames per second, there is a severe amount of picture flicker. This is because every point in the image will have faded before the scanning mechanism can go back around to refresh it.

Figure 13The interlaced raster scan

Televisions could be designed to reduce flicker by increasing the persistence of the screen. However this would mean any rapid movement on the screen would be seen as blurring and streaking.

You could increase the frame rate but this would increase bandwidth.

The solution is to interlace the raster scan. Interlaced scans scan the odd numbered lines first, from top to bottom. Then the raster scan starts from the top again and scans the even lines from top to bottom.

This method of scanning reduces flicker by effectively writing an image at twice the frame rate.

Each of the scans is called a field, and two interlaced field make up a frame.

Half lines

Modern video standards also take into account that each line in the raster scan is not exactly horizontal. In fact the raster scan is progressing slowly from the top of the image to the bottom at a constant rate. The left side of each line is actually slightly lower than the right side.

Therefore video standards have an odd number of lines per frame. The first field of each frame begins with a whole line and ends with a half line. The second field begins with a half line and ends with a whole line.

This system gives a more rectangular raster scanned image.

Figure 14Basic horizontal and vertical detail

Synchronisation

The basic principle

Synchronisation is the principle of making sure two pieces of equipment, that both have some kind of regular clock or rhythm to run at the same rate. The two pieces of equipment are said to be locked together.

Synchronisation is often done with some form of synchronisation signal, generally simply called a sync signal.

How does television sync?

All television equipment contains some form of clock or oscillator. This will have a natural frequency which is close to the correct frequency.

Somewhere in the television transmission station will be a master sync pulse generator containing a precision master oscillator. Its frequency is correctly set to within 1 cycle in several million.

All the equipment in the transmission station is locked to this master sync pulse generator. This is easy because the equipments own clock is running as about the same rate. The sync signal pulls the equipments own oscillator to exactly the correct frequency.

The transmission station will send out a television signal that contains sync pulses. All equipment from the transmission station to the television at home contains similar oscillators which are pulled to exactly the correct frequency by the sync pulses.

Line, or horizontal, sync pulses

Line sync pulses are parts of the video signal that define the beginning of each video line. They occur at a certain time during the horizontal blanking interval.

Line sync pulses are short intervals of time where the video signal drops below the voltage specified for black (the blanking level).

Line sync pulses have a particular shape, because they are bandwidth limited. The beginning and end of the pulses are sloped. The beginning of the video line is specified as the mid-point of the slope at the beginning of the sync pulse.

These pulses are placed some time during the horizontal interval. Their position relative to the beginning of the active line is set and known, so once the position of the pulse is found the beginning of the active line is known.

Vertical sync pulses

The vertical blanking interval is more complex, and is relatively longer, than the horizontal blanking interval. The time interval is the same as many video lines. It contains a complex series of pulses that define the beginning of each field and each frame.

Blanked vertical lines

The vertical interval starts and finishes with a few blanked video lines. These are simply video lines with their respective horizontal sync pulses, but with the active line period blanked as well.

Equalising pulses

The vertical interval contains a number of equalising pulses near to the end of one field and the start of the next field. Equalising pulses are shorter than line sync pulses and occur every half line.

The reason for this is so that there is a same pattern of equalising pulses for every field, even though the transition between the first field and the second is half way through one line.

Broad pulses

Broad pulses are placed in between the two groups of equalisation pulses. These are very wide pulses, in fact, so wide that only a small portion of time is spent not in a broad pulse.

Definition of the start of the field

The definition of the start of each field is the beginning of the first broad pulse.

Part 5 The monochrome NTSC signal

The 405 line system

The first important monochrome video signal was the 405 line monochrome system adopted by many countries around the world.

Although an important video standard in its time, the 405 line standard is now obsolete. Furthermore it is different from any of the modern video standards.

Therefore we will look at the 525 line monochrome standard as the first important and relevant standard.

The 525 line monochrome system

The 525 line monochrome standard was proposed by the American NTSC (National Television Standards Committee) and quickly became popular.

This standard formed a strong basis for the existing 525 line colour system used by many countries around the world, and so it seems sensible to study it first.

The 525 line monochrome system has 525 lines per video frame, with 262.5 lines per field.

Frame rate and structure

The chosen frame for NTSC was 30 frames per second or 60 fields per second. It is commonly thought that this was so that NTSC televisions could be locked to the mains power. This is only half true. Mains power alternating frequency is not accurate enough to provide a reliable synchronisation signal for television receivers. Television equipment does not use mains as a locking signal. However if television equipment is not somehow linked to mains, the resulting beating and aliasing frequencies can cause undesirable effects on the screen. Making the frame rate the same as the mains power frequency at least makes these undesirable effects stand still.

Field 1 starts on line 1. There are 6 equalisation pulses, then 6 broad pulses, then 6 more equalisation pulses. Normal horizontal syncs starts on line 10.

The first active video line is line 22, and the last is line 262. Half of line 263 is active.

Field 1 starts half way through line 263 with 6 equalisation pulses, 6 broad pulses and 6 more equalisation pulses. Normal horizontal syncs start at the beginning of line 273.

The first active video line is line 285 and the last is line 525.

Field start displacement

The trigger point for the start of a field is normally the first broad pulse. This is the point television receivers use to start the next field. However the official start point of each field is the beginning of the first broad pulse.

This gives a discrepancy between the technical start of each field and the line numbers. The first broad pulse is at the start of line 4, and half way through line 266.

Line rate and structure

The line rate is simply the frame rate multiplied by 525, or 15.75kHz.

Disregarding the vertical interval, all NTSC lines have the same basic structure.

Bandwidth considerations

The video signal can have energy that can stretch to 10Mhz and beyond. However, because of the highly repetitive nature of video, with each video line similar to the one before and after, and each video field and frame similar to the one before and after, most of the energy is centred around harmonics of line, field and frame rate. This makes the bandwidth look like a series of spikes, with very little between them.

Figure 15Video signal bandwidth

The television signal is modulated onto a radio frequency carrier before being sent to the transmitter mast and out to the home. The harmonics may possibly spread out either side of the carrier to 10MHz or more, giving a possible total bandwidth of over 20MHz. These spreads either side of the carrier are called the upper and lower sidebands.The regulatory authorities assigned a 6MHz bandwidth to each television channel. The designers of the original television standard therefore had to devise a scheme for restricting the video signal down to a 6MHz limit.

Figure 16Video channel bandwidth

Filters are used to cut off as much of the lower sideband as possible. It is not possible to cut everything off, so the filter restrains the lower sidebands to just 1.25MHz. What is left is commonly called the vestigal sideband.

The upper sideband is filtered and restricted to about 4.2MHz. Filters cannot create a sharp clean cut-off at 4.2MHz, but rather a smooth roll-off that disappears to zero just below 4.5MHz.A simple audio carrier is placed at 4.5MHz, clear of the video signal. Its sidebands do not extend very far and there is nothing left at 4.75MHz.Thus the total bandwidth including the video and audio signals is constrained to 6MHz.Quality considerations

The low frequency detail of the video signal is centred around the carrier frequency and the low order sidebands. Fine detail is centred around the high frequency sidebands above 4MHz. It is worth remembering that random noise will also tend to be centred around the high frequency sidebands.

Most home television receivers cannot show much detail above 4MHz. It is therefore pointless trying to transmit this level of detail to the home.

Radio spectrum and television channelsThe regulatory authorities specified a series of analogue television channels 6MHz apart. Each video carrier is 1.25MHz from the bottom of the channel, and each audio carrier is 5.75MHz from the bottom of the carrier (4.5MHz above the video carrier).

Television companies have the responsibility to ensure that each channel they transmit has carriers at exactly the correct allocated frequency, and that the bandwidth is properly filtered to constrain it to within the 6MHz limit.

Part 6 Colour and television

Using additive primary colours

The additive primary colour principle has particular relevance to television because it uses light to detect the image in the camera and to display it in the television set at the other end.

The colour television camera splits the image into three separate images, one for the Red part of the image, one for Green and one for Blue.

The colour television set has three sets of phosphor dots, one type that shine Red, one type that shine Green and the last type that shine Blue. The television set also has three electron guns, each one targeting one set of phosphor dots.

Original plans

The original idea was to use Red, Green and Blue throughout the whole transmission system, from camera to television set.

Both RCA and CBS (amongst others) developed systems that sequentially send Red, Green and Blue parts of the original image over a normal monochrome transmission system.

RCA chose to send dots of colour, Red Green Blue in a rotating sequence. CBS chose to filter successive video fields through a rotating Red Green Blue filter wheel.

Neither system worked too well. What was needed was a system that added some colour element to the existing monochrome signal, allowing those with monochrome television sets to watch television with the same quality as before, but allowing those with new colour televisions to see that same basic quality of image in colour.

Ensuring compatability

The original ideas for a colour television system were not popular because they were not compatible with the existing monochrome standard.A compatible monochrome signal

The colour video camera produces three separate Red, Green and Blue images. In theory simply mixing these three in equal proportions should give a perfect White.

The human eye is more sensitive to different Green than to Red or Blue. Therefore any miss-calculations in generating the Green primary colour in the television set would be more obvious that for Red or Blue.

The proportions of Red, Green and Blue was therefore adjusted to match human eye characteristics, standard luminosity curves, and make up for the non-linear nature of the light/voltage characteristics of a standard video camera and voltage/light characteristics of the standard television set. The equation for White (Y) is therefore :-

Y = 0.299R + 0.587G + 0.114B

This provided for a perfectly balanced monochrome signal that could be used to generate a standard monochrome signal compatible with existing monochrome television sets.

Maintaining compatible channel bandwidth

The regulatory authorities are constantly being pressured to provide space on the limited radio spectrum for all kinds of radio services, including commercial radio and television stations, airline radio communications, ambulance, police and other emergency services, radio control model enthusiasts, citizen band radio and HAM radio.

They were therefore not prepared to allocate more of the precious radio bandwidth to television companies wanting to switch from monochrome to colour.Designers had therefore to somehow fit the colour television signal into the existing 6MHz allocated to them for monochrome television.

Adding colour

Colour difference signals

There are three theoretical colour difference signals, each one being the difference on a primary colour from White. The colour difference signals are therefore (R-Y), (G-Y) and (B-Y).

It is possible to generate any hue, saturation of luminance using any three of the four signals, Y, (R-Y), (G-Y) and (B-Y). It is also possible to generate the Y signal or any of the three primary colours from any three of these four signals.

The Y signal was an essential requirement of any compatible colour system. As already mentioned this is the same as a standard monochrome signal.

A decision had to be made as to which two of the three available colour difference signals would be used.

The Green signal is a much higher proportion of Y than either Blue or Red. Therefore any miscalculation in Green will not be so obvious as it would be for either Red or Blue.

It was therefore decided to use the Red and Blue colour difference signals (R-Y) and (B-Y).

Generating the (R-Y) and (B-Y) colour difference signals

Generating the colour difference signals is a simple piece of mathematics. The relationship between the Y signal and the three primary colour signals has already been established. Thus the (R-Y) colour difference signal is simply :-

R-Y = R - (0.299R + 0.587G + 0.114B)

= R-0.299R 0.587G 0.114B

= 0.701R 0.587G 0.114B

Likewise the (B-Y) signal can be derived in the same way.

B-Y= B - (0.299R + 0.587G + 0.114B)

= 0.299R 0.587G + B 0.114B

= 0.299R 0.587G + 0.886B

Component colour video signals

Component colour video signals can either be in the original R, G, B form, or more commonly, are defined as the Y, (R-Y) and (B-Y) signals. Their relationship to the original primary colour signals is as previously mentioned, i.e. :-

Y = 0.299R + 0.587G + 0.114B

(R-Y) = 0.701R 0.587G 0.114B

(B-Y) = 0.299R 0.587G + 0.886B

Figure 17Basic component video signalCombining R-Y & B-Y

Colour television requires that there be just one colour signal. This must therefore be a combination of the R-Y and B-Y contributions. The designers of the first popular colour television standard decided to combine the two colour difference signals onto a special carrier called a subcarrier, because its frequency is under the main RF carrier used to transmit the video signal.

Quadrature amplitude modulation

The designers devised an ingenious way of modulating the two colour signals onto one carrier by using quadrature amplitude modulation.

Amplitude modulation is simple to achieve and to understand. The amplitude of the carrier is simply the level of the signal being modulated. What results is a steady frequency sine wave with varying amplitude.

Figure 18Quadrature vector representative

This sine wave can be thought of as a rotating vector. The vector is rotating in an anticlockwise direction and its length defines the amplitude of the signal.

It becomes easy to see how two signals can be modulated onto one subcarrier when you consider them as vectors. One of the signals can be modulated on a carrier that is delayed by 1/4 cycle (90 degrees). When the two modulated signals are combined they will not interfere with each other because they are 90 degrees apart.

The subcarrier is sent with the video signal. This makes decoding the two colour difference signals easy. You simply look at the amplitude of the signal in phase with the subcarrier, and the amplitude of the signal 90 degrees out of phase.

Video signal spectra

The monochrome signal

As explained on page 50, the monochrome video signal is highly repetitive, and the signals spectrum is not a smooth spread of energy from DC to high frequency. There are very definite energy peaks at harmonics of line rate, field rate and frame rate. There is very little energy between these peaks.

When the monochrome signal is modulated onto the radio carrier, sidebands would normally extend above and below the carrier with energy peaks at harmonics of line, field and frame rate. However the monochrome signal is filtered, and the lower sidebands are cut. The upper sidebands are filtered to about 4.2MHz.

The colour signal

The basic colour signal has the same bandwidth as the monochrome signal. When modulated onto the subcarrier it has the same basic bandwidth extending either side of the subcarrier frequency, and its energy is centred around harmonics of line rate, field rat