Camcorder - CTS references

8/10/2019 Camcorder - CTS references

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A camcorderis a portable consumer electronicsdevice for recording video

and audiousing a built-in recorder unit. The camcorder contains both a video

cameraand a video recorderin one unit, hence its compound name. This

compares to previous technology where an acquisition and recording devices

would be separate.

The earliest camcorders, developed by companies such as JVC, ony, and

!oda", used analog videotape. ince the #$$%s recording onto digital tape

has become the norm. tarting from early &%%%s tape as storage media is

being gradually replaced with tape-free solutions li"e optical dis"s, hard dis"

drives and solid-state memory.

All tape-based camcorders have removable media in form of video cassettes.

olid-state camcorders can have either removable media in form of memory

cards, or built-in memory, or both. '((-based camcorders usually have non-

removable media in form of a hard dis" drive.

Camcorders that do not use magnetic tape are often called tapeless

camcorders. Camcorders that use two different types of media, li"e built-in

'(( and memory card, are often called hybrid camcorders.

'istory

)efore the camcorder. This separate portable )etama*recorder and camera

arrangement slightly predates the first camcorders

Video cameras were originally designed for broadcastingtelevisionimages +

see television camera. Cameras found in television broadcast centres were

e*tremely large, mounted on special trolleys, and wired to remote recorders

located in separate rooms. As technology advanced, miniaturiation
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5ithin a short time JVC released its own camcorder using its pre-e*isting

V'-C format. The V'-C cassette held enough tape to record ?% or #&%

minutes of V' video, while a mechanical adapter enabled playbac" of V'-

C videocassettes in home VC/s. This first model can be seen in the movie

Back to the Future.@#After seeing the popularity of the small V'-C7palmcorders7, ony redesigned its )etama* system to create the Video;

standard. Video; eliminated the problem of short running time, by using an

all-new metal composition video cassette. ; mm video used a tape whose

width is ==B less than V'4)etama* tape 0#&.D mm1, allowing even further

miniaturiation in the recorder9s tape-transport assembly and cassette media.

)oth V'-C and ; mm video represented a trade-off for the consumer.

Although the Video; and 'i; camcorders produced quality equal to V'-C

and uper V'-C camcorders 0&E%4?&% lines horiontal1, the standard ; mmcassette had the advantage with up to two hours length 0four hours in slow

mode1. Fn the down side, since the ; mm format was incompatible with V',

; mm recordings could not be played in consumers9 V' VC/s. Gqually

important entry-level V'-C camcorders were priced less than ; mm units,

and thus neither 7won7 the war. :t became a stalemate. 0ide note - :n #$;8

companies li"e anasonicbegan releasing full-sied V'4-V'

camcorders, which offered up to = or $ hours record time, and thus found a

niche with videophiles, industrial videographers, and college TV studios.1

:n the mid-#$$%s, the camcorder reached the digitalera with the introduction

of (V and mini(V. :ts cassette media was even smaller than ; mm media,

allowing another sie reduction of the tape transport assembly. The digital

nature of mini(V also improved audio and video quality over the best of the

analog consumer camcorders 0V'-C, 'i;1, although some users still prefer

the analog nature of 'i; and uper V'-C, since neither of these produce

the 7bac"ground blur7 or 7mosquito noise7 of (igital compression. Variations

on the (V camcorder include the (igital;camcorder and the >GH&-based

(V(camcorder.

The evolution of the camcorder has seen the growth of the camcorder mar"et

as price reductions and sie reductions ma"e the technology more accessible

to a wider audience. 5hen camcorders were first introduced, they were bul"y

shoulder-operated luggables that cost over I#,E%% 2 dollars @citation needed.As of
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&%%;, an entry-level camcorders fit in the palm of a person9s hand and is sold

at a retail price of appro*imately I#%% 2 dollars

Fverview

Major components

Camcorders contain = ma6or components lens, imager, and recorder. The

lens gathers and focuses light on the imager. The imager 0usually a CC(or

C>Fsensor on modern camcorders< earlier e*amples often used vidicon

tubes1 converts incident light into an electrical 0video1 signal. inally, the

recorder encodes the video signal into a storable form. >ore commonly, the

optics and imager are referred to as the camerasection.

The lensis the first component in the camera-section9s 7light-path7. The

camcorder9s optics generally have one or more of the following ad6ustments

aperture 0to control the amount of light1, oom 0to control the field-of-view1,

and shutter speed 0to capture continuous motion.1 :n consumer units, these

ad6ustments are automatically controlled by the camcorder9s electronics,

generally to maintain constant exposureonto the imager. rofessional units

offer direct user control of all ma6or optical functions 0aperture, shutter-speed,

focus, etc.1

The imagersection is the eyeof the camcorder, housing a photosensitive

device0s1. The imager converts light into an electronic video-signal through an

elaborate electronic process. The camera lens pro6ects an image onto the

imager surface, e*posing the photosensitive array to light. The light e*posure

is converted into electrical charge. At the end of the timed e*posure, the

imager converts the accumulated charge into a continuous analog voltage at

the imager9s output terminals. After scan-out is complete, the photosites are

reset to start the e*posure-process for the ne*t video frame. :n modern

0digital1 camcorders, an analog-to-digital 0A(C1 converter digities the imager

0analog1 waveform output into a discrete digital-video signal.The third section, the recorder, is responsible for writing the video-signal onto

a recording medium 0such as magnetic videotape.1 The record function

involves many signal-processing steps, and historically, the recording-process

introduced some distortion and noise into the stored video, such that playbac"
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of the stored-signal may not retain the same characteristics4detail as the live

video feed.

All but the most primitive camcorders imaginable also need to have a

recorder-controlling section which allows the user to control the camcorder,

switch the recorder into playbac" mode for reviewing the recorded footage

and an image control section which controls e*posure, focus and white-

balance.

The image recorded need not be limited to what appeared in the viewfinder.

or documentation of events, such as used by police, the field of view

overlays such things as the time and date of the recording along the top and

bottom of the image. uch things as the police car or constable to which the

recorder has been allotted may also appear< also the speed of the car at the

time of recording. Compass direction at time of recording and geographical

coordinates may also be possible. These are not "ept to world-standard fieldsini(V storage allows full resolution video 0D&%*ED8for AL,D&%*?;% for KTC1, unli"e previous analogue video standards. (igital

video doesn9t e*perience colour bleeding, 6itter, or fade, although some users

still prefer the analog nature of 'i; and uper V'-C, since neither of these

produce the 7bac"ground blur7 or 7mosquito noise7 of (igital compression. :n

many cases, a high-quality analog recording shows more detail 0such as
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rough te*tures on a wall1 than a compressed digital recording 0which would

show the same wall as flat and featureless1.

The highest-quality digital formats, such as >ini(V and (igital )etacam, have

the advantage over analog of suffering little generation lossin recording,

dubbing, and editing 0>GH-& and >GH-? do suffer from generation loss in

the editing process only1. 5hereas noiseand bandwidthissues relating to

cables, amplifiers, and mi*erscan greatly affect analog recordings, such

problems are minimal in digital formats using digital connections 0generally

:GGG #=$?, (:4(T:, or '(>:1.

Although both analog and digital can suffer from archival problems, digital is

more prone to complete loss. Theoretically digital information can be stored

indefinitely with ero deterioration on a digital storage device 0such as a hard

drive1, however since some digital formats 0li"e mini(V1 often squeee trac"s

only #% micrometers apart 0versus E%% Mm for V'1, a digital recording is

more vulnerable to wrin"les or stretches in the tape that could permanently

erase several scenes worth of digital data. Fn analog media similar damage

barely registers as 7noise7 in the video, still leaving a deteriorated but

watchable video. Gven digital recordings on (V( are "nown to suffer from

(V( rotthat permanently erase huge chun"s of data. Thus the one

advantage analog seems to have in this respect is that an analog recording

may be 7usable7 even after the media it is stored on has suffered severedeterioration whereas it has been noticed@#that even slight media

degradation in digital recordings may cause them to suffer from an 7all or

nothing7 failure, i.e. the digital recording will end up being totally un-playable

without very e*pensive restoration wor".

Modern recording media

For more information, see tapeless camcorder.

ome recent camcorders record video on flash memorydevices, >icrodrives,

small hard dis"s, and sie-reduced (V(-/A>or (V(-/susing >GH-#,

>GH-&or >GH-?formats. 'owever because these codecs use inter-frame

compression, frame-specific-editing requires frame regeneration, which incurs

additional processing and can cause loss of picture information. 0:n

professional usage, it is common to use a codec that will store every frame

inidividually. This provides easier and faster frame-specific editing of scenes.1
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>ost other digital consumer camcorders record in (Vor '(Vformat on tape

and transfer content over ire5ire0some also use 2) &.%1 to a computer,

where the huge files 0for (V, #H) for ? to ?.8 minutes in AL4KTC

resolutions1 can be edited, converted, and 0with many camcorders1 also

recorded bac" to tape. The transfer is done in real time, so the completetransfer of a 8% minute tape needs one hour to transfer and about #=H) dis"

space for the raw footage only - e*cluding any space needed for render files,

and other media. Time spent in post-production 0editing1 to select and cut the

best shots varies from instantaneous 7magic7 movies to hours of tedious

selection, arrangement and rendering.

Consumer market

As the mainstream consumer mar"et favors ease of use, portability, and price,

consumer camcorders emphasie these features more than raw technical

performance. or e*ample, good low-light capabilities require large capturing

chips, which affects price and sie. Thus, consumer camcorders are often

unable to shoot useful footage in dim light 0though some units, particularly

single-chip units by ony, offer night visioncapability1. >anual controls need

space, either in menus or as buttons and ma"e the use more complicated,

which goes against the requirement of ease of use. Consumer units offer a

plethora of :4F options 0:GGG #=$?4irewire, 2) &.%, Composite and -

Video1, but lac" many manual settings, often e*cluding video e*posure, gaincontrol, or sound level management. or the beginner, entry-level camcorders

offer basic recording and playbac" capability.

or the sophisticated hobbyist, high-end units offer improved optical and video

performance through multi-CC( components and name-brand optics, manual

control of camera e*posure, and more, but even consumer camcorders which

are sold for I#%%% such as the anasonic H&E% are not well-suited for

recording in dim light. 5hen dimly-lit areas are brightened in-camera or in

post-production, considerable noise distracts the viewer.
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JVC HN->HEEE hybrid camcorder 0>GH-& (-Video1

)efore the st century, consumer video editing was a difficult tas" requiring a

minimum of two recorders. Kow, however, a contemporary ersonal

Computerof even modest power can perform digital video editingwith editing

software. >any consumer camcorders bundle a light0feature-limited1 version

of such software, as do some computers, and more advanced software is

widely available at a variety of price points.

As of &%%D, analog camcorders are still available but not widely mar"eted

anymore< those that are still available are often less than 2I&E%, but require

special capture hardware for non-linear editing. :n terms of sales, mini(V

camcorders 0and to a much lesser e*tent, (igital;1 dominate most first world

mar"ets. Camcorders which record directly on (V( media are also on therise, primarily among users with no plans to edit their footage. Konetheless,

software for editing video files created by (V( camcorders is available,

including 5omble (V( and Video/edo.

'ard dis" based camcorders are appearing as well< JVC and ony are the

primary manufacturers of these units. :ncreased storage capacity over other

types of media is the main advantage with these models< however, with this

follows a slightly reduced image quality and loss of fle*ibility when compared

to other formats such as >ini(V, ma"ing the ease of transferring the footageto a C for quic" editing the main attraction of 'ard dis" camcorders

Technology

A charge-coupled device0CCD1 is an analog shift register, enabling analog

signals 0electric charges1 to be transported through successive stages

0capacitors1 controlled by a cloc"signal. Charge coupled devices can be used

as a form of memory or for delaying analog, sampled signals. Today, they are

most widely used for serialiing parallel analog signals, namely in arrays of

photoelectric light sensors. Kot all image sensorsuse CC( technology< fore*ample, C>Fchips are also commercially available.

7CC(7 refers to the way that the image signal is read out from the chip. 2nder

the control of an e*ternal circuit, each capacitor can transfer its electric

chargeto one or other of its neighbors. CC(s are used in digital photography

and astronomy0particularly in photometry1, sensors, electron microscopy,
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medical fluoroscopy, optical and 2Vspectroscopyand high speed techniques

such as luc"y imaging.

A specially developed CC( used for ultravioletimaging in a wire bonded pac"age.

'istory

Gugene . Lally of the Jet ropulsion Laboratory wrote a paper published in

#$8#, 7>osaic Huidance for :nterplanetary Travel7, illustrating a mosaic array

of optical detectors that formed a photographic image using digital

processing. (igital photography was conceived by this paper. Lally noted

such an optical array required development so digital cameras could be

produced. The required array consisting of CC( technology was invented in#$8$ by 5illard )oyleand Heorge G. mithat AT3T )ell Labs. The lab was

wor"ing on the picture phone and on the development of semiconductor

bubble memory. >erging these two initiatives, )oyle and mith conceived of

the design of what they termed 9Charge 7)ubble7 (evices9. The essence of

the design was the ability to transfer charge along the surface of a

semiconductor. As the CC( started its life as a memory device, one could

only 7in6ect7 charge into the device at an input register. 'owever, it was

immediately clear that the CC( could receive charge via the photoelectric

effectand electronic images could be created. )y #$8$, )ell researchers were

able to capture images with simple linear devices< thus the CC( was born.

everal companies, including airchild emiconductor, /CAand Te*as

:nstruments, pic"ed up on the invention and began development programs.

airchild was the first with commercial devices and by #$D? had a linear E%%

element device and a &-( #%% * #%% pi*el device. 2nder the leadership of
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!auo :wama, onyalso started a big development effort on CC(s involving

a lot of money. Gventually, ony managed to mass produce CC(s for their

camcorders. )efore this happened, :wama died in August #$;&.

ubsequently, a CC( chip was placed on his tombstone to ac"nowledge his

contribution.@#.

:n January &%%8, )oyle and mith were awarded the Kational Academy of

Gngineering Charles tar" (raper rie for their wor" on the CC(@&.

)asics of operation

:n a CC( for capturing images, there is a photoactive region 0an epita*ial

layer of silicon1, and a transmission region made out of a shift register 0the

CC(, properly spea"ing1

An image is pro6ected by a lenson the capacitor array 0the photoactive

region1, causing each capacitor to accumulate an electric charge proportional

to the lightintensity at that location. A one-dimensional array, used in line-

scan cameras, captures a single slice of the image, while a two-dimensional

array, used in video and still cameras, captures a two-dimensional picture

corresponding to the scene pro6ected onto the focal plane of the sensor. Fnce

the array has been e*posed to the image, a control circuit causes each

capacitor to transfer its contents to its neighbor. The last capacitor in the array

dumps its charge into a charge amplifier, which converts the charge into avoltage. )y repeating this process, the controlling circuit converts the entire

semiconductor contents of the array to a sequence of voltages, which it

samples, digities and stores in some form of memory. These stored images

can then be transferred to a printer, digital storage device or video display.

(etailed physics of operation

The photoactive region of the CC( is, generally, an epita*iallayer of silicon. :t

has a doping of pO 0)oron1 and is grown upon the substratematerial, often pO

O. :n buried channel devices, the type of design utilied in most modern

CC(s, certain areas of the surface of the silicon are ion implanted with

phosphorus, giving them an n-doped designation. This region defines the

channel in which the photogenerated charge pac"ets will travel. The gate

o*ide, i.e. the capacitor dielectric, is grown on top of the epita*ial layer and

substrate. Later on in the process polysilicon gates are deposited by chemical
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vapor deposition, patterned with photolithography, and etched in such a way

that the separately phased gates lie perpendicular to the channels. The

channels are further defined by utiliation of the LFCF process to produce

the channel stop region. Channel stops are thermally grown o*ides that serve

to isolate the charge pac"ets in one column from those in another. Thesechannel stops are produced before the polysilicongates are, as the LFCF

process utilies a high temperature step that would destroy the gate material.

The channels stops are parallel to, and e*clusive of, the channel, or 7charge

carrying7, regions. Channel stops often have a pO doped region underlying

them, providing a further barrier to the electrons in the charge pac"ets 0this

discussion of the physics of CC( devices assumes an electron transfer

device, though hole transfer is possible1.

7Fne-dimensional7 CC( from a fa* machine.

Fne should note that the cloc"ing of the gates, alternately high and low, will

forward and reverse bias the diode that is provided by the buried channel 0n-

doped1 and the epita*ial layer 0p-doped1. This will cause the CC( to deplete,

near the p-n 6unctionand will collect and move the charge pac"ets beneath

the gates P and within the channels P of the device.

:t should be noted that CC( manufacturing and operation can be optimied

for different uses. The above process describes a frame transfer CC(. 5hile

CC(s may be manufactured on a heavily doped pOO wafer it is also possible

to manufacture a device inside p-wells that have been placed on an n-wafer.

This second method, reportedly, reduces smear, dar" current, and infrared

and red response. This method of manufacture is used in the construction of

interline transfer devices.

Architecture

The CC( image sensors can be implemented in several different

architectures. The most common are full-frame, frame-transfer and interline.
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The distinguishing characteristic of each of these architectures is their

approach to the problem of shuttering.

:n a full-frame device, all of the image area is active and there is no electronic

shutter. A mechanical shutter must be added to this type of sensor or the

image will smear as the device is cloc"ed or read out.

5ith a frame transfer CC(, half of the silicon area is covered by an opaque

mas" 0typically aluminium1. The image can be quic"ly transferred from the

image area to the opaque area or storage region with acceptable smear of a

few percent. That image can then be read out slowly from the storage region

while a new image is integrating or e*posing in the active area. rame-

transfer devices typically do not require a mechanical shutter and were a

common architecture for early solid-state broadcast cameras. The downside

to the frame-transfer architecture is that it requires twice the silicon real estate

of an equivalent full-frame device< hence, it costs roughly twice as much.

The interline architecture e*tends this concept one step further and mas"s

every other column of the image sensor for storage. :n this device, only one

pi*el shift has to occur to transfer from image area to storage area< thus,

shutter times can be less than a microsecond and smear is essentially

eliminated. The advantage is not free, however, as the imaging area is now

covered by opaque strips dropping the fill factorto appro*imately E%B and the

effective quantum efficiencyby an equivalent amount. >odern designs haveaddressed this deleterious characteristic by adding microlenses on the

surface of the device to direct light away from the opaque regions and on the

active area. >icrolenses can bring the fill factor bac" up to $%B or more

depending on pi*el sie and the overall system9s optical design.

The choice of architecture comes down to one of utility. :f the application

cannot tolerate an e*pensive, failure prone, power hungry mechanical shutter,

then an interline device is the right choice. Consumer snap-shot cameras

have used interline devices. Fn the other hand, for those applications thatrequire the best possible light collection and issues of money, power and time

are less important, the full-frame device will be the right choice. Astronomers

tend to prefer full-frame devices. The frame-transfer falls in between and was

a common choice before the fill-factor issue of interline devices was
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addressed. Today, the choice of frame-transfer is usually made when an

interline architecture is not available, such as in a bac"-illuminated device.

CC(s containing grids of pi*elsare used in digital cameras, optical scanners

and video cameras as light-sensing devices. They commonly respond to D%B

of the incidentlight 0meaning a quantum efficiency of about D%B1 ma"ing

them far more efficient than photographic film, which captures only about &B

of the incident light.

CC( from a &.# megapi*elArgusdigital camera.

CC( from a &.# megapi*el'ewlett-ac"arddigital camera.

>ost common types of CC(s are sensitive to infraredlight, which allows

infrared photography, night-visiondevices, and ero lu*0or near ero lu*1

video-recording4photography. )ecause of their sensitivity to infrared, CC(s

used in astronomy are usually cooled to liquid nitrogentemperatures,

because infrared blac" body radiationis emitted from room-temperature

sources. Fne other consequence of their sensitivity to infrared is that infrared

from remote controlswill often appear on CC(-based digital cameras or

camcorders if they don9t have infrared bloc"ers. Cooling also reduces the

array9s dar" current, improving the sensitivity of the CC( to low light

intensities, even for ultraviolet and visible wavelengths.
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Astronomical CC(s

(ue to the high quantum efficiencies of CC(s, linearity of their outputs 0one

count for one photon of light1, ease of use compared to photographic plates,

and a variety of other reasons, CC(s were very rapidly adopted byastronomers for nearly all 2V-to-infrared applications.

Thermal noise, dar" current, and cosmic raysmay alter the pi*els in the CC(

array. To counter such effects, astronomers ta"e an average of several

e*posures with the CC( shutter closed and opened. The average of images

ta"en with the shutter closed is necessary to lower the random noise. Fnce

developed, the Qdar" frameR average image is then subtractedfrom the open-

shutter image to remove the dar" current and other systematic defects in the

CC( 0dead pi*els, hot pi*els, etc.1. The 'ubble pace Telescope, inparticular, has a highly developed series of steps 0Qdata reduction pipelineR1

used to convert the raw CC( data to useful images. ee@=for a more in-depth

description of the steps in processing astronomical CC( data.

CC( cameras used in astrophotographyoften require sturdy mounts to cope

with vibrations and breees, along with the tremendous weight of most

imaging platforms. To ta"e long e*posures of gala*ies and nebulae, many

astronomers use a technique "nown as auto-guiding. >ost autoguiders use a

second CC( chip to monitor deviations during imaging. This chip can rapidly

detect errors in trac"ing and command the mount9s motors to correct for them.

Array of =% CC(s used on loan (igital "y urveytelescope imaging camera, an

e*ample of 7drift-scanning.7
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An interesting unusual astronomical application of CC(s, called 7drift-

scanning7, is to use a CC( to ma"e a fi*ed telescope behave li"e a trac"ing

telescope and follow the motion of the s"y. The charges in the CC( are

transferred and read in a direction parallel to the motion of the s"y, and at the

same speed. :n this way, the telescope can image a larger region of the s"ythan its normal field of view. The loan (igital "y urveyis the most famous

e*ample of this, using the technique to produce the largest uniform survey of

the s"y yet.

Color cameras

A)ayer filteron a CC(

An /H)G filteron a CC(

CC(-Colorsensor
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Canon owerhot AD&% :has an #4&,E inch CC(-Colorsenor inside

(igital color cameras generally use a )ayer mas"over the CC(. Gach square

of four pi*els has one filtered red, one blue, and two green 0the human eyeis

more sensitive to green than either red or blue1. The result of this is that

luminanceinformation is collected at every pi*el, but the color resolution is

lower than the luminance resolution.

)etter color separation can be reached by three-CC( devices 0=CC(1 and a

dichroic beam splitter prism, that splits the imageinto red, greenand blue

components. Gach of the three CC(s is arranged to respond to a particular

color. ome semi-professional digital video camcorders 0and most

professionals1 use this technique. Another advantage of =CC( over a )ayer

mas" device is higher quantum efficiency0and therefore higher light sensitivity

for a given aperture sie1. This is because in a =CC( device most of the light

entering the aperture is captured by a sensor, while a )ayer mas" absorbs a

high proportion 0about &4=1 of the light falling on each CC( pi*el.

ince a very-high-resolution CC( chip is very e*pensive as of &%%E, a =CC(

high-resolution still camera would be beyond the price range even of many

professional photographers. There are some high-end still cameras that use a

rotating color filter to achieve both color-fidelity and high-resolution. These

multi-shot cameras are rare and can only photograph ob6ects that are not

moving.

Sensor sizes

ensors 0CC( 4 C>F1 are often referred to with an imperial fraction

designation such as #4#.;7 or &4=7, this measurement actually originates bac"

in the #$E%9s and the time of Vidicon tubes. Compact digital cameras and

(igicams typically have much smaller sensors than a (igital L/ and are

thus less sensitive to light and inherently more prone to noise. ome
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e*amples of the CC(s found in modern cameras can be found in this tablein

a (igital hotography /eview article

Type Aspect Ratioidthmm

!eightmm

Diagonalmm

Areamm"

RelativeArea

#487 ?= &.=%% #.D=% &.;D; =.$D$ #.%%%

#4?7 ?= =.&%% &.?%% ?.%%% D.8;% #.$=%

#4=.87 ?= ?.%%% =.%%% E.%%% #&.%%% =.%#8

#4=.&7 ?= ?.E=8 =.?#8 E.8D; #E.?$E =.;$?

#4=7 ?= ?.;%% =.8%% 8.%%% #D.&;% ?.=?=

#4&.D7 ?= E.&D% =.$8% 8.E$& &%.;8$ E.&?E

#4&7 ?= 8.?%% ?.;%% ;.%%% =%.D&% D.D

#4#.;7 ?= D.#D8 E.=#$ ;.$=& =;.#8$ $.E$=

&4=7 ?= ;.;%% 8.8%% ##.%%% E;.%;% #?.E$D

#7 ?= #&.;%% $.8%% #8.%%% #&&.;;% =%.;;&

?4=7 ?= &&.E%% #;.%%% &;.;#? ?%E.%%% #%#.D;?

#ther image sizes as a comparison

A-C =& &E.#%% #8.D%% =%.#?; ?#$.#D% #%E.=?8

=Emm =& =8.%%% &?.%%% ?=.&8D ;8?.%%% D.#?%

8?E ?= E8.%%% ?#.E%% 8$.D%# &=&?.%%% E;?.%88

Three-CCDor $CCDis a term used to describe an imaging systememployed

by some still cameras, videocameras, telecineand camcorders. Three-CC(

cameras have three separate charge-coupled devices0CC(s1, each one

ta"ing a separate measurement of red, green, and blue light. Light coming

into the lens is split by a trichroic prism assembly, which directs the

appropriate wavelength ranges of light to their respective CC(s. Three-CC(

cameras are generally regarded to provide superior image quality to cameras

with only one CC(. )y ta"ing a separate reading of red, green, and blue

values for each pi*el, three-CC( cameras achieve much better precision than

single-CC( cameras. Almost all single-CC( cameras use a bayer filter, which

allows them to detect only one-third of the color information for each pi*el.
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The other two-thirds must be interpolatedwith a demosaicingalgorithm to 9fill

in the gaps9.

The combination of the three sensors can be done in the following ways

Composite sampling, where the three sensors are perfectly aligned to avoid

any color artifact when recombining the information from the three color

planes

i*el shifting, where the three sensors are shifted by a fraction of a pi*el. After

recombining the information from the three sensors, higher spatial resolution

can be achieved.@citation neededi*el shifting can be horiontal only to provide

higher horiontal resolution in standard resolution camera, or horiontal and

vertical to provide high resolution image using standard resolution imager for

e*ample. The alignment of the three sensors can be achieved by micro

mechanical movements of the sensors relative to each other.

Arbitrary alignment, where the random alignment errors due to the optics are

comparable to or larger than the pi*el sie.

Three-CC( cameras are generally more e*pensive than single-CC( cameras

because they require three times as many elements to form the image

detector, and because they require a precision color-separation beam-splitter

optical assembly.

The concept of cameras using three image pic"ups, one for each primary

color, was first developed for color photography on three glass plates in the

late nineteenth century, and in the #$8%s through #$;%s was the dominant

method to record color images in television, as other possibilities to record

more than one color on the video camera tubewere difficult.

Three-CC( cameras are often referred to as 7three-chip7 cameras< this term

is actually more descriptive and inclusive, since it includes cameras that use

C>Factive pi*el sensorsinstead of CC(s.
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A color-separation beam splitter prism assembly, with a white beam entering the

front, and red, green, and blue beams e*iting the three focal-plane faces.

A hilips type trichroic beam splitter prism schematic, with a different color

separation order than the assembly shown in the photo. The red beam undergoes

total internal reflectionat the air gap, while the other reflections are dichroic.

Gfficiency

(ielectric mirrors can be produced as low-pass, high-pass, band-pass, or

band-stop filters. :n the e*ample shown, a red and a blue mirror reflect the

respective bands bac", somewhat off a*is. The angles are "ept as small as

practical to minimie polariation-dependent color effects. To reduce

unwanted reflections, air-glass interfaces are minimied< the image sensors

may be attached to the e*it faces with an inde*-matched optical epo*y,
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sometimes with an intervening color trim filter. The hilips type prism includes

an air gap with total internal reflection in one light path, while the other prism

shown above does not. A typical )ayer filtersingle-chip image sensor absorbs

at least two-thirds of the visible light with its filters, while in a three-CC(

sensor the filters absorb only stray light and invisible light, and possibly a littlemore for color tuning, so that the three-chip sensor has better low light

capabilities.
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