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DIGITALCAMERAS
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Introduction In the past twenty years, most of the major
technological breakthroughs in consumerelectronics have really been part of onelarger breakthrough:-
converting conventional analoginformation (represented by a fluctuating
wave) into digital information(represented by ones and zeros, or bits).This fundamental shift in technologytotally changed how we handle visualand audio information -- it completelyredefined what is possible.
The digital camera is one of the mostremarkable instances of this shift
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Introduction Essentially, a digital image is just a long string
of 1s and 0s that represent all the tiny coloreddots -- or pixels -- that collectively make up theimage.
This can be done by sampling the original lightthat bounces off the subject, immediately
breaking that light pattern down into a series ofpixel values.
Just like a conventional camera, it has a series oflenses that focus light to create an image of ascene. But instead of focusing this light onto apiece of film, it focuses it onto
a semiconductor device that records lightelectronically. A computer then breaks thiselectronic information down into digital data.
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CCD and CMOS: FilmlessCameras
Instead of film, a digital camera has a sensorthat converts light into electrical charges.
The image sensor employed by most digitalcameras is a charge coupled device (CCD).Some cameras use complementary metal oxidesemiconductor (CMOS) technology instead.
Both CCD and CMOS image sensors convert
light into electrons. A simplified way to think about these sensors is
to think of a 2-D array of thousands or millionsof tiny solar cells.
Once the sensor converts the light intoelectrons, it reads the value (accumulatedcharge) of each cell in the image. This is wherethe differences between the two main sensortypes kick in:
CCD
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CCD and CMOS: FilmlessCameras
A CCD transports the charge across thechip and reads it at one corner of thearray. An analog-to-digital converter(ADC) then turns each pixel's value into adigital value by measuring the amount ofcharge at each photosite and converting
that measurement to binary form. CMOS devices use several transistors at
each pixel to amplify and move thecharge using more traditional wires.
CMOS
Sensor
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CCD
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CMOS SENSOR
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Pros And Cons of The Two
Sensors CCD sensors create high-quality, low-noise images. CMOS sensors are
generally more susceptible to noise.
Because each pixel on a CMOS sensor has several transistors locatednext to it, the light sensitivity of a CMOS chip is lower. Many of the
photons hit the transistors instead of the photodiode. CMOS sensors traditionally consume little power. CCDs, on the other
hand, use a process that consumes lots of power. CCDs consume asmuch as 100 times more power than an equivalent CMOS sensor.
CCD sensors have been mass produced for a longer period of time, sothey are more mature. They tend to have higher quality pixels, andmore of them.
Although numerous differences exist between thetwo sensors, they both play the same role in the
camera -- they turn light into electricity.
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CCD vs. CMOS Sensors
CCD CMOS
cost expensive to producebecause of specialmanufacturing methodsemployed
inexpensive because CMOSwafers are used for manydifferent types ofsemiconductors
power consumes upto 100x more
power than CMOS
low power consumption
noise high quality, low noise images susceptible to noise
maturity produced for longer period;higher quality images,
more pixels
less mature but equal in lowand middle range
resolutions to CCD
Extendedfunctionality
technically feasible; otherchips are used
other circuitry easilyincorporated on samechip
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Digital Camera Resolution The amount of detail that the camera can capture is
called the resolution, and it is measured in pixels. Themore pixels a camera has, the more detail it can captureand the larger pictures can be without becoming blurry or"grainy."
Some typical resolutions include: 256x256 - This is 65,000 total pixels. 640x480 - This resolution is ideal for e-mailing pictures or
posting pictures on a Web site. 1216x912 - This is a "megapixel" image size -- 1,109,000 total
pixels 1600x1200 - With almost 2 million total pixels. You can print a
4x5 inch. 2240x1680 - Found on 4 megapixel cameras. Prints up to 16x20
inches. 4064x2704 - A top-of-the-line digital camera with 11.1
megapixels. You can create 13.5x9 inch prints with no loss ofpicture quality.
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Capturing Color Unfortunately, each photosite is colorblind. It only keeps
track of the total intensity of the light that strikes itssurface. In order to get a full color image, most sensorsuse filtering to look at the light in its three primary colors
Once the camera records all three colors, it combinesthem to create the full spectrum.
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Capturing Color
The highest quality cameras use three separate sensors,each with a different filter. A beam splitter directs lightto the different sensors.
Each sensor gets an identical look at the image; but
because of the filters, each sensor only responds to oneof the primary colors
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Capturing Color
Another method is to rotate aseries of red, blue and greenfilters in front of a single sensor.The sensor records three
separate images in rapidsuccession. This method alsoprovides information on allthree colors at each pixellocation; but since the threeimages aren't taken at preciselythe same moment, both the
camera and the target of thephoto must remain stationaryfor all three readings.
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Capturing Color
So basically a camera captures each image on
a separate CCD array.
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PIXEL
A pixel is a contraction if the term PIcture ELement.Digital images are made up of small squares, just likea tile mosaic on your kitchen or bathroom wall.
Though a digital photograph looks smooth andcontinuous just like a regular photograph, it's actually
composed of millions of tiny squares as shown below.
On the left the full image, on the right the area in the red square magnified to
show individual pixels
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PIXELS
Each pixel in the image has a numerical value ofbetween 0 and 255 and is made up of three colorchannels. So for example a pixel could be 37-red, 76-
green and 125-blue and it would then look like this If it was 162-red, 27-green and 12-blue, it would look like
this
There are over 16 million possible combinations usingthis scheme and each one represents a different color
Each color in this scheme can be represented by an 8-bitnumber (byte), so the color of each pixel is defined bythree color bytes.
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What is Autofocus?
Autofocus (AF) really could be called power-focus, as it often uses acomputer to run a miniature motorthat focuses the lens for you.
Depending on the distance of the subject from the camera, the lens
has to be a certain distance from the film to form a clear image. In most modern cameras, autofocus is one of a suite of automatic
features that work together to make picture-taking as easy aspossible. These features include:
Automatic film advance Automatic flash
Automatic exposure
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There are two types of autofocus systems:
active and passive. Some cameras may have a
combination of both types, depending on theprice of the camera. In general, less expensive
point-and-shoot cameras use an active system,
while more expensive SLR (single-lens reflex)
cameras with interchangeable lenses use thepassive system.
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Active Auto Focus: In 1986, the Polaroid Corporation used a form of sound navigation
ranging (SONAR), like a submarine uses underwater, to bounce asound wave off the subject.
The Polaroid camera used an ultra-high-frequency sound emitter andthen listened for the echo.
The Polaroid Spectra and later SX-70 models computed the amount oftime it took for the reflected ultrasonic sound wave to reach the camera
and then adjusted the lens position accordingly. But It has its own limitations. Active autofocus on today's cameras uses an infrared signal instead of
sound waves, and is great for subjects within 20 feet Infrared systems use a variety of techniques to judge the distance.
Typical systems might use:
Triangulation Amount of infrared light reflected from the subject Time
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The Advances
A Casio employeedisplays thedigital cameraExilim EX-S880during a pressconference. The
camera featuresa pre-installed
YouTube Capturesoftware to easily
upload videos tothe Web site.
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GPS Photo Taggers
GPS photo taggers let you mark
the location of your photo and if
you upload your geotaggedphotos to Flickr, other people can
see them and where you took
them.
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Instant Photo Printers
Polaroid is teaming with its
spinoff company to make an
instant, ink-free mobile photo
printers. See what you can do
with an iPhone camera next.
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Security Camera within your Camera!
Watch out! Who knows who or what is watching you with that
seemingly unattended iPhone. An iPhone security camera is built
right into your iPhone, but requires some hacking. See how the
police use security cameras next.
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Cameras to solve Crime!
CBI technicians use these camera
setups to photograph recoveredfingerprints to use in comparison and
for running through the AFIS system.
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High Speed Photography
The sound of a gun firing the bullet
actually triggered the flash for this photo,
not the photographer. High-speed
photography can be used to investigate
events such as car wrecks that happenvery quickly.
This photo shows a water balloon just
as it bursts. Notice how the
background of the photograph is
completely dark; a brief flash of light
is the only thing that catches the
image.
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Cameras to Drive at Night
BMW's Night Vision with Pedestrian
Detection system allows drivers to see
what (or who) is down the road -- even
on the darkest nights.
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The EYE Camera!
Stanislavs Bardins of Munich's Ludwig-
Maximilians-University demonstrates the
prototype of a video camera controlled by
the eyes. The camera could be used in
application fields of psychology and
market research.
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